摘要:

ISSN 0300-9599 JCFTAR 82 ( I 2 ) 3525-371 9 (1 986) JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions I Physical Chemistry in Condensed Phases 3525 3535 3553 3561 3569 3587 360 1 361 1 3625 3635 3647 3657 3667 368 1 3697 3709 3717 CONTENTS Fourier Transform Infrared Studies of the Irreversible Oxidation of Cyanide at Platinum Electrodes A. S. Hinman, R. A. Kydd and R. P. Cooney The Dielectric Properties of Zeolites in Variable Temperature and Humidity A. R. Haidar and A. K. Jonscher The Time-domain Response of Humid Zeolites A. K. Jonscher and A. R. Haidar Molecular-orbital Studies of C-H Bond Scission induced by Ionizing Radia- tion T. Tada Zeolites treated with Silicon Tetrachloride Vapour. Part 2.-Sorption Studies M. W. Anderson and J. Klinowski Studies of Propene Oxidation over Mixed Uranium-Antimony Oxides F.J. Farrell, T. G. Nevell and D. J. Hucknall Adsorption and Desorption Kinetics of Oxygen on Tin-Antimony Oxide Cat a1 y st by Quasi -cons tan t Coverage Met hods M-C. Bacchus-Montabonel and CO Adsorption at 77 K on KCl Films. An Infrared Investigation D. Scarano and A. Zecchina The Utilization of Time-resolved Dielectric Loss to probe the Role of the Surface in Heterogeneous Photochemistry C. J. Dobbin, A. R. McIntosh, J. R. Bolton, Z. D. Popovic and J. R. Harbour Polysilicate Equilibria in Concentrated Sodium Silicate Solutions I. L. Svensson, S. Sjoberg and L-0. Ohman Potentials of Ion-exchanged Synthetic Zeolite-Polymer Membranes M. Demertzis and N. P. Evmiridis Adsorption and Reduction of Nitrogen Monoxide by Potassium-doped Carbon T.Okuhara and K. Tanaka Physicochemical Properties and Isomerization Activity of Chlorinated Pt/Al,O, Catalysts A. Melchor, E. Garbowski, M-V. Mathieu and M. Primet Excess Pressures for Aqueous Solutions M. J. Blandamer, J. Burgess and A. W. Hakin Effect of Temperature on the Point of Zero Charge and Surface Dissociation Constants of Aqueous Suspensions of y-Al,O, K. Ch. Akratopulu, L. Vordonis and A. Lycourghiotis Thermal Decomposition of Solid Sodium Bicarbonate M. C. Ball, C. M. Snelling, A. N. Strachan and R. M. Strachan Reviews of Books J-P. Joly I I7ISSN 0300-9599 JCFTAR 82 ( I 2 ) 3525-371 9 (1 986) JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions I Physical Chemistry in Condensed Phases 3525 3535 3553 3561 3569 3587 360 1 361 1 3625 3635 3647 3657 3667 368 1 3697 3709 3717 CONTENTS Fourier Transform Infrared Studies of the Irreversible Oxidation of Cyanide at Platinum Electrodes A.S. Hinman, R. A. Kydd and R. P. Cooney The Dielectric Properties of Zeolites in Variable Temperature and Humidity A. R. Haidar and A. K. Jonscher The Time-domain Response of Humid Zeolites A. K. Jonscher and A. R. Haidar Molecular-orbital Studies of C-H Bond Scission induced by Ionizing Radia- tion T. Tada Zeolites treated with Silicon Tetrachloride Vapour. Part 2.-Sorption Studies M. W. Anderson and J. Klinowski Studies of Propene Oxidation over Mixed Uranium-Antimony Oxides F. J. Farrell, T. G. Nevell and D. J. Hucknall Adsorption and Desorption Kinetics of Oxygen on Tin-Antimony Oxide Cat a1 y st by Quasi -cons tan t Coverage Met hods M-C.Bacchus-Montabonel and CO Adsorption at 77 K on KCl Films. An Infrared Investigation D. Scarano and A. Zecchina The Utilization of Time-resolved Dielectric Loss to probe the Role of the Surface in Heterogeneous Photochemistry C. J. Dobbin, A. R. McIntosh, J. R. Bolton, Z. D. Popovic and J. R. Harbour Polysilicate Equilibria in Concentrated Sodium Silicate Solutions I. L. Svensson, S. Sjoberg and L-0. Ohman Potentials of Ion-exchanged Synthetic Zeolite-Polymer Membranes M. Demertzis and N. P. Evmiridis Adsorption and Reduction of Nitrogen Monoxide by Potassium-doped Carbon T. Okuhara and K. Tanaka Physicochemical Properties and Isomerization Activity of Chlorinated Pt/Al,O, Catalysts A. Melchor, E. Garbowski, M-V. Mathieu and M. Primet Excess Pressures for Aqueous Solutions M. J. Blandamer, J. Burgess and A. W. Hakin Effect of Temperature on the Point of Zero Charge and Surface Dissociation Constants of Aqueous Suspensions of y-Al,O, K. Ch. Akratopulu, L. Vordonis and A. Lycourghiotis Thermal Decomposition of Solid Sodium Bicarbonate M. C. Ball, C. M. Snelling, A. N. Strachan and R. M. Strachan Reviews of Books J-P. Joly I I7

ISSN:0300-9599    

DOI:10.1039/F198682FX001

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

JOURNAL OF THE CHEMICAL SOCIETY 1 7 15 21 41 49 61 69 75 83 93 101 Faraday Transactions II, Issue 1, I986 Molecular and Chemical Physics For the benefit of readers of Faraday Transactions I, the contents list of Faraday Transactions 11, Issue 1 is reproduced below. Nuclear Magnetic Resonance Investigation of Lithium Diffusion in Li,AlO, T. Matsuo, T. Shibuya and H. Ohno Thermally Stimulated Depolarisation Currents in Stearic Acid Multilayers M. A. Careem and A. K. Jonscher Vibronic Exciton Bands. Adsorption Spectra of Eosin Y Dimers D. Fornasiero and T. Kurucsev Kinetic Study of Mg(3 Mg(3 lP1) and Mg(4 3S1), including Energy Pooling, following Pulsed Dye-laser Excitation at h = 457.1 nm [Mg(3 ,P1) + Mg(3 l&)] D. Husain and G. Roberts A profile-refinement Approach for Normal-coordinate Analyses of Inelastic Neutron-scattering Spectra G.J. Kearley Structural Analysis of AlC1,-n-Butylpyridinium Chloride Electrolytes by X-Ray Diffraction S. Takahashi, N. Koura, M. Murase and H. Ohno Bonding in B,Hi- and other closo-Boranes P. W. Fowler An Ab Initio Study of the Ground and Excited States of CuH, and CuHi M. T. Nguyen, M. A. McGinn and N. J. Fitzpatrick The Physical Origin of Negative Capacitance A. K. Jonscher Solid-state Characterisation of the 7,7,8,8-Tetracyano-p-quinodimethane Salt of the 5,5-Dimethyldibenzophospholium Cation G. J. Ashwell, D. W. Allen, A. Graja and R. swietlik A Refined Study of the Ionization Energies of Phosphorus and Nitrogen Trihalides B. D. El-Issa and H. M. Zanati Isotherms of the Hydrogen-Hafnium System K. Yura, S.Naito, M. Mabuchi and T. Hashino (i)The following papers were accepted for publication in J. Chem. SOC., Faraday Trans. Z during October. 5 / 2 4 5/436 5/493 5/505 5/809 5/880 5/905 5/906 5/986 Structural Relationships in the Reduction of the Vanadia-Molybdena Inter- mediate Compound M. Najbar Photocatalytic Dehydrogenation of Liquid Propan-2-01 by TiO,. Part 1. Kinetics I. M. Fraser and J. R. MacCallum Catalytic Reactions on Metal-supported Semiconductors. Oxidation of CO over ZnO Films on Silver E. Weiss and M. Folman Interpretation of Acidic and Physical Properties of Solid Acid Catalysts based on Adsorption of Basic Molecules in Non-polar Solvents S. Mishima and T. Nakajima Catalytic Properties of Magnesium Oxides doped with Sodium Compounds T.Matsuda, Z. Minami, Y. Shibata, S. Nagano, H. Miura and K. Sugiyama The Oxidation of Carbon Monoxide on a Platinum Catalyst at Atmospheric Pressure P. Cameron, R. P. Scott and P. Watts General Formulae for the Curvature Dependence of Droplets and Bubbles J. Schmelzer and R. Mahnke On the Curvature Dependence of Surface Tension of Small Droplets J. Schmelzer Metal-Ligand Complex Formation in the Presence of Ionic Micelles. Equi- librium and Kinetics of the Reaction between Cupric Ion and Benzoylacetone in the Presence of Ionic Micelles of SDS or DTACL Y. Miyake, M. Shigeto and M. Teramoto 5 / 1019 Concentration Polarization and Water Dissociation in Ion Exchange Membrane Electrodialysis. Mechanism of Water Dissociation Y. Tanaka and M. Seno 5 / 1039 One-electron Oxidation of Iron(r1) Complexes of Tryptophan and Histidine : A Pulse-radiolysis Study B. J.Parsons, M. Al-Hakim, G. 0. Phillips and A. J. Swallow 5 / 1083 Heat Capacity, Compressibility and Expansion of Associated Systems. General Formulae based on the Theory of Association Equilibria J. Pouchley 5 / 1 1 18 Kinetics of the Solvolysis of the cis-Chlorothiocyanatobis( 1,2-diaminoethane) cobalt(II1) Ion in Water + t-Butyl Alcohol A. E. Eid and C. F. Wells 5 / 1 1 19 Electron Spectroscopic Studies of Formic Acid Adsorption and Oxidation on Cu and Ag dosed with Barium M. Ayyoob and M. S. Hegde 5 / 1 130 Interfacial Tension Minima in Oil-Water-Surfactant Systems. Effects of Alkane Chain Length and Presence of n-Alkanols in Systems containing Aerosol OT R. Aveyard, B.P. Binks and J. Mead 5 / 1 135 Catalysis by Amorphous Metal Alloys. Part 4.-Structural Modification towards Metastable States and Catalytic Activity of Amorphous Ni,,B,, Ribbon Alloy H. Yamashita, M. Yoshikawa, T. Funabiki and S. Yoshida 5 / 1 167 Electrode Kinetics of the Cdll/Cd(Hg) System in Ethylene Glycol-Water Mixtures J. A. Garrido, R. M. Rodriguez, E. Brillas and J. Domenech 5 / 1 176 Application of the Competitive Preferential Solvation Theory to Ion-Molecule Interactions B. Parbhoo and 0. B. Nagy 5 / 1200 Paramagnetic Metal and Oxygen Species observed with Rh/A1,0, and Rh/ZrO, Dependence on the Decarbonylation Temperature of [Rh,(CO),,] on Alumina and Zirconia Supports A. Gervasini, F. Morazzoni, F. Pinna, D. Strumolo, G. Strukul and L. Zanderighi 5/1202 Mixed Adsorption of a Non-ionic and an Anionic Surfactant at the Carbon/Aqueous Solution Interface M. J.Hey, J. W. Mactaggart and C. H. Rochester (ii)5 / 1204 Determination of Micelle Size and Polydispersity by Fluorescence Quenching. Theory and Numerical Results G. G. Warr and F. Grieser 5 / 1205 Determination of Micelle Size and Polydispersity by Fluorescence Quenching. Experimental Results G. G. Warr, G. Grieser and D. F. Evans 5/1221 Solution Properties of Water in Molten AgN0,-LiNO, Mixtures as derived from Vapour Pressure Measurements on AgN0,-LiN0,-H,O Melts Z. Kodejs and G. A. Sacchetto 5/ 1342 Contamination by Coherent Scattering of the Elastic Incoherent Structure Factor observed in Neutron Scattering Experiments B. Gabrys, J. S. Higgins and 0.Scharpf 5 / 1343 Short-range Order in Amorphous Poly(methy1 methacrylate) B. Gabrys, J. S. Higgins and 0. Scharpf 5/ 1363 Re,O,/Al,O, * B,O, Metathesis Catalysts X. Xiaoding, C. Boelhouwer, J. I. Benecke, D. Vonk and J. C. Mol 5/1373 Complexation of Roccelin by P-Cyclodextrin R. J. Clarke, J. H. Coates and S. F. Lincoln 5 / 1374 Inhibition of the Thin-film Oxidation of n-Dodecane by p-Methoxyphenol A. D. Ekechukwu and R. F. Simmons 5 / 1412 Rates and Activation Parameters of Alkaline Hydrolysis of 2-Carbo- methoxypropionate Ion in Aqueous Mixtures of DMSO P. K. Biswas and M. N. Das 5 / 1420 Rotamerism and Trans-Cis Photoisomerization of 1 -(2-Naphthyl)-2-(n’- pyridy1)ethylenes studied by Stationary and Pulsed Fluorescence Techniques G. Bartocci, F. Masetti, U.Mazzucato, A. Spallett and M. C. Bruni 5 / 1490 Acid-Base Equilibria in Polyelectrolyte Systems H. Vink 5/1491 Radical Cations of Orangic Carbonates of Trimethyl Borate and of Methyl Nitrate. A Radiation-Electron Spin Resonance Study N. S. Ganghi, D. N. Ramakrishna Rao and M. C. R. Symons 5/ 1556 Deuterium Longitudinal Nuclear Magnetic Relaxation of Heavy Water in Alkylammonium Chloride Solutions. Effect of Deuterium Exchange between Water and Polar Heads M. P. Bozonnet-Frenot, J. P. Marchal and D. Canet 5/ 1565 Photochemistry of Methyl Viologen in Aqueous Solution containing Polymeric Carboxylic Acids R. D. Stramel and J. K. Thomas 5/ 1704 Thermal Desorption and Infrared Studies of Primary Aliphatic Amines adsorbed on Haematite (a-Fe,O,) U. Marx, R. Sokoll and H.Hobert (iii)Aveyard, R., 125 Baldwin, R. R., 89 Binks, B. P., 125 Bloemendal, M., 53 Chiou, C. T., 243 Clark, S., 125 Dawber, J. G., 119 Dean, C. E., 89 Fisher, D. T., 119 Funabiki, T., 35 Gormally, J., 157 Handn, O., 77 Heatley, F., 255 Hedges, W. M., 179 Higson, S., 157 Honeyman, M. R., 89 Hunt, D. J., 189 Iizuka, T., 61 Ikeda, H., 61 Jackson, S. D., 189 Jaeger, N., 205 Cumulative Author Index 1986 Kevan, L., 213 Khoo, K. H., 1 Kleine, A., 205 Lang, J., 109 Leaist, D. G., 247 Lim, T-K., 69 Logan, S. R., 161 Malliaris, A., 109 Manes, M., 243 Marcus, Y., 233 Mead, J., 125 Miyamoto, A., 13 Morgan, H., 143 Mori, K., 13 Moyes, R. B., 189 Murakami, Y., 13 Narayana, M., 213 Okazaki, S., 61 Ooe, M., 35 Pethig, R., 143 Pletcher, D., 179 Rideout, J., 167 Rosenholm, J.B., 77 ROUW, A. C., 53 Ryder, P. L., 205 Salmon, G. A., 161 Sark,’.ny, A., 103 Shindo, H., 45 Somsen, G., 53 Symons, M. C. R., 167 Tanaka, T., 35 Walker, R. W., 89 Warhurst, P. R., 119 Wells, P. B., 189 Whyman, R., 189 Wiens, B., 247 Wren, B. W., 167 Yoshida, S., 35 Zana, R., 109 Schulz-Ekloff, G., 205PAGE MISSINGPAGE MISSINGNOMENCLATURE A N D SYMBOLISM Units and Symbols. The Symbols Committee of The Royal Society, of which The Royal Society of Chemistry is a participating member, has produced a set of recommendations in a pamphlet ‘Quantities, Units, and Symbols‘ (1 975) (copies of this pamphlet and further details can be obtained from the Manager, Journals, The Royal Society of Chemistry, Burlington House, London W1 V OBN). These recommendations are applied by The Royal Society of Chemistry in all its publications.Their basis is the ’ SystBme International d‘Unit6s’ (SI). A more detailed treatment of units and symbols with specific application to chemistry is given in the IUPAC Manual of Symbols and Terminology for Ph ysicochemical Quantities and Units (Pergamon, Oxford, 1 979). Nomenclature. For many years the Society has actively encouraged the use of standard IUPAC nomenclature and symbolism in its publications as an aid to the accurate and unambiguous communication of chemical information between authors and readers. In order to encourage authors to use IUPAC nomenclature rules when drafting papers, attention is drawn to the following publications in which both the rules themselves and guidance on their use are given: Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H (Pergamon, Oxford, 1979 edn).Nomenclature of Inorganic. Chemistry (Butterworths, London, 1 971 , now publis- hed by Pergamon). Biochemical Nomenclature and Related Documents (The Biochemical Society, London, 1978). A complete listing of all IUPAC nomenclature publications appears in the January issues of J. Chem. Soc., Faraday Transactions. It is recommended that where there are no IUPAC rules for the naming of particular compounds or authors find difficulty in applying the existing rules, they should seek the advice of the Society‘s editorial staff.THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 81 Lipid Vesicles and Membranes Loughborough University of Technology, 15-17 April 1986 Organising Committee: Professor D.A. Haydon (Chairman) Professor D. Chapman Mrs Y. A. Fish Dr M. J. Jaycock Dr I. G. Lyle Professor R. H. OttewiII Dr A. L. Smith Dr D. A. Young The aim of the meeting is to discuss the physical chemistry of lipid membranes and their interactions, in particular theoretical and spectroscopic studies, polymerised membranes, thermodynamics of bilayers and Iiposomes, mechanical properties, encapsulation and interaction forces between bilayers leading to fusion but excluding preparation and characterisation methodology. The programme and application form may be obtained from: Mrs Y . A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO.82 Dynamics of Molecular Photof rag mentat ion University of Bristol, 15-1 7 September 1986 Organising Committee : Professor R. N. Dixon (Chairman) Dr G. G. Balint-Kurti Dr M. S. Child Professor R. Donovan Professor J. P. Simons The discussion will focus on the interaction of radiation with small molecules, molecular ions and complexes leading directly or indirectly to their dissociation. Emphasis will be given to contributions which trace the detailed dynamics of the photodissociation process. The aim will be to bring together theory and experiment and thereby stimulate important future work. The preliminary programme may be obtained from: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN (viii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM NO. 21 Promotion in HeterogeneousCatalysis University of Bath, 23-25 September 1986 Organising Committee : Professor F.S. Stone (Chairman) Dr R. Burch Mrs Y. A. Fish The symposium will form the Faraday Division Programme at the 1986 Autumn meeting of the Royal Society of Chemistry, however, it will be conducted as a discussion meeting, with pre-printed papers and subsequent publication, following the style of the traditional Faraday discussions and symposia. The role of promoters is of intrinsic interest as well as being important for many industrial processes. Promoters are used for three purposes, t o improve catalyst activity, to increase selectivity for the desired reaction, and to prolong catalyst life at high activity and selectivity.There are current advances in both exprimental and theoretical aspects of promoter action, making this an opportune time for a Faraday symposium. Attention will be focussed on the role of promoters in enhancing activity and selectivity. Three areas will be highlighted - model studies using well-defined surfaces such as single crystals, characterization of promoter function in real catalysts, and theoretical aspects of promotion. The mechanisms of promoter action in metal, oxide and sulphide catalysts will be discussed. Dr R. W. Joyner Professor J. Pritchard Dr D. A. Young (Editor) Further information may be obtained from: MrsY. A. Fish,The Royal Societyof Chemistry, Burlington House, London WlVOBN.THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM NO. 22 Interaction-induced Spectra in Dense Fluids and Disordered Solids University of Cambridge, 10-1 1 December 1986 Organising Committee: Professor A. D. Buckingham (Chairman) Dr R. M. Lynden-Bell Dr P. A. Madden Professor E. W. J. Mitchell Dr J. Yarwood Dr D. A. Young Mrs Y. A. Fish Whilst interaction-induced spectra have been studied in the gas phase for many years, their importance in the spectroscopy of condensed matter has been appreciated only relatively recently. At present a considerable number of studies of induced spectra are taking place in what are (nominally) widely separated fields of study. It is highly desirable t o bring these communities together so that common issues can be identified and the progress of one field appreciated in another.The preliminary programme may be obtained from : Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBNTHE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 83 Brownian Motion University of Cambridge, 7-9 April 1987 Organising Committee Dr M. La1 (Chairman) Dr R. Ball Dr E. Dickinson Dr J. S. Higgins Dr P. N. Pusey Dr D. A. Young Mrs Y. A. Fish The aim of the meeting is to discuss new developments in the experimental and theoretical studies of Brownian motion of colloidal particles and macromolecules, with particular emphasis on the dynamics of aggregate formation and breakdown, computer simulation and many- body hydrodynamic interactions. Contributions for consideration by the Organising Committee are invited and abstracts of about 300 words should be sent by 15 June 1986 to: Dr M .Lal, Unilever Research, Port Sunlight Laboratory, Bebington, Wirral L63 3JW Full papers for publication in the Discussion volume will be required by December 1986 THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 84 Dynamics of Elementary Gas-phase Reactions University of Birmingham, 14-1 6 September 1987 Organising Committee: Professor R. Grice (Chairman) Dr M. S. Child Dr J. N. L. Connor Dr M. J. Pilling Professor I. W. M. Smith Professor J. P. Simons The Discussion will focus on the development of experimental and theoretical approaches to the detailed description of elementary gas-phase reaction dynamics.Studies of reactions at high collision energy, state-to-state kinetics, non-adiabatic processes and thermal energy reactions will be included. Emphasis will be placed on systems exhibiting kinetic and dynamical behaviour which can be related to the structure of the reaction potential-energy surface or surfaces. Contributions for consideration by the Organising Committee are invited. Titles should be submitted as soon as possible and abstracts of about 300 words by 30 September 1986 to Professor R. Grice, Chemistry Department, University of Manchester, Manchester M13 9PLJOURNAL OF CHEMICAL RESEARCH Papers dealing with physical chemktry/chemical physics which have appeared recently in J.Chern.Research, The Royal Society of Chemistry's synopsis t microform journal, include the following : Radical Cations of Di-, Tri-, and Tetra-bromoethane formed by Radiolysis: an Electron Spin Resonance Study Martyn C.R. Symons (1 985, Issue 8) The Use of Deuterium N.m.r. Spectroscopy in Mechanistic Studies of Alkane-exchange Reactions on Supported Platinum and Rhodium Catalysts Ronald Brown, Charles Kemball, James A. Oliver, and Ian H. Sadler (1 985, Issue 9) Electron Spin Resonance Investigation of Environmental Effects in the Photosensitised Reaction of Uranyl Ion with Thioethers Hanna B. Ambroz andTerence J. Kemp (1 985, Issue 9) The Iron-Vanadium-Oxygen System at 11 23, 1273 and 1373 K. Part 2. Activities in Fe,O,- FeV,O, Spinel Solid Solutions Larbi Marhabi, Marie-Chantal Trinel-Dufour, and Pierre Perrot (1 985, Issue 10) Complexes of Sodium, Potassium, Magnesium, and Calcium Cations with the Lysocellin lonophore in Methanol Jean Juillard, Claude Tissier, and Georges Jeminet (1 985, Issue 10) Is Singlet Cyclopentyne a True Minimum on the C,H, Potential-energy Hypersurface? Santiago Olivella, Miquel A.Pericas, Antoni Riera, and Albert Sole (1985, Issue 10) Clay- and Zeolite-catalysed Cyclic Anhydride Formation Richard W. McCabe, John M . Adams, and Keith Martin (1 985, Issue 11) Predicted Binding Energies of Dihydrofolate Reductase Inhibitors Alistair F. Cuthbertson and W. Graham Richards (1985, Issue 11) FARADAY DIVISION INFORMAL AND GROUP MEETINGS Division-Endowed Lecture Symposium Perspectives in Colloid Science (including the Liversidge Lecture by R. H. OttewiII) To be held at Imperial College, London on 1 9 February 1986 Further information from Mrs Y.A. Fish, The Royal Society of Chemistry, Burlington House, London W1 V OBN Theoretical Chemistry Group Post graduate Students' Meeting To be held at University College, London on 5 March 1986 Further information from Dr G. Doggett, Department of Chemistry, University of York, York YO1 5DD Electrochemistry Group Graduate Students' Meeting To be held at Imperial College, London on 5 March 1986 Further information from Or G. H. Kelsall, Department of Mineral Resources, Imperial College, London SW7 2BPNeutron Scattering Group Workshop on Neutron Scattering Data Reduction To be held at the Rutherford Appleton Laboratory, Didcot, on 13-1 4 March 1986 Further information from Mrs M.Sherwin, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX1 1 OQX Molecular Beams Group with CCP6 Molecular Scattering-Theory and Experiment To be held at the University of Sussex on 19-21 March 1986 Further information from Dr A. Stace, School of Molecular Sciences, University of Sussex, Falmer, Brighton BN1 9QJ Division with the Institute of Physics, Institute of Mechanical Engineers, Plastic and Rubber Institute and the Institute of Chemical Engineers Tribology in Powder Conveying and Processing : Powder Compaction and Interface Shear To be held at the University of Bradford on 26 March 1986 Further information from Dr B. Briscoe, Department of Chemical Engineering, Imperial College, London SW7 2BY Electrochemistry Group New Techniques for the Characterisation of Electrodes and their Reactions To be held at St Catherine's College, Oxford on 7-9 April 1986 Further information from Dr S.P. Tyefield, CEGB, Rs Dept, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB Divisio n-A nn ual Congress Structure and Reactivity of Gas Phase Ions To be held at the University of Warwick on 8-1 1 April 1986 Further information from Professor K. R. Jennings, Department of Molecular Sciences, University of Warwick, Coventry CV4 7AL Polymer Physics Group with the Statistical Mechanics and Thermodynamics Group Macromolecular Flexibility and Behaviour in Solution To be held at the University of Bristol on 16-1 8 April 1986 Further information from the The Meetings Officer, The Institute of Physics, 47 Belgrave Square, London SWlX 8QX Division with the Societd Franpaise de Chimie, Deutsche Bunsen Gesellschaft fur Ph ysikalische Chemie and Associazione ltaliana di Chimica Fisica Dynamics of Molecular Crystals To be held at Grenoble, France on 30 June to 4 July 1986 Further information from Dr C.Troyanowsky, 10 rue Vauquelin, 75005 Paris, France Industrial Physical Chemistry Group Physical Chemistry of Water Soluble Polymers To be held at Girton College, Cambridge on 1-3 July 1986 Further information from Dr I. D. Robb, Unilever Research Laboratory, Port Sunlight, Bebington, Wirral, L63 3JW Division with the Institute of Physics, Institute of Mechanical Engineers, Plastic and Rubber Institute and Institute of Chemical Engineers Tribology in Powder Conveying and Processing : Wear Attrition in Powder Flows To be held at the University of Birmingham on 2 July 1986 Further information from Dr B.Briscoe, Department of Chemical Engineering, Imperial College, London SW7 2BY (Xi)Gas Kinetics Group and Division de Chimie-Physique de la Societe Franqaise de Chimie 9th International Symposium on Gas Kinetics To be held in Bordeaux, France on 20-25 July 1986 Further information from Dr R. Lasclaux, Lab. Photophys. Photochim. Moleculaire, Universitk de Bordeaux I, 33405 Talence Cedex, France Polymer Physics Group Biologically Engineered Polymers To be held at Churchill College, Cambridge on 21-23 July 1986 Further information from Dr M. J. Miles, AFRC Food Research Institute, Colney Lane, Norwich NR4 7UA Polymer Physics Group with the British Rheological Society Deformation in Solid Polymers To be held at the University of Leeds on 9-1 1 September 1986 Further information from Dr J.V. Champion, Department of Physics, City of London Polytechnic, 31 Jewry Street, London EC3N 2EY Carbon Group Carbon Fibres-Properties and Applications To be held at the University of Salford on 15-1 7 September 1986 Further information from The Meetings Officer, The Institute of Physics, 47 Belgrave Square, London SW1X 8QX Electrochemistry Group with the Electr oanaly tical Group New Electrode Materials for Electrochemistry and Electroanalytical Applications To be held at Imperial College, London on 15-1 7 September 1986 Further information from Professor W. J. Albery, Department of Chemistry, Imperial College, London SW7 2AZ Division with the Surface Reactivity and Catalysis Group-Autumn Meeting Promotion in Heterogeneous Catalysis To be held at the University of Bath on 23-25 September 1986 Further information from Professor F.S. Stone, School of Chemistry, University of Bath, Bath BA2 7AY (xiii)MINUTES OF THE THIRTEENTH ANNUAL GENERAL MEETING OF THE FARADAY DIVISION The Thirteenth Annual General Meeting of the Faraday Division of the Royal Society of Chemistry was held at 9.00am on Tuesday 2 April 1985 at the Babbage Lecture Theatre, Cambridge with Professor P. Gray, C.Chem., F.R.S.C., F.R.S. in the Chair. 1. Minutes The Minutes of the 12th Annual General Meeting which were tabled, had been printed in Faraday Transactions and were approved. 2. Annual Report THE 1984 ANNUAL REPORT OF THE FARADAY DIVISION General Discussion No.77 on ‘Interfacial Kinetics in Solution’ was held at the University of Hull on 9-11 April at which there were 74 participants including 27 from overseas from 14 countries. The Chairman of the Organising Committee was Professor D. H. Everett and the topic was put forward by Dr M. Spiro. The second Discussion of the year was number 78 on ‘Radicals in Condensed Phases’ held at the University of Leicester on 4-6 September. It attracted 74 participants of whom 30 were from overseas representing 11 countries. The chairman of the Organising Committee was Professor M. C. R. Symons. The 1984 Symposium was held in Cambridge on 12-13 December on ‘Molecular Electronic Structure Calculations: Methods and Applications’ at which there were 127 participants including 40 from 13 overseas countries.The third Lennard-Jones Lecture (sponsored by Unikver) was given at the Symposium by Dr N. C. Handy of the University of Cambridge. The Symposium, which was number 19 in the series, was organised by Professor A. D. Buckingham. Successful poster sessions were held at the September Discussion and the Symposium. The 1984 Annual Chemical Congress was held at the University of Exeter on 16-19 April to which the Faraday Division contributed a symposium on ‘ Electronic Processes in Thin Films and Novel Conductors’ which was convened by Dr D. R. Rosseinsky jointly with the Molecular Crystals Group. The Division’s contribution to the 1984 Autumn Meeting held at Hull on ‘Combustion Chemistry in the Gas Phase’ was convened by Dr R.W. Walker in collaboration with the Gas Kinetics Group. The 1984 Bourke Lectures were given by Professor V. Ponec of the University of Leiden, The Netherlands at Teesside Surface Science Club in Stockton-on-Tees, University College Dublin, the University of Bath and Queen Mary College, London. The topics of his talks were ‘ Catalysis of CO Hydrogenation and the Synthesis of Oxygen-Containing Molecules’, ‘Ensemble Size and Ligand Effects in the Catalysis of Hydrocarbon Reactions on Alloys’ and ‘Particle Size Effects, Promotion and Metal Support Interaction in Heterogeneous Catalysts’. The Division held two London Symposia arranged around endowed lectures of the RSC in 1984. The first was on 9 February on ‘The Selective Use and Disposal of Energy in Elementary Processes’ which included the Tilden Lecture by Dr I.W. M. Smith and the Meldola Lecture by Dr I. Powis. The second was on ‘Phase Equilibrium and Interfacial Structure’ on 10 December which included the Centenary Lecture by Professor B. Widom (Cornell University, U. S . A.) . One Joint meeting was held with the Institute of Physics on 21 November on ‘Drying and Curing: Theory and Practice’. The sixth in the series of joint meetings with the Deutsche Bunsen Gesellschaft fur Physikalische Chemie ; Societe de Chimie Physique; and Associazione Italiana di Chimica Fisica ’ was held in Tutzing, West Germany on ‘ Laser Studies in Reaction Dynamics’ and was organised by a committee under the chairmanship of Professor J.Troe. The Division was represented on the Organising Committee by Dr I. W. M. Smith. The Subject Groups affiliated to the Division maintained vigorous activity in 1984 organising (xiv)a range of meetings both independently and in collaboration with other Groups and in some cases with outside bodies. Group meetings included : Prediction of Fluid Properties (Statistical Mechanics and Thermodynamics Group) Combustion Kinetics (Gas Kinetics Group) Theoretical Chemistry (Theoretical Chemistry Group) Quantum Molecular Motion in Crystals and Intercalates and on Surfaces (Neutron Sciences Related to the Usage of Pitch and Coke (Carbon Group) Pore Structure and Gas Flow in Graphites (Carbon Group) Thermodynamics of Mixed Polymer Systems (Statistical Mechanics and Thermodynamics Studies on Model Catalysts-Their Impact on Applied Catalysis (Surface Reactivity and Theory of Localized States in Condensed Matter (Polar Solids Group with Daresbury Engineering Aspects of Electrochemistry (Electrochemistry Group with the Electrochemical Models of Polymer Deformation (Polymer Physics Group) The Metal-Polymer Interface (Industrial Physical Chemistry Group) 6th International Symposium on Gas Kinetics (Gas Kinetics Group) Cell Adhesion to Solid Surfaces (Industrial Physical Chemistry Group) Cruickshank Symposium : Modern Experimental and Theoretical Studies and Molecular Structure (Theoretical Chemistry Group, Department of Chemistry, UMIST, British Crystallographic Association and the Chemical Crystallography Group) Scattering Group) Group) Catalysis Group) Laboratory) Technology Group of the S.C.I.) Waddington Memorial Lecture (Neutron Scattering Group) New Directions in Molecular Beams (Molecular Beams Group) Electrolytic Bubbles (Electrochemistry Group with the Electrochemical Group of the S.C.I.) Kinetics and Mass Transport of Silicate and Oxide Systems (Polar Solids Group with the Dynamic Surface Tension Effects in Aeration and Foaming (Colloid and Interface Science The Electrical Double Layer (Electrochemistry Group with the Statistical Mechanics and Refractory Applications of Carbon (Carbon Group) Organic Electrosynthesis (Electrochemistry Group with the New Science Group of I.C.I.) Neutron Scattering from Aqueous Systems (Neutron Scattering Group) Fundamental Aspects of Polymer Flammability (Polymer Physics Group) Polymers in a Marine Environment (Polymer Physics Group with the Institute of Marine Applications of Thermal Methods in Catalysis (Surface Reactivity and Catalysis Group with CARS, Diode Laser and Microwave Spectroscopy (High Resolution Spectroscopy Group) Colloidal Aspects of Cohesive Sediments (Colloid and Interface Science Group with the Colloid and Surface Science Group of the S.C.I.) Neutrons in Magnetism (Neutron Scattering Group) British Ceramic Society, Institute of Physics and the Mineralogical Society) Group with the Colloid and Surface Group of the S.C.I.) Thermodynamics Group) Engineers) the Thermal Methods Group) The third R.A. Robinson Memorial Lectures were given by Dr A. K. Covington of the University of Newcastle upon Tyne at the Universities of Singapore, Penang and Kuala Lumpur in January.The 1984 Marlow Medal was awarded to Dr N. V. Richardson of the University of Liverpool, distinguished for his contributions to surface chemical physics using angle resolved photo- electron spectroscopy, vibrational spectroscopy and group theoretical analysis. There were three meetings of the Faraday Editorial Board and a Council Working Party to consider the future development of Faraday Transactions was set up under the chairmanship of Professor Sheppard. The first change to be agreed was the inclusion of the annual Symposium series in an issue of the Transactions beginning in 1985. Further significant changes in the Transactions were discussed by both groups and firm recommendations were made to Council.(xv)Contact with members was maintained through Newsletter 11 which was circulated in February. Membership of the Division in 1984 was 4064 of whom 2952 were in the U.K. and 1112 overseas, a slight decrease on 1983. Treasurer’s Report The Treasurer reported verbally on the Division’s financial performance in 1984 as the R.S.C. accounts for the period were not finalised. Divisions received an allocation from the R.S.C. to run their activities which covered such costs as Council and Committee travel, printing, postage and support for scientific meetings. The Discussions and Symposia were budgeted to be self-financing. He reported that the Faraday Division had had a satisfactory year in spite of the two Discussions having lower than average attendances.Elections to Council Members of Council elected to take office from the Society’s Annual General Meeting in July 1985 were announced as follows: President: PROFESSOR N. SHEPPARD 1987 Vice-presidents who have held ofice as President PROFESSOR D. H. EVERETT PROFESSOR J. S. ROWLINSON PROFESSOR D. H. WHIFFEN PRomso~ F. C . TOMPKINS PROFESSOR P. GRAY Vice- Presidents PROFESSOR H. M. FREY 1988 PROFESSOR R. PARSONS 1987 PROFESSOR J. H. PURNELL 1988 PROFESSOR J. P. SIMONS 1988 PROFESSOR F. S. STONE PROFESSOR M. C. R. SYMONS DR D. A. YOUNG Ordinary Members DR M. S. CHILD 1986 DR J. S. HIGGINS PROFESSOR R. N. DIXON 1988 PROFESSOR J. H. KNOX PROFESSOR T. EDMONDS 1988 DR M. LAL DR A. K. GALWEY 1986 PROFESSOR R. H. OTTEWILL PROFESSOR. GRICE 1987 PROFESSOR J. N.SHERWOOD 1987 1987 1987 1987 1987 1986 1986 1988 Honorary Secretary: Professor J. P. SIMONS Honorary Treasurer: Professor R. H. OTTEWILL The President thanked the retiring members of Council, Dr Smith, Dr Ulstrup and Professor Williams. 5. Review of Future Activities The President drew attention to the programme of future activities which had been tabled. In particular, he drew attention to the General Discussion on ‘ Physical Interactions and Energy Exchange at the Gas-Solid Interface’ to be held in July 1985 at McMaster University in Canada. Members were reminded that the Conference Committee welcomed suggestions of topics for General Discussions and Symposia which could be submitted to any Divisional Officer. At the conclusion of the meeting, Professor Gray thanked the Secretary of the Division, Mrs Angela Fish, for the help and support he had received from the Divisional office during his term as President.(xvi)Deposition of Data-Supplementary Publications Scheme Preamble The growing volume of research that produces large quantities of data, the increasing facilities for analysing such data mechanically, and the rising cost of printing are each making it very difficult to publish in the Journal the full details of the experimental data which become available. Moreover, whilst there is a large audience for the general method and conclusions of a research project, the number of scientists interested in the details, and in particular in the data, of any particular case may be quite small. The British Library Lending Division (B.L.L.D.) in consultation with the Editors of scientific journals, has developed a scheme whereby such data and detail may be stored and then copies made available on request at the B.L.L.D., Boston Spa.The Society is a sponsor of this scheme and has indicated to the B.L.L.D. its wish to use the facilities available in this 'Supplementary Publications Scheme'. Bulk information (such as computer programs and output, evidence for amino-acid sequences, spectra, etc.), which accompany papers published in issues of the Society's Journal may be deposited, free of charge, with the Supplementary Publications Scheme, either at the request of the author and with the approval of the referees or on the recommendation of referees and the approval of the author.The Scheme Under this scheme, authors should submit articles and the supplementary material to the Journalsimultaneously in the normal way, and both will be refereed. If the paper is accepted for publication the supplementary material is then sent by the Society to the B.L.L.D. where it is stored. Copies are obtainable by individuals both in the U.K. and abroad on quoting a supplementary publication number that appears in the parent article. Preparation of Material Authors are responsible for the preparation of camera-ready copy according t o the following specifications (although the Society is prepared to help in case of difficulty). (a) Optimum page size for text or tables in typescript: up to 30 cm x 21 cm. ( b ) Limiting page size for text or tables in typescript: 33 cm x 24 cm.( c ) Limiting size for diagrams, graphs, spectra, etc.: 39 cm x 28.5 cm. ( d ) Tabular matter should be headed descriptively on the first page, with column (e) Pages should be clearly numbered. headings recurring on each page. It is recommended that all material which is to be deposited should be accompanied by some prefatory text. Normally this will be the summary from the parent paper and authors will greatly aid the deposition of the material if a duplicate copy of the summary is provided. If authors have the facilities available the use of a type face designed to be read by computers is encouraged. (xvii)Deposit ion The Society is responsible for the deposition of the material with the B.L.L.D. The B.L.L.D. does not receive material direct from authors since the Library wishes to ensure that the material had been properly and adequately refereed.Action by the Society The Society normally receives a manuscript for publication together with any supplementary material for deposition and circulates all of this to referees in the normal way. When the edited manuscript is sent to the printers the supplementary material is sent for deposition to the B.L.L.D. and a publication number is issued. The Society adds to the edited manuscript a footnote indicating what material has been deposited in the Supplementary Publications Scheme, the number of pages it occupies, the supplementary publication number, and details as to how copies may be obtained. Avai la bi I i ty Copies of Supplementary Publications may be obtained from the B.L.L.D.on demand by organisations which are registered borrowers. They should use the normal forms and coupons for such requests addressing them as follows: Mr J. P. Chillag, British Library Lending Division, Boston Spa, Wet herby, West Yorkshire, LS23 7BQ, U.K. Non-registered users may also obtain copies of Supplementary Publications but should first apply for price quotations. These are available from the Loans Office at the above address. In all correspondence with the B.L.L.D. or the Society authors must cite the supplementary publication number. International Collaboration A similar scheme (known as the National Auxiliary Publications Service) is being operated in the U.S.A. by the American Society for Information Science. Similar schemes are also being contemplated in other countries.The provision of reciprocal arrangements for the exchange of supplementary data between the various national deposition centres is being investigated. (XViii)APPENDIX IUPA C Publications on Nomenclature and Symbolism 1 .O Compilations 1.1 Nomenclature of Organic Chemistry, a 550-page hard- cover volume published in 1979, available from Pergamon, Oxford. Section A: Hydrocarbons Section B: Fundamental heterocyclic systems Section C: Characteristic groups containing carbon, hy- drogen, oxygen, nitrogen, halogen, sulphur, selenium, and tellurium Section D: Organic compounds containing elements not exclusively those referred to in the title of Section C Section E: Stereochemistry Section F: General principles for the naming of natural products and related compounds Section H: Isotopically modified compounds 1.2 Nomenclature of Inorganic Chemistry, a 1 10-page hardcover volume published in 1970, available from Pergamon, Oxford.Chapter 1: Elements Chapter 2: Formulae and names of compounds in general Chapter 3: Names for ions and radicals Chapter 4: Iso- and hetero-polyanions Chapter 5: Acids Chapter 6: Salts and salt-like compounds Chapter 7: Co-ordination compounds Chapter 8: Addition compounds Chapter 9: Crystalline phases of variable composition Chapter 10: Polymorphism Chapter 11: Boron compounds 1.3 Biochemical Nomenclature and Related Documents, a 220-page softcover manual published in 1978 by The Bio- chemical Society for IUB, and available from the Biochemical Society Book Depot, P.O.Box 32, Commerce Way, Colchester, Essex C 0 2 8HP. The contents are as follows: General Nomenclature of organic chemistry. Section E: Stereo- chemistry (1974) Nomenclature of organic chemistry. Section F Natural products and related compounds (1976) Nomenclature of organic chemistry. Section H: Isotopically modified compounds (1977) Isotopically labelled compounds: common biochemical practice Recommendations for measurement and presentation of biochemical equilibrium data (1976) Abbreviations and symbols for chemical names of special interest in biological chemistry (1965) Abbreviations and symbols: a compilation (1976) Citation of bibliographic references in biochemical journals (1971) Amino acids, peptides and proteins Nomenclature of a-amino acids (1974) Symbols for amino-acid derivatives and peptides (1971) Rules for naming synthetic modifications of natural Abbreviated nomenclature of synthetic polypeptides or polymerized amino acids (1971) A one-letter notation for amino-acid sequences (1968) Abbreviations and symbols for the description of the conformation of polypeptide chains (1969) Nomenclature of peptide hormones (1974) Recommendations for the nomenclature of human im- munoglobulins Protein data bank.A computer-based archival file for macromolecular structures (1977) Nomenclature of multiple forms of enzymes (1976) Nucleotides and nucleic acids Abbreviations and symbols for nucleic acids, poly- nucleotides and their constituents (1970) Lipids Nomenclature of lipids (1976) Nomenclature of steroids (1967) Nomenclature of quinones with isoprenoid side chains (1973) Tentative rules for the nomenclature of carotenoids (1970).Amendments (1974) Nomenclature of tocopherols and related compounds (1973) Carbohydrates, etc. Tentative rules for carbohydrate nomenclature. Part 1 (1969) Nomenclature of cyclitols (1973) Phosphorus-containing compounds Nomenclature of phosphorus-containing compounds of biochemical importance (1976) Miscellaneous Trivial names of miscellaneous compounds of importance in biochemistry (1965) Nomenclature and symbols for folk acids and related compounds (1965) Nomenclature for vitamins 8-6 and related compounds (1973) Nomenclature of corrinoids (1973) 1.4 Compendium of Analytical Nomenclature, a 222-page volume published in 1978, availablein hardcover and softcover from Pergamon, Oxford.Chapter 1: Recommendations for the presentation of the results of chemical analysis Chapter 2: Recommendations for terminology to be used with precision balances Chapter 3: Recommended nomenclature for scales of working in analysis Chapter 4 Recommendations on nomenclature for contamination phenomena in precipit- ation from aqueous solution Chapter 5: Recommended nomenclature for auto- matic analysis Chapter 6: Recommendations for nomenclature of thermal analysis Chapter 7: Recommendations for nomenclature of ~~ peptides ( 1966) mass spectrometry (xix)Chapter 8: Chapter 9: Chapter 1 0 Chapter 11: Chapter 12: Chapter 13: Chapter 1 4 Chapter 15: Chapter 1 6 1 8 : Chapter 19: Chapter 20: Chapter 21: Appendix: Recommended nomenclature for titri- metric analysis Report on the standardization of pH and related technology Practical measurements of pH in amphi- protic and mixed solvents Recommended symbols for solution equi- libria Recommended nomenclature for liquid- liquid distribution Recommendations on nomenclature and presentation of data in gas chromato- graphy Recommendations on nomenclature for chromatography Recommendations on ion-exchange no- menclature Nomenclature, symbols, units and their usage in spectrochemical analysis.I, General atomic emission spectroscopy. 11, Data interpretation. 111, Analytical flame spectroscopy and associated non-flame procedures Classification and nomenclature of elec- troanalytical techniques Recommendations for sign conventions and plotting of electrochemical data Recommendations for nomenclature of ion-selective electrodes Recommendations on the usage of the terms ‘equivalent’ and ‘normal’ 2.0 Documents not included in the compil- 2.1 Nomenclature and symbolism for amino acids and peptides (Pure Appl.Chem., 1984,56, 595; Eur. J. Biochem.. 1984,138,9). Guide to trivial names, trade names, and synonyms for substances used in analytical chemistry (Pure Appl. Chem., 1978, 50, 339). Nomenclature of inorganic boron compounds (Pure Appl. Chem., 1972, 30, 681). Conformational nomenclature for five- and six-membered ring forms of monosaccharides and their derivatives (provisional) (Pure Appl. Chem., 1981. 53, 1901; Eur. J. Brochem., 1980, 111, 295). Abbreviated terminology of oligosaccharide chains (provi- sional) (Pure Appl.Chem., 1982, 54, 1517; J. Biol. Chem., 1982, 257, 2347). Polysaccharide nomenclature (provisional) (Pure Appl. Chem., 1982, 54, 1523; J. Biol. Chem., 1982,257, 3352). Nomenclature of unsaturated monosaccharides (provisional) (Pure Appl. Chem., 1982,54,207; Eur. J. Biochem., 1981,119, 1 ; errata Eur. J. Biochem., 1982, 125, 1). Nomenclature of branched-chain monosaccharides (provi- sional) (Pure Appl. Chem., 1982, 54,21 I; Eur. 1. Biochem., 1981, 119, 5; errata Eur. J. Biochem., 1982, 125, I). Symbols for specifying the conformation of polysaccharide chains (provisional) (Pure Appl. Chem., 1983, 55, 1269; Eur. J. Biochern., 1983, 131, 5). ations Nomenclature of Elements and Compounds 2.1.1 Amino acids and Peptides 2.1.2 Analyticul Reagents 2.1.3 Boron Compounds 2.1.4 Carbohydrates 2.1.5 Elements Recommendations for the names of elements of atomic number greater than 100 (Pure Appl.Chem., 1979, 51, 381). Enzyme Nomenclature (1984), published by Academic Press in hardcover and softcover editions. 2.1.7 Heterocyclic Compounds Revision of the extended Hantzsch-Widman system of nomen- clature for heteromonocycles (Pure Appl. Chem., 1983,55,409). Nomenclature of inorganic chemistry. Part 11. 1. Isotopically modified compounds (Pure Appl. Chem., 198 1, 53, 1887). Treatment of variable valence in organic nomenclature (Pure Appl. Chem., 1984, 56, 769). Nomenclature of hydrides of nitrogen and derived cations, anions, and ligands (Pure Appl. Chem., 1982, 54, 2545). Abbreviations and symbols for the description of conformations of polynucleotide chains (provisional) (Pure Appl.Chem., 1983, 55, 1279; Eur. J. Biochem., 1983, 131, 9). Extension of Rules A-1.1 and A-2.5 concerning numerical terms used in organic chemical nomenclature (provisional) (Pure Appl. Chem., 1983, 55, 1463). Nomenclature of regular single-strand organic polymers (Pure Appl. Chem., 1976, 48, 373). Nomenclature for regular single-strand and quasi single-strand inorganic and co-ordination polymers (Pure Appl. Chem., 1985, 57, 149). Source-based nomenclature for copolymers (Pure Appl. Chem., 1985, 57, 1427). Stereochemical definitions and notations relating to polymers (Pure Appl. Chem., 1981,53, 733). List of standard abbreviations (symbols) for synthetic polymers and polymer materials (Pure Appl.Chem., 1974, 40, 473). Basic definitions of terms relating to polymers (Pure Appl. Chem., 1974,40,477). 2.1.14 Retinoids Nomenclature of retinoids (provisional) (Pure Appl. Chem., 1983, 55, 721; Eur. J. Biochem., 1982, 129, 1 ) . 2.1.15 Tetrapyrroles Nomenclature of tetrapyrroles (provisional) (Pure Appl. Chern., 1979, 51, 2251). 2.1.16 Tocopherols Nomenclature of tocopherols and related compounds (Pure Appl. Chem., 1982,54, 1507; Eur. J. Biochem., 1982, 123,473). Nomenclature of Vitamin D (provisional) (Pure Appl. Chem., 1982, 54, 1511; Eur. J. Biochem., 1982, 124, 223). Chemical nomenclature and formulation of compositions of synthetic and natural zeolites (Pure Appl. Chem., 1979,51,1091). 2.1.6 Enzymes 2.1 .8 Isotopically Modified Compounds 2.1.9 Lurnbdu Convention 2.1.10 Nitrogen Hydrides 2.1.1 1 Nucleotides 2.1.12 Numerical Terms 2.1.13 Polymers 2.1.17 Vitamins 2.1.18 Zeolites 2.2 Terminology, Symbols, and Units, and Presentation of Results 2.2.1 General Glossary of terms used in physical organic chemistry (Pure Appl.Chem., 1983, 55, 1281). Manual of symbols and terminology for physicochemical quantities and units (Pure Appl. Chem., 1979, 51, 1, also avail- able from Pergamon, Oxford, as a 40-page softcover booklet).2.2.2 Analytical Nomenclature, symbols, units, and their usage in spectro- chemical analysis. Part IV, X-Ray emission spectroscopy (Pure Appl. Chem., 1980, 52, 2543). Part V, Radiation sources (Pure Appl. Chem., 1985,57, 1453). Part VI, Molecular luminescence spectroscopy (Pure Appl.Chem., 1984, 55, 231). Recommendations for nomenclature, standard procedures, and reporting of experimental data for surface analysis techniques (Pure Appl. Chem., 1979, 51, 2243). Glossary of terms used in nuclear analytical chemistry (provisional) (Pure Appl. Chem., 1982, 54, 1533). Recommendations for publication of papers on a new analytical method based on ion exchange or ion-exchange chroma- tography (Pure Appl. Chem., 1980,52, 2555). Recommendations for presentation of data on compleximetric indicators. 1. General (Pure Appl. Chem., 1979, 51, 1357). Recommendations for publishing manuscripts on ion-selective electrodes (Pure Appl. Chem., 1981, 53, 1907). Recommendations on use of the term amplification reactions (Pure Appl. Chem., 1982, 54, 2553).Recommendations for the usage of selective, selectivity, and related terms in analytical chemistry (Pure Appl. Chem., 1983, 55, 553). Proposed terminology and symbols for the transfer of solutes from one solvent to another (Pure Appl. Chem., 1978, 50, 589). Nomenclature, symbols and units recommended for in situ microanalysis (provisional) (Pure Appl. Chem., 1983, 55, 2023). Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Pure Appl. Chem., 1984, 56, 567). Quantities and units in clinical chemistry (Pure Appl. Chern., 1979, 51, 2451). Quantities and units in clinical chemistry: nebulizer and flame properties in flame emission and absorption spectrometry (provisional) (Pure Appl. Chem., 1984, 56, 1499).List of quantities in clinical chemistry (Pure Appl. Chem., 1979, 51, 2481). Definitions, terminology, and symbols in colloid and surface chemistry. 1 (Pure Appl. Chem., 1972,31,577). 11, Heterogeneous catalysis (Pure Appl. Chem., 1976, 46, 71). Part 1.14 Light scattering (provisional) (Pure Appl. Chem., 1983, 55, 931). Reporting experimental pressure-area data with film balances (Purr Appl. Chem., 1985, 57, 621). Reporting physisorption data for gasisolid systems with special reference to the determination of surface area and porosity (Pure Appl. Chem., 1985, 57, 603). Nomenclature for transfer phenomena in electrolytic systems (Pure Appl. Chem., 1981, 53, 1827). Electrode reaction orders, transfer coefficients, and rate constants-amplification of definitions and recommendations for publication of parameters (Pure Appl.Chem., 1980,52,233). Recommended terms, symbols, and definitions for electro- analytical chemistry (Pure Appl. Chem., 1985, 57, 1491). Classification and nomenclature of electroanalytical techniques (Pure Appl. Chem., 1976, 45, 81). Recommendations for sign conventions and plotting of electro- chemical data (Pure Appl. Chem., 1976, 45, 131). Electrochemical nomenclature (Pure Appl. Chem.. 1974, 37, 2.2.3 Clinical 2.2.4 ColloidLy and Surface Chemistry 2.2.5 Electrochemistry 499). Recommendations on reporting electrode potentials in non- aqueous solvents (Pure Appl. Chem., 1984, 56,461). Definition of pH scales, standard reference values, measurement of pH and related terminology (Pure Appl.Chem., 1985, 57, 531). Symbolism and terminology in chemical kinetics (provisional) (Pure Appl. Chem., 1981, 53, 753). Recommended standards for reporting photochemical data (Pure Appl. Chem., 1984, 56, 939). Expression of results in quantum chemistry (Pure Appl. Chem., 1978, 50, 75). Nomenclature for straightforward transformations (provi- sional) (Pure dppl. Chem., 1981, 53, 306). Selected definitions, terminology, and symbols for rheological properties (Pure Appl. Chew., 1979, 51, 1215). Recommendations for publication of papers on methods of molecular absorption spectrophotometry in solution (Pure Appl. Chem., 1978, 50, 237). Nomenclature and spectral presentation in electron spectros- copy resulting from excitation by photons (Pure Appl. Chem., 1976, 45, 221).Recommendations for the presentation of infrared absorption spectra in data collections. A, Condensed phases (Pure Appl. Chem., 1978, 50, 231). Definition and symbolism of molecular force constants (Pure Appl. Chem., 1978, 50, 1709). Recommendations for symbolism and nomenclature for mass spectrometry (Pure Appl. Chem., 1978, 50, 65). Nomenclature and conventions for reporting Mossbauer spectroscopic data (Pure Appl. Chem., 1976, 45, 21 1). Recommendations for the presentation of NMR data for publication in chemical journals. A, Proton spectra (Pure Appl. Chem., 1972,39,625). B, Spectra from nuclei other than protons (Pure Appl. Chem., 1976, 45, 217). Presentation of Raman spectra in data collections (Pure Appl. Chem., 1981, 53, 1879). Names, symbols, definitions and units of quantities in optical spectroscopy (Pure Appl.Chem., 1985, 57, 105). Nomenclature of thermal analysis. I (Pure Appl. Chem., 1974 37, 439). 11, DTA and TG apparatus and technique. 111, DTA and TG curves (Pure Appl. Chem., 1980, 52, 2387). IV. (provisional) (Pure Appl. Chem., 1981, 53, 1597). Calorimetric measurements on cellular systems: recommend- ations for measurements and presentation of results (provi- sional) (Pure Appl. Chem., 1982,54, 671). A guide to procedures for the publication of thermodynamic data (Pure Appl. Chem., 1972, 39, 395). Assignment and presentation of uncertainties of the numerical results of thermodynamic measurements (Pure Appl. Chrm., 198 1, 53, 1 805). Notation for states and processes; significance of the word ‘standard’ in chemical thermodynamics and remarks on commonly tabulated forms of thermodynamic functions (Pure Appl.Chem., 1982, 54, 1239). 2.2.6 Kinetics 2.2.7 Photochemistry 2.2.8 Quantum Chemistry 2.2.9 Reactions 2.2.10 Rheological Properties 2.2.1 1 Spectroscopy 2.2.12 Thermal Analysis 2.2.1 3 Thermodynamics (xxi)2.2.2 Analytical Nomenclature, symbols, units, and their usage in spectro- chemical analysis. Part IV, X-Ray emission spectroscopy (Pure Appl. Chem., 1980, 52, 2543). Part V, Radiation sources (Pure Appl. Chem., 1985,57, 1453). Part VI, Molecular luminescence spectroscopy (Pure Appl. Chem., 1984, 55, 231). Recommendations for nomenclature, standard procedures, and reporting of experimental data for surface analysis techniques (Pure Appl. Chem., 1979, 51, 2243).Glossary of terms used in nuclear analytical chemistry (provisional) (Pure Appl. Chem., 1982, 54, 1533). Recommendations for publication of papers on a new analytical method based on ion exchange or ion-exchange chroma- tography (Pure Appl. Chem., 1980,52, 2555). Recommendations for presentation of data on compleximetric indicators. 1. General (Pure Appl. Chem., 1979, 51, 1357). Recommendations for publishing manuscripts on ion-selective electrodes (Pure Appl. Chem., 1981, 53, 1907). Recommendations on use of the term amplification reactions (Pure Appl. Chem., 1982, 54, 2553). Recommendations for the usage of selective, selectivity, and related terms in analytical chemistry (Pure Appl. Chem., 1983, 55, 553). Proposed terminology and symbols for the transfer of solutes from one solvent to another (Pure Appl.Chem., 1978, 50, 589). Nomenclature, symbols and units recommended for in situ microanalysis (provisional) (Pure Appl. Chem., 1983, 55, 2023). Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Pure Appl. Chem., 1984, 56, 567). Quantities and units in clinical chemistry (Pure Appl. Chern., 1979, 51, 2451). Quantities and units in clinical chemistry: nebulizer and flame properties in flame emission and absorption spectrometry (provisional) (Pure Appl. Chem., 1984, 56, 1499). List of quantities in clinical chemistry (Pure Appl. Chem., 1979, 51, 2481). Definitions, terminology, and symbols in colloid and surface chemistry. 1 (Pure Appl.Chem., 1972,31,577). 11, Heterogeneous catalysis (Pure Appl. Chem., 1976, 46, 71). Part 1.14 Light scattering (provisional) (Pure Appl. Chem., 1983, 55, 931). Reporting experimental pressure-area data with film balances (Purr Appl. Chem., 1985, 57, 621). Reporting physisorption data for gasisolid systems with special reference to the determination of surface area and porosity (Pure Appl. Chem., 1985, 57, 603). Nomenclature for transfer phenomena in electrolytic systems (Pure Appl. Chem., 1981, 53, 1827). Electrode reaction orders, transfer coefficients, and rate constants-amplification of definitions and recommendations for publication of parameters (Pure Appl. Chem., 1980,52,233). Recommended terms, symbols, and definitions for electro- analytical chemistry (Pure Appl.Chem., 1985, 57, 1491). Classification and nomenclature of electroanalytical techniques (Pure Appl. Chem., 1976, 45, 81). Recommendations for sign conventions and plotting of electro- chemical data (Pure Appl. Chem., 1976, 45, 131). Electrochemical nomenclature (Pure Appl. Chem.. 1974, 37, 2.2.3 Clinical 2.2.4 ColloidLy and Surface Chemistry 2.2.5 Electrochemistry 499). Recommendations on reporting electrode potentials in non- aqueous solvents (Pure Appl. Chem., 1984, 56,461). Definition of pH scales, standard reference values, measurement of pH and related terminology (Pure Appl. Chem., 1985, 57, 531). Symbolism and terminology in chemical kinetics (provisional) (Pure Appl. Chem., 1981, 53, 753). Recommended standards for reporting photochemical data (Pure Appl. Chem., 1984, 56, 939). Expression of results in quantum chemistry (Pure Appl. Chem., 1978, 50, 75). Nomenclature for straightforward transformations (provi- sional) (Pure dppl. Chem., 1981, 53, 306). Selected definitions, terminology, and symbols for rheological properties (Pure Appl. Chew., 1979, 51, 1215). Recommendations for publication of papers on methods of molecular absorption spectrophotometry in solution (Pure Appl. Chem., 1978, 50, 237). Nomenclature and spectral presentation in electron spectros- copy resulting from excitation by photons (Pure Appl. Chem., 1976, 45, 221). Recommendations for the presentation of infrared absorption spectra in data collections. A, Condensed phases (Pure Appl. Chem., 1978, 50, 231). Definition and symbolism of molecular force constants (Pure Appl. Chem., 1978, 50, 1709). Recommendations for symbolism and nomenclature for mass spectrometry (Pure Appl. Chem., 1978, 50, 65). Nomenclature and conventions for reporting Mossbauer spectroscopic data (Pure Appl. Chem., 1976, 45, 21 1). Recommendations for the presentation of NMR data for publication in chemical journals. A, Proton spectra (Pure Appl. Chem., 1972,39,625). B, Spectra from nuclei other than protons (Pure Appl. Chem., 1976, 45, 217). Presentation of Raman spectra in data collections (Pure Appl. Chem., 1981, 53, 1879). Names, symbols, definitions and units of quantities in optical spectroscopy (Pure Appl. Chem., 1985, 57, 105). Nomenclature of thermal analysis. I (Pure Appl. Chem., 1974 37, 439). 11, DTA and TG apparatus and technique. 111, DTA and TG curves (Pure Appl. Chem., 1980, 52, 2387). IV. (provisional) (Pure Appl. Chem., 1981, 53, 1597). Calorimetric measurements on cellular systems: recommend- ations for measurements and presentation of results (provi- sional) (Pure Appl. Chem., 1982,54, 671). A guide to procedures for the publication of thermodynamic data (Pure Appl. Chem., 1972, 39, 395). Assignment and presentation of uncertainties of the numerical results of thermodynamic measurements (Pure Appl. Chrm., 198 1, 53, 1 805). Notation for states and processes; significance of the word ‘standard’ in chemical thermodynamics and remarks on commonly tabulated forms of thermodynamic functions (Pure Appl. Chem., 1982, 54, 1239). 2.2.6 Kinetics 2.2.7 Photochemistry 2.2.8 Quantum Chemistry 2.2.9 Reactions 2.2.10 Rheological Properties 2.2.1 1 Spectroscopy 2.2.12 Thermal Analysis 2.2.1 3 Thermodynamics (xxi)

ISSN:0300-9599    

DOI:10.1039/F198682BP003

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

FA RA DA Y 1RA N SA CTlO N S AND SYMPOSIA From the Royal Society of Chemistry FARADAY TRANSACTIONS II Molecular and Chemical Physics SPECIAL ISSUE - AUGUST 1986 Professor Alan Carrlngton delbred the 1985 Faraday lecture at the Royal lnsmutlon on 10th December, 1985. As a compliment to Professor Carrington, a group of his colleagues and Mends submitted original papers on the general theme of Molecular Dynamics and Spectroscopy. These papers are collected in the present Issue. CONTENTs: The Faraday Lecture: Spectroscopy of Molecular Ions at thelr Dissociation Limits A. Carrington The Spectroscopy, Photophysics and Photochemistry of Clusters of Metrazlne D. H. Levy Spectroscopy of Transient Species produced by Photodissociation or Photoionizatlon in a Supersonlc Free-jet Expansion T.A. Mlller Molecukr-beam Infrared Spectroscopy of the Ar-N,O van der Waals Molecule J. Hodge, G. D. Hayman, T. R. Dykeand B. J. Howard The Estimation of Vlbrational Predissociation Ufetimes M. S. Chlld The Infrared Spectrum of H; and its Isotopomers. A Challenge to Theory and Experlment J. Tennyson and B. T. Sutcliffe The Augmented Secular Equation Method for calculating Spectra of van der Waals Complexes. Application to the Infrared Spechum of Ar-HCI J. M. Hutson Quantum-mechanical Wavepacket Dynamics of the CH Group in Symmetric- top X,CH Compounds using Effecttve Hamiltonians from Hlgh-resolution Spectroscopy R. Marguardt, M. Quack, J. Stohner and f. Sutcllffe Internal Dynamics of Subunits and Bondlng Force Constants In Weakly Bound Dlmers P. Cope, D.J. Mlllerand A. C. fegon Internal Dynamics and HF Bond Lengthenlng In the Hydrogen-bonded Heterodimer CH,CN . . . HF determined from Nuclear Hyper-fine Structure in its Rotational Spectrum P. Cope, D. J. Miller, L. C. Willoughbyand A. C. fegon Pumping and Rshing. Double-resonance Measurements on Molecular Jets U. Veeken, N. Damand J. Reuss nme-resow Fluorescence of Jet-cooled Carbazoles and thelr Weak Complexes A. R. Auty, A. C. Jones and D. Philllps Prediction of the Ct(*P, J/CI(P,J Branching Ratio in the Photodissociation of HCI S. C. GIvertzand 6. C. Ballnt-Kurt/ Hlgh-resolution Laser Photofragment Spectroscopy of CH' P. J. Sam, J. M. Walmsleyand C. J. Whitham Asymmetric Uneshapes associated with Predissociating levels M. N. R. Ashfold, R. N. Dixon, J. D. Prince, B.Tutcherand C. M. Westem A Threshold-photoelectron Ruorescence-Photon Coincidence Study of Radlatlonless TransMons in the B ,iI State of BCN+ €. Castellucci, G. Dulardin and S. leach Cornpetthe Channels in the Interaction of Xe('P,) with CI,, Br, and I,. Atom Transfer, Excitation Transfer, Energy Disposal and Product Alignment K. Johnson, R. Pease, J. P. Simons, P. A. Smith and A. Kvaran Mco Non-RSC Momkn P14.30 ($27.70) RSC Momkn M.00 Payment should accompany ordon for lhlr Ihm. RSC Members should send their orders to: Membershlp Manager, The Royal Society of Chemistry, 30 Russell Square, London WC1 B SDT. Non-RSC Members should send their orders to: The Royal Socleiy of Chemistry, Distribution Centre, Blackhorse Road. Letchwotth, Herts SG6 1 HN. Faraday Discussions No.80 Physical Interactions and Energy Exchange af the Gas-Solid Interface [his publication discusses aspects of current research on the gas-solid Interface: elastic, inelastic and dlssipattve scattering of atoms and molecules from cfystal surfaces; the structure and dynamics of physisorbed species, including overlayers. Emphasis Is placed on the themes of physical interactions and energy exchange rather than on molecular beam technology or the phenomenology of phase tmnsmons in overlayen. The interplay between theory and experlment is stressed as they relate to the nature of atom and molecule-surface interaction potentials including many body effects. Faraday Discussions No. 80 (1986) Softcevor Prico 531 .OO ($60.00) RSC Mombon J66.25 ROYAL SOCIETY OF CHEMISTRY Information Services (xiii)FA RA DA Y 1RA N SA CTlO N S AND SYMPOSIA From the Royal Society of Chemistry FARADAY TRANSACTIONS II Molecular and Chemical Physics SPECIAL ISSUE - AUGUST 1986 Professor Alan Carrlngton delbred the 1985 Faraday lecture at the Royal lnsmutlon on 10th December, 1985.As a compliment to Professor Carrington, a group of his colleagues and Mends submitted original papers on the general theme of Molecular Dynamics and Spectroscopy. These papers are collected in the present Issue. CONTENTs: The Faraday Lecture: Spectroscopy of Molecular Ions at thelr Dissociation Limits A. Carrington The Spectroscopy, Photophysics and Photochemistry of Clusters of Metrazlne D. H. Levy Spectroscopy of Transient Species produced by Photodissociation or Photoionizatlon in a Supersonlc Free-jet Expansion T.A. Mlller Molecukr-beam Infrared Spectroscopy of the Ar-N,O van der Waals Molecule J. Hodge, G. D. Hayman, T. R. Dykeand B. J. Howard The Estimation of Vlbrational Predissociation Ufetimes M. S. Chlld The Infrared Spectrum of H; and its Isotopomers. A Challenge to Theory and Experlment J. Tennyson and B. T. Sutcliffe The Augmented Secular Equation Method for calculating Spectra of van der Waals Complexes. Application to the Infrared Spechum of Ar-HCI J. M. Hutson Quantum-mechanical Wavepacket Dynamics of the CH Group in Symmetric- top X,CH Compounds using Effecttve Hamiltonians from Hlgh-resolution Spectroscopy R. Marguardt, M. Quack, J. Stohner and f. Sutcllffe Internal Dynamics of Subunits and Bondlng Force Constants In Weakly Bound Dlmers P.Cope, D. J. Mlllerand A. C. fegon Internal Dynamics and HF Bond Lengthenlng In the Hydrogen-bonded Heterodimer CH,CN . . . HF determined from Nuclear Hyper-fine Structure in its Rotational Spectrum P. Cope, D. J. Miller, L. C. Willoughbyand A. C. fegon Pumping and Rshing. Double-resonance Measurements on Molecular Jets U. Veeken, N. Damand J. Reuss nme-resow Fluorescence of Jet-cooled Carbazoles and thelr Weak Complexes A. R. Auty, A. C. Jones and D. Philllps Prediction of the Ct(*P, J/CI(P,J Branching Ratio in the Photodissociation of HCI S. C. GIvertzand 6. C. Ballnt-Kurt/ Hlgh-resolution Laser Photofragment Spectroscopy of CH' P. J. Sam, J. M. Walmsleyand C. J. Whitham Asymmetric Uneshapes associated with Predissociating levels M.N. R. Ashfold, R. N. Dixon, J. D. Prince, B. Tutcherand C. M. Westem A Threshold-photoelectron Ruorescence-Photon Coincidence Study of Radlatlonless TransMons in the B ,iI State of BCN+ €. Castellucci, G. Dulardin and S. leach Cornpetthe Channels in the Interaction of Xe('P,) with CI,, Br, and I,. Atom Transfer, Excitation Transfer, Energy Disposal and Product Alignment K. Johnson, R. Pease, J. P. Simons, P. A. Smith and A. Kvaran Mco Non-RSC Momkn P14.30 ($27.70) RSC Momkn M.00 Payment should accompany ordon for lhlr Ihm. RSC Members should send their orders to: Membershlp Manager, The Royal Society of Chemistry, 30 Russell Square, London WC1 B SDT. Non-RSC Members should send their orders to: The Royal Socleiy of Chemistry, Distribution Centre, Blackhorse Road. Letchwotth, Herts SG6 1 HN. Faraday Discussions No. 80 Physical Interactions and Energy Exchange af the Gas-Solid Interface [his publication discusses aspects of current research on the gas-solid Interface: elastic, inelastic and dlssipattve scattering of atoms and molecules from cfystal surfaces; the structure and dynamics of physisorbed species, including overlayers. Emphasis Is placed on the themes of physical interactions and energy exchange rather than on molecular beam technology or the phenomenology of phase tmnsmons in overlayen. The interplay between theory and experlment is stressed as they relate to the nature of atom and molecule-surface interaction potentials including many body effects. Faraday Discussions No. 80 (1986) Softcevor Prico 531 .OO ($60.00) RSC Mombon J66.25 ROYAL SOCIETY OF CHEMISTRY Information Services (xiii)

ISSN:0300-9599    

DOI:10.1039/F198682BX005

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J . Chem. Soc., Faraday Trans. I , 1986, 82, 13-34 Activity and Selectivity in Catalytic Reactions of Buta- 1,3-diene and But-1 -ene on Supported Vanadium Oxides Kenji Mori Kinu-ura Research Department, JGC Corp., Sunosaki-cho, Handa, Aichi 475, Japan Akira Miyamoto"? and Yuichi Murakami Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464, Japan The activity and selectivity in the oxidation of buta-1,3-diene, and oxidation and isomerization of but-1 -ene on unsupported and supported V,O, catalysts have been investigated in terms of the catalyst structure. The rate of oxidation is mainly determined by the number of surface V=O species on the catalyst for both buta-1,3-diene and but-1-ene. The roughness of the V,O, surface affected the activity for buta-173-diene, but not for but-I-ene oxidation. It was also found that TiO, support increases the activity of the surface V=O for but- 1-ene oxidation.The selectivity to maleic anhydride was determined by the number of V,O, layers on the support for both reactions. When the number of V,O, layers was 1 or 2, the selectivity was low, while it increased markedly with an increase in the number of V,O, layers to 5, and attained a constant value above 5 layers. Both V,Oj and support were active for the isomerization of but-1-ene to cis- and trans- but-2-ene. On V,O,, the cisltrans ratio was low, while it was as high as 3 for the A1,0, support. The rate and selectivity of the isomerization on supported catalysts were explained in terms of the structure of V,O, on the support.Difference in the structure-activity/selectivity correlation between oxidation and isomerization and that between but- 1 -ene oxidation and buta- 1,3-diene oxidation were also discussed. Supported metal oxide catalysts exhibit differing degrees of catalysis depending on the kind of support and on the composition of the cata1yst.lt2 However, the activity and selectivity on the supported metal-oxide catalyst have not been well clarified in terms of the structure of the metal oxide on the support. This seems to be due the lack of a well established method to determine the structure of such catalysts and, more especially, the number of active sites. For supported vanadium oxide catalysts, we have previously established the rectangular-pulse technique which allows the determination of the number of surface V=O species and the number of V205 layers on ~ u p p o r t .~ Furthermore, the structures of V205/Ti02 and V205/A1203 catalysts have been determined by various physico-chemical measurements together with the rectangular pulse techniq~e.~ By investigating the oxidation of benzene on well characterized vanadium oxide catalysts, the activity and selectivity in benzene oxidation have been revealed in terms of the structure of V205 on the s ~ p p o r t . ~ Since the structure-activity/selectivity correlation is expected to change greatly with the type of r e a c t i ~ n , ~ - ~ it seems interesting to investigate the correlation for various reactions. The purpose of this study is then to investigate the structure-activity/selectivity correlation for the reactions of buta- 173-diene and T Present address : Department of Hydrocarbon Chemistry, Faculty of Engmeering, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606, Japan.14 Supported Vanadium Oxide Catalysts Table 1.Physical and catalytic properties of unsupported V,O, catalysts for the oxidation of buta- 1 ,3-dienea ~~~ ~~~~~~ ~ L (W%E.T.) R, (RO/SB.E.T.) S(MA S(C0 SB.E.T. /pmd /pmol /pmol /pmol TF, +FR) +CO,) S(C0) catalyst /m2 g-l g-l m-, 8-I s-l m-, s-l /ks-l ( 7 3 (%I / w a I v,o,-u 5.4 22 4.1 12.2 2.26 555 60 40 1.35 V,O,-F 0.8 4 5.0 0.27 0.34 68 65 35 1.32 V,O,-RO 0.8 4 5.0 0.51 0.64 128 64 34 1.36 a SB. E.T., the B.E.T. (Brunauer-Emmett-Teller) surface area; L, the number of surface V=O species; R,, reaction rate; TFo, turnover frequency for the oxidation; S(MA + FR), selectivity to maleic anhydride and furan; S(CO+CO,), selectivity to CO and CO,; S(CO), selectivity to CO; S(CO,), selectivity to CO,.Reaction conditions: temperature = 622 K; partial pressure of buta-1,3-diene = 0.0074 atm; partial pressure of 0, = 0.397 atm. but- 1 -ene. These reactions were selected because (i) the partial oxidation product (maleic anhydride) is common to both reactants enabling us to discuss effects of the structure of the reactant molecule on the structure-activity/selectivity lo. l1 (ii) the isomerization of but-1-ene to cis- and trans-but-2-ene proceeds in addition to the oxidation and we can compare the structure-activity/selectivity correlation for the isomerization with that for the o ~ i d a t i o n , l ~ - ~ ~ and (iii) the reactions are important for the industrial production of maleic anhydride.Experimental Catalysts A V,O,-U catalyst was prepared by the thermal decomposition of NH4V0, in a stream of 0, at 773 K. A V,O,-F catalyst was prepared by fusing the V,O,-U catalyst at 1073 K for 18 h in air, followed by gradual cooling to room temperature. A V,O,-RO catalyst was prepared from the V,O,-F catalyst by the reduction-oxidation treatment, i.e. reduction in flowing H, at 673 K for 1 h followed by reoxidation in flowing 0, (20%) at 673 K for 1 h (this cycle was repeated 5 times). The number of surface V=O species (L) on the catalysts has been determined by using the rectangular-pulse technique3 and the results are shown in table 1 together with the results of the B.E.T.surface area (SB.E,.T.). The number of V,O, layers (N) for the catalysts was calculated from L using: N = 2/[J94(V,O,)I (1) where M(V,O,) is the molecular weight of V,O,. According to the results of X-ray diffraction, u.v.-visible spectra, i.r. spectra, X-ray photoelectron spectra and scanning electron micrographs of the catalysts,*> electronic properties of the catalysts do not change while the surface of V,O,-U or V,O,-RO is rougher than that of V,O,-F. TiO, (anatase) was prepared by hydrolysis of Ti(SO,), followed by calcination in air at 873 K, while Al,O, was commercially available (Sumitomo y-Al,03). B.E.T. surface areas of TiO, and Al,03 were 48 and 230m2 g-l, respectively.Vanadium oxides supported on carriers were prepared by impregnation of the carrier with an oxalic acid solution of NH,VO, followed by calcination at 773 K in a stream of 0, for 3 h. V,O,/TiO, and V,O,/Al,O, monolayer catalysts were prepared from V,O,/TiO, (10 mol % V,O,) and V,0,/Al,03 (25 mol % V,O,), respectively, in a manner similar to that described by Yoshida et aZ.15 The number of surface V=O species (L), the number of V,O, layers on the support (N), and the B.E.T. surface area of the supported catalysts have been determined4 and the results are shown in table 2, ML is the percentageK. Mori, A . Miyamoto and Y. Murakami 15 Table 2. Physical and catalytic properties of V,O,/TiO, and V,O,/AI,O, catalysts for the oxidation of buta-1 ,3-dienea ~- L R O S(MA S(C0 catalyst SB- E.T./pmol ML /pmol TF, +FR) +CO,) S(C0) (mol%V,O,) /m2 g-l ggl N (%) g-l sP1 /ks-l (2;) (%I /S(CO,) ~ _ _ 1 2 5 10 25 50 monolayer 2 5 10 25 35 50 monolayer 47 45 26 23 10 32 7.4 22 1 219 168 114 101 66 174 5.4 V,O,/TiO, 56 1-2 32 5.49 120 1-2 67 13.5 184 2-3 280 39.3 135 5-8 600 25.5 60 3WO 2800 21.5 31 5&60 6400 15.3 126 1 ~ 14.0 V2°5/A1203 3 1-2 11 0.35 77 1-2 27 4.03 355 1-3 67 18.2 405 2 4 220 28.2 249 5-15 660 15.8 365 3-7 330 24.5 20 1 - 1.18 22 504 12.2 v,o,-u 98 I12 21 3 189 358 492 111 117 52 51 70 67 64 59 555 32 41 60 60 56 61 41 9 28 51 56 57 55 27 60 68 59 40 40 44 39 59 91 72 49 44 43 45 73 40 -~ 0.89 0.97 1.22 1.35 1.44 1.44 1.03 0.54 0.57 0.75 1.20 1.16 1.25 0.55 1.35 N , number of V,O, layers on support; ML, percent theoretical monolayer of V,O, calculated from eqn (2); for the definition of S,.,.,., L, Ro, TF,, S(MA+FR), S(CO+CO,), S(C0) and S(CO,), see table 1.Reaction conditions: temperature = 622 K; partial pressure of buta-1,3-diene = 0.0074 atm; partial pressure of 0, = 0.397 atm. theoretical monolayer of V205,16 which is calculated from the V,O, content (x) and %.FA using: 100 (% 1 Nx4V,O,) ML = xM(V,O,) + (1 - x) M(support) SB. E.'V. where N is the Avogadro number, a(V,O,) is the area occupied by a V,O, unit (20.6 A,); and M(support) is molecular weight of the support (TiO, or A1203). Unless stated otherwise, the particle size of the catalyst was 28-48 mesh. Catalytic Activity Measurements Kinetic studies were carried out by using the continuous-flow reaction technique under the following conditions; total pressure = 1 atm (1 atm = 101.3 kPa), temperature = 58&666 K, partial pressure of 0, (Po) = M.467 atm, partial pressure of buta-1,3- diene = 0.0074 atm, partial pressure of but-1-ene = 0.0079 atm, and nitrogen was used as a balance gas.Reaction products identified were maleic anhydride (MA), furan(FR), CO, and CO, for the reaction of buta-1,3-diene, and MA, CO, CO,, cis-but-2-ene and trans-but-2-ene for the reaction of but-1-ene. The rate of formation of MA was determined by titration with 0.1 mol dm-3 NaOH after its collection in water. FR, CO, CO,, cis-but-2-ene and trans-but-2-ene were analysed by using gas chromatography. Particular care was paid to remove the heat of reaction and thus control the reactor16 Supported Vanadium Oxide Catalysts temperature (k 1 K).The glass reactor was heated to the reaction temperature by using a fluidized bed of sand, and the catalyst was diluted with a-Al,O,. Characterizations of Catalysts A catalyst in the steady-state reaction was rapidly cooled down to room temperature to measure the steady-state catalyst structure. 1.r. spectra of the catalyst were observed on a Jasco-EDR-3 1 emissionless i.r. diffuse-reflectance spectrometer using KBr as a diluent . l7 Results Effects of 0, Partial Pressure on Reaction Rates and Catalyst Structures for Buta-l,3-diene Oxidation In the oxidation of buta-l,3-diene on vanadium oxide catalysts, the following reactions were found to take place: C4H6 C4H203(MA) (3) C,H6 + C,H,O(FR) (4) C,H, + 4CO ( 5 ) C,H, + 4C0,.(6) From the stoichiometries of eqn (3)-(6), the rate of formation of each product [R(MA), R(FR), R(CO), R(CO,)] is defined as the rate of buta-l,3-diene converted to the product. It has been shown that MA is consecutively formed through FR,,.18 and this was confirmed in the present study. Taking this into account, the rate of formation partial oxidation products (MA and FR) [R(MA + FR)] or total oxidation products (CO and CO,) [R(CO+CO,)] is defined by eqn (7) and (8), respectively: R(MA+FR) = R(MA)+R(FR) (7) R(C0 + CO,) = R(C0) + R(C0,). (8) The total reaction rate (R,) and selectivites to partial oxidation products [S(MA + FR)], total oxidation products [S(CO + CO,)], CO[S(CO)] and CO,[S(CO,)] are given by eqn (9)-( 12), respectively : R, = R(MA + FR) + R(C0 + CO,) S(MA+FR) = R(MA+FR)/R, (9) S(C0 + CO,) = R(C0 + CO,)/K" (10) S(C0) = R(CO)/R, (1 1) S(C0,) = R(CO,)/R,.(12) Fig. 1 shows effects of Po on R,, R(MA+FR) and R(CO+CO,) for the V,O,-U catalyst at 622 K. The rates increased gradually with increasing Po to 0.3 atm, while they are almost constant when Po > 0.3 atm. In spite of the change of the reaction rates with Po, S(MA + FR), S(C0) and S(C0,) are independent of Po) as shown in fig. 2. The reaction rates decreased gradually after the stoppage of 0, supply and attained a negligible value 8 h after the reaction began. It was also confirmed that both the reaction rate and i.r. spectrum of the catalyst attained a steady state under this condition. Fig. 3 shows the i.r. spectra of the V,05-U catalyst in the steady-state reaction at variousK.Mori, A . Miyamoto and Y. Murakami 17 12 r 0 0.1 0,2 0 , 3 0,4 0,s Po/atm Fig. 1. Effect of Po on R,, R(MA + FR), and R(C0 + CO,) for buta- 1,3-diene oxidation on V,O,-U at 622K. 0, R,; 0, R(MA+FR); 0, R(CO+CO,). Partial presence of buta-1,3- diene = 0.0074 atm, W/F = 220 g s rnol-'. 0 0,l 0 , 2 0 , 3 0,4 0,5 Po/atm Fig. 2. Effect of Po on S(MA+FR), S(CO), and S(C0,) for buta-1,3-diene oxidation on V,O,-U at 622 K. 0, S(MA+ FR); 0, S(C0); A, S(C0,). Partial pressure ofbuta-173-diene = 0.0074 atm. partial pressures of 0,. With Po > 0.298 atm the catalyst in the steady-state reaction gave absorption bands at 1020 and 825 cm-l which are assigned to the stretching vibration of V=O species and the coupled vibration between V=O and V-0-V, respe~tive1y.l~~ 2o These absorptions gradually decrease as Po decreases below 0.298 atm, and new absorption bands at 990 and 910 cm-l are observed for the catalyst in the steady-state reaction when Po < 0.149 atm.These bands are assigned to lattice vibrations of V,0,.21 In order to quantify the change in the amount of V=O species with changing Po the relative absorbance at 1020 cm-I was calculated from the spectra in fig. 3 and the results are shown in fig. 4. As shown, the amount of V=O species increases almost linearly with Po to 0.298 atm and it is constant above this value.18 Supported Vanadium Oxide Catalysts wavenumberlcm-' Fig. 3. Infrared spectra of V,O,-U in the steady state of buta-1,3-diene oxidation at various partial pressures of 0,.Temperature = 622 K, partial pressure of buta-1,3-diene = 0.0074 atm. The numbers in parentheses represent the partial pressures of 0,. Activity and Selectivity in Buta-l,3-diene Oxidation under Conditions of Excess Oxygen Table 1 shows results of Ro, Ro/SB. E.T., S(MA + FR), S(C0 + CO,) and S(CO)/S(CO,) for unsupported vanadium oxide catalysts under excess oxygen conditions where the reaction rate was zeroth order with respect to Po and where the catalyst was confirmed to be in the highest oxidation state, i.e. V5+. In accordance with the decrease in SB,E.T., Ro for V,O,-F or V,O,-RO is much smaller than that for V20,-U. It should be noted that the specific activity (RO/SB.E.T.) for V,O,-U is much larger than that for V,O,-F and that for V,O,-RO is larger than that of V,O,-F.In contrast to the behaviour of the reaction rate, the selectivity, S(MA + FR), S(C0 + CO,) or S(CO)/S(CO,), does not change significantly with the kind of unsupported V,05. Table 2 shows results of Ro, S(MA+FR), S(CO+CO,) and S(CO)/S(CO,) for V,O,/TiO, and V,O,/Al,O3 catalysts with various V,O, contents. TiO, or Al,O, alone had a negligible activity for the buta-1,3-diene oxidation. The reaction rate (R,) for V,O,/TiO, increases markedly with an increase in V205 content from 0 to 5 mol % , passes a maximum at 5 mol % V,O,, and then decreases to the value of V,O,-U with further increase in V,O, content. The selectivity to MA and FR[S(MA+FR)] is low for V,O,/TiO, containing 1-2 mol % V,O,, while it is as high as 60% for catalysts with V,O, contents > 5 mol % .V2O,/A1,O3 with low V,05 content (2 mol % ) has a negligible activity.Ro increases markedly with increasing V,O, content from 5-25 mol % . R, forK . Mori, A . Miyamoto and Y. Murakami 19 0 0 , l 0.2 0 . 3 0,4 0,5 Po/atm Fig. 4. Amount of V=O in V,O,-U in the steady state of buta-1,3-diene oxidation at various pressures of 0,. V,O,/Al,O, (25 mol % V,O,) is considerably higher than Ro for V,O,/TiB, (5 rnol % V,O,). S(MA+ FR) for V,O,/A1,0, with low V20, content (2-5 mol "/o ) i s very low, while it increases markedly in the range from 5-25 mol:< and attains a constant value above 25 mol % . S(MA + FR) for the monolayer V,O,/TiO, and V,O,/Al,O, is low and total oxidation of buta- 1,3-diene to CO and CO, takes place preferentially.Although tables 1 and 2 show results for the reaction at 622 K, similar relationships were found to hold at any temperature examined (59G658 K). The apparent activation energy for R, was 20 kcal mol-1 for V,O,-U, 27 kcal mol-1 for V,O,-F, 25 kcal mol-l for V,O,-RO, 19-20 kcal mol-1 for V,O,/TiO, and 27-30 kcal mol-1 for V,O,/Al,O,. The selectivity to MA and FR decreased only sightly with increased temperature. Effects of P, on Rates and Catalyst Structures for But-1-ene Oxidation In the reaction of but-1-ene on vanadium oxide catalysts, the following reactions were found to take place: but-1 -ene (B) + 30, -+ C,H,O,(MA) + 3H,O (13) but- 1 -ene (B) + 40, -+ 4C0, + 4H,O (14) but-1-ene (B)+602 -+ 4C0,+4H20 (15) (16) (17) As with the case for buta-1,3-diene rate of formation of each product [R(MA), R(CO), R(CO,), R(c-B), or R(t-B)] is defined as the rate of but-1-ene converted to the product.Reactions (1 3)-( 15) are oxidation of but- 1 -ene, while reactions (1 6) and (1 7) are isomerization of the reactant. Rates of oxidation (R,) and isomerization (RI), total reaction rate (R), and selectivities to the oxidation products (S,) and isomerization product (S,) are then given by the following: but-1-ene (B) + cis-but-2-ene (c-B) but-I -ene (B) + trans-but-2-ene(t-B). R , = R(MA) + R(C0) + R(C0,) RI = R(c-B) + R(t-B) (18) (19)20 Supported Vanadium Oxide Catalysts 2,4 I 1 L 1 1 0 . 1 0.2 0 . 3 0,4 0 , 5 Po/atm Fig. 5. Effect of Po on R,, R(MA), R(C0) and R(C0,) for but-1-ene oxidation on V,O,-U at 648 K. 0, R,; 0, R(MA); A, R(C0); 0, R(C0,).Partial pressure of but-1-ene = 0.0079 atm, W/F = 5 13 g s rnolp1. R = Ro+RI (20) so = R,/R (21) S I = R,/R. (22) S(MA) = R(MA)/Ro (23) S(C0) = R(CO)/R, (24) S(C0,) = R(CO,)/R,. (25) S(c/t) = R(c-B)/R(t-B). (26) Selectivities to MA[S(MA)], CO[S(CO)] and CO,[S(CO,)] in the oxidation of but- 1 -ene are defined by: The cisltrans ratio [S(c/t)] in the isomerization of but-1-ene is similarly given by: Fig. 5 shows the effect of Po on R,, R(MA), R(C0) and R(C0,) for the V,O,-U catalyst at 648 K. The rates increase gradually with increasing Po to 0.15 atm, while they are almost constant at Po > 0.15 atm. In spite of the change the reaction rates with Po, S(MA), S(C0) and S(C0,) are independent of Po as shown in fig. 6. Fig. 7 shows the effect of Po on R,, R(c-B) and R(t-B) for V,O,-U at 648 K.Similar to the result for the oxidation (fig. 5), the rates increase gradually with increasing -Po to 0.15 and are almost constant at Po > 0.15 atm. It should be noted that the isomerization does not proceed in the absence of 0,, the same behaviour as that for the oxidation. Fig. 8 shows the results of S(c/t) and SI at various Po. When Po is high, trans-but-2-ene is preferentially formed, while the yield of cis-but-2-ene is slightly higher than that of trans-but-2-ene when Po is low. The value of S , is almost independent of Po except for the value at low Po where oxidation is slightly more favourable than isomerization. After the stoppage of 0, supply, the rates decreased gradually with increasing time and attained a negligible value at 8 h after the reaction began (similar to buta- 1,3-diene).It was confirmed that both the reaction rate and i.r. spectrum of the catalyst attainedK . Mori, A . Miyamoto and Y. Murakami 40 I-.------ 21 I 1 1 I I 0 0,1 0-2 0 , 3 0.4 0 . 5 Po/atm Fig. 6. Effect of Po on S(SM), S(C0) and S(C0,) for but-1-ene oxidation on V,O,-U at 648 K . 0, S(MA); A, S(C0); 0, S(C0,). Partial pressure of but-1-ene = 0.0079 atm. Po/atm Fig. 7. Effect of Po on R,, R(t-B) and R(c-B) for V,O,-U at 648 K. 0, R,, A, R(t-B); 0, R(c-B). Partial pressure of but-1-ene = 0.0079 atm, W/F = 513 g s mol-’. a steady state under this condition. Similar to the case for buta- I ,3-diene, the absorbance at 1020 cm-l was calculated from the i.r. spectra at various Po and the results are shown in fig.9. As shown, the amount of V=O species increases almost linearly with the increase in Po < 0.149 atm and it is constant above this value of Po. Activity and Selectivity in the Oxidation of But-l-ene under Excess Oxygen Conditions Table 3 shows results for Ro, RO/SR.E.T., S(MA), S(C0) and S(C0,) for unsupported vanadium oxide catalysts under excess oxygen conditions where the reaction rate was zeroth order with respect to Po and where the catalyst was confirmed to be in the highest oxidation state, i.e. V5+. In accordance with the decrease in SR.E.rr., R, for V,O,-F or22 Supported Vanadium Oxide Catalysts t 1 O a 4 1 I I I I 10 0 0,l 0,2 0 , 3 0,4 0.5 Po/atm Fig. 8. Effect of Po on S, and S(c/t) for V,O,-U. I I I 0,l 0,2 0 , 3 0,4 0,s 6 - I 0 Po/atm Fig.9. Amount of V=O in V,O,-U in the steady state of but-I-ene oxidation at various partial pressures of 0,. Table 3. Oxidation of but- 1 -ene on unsupported V,O, catalystsa _ ~ _ ~ _ _ _ _ _ _ -~ R, (ROISl3. E.T.) /pmol /pmol TF, S(MA) S(C0) S(C0,) catalyst g-l s-l mP2 s-' /ks-l (%I (%I (%> V,O,-U 0.91 0.17 43 46 31 23 V,O,-F 0.090 0.1 1 23 42 32 26 V,O,-RO 0.100 0.13 25 42 33 25 a R,, reaction rate for the oxidation; TF,, turnover frequency for the oxidation; S(MA), selectivity to maleic anhydride ; S(CO), selectivity to CO; S(CO,), selectivity to CO,. Reaction condi- tions: temperature = 622 K; partial pressure of but-1-ene = 0.00 79 atm; partial pressure of 0, = 0.397 atm.K . Mori, A . Miyamoto and Y. Murakami Table 4.Oxidation of but-1-ene on V,O,/TiO, and V,0,/A1,03 catalystsa R O /,urn01 TF, S(MA) S(C0) S(C0,) catalyst g-ls-l /ks-l (%) (%) (%) 1 2 5 10 25 50 mono 1 aye r 2 5 10 25 35 50 monolayer 5.38 11.2 17.7 13.1 5.64 2.11 11.3 0.12 1.23 9.94 17.0 15.0 10.7 0.84 0.94 V,O,/TiO, 96 24 93 32 96 40 97 45 94 47 68 48 90 33 40 0 16 7 28 28 42 41 41 43 43 47 42 0 43 46 V2°5/A1203 v,o,-u 37 34 36 33 32 32 34 34 33 25 32 32 29 31 31 39 34 24 22 21 20 33 66 60 47 27 25 24 69 23 23 a For the definition of R,, TF,, S(MA), S(CO), and S(CO,), see table 3. Reaction conditions: temperature = 622 K; partial pressure of but-1-ene = 0.0079 atm; partial pressure of 0, = 0.397 atm. V,O,-RO is much smaller than that for V,O,-U. However, note that the specific activity (Ro/SB.E.T.) is almost constant and that for V,O,-F is only sightly smaller than that for V,O,-U or V,O,-RO.The selectivity, S(MA), S(C0) or S(CO,), does not change significantly with the kind of unsupported V,O,. Table 4 shows results of R,, S(MA), S(C0,) for V,O,/TiO, and V205/A1,0, catalysts with various V,O, contents. TiO, or Al,O, alone had a negligible activity for the but- 1 -ene oxidation. R, for V,O,/TiO, increased markedly with an increase in V,O, content from 0-5 mol% , passed a maximum at 5 mol % V,O,, and then decreased to the value of V,O,-U with further increase in V,05 content. S(MA) is low for V,O,/TiO, containing 1 or 2 mol % V,O,, while it is as high as 40% for catalysts with > 5 mol V,O, . V205/A1,03 with low V,O, content (2 mol%) has only a negligible activity.R, increases markedly with increasing V,O, content from 5-25 mol % . R, for V,0,/A1,03 (25 mol % V,O,) is considerably higher than R, for V,O,/TiO, ( 5 mol % V,O,). S(MA) for V205/A1203 with low V,O, content (2-5molX) is very low, while it increases markedly in the range from 5-25 mol% and attains a constant value above 25 mol % . S(MA) for the monolayer V,O,/TiO, and V,O,/Al,O, is low and total oxidation of but- 1 -ene to CO and CO, takes place preferentially. Although tables 3 and 4 show results for the reaction at 622 K, similar relationships were found to hold at any temperature examined (580 - 666 K). The apparent activation energy for R, was 25-26 kcal mol-1 for unsupported V,O, catalysts, 22-23 kcal mol-1 for V,O,/TiO,, and 25-27 kcal mol-1 for V,0,/Al,03.24 Supported Vanadium Oxide Catalysts Table 5.Isomerization of but- 1 -ene on unsupported V,O, catalystsn v,o,-u 1.17 0.22 53 20 33 0.60 55 V,O,-RO 0.12 0.15 30 13 18 0.7 1 55 V205-F 0.10 0.13 25 10 15 0.67 52 a R,, rate of isomerization; TF,, turnover frequency for the isomerization ; TF(c-B), turnover frequency for the isomerization to cis-2-butene ; TF(t-B), turnover frequency for the isomerization to trans-but-2-ene; S,, selectivity to isomerization. Reaction conditions: temperature = 622 K; partial pressure of but-1-ene = 0.0079 atm; partial pressure of 0, = 0.397 atm. Table 6. Isomerization of but-1 -ene on V,O,/TiO, and V,O,/Al,O, catalystsn Oh I 2 5 10 25 50 monolayer Oh 2 5 10 25 35 50 monolayer 0.72 3.35 7.07 8.30 5.31 3.24 1.65 6.96 0.12 0.25 3.40 13.9 10.7 13.8 8.29 3.23 1.17 T 4 TF(c-B) /ks-l /ksP1 - 60 59 45 39 54 53 55 - 83 44 39 26 38 33 161 53 V,O,/TiO, 26 26 19 17 22 20 25 - V,O,/A1203 - 53 28 22 13 16 14 94 V,O,-U 20 - 0.57 34 0.78 33 0.78 26 0.74 22 0.76 32 0.70 33 0.62 31 0.80 - 3.00 30 1.78 16 1.70 18 1.22 13 0.95 22 0.70 19 0.72 68 1.39 100 38 39 32 29 36 44 38 100 67 73 58 38 48 43 79 33 0.60 55 ~~ ~ a For the definition of R,, TF, TF(c-B), TF(t-B), S(c/t) and S,, see table 5.Reaction conditions: temperature = 622 K; partial pressure of but-1-ene = 0.0079 atm; partial pressure of 0, = 0.397 atm. TiO, or A1,0, support alone. Activity and Selectivity in the Isomerization of But-l-ene under Excess Oxygen Conditions Table 5 shows results for R,, R,/SR. E.T., S(c/t) and S, for unsupported vanadium oxide catalysts under excess oxygen conditions.In line with the result for the oxidation (table 3), R, for V,O,-F or V,O,-RO is much smaller than that for V,O,-U. However, the specific activity (RI/SB.E.T.) is almost constant and that for V,O,-F is only slightlyK. Mori, A . Miyamoto and Y. Murakami 25 smaller than that for V205-U or V,O,-RO. S(c/t) and S , are almost constant and independent of the kind of unsupported V205. Table 6 shows results for R,, S(c/t) and S, for V,O,/TiO, and V,O,/Al,O, catalysts with various V,05 contents. In contrast to the behaviour in the oxidation, TiO, or A1,0, support alone exhibits a considerable activity for but- 1 -ene isomerization, although it is smaller than that for the supported V205 catalyst. R, for V,O,/TiO, increases markedly with an increase in V205 content from 0-5 m o l x , passes a maximum at 5 m o l x , and then decreases to the value of V20,-U with further increase in V,O, content.The S(c/t) for V,O,/TiO, is almost constant and independent of the V,05 content. V205/A1203 with low V205 content (2 mol%) shows low activity. R, increases markedly with increasing V,05 content from 5-10 mol:4. S(c/t) = 3 for the A1,0, support and is much higher for the unsupported V,05. As the V,O, content increases to 35 mol % , S(c/t) decreases gradually to the value for the unsupported V,05. S(c/t) for the monolayer V20,/Al,03 is also considerably higher than that of the unsupported V,03. Although tables 5 and 6 show results for the reaction at 622 K, similar relationships were found to hold at any temperature examined (580-666 K).The apparent activation energy for R, was 20-23 kcal mol-l for the unsupported V,O, catalysts, 21-23 kcal mol-1 for V,05/Ti02 and 24-26 kcal mol-l for V,05/Al,03. Discussion Active Oxygen Species for the Oxidation of Buta-1,3-diene and But-1-ene As shown in fig. 1, the rate of buta-1,3-diene oxidation increased with increasing Po up to 0.3 atm for V,O,-U and attained a constant value above this value of Po. The steady-state amount of the V=O species in the catalyst changed with Po similarly to the reaction rate (fig. 4). This suggests that the reaction proceeds by the reduction-oxidation mechanism (or Mars-van Karevelen mechanism)22 and that the active oxygen species for the buta-1,3-diene oxidation is surface V=O species, in accordance with the conclusion obtained by Akimoto et al.23 Adsorbed oxygen species are not responsible for this reaction, because no adsorbed oxygen species, such as O;, 0- or O;, were detected on the catalysts by either e.s.r.or t.p.d. measurements. The observed relationship between reaction rate and Po (fig. 1) can be explained in terms of the reduction-oxidation mechanism as follows: In the absence of 0, (Po = 0 atm), the catalyst is in the reduced state and no surface V=O species is present to oxidize buta-1,3-diene. As Po increases, reoxidation increases the oxidation state of the catalyst to increase the number of surface V=O species. This means that the reaction rate increases with increasing Po. In the presence of excess oxygen (P> 0.3 atm), the catalyst is in the highest oxidation state, i.e.V,O,. Therefore, the increase in Po does not lead to further increase in the oxidation state or the number of surface V=O species. Thus the reaction rate does not increase with Po under excess oxygen conditions. As shown in fig. 5 and 9, the behaviour of the reaction rate and the amount of V=O at various Po in but-1-ene oxidation are similar to those in buta-l,3-diene oxidation. Therefore, but-1 -ene oxidation also proceeds by the reduction-oxidation mechanism and the active oxygen species is surface V=O species. Structure Sensitivity of Buta-1,3-diene Oxidation The surface of V,05-F has been found to be significantly different from that of V,O,-U or V20,-R0.8~g Since the surface V=O species has been found to be the active oxygen species for buta- 1,3-diene oxidation, the turnover frequency (TF,) for this reaction can be defined by TF" = R,/L.(27)26 Supported Vanadium Oxide Catalysts Values of TF, at 622 K were calculated from the results of R, and L for various catalysts and the results are shown in table 1. It is evident that TF, changes significantly with the type of catalyst; TF, (V,O,-U) % TFo (V,O,-RO) > TF, (V,O,-F). This behaviour is in contrast to those in the benzene oxidation,, and indicates that buta-1,3-diene oxidation on V,O, catalysts is a structure-sensitive reaction. Fusion of a solid would generally lead to a smooth surface with a decreased number of surface defects (e.g. steps, kinks or vacancies), while severe redox treatment of a solid with few surface defects would tend to increase their number.Furthermore, no impurity peaks were observed in the X.P.S. spectrum of V,O,-U, V,O,-F or V,O,-RO. Since the surface V=O species has been shown to be the active oxygen species, the surface V=O species at the surface defects are considered to be much more active than that in the smooth (010) plane. Structure Sensitivity of But-1-ene Oxidation Values of TF, were calculated from the results of R, and L for various catalysts aiid results are also shown in tables 3 and 4. TF, changes only slightly with the kind of unsupported catalysts, a behaviour in contrast to that in buta-l,3-diene oxidation. Thus, the surface V=O species at the surface defects are considered to have almost the same activity as that in the smooth (010) plane in this case.Activity of Supported Catalysts for Buta-l,3-diene Oxidation In general, the activity of a supported catalyst is determined by two factors; (i) the number of active sites and (ii) the specific activity of the active site, i.e. the turnover frequency. The separation of these two factors is indispensable for detailed understanding the role of support in a given reaction. As shown in table 2, R, for V,O,/Al,O, and V,O,/TiO, catalysts is larger than that for V,O,-U, indicating the promoting effect of A1,0, or TiO, support. The number of surface V=O species ( L ) for V,O,/Al,O, and V,O,/TiO, catalysts is much larger than that for the unsupported V,05, while the turnover frequency (TF) for the supported catalysts is smaller than that for the V,O,-U.This means that the effect of A1,0, or TiO, is to increase the number of surface V=O species, but the specific activity of the surface V=O species is not increased by the support. Fig. 10 shows the relationship between TF and the number of V,O, layers ( N ) for V,O,/TiO, and V,O,/Al,O,. TF for V,O,/TiO, decreases monotonically with decreasing number of V,O, layers on TiO,. This indicates that the retarding effect of TiO, on the specific activity of the surface V=O species becomes greater as the number of V,O, layers decreases. According to Vejux and C~urtine,~* there is a remarkable fit of the crystallographic patterns between the (010) face of V,O, and the TiO, surface. It is therefore considered that a smooth V,O, surface with few defects is formed for the V,O,/TiO, catalysts having a low concentration of V,O,, and that the number of surface defects increases with the content of V,O,.The activity of V=O at the surface defect is much higher than that in the smooth (010) face hence the significant reduction in TF for V,O,/TiO, compared with that for V,O,-U and the increase in 7 7 with increasing content of V,O, in V,O,/TiO,. Selectivity in Buta-1,3-diene Oxidation Fig. 11 shows relationship between the selectivity to partial oxidation products [S(MA + FR)] and the conversion of buta- 1,3-diene, which were obtained from the results under excess oxygen conditions at various temperatures. S(MA + FR) is independent of the conversion for any catalyst. This indicates that consecutive oxidation of the partial oxidation product to CO or CO, was negligible under the present experimentalK.Mori, A . Miyamoto and Y. Murakami 27 1 2 10 190 503 no. of Vz05 layers (N> Fig. 10. Relationshp between the turnover frequency (TF,) for buta- 1,3-diene oxidation and the number of V,O, layers on support. 0, V,O,/TiO,; A, V,O,/Al,O,; a, V,O,-U. I I 0 10 20 30 40 5 conversion (%) Fig. 11. Relationship between the conversion and selectivity for buta-l,3-diene oxidation on unsupported V,O,, V,O,/TiO,, and V,O,/Al,O, catalysts. A, V,O,-U ; A, V,O,-F ; A, V,O,-RO. 0, 0, @, (>, 8, 0, are V,O,/TiO, with V,O, contents 1, 2, 5 , 10, 25, 50 m o l x , and the monolayer catalyst, respectively. 0, o>, ($, 0, 0 , 0, + are V,O,/Al,O, with V,O, contents 2, 5. 10, 25, 35, 50 mol % , and the monolayer catalyst, respectively.Reaction temperature = 590- 658 K, partial pressure of buta-1,3-diene = 0.0074 atm, partial pressure of 0, = 0.397 atm. conditions. In other words, the difference in selectivity among the catalysts is not brought about by the consecutive oxidation of the partial oxidation product. As shown in fig. 4, the oxidation state of the V,O,-U catalyst changes greatly with Po. Under excess oxygen conditions, the catalyst is kept in the highest oxidation state (V5+) while it is reduced as Po decreases. As shown in fig. 2, S(MA + FR), S(C0,) and S(C0) do not change with Po. This means that the selectivity in buta- 1,3-diene oxidation is independent of the oxidation state of the catalyst, at least under the present experimental conditions (conversion of buta- 1,3-diene < 40 % , consecutive oxidation of the partial oxidation product to CO and CO, is negligible and the catalyst is in its steady state at a given level of Po).Table 1 shows that the selectivity is almost independent of the kind of unsupported V,O, catalysts, in contrast to the behaviour of the activity of the catalyst. This indicates that the selectivity is not affected by a change in the surface structure. The selectivity under excess 0, conditions changes greatly with the catalysts (table 2). Fig. 12 shows plots of the selectivity to partial oxidation products [S(MA + FR)] against the number28 60- 2o Supported Vanadium Oxide Catalysts 9 0 0 y.-.-. 0 / 0 4 4QcI b I &I Fig. 12. Relationship between the selectivity for buta-1,3-diene oxidation and the number of V,O, layers on the support.0, V,O,/TiO,; A, V,O,/Al,O,; 0 , V,O,-U. of V,O, layers on support (N). When N = 1 or 2, S(MA + FR) is low, while it increases markedly with an increase in N to 5, and attains a constant value above 5 layers. It is interesting to note that the relationship between S(MA + FR) and N is quite similar for both V,O,/TiO, and V,O,/Al,O, catalysts, while the structures of the V,O,/TiO, catalysts differ significantly from those of V,O,/Al,O, catalysts.4 This indicates that the number of V,O, layers is an important factor for determining the selectivities in the oxidation of buta-l,3-diene; V,O, layers are necessary for the selective oxidation of buta-l,3-diene to FR or MA. The structure-selectivity correlation for buta- 1,3-diene oxidation is similar to that for benzene oxidation., The roughness of the catalyst surface does not affect the selectivity for both reactions.The number of V,05 layers is an important factor determining the selectivity for both reactions: the monolayer catalyst exhibits low selectivity to the partial oxidation product and V,O, layers are necessary for the selective oxidation. Although further studies are necessary to clarify molecular mechanism for the correlation between S(MA+FR) and N , a discussion similar to that described for benzene oxidation may be applicable to buta- 1,3-diene oxidation. As described above, the reaction proceeds by the reduction-oxidation mechanism and the surface V=O species has the active role, It has also been shown that there are Brarnsted acid sites adjacent to the surface V=O species on the supported vanadium oxide cataly~t.~.l9 These suggest that the buta-1,3-diene molecule is adsorbed and activated on the Brmsted acid site and that the reaction is initiated by the nucleophilic attack of the oxygen atom of a surface V=O species to the adsorbed buta-l,3-diene molecule to form an intermediate. Judging from the stoichiometry of the reaction (fig. 3 and 4), subsequent introduction of oxygen atoms to the intermediate species is necessary to complete the reaction. Since the reaction proceeds by the reduction-oxidation mechanism, these oxygen atoms are not directly supplied from gaseous 0,, but supplied by the oxygen of the catalyst. It is well known that the oxygen of V,O, can migrate from the bulk to surface.When the V,O, layers on support are sufficiently thick, the oxygens in the V20, layers can be supplied to oxidize the intermediate species. As for a catalyst with monolayer V,O, or with very thin V20, layers on support, oxygen cannot be supplied from the bulk, but is supplied by the migration of surface oxygen. This change in the mode of oxidation of the intermediate species with the number of V20, layers may provide one of the reasons for the correlation between S(MA+ FR) and N . The change in S(CO)/S(CO,) with the catalyst (table 2) may also be explained by the change in the mode of oxidation of the intermediate species. According to Bond et al.25 the active phase in buta-1,3-diene oxidation is the binaryK.Mori, A . Miyamoto and Y. Murakami 29 oxide Vo.04Tio.9602. The presence of binary oxide was not confirmed for the present catalyst, probably because the calcination temperature was considerably lower than that used by Bond et al. Since the electronic state of vanadium is greatly modified by the formation of the binary oxide, the structure-activity/selectivity correlation for such catalysts may provide an interesting subject for future investigation. Activity of Supported Catalysts for But-1-ene Oxidation Ro for V,O,/Al,O, is greater than that for the unsupported V,O, (table 4), indicating the promoting effect of the A1,0, support. The number of surface V=O species on V,O,/A1,0, is much greater than that on unsupported V,O,, while TFo for V,O,/Al,O, is not greater than that for unsupported V,O,.This means that the promoting effect of Al,O, is to increase the number of active sites. The rate for V,O,/TiO, is also much larger than that for unsupported V,O,. Both L and TFo are increased by supporting V,O, on TiO,. This means that the promoting effect of the TiO, support is caused by two factors: an increase in the number of surface V=O species and an increase in the activity of these species. It is well known that oxygen evolution from V,O, in V,O,/TiO, (anatase) occurs at a temperature much lower than that in unsupported V,0,.661 26 Thus it is believed that the V=O species on V,O,/TiO, are catalytically more active those on unsupported V,O,. The result shown in table 4 provides experimental evidence for the validity of this inference.Selectivity in But-1-ene Oxidation Fig. 13 shows some examples of relationships between the selectivity in but-1-ene oxidation [S(MA) and S(CO)] and the conversion of but-1 -ene, which were obtained from the results under excess oxygen conditions at various temperatures. Either S(MA) or S(C0) is independent of the conversion for any catalyst. This indicates that consecutive oxidation of MA to CO and CO, (or CO to CO,) is negligible under the present experimental conditions. In other words, the difference in the selectivity among catalysts is brought about by the difference in the catalyst structure, but not by consecutive oxidation. The oxidation state of the V,O,-U catalyst changes greatly with Po (fig. 9). Under excess oxygen conditions, the catalyst is kept in the highest oxidation state (V5+) while it is reduced as Po decreases.As shown in fig. 6, S(MA), S(C0,) and S(C0) do not change with Po. This means that the selectivity in but-1-ene oxidation is independent of the oxidation state of the catalyst, at least under the present experimental conditions (consecutive oxidation is negligible and the catalyst is in its steady-state at a given level Table 3 shows that the selectivity is almost independent of the kind of unsupported V,O, catalysts, indicating that it is not affected by a change in the surface roughness. On the other hand, the selectivity under excess 0, condition (table 4) changes greatly with the catalysts. Fig. 14 shows the selectivity to maleic anhydride [S(MA)] against the number of V,O, layers on support.When N = 1 or 2, S(MA) is low, while it increases markedly with an increase in N to 5, and attains a constant value above 5 layers. It is interesting to note that the relationship between S(MA) and N is almost common to both V,O,/TiO, and V,O,/Al,O, catalysts, while the structures of the V,O,/TiO, catalysts differ significantly from those of V,O,/Al,O, cataly~ts.~ This indicates that the number of V,O, layers is an important factor for determining the selectivities in the oxidation of but-1-ene; V,O, layers are necessary for the selective oxidation of but-1-ene to MA. of Po).30 Supported Vanadium Oxide Catalysts Q 20 I 0 20 40 60 conversion (70) 0 Fig. 13. Relationship between the conversion and selectivity for but- 1 -ene oxidation on unsupported V,O,, V,O,/TiO, and V,O,/Al,O, catalysts. A, V,O,-U; A, V,O,-F; A, V,O,-RO.0 , 0 , 0 , 0, 9. + are V,O,/TiO, with V,O, contents 1, 2, 5, 10, 25 and 50 m o l x , respectively. 0, a, @, 0, 0, are V,O,/A1,0, with V,O, contents 2, 5 , 10, 25, 35 and 50 m o l x , respectively. Reaction temperature = 580-666 K, partial pressure of but-1-ene = 0.0079 atm, partial pressure of 0, = 0.397 atm. k , , . ,,,., , , , , , , * , , , , 0 1 2 10 100 500 no. of V , 0 5 layers (N) Fig. 14. Relationship between the selectivity for but-1-ene oxidation and the number of V,O, layers on support. 0, V,O,/TiO,; A, V,O,/Al,O,; 0, V,O,-U. Active Sites for Isomerization Fig. 15 shows some examples of relationships between S(c/t) and the conversion of but-1-ene, which were obtained from the results under excess oxygen conditions at various temperatures.S(c/t) is independent of the conversion for any catalyst, indicating that consecutive isomerization of cis-but-2-ene to trans-but-2-ene or of trans-but-2-ene to cis-but-2-ene was negligible under the present experimental conditions. According to the results of previous investigations on the isomerization ofK. Mori, A . Miyamoto and Y. Murakami 31 I 1 1 60 0,21 0 20 40 1 conversion (%) 1 Fig. 15. Relationship between the conversion and S ( c / t ) for but-1-ene isomerization on unsupported V,O,, V,O,/TiO,, and V,O,/Al,O, catalysts. A, V,O,-U; A, V,O,-F; A, V,O,-RO. 0, 0 , 0 , 0 , 8, 4 are V,O,/TiO, with V,O, contents 1, 2, 5, 10, 25 and 50 mol % , respectively. 0, (3, 0, 8, 8, are V,O,/Al,O, with V,O, contents 2, 5, 10, 25, 35 and 50 mol%, respectively. Reaction temperature = 580-666 K, partial pressure of but-1-ene = 0.0079 atm, partial pressure of 0, = 0.397 atm.but-1-ene,l2-l4 the value of S(c/t) is a sensitive reflection of the reaction mechanism: if the reaction proceeds on the Brsnsted acid site, the s-butyl cation is formed as an intermediate to give 0.5 < S(c/t) < 1 .O. If a n-ally1 anion intermediate is formed by the interaction of but-1-ene with metal oxides such as MgO, ZnO, La,O, and A1,0,, S(c/t) > 2. As shown in table 5, S(c/t) for the unsupported V205 is in the range 0.6-0.7, suggesting that Brsnsted-acid site plays an important role as an active site for the isomerization of but-1-ene. This is consistent with the results of characterization of the unsupported V,05 because i.r.spectra of NH, and pyridine adsorbed on the unsupported V205 indicate the presence of the Brsnsted-acid site on the catalyst, but not of the Lewis-acid ~ i t e . ~ , ~ ~ As shown in table 6, Al,O, support alone gives a value of S(c/t) as high as 3. This is also consistent with the presence of the Lewis-acid site and the absence of the Brsnsted-acid site as revealed by i.r. ~pectra.~ The value of S(c/t) for TiO, support alone (0.67) is also consistent with the results of i.r. spectra of NH, and pyridine on TiO,, since the presence of the Brsnsted-acid site has been confirmed in addition to the Lewis-acid site.4 S(c/t) for V,O5/Al@, decreases gradually with the increase in V,O, content from 0 to 35 mol % .This can be explained in terms of the structure of the V205/Al,0, catalyst as follows: when the V,05 content is 25 mol % or lower, the A1,0, surface is not completely covered by v205,4 therefore the isomerization can proceed on both A120, and V205 surfaces, leading to a value of S(c/t) between 3.0 (A1203 support alone) and 0.7 (V,O, alone). When the V,O, content is 35 mol % or higher, the whole Al,O, surface is covered with V205 layers and S(c/t) for the catalyst is close to the value for the unsupported V,O,. As for the monolayer V,O,/Al,O, catalyst, a considerable portion of A120, is exposed to the catalyst ~urface.~ This explains high value of S(c/t) for the monolayer V,05/A1,0, catalyst. S(c/t) for the V205/Ti02 catalyst is almost constant and close to the value for the unsupported catalyst, indicating that the Brsnsted acid site is important for the isomerization of but-1-ene on a V205/Ti02 catalyst.2 F A R 132 Supported Vanadium Oxide Catalysts As shown in fig. 7, the rate of but-1-ene isomerization increases with increasing Po to 0.1 5 atm for V,O,-U and attains aconstant value above this value of Po. The steady-state amount of the V5+=0 species in the catalyst changes with Po similarly to the reaction rate (fig. 9). Since the Brsnsted-acid site is the active site for the isomerization of but-1-ene on the unsupported vanadium oxide catalyst, this suggests that the surface V=O species play an essential role in promoting the reaction on the Brsnsted-acid site. According to quantum-chemical calculations of vanadium oxide clusters with various oxidation states,28 the V5+=0 species effectively increases the positive charge on the Brsnsted-acid site adjacent to the V5+=0 species, while its reduction leads to the decrease in the positive charge of the Brsnsted-acid site.This suggests that the promoting effect of the surface V5+=0 species on the isomerization is brought about by the increase in the strength of the Brsnsted-acid site. Difference in the Catalytic Behaviour between Oxidation and Isomerization Judging from the stoichiometries of the oxidation [eqn (1 3)-( 15)] and isomerization [eqn (1 6-1 7)], the structure-activity/selectivity correlation for the oxidation is expected to be different from that for the isomerization. If we take into account the effect of Al,O, or TiO, support on the isomerization, however, the catalytic behaviour in the isomerization is apparently very similar to that in the oxidation : R , and R, change similarly with the treatment of the unsupported V,O, catalyst (tables 3 and 5 ) and with Po (fig.5 and 7). This can be seen quantitatively in the value of S, (percentage of the isomerization rate in the total reaction rate). ST is almost constant and independent of the kind of unsupported catalyst (table 5 ) or Po (fig. 8). Similarly, S , for supported catalysts (except for the one with low V,O, content) does not differ significantly from that for the unsupported V,O, (table 6). The surface V=O species is the active oxygen species for the oxidation of but-1-ene. As discussed above, surface V=O also plays an essential role in the isomerization of but-1-ene by increasing the strength of the Brsnsted-acid site which is the active site for isomerization.This explains the apparent similarity in the catalytic behaviour between the isomerization and oxidation. A closer inspection of the turnover frequency for the isomerization (TF,) (table 6) indicates that TiO, support does not increase TF, for unsupported V,O,, in contrast to the behaviour in oxidation (table 4). This can also be explained in terms of the above mentioned difference in the role of surface V=O between both reactions. Difference in the Structure-Activity/Selectivity Correlation between But-1 -ene Oxidation and Buta-1,3-diene Oxidation According to Ai et the oxidation of but-1-ene to MA proceeds by the following mechanism : but-1-ene buta-1,3-diene - furan - MA co, co2 1 co, coz co, co, Although no buta-1,3-diene or furan was detected as a reaction product, the present results are consistent with this mechanism.This is because the turnover frequency for but-1 -me oxidation is much smaller than that for buta-1,3-diene oxidation and because the relationship between S(MA) and N (fig. 14) is similar to that for buta-1,3-diene oxidation. It should however be noted that the structure-activity correlation for but- 1 -ene oxidation is much different from that of the buta-1,3-diene oxidation. In contrast to theK. Mori, A . Miyamoto and Y. Murakami 33 behaviour in but-l-ene oxidation, the activity for buta-l,3-diene oxidation is very sensi- tive to the change in surface structure of V,O,; TFo for V,O,-F is much smaller than that for V,O,-U or V,O,-RO.Furthermore, TiO, support does not increase TF, in buta- 1,3-diene oxidation. Judging from eqn (28) the role of catalyst in the oxidation of but- 1 -ene to buta-173-diene is to abstract two hydrogen atoms from but-l-ene. On the other hand, the role in the oxidation of buta-1,3-diene to furan involves (i) donation of an oxygen atom, (ii) abstraction of two hydrogen atoms, and (iii) transformation of the geometry of conjugated dienes from s-trans to s-cis structures: CH-CH - II II CH C H , \ / CH2 \\ CH- CH \\ CH2 0 We have previously demonstrated for the oxidation of H, and CO on vanadium oxide catalysts that role of catalyst in a reaction significantly affects the structure sensitivity of the reaction.29 The role of the surface V=O in the H, oxidation (a structure-insensitive reaction) is to dissociate H-H bonds and form V-OH species, while that in the CO oxidation (a structure-sensitive reaction) is to donate its oxygen to a CO molecule to form a CO, molecule.Thus, the abovementioned differences in the role of the catalyst would explain the difference in the structure-activity correlation between but- 1 -ene oxidation and buta- 1,3-diene oxidation This work was partially supported by a Grant-in-Aid for Scientific Research (no. 59470097) and for Encouragement of Young Scientists (no. 59750655) from the Ministry of Education, Science and Culture, Japan. References 1 2 3 4 5 6 7 8 9 10 (a) C. F. Cullis and D. J. Hucknall, Catalysis (The Chemical Society, London, 1982), vol.5, p. 273; (6) M. S. Wainwright and N. R. Foster, Catal. Rec., 1979, 19, 21 1 ; (c) D. B. Dadyburjoir, S. S. Jewur and E. Ruckenstein, Catal. Rev., 1979, 19, 293; ( d ) A. Bielanski and J. Haber, Catal. Reti., 1979. 19, 1 ; (e) J. Haber, Proc. 8th Int. Congr. Catal. (West Berlin, 1984), 1-85 and references therein. D. J. Hucknall, Selective Oxidation of Hydrocarbons (Academic Press, London, 1974), p. 75 and references therein. (a) A. Miyamoto, Y. Yamazaki, M. Inomata and Y. Murakami, J. Phj,s. Chem., 1981, 85, 2366; (h) M. Inomata, A. Miyamoto and Y. Murakami, J . Phys. Chem., 1981, 85, 2372. (u) M. Inomata, K. Mori, A. Miyamoto, T. Ui and Y. Murakami, J. Phys. Chem., 1983, 87, 754; (b) M. Inomata, K. Mori, A. Miyamoto and Y.Murakami, J. Phys. Chem., 1983,87,761; (c) Y. Murakami, M. Inomata, K. Mori, T. Ui, K. Suzuki, A. Miyamoto and T. Hattori, Preparation of Catalysts III, ed. G. Poncelet, P. Grange and P. A. Jacobs (Elsevier, Amsterdam, 1983), p. 531. (a) K. Mori, M. Inomata, A. Miyamoto and Y. Murakami, J. Chem. Soc., Faraday Trans. I , 1984,80, 2655; (b) K. Mori, M. Inomata, A. Miyamoto and Y. Murakami, J. Phys. Chem., 1983, 87, 4560. (a) G. C. Bond and K. Briickman, Faraday Discus3 Chem. Soc., 1981, 72, 235; (h) D. J. Cole, C. F. Cullis and D. J. Hucknall, J. Chem. Soc., Faraday Trans. 1, 1976, 72, 2185; (c) A. J . van Hengstum, J. G. van Ommen, H. Bosch and P. J. Gellings, Proc. 8th Int. Congr. Cutal. (West Berlin, 1984), vol. IV, p. 297; ( d ) R. Koziolowski, R.F. Pettifier and J. M. Thomas, J . Phys. Chem., 1983, 87, 5175; (e) T. Ono, Y. Nakagawa, H. Miyata and Y. Kubokawa, Bull. Chem. Soc. Jpn, 1984, 57, 1205; (e) I. E. Wachs, S. S. Chan, C. C. Chersich and Y. Saleh, Catalysis on the Energy Scene, ed. S. Kaliaguine and A. Mahay (Elsevier, Amsterdam, 1984), p. 275; ( f ) R. D. Srivastava and A. B. Stiles, J. Catal., 1982, 77, 192. A. Miyamoto, K. Mori, M. Inomata and Y. Murakami, Proc. 8th Int. Congr. Catal. (West Berlin, 1984), W-285 and references therein. K. Mori, A. Miyamoto and Y. Murakami, J . Phys. Chem., 1984,88, 2735. K. Mori, A. Miyamoto and Y. Murakami, J . Phys. Chem., 1984, 88, 2741. (a) G. Centi, I. Manenti, A. Riva and F. Trifiro, Appl. Catul., 1984, 9, 177; (b) L. Morselli, F. Trifiro and L. Urban, J. Catal., 1982, 75, 112; (c) F.Cavani, G . Centi and F. Trifiro, Ind. Eng. Chem., Prod. ,.a L-L34 Supported Vanadium Oxide Catalysts Res. Dev., 1983,22,570; ( d ) W. E. Slinkard and P. B. Degrrot, J . Catal., 1981,68,423; (e) R. L. Varma and D. N. Saraf, J . Catal., 1978,55,361; (f) M. Nakamura, K. Kawai and Y . Fujiwara, J . Catal., 1974, 34,345; (g) T. Seiyama, K. Nita, T. Maehara, N. Yamazoe and Y. Takita, J. Catal., 1977,49, 164, and references therein. 11 (a) M. Ali, K. Harada, and S . Suzuki, Kogyo Kaguku Zassi, 1970, 73, 524; (6) M. Ai, J . Catal., 1981, 67, 110; (c) M. Ai, Bull. Chem. SOC. Jpn, 1970, 43, 3490; ( d ) M. Ai, Bull. Chem. SOC. Jpn, 1977, 50, 355; (e) M. Ai, J. Catal., 1975,40,318; (f) M. Ai, T. Niikuni and S. Suzuki, Kogyo Kagaku Zassi, 1970, 73, 165, and references therein. 12 J. W. Hightower and W. K. Hall, Chem. Eng. Prog., Symp. Ser., 1967, 63, 122, and references therein. 13 K. Tanabe, Solid Acids and Bases (Kodansha, Tokyo and Academic Press, London, 1970), chap. 5, and references therein. 14 (a) J. Goldwasser and W. K. Hall, J . Catal., 1981,71,53; (6) M. P. Rosynek, J. S. Fox and J. L. Jensen, J . Catal., 1981, 71, 194; (c) H. Forster and R. Seeleman, J . Chem. SOC., Faraday Trans. I , 1978, 74, 1435; ( d ) E. A. Irvine and D. Taylor, J. Chem. SOC., Furaday Trans. I, 1978, 74, 1590; (e) H. Hattori, K. Maruyama and K. Tanabe, Bull. Chem. Soc. Jpn, 1977,50,2187; v) S . Tsuchiya, M. Mikami and H. Imamura, Bull. Chem. SOC. Jpn, 1984, 57, 571, and references therein. 15 S. Yoshida, T. Iguchi, S. Ishida and K. Tarama, Bull. Chem. SOC. Jpn, 1972, 45, 476. 16 F. Roozeboom, T. Fransen, P. Mars and P. J. Gellings, 2. Anog. Allg. Chem., 1979, 25, 449. 17 M. Niwa, T. Hattori, M. Takahashi, K. Shirai, M. Watanabe and Y. Murakami, Anal. Chem., 1979, 51, 46. 18 (a) M. Ai, K. Harada and S . Suzuki, Kogyo Kagaku Zassi, 1970, 73, 524; (b) M. Ai, J . Catal., 1981, 67, 110; (c) F. Cavani, G. Centi, I. Manenti, A. Riva and F. Trifiro, Znd. Eng. Chem., Prod. Res. Dev., 1983,22, 565; ( d ) F. Cavani, G. Centi and F. Trifiro, Znd, Eng. Chem., Prod. Res. Dev., 1983, 22, 570 and references therein. 19 M. Inomata, A. Miyamoto and Y . Murakami, J. Catal., 1980, 62, 140. 20 K. Tarama, S. Yoshida, S. Ishida and H. Kakioka, Bull. Chem. Soc. Jpn, 1969, 41, 2840. 21 L. D. Frederickson and D. M. Hansen, Anal. Chem., 1963, 35, 818. 22 P. Mars and D. W. van Krevelen, Chem. Eng. Sci., 1951, 3, 41. 23 M. Akimoto, M. Usami, and E. Echigoya, Bull. Chem. SOC. Jpn, 1978, 51, 2195. 24 A. Vejux and P. Courtine, J. Solid State Chem., 1978, 23, 93. 25 G. C. Bond, A. J. Sarkany and G. D. Parfitt, J . Catal., 1979, 57, 176. 26 (a) A. Vejux and P. Courtine, J. Solid State Chem., 1978, 23, 93; (b) G. C. Bond, A. J. Sarkany arid 27 M. Inomata, A. Miyamoto and Y. Murakami, J . Catal., 1980, 62, 140. 28 A. Miyamoto, M. Inomata, A. Hattori, T. Ui and Y. Murakami, J. Mol. Catal., 1982, 16, 315. 29 K. Mori, M. Miura, A. Miyamoto and Y . Murakami, J . Phys. Chem., 1984, 88, 5232. G. D. Parfitt, J. Catal., 1979, 57, 176. Paper 4/ 1995; Received 22nd Noaember, 1984

ISSN:0300-9599    

DOI:10.1039/F19868200013

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I , 1986, 82, 3 5 4 3 Formation of an Epoxide Intermediate in the Photo-oxidation of Alkenes over Silica-supported Vanadium Oxide Tsunehiro Tanaka, Masaharu Ooe, Takuzo Funabiki and Satohiro Yoshida* Department of Hydrocarbon Chemistr?; and Division of Molecular Engineering, Kyoto University, Kyoto 606, Japan Photo-induced isomerization of propene oxide and photo-oxidation of ethene have shown that photo-oxidation of alkenes proceeds by a mechanism involving not only the oxidative cleavage of the olefinic double bond and oxidation via 71-ally1 intermediates, but also the formation of epoxides as a precursor. The product distribution in the photo-oxidation of butenes is well explained by the mechanism. A tracer study using 1 8 0 2 has indicated that oxygen involved in the epoxide intermediate comes from the lattice oxygen of the catalyst.Vanadium oxide supported on silica acts as a catalyst in the photo-oxidation of propene to produce aldehydes as the main products at a high level of conversion.l This is in marked contrast to the catalysis by TiO, which gives CO, as a main product even at a low conversion level (0.055%).2 In previous work we studied the mechanism of photo-oxidation of propene over V,O,/SiO, and proposed that the reaction proceeds along two pathway^.^ One is the double-bond fission of propene to form ethanal and the other is the formation of a n-ally1 intermediate by hydrogen abstraction from propene with adsorbed oxygen. The n-ally1 intermediate is fairly stable at room temperature and is decomposed thermally to form acrylaldehyde selectively.We have also shown that the oxygen atom in these aldehydes comes from lattice oxygen. In the proposed mechanism, the formation of propanal which was found as a minor product was neglected. The present work was carried out to elucidate the reaction path leading to propanal. A general mechanism for the photo- oxidation of lower alkenes over V,O,/SiO, will be discussed. Ex per imen t a1 V,O,/SiO, (V,O,, 5 wt%) was prepared conventionally by impregnating silica in an aqueous solution of ammonium metavanadate,4 and was treated with 60 T0rr.f. oxygen at 673 K for several hours before each run. The reactants were commercially supplied and purified by vacuum distillation at low temperature. lS0, was supplied from CEA-SEN Saclay (purity 99.88 %) and used without further purification.The reactions were performed in a conventional closed circulating system described el~ewhere.~ U.V. light was irradiated at room temperature from a 500 W Xe lamp through a glass filter transparent to wavelengths A > 300 nm. The temperature of the catalyst bed was elevated by ca. 10 K by the U.V. irradiation. Products were analysed by g.1.c. and mass spectrometry. Products were collected by the following steps: (A) after a reaction, products in the gas phase were frozen out in a liquid nitrogen trap in the dark at room temperature; (B) the catalyst was irradiated in vacuo to check photodesorption of the adsorbed species; and ( C ) the catalyst was heated in the dark to 473 K to collect the t 1 Torr z 133.3 Pa.3536 Photo-oxidation of Alkenes over Vanadium Oxide thermally desorbed products. Of these steps, A and B gave nearly the same distribution of products. Thus, except in specified cases, the amounts of products collected in steps A and B were summed and presented as the amount (A + B). Experiments under the same conditions were performed from twice or more in order to check the reproducibility of each result. The composition of products was highly reproducible, but the total yield of products was slightly affected by the different batches of the catalyst. However, the dispersion of data was not so large as to affect the points of the argument. The highest yields of products obtained under the same conditions are presented in the tables.Results Reaction of Propene Oxide As described previously, the photo-oxidation of propene over V,O,/SiO, formed CH,CHO, C,H,CHO and CH,=CHCHO with the mole ratio of 59: 10:39 at 41.5% conversion and in a 34% yie1d.l We have proposed a mechanism3 which explains the formulation of CH,CHO and CH,=CHCHO, but the formation of C,H,CHO was left unexplained. Since it is probable that C,H,CHO, is formed uia propene oxide, we investigated the reactivity of propene oxide over V,O,/SiO,. Results are given in table 1. When propene oxide was adsorbed on the catalyst in the absence of oxygen in the dark at room temperature and products were collected by heating the catalyst up to 473 K in the dark (step C), the desorbed gases were propene oxide, propanal, ethanal, acrylaldehyde and propene.The same products were formed in the photo-oxidation of propene,l while the product distribution was different. Propanone was not formed in either case. When the catalyst adsorbing propene oxide in the dark was irradiated for 30 min at room temperature and was then heated to 473 K in the dark, conversion of propene oxide and yield of products increased significantly. The percentage of C,H,CHO in the products decreased and that of CH,CHO increased in comparison with the results in the case without irradiation. Some portion of each product was photodesorbed (step B) and thermally desorbed (step C). Ethanal and propene were collected mainly in step B, propanal and acryl- aldehyde in step C. The former result suggests that the fission of the C-C bond and abstraction of oxygen to form ethanal and propene, respectively, occur in the photo- process but not in the thermal process.It was found that the presence of oxygen has little effect on the selectivity. These results indicate that propene oxide is converted predominantly to propanal and the U.V. irradiation greatly promotes the conversion of propene oxide, suggesting that propene oxide is one of intermediate in the photo- oxidation of propene. Photo-oxidation of Ethene The photo-oxidation of ethene was much more sluggish than that of propene and produced ethanal and carbon dioxide in the mole ratio of 39:61 at 5.8% conversion of ethene. 36.2% of produced ethanal and ca. 70% of carbon dioxide were collected in step A + B. Ethanal may be formed via ethene oxide.In order to clarify the source of oxygen incorporated into the products, oxygen tracer experiments were carried out in a series over the same catalyst. The first reaction (run 1) was performed with 1 6 0 2 , the second (run 2) and the third (run 3) with lSO, and the last (run 4) was performed with l60, again. Fig. 1 shows the mass spectra of products in runs 1 and 3 and table 2 summarizes the relative peak heights at selected m/e relating to the products. Pattern coefficients of fragment ions of ethanal were determined as 100.0 (m/e = 29, CHO+), 22.4 (m/e = 44, parent peak) and 16.2 (m/e = 43, CH,CO+) from the results for pure ethanal under the same analytical conditions. The ratio of peakT. Tanaka, M. Ooe, T. Funabiki and S . Yoshida 37 Table 1. Reaction of propene oxide over V,O,/SiO, U.V.products/pmol' /,umola /,urn01 tion* (% )" collectiond CH,CHO C,H,CHO CH,=CHCHO CH,=CHCH, PO 0, irradia- conv. product ~~~ -~ ~ ~~~ ~~ 32.6 0.0 dark 38.7 C 0.7 9.4 1 .o 1.4 30.6 0.0 U.V. 96.6 B,C 5.7(3.6) 18.6(1.1) 1.3(0.1) 3.8(2.3) 48.0 101.2 U.V. 90.9 A+B,C 9.9(7.8) 27.8(0.7) 2.4(0.1) 3. q2.2) ~ ~~~ ~ a Initial amount of propene oxide. * Irradiation time 30 min. " Based on propene oxide. collecting products. Steps A+B, B and C : see text. parentheses are the amount of products collected in step A + B or B. Procedure for A small amount of CO, was detected. The values in + 0 s? I 0 I 1 I I I I I I I I I I I I I I I I I I I I I I I I + + 0 '0 0 aD 0 I I 0 u u I I I + N 0 0 z I I I I I I I I I I I ] I ! I I I I 2 9 30 31 " 43 44 45 46 47 48 mle Fig.1. Mass spectra of products obtained from photo-oxidation of ethene. Full line, run 1 (table 2); dotted line, run 3 (table 2). heights of m/e = 29 and 43 (run 1) was in accordance with the mass pattern of ethanal. The peak of m/e = 44 is higher than that of the estimated value from the coefficients because of the contribution of carbon dioxide (CO;). One may conjecture that the small, but obvious peak of m/e = 30 is assigned to a parent peak of formaldehyde (H,CO+) formed via oxidative cleavage of ethene. However, analysis of products by g.1.c. did not indicate any trace of formaldehyde. This peak was always observed when any substance having m/e = 29 peak was measured, suggesting that the m/e = 30 peak is due to re- combination of fragment ions in the mass chamber.Therefore, this peak can be neglected. In runs 2 and 3, new peaks of m/e = 31 (CH180+) and 45 (CH,C180S) due to ethanal containing l80 appeared. The peak heights of these peaks increased from run 2 to 3, but they were much smaller than those of m/e = 29 (CH160+) and 43 (CH3C160+). In ad- dition, new peaks ofm/e = 46 and 48 due to C180160+ and C180z appeared after run 2 and the peak heights increased slightly from run 2 to 3. In run 4, m/e = 31 and 45 peaks still remained in spite of the reaction with 1 6 0 , and the peak heights of m/e = 29, 3 1,43 and38 Photo-oxidation of Alkenes over Vanadium Oxide Table 2. Mass pattern of products in the photo-oxidation of ethene relative peak height of mass number (rn/e)b runa 29 30 31 43 44 45 46 48 ~- ~~~~~ ~~~ 1 100.0 9.4 0.0 15.0 62.8 0.0 0.0 0.0 2 92.1 10.5 7.2 13.1 34.8 1.4 10.1 9.5 3 80.6 8.4 20.2 12.5 34.5 3.2 12.9 14.9 4 93.5 9.5 16.9 13.7 55.9 4.6 6.0 0.0 ~~~~ a Ethene and oxygen : 58.0 pmol.Photo-oxidation was performed by varying the atmosphere successively as follows: ( l ) , 1 6 0 2 ; (2), ‘*02; (3), 1 8 0 2 ; (4), 1 6 0 2 . Irradiation time was 30 min in each atmosphere. Peak heights relative to that of m/e = 29 in run 1. 0 0 * 5 1 .o 1.5 2 .o Po2 Fig. 2. Influence of partial pressure of oxygen on the yields of products. C,H,, 58.0pmol; 0, CH,CHO; A, CO,. 45, which correspond to ethanal, were not very different from those in run 3. On the other hand, the peak height of m / e = 46 decreased and the peak of m / e = 48 vanished with the increase in the peak height of m/e = 44.These peaks of m/e = 44,46 and 48 are due mainly to carbon dioxide. The formation of carbon dioxide containing l60 in runs 2 and 3 and containing l80 in run 4 suggests that lattice oxygen is also incorporated into carbon dioxide. The peaks due to fragments of ethanal were less dependent on whether lAOZ or l60, was used than those due to carbon dioxide. This result indicates that the oxygen atom of the ethanal comes from the lattice oxygen of the catalyst and infers the formation of an intermediate of epoxide type. The result that ethanal containing l80 was detected even when the reaction was performed with lSO, over the same catalyst (run 4) indicates that gaseous oxygen is consumed not only in the formation of carbon dioxide but alsoT. Tanaka, M.Ooe, T. Funabiki and S. Yoshida 39 in the reoxidation of the catalyst. As shown in fig. 2, the formation of ethanal depended upon partial pressure of oxygen, and ethanal was not formed in the absence of oxygen. The curves of ethanal and carbon dioxide in fig. 2 clearly indicate that conversion of ethanal to carbon dioxide is promoted at the higher partial pressure of oxygen. Photo-oxidation of Butenes To clarify the formation of the epoxide type intermediate, butenes are more suitable substances than ethene and propene because the variety of products gives more information than that from ethene and propene. The results are given in tables 3-5. It is evident that oxidation hardly proceeds without oxygen. Isomerization of butenes did not occur in the dark, however U.V.irradiation induced isomerization, although the extent was small in the 30 min irradiation and independent of the pressure of oxygen. Oxidation products were those formed by bond fissions (CH,CHO, CH,CH,CHO, CH,=CHCHO), saturated ketone and aldehyde (CH,COC,H,, n-C,H,CHO), unsaturated ketone and aldehyde (CH,COCH=CH,, CH,CH=CHCHO), and buta- 1,3-diene. The composition of those products was dependent on the structure of the butenes. The main product from but-1-ene was CH,CH,CHO, but the yield of n-C,H,CHO was fairly large (table 3). On the other hand, the main product from but-2-enes was CH,CHO (tables 4 and 5). In the case of cis-but-2-ene, yields of products other than CH,CHO and buta-l,3-diene were very low. In the case of trans-but-2-ene, yields of CH,COC,H, and buta-1,3-diene are higher than those of other products except for CH,CHO.It is noted that buta-1,3-diene is produced even in the absence of oxygen, but the yield of buta-1,3-diene is increased in the presence of oxygen. These results suggested that hydrogen abstraction from butenes is effected not only by the photoformed hole centre (Orattice) likewise from CH,,6 but also by the adsorbed oxygen.' It was also observed that the yield of buta-1,3-diene obtained by the step C increased when the reaction was performed in the presence of oxygen. This supports the suggestion that the n-ally1 intermediate formed by the abstrac- tion of hydrogen from butene by the adsorbed oxygen is thermally converted to Table 3. Composition of organic compounds in the reaction of but- 1-ene over U.V.irradiated V,O,/SiO,a ~ ~~ ~ yield/pmolb products with 0,' without 0, CH,=CH, 0.4 (0.0) 0.2 (0.1) CH,=CHCH, 0.3 (0.2) 0.5 (0.4) CH,=CHC,H, 19.8 (19.3) 37.6 (37.6) t-CH,,CH=CHCH, 0.2 (0.1) 1.8 (1.7) CH,=CHCH=CHI 2.3 (0.6) 1.5 (1.2) c-CH,CH=CHCH, 0.1 (0.0) 2.0 (2.0) CH,CHO 2.2 (1.6) 0.2 (0.0) C,H,CHO 10.5 (9.0) 0.2 (0.0) CH,=CHCHO 0.9 (0.8) tr" C H ,COC , H , 0.5 (tr) tr n-C,H,CHO 3.5 (1.4) - CH,=CHCOCH, 0.5 (0.2) - CH ,3C H =CH C H 0 1.3 (0.2) _ _ ~ ~~~~ ~~ ~~ ~~~ a Initial amount of but-I-ene: 55 pmol. Irradiation time: 30 min, at room temperature. Values in parentheses are the amounts of products collected in step A + B. 90 pmol. Trace,40 Photo-oxidation of Alkenes over Vanadium Oxide Table 4. Composition of organic compounds in the reaction of trans-but-2-ene over U.V.irradiated V,O,/SiO,a yield/pmol* products with 0,' without 0, - __ CH,=CH, 0.3 (0.3) 0.3 (0.3) CH,=CHCH, 0.2 (0.2) trd CH,=CHC,H, 0.3 (0.3) 0.6 (0.6) t-CH,CH=CHCH, 26.0 (25.7) 30.7 (30.6) c-CH,CH=CHCH, 2.8 (2.6) 3.0 (2.9) CH,=CHCH=CH, 2.6 (1.2) 1.6 (1.4) CH,CHO 15.9 (14.3) 0.6 (0.1) C,H,CHO 0.3 (0.3) tr CH,COC,H, 1.5 (0.1) - n-C,H,CHO 0.2 (tr) ~ CH,=CHCOCH, 0.2 (tr) - CH,CH=CHCHO 1.7 (0.6) - CH,=CHCHO 0.3 (0.2) - - a-d See footnotes in table 3. trans-But-2-ene (55 pmol) was used. Table 5. Composition of organic compounds in the reaction of cis-but-2-ene over U.V. irradiated V,O,/SiO," ~ - - ~ ~~~~~ yield/prnol" products with 0,' without 0, CH,=CH, CH,=CHCH, CH,=CHC,H, t-CH,CH=CHCH, c-CH,CH=CHCH, CH,=CHCH=CH, CH,CHO C,H,CHO CH,=CHCHO CH,COC,H, n-C,H,CHO CH,=CHCOCH,, CH,CH=CHCHO 0.4 (0.0) 1.0 (0.6) 0.5 (0.3) 5.3 (5.2) 20.0 (19.7) 25.4 (19.7) 0.3 (0.2) 0.3 (0.1 j 0.7 (0.1) 0.3 (0.1 j 5.3 (1.8) 0.1 (0.0) 0.2 (0.0) 0.3 (0.2) 0.1 (tr) 0.6 (0.5) 7.1 (7.0) 29.5 (28.7) 1.4 (1.3) 1.1 (1.0) trd a-d See footnotes in table 3.cis-But-2-ene (55 pmol) was used. buta-l,3-diene. The result that propanal from but-l-ene and ethanal from the but-2-enes are collected mainly in step A + B indicates that thermal energy is less important in the double-bond fission of butenes. Discussion Epoxide Route and Mechanism In the photo-oxidation of propene over V,O,/SiO,, propanal was formed as a minor product in addition to the main products, ethanal and acrylaldehyde. In a previousT.Tanaka, M. Ooe, T. Funabiki and S. Yoshida 41 paper,3 we neglected the reaction path for the formation of propanal. The present result that propanal was formed as a main product in the reaction of propene oxide suggests strongly that propene oxide is one intermediate in the photo-oxidation of propene. Acceleration of the reaction of propene oxide by U.V. irradiation can explain why the propene oxide is not detected during photo-oxidation of propene. Propene oxide as an intermediate in the photo-oxidation of propene was proposed by Pichat et aL2 They detected a small amount of propene oxide in the photo-oxidation of propene over TiO, and proposed that the oxygen species attacking propene to form the unstable primary product in question might be adsorbed atomic oxygen with neutral charge.8 Over U.V.irradiated TiO,, Djeghri and Teichnerg also reported the formation of alkene oxide in the photo-oxidation of pentanes. Previously, we have proposed that a 1 : 1 complex of propene and molecular oxygen is formed in the first stage of the rea~tion.~ The dependence of the reactivity of ethene photo-oxidation on partial pressure of oxygen as illustrated in fig. 2 is probably caused by the formation of a similar complex between ethene and oxygen, resulting in the very small degree of reaction in the absence of oxygen. The formation of such a complex was inspected by quantum chemical calculations.1° The calculations suggested that the ethene is adsorbed onto the lattice oxygen (V=O) to form species like ethene oxide. The photo-formation of species like alkene epoxide was also reported by Anpo and Kubokawa based on e.s.r.data." Subsequent adsorption of molecular oxygen on vanadium ions may cause the removal of the species from the site. Tracer studies using 1 8 0 , support the theory that lattice oxygen is transferred to the alkene. If isomerization of ethene oxide occurs, the formation of ethanal from ethene by photo-oxidation over V,O,/SiO, supports the presence of the epoxide route. The difference in reactivity between ethene and propene must be due to the different formation constants of the adsorbed species and the presence of the methyl hydrogen in propene which is withdrawn to form a n-ally1 intermediate. The photo-oxidation of propene over V,O,/SiO, is explained in scheme 1 .d ou b le-bond- fission CH3CHO H,C-CH-.-CII, CH*=CHCHO - CHsCH2CHO I epoxide formation H2C-CHCH3 '0' Scheme 1 The first route is the oxidative cleavage of the double bond to form ethanal, the second is the formation of a n-ally1 intermediate which is converted to acrylaldehyde, and the third is the formation of propene oxide which is isomerized to propanal. The second route is not possible in the case of ethene, but is predominant in the case of propene. We have concluded that thermal energy must not be required to complete the first route (double bond fission), but is required in the second route (n-ally1 intermediate oxidation).3 As for the third route, containing an epoxide intermediate, the following results have indicated that thermal energy also plays an important role in isomerization of the42 Photo-oxidation of Alkenes over Vanadium Oxide Table 6.Amount of ethanal collected after photo-oxidation of ethanal and adsorption of ethanal on V,O,/SiO, ________ ___ _ _ ~ _ _ _ ~ _ _ _ _ _ _ _ _ _ _ _ _ ~ _ _ ~~~ __ __ ___ ~ _ _ reaction total amount of amount of ethanal collected in each step (%) ethanal/pmol A B C oxidation of ethene adsorption of ethanal (58 pmol)a (3.2 pmol) 1.5 11 25 64 2.9 77 23 - Irradiation time: 30 min. O,, 60 pmol. activated epoxide to aldehyde or ketone. Thus, (i) propanal was formed by thermal treatment of adsorbed propene oxide; (ii) U.V. irradiation of the catalyst (for propene oxide) enhances the reactivity only; (iii) not only is isomerization photo-induced, the activation of the epoxide is also promoted by irradiation; (iv) as seen in table 6, most of the adsorbed ethanal could be recovered after irradiation, but ethanal formed in the photo-oxidation of ethene was mostly collected thermally in step C, indicating that thermal energy is essential to convert an activated epoxide intermediate to final products.Mechanism of Photo-oxidation of Butenes When the three routes are applied to the case of butenes, products other than CH,=CHCHO are explained as shown in scheme 2. (1) double-bond-fission route (0) CH2=CHC2H5 - C2H5CH0 (3) epoxide route CHO / Scheme 2 The oxidative cleavage of the C=C double bond will lead to C,H,CHO formation from but-1-ene and CH,CHO formation from but-2-enes as the major products. Formation of CH,CHO from but- 1 -ene indicates the isomerization of a part of but- 1 -ene to but-2-ene before the oxidative cleavage. The low yields of C,H,CHO from but-2-enes reflects the fact that the isomerization of but-2-enes to but-1-ene hardly occurs.T.Tanaka, M. Ooe, T. Funabiki and S. Yoshida 43 The folmation of CH,=CHCHO is rather difficult to explain by simple routes. The species might be formed by the oxidative cleavage of the n-ally1 intermediates or buta-1,3-diene, but we do not have any data for specification of the formation process. The saturated ketone and aldehyde, CH,COC,H, and n-C,H,CHO, are probably formed via epoxide intermediates. 1-Epoxybutane can form both products, but 2- epoxybutane forms only CH,COC,H,. Since the oxygen atom in all alkene epoxide prefers to be transferred to the terminal position, as found in the isomerization of propene oxide, the predominant formations of n-C,H,CHO from but-1 -ene and CH,COC,H, from but-2-enes are consistent with the 1- and 2-epoxybutane intermediates in each reaction.Unsaturated aldehyde and ketone (CH,CH=CHCHO and CH,=CHCOCH,) and buta- 1,3-diene may be formed via a n-methylallyl intermediate. Since but-1 -ene and trans-but-2-ene may be converted to a syn-n-methylallyl intermediate, the composition of the above three products is not so different. In the case of cis-but-2-ene, the yield of buta-l,3-diene becomes very high compared with other two products. This is probably because the anti-n-methylallyl intermediate is less stable than the syn isomer and the dehydrogenation proceeds before the oxygen addition. Products other than formed by the double bond fission, i.e. buta-1,3-diene9 CH3COC2Hs, n-C,H,CHO, CH,=CHCOCH, and CH,CH=CHCHO, are mostly obtained in step C. This result supports that the epoxide and n-ally1 routes which require thermal energy are involved in the photo-oxidation of butenes. This work was partially supported by a grant-in-aid for scientific research from the Japanese Ministry of Education. References 1 S. Yoshida, Y. Magatani, S. Noda and T. Funabiki, J. Chem. SOC., Chem. Commun., 1982, 601. 2 P. Pichat, J-M. Herman, J. Disdier and M-N. Mozzanega, J. Phys. Chem., 1979, 83, 3122. 3 S. Yoshida, T. Tanaka, M. Okada and T. Funabiki, J . Chem. SOC., Faraday Trans. 1, 1984, 80, 119. 4 S. Yoshida, T. Matsuzaki, T. Kashiwazaki, M. Mori and K. Tarama, Bull. Chem. SOC. Jpn, 1974, 47, 5 S. Yoshida, Y. Matsumura, S. Noda and T. Funabiki, J . Chem. SOC., Faraday Trans. 1, 1981,77, 2237. 6 S. L. Kaliaguine, B. N. Shelimov and V. B. Kazansky, J. Catal., 1978, 55, 384. 7 M. Iwamoto and J. H. Lunsford, J. Phys. Chem., 1980, 84, 3079. 8 J. M. Hermann, J. Disdier, M-N. Mozzanega and P. Pichat, J. Catal., 1979, 60, 369. 9 N. Djeghri and S. J. Teichner, J . Catal., 1980, 62, 99. 1564. 10 H. Kobayashi, M. Yamaguchi, T. Tanaka and S. Yoshida, J. Chem. SOC., Faraday Trans. I , in 11 M. Anpo and Y. Kubokawa, J. Catal., 1982, 75, 204. press. Paper 4/ 1968 ; Received 19th Nocember, 1984

ISSN:0300-9599    

DOI:10.1039/F19868200035

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I , 1986, 82, 45-51 Raman Spectroscopic Observation of Adsorbates on Ag during Electrochemical Reduction of Nitrobenzene Hitoshi Shindo National Chemical Laboratory for Industry, Tsukuba Research Center, Yatabe, Ibaraki 305, Japan Raman spectroscopic observation of the surface of a silver electrode during potentiostatic reduction of nitrobenzene in neutral and alkaline aqueous solutions has revealed adsorption of at least four chemical species at different potentials. At - 0.5 V (us. SCE), where the reduction starts, trans-azobenzene was detected with two other species. Raman bands of adsorbed aniline were observed at more cathodic potentials. When aniline was adsorbed from its aqueous solution, three of the above four species except azobenzene were detected on the electrode.Adsorbed aniline lies flat on the surface. Since its discovery by Fleischmann et aI.,l surface enhanced Raman scattering (SERS)2~ has been applied to the studies of the structure of molecules in their adsorption states. Acquisition of such data is most welcome in the fields of heterogeneous catalysis and electrochemical synthesis where surface adsorbates play important roles. In situ analysis of interfacial structure with Raman spectroscopy seems to have its greatest advantage there. The reduction of nitrobenzene is one of the most studied reactions in electrochemistry. Various products, including dimeric compounds, are selectively by altering reaction conditions. However, the mechanism of the change in the selectivity with change of voltage, pH, solvent, electrode materials, etc.has not yet been clarified in detail owing to the lack of information on the chemical structure of the interfacial region. The author has applied SERS to the study of adsorbates on a silver electrode during potentiostatic reduction of nitrobenzene in neutral and alkaline aqueous solutions. The main products are phenylhydroxylamine89 and aniline in these solutions. Experimental Experimental details of the measurement of Raman spectra have been given in previous reports1O* l1 and are only briefly described here. A silver plate (Furu-Uchi Chemicals, 99.99 % ) was polished to a mirror finish with alumina suspension (Baikalox, 0.05 pm) and was used as the working electrode after ultrasonic cleaning. A saturated calomel electrode (SCE) was used as the reference electrode.A platinum wire was used as the counter electrode and was placed in a separate compartment. As pretreatments of the silver electrode, hydrogen generation at -2.0 V (us. SCE, 20 s) and several oxidation- reduction cycles (ORC) between -0.2 and +0.3 V ( 3 s) were performed by potential steps. Silver is first oxidized to form AgCl and, then, reduced to Ag in the ORC. The measurements of Raman spectra using the 514.5 nm line of an argon ion laser [Coherent Radiation CR-8, 50 mW) and a double dispersion Raman spectrometer (JASCO R-800) were performed during potentiostatic reduction of nitrobenzene at given potentials. The sample solutions were prepared by dissolving nitrobenzene [(2.0-5.0) x 10-3 mol dm-3] and KCl (0.1 mol drn-,), a supporting electrolyte, in distilled water.The solutions were purged of dissolved oxygen by nitrogen bubbling. Buffer reagents (H,BO, 4546 H. Shindo and NaOH) were used when required. When strongly alkaline solutions were prepared, NaOH or KOH (0.1 mol dm-3) were used. Nitrobenzene (Wako Pure Chemical, GR grade) was purified by washing first with dilute H,SO,, then with dilute NaOH, followed by vacuum distillation. Aniline (Nakarai Chemicals, GR grade) was purified by vacuum distillation. Phenylhydroxylamine was synthesized by a literature method1, and was purified by recrystallizing from water. The main impurity was azoxybenzene. Phenylhydroxylamine was fairly stable when kept under vacuum in a refrigerator. Results and Discussion Reduction of Nitrobenzene Prior to Raman measurement, the electrochemistry of nitrobenzene was checked using the rotating ring-disc electrodes method.13 An unbuffered neutral solution of nitro- benzene with 0.1 mol dmP3 KCl was used first.Both ring and disc electrodes (Ag) were pretreated by H, generation. Nitrobenzene (2.0 x mol dmP3) was reduced mainly to PhNHOH (4e-reduction) in the potential range between - 0.5 and - 0.9 V. The product was detected by its electrochemical oxidation to PhNO at the ring electrode. When the potential of the disc electrode was scanned in a more cathodic range, formation of PhNH, (6e-reduction) occurred and became dominant at - 1.6 V. Use of KOH (0.1 mol dm-3) instead of KCl did not alter the shape of the current-potential curve extensively.The product molecules were identified from their U.V. absorption spectra in alkaline solution. Results of detailed electrochemical analysis for the alkaline solution will be reported e1~ewhere.l~ In the first series of Raman experiments nitrobenzene (5.0 x lop3 mol dmP3) was reduced in a neutral solution without buffer reagents. Changing the concentration of the reactant from (5.0 to 2.0) x lod3 mol dm-3 did not affect the results described below. As stated in the previous paragraph the reduction occurs at ca. - 0.5 V and at more cathodic potentials. Only weak Raman bands of the parent molecule and water were observed at -0.4 V and at more anodic potentials. When the voltage was set to -0.5 V and to more cathodic values, the reduction occurred and Raman spectra shown in fig.1 were observed. Each curve was obtained independently after cleaning by H, generation and an ORC treatment. The measurement was completed within the first six minutes of the potentiostatic reduction. At least four different chemical species, A-D, are observed in fig. 1. The species A which is strongly observed at -0.5 V has already been assigned to trans-azobenzene in the author’s previous reports.lo9 l 1 3 l5 To be accurate, spectra of two types of trans-azobenzene with different degrees of interaction with the surface are simultaneously observed15 as species A in fig. l ( a ) . The one with weaker surface interaction gave a spectrum very similar to that of the molecule in methanol solution. Large resonance enhancement is not expected in the tail of the n-n* transition of trans-azobenzenelG at 514.5 nm.The spectrum of the other species indicates a marked difference in the relative intensities of the Raman bands of vN=N and v ~ - ~ vibrations, which suggests a kind of complexation of azobenzene with the metal. The latter species becomes dominant with time. When the potential was lowered from - 0.5 to - 0.7 V, azobenzene was reduced to hydrazobenzene and the Raman bands of A disappeared. On the other hand, Raman bands of species D grew toward the more cathodic potentials as shown in fig. 1 (b)-(d). The bands assigned to species B and C were strongly observed in the potential range between -0.5 and -0.8 V. The possibility of observing adsorption of product molecules was checked first. Phenylhydroxylamine and aniline are expected as the final products of the reaction system.In addition, hydrazobenzene is also a possible reaction product, since its pre- cursor, azobenzene, has been detected on the electrode. The Raman spectra of the threeElectrochemical Reduction of Nitrobenzene 47 I D D 996 1600 1400 1200 1000 Raman shiftlcm-’ Fig. 1. Raman spectra of adsorbates on Ag observed during potentiostatic reduction of nitrobenzene (5 x lop3 mol dm-3) in a neutral aqueous solution [KCl 0.1 mol dmp3): (a) -0.5 V (cs. SCE); (b) -0.8 V; (c) - 1.0 V; ( d ) - 1.2 V. The spectral resolution is 5 cm-l. See ref. (1 1) and (15) for the frequencies and assignment of the bands denoted ‘A’. candidates are shown in fig. 2. Vibrational assignment for aniline has been given in the literatureI7-l9 and is reproduced in table 1.Apart from vibrations of the amino group the assignment seems mostly applicable to the other two molecules because they all have a common structure. The two bands of species D in fig. 1 (d) at 996 and 1025 cm-l resemble the bands in the same region in fig. 2(a) and (b), which are assigned to ring deformation (vI2) and C-H in-plane bending (v18J vibrations. If there are any Raman bands ofD in fig. 1 (d) in the frequency range 1100-1 500 cm-l they are obscured by the bands of other species. No C-H or N-H stretching vibration was clearly observed in the higher frequency range. Further comparison with the reference spectra was made in the lower frequency range. As will be seen in fig. 3 ( 4 , the lower frequency bands of D also resemble those in fig.2(a) and (b). It seems appropriate to assign D to adsorbed aniline or hydrazobenzene. However, it is difficult to determine which of the two is the correct answer just by discussing slight differences between the reference spectra. Adsorption of molecules generally causes changes in peak positions and intensities of Raman bands. It is noticeable in fig. 1 (a) and (b) that a large and broad background is observed from 1100-1700 cm-’. This might be attributable to Raman bands of carbon as observed by Mahoney et al.,l However, it is unlikely that the background came from impurities in the solution such as CO, and CO:-. Blank experiments without nitrobenzene did not show any such background even with addition of CO, or K,CO, (1 .O x lo-, mol dmp3) to the solution.The background appears only when Raman bands of A, B and C are strongly observed. Photodecomposition of adsorbates might be the cause of the background.48 H. Shindo 4 ----I- I 1 6 . L 1400 1000 600 2 00 Raman shift/cm-' Fig. 2. Raman spectra of several product molecules in nitrobenzene reduction: (a) aniline (neat liquid) ; (b) hydrazobenzene (solid) ; (c) phenylhydroxylamine (solid). The asterisks in (c) indicate Raman bands of trans-azoxybenzene as an impurity. The spectral resolution is 5 ern-'. See table I and ref. (1 7)-( 19) for vibrational assignment of aniline. Adsorption of Aniline In order to identify the adsorbates observed in fig. 1, adsorption of aniline was studied. The molecule was adsorbed from its 1.0 x lo-, mol dm-3 neutral aqueous solution.Potassium chloride (0.1 mol dm-3) was added. Following H, generation at - 2.0 V (20 s) and oxidation of Ag at +0.3 V (3 s), the potential was set to - 1.0 V. The Raman spectrum in fig. 3(b) was obtained. The neat spectrum of aniline is reproduced in fig. 3 (a). Peak positions of the bands in the two spectra [(a) and (b)] are in good agreement, although discrepancies are noticed in the relative intensities. The peak positions and approximate intensities of the two spectra are summarized in table 1 together with their assignment. If we neglect coupling of the -NH, vibrations with vibrations of the phenyl ring, we can assume C,, symmetry for the Ph-N group and discuss the geometry of adsorption from the change in intensity of the Raman spectra.Creighton,, proposed expressions of electromagnetic enhancement factors, depending upon symmetry species, of Raman intensities of adsorbed molecules and discussed the orientation of adsorbed pyridine on an Ag electrode. By comparing intensities of the Raman bands of aniline in its 'free' and adsorbed states, as shown in table 1, it is noticed that a, and b, bands are most enhanced by the adsorption, while the b, bands are least enhanced. It is thus concluded that at - 1 .O V and under the assumption of C,, symmetry, aniline is adsorbed on Ag with the phenyl ring lying flat on the surface. The nitrogen lone pair and phenyl 71 electrons are both likely to interact with the surface. However, the interaction seems to be weak since the change in peak positions on adsorption is rather small.When the electrode potential was stepped from - 1.0 to -0.6 V, the spectrum in fig. 3 (c) was observed. Marked differences are noticed, especially in the higher frequencyElectrochemical Reduction of Nitrobenzene Table 1. Assignment of aniline Raman bands 49 frequency and intensityC typea assignmentb neat/cm-' adsorbed/cm-l phenyl in-plane a1 b2 out-o f-plane a2 others 8a C-C stretch 19a C-C stretch C-N stretch 9a C-H bend 18a C-H bend 12 ring def. 1 ring breathing 6a ring def. 19b C-C stretch 14 C-C stretch 9b C--H bend 6b ringdef. C-N bend 10a C-H bend 16a ring def. 17b C-H bend 4 C-Hbend 10b C-H bend 11 C-H bend C-N bend NH, bend 2 x NH, wag? 2 x 10b ring def. 1602 s 1500 w 1278 m 1175 m 1027 s 996 s 814 s 530 m 1467 w 1341 vw 1154 m 619m 386 m 826 m 412 vw 883 vw 755 w 506 w 231 m 1618 w 1387 vw - - 1602 s - - 1175 w 1023 s 996 s ? - - - - 617 w - 822 s 409 m 884 m 749 m 698 w 508 m - - 1290 w - a By neglecting H atoms of -NH, group C,, symmetry was assumed.From ref. (1 8) [partly from ref. (19)]. Wilson numbering [ref. (20)] was used. Present work (resolution 2 cm-l). Intensity: s, strong; m, medium; w, weak; vw, very weak. range. It may be possible to explain the change of the spectrum from (b) to (c) in the frequency range below 900 cm-l as that caused by the change in geometry of adsorption. However, it is difficult to give such an explanation for the change in the 1100-1500 cm-l range. We therefore consider below the possibility of different adsorbates. Cyclic voltammograms indicate that aniline does not react in the potential range employed.However, it is possible that a limited amount of aniline is oxidized on the surface to form other adsorbates. Let us now compare the spectra of adsorbates derived from aniline with those observed during reduction of nitrobenzene. The spectrum in fig. 3(d) was observed during the reduction at -0.9 V in a neutral solution (5 x mol dm-3). The Raman bands of species D are in good agreement with the bands in fig. 3(b). The four other bands of species B and C in fig. 3 ( d ) or in fig. 1 in the 1100-1450 cm-l region, on the other hand, agree well with those observed in fig. 3 ( c ) . It is likely that the same species B, C and D are observed in fig. 3(b)-(d). The species D is assigned to adsorbed aniline lying flat on the electrode. The assignment of the bands at 1531 and 1558 cm-l in fig.3(c) is not known yet. Since species B and C appeared both in the reduction of nitrobenzene and adsorption of aniline, we should think about the molecules which would appear on the way when50 H . Shindo 996 1602 I 822 1027 I 1600 1400 1200 1000 800 600 400 Raman shiftlcm-' Fig. 3. Raman spectra of adsorbates derived from aniline and nitrobenzene: (a) aniline (neat); (b) adsorbed aniline (1 x loA2 mol dm-3 as.) at - 1 .O V (us. SCE); (c) following (b) the potential was changed to -0.6 V; ( d ) adsorbates (B, C and D in fig. 1) observed during reduction of nitrobenzene ( 5 x mol dm-3) at -0.9 V in a neutral solution. The spectral resolution is 5 cm-l [2 cm-l for curve (a)].we go from nitrobenzene to aniline in the reduction path. However, Raman spectra of B and C do not resemble those of nitrosobenzene, nor phenylhydroxylamine. The possi- bility of other species, for instance, dissociatively adsorbed species, should also be checked. Kishi et aZ.23 reported the observation, by X.P.S. measurement of the N 1s band, of PhNH(ads), PhN(ads) and PhNO(ads) on Ni and Fe which were derived from nitrobenzene and aniline. Assignment of B and C to such species seems to explain well the behaviour of adsorbates observed on the Ag electrode. For instance, formation of azobenzene on the surface can be explained by dimerization of the adsorbates. However, no direct evidence for the assignment is available at present. Dependence on pH In the first series of experiments, nitrobenzene was reduced in a neutral solution without buffer reagents.In this case consumption of protons in the reaction increases the local pH in the vicinity the electrode. The Raman measurements with buffer solutions of pH 8.15 and 9.45 resulted in observation of similar adsorbates A-D on the electrode. Essentially the same process occurs on the surface as in the case without buffer reagents. Some differences are noticed, however. During the reduction at -0.5 V, Raman bandsElectrochemical Reduction of Nitrobenzene 51 of azobenzene were more weakly observed and those of aniline were more strongly observed in the buffered solutions. When the behaviour of adsorbates is quantitively studied, controlling the pH will be more important.Cyclic voltammograms of nitrobenzene in alkaline (0.1 mol dm-3 KOH or NaOH) solutions clearly indicated a larger contribution of binuclear molecules, azobenzene and hydrazobenzene, in the reaction system. Stronger Raman bands of azobenzene were observed at -0.5 V in this case than in neutral solutions. In the previous section the author concluded that the species D is adsorbed aniline. There still remains a possibility that Raman bands of hydrazobenzene are overlapped with those of aniline. Hydrazobenzene seems to be stereochemically less favourable as an adsorbate on a flat surface. Because of its low solubility in water, however, it is probable that the molecule produced via azobenzene remains in the vicinity of the electrode in the form of organic multilayers.The author thanks the referees, whose valuable advice greatly helped improve the discussions in this paper. References 1 M. Fleischmann, P. J. Hendra and A. J. McQuillan, Chem. Phys. Lett., 1974, 26, 163. 2 Surface Enhanced Raman Scattering, ed. R. K. Chang and T: E. Furtak (Plenum Press, New York, 1982). 3 J. A.'Creighton, in Vibrational Spectroscopy of Adsorbates, ed. R. F. Willis (Springer-Verlag. Berlin, 4 C. L. Wilson and H. V. Udupa, Trans. Electrochem. SOC., 1952, 99, 289. 5 R. H. McKee and C. J. Brockman, Trans. Electrochem. Soc., 1932, 62, 203. 6 R. C. Snowdon, J . Phys. Chem., 1911, 15, 797. 7 K. Sugino and T. Sekine, J. Electrochem. Soc., 1957, 104, 497. 8 W. Kemula and T. M. Krygowski, in Encyclopedia of Electrochemistry of Elements, ed. A. J. Bard 9 G. Kokkinidis and K. Juttner, Electrochim. Acta, 1981, 26, 971. 10 H. Shindo, J. Hiraishi and C. Nishihara, Proc. 9th Int. Conf. Raman Spectroscopy, Tokyo 1984, p. 710. 11 H. Shindo and C. Nishihara, Surf. Sci., 1985, 158, 393. 12 0. Kamm, Org. Synthesis, Collective Volume 1 (Wiley, New York, 1967), 445. 13 W. J. Albery and M. L. Hitchman, Ring-Disc Electrodes (Clarendon Press, Oxford, 1971). 14 C. Nishihara and H. Shindo, to be published. 15 C. Nishihara, H. Shindo and J. Hiraishi, J. Electroanal. Chem., 1985, 191, 425. 16 S. Koide, Y. Udagawa, N. Mikami, K. Kaya and M. Ito, Bull. Chem. SOC. Jpn, 1972, 45, 3542. 17 A. Hirakawa and M. Tsuboi, Indian J . Pure Appl. Phys., 1978, 16, 176. 18 V. I. Berezin and M. D. Elkin, Opt. Spectrosc., 1974, 36, 528. 19 J. C. Evans, Spectrochim. Acta, 1960, 16, 428. 20 E. B. Wilson, Phys. Rev., 1934, 45, 706. 21 M. R. Mahoney, M. W. Howard and R. P. Cooney, Chem. Phys. Lett., 1980, 71, 59. 22 J. A. Creighton, Surf. Sci., 1983, 124, 209. 23 K. Kishi, K. Chinomi, Y. Inoue and S. Ikeda, J. Catal., 1979, 68, 228. 1980). (Dekker, New York, 1979), vol. XIII, chap. 2. Paper 412070; Received 7th December, 1984

ISSN:0300-9599    

DOI:10.1039/F19868200045

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. 1, 1986,82, 53-60 Cross Enthalpic Pair Interaction Coefficients with Water in N,N-Dimethylformamide and with N,N-Dimethylformamide in Water Michael Bloemendal, Aart C. Rouwt and Gus Somsen" Department of Chemistry, Free University, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands From earlier published enthalpies of solution of various organic compounds in binary solvent systems containing water and N,N-dimethylformamide (DMF), the enthalpic pair interaction coefficients (B:,) of these compounds with DMF in water as solvent, and with water in DMF as solvent have been evaluated. The organic solutes comprise urea, alkylsubstituted ureas, amides and alkanols. For water dissolved in DMF, enthalpic interaction coefficients have been obtained from microcalorimetrical dilution experiments.In water and DMF the various results differ considerably. In water a much larger variation in B!& is found than in DMF. In the former an almost constant CH, contribution to Bt,DMF is found for most homologous series. Branching of the alkyl chain in the organic compound hardly influences 132,DMF. The results indicate that hydrophobic interaction plays an important role. In DMF the results are less regular and branching effects are considerable. Hydrogen bonding has a large impact on Bt,H20. The relations between the enthalpic pair interaction coefficients on basis of the Savage and Wood additivity approach and the Barone method (square root rule) are tested. When sufficient functional groups are introduced, the Savage and Wood concept seems to work well for a large amount of molecules of different classes in water.The Barone approach seems to be more useful for the interaction between molecules with comparable functional groups. During recent years a number of reports have been published on the enthalpic interaction coefficients of solutes in dilute solutions on basis of the McMillan-Mayer In this approach, the enthalpic pair interaction coefficient, Bk, is related to the interaction between two solute molecules. As this interaction is mediated by the solvent, the values of Bk are influenced by the structure of the solvent, particularly that around the solute molecules. Values for the enthalpic pair interaction coefficient between similar solute molecules, Bkx, can be obtained from microcalorimetrically determined enthalpies of dilutionlo and calculated from the excess enthalpies of binary mixtures.l1 Values for the enthalpic pair interaction coefficients between unlike solute molecules, I?:&., have mostly been determined from the enthalpy of mixing of solutions of x and y in the same solvent.** 6 v 7 7 lo De Visser and coworkers12y l3 have shown that B:y values can also be obtained from data for the enthalpy of solution of a solute x in mixtures of the solvent with small amounts of a substance y (cosolvent), provided the enthalpies of solution are accurately known. Such enthalpies have been published by Rouw and Somsenl4~ l5 for several organic solutes in mixtures of water with DMF over the whole composition range. From these data it is possible to calculate the enthalpic pair interaction coefficients between these solutes with either DMF in the solvent water or with water in the solvent DMF. These B!& values are presented in this paper and compared with and B$y values obtained from enthalpies of dilution.Since the Bty value for H,O dissolved in DMF has t Present address : Sigma Coatings, Amsterdamseweg 14, 1422 AD Uithoorn, The Netherlands. 5354 Pair Interaction Coeflcients with DMF+ H 2 0 not been measured previously, we will also present microcalorimetrically determined enthalpies of dilution for H,O in DMF. In this paper the following abbreviations will be used: methanol, MeOH; ethanol, EtOH; propanol, PrOH ; butanol, BuOH ; pentanol, PeOH; formamide, FA; acetamide, AA; butyramide, BA; N-methylformamide, NMF; N-butylacetamide, NBA; N,N-dimethylformamide, DMF; N,N-dimethylacetamide, DMA; urea, U; methylurea, MeU ; dimethylurea, Me2U; tetramethylurea Me,U ; ethylurea, EtU.Experimental Results When a solute x is dissolved in a liquid mixture containing a large amount of a main solvent s and some cosolvent y, its standard molar enthalpy of solution, A,,,W(M) is dependent on the mole fraction of y, x,. De Visser et al." have shown that for xy -+ 0, the limiting slope b of the curve relating A,,,H"(M) to xs is related to B:y by b = 2 B;,/M, where M, is the molar mass of the solvent. De Visser et al. obtained values of b for different solutes by least-squares fitting of experimentally obtained As,, W(M) values in solvent mixtures with a low content of cosolvent y to the equation Asol W(M) = a + bx, + cx;.(2) Some years ago we measured accurate values of Asol W(M) for alkano1s,14 amides15 and substituted urea in mixtures of water and DMF over the whole composition range. A fit of the values at low DMF content (x,,, < 0.15) to eqn (2) and combination with eqn (1) yields enthalpic pair interaction coefficients between several organic molecules and DMF molecules in water. In an analogous way Bty values between those organic molecules and water in the solvent DMF have been obtained from data at low water content (xHz0 < 0.189). Both sets of BZy values are presented in table 1. We estimate the uncertainty of these coefficients at 15 . The value obtained for DMF in water as solvent (620 J kg molF2) refers to the interaction between two like molecules and may be compared with values obtained from enthalpies of dilution by Wood and Hiltziklg (578 J kg mol-2) and by Tasker and Wood20 (737 J kg mol-2).Table 1 also presents enthalpic interaction coefficients between like molecules, B;x, calculated from enthalpies of dilution in both water and DMF. Most data have been taken from the literature. Only the enthalpy of dilution of water dissolved in DMF has been determined experimentally by microcalorimetry . The experimental procedure has been described before.9$ 29 In table 2 we present the enthalpic change, AH, when nA moles of H 2 0 in DMF at molality mA,i are mixed with n, moles at H,O in DMF at molality rnB,i to give a solution with final molality m,.The relation between AH and the McMillan-Mayer enthalpic interaction coefficients is given by where Bh, is the nth enthalpic interaction coeffi~ient.~.~~ Values of Bh, can be obtained from a least-squares analysis of the results of table 2 in terms of eqn (3) to yield Bt = (- 160 & 1) J kg mo1-2 and Bk = (14.2 0.3) J kg2 molt3. The uncertainties'are the standard deviations. Only for these coefficients the Student's t-test indicated a probability of more than 95% that their values were not zero. Discussion Interaction Coefficients in Water In water all values of the enthalpic pair interaction coefficients between unlike molecules, Bty, except that for urea are positive. They become more positive when more or largerM. Bloemendal, A . C . Rouw and G.Somsen 55 Table 1. Enthalpic pair interaction coefficients in water and DMF", solute (4 solvent : water - - MeOH EtOH PrnOH Pr'OH BunOH BuiOH BusOH ButOH PenOH PetOH H2O FA NMF DMF AA DMA NBA BA U MeU 1,l -Me,U 1,3-Me2U Me,U EtU 530 [ 141" 760 [14] 1020 [14] 1020 [14] 1300 [14] 1240 [14] 1300 [14] 1270 [14] 1520 [14] 1580 [14] - 140 [IS] 420 [ 151 620 [ 151 190 [15] 750 [ 151 1270 [15] 660 I151 - 160 [23] 100 [ 151 280 [ 151 380 [15] 1180 [15] 340 [ 151 ( A ) alkanols 247 [16] 243 [17] 561 [17] 339 [ 181 1004 [17] 1000 [18] 916 [18] 657 [ 171 1757 [18] 0 (B) amides 272 [22] 12 [19] 962 [22] 1477 [22] - -77, - 115 [19, 201 578, 737 [19, 201 - (C) ureas -348 [13] -85 1251 38 [26] 35 [27] 2032 [28] 160 [27] solvent: DMF ____ - 80 [ 141' -20 [14] 10 [14] 70 [ 141 70 [14] 50 [14] 10 [14] 170 1141 70 [14] - 10 [14] - 100 [15] 0 [151 - -40 [15] - 180 [15] -60 [15] 30 [15] -230 [23] -230 [15] - 160 [15] -370 [15] - 10 [15] - 130 [15] - - - - - - - - - - - 160 100 [21]" 4 [211 0 -350 [13] 4 ~ 3 1 - 302 [ 1 31 -313 [9] - 5552 [24] -2200 [24] - 171 1 [24] -595 [24] - 17 [24] -2108 [24] - a Units J kg mol-2; Bxy from enthalpies of solution; B,, from enthalpies of dilution.in brackets denote references. Numbers In view of the accuracy of the data round values are given. alkyl groups are introduced into the molecules. Similar positive values for compounds containing alkyl groups were found in other investigation^.^? l2, 19* 22* 2 6 q 28 They are supposed to be due to a partial destruction of the hydrophobic hydration structures (cospheres) around the alkyl groups when these cospheres ~ v e r l a p . ~ ~ ~ 31 This process is accompanied by an increase in enthalpy, resulting in a positive contribution to the enthalpic pair interaction coefficient.Fig. 1 gives B!& in relation to the number of C atoms for sets of related compounds containing n-alkyl groups. For the n-alkanols, the unsubstituted amides AA and BA, and the monoalkyl ureas the slopes are nearly equal, suggesting that for each set of compounds the interaction between an additional CH, group and a DMF molecule is essentially similar. For these compounds the mean CH, increment is 244 & 22 J kg mo1-2. Within the experimental uncertainty this value equals the one obtained by Heuvelsland et a1.13 from their study on tetra-alkylammonium bromides (250f 14 J kg mol-2).However, it differs from the CH, increment between acetamides and corresponding formamides. From the results on FA, AA, DMF and DMA, we calculate a mean CH, increment of 90 J kg mo1k2 in the B:y values. On the other hand, it can be observed that the substitution of N-protons by methyl groups in56 Pair Interaction Coeficients with DMF+ H,O 1500 Table 2. Enthalpies of dilution of H,O dissolved in DMF at 25 "C" - pen7 mA,i n A mB,i nB mf AH 1200 N I - 8 900- Do Y c-, 1 600- sc aq 300 0- 0.3850 0.5507 0.6337 0.7329 0.9730 0.9349 1.2304 1.3276 1.4997 1.4377 1.8822 2.4994 2.1443 3.1926 - - 0.8232 1.7761 2.0458 3.0793 1.2238 3.9567 3.9432 5.61 19 6.3 130 2.7410 7.8222 10.0758 8.9360 11.3984 0 0 0 7.55 5.77 9.63 0 16.43 18.69 23.58 25.94 0 0 0 0 0 0 16.57 21.35 21.05 29.69 33.44 41.69 47.28 0 0 0 0 0.1377 0.3276 0.3800 0.4840 0.25 1 1 0.6 196 0.7329 0.9349 1.0580 0.4989 1.3276 1.8822 1.4997 2.1443 29.86 56.70 74.84 108.66 124.03 170.38 262.10 283.18 338.28 342.63 497.71 615.74 622.77 995.98 - 4.0 -3.1 - 1.0 + 0.4 - 0.9 + 0.2 + 1.1 + 1.9 -0.5 +0.5 + 1.8 + 1.3 + 1.4 - 0.7 a Units of mA,i and m,, mol kg-l; mB,i, mmol kg-l; nA, mmol; ng, pmol; AH, mJ.ArA) = 100 [AH(exptl) -AH(calc)/AH(exptl), where AH(ca1c) is calculated from eqn (3). NBA BunOH D, / / Prn OH / NMF, EtU McOH ,' MeU ' d' / / d -300' I I I I 1 I 0 1 2 3 4 5 6 7 nC Fig. 1. 13&F in relation to the number of C atoms for several compounds in water. formamide leads to a 'normal' CH, increment in Bgy (mean value 240 J kg moF2).Apparently the contribution to Bt as a result of the introduction of a CH, group in formamides to obtain acetamides is markedly different from that due to other methylene groups. It may be argued that this is caused by the acidic character of the formyl proton. However, this would mean that the difference in hydrophobicity, and hence in B$,M . Bloernendal, A . C . Rouw and G. Sornsen 57 Table 3. Contributions to BE,,,, of several functional groups in water" compound functional group ~~ alkanols OH formamides HCONH, ace tamides H,CCONH, unsubstituted amidesd H,CCONH, N-alkylureas H,NCONH, a Units: J kg rnol-,. This paper. Ref. estimated value6 calculated valueC 230 44 151 70 185 25 1 185 25 1 - 135 - 268 (22). Formamide not included. between acetamides and formamides is larger than that between other compounds differing by one CH, group.This is contrary to what is found. Since it is well known that the CH, group adjacent to the carbonyl group has a strong inductive influence on the electronic structure of the carbonyl we contribute the deviating CH, increment to a different interaction of the carbonyl group, when higher amides are compared with formamides. The broken lines in fig. 1 show the effects of alkyl substitution at the N atom on the pair interaction coefficients. Generally the increments are comparable to those in the previously mentioned homologous series. This is clearly demonstrated by the BtY. values of the two isomers DMA and BA which correspond within experimental error. It implies that in water the interaction of DMF with the functional groups CON, CONH and CONH, is more or less equal, indicating that the contribution of the N-bonded protons is negligible.A similar conclusion has been obtained by Wood and of substitution of N-protons by methyl groups is considered for the urea compounds, it appears that a reasonably constant CH, increment is found going from U through MU to 1,3-DMU. 1,l-DMU and Me,U seem to be at variance with this trend. However, in view of the uncertainty of the data all urea compounds may lie on a common line with a CH, increment close to the increments of the other sets of compounds. The constant CH, contribution to Bk,UMF for most homologous series makes it possible to estimate the contribution of the functional groups of these series to by extrapolating the linear relations in fig.1. Since the values of B!,DMF for the branched alkanols are more or less the same as those of their normal isomers they are included in the estimation of the contribution of the functional group in the alkanols. The results are collected in table 3 and will be discussed later. Generally the observations mentioned so far indicate that there is no preferential site for the interaction between DMF and alkanols, amides, monoalkyl urea and tetra-alkylammonium ions in water. The interaction enthalpy seems to be determined by the number of groups only. This suggests that the Savage and Wood additivity approach22 will be applicable for these compounds. In this approach each molecule is considered to be composed of a limited number of functional groups and a certain BiY value is assumed to be the sum of the interaction of all functional groups in the solute molecule x with all functional groups in the solute molecule, y, resulting in 20, 22 When the influence on Bk, = x.4d%J%i (4) 2 ,I where nXai is the number of groups i in molecule x, n y , j is the number of groups j in molecule y and hij is the enthalpic group interaction coefficient between the groups i and j [for details, see ref. (22)]. Tasker and Wood36 give a survey of group interaction coefficients based on experimental work of several authors. When, as in the original paper of Savage and Wood,22 a CH group is counted as 0.5 and a CH, group as 1.5 CH, groups, a value for BtH2,DMF of 200 J kg mol-2 is predicted on basis of their data set for amides.58 Pair Interaction Coeficients with DMF+ H,O Table 4.Prediction of BE,DMF from BEx and Bk,," in H,Ob according to Barone solute Bh,,(exptl) BFJcalc.) solute Bh,,(exptl) B:,(calc.) MeOH EtOH PrOH Pr'OH BunOH BuiOH BuSOH ButOH 530 760 1020 1020 1310 1240 1300 1270 _____ 380 380 570 440 760 760 730 620 NMF AA DMA NBA 1,l-Me,U 1,3-Me2U Me,U EtU 420 190 750 1270 280 380 1180 340 400 260 750 920 150 140 1080 300 " Ref. (19). Units J kg mol-,; rounded values are given. This value is comparable with the value of 244 22 J kg mo1P2 reported in this paper. From eqn (4) and the data of ref. (36) we have also calculated the enthalpic interaction coefficients between DMF and several functional groups. These coefficients are compared with the functional group contributions given in table 3 as a result of the extrapolation procedure mentioned above.The values are comparable, but definitely not similar. However, it should be realized that the group interaction coefficients used for the Savage and Wood prediction are based on data for different types of compounds. The OH interactions, for example, are based on a number of both hydroxy and polyhydroxy compounds. This, together with the different influence of the CO group in formamides as compared with acetamides, leads us to the conclusion that an important reason for less satisfactorily predictive results of the Savage and Wood approach lies in the simplification of functional group contributions. The almost constant CH, increment for most sets of compounds points to strong additivity as long as sufficient functional groups are introduced.For positive enthalpic pair interaction coefficients, Franks and coworkers37 have suggested using the expression BkY = (BixB;Y)$ in order to relate like and unlike pairs.? In table 4 we present values predicted according to eqn (5) together with the experimental ones. It is obvious that the empirical rule holds fairly well for compounds with related functional groups (DMF + amide or substituted urea), but fails for compounds with more different functional groups (DMF + alkanol). For many alkanols the experimental B!& value is even larger than either h,, or hYY. Comparing the predicting power of the method of Barone with that of Savage and Wood in aqueous systems, it seems that the former is more useful for interactions between molecules with comparable functional groups, whereas that of Savage and Wood gives better results for a large amount of molecules of different classes.Interaction Coefficients in DMF The B$,H20 values in DMF as solvent are presented in table 1 also. They show smaller variations in magnitude than those with DMF in water as the solvent. However, branching effects seem to be more important and the CH, increments are less constant, which suggests that in the solvent DMF a simple additivity approach will be more approximative. In fig. 2 we have plotted Bk,H20 of alkan-1-01s in relation to the number of C atoms in the alkan-1-01. The value of Bk20,H20 is also given in this figure. It fits onto the curve t This equation has been applied extensively by Barone and c o ~ o r k e r s .~ ~M . Bloemendal, A . C. Rouw and G. Somserz 59 200 100 P( 3 z r“ - 0 O? 7 --. G X cq -1 00 -200 I 1 1 1 1 1 PeOH Me0 I I I I I I 0 1 2 3 4 5 nC Fig. 2. B&z, in relation to the number of C atoms for alkan-1-01s in DMF. of the alkan-1-01s very well. Apparently, in this respect a water molecule at high dilution in DMF is comparable with other OH containing solutes. A similar conclusion was reached by Zegers and S ~ m s e n ~ ~ with respect to the partial molar volume of H,O at infinite dilution in DMF. Since water behaves as a ‘normal’ alkanol, we conclude that the interaction between a water and an amide molecule occurs predominantly along one hydrogen bond. It has been found for alkanols in polar solvents that an increase in chain length results in a decrease in the number and/or the strength of OH*-.OH hydrogen bond~,~O-~, which may also be the reason for the positive shift in with increasing chain length of the alkan-1-01s.It has been found also that branching of the alkyl chain has a strong influence on the OH-OH interaction^,^^-^^ which corresponds to the observed sensitivity of B~lkanol,H20 for branching. However, since Bk, HzO approaches zero for propan-1-01 with molar volume close to that of DMF, the results may also be related to volume effects. The values of Be,H20 of the amides are relatively small and do not show special trends. The cross enthalpic interaction coefficients represent the enthalpy change when solutes x and y interact with each other in a solvent.The comparatively small and scattered values for the amides may indicate that an important part of the H,O-amide interaction occurs via the CON group which solute and solvent molecules have in common. It has been found that in mixtures of alkanols and amides the OH*-.O=C interaction is indeed d ~ m i n a t i n g . ~ ~ BtY for the interaction between Me4U and H,O is almost zero. The 13k,H20 values for compounds with one or more NH groups are negative and comparable in magnitude ( - 160 to - 320 J kg mol-2). In this case the interaction is apparently dominated by the NH * * - OH hydrogen bond. As the proton-donating character of different ureas may differ con~iderably,~~-~~ differences in B!& values are not improbable. Since both Be, and B& are negative in DMF the Franks-Barone approach according to eqn ( 5 ) becomes in this case BEY = - (BEx B!,)a.( 6 )60 Pair Interaction Coeficients with DMF+ H,O Also with this modification the method appears to be unsuccessful. However, we have noticed that in water the Barone method applies best for related solute compounds. The same may be true in the solvent DMF and in that case the Barone equation should hold for interactions involving alkanols and water. Unfortunately data for alkanol-alkanol interactions in DMF are not yet available. This work was carried out under auspices of the Netherlands Foundation for Chemical Research (SON) and with financial aid from the Netherlands Organization for the Advancement of Pure Research (ZWO).We thank one of the referees for helpful comments. References 1 P. J. Rossky and H. L. Friedman, J . Phys. Chem., 1980, 84, 587. 2 L. R. Pratt and D. Chandler, J . Solution Chem., 1980, 9, 1. 3 F. Franks, M. Pedley and D. S. Reid, J. Chem. Soc., Faraday Trans. I , 1981, 77, 1341. 4 G. M. Blackburn, T. H. Lilley and E. Walmsley, J. Chem. SOC., Faraday Trans. I , 1982, 78, 1641. 5 E. Matteoli and L. Lepori, J. Phys. Chem., 1982, 86, 2994. 6 V. Abate, G. Barone, G. Castronuovo, V. Elia and E. Rizzo, J . Solution Chem., 1983, 12, 645. 7 J. J. Spitzer, I . R. Tasker and R. H. Wood, J . Solution Chem., 1984, 13, 221. 8 T. F. Wegrzyn, I. D. Watson and G. R. Hedwig, J . Solution Chem., 1984, 13, 233. 9 M. Bloemendal, K. Booy and G. Somsen, J . Solution Chem., 1984, 13, 281.10 J. E. Desnoyers, G. Perron, L. Avedikian and J-P. Morel, J. Solution Chem., 1976, 5, 631. 1 1 M. Bloemendal and G. Somsen, J . Chem. Soc., Faraday Trans. I , 1985, 81, 1015. 12 C. de Visser, W. J. M. Heuvelsland and G. Somsen, J. Solution Chem., 1978, 7, 193. 13 W. J. M. Heuvelsland, C. de Visser and G. Somsen, J . Chem. Soc., Faraday Trans. I , 198 1, 77, 1 191. 14 A. C. Rouw and G. Somsen, J . Chem. Thermodyn., 1981, 13, 67. 15 A. C. Rouw and G. Somsen, J. Chem. Soc., Faraday Trans. 1, 1982, 78, 3397. 16 E. Lange and H. G. Markgraf, Z . Elektrochem., 1950, 54, 73. 17 F. Franks, M. Pedley and D. S. Reid, J. Chem. Soc., Faraday Trans. I , 1976, 72, 359. 18 W. Dimmling and E. Lange, Z . Elektrochem., 1951, 55, 322. 19 R. H. Wood and L. H. Hiltzik, J . Solution Chem., 1980, 9, 45.20 I. R. Tasker and R. H. Wood, J. Solution Chem., 1982, 11, 295. 21 M. Bloemendal, A. Sijpkes and G. Somsen, to be published. 22 J. J. Savage and R. H. Wood, J . Solution Chem., 1976, 5, 733. 23 C. de Visser, H. J. M. Grunbauer and G. Somsen, Z . Phys. Chem. N.F., 1975, 97. 69. 24 M. Bloemendal and G. Somsen, J. Am. Chem. Soc., 1985, 107, 3426. 25 G. Barone, G. Castronuovo, V. Elia and A. Menna, J . Solution Chem., 1979, 8, 157. 26 V. Abate, G. Barone, G. Castronuovo, V. Elia and P. Masturzo, Gazz. Chim. Ital., 1981, 111. 85. 27 G. Barone, G. Castronuovo, V. Crescenzi, V. Elia and E. hzzo, J. Solution Chem., 1978, 7, 179. 28 V. Abate, G. Barone, P. Cacace, G. Castronuovo and V. Elia, J . Mol. Liq., 1983, 27, 59. 29 M. Bloemendal and G. Somsen, J . Solution Chem., 1983, 12, 83. 30 J. E. Desnoyers, M. Arel, G. Perron and C. Jolicoeur, J . Phys. Chem., 1969, 73, 3346. 31 F. Franks and D. S. Reid, in Water, a Comprehensive Treatise (Plenum Press, New York, 1973), 32 R. S. Drago, D. W. Meck, M. D. Joesten and L. La Roche, Inorg. Chem., 1963, 2, 124. 33 D. B. Henson and C. A. Swenson, J . Phys. Chem., 1973, 77, 2401. 34 R. A. Cox, L. M. Druett, A. E. Klausner, T. A. Modo, F. Wan and K. Yates, Can. J . Chem., 1981,59. 35 J. A. Yu and Y-S. Choi, Taehan Hwahakhoe Chi, 1983, 27, 399. 36 I. R. Tasker and R. H. Wood, J. Solution Chem., 1982, 11, 729. 37 S. Ablett, M. D. Barratt, F. Franks, M. D. Pedley and D. S. Reid in L’eau et les SystBmes Biologiques, 38 See for references: G. Barone, P. Cacace, G. Castronuovo and V. Elia, J. Solution Chem., 1984,13,625. 39 H. C. Zegers and G. Somsen, J . Chem. Thermodyn., 1984, 16, 225. 40 L. Pikkarainen, J. Chem. Eng. Data, 1983, 28, 381. 41 0. Kiyohara, S. C. Anand and G. C. Benson, J . Chem. Thermodyn., 1974, 6, 335. 42 L. Pikkarainen, J. Chem. Eng. Data, 1983, 28, 344. vol. 2, chap. 5. 1568. ed. A. Alfsen and A. J. Berteaud (Editions du CNRS, Paris, 1976), p. 105. Paper 51202; Received 4th February, 1985

ISSN:0300-9599    

DOI:10.1039/F19868200053

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. 1, 1986, 82, 61-68 The Support Effect of CuO Catalyst for the Reduction of Nitric Oxide with Hydrogen or Ammonia Tokio Iizuka" and Hideo Ikeda Department of Chemistry, Faculty of Science, Hokkaido Unicersity, Sapporo 060, Japan Susumu Okazaki Department of Industrial Chemistry, Faculty of Engineering, Ibaraki University, Hitachi 316, Japan The reduction of nitric oxide (NO) with H, or NH, over CuO, catalysts supported on ZrO, or TiO, has been investigated. The activity and selectivity of NO reduction were very sensitive to the types of support oxide. A gradual increase in activity of CuO/ZrO, for the reduction of NO with NH, was observed in the course of the reaction, while the activity of CuO/TiO, was rapidly reduced as the reaction proceeded under the same reaction conditions.For the reaction of NOfNH, in the presence of oxygen, however, CuO/ZrO, was less active than CuO/TiO,. Several states of Cu2+ on the surfaces of ZrO, or TiO, were detected by means of e.s.r. spectroscopy. Cu2+ ions on ZrO, were reduced more easily than those on TiO, and hence this catalyst was concluded to show a high activity in NO+NH, or NO+H, reactions . The catalytic reduction of NO is of considerable practical importance and of great interest in fundamental studies of heterogeneous catalysis. Various types of NO reduction reactions, e.g. those with H,, NH, or CO as a reductant, have been widely investigated to obtain a highly active cata1yst.l In many cases, the support of a catalyst often plays an important role in its catalytic activity.For the reduction of N,O with H,, MOO, supported on TiO, prepared from Ti(SO,), was reported to exhibit an anomalously high activity., For the reduction of NO with NH,, TiO, for Fe and V catalysts3? and active carbon for Cu catalysts were reported as effective supports.5 In this work, the catalytic activities of CuO, supported on TiO, or ZrO, were examined for the reduction of NO with H, or NH, and e.s.r. experiments were performed to elucidate the effect of the supports on the catalytic activity. Experiment a1 'The support oxide, ZrO,, was obtained by calcination of Zr(OH), at 500 "C for 2 h in air. Zirconium hydroxide was prepared by adding aqueous ammonia to an aqueous solution of ZrOCl,. The resulting precipitate was filtered off, washed with deionized water until no Cl- ions were detected in the washing water, and was then dried at 120 "C for 24 h.Titanium dioxide was obtained by calcination of titanic acid at 500 "C for 2 h in air. Titanic acid was prepared by pouring TiCl, into cold water, adding aqueous ammonia, filtering, washing, and drying at 120 "C for 24 h. The CuO/ZrO, catalyst was prepared by mounting the copper ammine complex by the ion exchange method followed by calcination at 350 "C for 2 h [CuO/ZrO,(i)]. Two kinds of CuO/TiO, were prepared in copper ammine complex solution; one by the ion exchange method [CuO/TiO,(i)] and 616 2, Reduction ofNO with H, or NH, l o o 3 A 0 5 15 30 4 5 60 reaction time/min N,, 1 N,O on CuO/TiO,(d). Fig. 1. Reduction of NO with H, at 280 "C. N,, A NH, on CuO/ZrO,(i); 0 N,, 0 N,O on CuO/TiO,(i); the other by the conventional impregnation method [Cul/TiO,(d)].These catalysts were heated in air at 350 "C for 2 h before use. The reactions NO+H, and NO+NH, were studied in a closed recirculation reactor having a volume of 400 cm3. A mixture containing 10 Torrt NO and 30 Torr H, (or NH,) was allowed to react at 220-280 "C. The reaction mixture was periodically analysed by gas chromatography. For the reaction of NO+NH, in the presence of air, a conventional flow reactor was used. The reactant flow rate was 35 cm3 min-l NO+ 35 cm3 rnin-l NH,+ 1350 cm3 min-l air and the space velocity was 20000 h-l. The conversion of NO was observed by a NO, analyser. The e.s.r. spectra were obtained by a Varian E3 spectrometer at room temperature or at liquid nitrogen temperature.Reaction Results The results of the NO + H, reaction are shown in fig. 1. Over CuO/ZrO,, the activity was very high and the products were only N, and H,O in the initial stage, but a gradual increase of NH, formation was observed in the course of the reaction. In contrast, the activity was low and the formation of N,O was observed along with N, over CuO/TiO,(i). Over CuO/TiO,(d), though the activity was almost the same as that of CuO/TiO,(i), the product was mainly N,O, and N, formation was negligible. The results of the NO + NH, reaction are shown in fig. 2. The product was exclusively N, over the all catalysts. The activity of CuO/ZrO, was also very high for this reaction. When the reaction was repeated after the complete conversion to N, was achieved over CuO/ZrO,, a gradual increase of activity was observed.However, the catalysts CuO/TiO,(i) and CuO/TiO,(d) showed low activities, and the decrease in activity was observed over both catalysts by the repetition of the NO+NH, reaction. The conversion of NO in the NO+NH, reaction in the presence of air at various reaction temperatures is depicted in Fig. 3. For this reaction, CuO/TiO,(d) showed the highest activity and CuO/ZrO, was least active. The activity of CuO/ZrO, showed two maxima at ca. 150 and 300 "C. t 1 Torr z 133.3 Pa.T. lizuka, H. Ikeda and S. Okazaki 63 2 reaction time/min Fig. 2. Reduction of NO with NH, at 220 "C. 0 CuO/ZrO,(i), 0 CuO/TiO,(i), a CuO/ TiO,(d). Samples were evacuated at 350 "C between each run.loo 1 100 200 300 4 00 TI" C Fig. 3. Reduction of NO with NH, in the presence of air at various temperatures. 0 CuO/ ZrO,(i), 0 CuO/TiO,(i), (j CuO/TiO,(d). E.S.R. Study Typical e.s.r. spectra of CuO/TiO,(d) are shown in fig. 4. After the oxidation of the sample at 350 "C with oxygen, a broad signal and axial symmetrical signal with parallel hyperfine structure of 78 G were observed in superposition [fig, 4(a)]. In addition to those signals, a pair of small peaks [P,(B)] were observed at both sides of the perpendicular position. When the sample was reduced at 220 "C with H,, the broad signal decreased in intensity and new signals appeared [fig. 4(b)]. The new signals are axial 3 F A R 164 Reduction ufNO with H, or NH, \ g I I (B) = 2.4 3 v ( b ) g I I (A) = 2 .3 5 ] Y V Fig.4. E.s.r. spectra of CuO/TiO,(d), (a) after the oxidation at 350 "C, (b) reduced with H, at 220 "C, ( c ) reduced at 270 "C, ( d ) after 75 min in NO + H, reaction at 280 "C, (e) after 15 min in NO + NH, reaction at 220 "C over the oxidized sample. symmetrical ones with larger hyperfine splitting in the parallel portion than that of the former peak and show another pair of peaks [P,(A)] inside the former pair [P,(B)]. With higher spectrometer gain, two sets of peaks with half the splitting constant of each parallel hyperfine structure of axial symmetrical species were observed. The pair peaks of P,(A) decreased, but P,(B) peaks did not show any change after the reduction at 270 "C with H, as shown in fig. 4(c). When the sample was treated with NO (10 Torr) + H, (10 Torr) at 280 "C for 75 min after the oxidation at 350 "C, the e.s.r.spectrum was almost the same as that obtained after the reduction at 220 "C with H, as shown in fig. 4(d). The same spectrum was also obtained after the reaction of NO+NH, at 220 "C for 15 min over the oxidized sample [fig. 4(e)]. In the case of CuO/TiO,(i), only a broad unsymmetrical signal was observed after oxidation at 350 "C as shown in fig. 5(a). When this sample was reduced with H, at 170 "C, an axial symmetrical species whose parallel hyperfine constant was 122 G and P,(A) pair peaks were observed [fig. 5(h)]. In the reaction of NO+H, at 280 O C , CuO/TiO,(i) was greatly reduced and P,(A) pair peaks increased distinctly with small peaks of Pl(B) as shown in fig.5 (c). When the oxidized CuO/TiO,(i) was contacted withT. Iizuka, H . Ikeda and S. Okazaki 65 YT g,= 2.05 + g1 Fig. 5. E.s.r. spectra of CuO/TiO,(i), (a) after oxidation at 350 "C, (b) reduced with H, at 170 "C, (c) after 30 min NO+ H, reaction at 280 "C over the oxidized sample, (d) after 15 min NO + NH, reaction at 220 "C over the oxidized sample. NO + NH, at 220 "C for 15 min, a broad unsymmetrical peak with a hyperfine constant of 160 G at gll = 2.21 was observed with small peaks of P,(A) [fig. 5(d)]. Oxidized CuO/ZrO, gave only a broad unsymmetrical peak at g z 2.1 as shown in fig. 6(a). The broad signal decreased in intensity drastically upon reduction when T > 100 "C. After the reduction at 220 "C for 15 min, the broad signal almost dis- appeared and a sharp axial symmetrical peak at g = 2.05 and gI1 = 2.30 was observed.In addition to this signal, a sharp singlet peak was superimposed in the perpendicular position of the Cu2+ signal. The spectrum is depicted in fig. 6(b). In the reaction of NO+H, at 280 "C, the catalyst was further reduced as shown in fig. 6(c). When the oxidized CuO/Zr02 was treated with the mixture of NO and NH, at 220 "C for 15 min, the sample was considerably reduced and the same hyperfine structure was observed in the parallel position as CuO/TiO,(i) in NO+NH,. The spectrum is shown in fig. 6(d). The intensity changes of Cu2+ on the catalysts after various treatments at different temperatures are shown in fig. 7. Discussion From the e.s.r. result, it is clear that at least two different states of Cu2+ exist on the surface of CuO/TiO,(d).The species which shows the parallel hyperfine structure of 78 G (B) was insensitive to the reduction and oxidation treatments. The pair of peaks which was denoted as P,(B) can be ascribed to the spin-exchanged pair species which had been observed in Cu(CH,COO), H,06> and CuY zeolite.8 The species of P,(B) was also insensitive to the reduction-oxidation treatments. Thus P,(B) species would be in the same state as the isolated Cu2+ which showed the hyperfine structure of 78 G. This 3-266 Reduction of NO with H, or NH, g=2.05 ( c ) Fig. 6. E.s.r. spectra of CuO/ZrO,(i), (a) after oxidation at 350 "C, (b) reduced with H, for 15 min at 220 "C, (c) after 30 min NO+H, reaction at 280 "C over the oxidized sample, ( d ) after 15 min NO + NH, reaction at 220 "C over the oxidized sample.4 0 o P 2 100 800 600 LOO 2 00 \ \ I I I I I 1 I I I I I I I 20 70 120 170 220 20 70 120 170 220 20 70 120 170 220 T/'C Fig. 7. E.s.r. intensity changes of the Cu2+ ion after the various treatments at different temperatures. 0 CuO/ZrO,(i), 0 CuO/TiO,(i), CuO/TiO,(d). ( a ) H,, (b) NO, (c) NO+NH,. state could be denoted as species B. After the reduction of CuO/TiO, (d), the broad rather symmetrical signal disappeared and the pair species P,(A) and the isolated species A which had the hyperfine structure of 122 G appeared. The broad symmetrical signal was ascribed to a non-linear pair in CuY zeolite by Chao and Lunsford.8 In this pair, it is thought that the exchange interaction involves many spins.On CuO/TiO,(d), itT. lizuka, H. Ikeda and S. Okazaki 67 would be reasonable to think that the many-spin-exchanged cluster of Cu2+ changed to the spin-exchanged pair and isolated Cu2+(A) upon reduction. Thus, the pair peaks of P,(A) would be ascribed to the spin-exchange of the Cu2+(A) pair. Species (A) was very sensitive to reduction-oxidation treatment in contrast to species (B). The hyperfine coupling constant of Cu2+(A) (122 G) was larger than that of Cu2+(B) (78 G) owing to the stronger interaction of Cu2+(B) with TiO, support than Cu2+(A). On CuO/TiO,(i), the main species was Cu2+(A), and the Cu2+(B) species was almost negligible. Thus, CuO/TiO,(i) is more easily reduced with H, compared to CuO/TiO,(d). The sample of CuO/ZrO,(i) showed a larger hyperfine coupling constant ( 1 57 G) than CuO/TiO,(i), and was reduced easier than CuO/TiO,(i).The order of reducibility of Cu2+ species corresponds well with the magnitude of the hyperfine coupling constant, Cu2+/Zr0, > Cu2+(A) > Cu2+(B). In the reaction of NO+H,, the catalyst was reduced gradually in the course of the reaction and the reaction rate became higher over the reduced catalyst. For this reaction, a redox mechanism on CuO or/and Cu+ has been propo~ed.~ The order of activity for the NO+H, reaction, CuO/ ZrO,(i) > CuO/TiO,(i) > CuO/TiO,(d), corresponds well with the reducibility of the catalyst. NO was reduced even to NH, in the final stage of reaction over CuO/ZrO,(i). At this stage it is probable that part of the Cu2+ was reduced to metallic Cu.In the e.s.r. spectrum of reduced CuO/ZrO,(i), a sharp singlet signal appeared in the perpendicular signal position of Cu2+. Though we cannot ascribe this signal to Cu metal because a free Cu atom is known to have an isotropic hyperfine splitting of 2100 G,1° the appearance of the sharp signal would have some correlation with the reduction of Cu2+ to the metallic state. On CuO/TiO,, neither the appearance of this signal nor the formation of NH, in the reaction of NO + H, were observed. Over CuO/TiO, (d), NO was reduced only to N,O. Since the species of Cu2+(B) was not reduced even at high temperature, only a small part of the Cu2+ would be responsible for the redox cycle in the reaction over this catalyst. For the reaction of NO+NH, it has been reported that the loss of activity is caused by the reduction of Cu2+ to Cu+ in the course of the reaction.11.12 Actually, over CuO/TiO,(i) and CuO/TiO, (d), the activity gradually decreased along with the colour change of catalyst from bright blue to red-brown in the reaction.In contrast to this, over CuO/ZrO,(i) the activity increased in the repeat reaction and the colour of the catalyst changed from bright blue to black. Since CuO/ZrO,(i) is more easily reduced in comparison to CuO/TiO,(i) or CuO/TiO,(d), metallic Cu has been formed in the course of the reaction and acts as an active site for the reduction of NO. The metallic state of Cu has been reported to show a high activity for this reaction via the dissociation of NH, over the surface.13~ l4 Thus, the activity over CuO/ZrO,(i) increased along with the reduction of Cu in the reaction.However, CuO/TiO,(i) and CuO/TiO,(d) were not reduced to the metallic state and lost their activity (probably as a result of the appearance of the Cu+ state). After exposure to NO+NH, gas, the hyperfine splitting of A , , = 160 G and A l = 25 G was observed on CuO/TiO,(i) and CuO/ZrO,(i), but was not seen on CuO/TiO,(d). This spectrum has been ascribed to the formation of the Cu(NH,), complex in zeolite-Y.ll It is probable that ammonia molecules can access Cu(A) on TiO, and Cu ion on ZrO, easily, but over CuO/TiO,(d), the interaction of Cu(B) with TiO, is strong and the ammine complex will not form. On the other hand, for the reduction of NO with NH, in the presence of air, CuO/TiO,(d) and CuO/TiO,(i) were active because the oxidized state of Cu was stable over their surfaces.Two maxima of the activity in the case of CuO/ZrO,(i) for the reduction of NO with NH, in the presence of air were observed. This phenomenon might have a correlation with the redox nature of the catalyst. Over CuO/ZrO,, the Cu2+ ion was greatly diminished in NO + NH, in the absence of oxygen at around 200 "C and was insufficiently oxidized at the same temperature in pure NO. At ca. 200 "C the Cu ion68 Reduction ofNO with H, or NH, on ZrO, was probably not oxidized completely and the activity was kept low around this temperature. The authors thank Prof. K. Tanabe and Prof. H. Hattori for helpful discussions. This work was supported by a Grant-in-Aid for Environmental Science No. 59035001 from the Ministry of Education, Science and Culture of Japan. References 1 M. Shelef, Catal. Rev., 1975, 11, 1. 2 S. Okazaki, N. Ohsuka, T. Iizuka and K. Tanabe, J. Chem. SOC., Chem. Commun., 1976, 654. 3 S. Kasaoka and T. Yamanaka, J . Chem. Soc. Jpn, 1977, 907. 4 S. Kasaoka, E. Kasaoka, T. Yamanaka and M. Ono, J . Chem. SOC. Jpn, 1978, 874. 5 F. Nozaki, K. Yamazaki and T. Inomata, Chem. Lett., 1977, 521. 6 B. Bleaney and K. D. Bowers, Proc. R. Soc. London, Ser. A , 1952, 214, 451. 7 H. Abe and J. Shimada, Phys. Rev., 1953,90, 316. 8 C. C. Chao and J. H. Lunsford, J. Phys. Chem., 1972,76, 1546. 9 J. W. London and A. T. Bell, J . Catal., 1973, 31, 96. 10 P. H. Kasai and D. Mcleod Jr, J . Chem. Phys., 1971, 55, 1566. 1 1 W. B. Williamson and J. H. Lunsford, J. Phys. Chem., 1976, 80, 2664. 12 M. Mizumoto, N. Yamazoe and T. Seiyama, J . Catal., 1979, 59, 319. 13 K. Otto, M. Shelef and J. T. Kummer, J . Phys. Chem., 1971, 75, 875. 14 K. Otto and M. Shelef, J. Phys. Chem., 1972,76, 37. Paper 51210; Received 5th February, 1985

ISSN:0300-9599    

DOI:10.1039/F19868200061

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. 1, 1986, 82, 69-75 An Application of the Gibbs-Duhem Relation to the Binary Mixed Electrolytes Tiong-Koon Lim Chemistry Department, University of Malaya, Kuala Lumpur 22- 11, Malaysia Numerical calculations of the activity coefficients of CoCl, in the binary mixture HCl-CoC1,-H,O at 25 "C using different methods are reported. From the results it is found that the recently derived general Gibbs-Duhem relation is useful in computing the activity coefficients of one electrolyte from another electrolyte whose activity coefficients can be experimentally fitted. For binary mixed electrolytes with a common ion it is well known that the activity coefficients can only be determined experimentally for one of its e1ectrolytes.l The cross-differential condition as required by the Gibbs-Duhem equation prevents the Harned coefficients being adjusted independently to give the best fit with experimental data. Theoretical methods are therefore required for the calculation of the activity coefficients of the other electrolyte which were not experimentally fitted. McKay2 was able to calculate Harned's coefficients for an electrolyte, using the Gibbs-Duhem condition, when it is known that Harned's rule3 applies to the other electrolyte.In another more convenient approach, Scatchard4 and Pitzer5y expressed activity coeffi- cients of both electrolytes in terms of the same set of parameters, so that the activity coefficients of both electrolytes can be calculated simultaneously from fitting the experimental activity coefficients of one of the electrolytes only.The same approach has also been used by Lim et al.'? to express activity coefficients of both electrolytes in terms of the mixing coefficients of A,Gex with an additional requirement that the higher-order limiting law9 must be satisfied. Recently'O it has been shown that the cross-differential condition leads to a general Gibbs-Duhem relation which interrelates the Harned coefficients of the two electrolytes; this enables the Harned coefficients of one electrolyte to be computed from the Harned coefficients of the other electrolyte. This paper produces some numerical results for this new method and compares the results with those obtained from the other methods. The Methods The activity coefficients of a binary electrolyte mixture with a common negative ion can be given by the Harned equation:ll or the following equivalent equations :' + M$' g ; if( YI)" +;( YI)?z+l n-o 6970 Gibbs-Duhern Equation for Binary Mixed Electrolytes + Mi1 g; (; (YI).-g YI)n+l . (4) n -o )I Here we assume that electrolyte A contains vA+ ion 1 and v, ion 3 with valency charges z , and z3, respectively, while similarly electrolyte B contains v$ ion 2 and vg ion 3 with charges z2 and z,, and vA = vA+ + v ~ etc. I is the total ionic strength, y is the fraction of the ionic strength due to electrolyte B, and Y = 1 -2y. M is the order of the equation and is taken as 2 throughout this paper. The coefficients gn are the mixing coefficients in the expression of the changes of excess Gibbs free energies, their statistical-mechanical expressions have been given elsewhere ; 8 1 their expressions in some semi-empirical methods are given as follows.In Pitzer's method, we have whereas in the Scatchard method they are defined by In the higher-order limiting-law (HOLL) method these parameters were forced to satisfy the higher-order limiting law and the consistency condition so that go = A In ~ + p ~ + v f i g , = constant. (7) Since g, is necessarily an I-independent constant in order to satisfy the Gibbs-Duhem cross-differential condition,l0 either the Pitzer parameters CMx, C,, and vMNX must be I-independent, as is usually assumed in the practical calculations, or their sum [which equals g, as defined in eqn (5)] must be a constant. In the above methods the Harned coefficients for both electrolytes A and B were expressed by the same set of parameters, so that both aAn and aBn can be obtained simultaneously from fitting experimental logy, data only. Recently a new method was proposed from which aBn can be obtained from the experimentally fitted aAn coefficients according to a general relation as required by the Gibbs-Duhem cross-differential condition.lO In this method aRn are related to a,, as follows: whereT- K .Lirn 71 Therefore, after all the aAn coefficients were obtained from fitting the experimental log yA values, daA,/dI can be computed, and a,, can be calculated from eqn (8) successively beginning with n = 1. In the calculation of the derivativesf(1) of a function f(1), a three-point Lagrangian formula may be used for all the intermediate ionic strengths I, : where whereas for the first and the last ionic strengths the usual two-point Newtonian formula can be applied.The above procedure of successive evaluation of a,, results in the following explicit relation : n=o r=j-n k=1 where ETo = r F$=O if r < O and D(lk) 1 The principal aim of this paper is to check the reliability of our a,, coefficients as computed from the Gibbs-Duhem general relation, eqn (8). The results thus obtained can be used to compute logy, and then compared with those calculated from other methods. The mixture being tested is HCl-CoCI, at 25 "C for I = 0.01, 0.03, 0.05, 0.08, 0.1, 0.5, 1, 2 and 3 mol kg-l. Experimental activity coefficients of HCl for this mixture have been reported elsewhere, and the calculated results using the Scatchard method, the Pitzer method and the HOLL method have also been r e p ~ r t e d .~ ? ~ ~ The calculated4 td Table 1. Calculated values of -log yB from various methodsa for the mixture HC1-CoC1,-H,O at 25 "C - ~- - Y R Scatchard Pitzer HOLL present average 0.0 0.064 371 0.130 609 0.248 701 0.368 853 0.498 856 0.625 563 0.753 900 0.0 0.080 617 0.126 678 0.269 531 0.366 31 1 0.495 172 0.631 279 0.758 658 0.878 071 0.935 600 0.0 0.063 189 0.154 162 0.226 463 0.376 733 0.500 640 0.610 933 0.758 761 0.897 366 0.087 03 (-0.4) 0.087 03 (-0.5) 0.087 02 (-0.4) 0.087 02 (-0.4) 0.087 02 (-0.5) 0.087 01 (-0.5) 0.087 01 (-0.5) 0.087 00 (-0.6) 0.135 7 (- 1.7) 0.135 7 (- 1.9) 0.135 7 (-2.1) 0.135 7 (-2.4) 0.135 8 (-2.4) 0.135 8 (-2.5) 0.135 9 (-2.3) 0.135 9 (-2.1) 0.135 9 (- 1.8) 0.136 0 (- 1.5) 0.163 4 (-8.4) 0.163 5 (-7.5) 0.163 6 (-6.4) 0.163 6 (-5.6) 0.163 8 (-4.2) 0.163 9 (-3.3) 0.164 0 (-2.6) 0.164 l (-2.0) 0.164 2 (- 1.7) I = 0.01 mol kg-l 0.090 26 (2.8) 0.090 08 (2.7) 0.089 89 (2.5) 0.089 59 (2.1) 0.087 74 (0.3) 0.087 68 (0.3) 0.087 62 (0.2) 0.087 51 (0.1) 0.089 31 (1.8) 0.089 04 (1.5) 0.088 82 (1.3) 0.088 62 (1.0) 0.087 42 (- 0.1) 0.087 32 (-0.2) 0.087 23 (-0.3) 0.087 14 (-0.4) I = 0.03 mol kg-l 0.141 2 (3.9) 0.137 l (-0.3) 0.140 8 (3.2) 0.137 0 (-0.6) 0.140 6 (2.8) 0.136 9 (-0.9) 0.140 1 (2.0) 0.136 7 (- 1.4) 0.139 7 (1.5) 0.136 5 (- 1.7) 0.139 3 (1.1) 0.136 4 (- 1.9) 0.139 0 (0.8) 0.136 2 (-2) 0.138 8 (0.8) 0.136 1(-1.9) 0.138 6 (1.0) 0.1360(-1.7) 0.138 6 (1.1) 0.1360(-1.5) I = 0.05 mol kg-' 0.170 2 (- 1.6) 0.165 3 (-6.5) 0.169 8 (- 1.2) 0.165 2 (-5.8) 0.169 4 (-0.6) 0.165 0 (-5.0) 0.169 0 (-0.2) 0.164 9 (-4.3) 0.168 5 (0.5) 0.164 7 (-3.3) 0.168 l ( l .0 ) 0.164 6 (-2.6) 0.167 9 (1.3) 0.164 5 (-2.1) 0.167 6 (1.5) 0.164 4 (- 1.7) 0.167 5 (1.6) 0.164 4 (- 1.5) 0.084 63 (-2.8) 0.084 91 (-2.5) 0.085 20 (- 2.2) 0.085 69 (- 1.8) 0.086 17 (- 1.3) 0.086 67 ( - 0.8) 0.087 13 (- 0.4) 0.087 57 (-0.01) 0.135 4 (-2) 0.137 0 (-0.6) 0.137 9 (0.1) 0.139 9 (0.8) 0.140 8 (2.6) 0.141 5 (3.3) 0.141 6 (3.4) 0.141 l(3.1) 0.140 1 (2.5) 0.139 4 (1.9) 0.188 l(16) 0.185 4 (14) 0.181 9 (12) 0.179 4 (10) 0.174 9 (6.9) 0.172 0 (4.9) 0.170 0 (3.4) 0.168 2 (2.1) 0.167 5 (1.6) 0.087 4 0.087 4 0.087 4 0.087 4 0.087 5 0.087 5 0.087 6 0.087 6 0.137 4 0.137 6 0.137 8 0.138 1 0.138 2 0.138 3 0.138 2 0.138 0 0.137 7 0.137 5 0.171 8 0.171 0 0.170 0 0.169 2 0.168 0 0.167 2 0.166 6 0.166 1 0.165 9T-K.Lim 73 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 z oo 8 II 4 0 E 0 II d v! II n 0 3 II +-4 P G F b YB Scatchard Pitzer HOLL present a1:erage x $ 3 h 0.177 1 (6.5) 0.171 8(1.2) 0.180 8 (10) 0.152 9 (- 18) 0.170 7 9 !i. 0.218 5 (- 10) 0.228 5 0 0.681 635 0.272 3 (1.7) 0.2718 (1.2) 0.273 2 (2.6) 0.265 3 (- 5.4) 0.270 7 3 0.286 9 (- 3.4) 0.2928 ? 0.303 5 bcr 0.0 0.037 2 (22) 0.036 1 (20) 0.046 8 (3 1 ) -0.057 6 (- 73) 0.015 7 G 0.121 202 0.063 6 (1 6) 0.063 8 (1 7) 0.068 9 (22) -0.007 3 (-55) 0.047 3 % 0.390 199 0.124 4 (7.9) 0.123 8 (7.3) 0.123 4 (6.9) 0.094 3 (-22) 0.1 16 5 g- 0.637 729 0.183 4 (2.2) 0.185 4 (4.2) 0.180 3 (-0.9) 0.175 7 (-5.5) 0.181 2 a h % 2 2 2 Table 1.(cont.) I ~~ ____ ___ ~- _ _ ~~ ~~~ ~- ______________~__ - I = 2 mol kg-' x 0.0 0.135 548 0.194 6 (5.2) 0.191 O(1.8) 0.197 7 (8.3) 0.174 4 (- 15) 0.189 4 0.405 646 0.231 7 (3.2) 0.230 2 (1.7) 0.233 6 (5.1) 0.805 475 0.291 4 (1.1) 0.290 9 (0.6) 0.291 9 (1.6) 0.887 185 0.304 3 (0.8) 0.303 7 (0.2) 0.304 6 (1.1) 0.301 3 (-2.2) 2. I = 3 mol kg-' Q 0.785 655 0.220 1 (0.7) 0.221 3 (1.9) 0.217 3 (-2.1) 0.218 9 (-0.5) 0.219 4 0.247 4 (0.4) 0.247 6 (0.6) 0.245 6 (- 1.5) 0.247 6 (0.6) 0.247 1 0.892 980 ~~ ~~ ~ ~ ______-- ~~ ~ ~ ~~ a CD were computed from the Scatchard parameters for single electrolytes in the HOLL method; M = 2 for all methods. 2T-K. Lim 75 log yB results as obtained from the present method using general Gibbs-Duhem relation are listed in table 1 together with those calculated from other methods.The average values of the four methods are shown in the last column of table 1. We multiply the difference between a calculated value and the average value by a factor of lo3 and placed it inside parentheses following the calculated value. From these values we know that the values of log yB calculated from the present method are just as good as those obtained from other methods, except at high concentrations. The disagreements at high concentrations are probably due to the following reasons. (a) At high concentration the interaction between ions are larger and thus the higher-order parameters with M 3 3 may be significant and cannot be neglected; this requires g , to be I-dependent at higher concentrations.(b) The separations between two ionic strengths are larger; this makes the calculation of the derivatives less accurate. Furthermore, we also observe that the agreements between various methods in the calculation of log yH are not as good as in the calculation of log yA. However, if we study the variation of the values of -log yR from large y , to small yB at constant I, we know that Pitzer’s method behaves similarly to the HOLL method, while the present work and the average values are also similar, with Scatchard’s method different from all the rest. Nevertheless, if we consider the changes from high I to low I then these variations in all the methods seem to follow a same pattern: generally all the methods show decrease at high I ; then whcn I falls, the present method shows a change from a decrease to an increase at I = 0.5, whereas the Pitzer method and the HOLL method show this change at I = 0.1, and the Scatchard method at I = 0.01.When I is further reduced, a second change is observed at I = 0.08 for all the methods except that of Scatchard; this suggests that this second change may exist in the Scatchard method only at a lower I value. There is also a change from an increase to a decrease at I = 0.03 for the present work and the average values; this change can probably be observed in the other methods only at very small I. Other mixtures have also been tested, but since the results are similar to those given here they will not be reported. We may therefore conclude that the Gibbs-Duhem relation, eqn (S), is useful in calculating aBn from the experimentally fitted aAn.However, at higher concentrations higher-order parameters and/or a closer separation between two ionic strengths may be needed. References 1 R. A. Robinson and R. H. Stokes, Electrolyte Solutions (Butterworths, London, 2nd edn, 1959). 2 H. A. C. McKay, Trans. Faraday Soc., 1955, 51, 903; Discuss. Faraday SOC., 1957, 24, 76. 3 H. S. Harned and B. B. Owen, The Physical Chemistry of Electrolyte Solutions (Reinhold, New York, 4 G. Scatchard, J . Am. Chem. Soc., 1961, 83, 2636; 1968, 90, 3124. 5 K. S. Pitzer, J . Phys. Chem., 1973, 77, 268. 6 K. S. Pitzer, in Activity Coeficients in Electrolyte Solutions, ed. M. R. Pytkowicz (C.R.C. Press, Boca 7 T-K. Lim, C. Y. Chan and K. H. Khoo, J . Solution Chem., 1980,9, 507. 8 T-K. Lim, Int. J. Quantum Chem., 16, 247. 9 H. L. Friedman, Ionic Solution Theory (Butterworths, London, 2nd edn. 1959); H. L. Friedman and 3rd edn, 1958). Raton, Florida, 1979), chap. 7. C. V. Krishnan, J . Phys. Chem., 1974, 78, 1929. 10 T-K. Lim, J . Chem. SOC., Faraday Trans I , 1985, 81, 1195. 11 R. H. Harned and R. A. Robinson, Multicomponent Electrolyte Solutions (Pergamon, Oxford, 1968). 12 K. H. Khoo, T. K. Lim and C. Y. Chan, J . Chem. SOC., Faraday Trans. I , 1978, 74, 2037. Paper 5/279; Receiued 18th February, 1985

ISSN:0300-9599    

DOI:10.1039/F19868200069

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J . Chem. Soc., Faraday Trans. 1, 1986, 82, 77-88 Volumetric Investigation of the Hydrotropic Action of Aqueous Sodium Propionate Solutions on Pentanol at 298 K Olav Hans& and Jar1 B. Rosenholm* Department of Physical Chernistry,oAbo Akademi, Porthansgatan 3-5, SF-20500 Abo, Finland The miscibility range for water - sodium propionate - pentanol mixtures has been determined at 298 K. The phase equilibria are compared with ‘normal’ and ‘ detergentless ’ microemulsion systems. Sodium propionate imposes a very slight salting out action (if any) on pentanol in dilute aqueous solutions. However, pentanol gains full miscibility with concentrated salt solutions. Volumetry was chosen to detect the interactions between the components since it has been found to monitor both changes in the environment of the hydrocarbon chains as well as large shifts in the polar association equilibria.According to the apparent molar volumes the enhanced solubility of pentanol is apparently obtained through dissociation of the alcohol com- plexes. Interestingly the concentrated hydrotrope solvent seems to be apolar in character. The state of the hydrotrope is almost entirely determined by the relative amount of (hydration) water. The interaction between pentanol and sodium propionate also seems to be of importance in dilute pentanol solutions. The absence of extended association structures in the system explains the difference between hydrotropy and normal solubilization, which is also evidenced by the volumetric behaviour of pentanol. On the other hand, the restriction of the mutual miscibility of the hydrotrope and the alcohol to the region where all the water is considered to be bound as hydration water of the ions marks the distinction between these systems and ‘ detergentless microemulsions ’.The modern and now generally accepted view is that microemulsions may be defined as isotropic and thermodynamically stable solutions of small polymolecular aggregates (micelles) dispersed in a pure or mixed solvent. The number of components in the system is normally three or four including a surfactant, a cosurfactant and one or two solvent components, i.e. water and oi1.l In some cases the cosurfactant is considered to be the solvent or a part of it. Owing to their dualistic nature, the surfactants associate in aqueous media in such a way that the hydrocarbon chains collect in the core of the oil/water (o/w) micelles.29 In this local apolar environment a small amount of oil can be dissolved (solubilized) into the aqueous solution.Similarly small amounts of water can be brought into oil solvents. Here the surfactants are reversing their molecular arrangement to form small polar droplets of solubilized water (w/o) mi~elles.~ Much of the effort to elucidate the changes in stability of the association structures has concentrated on the role played by the cosurfactant. This approach seems natural, since it is known from the phase diagrams published by Ekwal15 that a shortening of the chain length of e.g. an alcohol cosurfactant destabilizes the high-order phase structures (liquid-crystalline phases) to give stable solutions over wide composition ranges.The starting point for such studies has been the use of a real surfactant which is characterized by a cooperative association in aqueous solutions.6 The influence of ascending a homologous series of alcohols on the mutual miscibility of the components is illustrated in fig. 1. Less attention has been paid to the fact that the main changes introduced by the variation of the chain length of the cosurfactant are also produced if the chain of the 7778 Action of Aqueous Sodium Propionate on Pentanol W Fig. 1. The miscibility region (in black) of (i) a water-hexanol mixture with an alkyltrimethyl- ammonium bromide of varying chain length at 301 K [ref. (7)] and (ii) a water-sodium octanoate mixture with an alkanol of varying chain length at 293 K [ref.( 5 ) ] , respectively. The figure is drawn as an aid for the eye and thus the concentrations (in wt :<) and the liquid-crystalline phases are omitted from the figures. surfactant is varied, keeping the cosurfactant the same.’? As shown in fig. 1 there is a systematic change in miscibility when the chain length of one of the surfactants is varied. Despite the relationship in phase behaviour, the ability of ionic short-chain surfactants to enhance the solubility of water-insoluble components may be considered as different from normal solubilization. In contrast to surfactants, the association tendency of hydrotropes is weak.9 They are thus incapable of normal solubilization. To mark this distinction the effect has been denoted hydrotropy by Neuberg.l0 The special behaviour of short-chain surfactant solutions has attracted much discussion in early investigations on association phenomenal1* l2 and serves as a bridge between microemulsion systems and normal so1utions.13 A new situation is also introduced if the cosurfactant, e.g.the alcohol, is mutually soluble with water. In favourable cases very polar alcohols can, mixed with water, but without any ‘real’ surfactant, dissolve large amounts of oil. This kind of ‘detergentless microemulsion’ is characterized, as are the hydrotrope systems, by the absence of any well defined aggregate structure^.^^^ l5 The present paper constitutes one contribution in a series of investigations to characterize thermodynamically the properties of simple and complex surfactant systems.16-20 In the present case both of the surface-active components have only a limited miscibility with water.The interactions found should then be typical for ionic hydrotrope systems. The ‘surfactant’ is unable to associate to micellesg and the alcohol is only sparingly mutually soluble with water. Of the parameters available, volumetric properties seem to be particularly suitable since electrostatic and polar interactions contribute only secondarily to the total changes in the apparent molar volumes of the surfactant component^,^^-^^ making this parameter0. Hans& and J. B. Rosenholm 79 especially useful in rough model calculations of surfactant systems.24 The present mixed solvent system is, of course, not suitable for the type of closed structure modelling indicated above.Experiment a1 Chemicals Both the sodium 1 -propionate (SIGMA Chem. Co., > 99 % ) and the pentan-1 -01 (Merck AG, zur analyse, > 99 % ) were used without further purification. The water was distilled and passed through an ion-exchange resin. Its conductivity was 0.5 $3 cm-l. Instruments The densities were measured with an Anton-Paar vibrating-tube densitometer equipped with an external measuring cell (DMA 601). The calibrations were carried out against air and water. The apparatus has a sensitivity of ca. 1 x lop6 g ~ m - ~ . In all the experiments the temperature was maintained at 298.15 K. Phase Equilibria The extension of the solution phase of the water - sodium propionate - pentanol mixture was determined by visual observations at 298 K.Before inspection all the solutions were allowed to equilibriate in a thermostatted water bath for 7 days. The estimated accuracy is ca. 1 % . Mathematical Operations The densities (p) obtained were converted into molar volumes of solution by employing the following expression : where M(i) denotes the molar mass and x(i) the mole fraction of component i: n(i) refers to the amount (number of moles) of substance i ( n = 1-3). volume according to the equation [" = ' (pure) or O0 (infinite dilution)] The molar volume of solution was then recalculated in terms of the molar excess V: = vrn -C x(i) V" (i) = C x(i) VE(i). ( 3 ) The reference values used were V'(H20) = 18.068 cm3 mol-1 V'(C,OH) = 108.65 cm3 molt1.These were derived by recalculating the densities of the pure liquids or by extrapolating the apparent molar volumes of the salt to infinite The values found are close to those reported, e.g. in ref. (1 6), (26) and (27) (alcohol) and (25) (salt). The relationship between the molar excess volume and the apparent molar volume is given by the general formula Vm(NaC302) = 53.6 cm3 mol-180 Action of Aqueous Sodium Propionate on Pentanol Fig. 2. The thermodynamically stable liquid phase of the system water-sodium propionate- pentanol at 298 K. The concentrations are given in wt % . The solid lines drawn within the liquid phase refer to the solution series measured: binary system H,O-C,OH (1 and A), n(C,OH)/n(NaC,O,) = 2.0 (2) and = 1.0 (3), binary system H,O-NaC,O, (4), n(H,O)/n(NaC,O,) = 6.5 (B), and a constant percentage by weight for water of 30 (C), respectively.where V*(i) denotes the volume of the pure component i. In the case of the salt the volume of sodium propionate infinitely diluted in water ( Va) was used instead. Note that the apparent molar properties of complex multicomponent systems may in some instances be distorted owing to compensation effects.20 However, the relatively scarce number of experimental points prevented us from partially deriving the molar excess volume of Results and Discussion Three-component Phase Diagrams As is commonly done for three-component systems, the compositions are expressed in a triangular diagram ; each component increases in concentration counterclockwise, thus ending up with the pure component at eachcorner.Fig. 2 illustrates the thermodynamically stable isotropic solution phase (intersected by solid lines) of the water - sodium propionate - pentanol system. The right-hand corner of the triangle is characterized by a very large solubility gap between the liquid phase and hydrated salt. The right-hand boundary is defined by the minimum amount of water needed to hydrate the sodium carboxylate group, being determined by the hydration requirement of the alkali-metal The minimum amount of water needed to hydrate one mole of sodium carboxylate groups is 5-7 mol. The left-hand side of the triangle gives the mutual solubilities of water and pentanol. The logarithm of the solubility of n-alcohols in water from butanol to octanol has been found to be a linear function of the number of carbon atoms in the chain.’ The solubility of these alcohols has successfully been correlated with the surface contact between their hydrocarbon residues and water.30 For pentanol the solubility was found to be 2.2-2.3 % by weight.It is important to distinguish the process when water is dissolved in alcohols from the reverse case. Thus the logarithmic dependence indicated above is not regenerated. Recently it was concluded that the origin of the water solubility may be found in the polarity of the alcohol solvent. For hydrophobic long-chain alcohols all the water is consumed in complex formation while an increasing part of the water is distributed freely in polar short-chain alcohol^.^^^ 31 If the molar ratio of alcohol to water is used to express0.Hansen and J . B. Rosenholm 81 the saturation point then the distribution of water in the short-chain alcohols decreases the ratio from the constant value of ca. 2.7 prevailing for the longer homologue~.~~ The molar ratio of pentanol to water is reported to be 1.7-1.8 (ca. 10% by The ternary left-hand boundary departs from the binary saturated solutions. In the ternary solutions all the polar head groups must be fully hydrated before the distribution of water into the solvent is activated.20 If the maximum amount of water needed to hydrate the ionic groups fully [n(H,O)/n(NaC,O,) = 11-14] is assumed to be fully consumed by the sodium propionate, then the vertical left-hand phase border may be taken as determined by hydration water and water complexated with pentanol molecules.The latter fraction of water is successively diminished as the concentration of sodium propionate increases. It was concluded above that one should distinguish the present hydrotrope from micelle-forming surfactants. As indicated in fig. 1, the left-hand phase boundary never extends to high water fractions if the hydrophobicity of the ionic surfactant is insufficient for cooperative association. This is also true even if the chain of the cosurfactant, e.g. the alcohol, is lengthened.12 The mutual solubility of the components reaches its maximum when both of the surface-active components are chemically compatible (about the same chain length, branching etc.). In ' real ' ionic surfactant systems the water-rich part remains thermodynamically stable until a full miscibility between the cosurfactant and water is obtained (fig.1). Clearly it is the capability of the surfactant to associate which secures phase stability at high water contents. The largest continuous solution phase is obtained when the extensive association structures are destabilized with a short-chain cosurfactant (e.g. with water-soluble alcohols; fig. 1). With chemically compatible cosurfactants the long-chain surfactants form stable aggregates. Then the aqueous phase does not extend to cosurfactant contents higher than ca. 10% by weight. The critical micellization concentration is visible as a break point in the phase boundary from the binary water-surfactant axis to solutions richer in additive.The strong-associate stability of ionic surfactants is also manifested by the lamellar liquid-crystalline phase protruding between the two liquid phases to very high water contents5* (the liquid-crystal phases are omitted from fig. 1). The tie lines in the two-liquid phase region (left-hand side of the continuous solution phase) gives the distribution of the components between the liquids in equilibrium. As shown by Lawrence, the hydrotrope is distributed for short-chain homologues in favour of the water-rich r e g i ~ n . ~ For matching surfactants the distribution is almost equal between the alcohol and the aqueous phase. (The tie lines run almost parallel to the left-hand side of the triangle.) In the present case the wide and narrow water-rich phase indicates a distribution of NaC,02 in favour of the aqueous solution.However, the increased ionic strength does not enforce any marked salting-out of pentanol from the aqueous phase. 33 The Binary Systems Water-Pentanol and Water-Sodium Propionate In the dilute aqueous solutions short-chain alcohols show complex behaviour appearing as a minimum in the apparent and partial molar volumes. The minimum is shifted towards lower concentrations when the chain length is extended from methanol to propan01.~~ Hvidt et al. explained the minimum on the basis of a 'primitive equilibrium mixture model '.35 The volumetric parameters found characterize the highly cooperative association of water around the non-polar alkyl groups (hydrophobic solvation), giving a positive contribution, and the strong increase in the extent of solvation of the hydroxy groups, giving rise to a negative contribution. The small change found for &(C50H) up to the phase-separation limit (fig. 3) indicates that an efficient compensation between the two abovementioned effects occur.Since the slope is negative, then according to the model of Hvidt et al. hydrophobic82 Action of Aqueous Sodium Propionate on Pentanol 0.00 0.02 0.04 0.06 0.08 - ' t 18.0 -- I 0.70 0.80 0.90 1.00 1001 t 1 , . I X(C5 OH) 0.70 0.80 0.90 1.00 Fig. 3. Apparent molar volumes of both components of the binary system water-pentanol at 298.15 K. The upper scale refers to dilute aqueous solutions of pentanol [squares are experimental results, dots are from ref. (37)] and the lower to water diluted in pentanol (diamonds).solvation predominates in the dilute aqueous region. Another view is that the hydrocarbon residue induces a water structurization which is further enforced when the hydration shells initially overlap.36 Jolicoeur et al. investigated the volumetric and heat-capacity behaviour of a large number of alcohols in water.37 They found that the concentration dependence of the apparent molar volume was linearly and negatively dependent on the limiting volume of the alcohols in water and concluded that this was related to the hydrophobicity of the alcohol. Our concentration dependence and limiting value of 102.82 cm3 mol-l and B, = - 5.07 cm3 mo1-2 kg, respectively, are in close agreement with their values of &? = 102.88 cm3 mol-l and B, = - 4.55 cm3 molt2 kg (fig.3). Dilute solutions of water in alcohols have a special significance when one is trying to interpret the intermolecular hydrogen-bond equilibria, owing to the comparatively large solubility of water in all liquid alcohol^.^! 3 2 9 33 To our knowledge there was no systematic study focusing on the thermodynamic state of water diluted in alcohols prior to the paper of Jolicoeur et all6 They showed that the limiting volume of water in pentanol at 288.15, 298.15 and 308.15 K was 16.60, 16.86 and 17.25 cm3 mol-l, respectively. The values0. Hanskn and J . B. Rosenholm 83 found are close to the limiting volumes of 16.53, 16.89 and 17.33 cm3 mol-l reported by Sakurai and N a k a g a ~ a . ~ ~ Our limiting value of water, 16.93 cm3 mol-l, is close to the values reported for 298.15 K.The low molar volume of water should be connected with strong intermolecular hydrogen bonding.16 Fig. 3 illustrates how the initial limiting state is changed upon addition of water. As is seen, the slope of the apparent molar volume of water is positive, while a slight decrease is found for pentanol. One may interpret this observation as a partial liberation of water from the previously denser state to be dispersed freely in the solvent. In accordance with the negative slope of &(C205) part of the water remains tightly bound to the intermolecular complexes (J. B. Rosenholm, unpublished results). The point of saturation of water in pentanol is not reached in fig. 3. Its logarithmic temperature dependence is zero33 which, assuming ideal behaviour, implies that the phase separation is characterized by zero enthalpy or that both the enthalpy and entropy of the phase transition are zero.Similarly as for the alcohols, the thermodynamic behaviour of a number of straight- chain, branched, cyclic and aromatic surfactants having an equal number of carbon atoms have been rationalized using the surface area of the hydrocarbon residue.39 Fig. 4 illustrates the initial concentration dependence of aqueous sodium propionate solutions. The initial slope is only slightly positive ( B , = 0.9 cm3 mo1-2 kg) when corrected for ionic interactions, as is seen from the extended Debye-Huckel limiting slope (insert).25 This behaviour is typical for most surfactants in the range where no soiute-solute interaction is expected to occur.4o Since propionate has been found to be the last representative of the homologous series of sodium alkyl carboxylates not showing extended as~ociation,~~ 417 42 the interaction should be predominantly ionic in all solutions.The hydrocarbon residue is, however, still large enough to initiate typical hydrophobic effects on water s t r ~ c t u r e . ~ ~ - ~ ~ If the model of Hvidt is applied to this binary system also, the increase in the apparent molar volume of sodium propionate may be interpreted as a polar solvation effect. This is also evident from the positive change in the apparent molar volume of water as the hydrotrope concentration is increased (fig. 5). The Ternary System Water-Sodium Propionate-Pentanol The changes recorded accompanying the dilution of solutions of different molar ratios of pentanol to sodium propionate with water are shown in fig.5. The binary systems discussed above represent both extremes of an infinite and a zero molar ratio. The lines were chosen to record the changes occurring when the pentanol continuous phase is converted into an hydrotrope solution. Starting from the binary system of sodium propionate in water (fig. 5, line 4) it may be concluded that the overall change found (ca. 8 cm" mol-l) is close to values found for surfactants upon micellization.48 Although it seems unjustified to assume any extended association for propionate, the large positive change in apparent molar volume indicates significant changes in the environment of the hydrotrope. The full miscibility with pentanol indicates that most of the water may be assumed to be bound to the ions.The predominance of ionic hydration is supported by the nearly identical dependence of the apparent molar volumes on x(H,O) found for water and the salt (independent if the molar ratio of pentanol to sodium propionate is increased; lines 2-4 in fig. 5). The apparent molar volume of water seems to increase to very high values, which may be taken as evidence for a bulky ice-like hydration structure. When investigating the apparent molar volume of pentanol one may conclude that larger changes are produced when changing the molar ratio of pentanol to hydrotrope than upon dilution with water. In comparison with the binary system given in fig. 3 we note that the limiting volume of pentanol in water is 102.82 cm3 mol-l, i.e.some 6 cm3 mol-i lower than in the pure state. For the solutions discussed (lines 2 and 3, fig. 5) we observe a twofold but positive change.84 Action of Aqueous Sodium Propionate on Pentanol 64'62 .O 1 a a a a 0.00 0.04 0.08 0.12 0.16 X(NaC, 0,) Fig. 4. Apparent molar volume of aqueous sodium propionate solutions at 298.15 K in the most dilute region [asterisks and circles from ref. (25), triangles from ref. (16)]. The extended Debye-Hiickel limiting slope is given above: 4: = 53.4 cm3 mol-l, B, = 0.9 cm3 mol-* kg [data from ref. (25)]. In order to analyse further the state of the sparingly soluble pentanol we measured the change in volume as x(C,OH) was varied, keeping the molar ratio of water to sodium propionate constant (fig.6). Initially the apparent molar volume of pentanol remains constant upon dilution with the aqueous hydrotrope solution. When a high concentration of aqueous sodium propionate solution is approached there is, however, a dramatic increase ir. the volume of pentanol. Only by considering that the change upon micellization of surfactants is at the most of the order of 12-1 3 cm3 mol-1 can the increase be appreciated. There is, on the other hand, a very small variation in the apparent molar volumes of water and propionate over the same concentration range. This indicates that they are only marginally affected by mixing with pentanol. The small pocket observable in the dependence of the volumes of water and salt on the pentanol content is probably due to inaccuracy in the measurements.0.Hans& and J . B. Rosenholm 85 1 0 0 o! i i / I I , , , I I 0 0 0 0 0 0 t' 0 (D 0 0 9 7 0 286 Action of Aqueous Sodium Propionate on Pentanol N 0, 0 0, I0. Hans& and J . B. Rosenholm 87 The interaction between pentanol and sodium propionate was checked by keeping the weight fraction of water constant (line C, fig. 6). Although the mole fraction of water varies we note that the lines corresponding to the apparent molar volumes of both water and sodium propionate are almost vertical, illustrating the prime importance of water for hydration of the salt. Interestingly, the volumetric state of pentanol is almost equally dependent on the pentanol mole fraction, as it was when the molar ratio of water to hydrotrope was kept constant (line B).The key to the effect thus probably lies in the dissociation of the pentanol complexes when diluted in the hydrotrope solutions. The change in volume resembles the situation found when diluting alcohols in h y d r o c a r b o n ~ , ~ ~ - ~ ~ - 49 but is much larger than the change recorded when pentanol is diluted in water (fig. 3). Furthermore, the solubilization of alcohols in true surfactant solutions produces very small changes in the apparent molar volume from the molar volume of the pure The overall behaviour may thus be interpreted by the pentanol being dissolved in an apolar (aggregate) solvent. According to the results of Treszczanowicz and Benson, the change in volume increases when the size of the solvent molecules (aggregates) increases,22! 23 but the volume may also increase owing to steric mismatching of the components.21$ 49 The large magnitude of the change in &(C,OH) and the slight variation in &(NaC,O,) suggest, however, that the specific interaction between these two components is also of considerable importance for their volumetric state.Conclusions The solution phase of the water - sodium propionate - pentanol system extends from aqueous to pentanolic solutions. The propionate is unable to associate into micelles, and pentanol is only sparingly mutually soluble with water. Since pentanol is, on the other hand, fully miscible with concentrated aqueous proprionate solutions the behaviour may be considered typical of ionic hydrotrope systems.Volumetry was chosen as a probe of interactions between the components since it sensitively monitors both large shifts in the association equilibria of complexing agents and changes in the environment of the hydrocarbon chains. The volumetric state of water and salt was predominantly determined by their mutual interaction. Pentanol, on the other hand, experiences no change in its volumetric state over most of the phase area, provided that the hydration of the propionate is constant. Below x(C,OH) x 0.2 a large, positive change is observed in the apparent molar volume of pentanol. This effect may be related to dissociation of the pentanol complexes when diluted in the apolar hydrotrope solution. The relative changes in the apparent molar volumes of pentanol and sodium propionate suggest, however, that specific interactions between these two components contribute significantly to their volumetric states.The results presented suggest that, although normal solubilization is related to the hydrotropic action, there are well founded reasons to distinguish between these two effects. The restriction of the ternary solution phase to the range where all the water may be considered bound to the ionic hydrotrope, independent of the nature of the semi-polar solubilizate, marks the difference from detergentless microemulsion systems. J. B. R. thanks the Finnish Research Council for Natural Sciences for financial support. References 1 I. Danielsson and B. Lindman, Colloids Surt, 1981, 3, 391. 2 B. Lindman and H. Wennerstrom, Top.Curr. Chem., 1980, 87, 1 3 H. Wennerstrom and B. Lindman, Phys. Rep., 1979, 52, 1. 4 H-F. Eicke, Top. Curr. 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Eriksson, Thesis (Abo Akademi, SF-20500 Abo 50, Finland, 1982). 43 H. Snell and J. Greyson, J . Phys. Chem., 1970, 74, 2148. 44 J. Davies, S. Osmondroyd and M. C. R. Symons, J. Chem. Soc., Faraday Trans. 2, 1972, 4, 686. 45 0. D. Bonner, R. K. Arisman and C. F. Jumper, Z . Phys. Chem. (Leipzig). 1977, 258, 49. 46 J. Paquette and C. Jolicoeur, J. Solution Chem., 1977, 6. 1403. 47 C. Jolicoeur, J. Paquette and M. Lucas, J. Phys. Chem., 1978, 82, 1051. 48 J. B. Rosenholm, Colloid Polym. Sci., 1981, 259, 11 16. 49 K. N. Marsh and C. Burlitt, J . Chem. Thermodyn., 1975, 7, 955. ed. K. L. Mittal and E. J. Fendler (Plenum Press, New York, 1982), vol. 1, p. 431. p. 279. 1975), vol. 2, p. 339. Puper 5/370; Received 4th Murch, 1985

ISSN:0300-9599    

DOI:10.1039/F19868200077

出版商:RSC    

年代:1986

数据来源: RSC