摘要:

Contents 3663 3669 3675 3683 3693 370 1 3709 3717 3725 3737 Normal and Abnormal Electron Spin Resonance Spectra of Low-spin Cobalt(r1) IN,]-Macrocyclic Complexes. A Means of Breaking the Co-C Bond in B12 Co-enzyme M. Green, J. Daniels and L. M. Engelhardt The Interaction between Superoxide Dismutase and Doxorubicin. An Electron Spin Resonance Approach V. Malatesta, F. Morazzoni, L. Pellicciari-Bollini and R. Scotti Biomolecular Dynamics and Electron Spin Resonance Spectra of Copper Complexes of Antitumour Agents in Solution. Part 2.-Rifamycins R. Basosi, R. Pogni, E. Tiezzi, W. E. Antholine and L. C. Moscinsky An Electron Spin Resonance Investigation of the Nature of the Complexes formed between Copper(I1) and Glycylhistidine D. B. McPhail and B. A. Goodman A Vibronic Coupling Approach for the Interpretation of the g-Value Temperature Dependence in Type-I Copper Proteins M.Bacci and S. Cannistr aro The Electron Spin Resonance Spectrum of Al[C,H,] in Hydrocarbon Matrices J. A. Howard, B. Mile, J. S. Tse and H. Morris N; and (CN); Spin-Lattice Relaxation in KCN Crystals H. J. Kalinowski and L. C. Scavarda do Carmo Single-crystal Proton ENDOR of the SO, Centre in y-Irradiated Sulphamic Acid N. M. Atherton, C. Oliva, E. J. Oliver and D. M. Wylie Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice 1,. Part 1.-The 0- Radicals Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice I,. Part 2.-The HO, Radicals J. Bednarek and A. Plonka J. Bednarek and A. PlonkaContents 3663 3669 3675 3683 3693 370 1 3709 3717 3725 3737 Normal and Abnormal Electron Spin Resonance Spectra of Low-spin Cobalt(r1) IN,]-Macrocyclic Complexes.A Means of Breaking the Co-C Bond in B12 Co-enzyme M. Green, J. Daniels and L. M. Engelhardt The Interaction between Superoxide Dismutase and Doxorubicin. An Electron Spin Resonance Approach V. Malatesta, F. Morazzoni, L. Pellicciari-Bollini and R. Scotti Biomolecular Dynamics and Electron Spin Resonance Spectra of Copper Complexes of Antitumour Agents in Solution. Part 2.-Rifamycins R. Basosi, R. Pogni, E. Tiezzi, W. E. Antholine and L. C. Moscinsky An Electron Spin Resonance Investigation of the Nature of the Complexes formed between Copper(I1) and Glycylhistidine D. B. McPhail and B. A. Goodman A Vibronic Coupling Approach for the Interpretation of the g-Value Temperature Dependence in Type-I Copper Proteins M. Bacci and S. Cannistr aro The Electron Spin Resonance Spectrum of Al[C,H,] in Hydrocarbon Matrices J. A. Howard, B. Mile, J. S. Tse and H. Morris N; and (CN); Spin-Lattice Relaxation in KCN Crystals H. J. Kalinowski and L. C. Scavarda do Carmo Single-crystal Proton ENDOR of the SO, Centre in y-Irradiated Sulphamic Acid N. M. Atherton, C. Oliva, E. J. Oliver and D. M. Wylie Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice 1,. Part 1.-The 0- Radicals Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice I,. Part 2.-The HO, Radicals J. Bednarek and A. Plonka J. Bednarek and A. Plonka

ISSN:0300-9599    

DOI:10.1039/F198783FX029

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

Electrochemistry Group Workshop on Electrochemical Techniques and Instruments To be held at the University of Warwick on 6-7 January 1988 Further information from Dr P. N. Bartlett, Department of Chemistry, University of Warwick, Coventry CV4 7AL Surface Reactivity and Catalysis Group with the Process Technology Group and the Institute of Chemical Engineers Opportunities for Innovation in the Application of Catalysis To be held at Queen Mary College, London on 6-7 January 1988 Further information from Professor J. Pritchard, Queen Mary College, London Division with the Institute of Mathematics and its Applications Mathematical Modelling of Semiconductor Devices and Processes To be held at the University of Loughborough on 7-8 January 1988 Further information from the Institute of Mathematics, Maitland House, Warrior Square, Southend-on-Sea SS1 2JY Division London Symposium: Modern Electrochemical Systems To be held at Imperial College, London on 12 January 1988 Further information from Mrs Y.A. Fish, Royal Society of Chemistry, Burlington House, London W1V OBN Polymer Physics Group with the 3Ps Group Plastics, Packaging and Printing To be held at the Institute of Physics, 47 Belgrave Square, London on 18 February 1988 Further information from Dr M. Richardson, National Physical Laboratory, Teddington, Middlesex l w 1 1 OLW Theoretical Chemistry Group Postgraduate Students’ Meeting To be held at University College, London on 2 March 1988 Further information from Dr G. Doggett, Department of Chemistry, University of York, York Colloid and Interface Science Group with The Society of Chemical Industry and British Radio frequency Spectroscopy Group Spectroscopy in Colloid Science To be held at the University of Bristol on 5-7 April 1988 Further information from Dr R. Buscall, ICI Corporate Colloid Science Group, PO Box 11, The Heath, Runcorn WA7 40E Annual Congress: Division with Electrochemistry Group Solid State Materials in Electrochemistry To be held at the University of Kent, Canterbury on 12-15 April 1988 Further information from Dr J.F. Gibson, Royal Society of Chemistry, Burlington House, London W1V OBN Electrochemistry Group with The Society of Chemical Industry Electrolytic Bubbles To be held at Imperial College, London on 31 May 1988 Further information from Professor W. J. Albery, Department of Chemistry, Imperial College of Science and Technology, South Kensington, London SW7 2AY Electrochemistry Group with The Society of Chemical Industry Chlorine Symposium To be held at the Tara Hotel, London on 1-3 June 1988 Further information from Dr S.P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GLI 3 9BP Gas Kinetics Group Xth International Symposium on Gas Kinetics To be held at University College, Swansea on 24-29 July 1988 Further information from Dr G. Hancock, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 302 (xiii)Electrochemistry Group Workshop on Electrochemical Techniques and Instruments To be held at the University of Warwick on 6-7 January 1988 Further information from Dr P.N. Bartlett, Department of Chemistry, University of Warwick, Coventry CV4 7AL Surface Reactivity and Catalysis Group with the Process Technology Group and the Institute of Chemical Engineers Opportunities for Innovation in the Application of Catalysis To be held at Queen Mary College, London on 6-7 January 1988 Further information from Professor J. Pritchard, Queen Mary College, London Division with the Institute of Mathematics and its Applications Mathematical Modelling of Semiconductor Devices and Processes To be held at the University of Loughborough on 7-8 January 1988 Further information from the Institute of Mathematics, Maitland House, Warrior Square, Southend-on-Sea SS1 2JY Division London Symposium: Modern Electrochemical Systems To be held at Imperial College, London on 12 January 1988 Further information from Mrs Y.A. Fish, Royal Society of Chemistry, Burlington House, London W1V OBN Polymer Physics Group with the 3Ps Group Plastics, Packaging and Printing To be held at the Institute of Physics, 47 Belgrave Square, London on 18 February 1988 Further information from Dr M. Richardson, National Physical Laboratory, Teddington, Middlesex l w 1 1 OLW Theoretical Chemistry Group Postgraduate Students’ Meeting To be held at University College, London on 2 March 1988 Further information from Dr G. Doggett, Department of Chemistry, University of York, York Colloid and Interface Science Group with The Society of Chemical Industry and British Radio frequency Spectroscopy Group Spectroscopy in Colloid Science To be held at the University of Bristol on 5-7 April 1988 Further information from Dr R.Buscall, ICI Corporate Colloid Science Group, PO Box 11, The Heath, Runcorn WA7 40E Annual Congress: Division with Electrochemistry Group Solid State Materials in Electrochemistry To be held at the University of Kent, Canterbury on 12-15 April 1988 Further information from Dr J. F. Gibson, Royal Society of Chemistry, Burlington House, London W1V OBN Electrochemistry Group with The Society of Chemical Industry Electrolytic Bubbles To be held at Imperial College, London on 31 May 1988 Further information from Professor W. J. Albery, Department of Chemistry, Imperial College of Science and Technology, South Kensington, London SW7 2AY Electrochemistry Group with The Society of Chemical Industry Chlorine Symposium To be held at the Tara Hotel, London on 1-3 June 1988 Further information from Dr S. P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GLI 3 9BP Gas Kinetics Group Xth International Symposium on Gas Kinetics To be held at University College, Swansea on 24-29 July 1988 Further information from Dr G. Hancock, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 302 (xiii)

ISSN:0300-9599    

DOI:10.1039/F198783BX031

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

ISSN 0300-9599 JCFTAR 83(8) 2261-2692 (1 987) JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions I Physical Chemistry in Condensed Phases 226 1 227 1 2279 2289 2301 231 1 2317 233 1 2347 2359 2365 238 1 239 1 2407 242 1 2433 2449 75 CONTENTS Ionization Equilibria in Solutions of Cobalt(I1) Thiocyanate in N,N-Di- methylformamide Electron Spin Resonance Investigations of Ruthenium supported on y-Alumina M. G. Cattania Sabbadini, A. Gervasini, F. Morazzoni and D. Strumulo Study of the Support Evolution through the Process of Preparation of Rhodium/Lanthana Catalysts S. Bernal, F. J. Botana, R. Garcia, F. Ramirez and J. M. Rodriguez-Izquierdo Thermodynamic Properties of the PMMA-Acetonitrile- 1,4-Dioxane System I. Katime and J. Ramon Ochoa Molecular Mobility of Methane adsorbed on ZSM-5 containing CO-adsorbed Benzene, and the Location of the Benzene Molecules C.Forste, A. Germanus, J. KHrger, H. Heifer, J. Caro, W. Pilz and A. Zikanova Non-ideal Behaviour of Benzene Solutions of Tri-n-octylammonium Bromide and Cyclohexanol Corrosion of Ruthenium Dioxide Hydrate by CeIV Ions and other Oxidants A. Mills, S. Giddings and I. Patel Thermally Activated Ruthenium Dioxide Hydrate. A Reproducible, Stable Oxygen Catalyst Interfacial Tension Minima in Oil-Water-Surfactant Systems. Effects of Cosurfactant in Systems containing Sodium Dodecyl Sulphate R. Aveyard, B. P. Binks and J. Mead The Mechanism of Hydrogenolysis and Isomerization of Oxacycloalkanes on Metals. Part 8 .-New Results on the Mechanism of Hydrogenolysis of Oxiranes on Platinum and Palladium F.Notheisz, A. G. Zsigmond, M. Bart6k and G. V. Smith Primary Processes of Stabilizer Action in Radiation-induced Alkane Oxidation 0. Brede, R. Hermann and R. Mehnert Photoinduced Reactions of Methane with Molybdena Supported on Silica W. Hill, N. Shelimov and V. B. Kazansky Adsorption, Decomposition and Surface Reactions of Methyl Chloride on Metal Films of Iron, Nickel, Palladium, Lead, Gold and Copper A-K. M. Ali, J. M. Saleh and N. A. Hikmat Rotating Diffusion Cell Studies of Microemulsion Kinetics W. J. Albery, R. A. Choudhery, N. Z. Atay and B. H. Robinson Reactions of Alkylperoxyl Radicals in Solution. Part 1 .-A Kinetic Study of Self- reactions of 2-Propylperoxyl Radicals between 135 and 300 K J. E. Bennett, G. Brunton, J. R. Lindsay Smith, T.M. F. Salmon and D. J. Waddington Reactions of Alkylperoxyl Radicals in Solution. Part 2.-A Kinetic and Product Study of Self-reactions of 2-Propylperoxyl Radicals between 253 and 323 K J. E. Bennett, G. Brunton, J. R. Lindsay Smith, T. M. F. Salmon and D. J. Waddington Refractive Index and Excess Volume for Binary Liquid Mixtures. Part 1.- Analyses of New and Old Data for Binary Mixtures M. Nakata and M. Sakurai M. Pilarczyk, W. Grzybkowski and L. Klinszporn C. Klofutar and S. Paljk A. Mills, S. Giddings, I. Patel and C. Lawrence FAR IContents Sodium Ion Exchange on the 1,4,7,10,13,16-Hexaoxaoctadecanesodium( I) Cation (ma. 18C6]+) in Several Solvents. A Sodium-23 Nuclear Magnetic Resonance Study S. F. Lincoln, A. White and A. M. Hounslow Volume and Compressibility Changes in Mixed-salt Solutions at 25 "C K.Patil and G. Mehta Mechanism of Deuterium Addition and Exchange with Propene over Ni/SiO, and Pt/SiO, Catalysts at Low Temperatures Time-resolved Reflection Spectrum of Ordered Structure of Monodispersed Polystyrene Spheres in an Electric Field Effect of Neutral Polymers on the Ordering of Monodispersed Polystyrene Spheres T. Okubo Effect of Solvent on the Reactions of Coordination Complexes. Part 1 .--Kinetics of Solvolysis of cis-(Bromo)(benzimidazole)bis(ethylenediamine)cobalt( 111) in Methanol-Water Media A. C. Dash and N. Dash Towards a Complete Configurational Theory of Non-equilibrium Polymer Adsorption W. Barford and R. C. Ball Ultrasonic Relaxation Studies associated with the Interactions of Acetic Acid with Some Polyvinylpyridines in Aqueous Solution M.Stuckey, E. Wyn- Jones and T. Akasheh Solvent and Substituent Effects on Intramolecular Charge Transfer of Selected Derivatives of 4-Trifluoromethyl-7-aminocoumarin 35CI Nuclear Quadrupole Resonance and Infrared Spectroscopic Studies of Hydrogen Bonding in Complexes of Trichloroacetic Acid with Various Nitrogen and Oxygen Bases B. Nogaj, B. Brycki, Z. Dega-Szafran, M. Szafran and M. Makkowiak A Dye-sensitized Photocatalyst (p-Type CuCNS) for the Generation of Oxygen from Aqueous Persulphate K. Tennakone, S. Wickramanayake and M. U. Gunasekara The Two-electron Oxidation of Methyl Viologen. Detection and Analysis of Two Fluorescing Products D. W. Bahnemann, C-H. Fischer, E. Janata and A. Henglein An In Situ Mossbauer Spectroscopic Investigation of Titania-supported Iron- Ruthenium Catalysts F.J. Berry, L. Liwu, D. Hongzhang, L. Dongbai, T. Renyuan, W. Chengyu and Z. Su Enthalpies of Transfer of Tetra-alkylammonium Halides from Water to Water- Propan-1-01 Mixtures at 25 "C Coupled 13C Longitudinal and Transverse Magnetic Relaxation in Micellar and Non-micellar Sodium Octanoate F. Heatley Characterization of CO-Rh Species formed on Rh-Y Zeolite by Temperature- programmed Desorption and Infrared Techniques N. Takahashi, A. Mijin, T. Ishikawa, K. Nebuka and H. Suematsu Oxidation of 2,4-Dibromo-6-nitroaniline in Aqueous Sulphuric Acid Solutions on a Platinum Electrode Extended X-Ray Absorption Fine Structure Study of the Reaction between Silica-supported Copper(I1) Oxide Catalysts and Acetic Acid M.Nomura, A. Kazusaka, Y. Ukisu and N. Kakuta Electron-donor-Electron-acceptor Association Constants of Pyrene with 2,4,6- Trinitrotoluene in Solution determined by 'H-Nuclear Magnetic Resonance from Non-linear Scatchard Plots J. A. Chudek, R. Foster and F. Page Methyl Orange as a Probe of the Semiconductor-Electrolyte Interfaces in CdS Suspensions Complexation and Transfer Free Energies of Metal-ion Dibenzocryptates A. F. Danil de Namor, F. Femandez Salazar and P. Greenwood S. Naito and M. Tanimoto T. Okubo G. Chu and F. Yangbo G. Carthy, D. Feakins and W. E. Waghome S. Arias, E. Briqas and J. M. Costa A. Mills and G. Williams 2459 2467 2475 2487 2497 2505 2515 2525 2533 254 1 2553 2559 2573 2585 2593 2605 2619 2635 264 1 2647 2663Con tents 267 1 Hemimicelle Formation of Cationic Surfactants at the Silica Gel-Water Inter- face Y. Gao, J. Du and T. Gu 268 1 Determination of the Distribution of Aluminium in Zeolitic Frameworks T. Takaishi 75-2Con tents 267 1 Hemimicelle Formation of Cationic Surfactants at the Silica Gel-Water Inter- face Y. Gao, J. Du and T. Gu 268 1 Determination of the Distribution of Aluminium in Zeolitic Frameworks T. Takaishi 75-2

ISSN:0300-9599    

DOI:10.1039/F198783FP097

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

JOURNAL OF THE CHEMICAL SOCIETY 1287 1307 317 325 335 1367 1391 141 1 1427 1439 1445 1453 1465 1475 1487 1509 1519 Faraday Transactions II, lssue8,1987 Molecular and Chemical Physics For the benefit of readers of Faraday Transactions I, the contents list of Faraday Transactions 11, Issue 8, is reproduced below. Diffusiophoresis of a Rigid Sphere through a Viscous Electrolyte Solution D. C. Prieve and R. Roman Atomic Orbital Populations and Atomic Charges from Self-consistent Field Molecular Orbital Wavefunctions Energy Calibration and Peak Shifts of Ni,Fe Auger Spectra H. Saijo and R. Boucarut Magnetic-field Effect on Exciplex Luminescence. The trans-Anethole-9- Cyanophenanthrene System S. Basu, D. Nath and M. Chowdhury Invariants of Spherical Harmonics as Order Parameters in Liquids A.Baran- yai, A. Geiger, P. R. Gartrell-Mills, K. Heinzinger, R. L. McGreevy, G. Palinkas and I. Ruff Energy Levels of Ho3+ in HoCli- P. A. Tanner Energy Transfer in Spherical Geometry. Application to Micelles M. N. Berberan-Santos and M. J. E. Prieto The Conformations of some Simple Alcohols and Thiols C. Plant, K. Spencer and J. N. Macdonald Nuclear Magnetic Resonance Autocorrelation Spectroscopy K. Roth The Confined Rotator Model with the Harmonic Potential K. Pasterny and A. Kocot Neutron Scattering from Concentric Cylinders. Intraparticle Interference Function and Radius of Gyration I. Livsey Kinetics and Chemiluminescence in the Reaction of N Atoms with 0, and 0, A. J. Barnett, G. Marston and R. P. Wayne Absolute Absorption Cross-section Measurements on NO,.Evaluation of the Titration of NO, by NO in the Determination of Absolute Concentrations C. E. Canosa-Mas, M. Fowles, P. J. Houghton and R. P. Wayne Kinetics and Mechanism of Ultrafast Adiabatic Intermolecular and Intramolecular Proton- transfer Reactions of a Protonated Trimethyl- pyrichrominium Ion in its Fluorescent State J. Konijnenberg, A. H. Huizer, F. Th. Chaudron, C. A. G. 0. Varma, B. Marciniak and S. Paszye Photophysics and Photochemistry of Sulphonated Derivatives of 9,lO- Anthraquinone. ' Strong ' versus ' Weak ' Sensitisers J. N. Moore, D. Phillips, N. Nakashima and K. Yoshihara Arrhenius Parameters for the Reaction C,H, + 0, C,H, + HO, K. G. McAdam and R. W. Walker Time-resolved Resonance Raman Spectroscopy of the Triplet State and K.E. Edgecombe and R. J. Boyd (9Semi-reduced Form of Duroquinone I. McCubbin, D. Phillips and R. E. Hester 1525 Theories of Cloud-curve Phase Separation in Non-ionic Alkyl Polyoxyethyl- ene Micellar Solution 1543 The Temperature Dependence of the Yellow Glow from Active Nitrogen A. P. Billington, P. M. Borrell, P. Borrell and D. S. Richards 1555 High-temperature Photoelectron Spectroscopy. A Study of Niobium Monoxide and Tantalum Monoxide J. M. Dyke, A. M. Ellis, M. FehCr, A. Moms, A. J. Paul and J. C. H. Stevens 1 567 Temperature Dependence of the Luminescence of 2-Aminophenyl Phenylsulphone in Polar Solvents F. Barigelletti H. Evans, D. J. Tildesley and C. A. Leng 612225 612391 71026 71095 712 18 7/280 71236 71303 71530 7/584 The following papers were accepted for publication in J.Chern. Soc., Faraday Transactions I, during May. Rotational Relaxation Time and Conformation of Salt-free Sodium Polysty- renesulphonate as studied by the Conductance Stopped-flow Technique T. Okubo Micelle Formation of Ionic Amphiphiles : Thermochemical Test of a Thermodynamic Model I. Johnson, B. Jonsson and G. Olofsson Tin Oxide Surfaces. Part 1 7.-An Infrared and Thermogravimetric Analysis of the Thermal Dehydration of Tin(1v) Oxide Gel P. G.Harrison and A. Guest Radiotracer Studies of Chemisorption on Copper-based Catalysts. Part 1.-The Adsorption of Carbon Monoxide and Carbon Dioxide on Copper/ Zinc Oxide/Alumina and Related Catalysts S. Kinnaird, G. Webb and G. C. Chinchen Effect of Surface Hydroxyl Density on Photocatalytic Oxygen and Hydrogen Generation in Aqueous TiO, Suspensions Single-ion Enthalpies for Transfer among Dipolar Aprotic Solvents derived from Enthalpies of Solution of Potassium and Alkaline-earth(i1) Metal Cryptates in these Solvents A.F. Danil de Namor, T. Hill, R. A. C. Walker, E. C. Viguria and H. Berroa de Ponce Effects of Non-ionic Micelles on the Kinetics of the Electron-transfer Reactions of Iron(rr1) with Substituted Ferrocenes A. I. Carbone, F. P. Cavasino and C. Sbriziolo Micellar Structure and Micellar Inner Polarity of Octaethyleneglycol-n-Alkyl Ethers Y. Saito, I. Anazawa and T. Sat0 Thermodynamics of Ion Solvation in Mixed Aqueous Solvents. Part 1 .-Some Free Energies of Transfer of Hydrochloric Acid, Alkali-metal and Alkaline-earth Chlorides, and Potassium Halides in the TBA-Water System at 25 "C D.Feakins, P. J. M. McCarthy and T. A. Clune Thermodynamics of Micelle Formation of Alkali-metal Perfluorononanates in Water. Comparison with Hydrocarbon Analogues I. Johnson and G. Olofsson V. Oosawa and M. Gratzel (ii)71638 71784 71785 71786 71787 71863 7/898 71899 71900 7/90 1 Absorption and Diffusion of Sulphur Dioxide into Aqueous Sodium Chloride Solutions D. G. Leaist Normal and Abnormal E.S.R. Spectra of Low-spin Cobalt(n) INa]- Macrocyclic Complexes as a Means of Breaking the Co-C Bond in B12 Co- enzyme M. Green, J. Daniels and A. Harpur E.S.R. Spectra of a Ferromagnetic Alternating Spin Chain ( S , = 112, S, = 112) A. Caneschi, D. Gatteschi, C. Zanchini and P. Rey Interaction of Carbon Monoxide with Ru 6A1,0,.An E.S.R. Investigation M. G. Cattania, A. Gervasini, F. Morazzoni, R. Scotti and D. Strumolo Spectromagnetic Evidence for Spatial Correlation of Copper Centres in Phosphate Glasses and its Effect on the Charge-transport Processes D. Nar- ducci, c. M. Mari, S. Pizzini and F. Morazzoni An E.S.R. Study of Rutile and Anatase Titanium Dioxide Polycrystalline Powders treated with Transition-metal Ions A. Amorelli, J. C. Evans, C. C. Rowlands and T. A. Egerton A Vibronic Coupling Approach for the Interpretation of the Temperature Dependence in Type I Copper Proteins M. Bacci and S. Cannistraro Interaction between Superoxide Dismutase and Doxorubicin. An E.S.R. Approach The E.S.R. Spectrum of Al[C,H,] in Hydrocarbon Matrices J. A. Howard, B. Mile, J. S. Tse and H.Morris Multiple Resonances Involving E.S.R., N.M.R. and Optical Transitions K. Mobius V. Malatesta, F. Morazzoni, L. Pellicciari-Bonllini and R. Scotti (iii)Cumulative Author Index 1987 Agnel, J-P. L., 225 Akalay, I., 1137 Akasheh, T., 2525 Akitt, J. W., 1725 Albano, K., 21 13 Alberti, A., 91 Albery, W. J., 2407 Ali, A-K. M., 2391 Allen, G. C., 925, 1355 Andersen, A., 2140 Anderson, A. B., 463 Anderson, J. B. F., 913 Antholine, W. E., 151 Ardizzone, S., 11 59 Arias, S., 2619 Atay, N. Z., 2407 Atherton, N. M., 37, 941 Aun Tan, S., 2035 Aveyard, R., 2347 Avnir, D., 1685 Axelsen, V., 107 Bahnemann, D. W., 2559 Baker, B. G., 2136 Baldini, G., 1609 Ball, R. C., 2515 Balon, M., 1029 Barford, W., 25 15 Barratt, M. D., 135 Barrer, R. M., 779 Bartok, M., 2359 Basosi, R., 151 Bastein, A.G. T. M., 2103, 2129 Bastl, Z., 51 1 Bateman, J. B., 841 Battesti, C. M., 225 Baussart, H., 1711 Becker, K. A., 535 Bell, A. T., 2061, 2086, 2087, Bennett, J.E., 1805, 2421, 2433 Berclaz, T., 401 Berleur, F., 177 Bernal, S., 2279 Berroa de Ponce, H., 1569 Berry, F. J., 615, 2573 Bertagnolli, H., 687 Berthelot, J., 231 Beyer, H. K., 51 1 Bianconi, A., 289 Binks, B. P., 2347 Bjorklund, R. B., 1507 Blandamer, M. J., 559, 865, Blyth, G., 751 Boerio-Goates, J., 1553 Au, C-T., 2047 2088 1783 Bogge, H., 2157, 2157 Bond, G. C., 1963, 2071,2088, 2129, 2130, 2133, 2138, 2140 Borbdy, G., 51 1 Botana, F. J., 2279 Boucher, E. A., 1269 Brandreth, B. J., 1835 Braquet, P., 177 Brazdil, J. F., 463 Breault, R., 21 19 Brede, O., 2365 Brillas, E., 2619 Briscoe, B.J., 938 Bruce, J. M., 85 Brunton, G., 2421, 2433 Brustolon, M., 69 Brycki, B., 2541 Budil, D. E., 13 Bugyi, L., 2015, 2015 Bulow, M., 1843 Burch, R., 913, 2087, 2130, 2134, 2135, 2141, 2250 Burgess, J., 559, 865, 1783 Burggraaf, A. J., 1485 Burke, L. D., 299 Busca, G., 853, 1591, 2213 Buscall, R., 873 Cairns, J. A., 9 13 Carley, A. F., 351 Caro, J., 1843, 2301 Carthy, G., 2585 Cassidy, J. F., 231 Celalyan-Berthier, A., 401 Chadwick, D., 2227 Chalker, P. R., 351 Chandra, H., 759 Chengyu, W., 2573 Chieux, P., 687 Chinchen, G. C., 2193 Chittofrati, A., 1159 Choudhery, R. A., 2407 Christmann, K., 1975 Chu, G., 2533 Chudek, J. A., 2641 Clark, B., 865 Clausen, B. S., 2157 Clifford, A. A., 751 Colin, A. C., 819 Coller, B. A. W., 645, 657 Coluccia, S., 477 Compostizo, A., 819 Compton, R.G., 1261 Conway, B. E., 1063 Corvaja, C., 57 Costa, J. M., 2619 Chu, D-Y., 635 Couillard, C., 125 Courbon, H., 697 Craven, J. B., 779 Crossland, W. A., 37 D’Alba, F., 267 Danil de Namor, A. F., 1569, Dash, A. C., 1307, 2505 Dash, N., 2505 Daverio, D., 705 Davies, M. J., 1347 Davoli, I., 289 Dawber, J. G., 771 de Beer, V. H. J., 2145 De Doncker, J., 125 De Laet, M., 125 De Ranter, C. J., 257 Declerck, P. J., 257 Dega-Szafran, Z., 2541 Delafosse, D., 11 37 Qelahanty, J. N., 135 Delobel, R., 1711 Despeyroux, B. M., 2081, 2135 2171, 2243, 2255 Di Lorenzo, S., 267 Diaz Peiia, M., 819 DimitrijeviC, N. M., 1193 Dodd, N. J. F., 85 Dongbai, L., 2573 Du, J., 2671 Duarte, M. A., 2133 Ducret, F., 141 Dudikova, L., 51 1 Dusaucy, A-C., 125 Eicke, H.-F., 1621 Elbing, E., 657, 645 Elders, J.M., 1725 Empis, J. M. A., 43 Endoh, A., 41 1 Engberts, J. B. F. N., 865 Evans, J. C., 43, 135 Fahim, R. B., 1601 Fan, G., 323 Fatome, M., 177 Feakins, D., 2585 Fejes, P., 1109 Fischer, C-H., 2559 Fletcher, P. D. I., 985, 1493 Flint, N. J., 167 Formaro, L., 1159 Formosinho, S. J., 431 Forrester, A. R., 21 1 Forste, C., 2301 Forster, H., 1109 Foster, R., 2641 Fraissard, J., 451 2663AUTHOR INDEX Freude, D., 1843 Freund, E., 1417 Fricke, R., 1041 Fujii, K., 675 Fujitsu, H., 1427 Galli, P., 853 Gampp, H., 1719 Gao, Y., 2671 Garbowski, E., 1469 Garcia, R., 2279 Garrido, J., 1081 Garrone, E., 1237 Gellings, P. J., 1485 Geoffroy, M., 401 Germanus, A., 2301 Gervasini, A., 705, 2271 Giddings, S., 2317, 2331 Gilbert, B. C., 77 Gilbert, R.G., 1449 Goates, J. R., 1553 Goates, S. R., 1553 Goffredi, M., 1437 Golding, P. D., 1203 Goodman, D. W., 1963, 1967, 2071, 2072, 2073, 2075, 2082, 2086, 2251, 1967 Gottschalk, F., 571 Gozzi, D., 289 Grampp, G., 161 Grant, R. B., 2035 Gratzel, M., 1101 Grauer, G. L., 1685 Grauer, Z., 1685 Gray, P., 751 Greci, L., 69 Greenwood, P., 2663 Grieser, F., 591 Grigorian, K. R., 1189 Grimblot, J., 2170 Grossi, L., 77 Groves, G. S., 1281, 11 19 Grzybkowski, W., 281, 1253, Gu, T., 2671 Guardado, P., 559 Guilleux, M.-F., 1137 Gunasekara, M. U., 2553 Hada, H., 1559 Hagele, G., 1055 Hakin, A. W., 559, 865, 1783 Halawani, K. H., 1281 Hall, D. G., 967 Hall, M. V. M., 571 Haller, G. L., 1965, 2072, 2080, 2089, 2091, 2129, 2131, 2132, 2133, 2135, 2136, 2137, 2138, 2243 226 1 Halpern, A., 219 Hamada, K., 527 Harbach, C.A. J., 2035 Harendt, C., 1975 Harland, R. G., 1261 Harrer, W., 161 Harris, R. K., 1055 Hartland, G. V., 591 Hasegawa, A., 759 Hatayama, F., 675 Haul, R., 2083 Hayashi, K., 1795 Heatley, F., 517, 2593 Hemminga, M. A., 203 Henglein, A., 2559 Henriksson, U., 15 15 Hermann, R., 2365 Herold, B. J., 43 Hertz, H. G., 687 Hidalgo, J., 1029 Higgins, J. S., 939 Hikmat, N. A., 2391 Hilfiker, R., 1621 Hill, W., 2381 Hinderman, J. P., 21 19, 2142, Hindermann, J. P., 21 19 Holden, J. G., 615 Holloway, S., 1935 Hongzhang, D., 2573 Hounslow, A. M., 2459 Howe, A. M., 985, 1007 Howe, R. F., 813 Hudson, A., 91 Hunger, M., 1843 Hunter, R., 571 Hussein, F. H., 1631 Hutchings, G. J., 571 Ikeyama, N., 1427 Imamura, H., 743 Imanaka, T., 665 Ishikawa, T., 2605 Ismail, H.M., 1601 Ito, T., 451 Iwaki, T., 943, 957 Iwamoto, E., 1641 Jackson, S. D., 1835, 905 Jaenicke, W., 161 Janata, E., 2559 Janes, R., 383 Joyner, R. W., 1945, 1965, 2074, 2085, 2138, 2249 Juszczyk, W., 1293 Kakuta, N., 1227, 2635 Kaneko, M., 1539 Kanno, T., 721 Karger, J., 1843, 2301 Kariv-Miller, E., 1 169 Karpinski, Z., 1293 Katime, I., 2289 Kato, C., 1851 Kawaguchi, T., 1579 Kazansky, V. B., 2381 Kazusaka, A., 1227, 2635 Kerr, C W., 85 Kiennemann, A., 21 19 King, D. A., 1966, 2001, 2079, 2080, 2081 Kira, A., 1539 Kiricsi, I., 1109 Kitaguchi, K., 1395 Kiwi, J., 1101 Klein, J., 1703 2143 (v) Klinszporn, L., 2261 Klofutar, C., 23 11 Knozinger, H., 2088, 2171 Kobayashi, J., 1395 Kobayashi, M., 721 Koda, S., 527 Kondo, Y., 1089 Konishi, Y., 721 Koopmans, H. J.A., 1485 Kordulis, C., 627 Korf, S. J., 1485 Koutsoukos, P. G., 1477 Kowalak, S., 535 Kubelkova, L., 51 1 Kubokawa, Y., 675, 1761 Kumamaru, T., 1641 Kuroda, K., 1851 Kusabayashi, S., 1089 Kuzuya, M., 1579 La Ginestra, A., 853 Lackey, D., 2001, 2001 Lajtar, L., 1405 Lambelet, P., 141 Lambert, R. M., 1963, 1964, 2035, 2082,2083,2084 Lamotte, J., 1417 Lang, N. D., 1935 Laschi, F., 1731 Laurin, M., 21 19 Lavagnino, S., 477 Lavalley, J-C., 1417 Lawin, P. B., 1169 Lawrence, C., 2331 Lawrence, S., 1347 Le Bras, M., 1711 Leaist, D. G., 829 Lecomte, C., 177 Lee, E. F. T., 1531 Lengeler, B., 2157 Lercher, J. A., 2080, 2255 Leroy, J-M., 1711 Letellier, P., 1725 Levin, M. E., 2061 Lin, C. P., 13 Lin, Y-J., 2091 Linares-Solano, A., 1081 Lincoln, S.F., 2459 Lindgren, M., 893, 1815 Lippens, B. C., Jr, 1485 Liu, R-L., 635 Liu, T., 1063 Liwu, L., 2573 Loliger, J., 141 Lorenzelli, V., 853, 1591 Loretto, M. H., 615 Luckham, P. F., 1703 Lund, A., 893, 1815, 1869 Luo, H., 2103 Lycourghiotis, A., 627, Lynch, J., 1417 Lyons, C. J., 645 Lyons, M. E. G., 299 McAleer, J. F., 1323 Korth, H-G., 95 1179AUTHOR INDEX McCarthy, S. J., 657 McDonald, J. A., 1007 Machin, W. D., 1203 Mackowiak, M., 2541 MacLaren, J. M., 1945, 1965 McLauchlan, K. A., 29 Maestre, A., 1029 Maezawa, A., 665 Makela, R., 51 Manfredi, M., 1609 Maniero, A. L., 69, 57 Manzatti, W., 2213 Marchese, L., 477 Marcus, Y., 339 Mari, C. M., 705 Markarian, S. A., 1189 Martin Luengo, M. A., 1347, Martin-Martinez, J. M., 1081 Mashkovsky, A. A., 1879 Masiakowski, J.T., 893, 1869 Masliyah, J. H., 547 Matralis, H., 1179 Matsuura, H., 789 Maxwell, I. A., 1449 Mead, J., 2347 Mehandru, S. P., 463 Mehnert, R., 2365 Mehta, G., 2467 Meriaudeau, P., 21 13, 2140 Merwin, L. H., 1055 Micic, 0. I., 1127 Mijin, A., 2605 Mills, A., 2317, 2331, 2647 Mintchev, L., 2213 Miyahara, K., 1227 Miyata, H., 675, 1761, 1851 Mochida, I., 1427 Molina-Sabio, M., 1081 Monk, C. B., 425 Montagne, X., 1417 Morazzoni, F., 705, 2271 Morimoto, T., 943, 957 Moseley, P. T., 1323 Moyes, R. B., 905 Mozzanega, M-N., 697 Muller, A., 2157 Muiioz, M. A., 1029 Nabiullin, A. A., 1879 Naccache, C., 21 13 Nagao, M., 1739 Nagaoka, T., 1823 Nair, V., 487 Naito, S., 2475 Nakai, S., 1579 Nakajima, T., 13 15 Nakata, M., 2449 Napper, D. H., 1449 Narayanan, S., 733 Narducci, D., 705 Nayak, R.C., 1307 Nazer, A. F. M., 11 19 Nebuka, K., 2605 Nedeljkovic, J. M., 1127 Nenadovic, M. T., 1127 1651 Niccolai, N., 1731 Niemann, W., 21 57 Nishida, S., 1795 Nogaj, B., 2541 Nomura, H., 527 Nomura, M., 1227, 1779, 2635 Norris, J. 0. W., 1323 Norris, J. R., 13 Nerrskov, J. K., 1935 Notheisz, F., 2359 Nukui, K., 743 Nuttall, S., 559 O’Brien, A. B., 371 Ochoa, J. R., 2289 Odinokov, S. E., 1879 Ogura, K., 1823 Ohno, M., 1559 Ohno, T., 675 Ohshima, K., 789 Okabayashi, H., 789 Okamoto, Y., 665 Okubo, T., 2487,2497 Okuda, T., 1579 Okuhara, T., 1213 OMalley, P. J. R., 2227 Ono, T., 675, 1761 Otsuka, K., 13 15 Ott, J. B., 1553 Page, F., 2641 Paljk, s., 231 1 Pallas, N. R., 585 Parry, D. J., 77 Patel, I., 2317, 2331 Patil, K., 2467 Patrono, P., 853 Peden, C.H. F., 1967 Pedersen, E., 2157 Pedersen, J. A., 107 Pedulli, G. F., 91 Penar, J., 1405 Pendry, J. B., 1945 Perez-Tejeda, P., 1029 Pethica, B. A., 585 Pethrick, R. A., 938 Pfeifer, H., 2301 Pichat, P., 697 Pielaszek, J., 1293 Pilarczyk, M., 281, 2261 Pilz, W., 2301 Pizzini, S., 705 Poels, E. K., 2140 Pogni, R., 151 Pomonis, P., 627 Pomonis, P. J., 1363 Ponec, V., 1964, 1965, 2071, 2072, 2074, 2083, 2103, 2136, 2 138, 2 139, 2244, 225 1 Primet, M., 1469 Prins, R., 2087, 2 136, 2 137, 2145, 2169,2170, 2172 Priolisi O., 57 Pritchard, J.. 1963, 2085, 2249 Prugnola, A., 1731 Puchalska, D., 1253 Purushotham, V., 21 1 (vi) Radulovic, S., 559 Raffi, J. J., 225 Rajaram, R. R., 2130 Ramaraj, R., 1539 Ramirez, F., 2279 Ramis, G., 1591 Rees, L. V. C., 1531, 1843 Renyuan, T., 2573 Resasco, D.E., 2091 Reyes, P. N., 1347 Richards, D. G., 2138 Richter-Mendau, J., 1843 Riley, B. W., 2140, 2253 Ritschl, F., 1041 Riva, A., 2213 Riviere, J. C., 351 Roberts, M. W., 351, 2047, Robinson, B. H., 985, 1007, Rodriguez-Izquierdo, J. M., Rodriguez-Reinoso, F., 1081 Rollins, K., 1347 Roman, V., 177 RomBo, M. J., 43 Rooney, J. J., 2077, 2080, 2086, Rosseinsky, D. R., 245, 231 Rossi, C., 1731 Rowlands, C. C., 43, 135 Rubio, R. G., 819 Rudham, R., 1631 Sabbadini, M. G. C., 2271 Sakai, T., 743, 1823 Sakakini, B., 1975 Sakurai, M., 2449 Salazar, F. F., 2663 Saleh, J. M., 2391 Salmeron, M., 2061 Salmon, T. M. F., 2421, 2433 Sanchez, M., 1029 Sanfilippo, D., 2213 Sangster, D. F., 657 Saraby-Reintjes, A., 271 Sato, T., 1559 Saucy, F., 141 Savoy, M-C., 141 Sayed, M.B., 1149, 1751, 1771 Scholten, J. J. F., 1966, 2073, Schuller, B., 2103 Seebode, J., 1109 Segal, M. G., 371 Segre, U., 69 Sermon, P. A., 1347, 1369, 165 Seyedmonir, S., 813 Shelimov. B. N., 2381 Sheppard, N.. 1966, 2075 Sidahmed, I. M., 439 Simonian, L. K., 1189 Smith, D. H., 1381 Smith, G. V.. 2359 Smith. J. R. L.. 2421. 2433 2047, 2084, 2085, 2086, 2248 2407 2279 2089 2246, 2255, 2257 1667, 2175, 2243. 2256AUTHOR INDEX Soderman, O., 1515 Sokolowski, S., 1405 Solymosi, F., 2015, 2074, 2078, 2081, 2082, 2086, 2137, 2142, 2247 Somorjai, G. A., 2061 Spencer, M. S., 2193, 2245, Steenken, S., 113 Stevens, D. G., 29 Stevenson, S., 2175 Stone, F. S., 1237, 2080, 2084, Strumulo, D., 2271 Stuckey, M., 2525 Su, Z., 2573 Suda, Y., 1739 Suematsu, H., 2605 Sugahara, Y., 1851 Suppan, P., 495 Sustmann, R., 95 Suzuki, T., 1213 SvetliEid, V., 1169 Swartz.H. M., 191 Swift, A. J., 1975 Symons, M. C. R., 1, 383, 759 Szafran, M., 2541 Szostak, R., 487 Tabner, B. J., 167 Taga, K., 789 Takahashi, N., 2605 Takaishi, T., 41 1, 2681 Tan, W. K., 645 Tanaka, H., 1395 Tanaka, K., 1213, 1779, 1859 Tanaka, K-i., 1859 Tanimoto, M., 2475 Tempere, J.-F., 1137 Tempest, P. A., 925 Tennakone, K., 2553 Theocharis, C. R., 1601 2246, 2247, 2248, 2249, 2250 2254 Thiery, C. L., 225 Thomas, T. L., 487 Thomson, S. J., 1893, 1964, 1965, 2083 Thurai, M., 841 Tilquin, B., 125 Tomellini, M., 289 Tonge, J. S., 231, 245 Toprakcioglu, C., 1703 Topsse, H., 2157, 2169, 2171 Topsare, N-Y., 2157 Torregrosa, R., 108 1 Toyoshima, I., 121 3 Trabalzini, L., 151 Trifiro, F., 2213, 2246, 2251, Tsuchiya, S., 743 Tsuiki, H., 1395 Tsukamoto, K., 789 Turner, J.C. R., 937 Tyler, J. W., 925, 1355 Ueno, A., 1395 Ukisu, Y., 1227, 2635 Uma, K., 733 Unwin, P. R., 1261 Vaccari, A., 2213 Vachon, A., 177 van de Ven, T. G. M., 547 van den Boogert, J., 2103 van der Lee, G., 2103 van Santen, R. A., 1915, 1963, Varani, G., 1609 Vattis, D., 1179 Vickerman, J. C., 1975, 2075 Vincent, P. B., 225 Vink, H., 801, 941 Vissers, J. P. R., 2145 Vong, M. S. W., 1369, 1667 Vordonis, L., 627 Vuolle, M., 51 2254 1964, 2077, 2140, 2250 Vvedensky, D. D., 1945 Waddicor, J. I., 751 Waddington, D. J., 2421, Waghorne, W. E., 2585 Waller, A. M., 1261 Waters, P. N., 1601 Waugh, K. C., 2193 Wells, C. F., 939, 1119, 1281 Wells, P. B., 905 Whan, D. A., 2193 White, A., 2459 White, L.R., 591, 873 Whyman, R., 905 Wickramanayake, S., 2553 Williams, D. E., 1323 Williams, G., 2647 Williams, J. O., 323 Williams, R. J. P., 1885 Williams, W. J., 371 Wilson, H. R., 1885 Wilson, I. R., 645, 657 Winstanley, D., 1835 Wojcik, D., 1253 Wurie, A. T., 1651 Wyn-Jones, E., 2525 Xyla, A. G., 1477 Yamada, K., 743 Yamamoto, Y., 1641, 1795 Yamasaki, S., 1641 Yanagihara, Y., 1579 Yanai, Y., 1641 Yangbo, F., 2533 Yariv, S., 1685 Yonezawa, Y., 1559 Yoshino, T., 1823 Yun, D. L., 2251 Zaki, M. I., 1601 Zhang, Q., 635 Zikanova, A., 2301 Zsigmond, A. G., 2359 2433 (vii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION N o . 84 Dynamics of Elementary Gas-phase Reactions University of Birmingham, 14-16 September 1987 Organ ising 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. The final 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 SYMPOSIUM N o .23 Molecular Vibrations University of Reading, 15-16 December 1987 Organising Committee: Professor I. M. Mills (Chairman) Dr J. E. Baggott Professor A. D. Buckingham Dr M. S. Child Dr N. C. Handy Dr B. J. Howard The Symposium will focus on recent advances in our understanding of the vibrations of polyatomic molecules. The topics to be discussed will include force field determinations by both ab initio and experimental methods, anharmonic effects in overtone spectroscopy, local modes and anharmonic resonances, intramolecular vibrational relaxation, and the frontier with molecular dynamics and reaction kinetics. The final programme and application form 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 GENERAL DISCUSSION No.85 Solvat ion University of Durham, 28-30 March 1988 Organising Committee: Professor M. C. R. Symons (Chairman) Professor J. S. Rowlinson Professor A. K. Covington Dr I. R. McDonald The purpose of the Discussion is to compare solvation of ionic and non-ionic species in the gas phase and in matrices with corresponding solvation in the bulk liquid phase. The aim will be to confront theory with experiment and to consider the application of these concepts to relaxation and solvolytic processes. Contributions for consideration by the organising Committee are invited in the following areas: (a) Gas phase non-ionic clusters (b) Liquid phase non-ionic clusters (c) Gas phase ionic clusters (d) Liquid phase ionic solutions (e) Dynamic processes including solvolysis Further information may be obtained from: Mr.Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBM. Dr J. Yarwood Dr A. D. Pethybridge Professor W. A. P. Luck Dr D. A. Young THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION No. 86 Spectroscopy at Low Temperatures University of Exeter, 13-15 September 1988 Organising Committee: Professor A. C. Legon (Chairman) Dr P. B. Davies Dr B. J. Howard Dr P. R. R. Langridge-Smith Dr R. N. Perutz Dr M. Poliakoff The Discussion will focus on recent developments in spectroscopy of transient species (ions, radicals, clusters and complexes) in matrices or free jet expansions. The aim of the meeting is to bring together scientists interested in similar problems but viewed from the perspective of different environments.Contributions for consideration by the Organising Committee are invited. Titles should be submitted as soon as possible and abstracts of about 300 words by30 September 1987 to: Professor A. C. Legon, Department of Chemistry, University of Exeter, Exeter EX4 4QD. Full papers for publication in the Discussion volume will be required by May 1988.THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY WITH THE ASSOCIAZIONE ITALIANA DI CHIMICA FISICA, DIVISION DE CHlMlE PHYSIQUE OF THE SOCIETE FRANCAISE DE CHlMlE AND DEUTSCHE BUNSEN GESELLSCHAFT FUR PHYSIKALISCHE CHEMlE JOINT MEETING Structure and Reactivity of Surfaces Centro Congressi, Trieste, Italy, 13-16 September 1988 Organising Committee: M.Che V.Ponec F. S. Stone G. Ertl R. Rosei A. Zecchina The conference will cover surface reactivity and characterization by physical methods: (i) Metals (both in single crystal and dispersed form) (ii) Insulators and semiconductors (oxides, sulphides, halides, both in single crystal and dispersed forms) (iii) Mixed systems (with special emphasis on metal-support interaction) The meeting aims to stimulate the comparison between the surface properties of dispersed and supported solids and the properties of single crystals, as well as the comparison and the joint use of chemical and physical methods. Further information may be obtained from: Professor C.Morterra, lnstituto di Chimica Fisica, Corso Massimo D'Azeglio 48, 10125 Torino, Italy. THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM Orientation and Polarization Effects in Reactive Collisions To be held at the Physikzentrum, Bad Honnef, West Germany, 12-14 December 1988 Organising Committee: Professor S. Stolte Professor J. P. Simons Professor R. N. Dixon Dr K. Burnett Professor R. A. Levine The Symposium will focus on the study of vector properties in reaction dynamics and photodissociation rather than the more traditional scalar quantities such as energy disposal, integral cross-sections and branching ratios. Experimental and theoretical advances have now reached the stage where studies of Dynamical Stereochemistry can begin to map the anisotropy of chemical interactions.The Symposium will provide an impetus to the development of 3-0 theories of reaction dynamics and assess the quality and scope of the experiments that are providing this impetus. Contributions for consideration by the Organising Committee are invited in the following areas: (A) Collisions of oriented or rotationally aligned molecular reagents (B) Collisions of orbitally aligned atomic reagents (C) Photoinitiated 'collisions' in van der Waals complexes (D) Polarisation of the products of full and half-collisional processes Abstracts of about 300 words should be sent by 31 October 1987 to: Professor J. P. Simons, Department of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD Full papers for publication in the Symposium volume will be required by 15 August 1988.FARADAY DIVISION INFORMAL AND GROUP MEETINGS Industrial Physical Chemistry Group The Physical Chemistry of Small Carbohydrates (as part of the International Symposium on Solute-Solute-Solvent Interactions) To be held at the University of Regensburg, West Germany on 10-14August 1987 Further information from Dr F. Franks, Pafra Ltd, 150 Science Park, Milton Road, Cambridge CB44GG Industrial Physical Chemistry Group The Interaction of Biologically Active Molecules and Membranes To be held at Girton College, Cambridge on 8-10 September 1987 Further information from Dr T.G. Ryan, ICI New Science Group, PO Box 11, The Heath, Runcorn WA7 4QE Polymer Physics Group Biennial Meeting To be held at University of Reading on 9-1 1 September 1987 Further information from Dr D.Bassett, Department of Physics, University of Reading, Reading RG7 2AD Neutron Scattering Group Applications of Neutron and X-Ray Optics To be held at the University of Oxford on 14-15 September 1987 Further information from Dr R. K. Thomas, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ Surface Reactivity and Catalysis Group New Methods of Catalyst Preparation and Characterization To be held at Brunel University on 14-16 September 1987 Further information from: Dr M. Bowker, ICI New Science Group, PO Box 11, The Heath, Runcorn, Cheshire WA7 4QE Colloid and Interface Science Group Polydispersity in Colloid Science To be held at the University of Nottingham on 15-16 September 1987 Further information from Dr.R. Buscall, ICI plc, Corporate Colloid Science Group, PO Box 11,The Heath, Runcorn WA7 4QE Polymer Physics Group New Materials To be held at the University of Warwick on 22-25 September 1987 Further information from Dr M. J. Richardson, Division of Materials Applications, National Physical Laboratory, Queens Road, Teddington, Middlesex TW11 OLW Division Autumn Meeting Spectroscopy of Gas-phase Molecular Ions and Clusters To be held at the University of Nottingham on 22-24 September 1987 Further information from Professor J. P. Simons, Department of Chemistry, University of Nottingham, Nottingham NG7 2RD Polymer Physics Group with the Institute of Marine Engineers Polymers in a Marine Environment To be held in London on 14-16 October 1987 Dr G. J. Lake, MRPRA, Brickendonbury, Herts SG13 8NL E/ectrochemistry Group with the SCI Electrosynt hesis To be held at the University of York on 15-17 December 1987 Further information from Dr G. Kelsall, Department of Mineral Resources Engineering, Imperial College, London SW7 2 A ZNeutron Scattering Group Scattering from Disordered Systems To be held at the University of Bristoi on 16-18 December 1987 Further information from: Dr R. J. Newport, Physics Laboratory, The University, Canterbury, Kent CT2 7NR Electrochemistry Group Workshop on Electrochemical and Non-electrochemical Surface Spectroscopy To be held at the University of Southampton on 6-7 January 1988 Further information from: Dr S. P. Tyfield, Research Department, CEGB, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB Division with Electrochemistry Group: Annual Congress Solid State Materials in Electrochemistry To be held at the University of Kent at Canterbury on 12-15 April 1988 Further information from Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN Electrochemistry Group with the SCI Electrolytic Bubbles To be held at Imperial College, London on 21 May 1988 Further information from: Professor W. J. Albery, Department of Chemistry, Imperial College, London SW7 2AZ Gas Kinetics Group Xth International Symposium on Gas Kinetics To be held at University College, Swansea on 24-29 July 1988 Further information from: Dr G. Hancock, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ (xii)

ISSN:0300-9599    

DOI:10.1039/F198783BP101

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1987, 83 (8), 2261-2269 Ionization Equilibria in Solutions of Cobalt(@ Thiocyanate in N,N-Dimethylformamide Michal Pilarczyk," Waclaw Grzybkowski and Lucyna Klinszporn Department of Physical Chemistry, Institute of Inorganic Chemistry and Technology, Technical University of Gdansk, 80-952 Gdansk, Poland Visible absorption spectra and the molar conductance curve for Co(NCS), in N,N-dimethylformamide (DMF), together with the spectra for the Co(ClO,),-KNCS-DMF, Co(NCS),-KNCS-DMF and Co(NCS),-DMF- chlorobenzene systems, have been determined at 25 "C. The results indicate the formation of the CoNCS(DMF)l and Co(NCS),2- complexes in the Co2+-NCS--DMF systems. The stability constants are given by log p, = 4.5 kO.1 and log p4 = 12.2f0.3. The high stability of the tetrahedral Co(NCS),2- co-mplex leads to the formation of 2CoNCS(DMF)i * Co(NCS)q- complex electrolytes in the most concentrated solutions of Co(NCS), in DMF.The present work was undertaken in order to determine the coordination state of Co(NCS), in N,N-dimethylformamide. By establishing the nature of the coordination state we may obtain a description of the coordination form in which a salt exists in solution. We have shown in our previous paper1 that the coordination form of CoC1, in DMF solution is the Co(DMF)i+ - 2CoC1,DMF- complex electrolyte, this being the main way in which the solute exists in DMF over almost the entire concentration range. A solution of CoBr, in the same solvent may be considered as an equilibrium mixture of the Co(DMF)i+ - 2CoBr,DMF- and CoBr(DMF)l- CoBr,DMF- complex electro- lytes., As is seen, the electrolytic properties of the cobalt(rr) halides in DMF, as well as in other strongly polar donor solvents, are determined by the very high stability of complex anions of the CoX,L- type (where L denotes the solvent molecule) resulting from the known tendency of the Co2+ ion to occupy a tetrahedral environment. However, in extremely dilute solutions the salts dissociate into simple ions, showing that their coordination forms are the CoLi+ 2X- electrolytes.The formation of cobalt@) thiocyanate complexes in non-aqueous solvents was in- vestigated by several authors. Thus, Katzin and Gebert3 demonstrated the formation of the Co(NCS):- complex in acetone solutions. The Co2+-NCS--acetonitrile system was studied by L i b ~ i , ~ who established that the dissolution of anhydrous Co(NCS), in acetonitrile results in the formation of the CoNCS(CH,CN),+ - Co(NCS),CH,CN- com- plex electrolyte, the latter being the coordination form of the solute in this solvent.The formation of mono-, tri- and tetra-thiocyanate complexes of cobalt(r1) in DMSO and DMA was reported by G~tmann.~ Experiment a1 N,N-Dimethylformamide was dried using 4A molecular sieve and distilled under reduced pressure between 45 and 50 "C. The specific conductance of the final material was in the range (2.0-7.0) lo-* S cm-' at 25 "C. An ethanol solution of Co(NCS), was obtained by metathesis of strictly equivalent amounts of ethanol solutions of Co(NO,), and of KNCS. On cooling, the solid KNO, was filtered off and DMF was added to the resulting solution.This was followed 226 12262 Ionization Equilibria of Co(NCS), in DMF 70 C 600 500 I O C E 300 200 mr lUL n I 14 A " 500 60 0 700 X/nm Fig. 1. Absorption spectra of Co(NCS), solutions in DMF at 25 "C. The molar concentrations of Co(NCS), are: (1) 0.0002780, (2) 0.0004454, (3) 0.000671 6, (4) 0.0009486, (5) 0.001 306, (6) 0.001 732, (7) 0.002298, (8) 0.003 170, (9) 0.004277, (10) 0.005827, (11) 0.009672, (12) 0.01896, (13) 0.040 14; (14) 0.07597 mol dm-3. is the mean molar absorption coefficient of cobalt (11) in dm3 mol-' cm-'. by removing the excess of solvents under reduced pressure at ca. 65 "C. Thus the crystalline blue solids were obtained and recrystallized three times from anhydrous DMF.A DMF-solvated sample of Co(ClO,), was prepared from the corresponding hydrate by means repeated crystallization from anhydrous DMF.' KNCS was recrystallized twice from ethanol and dried in a vacuum at 80 "C. The stock solutions of Co(NCS), and Co(ClO,), were standardized by titration with EDTA. Solutions for measurements were prepared by weighed dilutions. The con- centrations were calculated using the known densities determined independently.M. Pilarczyk, W. Grzybkowski and L. Klinszporn 2263 " 500 600 700 X/nm Fig. 2. Absorption spectra of Co(ClO,),-KNCS solutions in DMF at 25 "C. The concentration of Co(ClO,), is constant (0.005 mol d~p-~), the concentrations of KNCS are, respectively : (1) 0.0, (2) 0.001436, (3) 0.002808, (4) 0.004548, (5) 0.005097, (6) 0.006022, (7) 0.006924 and (8) 0.007851 mol dm-3.Details of the measurement procedures were identical to those described previously.lT The spectra of the most concentrated solutions of Co(NCS), in DMF were recorded using the more dilute solutions as reference solutions; the band position was found to be independent of the salt concentration. Results and Discussion Fig. 1 shows the visible absorption spectra of a series of solutions of Co(NCS), in DMF within the concentration range 0.0003-0.08 mol dm-3. The spectrum of the most dilute solution (curve 1) consists of two bands with maxima at 535 and 624 nm. The first is characteristic of cobalt(r1) in an octahedral environment. However, the solutions of Co(ClO,), in DMF exhibit an absorption band with a maximum at 525 nm that is typical of the Co(DMF)i+ octahedral complex.' Inspection of fig.1 shows that increasing the concentration of the solute is accompanied by drastic changes in the spectrum of cobalt(rr), consisting of a rapid increase in intensity of the band with a maximum at 624 nm accompanied by developing a maximum at 588 nm. Further inspection shows that the band position is independent of the salt concentration, while a variation in intensity is observed. Moreover, the spectra fulfil the criterion for a single absorbing species. Formation of an octahedral complex, e.g. CoNCS(DMF)S, having a relatively low absorptivity may well occur without having a noticeable effect on the measured spectrum due to the thiocyanate complex of cobalt(1r). The band position, contour and high intensity are typical of cobalt(1r) in a tetrahedral environment.'.2 . 72264 Ionization Equilibria of Co(NCS), in DMF 2000 1500 E 1000 500 0 500 600 700 X/nm Fig. 3. Absorption spectra of Co(NCS),-KNCS solutions in DMF at 25 "C. The concentration of Co(NCS), is constant (0.001 mol dm-3), the concentrations of KNCS are, respectively: (1) 0.0005972, (2) 0.001 145, (3) 0.002204, (4) 0.004349, (5) 0.007611, (6) 0.011 15, (7) 0.051 73, (8) 0.103 26, (9) 0.208 75 and (10) 0.5234 mol dm-3. Fig. 2 shows the visible absorption spectra of a series of solutions containing Co(ClO,), at an approximately constant concentration of 0.005 mol dm-3 and KNCS at a number of different concentrations not exceeding a 2: 1 molar ratio of KNCS to Co(ClO,),.The addition of KNCS causes the development of the same absorption band, with maxima at 588 and 624nm, while the maximum characteristic of octahedral complexes of cobalt(r1) is gradually shifted from 525 nm (curve 1, no KNCS added) to 535 nm. Further changes in the spectrum of cobalt(@ produced by increasing the concentration of KNCS added to a 0.001 mol dm-3 solution of Co(NCS), in DMF are presented in fig. 3. At higher NCS- to Co2+ ratios an increase in the KNCS concentration results in a continued increase in the intensity of the band with maxima at 588 and 624nm and in the disappearance of the absorption band due to cobalt (11) in an octahedral environment. When the ratio of NCS- to Co2+ exceeds 50, a further increase in the KNCS concentration does not affect the spectrum, and the value of the mean molar absorption coefficient of cobalt(I1) reaches 1990 dm3 mol-' cm-' at 624 nm.The limiting spectrum is almost identical to the spectrum of Co(NCS)i- in acetonitrile solution reported by Libui., Essentially the same limiting spectrum was observed by Libui, irrespective of the nature of the solvent, at a high excess of NCS- anion in various solvents. Thus the light-absorbing complex of cobalt(I1) present in DMF solutions is the tetrahedral Co(NCS)q- complex anion. The spectral effects presented in fig. 2 suggest the formation of an octahedral complex of cobalt(r1) at lower NCS- to Co2+ ratios, i.e. in Co( ClO,),-KNCS-DMF and Co( NCS),-DM F solutions.M. Pilarczyk, W. Grzybkowski and L. Klinszporn 200 150 - d I 0 E -g 100 2 1/1 1 50 0.0 0.05 0.1 0.15 0.2 0.25 cdlmolf dm-3 2265 Fig. 4.Plot of the molar conductance against the square root of concentration for Co(NCS), in DMF at 25 "C. The conductometric curves expected for the Co2+.2NCS- and CoNCS+*NCS- electrolytes are represented by solid lines (1) and (2), respectively. Table 1. Molar conductance of Co(NCS), in DMF at 25 "C c/ 10-4 AIS c/ 10-4 A/S mol dm-3 cm2 mol-' mol dm-3 cm2 mol-' 0.9801 1.447 2.032 2.780 3.575 4.454 5.522 6.716 8.106 9.486 11.24 13.06 14.94 17.32 19.87 22.98 26.72 115.01 105.43 97.43 90.35 84.94 80.37 75.86 71.89 68.10 64.94 61.67 58.89 55.91 53.91 51.72 49.03 47.34 31.69 37.42 42.77 48.97 54.3 3 58.26 70.14 83.35 96.72 133.3 189.6 255.2 324.7 401.4 492.0 671.8 945.6 44.94 43.1 1 41.68 40.35 39.93 38.79 37.24 35.90 33.99 32.89 3 1.03 29.51 28.58 27.90 27.17 26.08 24.95 Fig. 4 shows the molar conductance curve of Co(NCS), in a DMF solution at 25 OC, while the experimental values are listed in table 1.Also shown in fig. 4 is the molar conductance curve predicted for the Co(DMF)%+ * 2NCS- complex electrolyte using known values of the ionic conductancesi8 (curve 1). The curve expected for CoNCS (DMF)l-NCS- electrolyte, i.e. for complete binding of one NCS- anion, is also given (curve 2). The latter estimation involves the assumption that iZ"[CoNCS(DMF)i] = 0.4 L" [Co(DMF)i+], in accordance with our previous ~bservations.~*~ The molar con- ductance curves calculated from the Robinson-Stokes equation run well above the2266 40' e ti g 20 < o m 1 Ionization Equilibria of Co(NCS), in DMF 500 e 400 500 400 300 E too 00 3 0 X/nm Fig.5. Absorption spectra and molar conductance of CoNCS, for the Co(NCS),-DMFxhloro- benzene system at 25 "C. The concentrations of Co(NCS), is constant (0.003 mol dm-3), the mole fractions of chlorobenzene are: (1) 0.0, (2) 0.078, (3) 0.242, (4) 0.628, (5) 0.919 and (6) 0.967. experimental points, except within the lowest concentration range (curve 2). This indi- cates a high degree of complex formation, markedly exceeding that corresponding to curve 2. However, the points obtained for concentrations < 0.0004 mol dm-3 clearly indicate that in infinitely dilute solutions the salt exists as Co(DMF):+-2NCS-. An abundance of the Co(NCS),2- complex in the most dilute solutions may be estimated by using the limiting value of the mean molar absorption coefficient of cobalt(rI), i.e. the value of the molar absorption coefficient of Co(NCS),2-.Thus, the rapid decrease of the molar conductance within the concentration range 0.000 1-0.0004 mol dm-3, in which the mole fraction of the tetrahedral complex is < 1 YO, may be associated with the formation of an octahedral thiocyanate complex of cobalt(rI), presumably the ionic monothiocyanate CoNCS(DMF)i complex. The relatively low value of the molar con- ductance at higher concentrations corresponds to a high degree of complex formation, but the small variation of conductivity with concentration is due to the formation of ionic species only. In order to investigate the possibility of the formation of a neutral complexes of cobalt@) in the Co(NCS),-DMF system we studied the effects which addition of a non- coordinating diluent of low polarity exerts on the spectrum and molar conductance ofM.Pilarczyk, W. Grzybkowski and L. Klinszporn 2267 600 400 E 200 0 0 0.005 0.010 0.02 0.04 0.06 CCo(SCN),lmol dm-3 Fig. 6. Plot of the mean molar absorption coefficient of cobalt(x1) against concentration for Co(NCS), at 25 "C at 624 nm. Co(NCS), in DMF solutions at a fixed concentration of 0.003 mol dm-3 at 25 "C. The effects generated by the addition of chlorobenzene up to mole fraction 0.967 are pre- sented in fig. 5. The addition of diluent initially causes an increase in intensity of the band due to the Co(NCS)q- complex. Further addition results in a marked change in the spectrum of cobalt(n), consisting of a decrease of the mean molar absorption coefficient and the disappearance of the maximum at 588 nm.When chlorobenzene mole fraction exceeds 0.8 the intensity of the band increases again. These spectral changes are ac- companied by a distinct decrease in the molar conductance of Co(NCS),. Its value is 0.34 S cm2 mol-' for mole fraction 0.967, while the value for the corresponding DMF solution is 45.8 S cm2 mol-'. It may be anticipated that the dilution of DMF with a coordinatively inactive solvent will shift the equilibria in solution towards complex formation owing to both the partial neutralization of the charge and a lowering of the activity of DMF. Moreover, a lowering of the dielectric constant is favoured by the existence of electrically neutral complexes. Thus, it is evident that the tetrahedral complex of cobalt(1r) existing in the presence of a large excess of the inert diluent is the pseudotetrahedral Co(NCS), (DMF), complex.We infer that the complex is absent in DMF solutions of Co(NCS),. The results obtained permit a calculation of the equilibrium concentration of Co(NCS)t-. Thus, ignoring absorption due to the octahedral complexes, the mole fraction of Co(NCS)t- may be calculated as c, I5 E4 _ - _ - where denotes the mean molar absorption coefficient of cobalt(I1) and e, is the molar absorption coefficient of the Co(NCS),-, complex. Fig. 6 shows the value of Eat 624 nm plotted against the concentration of Co(NCS), in DMF solution. As is seen, E+ 660 dm3 mol-lcm-' for the most concentrated solution.Taking into account the value of 1990 dm3 mol-' cm-' for E , at 624 nm, the mole fraction of Co(NCS)i- complex in the most concentrated solution is 0.33. Assuming complete binding of the thiocyanate anions, the most concentrated solution of Co(NCS), may be considered as a solution of the 2CoNCS(DMF)i - Co(NCS)q- complex electrolyte. The appreciable stability of the monothiocyanato octahedral complexes of cobalt(n) in strong donor solvents was discussed by Lib&.,2268 n E E: .3 c, m Q 0 & E - Fig. 7. Ionization Equilibria of Co(NCS), in DMF 100, 1 6 6 ‘lo -3 .O -2.5 -2.0 -1.5 -1.0 log CCo(NCS), The ranges of existence of the thiocyanate complexes of cobalt@) in DMF solutions of Co(NCS), at 25 “C. Taking into account the results discussed above we consider that the main coord- ination equilibria responsible for the observed properties of Co(NCS), in DMF solutions are the following: and Co(DMF),2++NCS-+ CoNCS(DMF),+ +DMF (2) CoNCS(DMF),+ +3NCS-+ Co(NCS)i +5DMF.(3) The first determines the properties of the dilute solutions, while both equilibria are responsible for the properties of concentrated solutions. The results above provide a possibility of calculating stability constants of the com- plexes present in the Co2+-NCS--DMF system. In this respect the data obtained for the two-component solutions, i.e. the Co(NCS), - DMF system, are more useful than the data for the three-component systems, since the number of different equilibria is reduced to a minimum. In the calculations we assumed the formation of only the CoNCS (DMF); and Co(NCS)q- complexes, the corresponding stability constants being defined as ” and c1 = c,”CS-] (4) where c,, c,, c4 and PCS-1 denote equilibrium concentrations of Co(DMF),2+, CoNCS(DMF);, Co(NCS)q-, and NCS-, respectively, and and y4 are quotients of the respective activity coefficients.Variations in the activity coefficients with the ion-size parameter, Bi, the latter being estimated from conductometric datas,* as 3.4, were assumed to follow the Debye-Huckel equation. Taking into account the equations arising from the material balance for the cation and anion we attempted to find the best values of p, and pa describing the spectral properties of the system. The calculations were performed for 10 solutions in the range of moderate concentrations of Co(NCS), in DMF.The resulting values of the logarithms of the stability constants of CoNCS (DMF); and Co(NCS)i- are 4.5 kO.1 and 12.2 k0.3, respectively, at 25 O C . Equilibrium concentrations of the single complexes found at the same time for different concen- trations of Co(NCS), have been used for preparing the distribution diagram shown in fig. 7. - The most striking feature of the Co2+-NCS--DMF system is the very high stability of the Co(NCS)i- complex, resulting in the formation of the 2CoNCS(DMF),+ Co(NCS)q- complex electrolyte in the most concentrated solutions of Co(NCS), in DMF. In previous papers we have shown that the most important factor controlling the elec-M. Pilarczyk, W. Grzybkowski and L. Klinszporn 2269 trolytic properties of the DMF solutions of cobalt(I1) halides is the high stability of the pseudotetrahedral trichloro- and tribromo-complexes of cobalt(r1).As a consequence, a solution of CoCI, may be considered as a solution of the Co(DMF),2+ - 2CoC1,DMF- complex electrolyte,' while the properties of solutions of CoBr, may be explained in terms of the coexistence of two complex electrolytes, i.e. CoBr(DMF)i * CoBr,DMF- and Co(DMF)i+- 2CoBr,DMF-., The observed difference may be related to the specific donor properties of the NCS- anion arising from bonding interactions and resulting in the stability of Co(NCS):-. The same effect seems to be responsible for complex formation in the Co2+-NCS--acetonitrile system. The similarity of donor groups results in the stability of the Co(NCS),CH, CN- complex anion.4 This work was supported by Problem MR-1-11, Poland. References 1 W. Grzybkowski and M. Pilarczyk, J. Chem. SOC., Faraday Trans. I , 1986, 82, 1703. 2 M. Pilarczyk and L. Klinszporn, Electrochim. Acta, 1986, 31, 185. 3 L. I. Katzin and E. Gebert, J. Am. Chem. SOC., 1950, 72, 5659. 4 W. LibuS, Roczn. Chem., 1961, 35, 41 1. 5 V. Gutmann, Monatsh. Chem., 1968, 99, 751. 6 W. LibuS, B. Chachulski, W. Grzybkowski, M. Pilarczyk and D. Puchalska, J. Solution Chem., 1981, 7 L. Sestilli, C. Furlani and G. Festucia, Inorg. Chim. Acta, 1970, 4, 542. 8 J. E. Prue and P. J. Sherrington, Trans. Faraday SOC., 1961, 57, 1795. 9 W. Grzybkowski and M. Pilarczyk, J. Chem. SOC., Faraday Trans. 1, 1983, 79, 2319. 10, 631. Paper 61248; Received 3rd March, 1986

ISSN:0300-9599    

DOI:10.1039/F19878302261

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1987, 83 (8), 2271-2277 Electron Spin Resonance Investigations of Ruthenium supported on ?-Alumina Maria Grazia Cattania Sabbadini Centro C.N.R. per lo Studio sulle- Relazioni tra Struttura e Reattivita Chimica, Universita di Milano, Via Golgi 19, 20133 Milano, Italy Antonella Gervasini, Franca Morazzoni* and Donatella Strumulo Dipartimento di Chimica Inorganica e Metallorganica e Centro C.N.R., Universita di Milano, Via Venezian 21, 20133 Milano, Italy We report an electron spin resonance investigation performed on alumina- supported ruthenium, Ru/y-Al,O,, obtained by decarbonylation (pyrolysis or H, reduction) of Ru,(CO),,/y-Al,O,. The spectra observed after Ru/ y- A1,0, was in contact with o,, CO, NO ‘probe’ molecules allow one to distinguish superoxide, carbonyl and nitrosyl paramagnetic derivatives of ruthenium, and show that ruthenium centers in formal oxidation states other than the zero metal state become stable by interaction with y-Al,O,.The strength of the interaction between paramagnetic ruthenium centres and n*-acceptor molecules (02, CO and NO) is dependent both on the n*- acceptor molecules and on the decarbonylation method. In recent years several investigations have been made in order to characterize the electronic properties of supported transition-metal centres. A specific effort has been made to relate the electronic state of the metal to the activity and selectivity of the dispersed metal system used as catalyst in a given reaction. Associated with the above- mentioned properties is the interaction between the metal component and the support; this plays a decisive role owing to the close relationship between the metal and the support, which greatly affects the interaction of the metal with the chemisorbed reactants.’ Since it was discovered that the supported metal particles are not completely reduced and that dispersed metal ions are stable at the metal-support interface, the investigation of the paramagnetic species by e.s.r.spectroscopy has come to be considered as a possible way of understanding the electronic properties of the system. We report here the results of an e.s.r. study of Ru/yA1203 samples, obtained by Ru3(CO),,/lj-A1203 decarbonylation, performed with the following objectives : (i) to characterize the paramagnetic oxidation states of ruthenium originating from the metal-oxide interaction ; (ii) to study the chemical interaction between metal centres and appropriate ‘probe’ molecules (02, CO and NO).The use of such molecules may help to increase the sensitivity of the e.s.r. technique when the resonance lines of simple transition-metal ions are too broad to be assigned; it is already known that when compared to the resonance lines of noble-metal ions those characteristic of superoxo or carbonyl complexes are narrower. Moreover, the same molecules are frequent substrates in catalytic reactions involving ruthenium, i.e. the Fisher-Tropsch reaction3 and reduction of NO with CO and H2,4 so that any electronic studies of their interaction with the metal should increase our knowledge of the reaction mechanism.227 I2272 E.S.R. Study of Ruthenium on y-Alumina Ex primen t a1 Preparation of the Samples Ru/y-Al,O, samples composing 1.57 g Ru per 100 g y-Al,O, were obtained by thermal decarbonylation of the precursor Ru,(CO),,/y-Al,O, at 673 K. An Ru,(CO),, solution (containing the appropriate concentration of the cluster) in anhydrous deaerated dichloromethane was added dropwise, under an inert atmosphere, to deaerated y-Al,O, suspended in the same solvent. When the addition was complete, the mixture was allowed to equilibrate for 2 h while being stirred; the solid was then filtered off. Samples were dried in vacuo at room temperature for 2 h and stored under an inert atmosphere. Contact with air was avoided throughout the procedure.Ru,(CO),,/y-A120, gave Ru/ y-Al,O, by two different methods : (a) pyrolysis in vacuo (Ru,/y-Al,O,) and (b) reduction in an H, stream (Ru,/y-Al,O,). Using a standard gas-vacuum line the pyrolysis was carried out in vacuo ( loA3 Pa) at 673 K for 2 h, in a small flask connected to an e.s.r. tube (internal diameter 3 mm). The complete decarbonylation was monitored by i.r. spectroscopy. Reduction treatments were performed in a special tube connected to an e.s.r. cell; the H, stream (166 cm3 min-') flowed at 673 K for 2 h through a porous septum on which the catalyst precursor Ru3(C0),,/ y-Al,O, was placed. Ru,(CO),, was a pure reagent from Strem Chemicals. y-Al,O, was Ketjen grade-A from Akzo-Chemie. It was thermally pretreated in an 0, stream at 773 K for 4 h in order to avoid carbonaceous impurities and then cooled from 773 K to room temperature in an N, stream.Pretreated y-Al,O,, as well as metal- containing samples, was pyrolysed [y-Al,O,(P)] or reduced [y-Al,O,(R)] under the conditions already described. After decarbonylation and before the gas treatments Ru,,,/y-Al,O, were kept in an inert atmosphere. Gas Treatment Contact with gases (O,, CO and NO) at controlled pressures was carried out on a gas- vacuum line. Pure 0, was dried over molecular sieves. Samples were contacted at room temperature with a 26.6 kPa 0, pressure; after 5 min contact the 0, was pumped off to 13.3 Pa to eliminate the major part of the paramagnetic physisorbed gas; the e.s.r. spectrum was then recorded. Pure CO from SIO Blu Gas was used without further purification.All samples were contacted with a 26.6 kPa CO pressure at room temperature and the e.s.r. spectrum was recorded under the same CO pressure. Pure NO from SIO Blu Gas was used without further purification. NO has introduced into the samples at room temperature and at pressures of 9.3 and 26.6 kPa. Samples were then cooled at the temperature of liquid nitrogen for 30min before recording the e.s.r. spectrum; this was to enable the physisorbed NO to be converted into solid diamagnetic N,O,. Specific details are given in the results section. Apparatus A conventional X-band E-109 Varian spectrometer, equipped with an automatic temperature control, was employed. The g values were standardized against 2,2- diphenyl-1-picrylhydrazyl. Computational Methods The spin concentration of the magnetically diluted species were determined by double integration of the area of the resonance lines.The reference area was that of the Varian weak pitch (lo1, spin cm-l). The sensitive region of the e.s.r. cavity was 1 cm in lengthM. G. Cattania Sabbadini, A . Geruasini, I - 0 0 0 0 0 0 9 9 9 9 < v 1" d 0 0 0 0 m I 2 O ,c.l X x m I 53 X x d 0 0 F. Morazzoni and D. Strumolo 22732274 E.S.R. Study of Ruthenium on y-Alumina Fig. 1. X-Band e m . spectra recorded at 123 K of (a) Ru,/y-Al,O, and (6) Ru,/y-Al,O, in an argon atmosphere. Lines with asterisks are due to Fe3+ impurities. and the internal radius of the e.s.r. tube was 1.5 mm. The apparent density of the catalysts was 1 g ern-,. All e.s.r. data are reported in table 1.The spin concentration of the paramagnetic species containing ruthenium was ca. 1015 spin g-l. Results Vacuum-pyrolysed Samples Y -A12 0, The e x . spectrum of y-Al,O,(P) recorded in an argon atmosphere shows the resonance lines of Fe3+ impurities in a tetragonal field symmetry ( g = 4.2, lines marked by an asterisk in fig. 1) and of a radical species (g = 2.00) which was not observed on y-Al,O, before vacuum treatment. Treatments with 0, and CO gases did not affect the spectrum of y-Al,O,(P). After NO absorption (9.3 kPa), y-Al,O,(P) changed colour from white to pale yellow. The spectrum was recorded after the sample, contacted with NO (9.3 Pa) at room temperature, was cooled at liquid N, temperature for 30 min. The shape of the lines and the g tensor components (8, = 1.99 g,, = 1.95) [fig.4(a) later] are in agreement with the data reported by Lunsford for NO adsorbed on an A1,0, surface as A13+-N0.5 No hyperfine structure was observed. The paramagnetic species could be easily removed by degassing the samples for 1 min to 133 Pa at room temperature. A fresh adsorption of NO (9.3 kPa) restored the signal. Ru,ly-A120, The pyrolysis of pale brown Ru,(CO),,/y-Al,O, samples lead to a dark-grey dispersed metal system Ru,/y-Al,O, whose e.s.r. lines, in an argon atmosphere, were the same as those observed on the y-Al,O, support [fig. l(a)]. No paramagnetic species due to transition-metal centres were observed. The e.s.r. spectrum of Ru,/y-Al,O,, contacted with 0, (see experimental section) shows new strong resonance lines [fig.2(a)]. Two paramagnetic 0, species with axial symmetry were observed, distinguishable by theirM. G. Cattania Sabbadini, A . Gervasini, F. Morazzoni and D. Strumolo 2275 H 40 G --t Fig. 2. X-Band e.s.r. spectra recorded at 123 K of (a) RuJy-Al,O, and (b) RuJy-Al,O, in an 0,(13.3 Pa) atmosphere. different g,, values : species A (6 = 2.063) and species B (ga = 2.034). The shapes of the lines and the values of the magnetic tensor components suggest that the resonances are due to 0; attached to different positively charged centres.' Unfortunately the absence of any hyperfine interaction precludes further details. The formation of superoxide is promoted by ruthenium, as the signals described above are not present after contacting y-Al,O,(P) with 0,. Both A and B species cannot be removed by vacuum (lo-, Pa, room temperature, 1 h) or thermal vacuum treatments Two different paramagnetic species are observed in the e.s.r.spectra of Ru,/y-Al,O, contacted with CO[fig. 3(a)]. One, referred as species C, is also formed by CO contact on RuJy-Al,O, (see later), and its axial symmetry (gy = 2.045 gC, = 2.00) is clearly visible. For the other species, referred as D, only the g feature at 2.055 can be quoted with certainty. The signals of the two species are very similar in shape and width to those reported by Knozinger el al. for osmium carbonyl derivatives' on Os/y-Al,O,; we suggest, on the basis of this work, that Ru is present in our systems as a carbonyl derivative with two different metal electronic configurations, probably Ru"' and Ru', both e.s.r.-active.Different stabilities were observed for the two derivatives: D is removed by vacuum treatment (loY3 Pa, room temperature, 1 h), while C is thermally and vacuum stable (lo-, Pa, 100 OC, 1 h). The adsorption of NO gas on Ru,/y-Al,O, (contact pressure 9.3 and 26.6 kPa, see experimental section) leads to e.s.r. spectra like those of y-Al,O,(P) in the same conditions. The resonance lines are very strong (gl = 1.99 g,, = 1.95) and are not distinguishable from those assigned to NO bonded to the surface A13+ centres. However, if we lower the NO pressure to 133 Pa, the spectrum of Ru,/y-Al,O, [fig. 4(b)J resolves into signals characteristic of NO metal adducts,8 with a detectable, although not well resolved, magnetic interaction between the unpaired electron of NO and the 14N ( I = I ) nucleus.Magnetic tensor components are almost isotropic, with g,, x g,, x g,, x g, and Aiso x 35 G. The decrease in NO pressure does not affect the stability of the paramagnetic species, unlike the case on the y-Al,O,(P) support. The paramagnetic species is also stable to vacuum treatment (lo-, Pa, room temperature). It may be suggested that an Ru-NO bond interaction is active and that the NO molecule supplies a covalent contribution to the interaction with the metal centre. The Pa, 100 "C, 1 h).2276 E.S.R. Study of Ruthenium on y-Alumina 40 G 40 G Fig. 3. X-Band e.s.r. spectra recorded at 123 K of (a) Ru,/y-Al,O, and (b) Ru,/y-Al,O, in a CO (26.6 kPa) atmosphere. magnetic parameters can be interpreted as being due to Ru" nitrosyl adducts.If the contact of Ru,/y-Al,O, with NO follows that with CO, all the species stable after CO contact are removed in favour of those stable after NO contact, in agreement with the i.r. data of the literat~re.~ Reduced Samples In an argon atmosphere the e.s.r. spectrum of y-A1203(R) shows no large differences from that of y-Al,O,(P). Contacts with NO at a pressure of 9.3 and 26.6 kPa leads to the disappearance of the lines at g = 1.93. Paramagnetic A13+-NO species were not observed. With regard to this absence it is probable that the H, treatment induces a lower surface acidity of A13+ centres in y-Al,O,(R) with respect to y-Al,O,(P), so that the strength of the A1-NO bond interaction decreases. The signals at g = 1.93 are restored by degassing the samples to 133 Pa for 1 min at room temperature.In an argon atmosphere Ru,/y-Al,O, shows additional slightly anisotropic lines at g = 1.93 [fig. 1 (b)] visible both at room temperature and at - 150 "C. The attribution of this signal to Ru paramagnetic species can be excluded on the bases of its narrowness and of the appearance of the same signal, although less strong, in the y-Al,O,(R) spectrum. Once the attribution to Ru centres was excluded, further investigation of this signal was not considered. The conventional contact of 0, with RuR/y-Al,O, induces the formation of only one 0; derivative, already referred as species B [fig. 2(b)]. On the other hand species B is not stable to vacuum treatment (lo-, Pa, room temperature, 1 h), probably because of the general lower Lewis acidity of the positive surface centres in the H,-reduced catalysts.M. G.Cattania Sabbadini, A . Geruasini, F. Morazzoni and D. Strumolo 2277 J DPPH Fig. 4. X-Band e.s.r. spectra recorded at 123 K of (a) pAl,O,(P) in an NO (9.3 kPa) atmosphere and (b) Ru,/y-A120, in an NO (13.3 lo-, kPa) atmosphere. Contact with CO gave only the Ru carbonyl derivative referred as species C [Fig. A paramagnetic adduct resulting from contact with NO was also observed in RuJy- Al,O,; however, the resonances are not easily distinguishable because of the presence of support lines in the same region and because of their intrinsic lower intensity with respect to those observed on RuJy-Al,O,. 3 (4. Conclusions The paramagnetic species which become stable after Ru/ y-Al,O, was contacted with ‘probe’ molecules allow us to establish that some ruthenium centres are present on the alumina surface in oxidation states different from zero. Positively charged metal centres arise from the interaction between ruthenium and acidic centres of the y-Al,O, support.The use of a carbonyl precursor, instead of the salt, precludes the suggestion that positive Ru centres could originate from an incomplete reduction of the salt. Strong interactions are observed between the metal centre and z*-acceptor molecules ; the type and degree of stability of the surface species depend on the choice of chemisorbed molecule and on the decarbonylation method which is employed. References 1 T. Hulzinga and R. Prins, J. Phys. Chem., 1983, 87, 173 and references therein. 2 B. L. Gustafson, Mei-Jan Lin and J. H. Lunsford, J. Phys. Chem., 1980, 84, 3211. 3 M. A. Vannice, in Catalysis Science and Technology, ed. J. R. Anderson and M. Boudart, (Springer- 4 T. P. Kobylinski and B. W. Taylor, J. Catal., 1974, 33, 376. 5 J. H. Lunsford, J. Phys. Chem., 1968, 72, 4163; J. Catal., 1969, 14, 379. 6 J. H. Lunsford, Catal. Rev., 1973, 8, 135. 7 V. A. Shvets, A. L. Tarasov, V. B. Kazansky and H. Knozinger, J . Catal., 1984, 86, 223. 8 P. H. Kasai and R. M. Gaura, J . Phys. Chem., 1982, 4257; P. H. Kasai and R. J. Bishop Jr, J . Am. 9 A. Davydov and A. T. Bell, J. Catal., 1977, 49, 345. Verlag, Berlin, 1981), vol. 3, chap. 3, pp. 154-159. Chem. SOC., 1972, 94, 5560. Paper 61728; Received 14th April, 1986

ISSN:0300-9599    

DOI:10.1039/F19878302271

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. 1, 1987, 83 (8), 2279-2287 Study of the Support Evolution through the Process of Preparation of Rhodium/Lanthana Catalysts Serafin Bernal," Francisco J. Botana, Rafael Garcia, Francisco Ramirez and Jo& M. Rodriguez-Izquierdo Departamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Cadiz, Apartado 40, Puerto Real, 11510 Cadiz, Spain The evolution undergone by the support throughout the processes involved in the preparation of some lanthana-supported rhodium catalysts has been studied by thermal gravimetry, temperature-programmed decomposition - mass-spectrometry, temperature-programmed reduction - mass-spectrom- etry and X-ray diffraction. Following the impregnation process, the support consists of partially carbonated lanthanum hydroxide.A study of the re- duction process shows that, at 623 K, a catalyst that can be described as Rh/LaO(OH) is obtained. Reduction temperatures as high as 723 K are necessary to prepare true Rh/La,O, catalysts. In contrast to results observed for the dehydration of the support, the reduction of the carbonated phase on lanthana is strongly activated by the presence of the supported rhodium. Recently the number of papers published dealing with lanthanide-oxide-supported metal catalysts has risen steeply for several reasons : on the one hand, when used for CO and CO, hydrogenation, these catalysts show a high selectivity towards oxygenated products ;1-9 on the other hand, quite singular metal-support interaction phenomena have been reported on some of these catalystsl0-l2.In contrast to classic supports such as silica or alumina, the rare-earth oxides, when exposed to atmospheric H,O and CO, at normal temperature and pressure, undergo strong hydration and carbonation phenomena13-17. Accordingly, if 4foxides are not very carefully manipulated, which is the case in most reports that have appeared up to now, the initial support phases used in the preparation of M/4foxide catalysts are not in fact lanthanide oxides, but the phases resulting from their hydration and carbonation. The nature of these phases, on the other hand, depends on the 4fion inv01ved.~~-~' Since the lanthanide sesquioxides, when used as starting phases in the preparation of supported-metal catalysts, are usually hydrated and carbonated in bulk, they may undergo notable structural and chemical transformations throughout the whole process of dispersal of the metal, i.e.impregnation, drying treatments and reduction. Likewise, depending on the particular conditions under which the reduction is carried out, phases other than true 4f oxides might well constitute the actual support. Accordingly, in order to understand thoroughly the behaviour of this interesting group of catalysts, the singularities of the rare-earth oxides outlined above should be taken into account. In other words, the true nature of these supports and their evolution throughout the entire preparation process of the supported phases should be investigated in detail. In the present work, based on our previous knowledge of the behaviour of lanthanum oxide exposed to the air,16 the processes involved in the preparation of some lanthana- supported rhodium catalysts have been studied.have prepared and stored various M/La,03 catalysts before Since several authorsg. 22792280 Rhodium - Lanthana Catalysts studying them, the behaviour of Rh/La,O,, when exposed to air, and the process of its re-reduction have also been investigated. Experimental The lanthanum oxide studied here was a 99.9 YO pure sample from Ventron. In order to work with a well known phase, the oxide was exposed to air for several weeks before its use as starting material in the preparation of the supported phases. The behaviour of this lanthana sample, when aged in air, was found to be similar to that reported by us for three other samples of this oxide.'' The B.E.T.surface area of the Ventron sample stabilized in air, as deduced from its nitrogen adsorption isotherm at 77 K, was 10 m2 g-'. The rhodium salt used here was Rh(NO,).xH,O, 36% Rh, from Ventron. The rhodium nitrate, obtained from an aqueous solution, was deposited on to the support by the incipient-wetness impregnation technique. In order to achieve a final rhodium loading of 1 YO, six successive cycles of impregnation at 298 K, and drying in air at 383 K for 10 h, were necessary. The B.E.T. surface area of the impregnated sample was also 10 m2 g-'. This value was not significantly modified after the reduction treatments at both 623 and 723 K. The thermogravimetric analysis (t.g.) experiments were carried out in a Mettler microbalance, model ME-21.All these experiments were performed in a flow of gas, either He or H,, the rate of flow always being 1 x lo-' m3 s-' (60cm3min-'). The linear heating rate was 0.1 K s-l. The temperature-programmed decomposition (t.p.d.) and temperature-programmed reduction (t.p.r.) experiments were recorded under the following conditions : flow of gas (either He or H2): 1 x lo-' m3 s-'; heating rate: 0.1 K s-'. The analysis of evolved gases was carried out by means of Vacuum Generators Spectralab SX-200 mass spectrometer interfaced to an Apple IIe microcomputer. The experimental apparatus for t.p.d. (or t.p.r.) - mass-spectrometer used here has been described elsewhere. lS X-Ray diffraction studies were carried out with a Siemens instrument, model D-500, using Cu K, radiation.Results and discussion Lanthanum oxide, when exposed to atmospheric CO, and H,O for a few hours (ca. 24 h) at normal temperature and pressure is completely transformed into partially carbonated lanthanum hydroxide." Therefore, in our case the starting support sample was not La,03, but the phases resulting from its hydration and carbonation in air. Taking into account the procedure followed to deposit the rhodium salt on to the support, we have also investigated the evolution undergone by the sample aged in air when submitted to six successive cycles of wetting in distilled water and drying in air at 383 K, as in the impregnation process. The sample resulting from the treatment above, which in order to be distinguished from the true lanthanum oxide will hereafter be referred to as La,03*, has been investigated by X-ray diffraction, t.p.d.-m.s.and t.g. Fig. 1 summarizes the results of this characterization study. From a comparison of the results in fig. 1 with those reported in ref. (16) for lanthana simply aged in air, no difference can be noted. As in ref. (16), the X-ray diffraction pattern, which does not allow the identification of carbonated phases, agrees well with that of La(OH),. However, it is obvious from the t.p.d.-m.s. diagrams in fig. l(b) that carbonation of the sample has occurred. Furthermore, from analogies found between the so-called La203* sample and that simply aged in air, the same reaction scheme228 1 S. Bernal et al. 1 ( a ) 50 ~ 40 30 201" 20 10 c ( b ) i i i .. . . . .. . *: i \ : . _ . . : ;, : .. i i . . . . . . . . ....... 373 573 773 973 1173 I , 373 573 773 973 T/K Fig. 1. Characterization studies on Laz03*. (a) X-ray, diffraction pattern. (b) T.p.d.-m.s. traces for water ( m / z = 18, -), and carbon dioxide (m/z = 44, - -). (c) T.g. diagram in flowing He (weight of sample, 9 1.8 mg). proposed in ref. (16) can now be applied to interpret the thermal evolution of La2(0H)6-!2dC03)Z (x l) M La,O,CO, La202C0, In accordance with the scheme above, the amount of CO, taken up by La,O,* can be estimated from the last step of the t.g. diagram in fig. l(c). When referred to 1 nm2 of B.E.T. surface area, this amount is found to be 30 molecules per nm2, much larger than 8 molecules per nm2, the value proposed by Rosynek,' for the surface carbonation of La,O,.In brief, La,O,* is carbonated in bulk. The thermal evolution, in flowing helium, of Rh(NO,),/La,O,* is reported in fig. 2(a). For comparative purposes, the t.g. trace for La,O,* shown in fig. 1, is also included in fig. 2 (b). From a comparison of figs. 2 (a) and (b) it can be deduced that the impregnation process does not induce significant alterations on the support. In fact, the only difference between traces (a) and (b) is the larger weight loss occurring up to 573 K on trace (a). This difference should be related to the decomposition of the rhodium nitrate.2282 Rhodium - Lanthana Catalysts 373 573 773 973 T/K Fig. 2. T.g. diagrams corresponding to (a) decomposition in flowing He of 99.6 mg of Rh(NO,),/La,O,*. (b) Decomposition in flowing He of 91.8 mg of La,O,*.(c) Reduction in flowing H, of 104.8 mg of Rh(NO,),/La,O,*. When Rh(N0,),/La203* is decomposed in flowing H,, the t.g. diagram [fig. 2(c)], is different from those reported in fig. 2(a) and (b). On the one hand, the weight loss taking place at 373473 K is much better defined in fig. 2(c), which suggests that the reduction of Rh(NO,), occurs within a shorter range of temperature than its decomposition in flowing helium. On the other hand, the last decomposition step in fig. 2(a) and (b), that corresponding to the evolution of CO,, completely disappears in fig. 2 (c). Accordingly, in the presence of rhodium the reduction of the carbonated phase on the support is strongly activated. In order to gain further insight into the process occurring throughout the preparation of the lanthana-supported rhodium catalysts, we have also investigated by t.p.r.-m.s.the thermal evolution of La,O,* (fig. 3) and Rh(NO,),/La,O,* (fig. 4). As can be seen in fig. 3, the decomposition in flowing H, of La,O,* takes place in three steps. The first two steps correspond to the evolution of H,O and, as in the case of the decomposition in flowing He [fig. l(c)], can be assigned to the dehydration of La,O,*. The third step, on the contrary, starts at a lower temperature (773 K) than that found in fig. l(c) for the evolution of CO,. Furthermore, this third step implies the evolution of CH, (m/z = 16 and 14), H,O (m/z = 18) and CO (m/z = 28). Therefore, when only the support is heated, in flowing H,, at temperatures above 773 K, the reduction of the carbonated phase occurs.If, in a parallel experiment to that reported in fig. 3, the thermal evolution in flowing H, of Rh(NO,),/La,O,* is studied (fig. 4), the reduction of the carbonated phase, as deduced from the observation of CH, and CO, starts at ca. 473 K and is completed below 773 K. These results, consistent with the t.g. study reported in fig. 2(c), confirm the activation by the metal of the reduction of the carbonated phase on the support. The results above, on the other hand, suggest that the reduction of the rhodium nitrate to the metal should occur below 473 K. In effect, as deduced from both the t.g. trace in fig. 2(c), mentioned above, and the evolution of NH,, suggested by the t.p.r. diagrams corresponding to m/z = 17 and m/z = 16 in fig.4, the reduction of Rh(NO,), takes place within the range 373473 K.S. Bernal et al. 2283 1 1 1 1 , 1 1 1 1 l l I l 1 1 1 1 1 373 573 773 973 1173 T/K Fig. 3. T.p.r.-m.s. study of La203* (weight of sample, 50 mg). Also, in contrast to what is observed in fig. 3, the reduction of the carbonated phase, in the presence of metal (fig. 4) takes place through a complex mechanism in which at least two steps can be distinguished. These two steps, centred at 573 and 723 K, agree approximately with the two stages through which the dehydration of the support occurs. Accordingly, the last two steps of the t.g. diagram in fig. 2(c) should include both the weight loss due to the dehydration of the support and that corresponding to the reduction of the carbonated phase.Contrary to what is suggested in ref. (1 l), our results show that the dehydration of the support is not activated by the metal. The differences observed in ref. (1 1) between the X-ray photoelectron spectra obtained after heating in H, (a) the support only and (b) a lanthanum oxide-supported palladium phase should be reasonably interpreted as being due to the activation by the metal of the reduction of the carbonated phase on the support, rather than to its dehydration. The activation by the supported metal of the reduction of carbonate species on lanthana has also been reported in ref. (21). In accordance with our results, in order to obtain true lanthanum oxide-supported metal catalysts, either special procedures, including the calcination of the starting sup- port phase at temperatures as high as 1100-1200 K and its further manipulation in the absence of H20 and CO,, are followed, or reduction temperatures of ca.723 K are used. Otherwise, phases other than lanthanum oxide would constitute the actual support. Since most of the papers dealing with M/La20, catalysts which have appeared up to the present have not taken into account the singularities of this support, particularly its likely carbonation in the bulk oxide when manipulated in air for a few hours, it is our opinion that in many cases catalysts improperly described as lanthana-supported metal phases have been investigated.2284 Rhodium - Lanthana Catalysts \ ” 1-14 16 17 1 1 1 1 1 1 1 1 , 1 1 , 1 1 1 1 1 1 373 573 773 973 1173 TlK Fig.4. T.p.r.-m.s. study of Rh(NO,),/La,O,* (weight of sample, 50mg) m/z values are as marked. .... ................................ - ._.._....._. 373 473 573 673 773 TIK Fig. 5. Study of thermogravimetric analysis of the reduction by steps of 86 mg of Rh(NO,),/ La,O,*.S. Bernal et al. ( C ) 50 40 30 20 10 50 40 30 20 10 50 40 30 20 10 281" Fig. 6. X-Ray diffraction patterns corresponding to (a) Rh(N03)3/La203*, (6) the catalyst resulting from the reduction of (a) at 623 K and (c) the catalyst resulting from the reduction of (a) at 723 K. 373 573 773 973 TIK Fig. 7. Thermal evolution in (a) flowing He and (b) flowing H, of a Rh/La,O, catalyst exposed to air for 24 h. [The catalyst was obtained from the reduction at 723 K of 79.6 mg of Rh(NO,),/La,O,*.]2286 Rhodium - Lanthana Catalysts It can also be deduced from our results that, when the reduction of the precursor is carried out at 623 K, a relatively well defined support is obtained. In effect, fig.5 depicts the t.g. diagram corresponding to the reduction by steps of Rh(NO,),/La,O,*. The upper part of the figure accounts for the weight loss observed when the sample is heated to 623 K and held at this temperature for 1 h (dotted line) in flowing H,. If, after this reduction treatment, the temperature is raised again, in a flow of H,, the t.g. diagram shown in the bottom of fig. 5 is obtained. When the lower and upper parts of fig. 5 are brought together, the resulting t.g. diagram is similar to that reported in fig. 2(c). In accordance with the results included in fig.2 4 , discussed above, and the reaction scheme proposed in ref. (16) and reproduced here in order to interpret the thermal decomposition of La,O,*, it can be concluded that, when Rh(NO,),/La,O,* is reduced, in a flow of H, for 1 h at 623 K, a catalyst consisting of Rh dispersed on partially carbonated lanthanum oxydroxide, LaO(OH), is obtained. In order to confirm the statement above, the phases resulting from the reduction of Rh(NO,),/La,O,* at both 623 and 723 K have been studied by X-ray diffraction. Fig. 6 shows the corresponding diffraction patterns and includes the diffraction pattern of Rh(NO,),/La,O,*. The three diffraction patterns are quite different from each other. That of Rh(NO,),/La,O,* is similar to the one depicted in fig. 1 for La,O,*, and can be assigned to La(OH),.With regard to the diagram for the catalyst reduced at 623 K, as suggested above only diffraction lines corresponding to LaO(0H) can be observed. Finally, the catalyst reduced at 723 K for 1 h shows the diffraction pattern of hexagonal La,O,, which confirms the conclusion drawn from t.g. and t.p.r.-m.s. in the sense that, at 723 K, a true Rh/La,O,. catalyst is obtained. Since some of the authors working on lanthanum-oxide-supported metal catalysts store the prepared catalysts for some undefined time before studying them, we have also investigated the behaviour with regard to atmospheric H,O and CO, of a sample of Rh/La,O,. For this purpose a catalyst reduced at 723 K as indicated above was cooled in a flow of H, to ambient temperature; then a flow of He was passed over the sample for 1 h, which was finally exposed to air at ambient temperature for 24 h.Fig. 7 ( a ) shows the t.g. diagram, in a flow of He, of the Rh/La,O, catalyst stabilized in air. When this diagram is compared to that reported in fig. 1 (c), it may be concluded that, in the present case, the presence of dispersed metal on lanthana does not modify the behaviour of the support when exposed to air. The t.g. trace corresponding to the reduction, in flowing H,, of the Rh/La,O, catalyst aged in air is depicted in fig. 7 ( b ) . This trace is quite similar to that reported in fig. 2(c). Accordingly, as far as the evolution of the support throughout the reduction process is concerned, no significant difference should be observed between the catalyst prepared by reduction of Rh(NO,),/La,O,* and that obtained by reducing Rh/La,O, previously stabilized in air.Conclusions In summary, data concerning the evolution undergone by the support throughout the processes involved in the preparation of some lanthana-supported rhodium catalysts have been reported. Although the hydration of lanthanum oxide, when manipulated as is usual in order to prepare M/La,O, catalysts, has been considered by some a ~ t h o r s , ~ ~ - ~ * the carbonation in the bulk oxide, as well as the evolution of this carbonated phase throughout the reduction process, have not been sufficiently stressed. This omission, which is related to the smaller number of papers specifically devoted to the study of the behaviour of 4f oxides simply exposed to air, is however very important if one is to determine the nature of the support phase, and, ultimately, to understand thoroughly the behaviour of this novel type of supported-metal catalyst.The present work has been supported by the Cornision Asesora de Investigacidn Cientifica y TCcnica (CAICYT).S. Bernal et al. 2287 References 1 M. Ichikawa, Bull. Chem. SOC. Jpn, 1978, 51, 2273. 2 M. Ichikawa, Chemtech, 1982, 12, 674. 3 E. Ramaroson, R. Kieffer and A. Kiennemann, J. Chem. SOC., Chem. Commun., 1982, 645. 4 E. Ramaroson, R. Kieffer and A. Kiennemann, J. Chim. Phys., 1982, 79, 759. 5 E. K. Poels, E. H. Van Broekhaven, W. A. A. Van Barneveld and V. Ponec, React. Kinet, Catal. Lett., 6 Yu. A. Ryndin, R. F. Hicks and A. T. Bell, J. Catal., 1981, 70, 287.7 R. F. Hicks and A. T. Bell, J . Catal., 1985, 91, 104. 8 C. Sudhakar and M. A. Vannice, J. Catal., 1985,%, 227. 9 R. P. Underwood and A. T. Bell, Appl. Catal., 1986, 21, 157. 1981, 18, 223. 10 A. Maubert, G. A. Martin, H. Praliaud and P. Turlier, React. Kinet. Catal. Lett., 1984, 24, 183. 11 T. H. Fleisch, R. F. Hicks and A. T. Bell, J. Catal., 1984, 87, 398. 12 R. F. Hicks, Q. J. Yen and A. T. Bell, J. Catal., 1984, 89, 498. 13 S. Bernal, R. Garcia, J. M. Lopez and J. M. Rodriguez-Izquierdo, Collect. Czech. Chem. Commun., 14 S. Bernal, F. J. Botana, R. Garcia and J. M. Rodriguez-Izquierdo, Thermochim. Ada, 1983, 66, 139. 15 R. Alvero, J. A. Odriozola, J. M. Trillo and S. Bernal, J. Chem. SOC. Dalton Trans., 1984, 87. 16 S. Bernal, J. A. Dim, R. Garcia and J. M. Rodriguez-Izquierdo, J. Muter. Sci., 1985, 20, 537. 17 S. Bernal, F. J. Botana, J. Pintado, R. Garcia and J. M. Rodriguez-Izquierdo, J. Less Common Met., 18 R. F. Hicks and A. T. Bell, J. Catal., 1984, 90, 205. 19 S. Bernal, R. Garcia and J. M. Rodriguez-Izquierdo, Thermochim. Acta, 1983, 70, 249. 20 M. P. Rosynek and D. T. Magnuson, J. Catal., 1977, 48, 417. 21 V. L. Kuznetsov, I. L. Mudrakovskii, A. V. Romanenko, A. V. Pashis, V. M. Mastikhin and Yu. I. 22 S. S. Chan and A. T. Bell, J. Catal., 1984, 89, 433. 23 M. D. Mitchell and M. A. Vannice, Ind. Eng. Chem. Fundam., 1984, 23, 88. 24 C. Sudhakar and M. A. Vannice, Appl. Catal., 1984, 14,47. 1983,48, 2205. 1985, 110, 433. Yermakov, React. Kinet. Catal. Lett., 1984, 25, 137. Paper 6/819; Received 28th April, 1986

ISSN:0300-9599    

DOI:10.1039/F19878302279

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1987, 83 (8), 2289-2300 Thermodynamic Properties of the PMM A-Acetoni trile- 1,4-Dioxane Sys tem Issa Katime* and Jo& Ramon Ochoa Grupo de Macrornoleculas, Facultad de Ciencias, Universidad del Pais Vasco, Apartado 644, Bilbao, Spain Thermodynamic properties of atactic poly(methylmethacry1ate) in an ace- tonitrile-1,4-dioxane binary mixture have been studied at 298 K by vis- cometry and laser light scattering. Both techniques make evident a strong synergistic effect with its maximum close to U, = 70 YO 1,4-dioxane. The preferential sorption parameter A as obtained by laser light scattering is practically equal to zero over the whole composition range. The experi- mental values compare favourably with those obtained theoretically from several ternary solution theories.Polymer ternary systems present some special characteristics which have made them the centre of a great deal of experimental and theoretical work1-' in order to extend the knowledge of solvent-polymer interactions. These characteristics include the preferential sorption phen~menon,~' lo cosolvencyll' l2 and non-cosolvency,13 phenomena which in- dicate the importance of liquid-liquid interactions as well as polymer-solvent ones in the study of the ternary systems. Several years ago1*-19 we began in our laboratory the systematic study of polymer ternary systems. In this paper we report the study of ternary system PMMA-acetonitrile -1,4-dioxane at 298 K, using viscometry and laser light scattering (1.1s.). Experimental All solvents used in this work were from Scharlau (p.a.).Binary mixtures were made up by volume and their composition is given by means of volume fractions, U2, of 1,4-dioxane before mixing. Polymer Fractions The poly(methylmethacry1ate) (PMMA) sample was prepared by free-radical poly- merization at 343 K in benzene solution, initiated with 1,2-azobis(isobutyronitrile) (AIBN). It was divided into ten fractions by fractional precipitation from benzene solution with methanol. Four of these fractions were used for physical measurements. Their weight-average molecular weights ranged from 1.5 x lo4 to 9.9 x lo4. Polydis- persities, determined by g.p.c., lay between 1.3 and 1.4. Viscometry Measurements were carried out in a modified, previously calibrated Ubbelohde vis- cometer at 298 K.Intrinsic viscosities (v) were calculated by means of the Huggins relationship :20 v s p l C = v +kH(V)2C (1) where ftsp is the specific viscosity, c is the concentration (in g dm-3 x 10) and kH is the Huggins constant. 76 2289 FAR 12290 PMMA-Acetonitrile-l,4-Dioxane Thermodynamics the Mark-Houwink-Sakurada equation : The relationship between intrinsic viscosity and molecular weight can be expressed by where the exponent A depends on chain solvation and, for random coils, lies between 0.5 and 0.8. The unperturbed dimensions, Ke, have been evaluated using the Stockmayer- Fixman theory :14 qM-' = K0+0.5lCD, B d where B is the long-range interaction parameter and CD, represents the Flory-Fox viscosity constant for theta solvents (theoretical value 2.87 x 10,' for q in lo-' dm3 g-').Laser Light Scattering Laser light scattering (1.1s.) measurements were carried out at 298 K for three fractions with a modified FICA 42000 light-scattering photometer, where both light source and optical block of the incident beam were replaced by an He-Ne laser (Spectra Physics, model 157), which emits at 633 nm with a power of 3 mW. The photogoniodiffusometer was calibrated with benzene using natural light and taking the Rayleigh ratio as R, = 8.96 x cm-1.21 All solutions were clarified by centrifugation for 2 h at 14000 cycle min-'. Molecular weights, second virial coefficients (A,) and mean square radii of gyration ((s2)>3 were obtained by means of Zimm plots2, Preferential sorption co- efficients were calculated using the equation23 where M and M* are the true and the apparent weight-average molecular weights, respectively, (dn/dc),* is the refractive index increment at constant composition of the binary solvent mixture and dn/dU, is the refractive index increment of the binary solvent mixture with composition of component 2 (1,4-dioxane in our case).Therefore, A. represents the volume of 1,4-dioxane in excess (if M* < M) or in deficit (if M* > M ) in the vicinity of the polymer chain. Apparent second virial coefficients A,* determined experimentally were corrected for the effects of preferential solvation by means of the expression2* A , = A,*(M*/M). (3) Refractive index increments (633 nm and 298 K) were measured in a Brice-Phoenix differential refractometer using the He-Ne laser (Spectra Physics, model 156) as a light source, which emits with a power of 1 mW.The excess Gibbs function for the binary mixture acetonitrile-l,4-dioxane was determined by 1.1s. following the method developed by Coumou and Ma~kor.,~-,' Results and Discussion Excess Gibbs Function @ The excess Gibbs function , GE, free energy of mixing, G,, and ideal free energy, GI,,, of binary the mixture acetonitrile-l,4-dioxane as obtained by 1.1s. measurements at 298 K are shown in fig. 1 as a function of volume fraction of 1,4-dioxane, U,. A small positive GE, not large enough to cause G , to show a plateau, means that, compared with an ideal mixture, a tendency exists to favour slightly like contacts over unlike ones.I. Katime and J. Ramon Ochoa I 229 1 0 0.2 0.4 0.6 0.8 1 u2 Fig.1. Excess Gibbs function, G", free energy of mixing, G", and ideal free energy, Gid, of the binary mixture acetonitrile-1,4-dioxane as a function of U,, at 298 K. Viscosity Intrinsic viscosities, 7, and Huggins constants for the system PMMA-acetonitrile-l,4- dioxane at 298 K are given in tables 1 and 2, respectively, for several fractions. Fig. 2 shows the variation of the Mark-Houwink-Sakurada constants k and a for this system. Previously, we have seen that GE for the acetonitrile-174-dioxane binary mixture is positive over the entire composition range. Therefore, according to Dondos and Pat- terson,28 intrinsic viscosities of poly(methylmethacry1ate) should be higher in the binary mixture than in both pure solvents; i.e. a synergistic effect should occur in this system.The 27 values given in table 1 do not verify this prediction, probably owing to the low GE values of the binary mixture. However, in fig. 2 the synergistic effect is easily observed by taking into account the variation of the a constant of Mark-Houwink-Sakurada theory, which presents a maximum close to Uz = 0.6-0.7. Its high value at this com- position (a =4.76) reveals that this binary mixture behaves as a good solvent for poly(methylmethacry1ate). This is also seen in the variation of the interaction parameter B obtained from the Stockmayer-Fixman equation, which is plotted in fig. 3 together with the KO parameter. Poly(methylmethacry1ate) association in acetonitrile has been studied by several w ~ r k e r s . ~ ~ ~ ~ ~ This phenomenon is probably due to the fact that acetonitrile is a highly self-associated liquid.In table 2 we can see the Huggins constant values for all fractions and compositions. Except for the three higher molecular weights at Uz = 0.2, the Huggins constants are lower than 0.4, which is a typical value for unassociated coils in good solvents. In addition, in all cases, k , decreases when the amount of 1,4-dioxane in the mixture increases. All these facts explain the synergistic effect : addition of 174-dioxane to acetonitrile 76-22292 PMMA-Acetonitrile-l,4Dioxane Thermodynamics 0.75 0.73 a 0.70 0.68 0.65 Table 1. Intrinsic viscosities for PMMA-acetonitrile-1 ,Cdioxane as a function of 1,cdioxane composition U, at 298 K - - - - - n;i, 0.2 0.4 0.5 0.6 0.8 0.9 1 I I I I I I I I I 0.493 0.500 150.000 0.317 0.398 0.40 1 0.448 380.000 0.560 0.745 0.801 0.858 0.938 0.950 603.000 0.740 1.090 1.126 1.250 I .335 1.340 990.000 1.075 1.545 1.634 1.880 1.950 1.950 Table 2.Huggins constants at 298 K as a function of 1,4-dioxane composition, for several fractions i@W 0.2 0.4 0.5 0.6 0.8 0.9 150.000 0.321 0.356 0.365 0.376 0.296 0.149 380.000 0.412 0.329 0.303 0.294 0.343 0.279 603.000 0.579 0.344 0.338 0.320 0.339 0.304 990.000 0.555 0.366 0.327 0.295 0.255 0.245 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 u2 Fig. 2. Plot of k and a constants of Mark-Houwink-Sakurada us. composition U, for the system PMMA-acetonitrile-l,4-dioxane at 298 K.I. Katime and J. Ramon Ochoa 2293 8.4 - 8.0 - " I 09 * 7.6 - 2 2 7.2 - 3 I 6 . 8 - 6.4 - 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 u2 Fig.3. Plot of Kg and B parameters at 298 K us. 1,4-dioxane composition, U,, for the PMMA- acetonitrile-1 ,Cdioxane system. (a theta solvent for PMMA) breaks its self-association. The free molecules, highly polar acetonitrile together with 1,4-dioxane (a good solvent for PMMA), can interact with the polar side groups of PMMA, producing the synergistic phenomenon experimentally observed . Fig. 3 shows the variation of the parameter KO with the composition, Uz. It can be seen that KO, and therefore the unperturbed dimensions of the macromolecular coil, increases with Uz and with increasing solvent power of the binary mixture. This is expected because the solvation of the macromolecular coil by a good solvent produces swelling, which decreases the short-range interactions and, consequently, increases the unperturbed dimensions of the polymer.Eliminating the effect of the polymer conformation in solution (by dividing k of the Mark-Houwink-Sakurada equation by KO) and the effect of the solvent power of the binary mixture [by subtracting 0.5 from a], the plot of log (k/K& us. (a-0.5) should be a straight line. Fig. 4 shows that all experimental points are found to be on a straight line, demonstrating that the deviations of the KO parameter from its ideal value (ca. 5 x lo-' dm3 g-' for PMMA) is due to the solvating ability of the ~ o l v e n t . ~ ' * ~ ~ Likewise, several attempts to relate k , to the solvating ability have been made.33-3s Abdel-Azim and gave the following expression : k, a; = k,, + CBNdKi' a;' (4) where a, is the linear expansion coefficient (equal to 1 when the system is under theta solvent conditions), C is a constant and k,, is the Huggins constant under theta conditions.According to eqn (4) a plot of k , at vs. BNit4i/Kea, should be a straight line. This plot can be seen in fig. 5. Finally, we wanted to correlate experimentally observed intrinsic viscosities and2294 2 - 1 - 0- PMMA-Acetonitrile-1,4-Dioxane Thermodynamics -+-+-- I ' I ' + + A 9 + +* 0 0.1 0.2 0.3 0.4 (a -0.5) Fig. 4. Plot of log (k/K,) us. (a-0.5) for the PMMA-acetonitrile-l,4-dioxane system. O F U X * 1 . 0 1 2 3 4 5 6 BNM+IK, a,, Fig. 5. Correlation between k, and the solvating ability of the solvent for the system studied here. theoretically predicted intrinsic viscosities of ternary polymer solutions.The theories used the lattice coordination index z as an adjustable parameter. In tables 3 and 4, the experimental q values of lowest and highest weight of PMMA and the one obtained from the Flory-Shultz theory3' ( z = co) and Noel-Patterson-Somcynsky theory? (z = finite number) are compared. As can be seen, viscosities obtained from Flory-Shultz theory (z = co) are higher than the experimental ones. Improvements are observed when the Noel-Patterson-Somcynsky theory is applied. Excellent agreement is obtained for z = 3. This coordination number was also used by other a u t h o r ~ ~ ~ - ~ ~ with good success. For systems in which specific interactions, such as hydrogen bonding, play an important role3? the agreement is not satisfactory.I.Katime and J. Ramon Ochoa 2295 Table 3. Comparison between the values for &fw = 150.000 at 298 K and those obtained from both Flory-Shultz ( z = GO) and Noel-Patterson- Somcyksky ( z = 3,4) theories 0.2 0.317 0.617 0.378 0.315 0.4 0.398 0.935 0.472 0.380 0.5 0.401 0.955 0.495 0.404 0.6 0.448 0.875 0.493 0.417 0.8 0.493 0.749 0.545 0.503 0.9 0.500 0.687 0.555 0.528 Table 4. Comparison between the experimental values of the intrinsic viscosity for &fW = 990.000 at 298 K and the value obtained from Flory- Shultz ( z = GO) and Noel-Patterson-Somcyksky (z = 3,4) theories 0.2 1.075 3.59 1.480 1.065 0.4 1.545 5.13 2.072 1.470 0.5 1.634 5.26 2.220 1.623 0.6 1.880 4.73 2.212 1.709 0.8 1.950 3.65 2.300 2.022 0.9 1.950 3.19 2.320 2.146 Laser Light Scattering Refractive index increments for several compositions are given in table 5.Fig. 6 shows the variations of the second virial coefficient, A,, with 1,4-dioxany content for three PMMA fractions and the mean-square radius of gyration, (.s2)z, for one PMMA fraction of molecular weight 993 000. The variation of the second virial coefficient confirms the synergistic effect observed by viscometry, with the optimum composition close to U, = 0.7. On the other hand, (3,); follows the same variation as A,; this has to be so since the macromolecular coil dimensions are closely related to the solvating ability of the solvent. In this case the preferential sorption coefficient can be considered to be practically zero over the whole composition range if we use the experimental results plotted in fig.7. In order to compare the experimental 3, values with those obtained from theory of polymer ternary solutions we have used the Read equation :' where v3 is the partial specific volume of the polymer, U, and U2 are the volume fractions of acetonitrile and 1,4-dioxane, respectively, I = VJ Vz (where V, and V, are the molar volume of acetonitrile and 1,4-dioxane, respectively) and x12, x13, x23 and xT are in- teraction parameters. Results are summarized in table 6 together with the experimental values for the fraction with molecular weight 212000. Read's equation generates three different values for each composition, depending on2296 PMMA - Ace t onit rile- 1,4- D ioxane Them ody nam ics Table 5. Refractive index increments for the PMMA-acetonitrile-l,4-dioxane system at 633 nm and 298 K as a function of 1,4-dioxane composition U, 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 dn/dc 0.128 0.122 0.115 0.109 0.102 0.096 0.098 0.083 0.076 0.06 - 300r 200 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 u2 Fig.6. Second virial coefficients for three PMMA fractions : m, M , = 2 12 000 ; x , M , = 6 16 000 ; A, M, = 993000, and mean-square radius of gyration for the fraction of M, = 993000 us. 1,4-dioxane composition at 298 K. the method used to calculate the ternary interaction parameter: ( a ) A, when the ternary interaction parameter', is calculated from the equation : where B is the polymer-solvent binary mixture interaction parameter, N is Avogadro's number and VM is the molar volume of the binary solvent mixture; (b) Ab when the ternary interaction parameter is calculated from the equation ( c ) A, when the ternary interaction parameter is obtained from the equation:32i33 6, = s, x , +s2 x,.x12 was obtained by 1.1s. measurements using the equation x12 = GE/RTxlx2 (see table 7), and both x13 (0.5) and x,~ (0.465) were obtained from viscometric measurements in the pure solvents using eqn (6). Preferential sorption coefficients (Ad) obtained from the equation of Pouchly et aZ.41*42 and using the ternary interaction parameter xT are alsoI. Katime and J. Ramon Ochoa 2297 0.02 t I 1 7 1 4- ;bo 0.02 1 I -0.02 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fig. 7. Preferential sorption coefficients at 298 K for three PMMA fractions in the system studied here: 0, M, = 212000; (>, M , = 616000 and 0, M , = 993000.Ul Table 6. Comparison between experimental A values, Aexpt, and those obtained from Read’s equation (Aa, Ab, A,) and Pouchly’s equation (A,) at 298 K 0.2 0.49 0.46 0.82 0.03 0.03 0.08 0.03 -0.08 0.4 0.48 0.48 0.58 0.06 0.06 0.07 0.06 -0.06 0.5 0.47 0.5 1 0.49 0.06 0.06 0.06 0.05 -0.03 0.6 0.47 0.56 0.41 0.04 0.03 0.04 0.04 0.01 0.8 0.47 0.65 0.36 0.00 -0.01 0.01 0.00 0.04 0.9 0.47 0.70 0.38 0.00 -0.02 0.00 0.00 0.06 a From eqn (6). * From eqn (7). From eqn (8). given in table 7. In all cases good agreement between both experimental and theoretical II values is found, although none of the theoretical relations is able to predict the inversion in solvatation at U2 = 0.55. This inversion is questionable, if we observe carefully fig.7. Both Read’s equation and Pouchly’s equation forecast practically zero preferential sorption. This can be accounted for by bearing in mind that the different affinities of the liquids for PMMA [given by (Zx23 -xi3 +I - l)] which favour low acetonitrile adsorption are compensated by the slight incompatibility between both liquids [given by (x12 -xT), low G, values]. This fact favours 1,4-dioxane adsorption with respect to the Pouchly e q ~ a t i o n . ~ ~ * * ~ First derivatives of both x12 and xT parameters are of the order of and 1 0-3, respectively, and therefore the term Ul U2(dxl2/d U, - dX,/d U,) is negligible for this system. Consequently both Read’s equation and Pouchly’s equation predict the same values for 1 (see 1, and 1, in table 6).In spite of the agreement between the experimental and theoretical 1 values there is an important difference between the X, values obtained from Scott’s equation and from the criterion of Blanks-Prausnitz. In effect, in table 6 it can be seen that the ternary interaction parameter, xT, calculated from Scott’s equation predicts that the optimum2298 PMMA-Acetonitrile-l,4-Dioxane Thermodynamics Table 7. GE (g mol-l), activity coefficients and x12 values at 298 K as a function of volume fraction, U,, of 1,4-dioxane 0.10 -1.980 0.20 - 1.250 0.30 -0.827 0.40 -0.484 0.45 -0.320 0.50 -0.154 0.55 0.001 0.60 0.183 0.70 0.56 1 0.80 1.030 0.90 1.780 2.71 1.84 1.26 0.812 0.596 0.389 0.174 -0.051 -0.542 -1.11 - 1.90 76 0.54 153 0.55 195 0.47 214 0.42 211 0.38 218 0.37 201 0.33 188 0.30 143 0.24 111 0.22 76 0.24 Table 8.Solubility parameters, 6(J ~rn-~);, for the binary mixture acetonitrile-l,4-dioxane 0.0 15.3 18.0 6.1 24.4" 0.1 15.4 17.0 6.2 23.4 0.2 15.6 15.9 6.3 23.2 0.3 15.8 14.6 6.4 22.4 0.5 16.2 11.8 6.6 21.1 0.7 16.6 8.5 6.9 19.9 0.8 16.9 6.5 7.0 19.4 0.9 17.2 4.3 7.2 19.1 1.0 17.5 1.8 7.4 19.1" a Mean values from ref. (33), (49), (50) and (52). composition of the system is close to U2 x 0.2, very different from the experimental result (Us = 0.7). However, the Blanks-Prausnitz criterion predicts it, at least quali- tatively. The Blanks-Prausnitz criterion43 arose as an attempt to predict in a reliable manner whether a certain solvent will dissolve a particular polymer. This approach is based on the solubility parameter and regular solution theory, as developed by Hildebrand and 45 According to this theory, the closer the solubility parameters of the liquid and the polymer, the higher is the solubility of the polymer in this solvent.This theory was extended and applied in order to predict both the solubilities of polymers in s o l v e n t ~ ~ ~ * ~ ' and limiting activity coefficients of binary liquid mixtures.48 Solubility parameters of the binary mixture acetonitrile-l,4-dioxane as obtained from eqn (8) are given in table 8. Solubility parameters, S, for each composition are divided into their three contributions due to dispersions forces S,, polar interactions, 6,, and hydrogen bonding, S,, in such a way that The solubility parameter of PMMA is S = 19.5 (J cm3)f.12 Consequently, according toI.Katime and J . Ramon Ochoa 2299 solubility parameter theory the composition of the acetonitrile-l,4-dioxane mixture which best dissolves PMMA will be in the range U2 = 0.7-0.8 (table 8), in excellent agreement with the results obtained from 1.l.s. and viscometry. References 1 I. Katime, L. Gargallo, D. Radic and A. Horta, Makromol. Chem., 1985, 186, 2125; R. H. Ewart, 2 I. Katime, L. C. Cesteros and C. Strazielle, J. Chem. SOC., Faraday Trans. 2, 1984, 80, 1215; R. L. 3 A. Horta and I. Katime, Macromolecules, 1984, 17, 2734; E. F. Casassa and H. Eisenberg, J. Phys. 4 W. R. Krigbaum and S. Bywater, J. Polym. Sci., 1954, 14, 241. 5 C. Cesteros, C. Strazielle and I. Katime, J. Chem. SOC., Faraday Trans. I, 1986, 82, 1321 ; A. R.Shultz 6 P. J. Flory and T. G. Fox, J. Am. Chem. SOC., 1951, 73, 1094. 7 R. Noel, D. Patterson and T. Somcynsky, J. Polym. Sci., 1960, 42, 561. 8 J. M. G. Cowie and S. Bywater, J. Macromol. Sci., 1966, 13, 581 ; J. M. G. Cowie, Eur. Polym. J., 1972, 9 B. E. Read, Trans. Faraday SOC., 1960, 56, 382. C. P. Roe, P. Debye and J. R. McCartney, J. Chem. Phys., 1940, 14, 687. Scott, J. Chem. Phys., 1949, 17, 268. Chem., 1960, 64, 753. and P. J. Flory, J. Polym. Sci., 1954, 15, 231. 8, 1325. 10 C. Strazielle and H. Benoit, J. Chem. Phys., 1961, 58, 675. 11 I. Katime, J. R. Ochoa and J. M. Teijon, J. Chem. SOC., Faraday Trans. 2, 1985, 81, 783; B. A. Wolf 12 J. R. Ochoa, B. Caballero, R. Valenciano and 1. Katime, Muter. Chem. Phys., 1983, 9, 477. 13 A. Horta and I.Fernandez Pierola, Polym. Bull., 1980, 3, 273. 14 I. Katime and R. Valenciano, Anal. Quim., 1980, 75, 258; I. Katime, P. Garro and J. M. Teijon, Eur. 15 I. Katime and R. Valenciano, Polym. Bull., 1980, 3, 431; 1. Katime and C. Strazielle, Makromol. 16 1. Katime, L. C. Cesteros and J. R. Ochoa, Polym. Bull., 1982, 6, 447; I. Katime, R. Valenciano and 17 I. Katime, J. R. Ochoa, L. C. Cesteros and J. Petiafiel, Polym. Bull., 1982, 6, 429; I. Katime, A. 18 I. Katime, J. R. Ochoa and L. C. Cesteros, Eur. Polym. J., 1983,19, 1167; I. Katime and R. Valenciano, 19 I. Katime and J. R. Ochoa, Eur. Polym. J., 1984, 20, 99; I. Katime, R. Valenciano and T. Nuiio, 20 M. L. Huggins, Chem. Rev., 1943,32, 195. 21 B. Millaud and C. Strazielle, Makromol. Chem., 1979, 180, 441.22 B. H. Zimm, J. Chem. Phys., 1948, 16, 1099. 23 C. Strazielle and H. Benoit, J. Chim. Phys., 1961, 59, 675. 24 J. M. G. Cowie and J. T. McCrindle, Eur. Polym. J., 1972,8, 1185; J. M. G. Cowie and I. J. McEwen, Macromolecules, 1974, 7, 291 ; J. M. G. Cowie, Pure Appl. Chem., 1970, 23, 355. 25 D. J. Coumou and E. L. Mackor, Trans. Faraday SOC., 1964,60,1726; D. J. Coumou, H. Hijmans and E. L. Mackor, Trans. Faraday Soc., 1964, 60, 2244. 26 1. Katime, L. C. Cesteros and C. Strazielle, J. Chem. SOC., Faraday Trans. 2, 1984, 80, 1215; B. M. Fechner and C. Strazielle, Makromol. Chem., 1972, 160, 195. 27 I. Katime and J. R. Ochoa, Makromol. Chem., 1983, 184, 2143. 28 A. Dondos and D. Patterson, J. Polym. Sci., Part A2, 1969, 7, 209. 29 A. Suzuki, T. Hiyoshi and H.Inagaki, J. Polym. Sci., Polym. Symp., 1977, 61, 291. 30 I. Fernandez Pierola and A. Horta, J. Chem. Phys., 1977, 77, 291. 3 I I. Katime, Quimica Fisica Macromolecular (Editorial Del Castillo, Madrid, 1979). 32 1. Katime, M. Garay and J. Francois, J. Chem. SOC., Faraday Trans. 2, 1985,81, 705. 33 S . Imai, Proc. R. SOC. London, Ser. A , 1969, 308, 497. 34 H. Yamakawa, Modern Theory of Polymer Solutions (Harper and Row, London, 1971). 35 A. A. Abdel-him and M. B. Huglin, Makromol. Chem., Rapid Commun., 1981, 2, 119. 36 A. R. Shultz and P. J. Flory, J. Polym. Sci., 1955, 15, 231. 37 L. C. Cesteros and I. Katime, Eur. Polym. J., 1984, 20, 237. 38 A. Dondos and H. Benoit, Inr. J. Polym. Muter., 1976, 4, 175. 39 A. A. Abdel-Azim and M. B. Huglin, Makromol. Chem., Rapid Commun., 1982, 3, 437. 40 A. A. Abdel-Azim and M. B. Huglin, Polymer, 1982, 23, 1859; I. Katime and M. T. Garay, Polym. and G. Blaum, J. Polym. Sci., 1975, 13, 1 11 5. Polym. J., 1975, 11, 881. Chem., 1977, 178, 2295. J. M. Teijon, Eur. Polym. J., 1979, 15, 261. Campos and J. M. Teijon, Eur. Polym. J., 1979, 15, 291. Polym. Bull., 1980, 3, 431. Polym. Bull., 1982, 6, 437. Commun., 1986, 27, 74.2300 PMMA - Ace t onitr ile- 1 4 - D ioxane Them ody nam ics 41 J. Pouchly, A. Zivny and K. Solc, J. Polym. Sci., 1968,23C, 245; J. Pouchly and A. Zivny, Makromol. 42 A. Zivny, J. Pouchly and K. Solc, Collect. Czech. Chem. Commun., 1967, 32, 2753; J. Pouchly and 43 R. F. Blanks and J. M. Prausnitz, Ind. Eng. Chem., 1964, 3, 1. 44 J. Hildebrand and R. Scott, The Solubility of Non-electrolytes (Reinhold, New York, 3rd edn, 1949). 45 J. Hildebrand and R. Scott, Regular Solutions (Prentice-Hall, Englewood Cliffs, N.J., 1962). 46 Ch. M. Hansen, J. Paint Technol., 1967, 39, 104. 47 C. A. Thomas and Ch. A. Eckert, Ind. Eng. Chem. Process Des. Dev., 1984,23, 194; D. M. Koenhen 48 Z. Righ~, Polymer, 1978, 19, 1229. Chem., 1982, 183, 3019. A. Zivny, Makromol. Chem., 1983, 184, 2081. and C. A. Smolders, J. Appl. Polym. Sci., 1975, 19, 1163. Paper 6/907; Received 12th May, 1986

ISSN:0300-9599    

DOI:10.1039/F19878302289

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. Soc., Faraday Trans. I , 1987, 83 (8), 2301-2309 Molecular Mobility of Methane adsorbed on ZSM-5 containing Co-adsorbed Benzene, and the Location of the Benzene Molecules Christoph Forste, Andreas Germanus, Jiirg Karger" and Harry Heifer Sektion Physik der Karl- Marx- Universitat Leipzig, German Democratic Republic Jiirgen Caro and Walther Pilz Zentralinstitut fur Physikdische Chemie der Akaakmie der Wissenschaften der DDR, Berlin, German Democratic Republic Arlette Zikanovai Heyrovsky Institute, Academy of Sciences of the CSSR, Praha, Czechoslovakia The molecular mobility of methane adsorbed on ZSM-5 as investigated by both the n.m.r. pulsed field gradient technique and proton magnetic relax- ation studies is found to decrease significantly with increasing amounts of coadsorbed benzene molecules.Comparison with a computer simulation of the random-walk process within the ZSM-5 network suggests that the channel intersections, rather than the channel segments between them, should form the adsorption sites of the benzene molecules. Both the second moments of the proton magnetic resonance lines of methane, as determined from the transverse relaxation times, and the laser-Raman spectra of benzene adsorbed on ZSM-5 are in agreement with this model. During the last few years the pentad-type zeolites have been seen as promising ad- sorbents and shape-selective catalysts. 1* Whereas single component studies of ben~ene~-~ and methaneS-l3 in ZSM-5 have been repeatedly presented in literature, in this paper the first results of two-component adsorption studies of methane-benzene mixtures on an almost Al-free ZSM-5 zeolite (silicalite2) are reported.From previous investigations it can be concluded that the diffusion coefficient D of methane adsorbed on ZSM-S2 is more than three orders of magnitude greater than that for benzene.l This experimental finding is in accordance with the fact that the kinetic diameter of a benzene molecule (0.585 nm") is approximately equal to the diameter of the ZSM-5 channels (ca. 0.55 nml*') and exceeds significantly the diameter of a meth- ane molecule (0.38 nm14). A model of the mixed adsorption of methane and benzene on ZSM-5 may therefore be based on the following assumptions: (i) because of their low self-diffusivity the benzene molecules may be regarded as fixed in space with respect to the mobile methane molecules; (ii) since the benzene molecules practically fill out the cross-section of the pore segment or channel intersection in which they are located, they represent obstacles for the diffusional motion of the methane molecules.The microdynamical behaviour of methane-benzene mixtures adsorbed on ZSM-5 was studied by the n.m.r. pulsed field gradient technique and proton magnetic relaxation time measurements. The application of combined n.m.r. methods has become a powerful tool for studying the sorption state and sorption dynamics of guest molecules in mic- roporous systems. 15-17 Especial benefit to the investigation of transport phenomena in heterogeneous systems has been given by the n.rn.r. pulsed field gradient technique.18* l9 The results obtained by n.m.r.methods are complemented by Raman spectroscopy investigations of the location of benzene molecules adsorbed on ZSM-5. 23012302 Mobility of CH, adsorbed on ZSM -5 Experimental We have applied laboratory-synthesized ZSM-5 with a silicon-to-aluminium ratio > 1000 and an average crystal size of 30 x 25 x 15 pm3 as determined by s.e.m. All n.m.r. samples were prepared according to the following procedure : the zeolite material was introduced into 8 mm 0.d. glass tubes and activated at 400 "C until the pressure was < 3 x Pa. After the activation, volumetrically determined amounts of the adsorbates were frozen into the glass tubes at liquid-nitrogen temperature. In all cases methane was adsorbed before introducing benzene.After loading the tubes were sealed off. To eliminate magnetic dipolar proton-proton interaction between the methane and benzene molecules the latter were used in the perdeuterated form. Therefore the primary information available from the proton magnetic resonance measurements refers to the microdynamical behaviour of the methane molecules. The loading of the samples cor- responds to 1 and 2 molecules methane per 0.25 unit cell for the proton magnetic relaxation and self-diffusion measurements, respectively, and to values between 0 and 1.4 benzene molecules per 0.25 unit cell. One unit cell (u.c.) of the ZSM-5 structure comprises four channel intersections and four straight and four sinusoidal pore segments. The self-diffusion measurements were carried out on a home-built pulsed field gradient spectrometer at a proton magnetic resonance frequency of 60 MHz." As previously described,15* 16* l9 self-diffusion data were determined by monitoring the proton magnetic resonance signal intensity as a function of the width of the pulsed field gradient.The proton magnetic relaxation time measurements were carried out using a home-built spectrometer with a resonance frequency of 90 MHz. The Raman spectra were measured using a home-made plane grating monochroma- tor2' with a photon-counting device and an argon laser ILA 120 (VEB Carl Zeiss Jena) at 488 nm and ca. 100 mW. Results and Discussion Intracrystalline Self-diffusion of Methane in the Binary Mixture Methane-Benzene adsorbed on ZSM-5 Fig. 1 shows values for the self-diffusion coefficient of methane adsorbed on ZSM-5 as a function of the amount of coadsorbed benzene, and it can be seen that the existence of the benzene molecules leads to a significant decrease in the methane mobility.In view of (i) the large difference in the mobilities of the two coadsorbed molecular species and (ii) the similarity in the cross-sections of the benzene molecules and the intracrystalline channels, it should be possible to simulate the influence of the benzene molecules on the methane mobility by introducing rigid obstacles into the channel network, thereby assuming that the number of obstacles is equal to the number of benzene molecules. It is evident that the effect of these obstacles on molecular diffusion should depend decisively on their position within the channel network: for benzene molecules located in the segments between the channel intersections, the passage through these segments only is prohibited, whereas benzene occupation of the channel inter- sections should lead to a blocking of all four adjacent channel segments.Fig. 2 shows the results of a computer simulation2' of the random-walk process in a two-dimensional channel network with obstacles distributed statistically (i) over the channel intersections, (ii) over the channel segments and (iii) over the whole network, i.e. over both channel intersections and segments. By allowing for different types of obstacle location these calculations represent an extension of the procedures presented by Ruthven22 and Theodorou and Wei.23 The transition probabilities for passing the obstacles have been chosen to be 0.004, 0.020 and 0.120, respectively.As expected, the influence of the obstacles distributed overC. Fiirste et al. 2303 t \. \ * \ 7 \* I .\ L \ t 2* no. of coadsorbed benzene molecules per 0.25 U.C. Fig. 1. Self-diffusion coefficient of methane adsorbed on ZSM-5 at 293 K vs. the amount of coadsorbed benzene. the channel intersections considerably exceeds the influence of the obstacles in the channel segments. As a consequence, a statistical distribution of the obstacles over both the channel segments and intersections (as indicated in fig. 2 for the medium transition probability) leads to an intermediate dependence between these two limiting cases. The computer calculation shows that the shape of the individual plots of In D vs.the amount N of introduced obstacles is typical of the given type of obstacle distribution, i.e. there is no possibility of transferring the In D us. N plots of one limiting case to those of the other by simply changing the transition probability across the obstacles. The experi- mental results on the influence of the coadsorbed benzene molecules on the methane mobility are found to be in good agreement with the theoretical dependence calculated according to model (i). Therefore one has to conclude that in the considered range of loading of the zeolite the benzene molecules are predominantly located in the channel intersections. In this way they effect a maximum hindrance of the intracrystalline translational motion of the coadsorbed methane molecules.Proton Magnetic Relaxation Studies Fig. 3 shows the temperature dependence of the longitudinal and transverse proton magnetic relaxation times and T, of methane adsorbed on ZSM-5 for different2304 Mobility of CH, adsorbed on ZSM -5 1 1 1 1 1 1 1 1 0.5 1.0 no. of obstacles per 0.25 U.C. or no. of coadsorbed benzene molecules per 0.25 U.C. Fig. 2. Computer simulation of the random-walk process in a two-dimensional network with obstacles distributed statistically in the pore segments (m), in the channel intersections (a) and in both the pore-segments and channel intersections (A) for transition probabilities to pass a barrier (obstacle) of 0.004 (-), 0.020 (-.-.-) and 0.120 (----), and comparison with the results of the methane self-diffusion measurements in ZSM-5 (0, cf.fig. 1). amounts of coadsorbed benzene. Following well established procedure^'^-^^ these data were used to characterize both molecular dynamics and arrangements. The quantity directly accessible by the longitudinal proton magnetic relaxation time is the molecular mean residence time z between two succeeding jumps, since it could be shown by an appropriate analysis15* 24 that for temperatures in the neighbourhood of the & minimum the longitudinal proton magnetic relaxation is controlled by magnetic dipolar interaction with paramagnetic impurities fixed in the zeolite lattice. This interaction is modulated through the translational motion of the molecules and hence at the minimum of & 15* l6 z = w;;s (1) where ores denotes the proton magnetic resonance frequency (27t x 90 x lo6 s-l) kept constant during the experiments.From the temperature dependence & in fig. 3 it follows that the coadsorption of benzene dramatically influences the proton magnetic relaxation behaviour of methane. Only for medium amounts of coadsorbed benzene can a well defined & minimum be observed in the temperature range studied. With increasingC. Fijrste et al. 2305 0 1 2 3 4 5 6 7 8 9 1 0 3 ~ / ~ Fig. 3. Proton magnetic relaxation times T, (full symbols) and T, (open symbols) of methane adsorbed on ZSM-5 as a function of temperature for 0 (A, A), 0.3 (0, O), 0.7 (V, V), and 1.4 (m, 0 ) coadsorbed molecules of perdeuterated benzene per 0.25 U.C. benzene concentrations the minimum is shifted to temperatures above this temperature interval, while for smaller sorbate concentrations the minimum is found at the lower end.For zero benzene adsorption the minimum is very much below the temperature range studied. Since according to condition (1) at the temperature of the q minima the values of z for methane adsorbed on the different samples are identical, the molecular mobility of methane is found to decrease with an increasing amount of coadsorbed benzene. This is the sequence observed in the n.m.r. self-diffusion studies. While the methane self- diffusivities for benzene concentrations above 0.6 molecules per 0.25 U.C. were found to be beyond the range directly accessible by the n.m.r. pulsed field gradient technique, the proton magnetic relaxation measurements allow us to consider a concentration range up to at least 1.4 molecules of benzene per 0.25 U.C.From the lowest and highest benzene concentrations (0 and 1.4 molecules per 0.25 u.c., respectively) and the extrapolated q minima (103K/Tk 8.5 and 5 2.5, respectively) according to eqn (1) one has to conclude that the methane mobility in the benzene-free sample at T 5 118 K will be attained in the sample with 1.4 molecules of benzene per 0.25 U.C. for temperatures k 400 K. Combining the self-diffusion data with the results of the q measurements, additional information about the elementary steps of molecular translational motion may be2306 Mobility of CH, adsorbed on ZSM -5 obtained. In the case of diffusion by activated jumps in a three-dimensional lattice the mean-square jump length may be estimated from the equation:25 (12) = 602 (2) where z denotes the mean molecular residence time between two succeeding jumps. Introducing eqn (1) into eqn (2) it follows that For the sample with 0.3 coadsorbed benzene molecules per 0.25 u.c., the self-diffusion coefficient of methane at the temperature of the minimum ( Tmin = 160 K) was obtained to be equal to (2.5 Ifr 1.5) x 10-l' m2 s;l.With this value and u),,, = 211. x 90 MHz eqn (3) yields an r.m.s. jump length of (12)s x 2 nm. According to the proposed model for a loading of 0.3 molecules per 0.25 U.C. ca. every third intersection is blocked by a benzene molecule. Hence the mean distance between two barriers should be of the order of three times the distance between two adjacent channel intersections, i.e.3 x(1-1.2) nm,lV2 so that jump lengths of the calculated value appear to be in reasonable agreement with the proposed distribution of the benzene molecules. It follows from the temperature dependence shown in fig. 3 that for temperatures below 160 K and for benzene concentrations above 0.3 molecules per 0.25 U.C. the transverse proton magnetic relaxation time & of methane remains constant. Approxi- mating the lineshape (and hence also the free-induction decay) of the proton magnetic resonance signal in these cases by a Gaussian function, the so-called second moment is given by the relation where y is the gyromagnetic ratio of the protons. On the other hand, using Van Vleck's formula15 the second moment can be calculated for a given spatial arrangement of the protons and deuterons in the sample.In order to decide whether the experimental values, determined via eqn (4) for the second moment, are in agreement with the proposed model, we consider a molecular arrangement characterized by the following assump- tions. (i) The loading of the ZSM-5 sample corresponds to two molecules of methane and one molecule of benzene per 0.25 U.C. (ii) Every channel intersection is occupied by a single benzene molecule. According to ref. (6) these molecules perform rapid rotation about their hexad axis so that the six deuterium nuclei may be regarded as localized in the centre of the molecule. (iii) Each pore segment contains one methane molecule, effectively captured between the two benzene molecules of the adjacent intersections. Since these methane molecules are able to perform rapid isotropic reorientation their intramolecular contribution to the second moment is negligible. Evidently, these conditions prescribe a special case of molecular arrangement, which is compatible with the proposed model.On the other hand, they allow a straightforward calculation of the second moment,24 leading to a value of 0.038 x T2. It can be seen from the comparison of this theoretical value with the experimental data for the different benzene loadings in table 1 that the absolute values of the transverse nuclear magnetic relaxation times in the low-temperature region are in fact in satisfactory agreement with the theoretical value anticipated on the basis of the suggested model.= 2(YW2 (4) Laser-Raman Spectroscopic Investigations and the Molecular Arrangement of Benzene in ZSM-5 According to potential calculations by Thomas and coworkers26 both the channel intersections and the pore segments might be expected to act as adsorption sites for benzene in ZSM-5. In the light of the presented pulsed field gradient and proton magneticC. F6rste et al. 2307 Table 1. Comparison of the experimental data for the second moment of methane in ZSM-5 with coadsorbed benzene, as determined via eqn (4) from the transverse nuclear magnetic relaxation times, T,, in the low-temperature region, with the theoretical value calculated on the basis of a specified molecular arrangement [(i)-(iii)] anticipated on the basis of the n.m.r.self- diffusion measurements benzene loading /molecules per 0.25 U.C. T,/F <(AB)2)/10-8 T2 experimental 0.3 450 0.014 0.7 300 0.03 1.4 200 0.07 theoretical 1 .o 0.038 I I 7QE nnn 992 jjIm-l 992 997 Fig. 4. Laser-Raman spectra of the silicalite framework (a) the adsorbate-adsorbent system benzene-silicalite (b) and the band of adsorbed benzene at 992 cm-I (slit width I cm-') for 1.1 (1) and 1.7 (2) molecules per 0.25 U.C. and comparison with the ,corresponding band in the gaseous state (---).2308 Mobility of CH, adsorbed on ZSM -5 relaxation measurements with coadsorbed methane, at benzene loadings below one molecule per 0.25 U.C. it seems more likely that the benzene molecules are located in the intersections. The proposed model is in accordance with the observation that up to benzene con- centrations of one molecule per 0.25 U.C.the heats of adsorption remain unchanged4 or decrease ~lightly,~ and that the entropy of adsorption decreases monotonically3* with increasing sorbate concentrations, as is expected in the case of localized adsorption on sites separated from each other. Furthermore, the proposed model implies that owing to the necessary rearrangements for sorbate concentrations above one molecule per 0.25 u.c., changes in the state of adsorption should occur. It is indeed remarkable that in this concentration range (probably as a consequence of a benzene-benzene interaction and accompanying molecular rearrangements) irregular heat effects were observed.* As a further technique sensitive to molecular interactions we have applied laser- Raman spectroscopy to benzene adsorbed on silicalite.Since the Raman spectrum of the unloaded silicalite [fig. 4(a)] has its most intense bands in the Si-0-Si symmetric bonding region at a frequency of 385 cm-' and in weak stretching modes near a frequency of 800 cm-l, the Raman bonds of adsorbed benzene molecules [fig. 4(b)] are only slightly disturbed by the silicalite spectrum. For benzene adsorbed on zeolite NaX Freeman and Unland2' found a one-mode behaviour for the strong Raman band at 992 cm-l (symmetry type A,) depending on the amount adsorbed. Contrary to this result, benzene adsorbed on ZSM-5 exhibits a characteristic two-mode behaviour. Fig. 4 (c) shows the laser-Raman spectra of benzene at concentrations of 1.1 and 1.7 molecules per 0.25 U.C.For smaller loadings only a single band is observed at a frequency of 992 cm-l, equal to that of benzene in the gaseous state. In full agreement with the suggested model, one has to conclude, therefore, that the benzene molecules are located at the most isotropic sites within the channel system, i.e. at the channel intersections. At higher sorbate concentrations an additional band at 997 cm-' appears and is attributed to benzene molecules on other adsorption sites, e.g. the pore segments between the intersections. References 1 D. H. Olson, G. T. Kokotailo, S. L. Lawton and W. M. Meier, J. Phys. Chem., 1981, 85, 2238. 2 E. M. Flanigan, J. M. Bennett, R. W. Grose, J. P. Cohen, R. L. Patton, R. M. Kirchner and J. V. Smith, Nature (London), 1978, 271, 512.3 C. G. Pope, J. Phys. Chem., 1984,88,6312. 4 R. Wendt, H. Thamm, K. Fiedler and H. Stach, 2. Phys. Chem. (Leipzig), 1985, 266, 289. 5 A. Zikanova, M. Biilow and H . Schlodder, Zeolites, 1987, 7, 115. 6 B. Zibrowius, M. Biilow and H. Pfeifer, Chem. Phys. Lett., 1985, 120, 420. 7 P. Wu, A. Debebe and Y . H. Ma, Zeolites, 1983, 3, 118. 8 U. Lohse and B. Fahlke, Chem. Tech., 1983, 35, 350. 9 H. Papp, W. Hinsen, N. T. Do and M. Baerns, Thermochim. Acta, 1984, 82, 137. 10 A. V. Kiseljev, A. A. Lopatkin and A. A. Schulga, Zeolites, 1985, 5, 261. 11 J. Caro, C. Hdevar, J. Karger and L. Riekert, zeolites, 1986, 6, 213. 12 J. Caro, M. Biilow, W. Schirmer, J. Kfirger, W. Heink, H. Heifer and S. P. Zdanov. J. Chem. SOC., 13 J. Caro, M. Biilow and J. Klrger, Chem. Eng. Sci., 1985, 40, 2169. 14 D. W. Breck, Zeolite Molecular Sieves (John Wiley, New York, 1974). I5 H. Heifer, in NMR-Basic Principles and Progress, ed. P. Diehl, E. Fluck and R. Kosfeld (Springer- Verlag, Berlin, 1972), vol 7, p. 53. 16 H. Heifer, Phys. Rep., 1976, 26, 293. 17 H. A. Resing, A h . Mol. Relax. Process., 1968, 1, 109. 18 J. Karger, A h . Colloid Interface Sci., 1985, 23, 129. 19 J. Klrger, H. Pfeifer and W. Heink, A h . Magn. Reson., 12, in press. 20 H. Drommert, E. Kleimon and W. Pilz, Exp. Techn. Phys., 1969, 17,498. 2 1 A. Germanus, Thesis (Karl-Marx-Universittit Leipzig, 1986). 22 D. M. Ruthven, Can. J. Chem., 1974, 52, 3523. Faraday Trans. 1, 1985, 81, 2541.C. Forste et al. 2309 23 D. Theodorou and J. Wei, J. Catal., 1983, 83, 205. 24 C. Forste, Diplomarbeit (Karl-Marx-Universitat Leipzig. 1985). 25 J. Klrger, S. P. a a n o v and A. Walter, 2. Phys. Chem. (Leipzig), 1975, u6, 319. 26 S. Ramdas, J. M. Thomas, P. W. Betteridge, A. K. Cheetham and E. K. Davies, Angew. Chem., 1984, 27 J. J. Freeman and M. L. Unland, J. Catal., 1978, 54, 183. 96, 629. Paper 61941; Received 15th May, 1986

ISSN:0300-9599    

DOI:10.1039/F19878302301

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J . Chern. Soc., Faraday Trans. I, 1987, 83 (8), 2311-2316 Non-ideal Behaviour of Benzene Solutions of Tri-n-octylammonium Bromide and Cyclohexanol Cveto Klofutar" and Spela Paljk J . Stefan Institute, E. Kardelj University of Ljubljana, 61000 Ljubljana, Yugoslavia The practical osmotic coefficients for the benzene-tri-n-octylammonium bromidexyclohexanol system have been determined by the cryoscopic method and expressions for the activity coefficients of both solutes in the ternary system have been deduced. The regression coefficients for these expressions have been obtained via the Gibbs-Duhem relation. The effects of different media on the solute activity coefficients have been elucidated by the total, primary and secondary medium effects. In addition, values of the partial molar Gibbs free energy of transfer at infinite dilution of tri-n-octylammonium bromide for various constant concentrations of cyclohexanol and vice versa have been determined, together with the limiting value of their derivatives. In the past, the non-ideality of benzene solutions of tri-n-alkylammonium salts was described on the basis of solute-solute interactions due to the mutual interactions of the dipoles of hydrogen-bonded ion pairs, while solute-solvent interactions in these systems were considered negligible.lP3 On the other hand, the non-ideality of benzene solutions of cyclohexanol was interpreted by the formation of higher oligomeric species due to the hydrogen bonds between alcohol molecules, as well as by solute-solvent interactions between alcohol molecules and the aromatic s01vent.~ In the present study some thermodynamic properties of benzene solutions of tri-n- octylammonium bromide and cyclohexanol have been determined with the aim of elucidating the colligative properties of a ternary system in which the mutual interactions of both solutes are not negligible.5 Experimental Benzene (Riedel de Haen) was purified as described in ref.(6). Tri-n-octylammonium bromide (TOAHBr) was prepared and purified as described in ref. (7), and cyclohexanol (ROH) (Riedel de Haen) was purified as described in ref. (4). Cryoscopic measurements were performed as described in ref. (3). Results and Discussion The activity coefficient of TOAHBr, In y,, in a ternary system may be given by m a In yz = C C Aijm~i2m!!; A,, = 0 i-0 j - 0 when Aij are the regression coefficients and m,(mol kg-l) and m,(mol kg-l) are the concentrations of TOAHBr and ROH, respectively.If relation (1) is expanded to all terms up to i = j = 4, it follows that In y, = A,, mi i- A,, m, +A,, m, i- A,, mi m, +Ao, mg + A,, mi i- A,, m, m, i- A,, mi mi i- AO3 mi +A4, mi -k A,, mi m, i- A,, m, mg +A,, mi rn; +A,, m:. 231123 1 2 The Benzene-Tri-n-octylammonium Bromide-Cyclohexanol System Taking into account for the activity coefficient of TOAHBr in a binary system, In y;, the expression3 relation (2) reduces to lny: = A,,m~+A,,m,+A,,m~+A,,m~ (3) In y, = In y: +A,, m3 + A,, mi m3 + A,, mi + A,, m, m3 + Al2m$m; +AO3m:+A,, mim, + A,, m2m; + A13 mi m: +A,, mb. (4) On the basis of the cross-differentiation relation and taking relation (4) for In y,, the following expression for the activity coefficients of ROH, In y3, in a ternary system is obtained: where In y,* is the activity coefficient of ROH in a binary ~ystem.~ For a ternary system the Gibbs-Duhem relation is given by 103 - d In a, +m, d ln (m, y,) +m3 d In (m, y 3 ) = 0 Ml (7) where a, is the activity of the solvent in the ternary system, defined as In a, = -a, (m, +m3) M1/103.(8) In relation (8) a, is the practical osmotic coefficient of a ternary system and Ml (g mol-l) is the molar mass of solvent. Using the above expressions for In a,, In y, and In y3 in the Gibbs-Duhem relation for a ternary system, after some mathematical manipulation, the following equation is obtained : A -- - A,, +All mi +2A,2 ma +A,, m 2 m 2 m3 which correlates the experimentally accessible quantity A/m, m3 = [(m, + m3)q5 - rn, q$; - m3 #,*]/m, m38(& and #,* are the practical osmotic coefficients of binary benzene solutions of TOAHBr and ROH, respectively) with the concentrations of TOAHBr and ROH.From relation (9), the regression coefficients A, [see relations (1)-(6)], can be obtained by the method of multiple linear regression.C. Klofutar and s. Paljk 2313 Table 1. Values of concentrations for TOAHBr and ROH, practical osmotic coefficients and A/ m2 m3 for the ternary system benzene-TOAHBr- ROH at the freezing point of benzene 0.059 0.059 0.059 0.059 0.059 0.059 0.059 0.120 0.120 0.121 0.121 0.121 0.121 0.122 0.185 0.185 0.185 0.186 0.186 0.186 0.187 0.252 0.253 0.253 0.254 0.254 0.255 0.255 0.323 0.324 0.324 0.325 0.326 0.326 0.327 0.023 0.045 0.067 0.088 0.108 0.127 0.146 0.024 0.046 0.068 0.090 0.1 10 0.130 0.149 0.024 0.048 0.070 0.092 0.1 13 0.133 0.153 0.025 0.049 0.072 0.094 0.1 16 0.136 0.157 0.025 0.050 0.073 0.096 0.1 18 0.140 0.161 0.601 0.649 0.672 0.685 0.687 0.690 0.689 0.457 0.484 0.504 0.514 0.523 0.53 1 0.540 0.380 0.390 0.406 0.4 12 0.426 0.435 0.442 0.332 0.339 0.348 0.359 0.364 0.370 0.379 0.293 0.300 0.303 0.309 0.316 0.322 0.327 1.700 1.687 1.647 1.535 1.540 1.432 1.349 2.319 2.249 2.1 15 2.046 1.937 1.806 1.641 2.337 2.339 2.103 2.046 1.838 1.699 1.592 1.973 1.947 1.831 1.679 1.603 1.521 1.401 1.687 1.642 1.613 1.526 1.429 1.340 1.270 The experimental data for the ternary system investigated are given in table 1.The practical osmotic coefficients at the freezing point of benzene, 8 (in K), were calculated via the relation3 where Ar = rT -r!(in a) is the difference of the thermistor resistance at the temperature of the freezing point of the solution, T (in K), and of the pure solvent, respectively, and KCry is a constant.From table 1 it can be seen that in the ternary system investigated the practical osmotic coefficients at constant concentration of TOAHBr increase with increasing concentration of ROH, and at constant concentration of ROH the p values decrease with increasing concentration of TOAHBr. P (4 +m3) = Kcry (ArIr*) (10)23 14 The Benzene-Tri-n-octylammonium Bromide-Cyclohexanol System r-----7 0.000 -0.100 n *m + --. i." W = -0:m -0.300 0.065 0.130 0.195 0.260 rnJmo1 kg-' Fig.1. The total medium effect for TOAHBr in the system investigated. Values of rn3 are marked on the curves. 0.300 n 0.050 $ E - W 0.030 0.060 OD90 0.120 rn,/mol kg-' Fig. 2. The total (-) and secondary (- - - - -) medium effects for ROH in the system investigated. Values of rn, are marked on the curves. The values of A/rn,rn, given in table 1 were calculated from the experimental data, and the values of q; and q,* were calculated at definite concentrations through relation (3) of ref. (3) and relation (3) of ref. (4), respectively. The regression coefficients A, were calculated via relation (9) by the method of multiple linear regression. The optimal number of terms used in the right-hand side of eqn (9) was obtained on the basisC.Klofutar and s. Paljk 231 5 of the minimum value of the standard error of the estimate. The values of constant A,, and of the partial regression coefficients obtained are as follows: Aol =3.93; A,, = = -34.4k4.1; A,, = -64.1 k 10.3. The standard error of the estimate is s = 0.04, and the coefficient of multiple correlation is R = 0.994. Values of q recalculated via relation (9) using the A, coefficients given above are within k 2 x of those given in table 1. On the basis of the regression coefficients A, obtained it can be seen that the activity coefficients of TOAHBr in benzene solutions at constant concentration of ROH [relation (4)] and vice versa [relation (6)] decrease with increasing concentration of TOAHBr and ROH, respectively. However, the effect of TOAHBr on the activity coefficimt of ROH is greater than that of ROH on the activity coefficient of TOAHBr.The effects of choice of media on the activity coefficients of the solutes investigated are shown in figs. 1 and 2.' The total medium effect is defined as the ratio of the solute activity coefficient in a ternary mixture to that in a binary mixture at the same solute concentration. The values of total medium effect for TOAHBr at constant concentration of ROH, In (y,/y,*), and for ROH at constant concentration of TOAHBr, In (y3/y:), are negative. In the case of TOAHBr with increasing concentration of TOAHBr these values reach a minimum at rn, x 0.15 mol kg-', while in the case of ROH they increase with increasing concentration of ROH over the whole concentration range studied.At a given concentration of one solute these effects are more pronounced the higher the concen- tration of the other solute. The limit to which the values of total medium effect converge as the concentration of the solute under investigation approaches zero is considered to be the primary medium effect. For TOAHBr the values of lim [In (y2/y3] = lirn [In y, as rn, + O at m3 = constant] are positive and close to zero, while in the case of ROH the corresponding values of lim [In (y3/$)] = lim [In y 3 as m3 + 0 at m, = constant] are negative and decrease with increasing concentration of TOAHBr. The difference between the total and primary medium effects is treated as the secondary medium effect. In the case of TOAHBr the secondary medium effect is practically equal to the total medium effect, while in the case of ROH these values are positive and, with increasing con- centration of ROH, increase in the same way as the total medium effect.The medium effects for the investigated systems may be considered to be a consequence of complex formation between the hydroxylic proton of the alcohol molecule and the bromide ion of the tri-n-octylammonium salt taking place via a hydrogen bond. The possibility of complex formation in such systems was confirmed on the basis of electric permittivity data" and on the basis of infrared spectroscopic data.ll For the investigated systems, complex formation between the two solutes may be deduced from the de- pendence of the practical osmotic coefficients as a function of concentration of cyclo- hexanol at constant concentration of tri-n-octylammonium bromide (see table 1).At a given salt concentration the practical osmotic coefficients increase slightly with increasing concentration of cyclohexanol. From this it may be concluded that the concentration of species of both solutes are reduced owing to complex formation between the hydroxylic proton and the bromide anion. The increase in chemical potential when 1 mol of TOAHBr is isothermally transferred from benzene at a given concentration of TOAHBr to a benzene-ROH mixture of the same concentration of TOAHBr : -38.2k2.3; A02 ~ - 6 . 2 k 2 . 0 ; A21 = 69.3k5.3; A12 =46.9*9.2; A03 =4.2&3.8; A31 TOAHBr (benzene) = TOAHBr (benzene + ROH) (1 1) is the excess partial molar Gibbs free energy, (J mol-l), for TOAHBr, and is equal to its partial molar Gibbs free energy of transfer, AG2,tr (J mol-l).12 This value at infinite dilution can be obtained from AG& = RT lirn (In y,) = RT(A,, m3 +A,, m: + A03 mi) (12)23 16 The Benzene-Tri-n-octylammonium Bromide-Cyclohexanol System at m, = constant, while, by analogy, for the isothermal transfer of ROH from benzene to a benzene-TOAHBr mixture ROH (benzene) = ROH (benzene +TOAHBr) (13) is obtained from AG& = RTlim(1n 7,) =RT A,,m,+-m~+-m~+--rn~) 2All ' 2A31 (14) 3 2 5 at m, =constant. The values of AG& obtained are positive, small and increase with increasing concentration of ROH: AG& = 1.2 J mol-' (m, = 0.05 mol kg-l); 9.7 J mol-' (m, = 0.10 mol kg-') and 32.9 J mol-' (m, = 0.15 mol kg-').Those of AG& are negative and decrease with increasing concentration of TOAHBr: AG& = -21.5 J mol-' (m, = 0.05 mol kg"), -534 J mol-' (m, = 0.15 mol kg-') and - 1310 J mol-' (m, = 0.30 mol kg-l).The limiting value of the derivatives of a AGZt,/6m3 as m, -+ 0 and of 6AG&,/6rn2 as m2 + 0 is equal to the value of RTA,, = 9.1 kJ rnol-, kg. We thank Mrs J. Burger for skilful technical assistance and the Slovene Research Community, Ljubljana, and the National Science Foundation, Washington, D.C. for financial support. References I C. Klofutar, 3. Paljk, and M. hmer, J. Chem. Soc., Perkin Trans. 2, 1978, 292. 2 C. Klofutar and 3. Paljk, J. Chem. Soc., Faraday Trans. I , 1979, 75, 825. 3 C. Klofutar and 3. Paljk, J. Chem. SOC., Faraday Trans. I , 1981, 77, 2705. 4 3. Paljk, C. Klofutar, D. Rudan-TasiE, J. Chem. Soc., Faraday Trans. I , 1985, 81, 1141. 5 E. A. Richardson and K. H. Stern, J. Am. Chem. Soc., 1960,82, 1296. 6 C. Klofutar, 3. Paljk and D. Kremser, J. Znorg. Nucl. Chem., 1975, 37, 1729. 7 C. Klofutar and 3. Paljk, J. Inorg. Nucl. Chem., 1978, 40, 515. 8 V. E. Bower and R. A. Robinson, J . Phys. Chem., 1963, 67, 1524. 9 H. S. Harned and B. B. Owen, The Physical Chemistry of Electrolytic Solutions (Reinhold, New York, 10 E. Grunwald, S. Highsmith and I. Ting-Po, in Ions and Zon Pairs in Organic Reactions, ed. M. Szwarc 1 1 S. C. Mohr, W. D. Wilk and G. M. Barrow, J. Am. Chem. Soc., 3048, 1965. 12 A. G. Morachevsky, N. A. Smymova, I. M. Balachova and I. B. Pukinsky, Thermodynamics of Diluted 2nd edn, 1950), p. 516. (Wiley, New York, 1974), vol. 2, p. 447. Solutions of Nonelectrolytes (Himia, Leningrad, 1982), p. 32. Paper 61996; Received 22nd May, 1986

ISSN:0300-9599    

DOI:10.1039/F19878302311

出版商:RSC    

年代:1987

数据来源: RSC