摘要:

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

ISSN:0300-9599    

DOI:10.1039/F198682FX031

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

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

ISSN:0300-9599    

DOI:10.1039/F198682BX033

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ISSN 0300-9599 JCFTAR 82(9) 262 1-3052 (1 986) 262 1 2627 2635 2645 265 1 2665 2673 269 1 2707 2719 2729 2735 2747 2755 2763 2773 278 1 279 1 JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions 1 Physical Chemistry in Condensed Phases CONTENTS Limitations of Evaluation Methods for Inhibited Oxidation Processes in the Liquid Phase K. He'berger, J. Lukaics and T. Vid6czy The Electrical Conductivity of Carbon-fibre Adsorbents. An Attempt to Discriminate between Chemisorption and Physisorption of Chlorine H. Tobias, H. Cohen and A. Soffer Effect of Support and Promoter on the Coadsorption of Carbon Monoxide and Hydrogen on Fischer-Tropsch Cobalt Catalysts R. Gopalakrishnan and B. Viswanathan Distribution of Silicon-to-Aluminium Ratios in Zeolite ZSM-5 J-C. Lin and K-J. Chao The Partitioning of Solutes between Water-in-Oil Microemulsions and Conju- gate Aqueous Phases P.D. I. Fletcher Catalytic Decomposition of Isopropanol over Chromite Spinels MCr,O, (M = Ni, Mn and Mg) K. Balasubramanian and V. Krishnasamy Stochastic Models of Multi-species Kinetics in Radiation-induced Spurs P. Clifford, N. J. B. Green, M. J. Oldfield, M. J. Pilling and S. M. Pimblott A New Equation for the Retention of Solutes in Liquid-Solid Adsorption Chromatography with Mixed Mobile Phases G. H. Findenegg and F. Koster Surface Acidity of some Re,O,-containing Metathesis Catalysts. An in situ Fourier-transform Infrared Study using Pyridine Adsorption X. Xiaoding, J. C. Mol and C. Boelhouwer Chemisorption and Catalysis by Metal Clusters. Hydrogenation of Ethene and Hydrogenolysis of Ethane catalysed by Supported Ruthenium Clusters derived from Ru,(CO),, and from H,Ru,(CO),, R.B. Moyes, P. B. Wells, S. D. Jackson and R. Whyman Electron Spin Resonance Evidence for the Structure of AgI1 and Ago Solvates in Acetonitrile M. C. R. Symons, D. Russell, A. Stephens and G. Eastland Direct Measurement of Temperature-dependent Interactions between Non-ionic Surfactant Layers P. M. Claesson, R. Kjellander, P. Stenius and H. K. Christenson Photocatalytic Dehydrogenation of Liquid Propan-2-01 by TiO,. Part 2.- Mechanism I. M. Fraser and J. R. MacCallum Conductivity of Unsymmetrical and Mixed Electrolytes. Dilute Aqueous Cad- mium Chloride and Barium Chloride-Hydrochloric Acid Mixtures at 298.15 K K. Indaratna, A. J. McQuillan and R.A. Matheson Transport Numbers of Dilute Aqueous Cadmium Chloride Solutions at 298.15 K K. Indaratna, A. J. McQuillan and R. A. Matheson Infrared Study of Water and Pyridine Adsorption on the Surface of Anhydrous Vanadyl Pyrophosphate S. J. Puttock and C. H. Rochester Concentration Effects in Exclusion Chromatography. Quantitative Prediction in 8-Polymeric Systems R. Tejero, V. Soria, B. Celda and A. Campos The Volumetric Behaviour of Poly(viny1 alcohol) in Aqueous Solution N. J. Crowther and D. Eagland 87 FAR 1280 1 281 1 2817 2825 2833 2843 2851 2863 2873 2887 2897 291 1 2915 2929 2933 2945 295 1 2965 2977 Contents The Accuracy of the Derjaguin Approximation for the Electrostatic Double- layer Interaction between Curved Surfaces bearing Constant Potentials E.Barouch, E. Matijevic' and V. A. Parsegian Free-energy Parameters for the Complexation of Metal Ions and Cryptand 222 in Propan-1-01 and for the Transfer and Partition of Cryptand 222 in Water- Alcohol Systems A. F. Danil de Namor, H. Berroa de Ponce and E. C. Viguria The Effect of Acid Treatment on the Properties of Dealuminated Y Zeolite M. J. Hey, A. Nock, R. Rudham, I. P. Appleyard, G. A. J. Haines and R. K. Harris Exchange of Metal Atoms in Solid Mixed-valence T1: TlrT1C16. Conductivity and Positron Annihilation Investigations S. M. Fernandez-Valverde and G. Dupliitre Radiation Generation of Radical Cations of Amides. An Electron Spin Reso- nance Study G. w. Eastland, D. N. R. Rao and M. C. R. Symons Interactions between Metal-complex Ions and Water.Part 3.-Entropies of Solution and Heat Capacity Changes of Metal-complex Ions in Water at 25 "C K. Kurotaki Zeolites treated with Silicon Tetrachloride Vapour. Part 3.-Atom-Atom Potential Calculations for the Adsorption of Xenon M. W. Anderson, J. Klinowski and J. M. Thomas Thermodynamic Parameters for Transfer of Resorcinol Monoethers from Water to Heptane and to Propylene Carbonate. Derivation and Analysis of Group Transfer Thermodynamic Parameters A. E. Beezer, P. L. 0. Volpe and W. H. Hunter Standard Thermodynamic Functions of the Gaseous Actinyl Ions MO;+ and for their Hydration Y. Marcus and A. Loewenschuss Adsorption and Decomposition of Mo(CO), in Zeolite NaY Y-S. Yong and R. F. Howe The Reversed-flow Gas-chromatography Technique applied to the Kinetics of the Methanation of Carbon Monoxide E.Dalas, N. A. Katsanos and G. Karaiskakis Inner-sphere Reorganization Energy of Ions in Solution using the Ion-Dipole Orbiting Potential M. S. Tunuli and S. U. M. Khan A Study of the Effects of Heat Treatment on the Physical Properties of the Carbon Black Vulcan 3 D. H. Everett and R. J. Ward Microcalorimetric Measurement of the Enthalpies of Transfer of a Series of rn-Alkokyphenols from Isotonic Aqueous Solution to Escherichia coli Cells A. E. Beezer, P. L. 0. Volpe, R. J. Miles and W. H. Hunter Electron Migration in Hydrated DNA and Collagen at Low Temperatures. Part 1.-Effect of Water Concentration D. van Lith, J. M. Warman, M. P. de Haas and A. Hummel Electron Migration in Hydrated DNA and Collagen at Low Temperatures. Part 2.-The Effect of Additives D.van Lith, J.Eden, J. M. Warman and A. Hummel Inferfacial Tension Minima in Oil-Water-Surfactant Systems. Systems con- taining Pure Non-ionic Surfactants, Alkanes and Inorganic Salts R. Aveyard and T. A. Lawless Aqueous Solutions containing Amino Acids and Peptides. Part 24.-Free Energetic and Enthalpic Coefficients for the Interactions of some Prolyl and Sarcosyl Terminally Substituted Compounds at 25 "C G. M. Blackburn, T. H. Lilley and P. J. Milburn Liquid Structure and Second-order Mixing Functions for Benzene, Toluene and p-Xylene with n-Alkanes G. Tardajos, E. Aicart, M. Costas and D. PattersonContents Application of a Solvent-coupled Model to a Calculation of Partial Molar Isobaric Heat Capacities of Neutral and Ionic Solutes in Aqueous Solution.Estimates of Isobaric Heat Capacities of Activation M. J. Blandamer, J. Burgess, A. W. Hakin and J. M. W. Scott Irrelevance of Gas Evolution to Oscillations in the Belousov-Zhabotinsky System R. M. Noyes Reactions of Recoil 38Cl Atoms with Dichloroethanes K. Berei, L. Vasaros and I. Kiss Infrared Study of the Adsorption of Carbon Monoxide, Carbon Dioxide, Acetic Acid and Acetic Anhydride on the Surface of Anhydrous Vanadyl Pyrophos- phate S. J. Puttock and C. H. Rochester Coadsorption of Methanol and Carbon Dioxide on Alumina J. Lamotte, 0. Saur, J-C. Lavalley, G. Busca, P. F. Rossi and V. Lorenzelli A Single-turnover (STO) Study of the Effect of Heat on Catalyst Activity R. L. Augustine and K. P. Kelly Infrared Study of the Adsorption of But-1-ene, Buta-l,3-diene, Furan and Maleic Anhydride on the Surface of Anhydrous Vanadyl Pyrophosphate S.J. Puttock and C. H. Rochester Reviews of Books G. Saville; N. M. Atherton; A. K. Covington; G. C. Bond; G. J. T. Tiddy; C. Kemball; Th. F. Tadros; 0. R. Brown; W. G. Richards; J. S. Higgins; D. Chapman; M. Spiro; G. Williams; D. E. Parry; J. C. R. Turner 2989 2999 3003 3013 3019 3025 3033 304 1 87-2Contents Application of a Solvent-coupled Model to a Calculation of Partial Molar Isobaric Heat Capacities of Neutral and Ionic Solutes in Aqueous Solution. Estimates of Isobaric Heat Capacities of Activation M. J. Blandamer, J. Burgess, A. W. Hakin and J. M. W. Scott Irrelevance of Gas Evolution to Oscillations in the Belousov-Zhabotinsky System R. M. Noyes Reactions of Recoil 38Cl Atoms with Dichloroethanes K. Berei, L. Vasaros and I. Kiss Infrared Study of the Adsorption of Carbon Monoxide, Carbon Dioxide, Acetic Acid and Acetic Anhydride on the Surface of Anhydrous Vanadyl Pyrophos- phate S. J. Puttock and C. H. Rochester Coadsorption of Methanol and Carbon Dioxide on Alumina J. Lamotte, 0. Saur, J-C. Lavalley, G. Busca, P. F. Rossi and V. Lorenzelli A Single-turnover (STO) Study of the Effect of Heat on Catalyst Activity R. L. Augustine and K. P. Kelly Infrared Study of the Adsorption of But-1-ene, Buta-l,3-diene, Furan and Maleic Anhydride on the Surface of Anhydrous Vanadyl Pyrophosphate S. J. Puttock and C. H. Rochester Reviews of Books G. Saville; N. M. Atherton; A. K. Covington; G. C. Bond; G. J. T. Tiddy; C. Kemball; Th. F. Tadros; 0. R. Brown; W. G. Richards; J. S. Higgins; D. Chapman; M. Spiro; G. Williams; D. E. Parry; J. C. R. Turner 2989 2999 3003 3013 3019 3025 3033 304 1 87-2

ISSN:0300-9599    

DOI:10.1039/F198682FP109

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

JOURNAL OF THE CHEMICAL SOCIETY 1297 1305 1315 1327 1339 1351 1365 385 399 413 1427 1445 1457 1469 1475 1481 1489 Faraday Transactions II, Issue 9, I986 Molecular and Chemical Physics For the benefit of readers of Faraday Transactions Z, the contents list of Faraday Transactions ZZ, Issue 9, is reproduced below. The Status of Transition-state Theory in Non-ideal Solutions and Application of Kirkwood-Buff Theory to the Transition State D. G. Hall Application of Gibbs-ensemble Methods to Reaction Kinetics in Non-ideal Systems D. G. Hall A311 and B3Z- Excited States of the SO Radical. Part 3.-The 0-0 Band Spectrum of the A 311,-X3E- Transition M. A. A. Clyne and P. H. Tennyson Properties of the Phenomenological Coefficients in the Cases of Dependent Fluxes and/or Dependent Forces.A Unified Theorem E. 0. Timmermann Velocity Correlation Functions in Different Reference Frames. Their Relation with Phenomenological and Empirical Transport Coefficients F. 0. Raineri and E. 0. Timmermann Salt Velocity Correlation Functions : A Microscopic Interpretation. Part 1 .- Solution of a Single Binary Electrolyte F. 0. Raineri and E. 0. Timmermann Shear Thinning and Thickening of the Lennard-Jones Liquid. A Molecular Dynamics Study D. M. Heyes Quantum Chemical Studies of Alumina. Part 3.-Acidity and Basicity of the Spinel-type Crystal H. Kawakami and S. Yoshida Transfer of Atoms, Ions and Molecular Groups in Solution. Part 4.-Methods for Metropolis/Monte Carlo Simulations P. P. Schmidt Pressure Dependence of the Reactions of HO, with C1 and ClO F.C. Cattell and R. A. Cox A Theoretical Characterization of some Diatomic Copper Species M. T. Nguyen, M. A. McGinn and N. J. Fitzpatrick Relative Rate Study of the Addition of HO, Radicals to C,H, and C3H, R. R. Baldwin, C. E. Dean and R. W. Walker Photo-oxidation of Methyl Orange Sensitised by Zinc Oxide. Part 1.- Mechanism J. R. Darwent and A. Lepre Photochemical Studies of Porphyrin-Melanin Interactions J. Bielec, B. Pilas, T. Sarna and T. G. Truscott Water Photolysis with Copper@) Chlorides K. Tennakone and S. Wickramanayake Methoxyl Radical Fluorescence in the Electron Impact Excitation of Dimethyl- ether and Related Compounds C. A. F. Johnson, S. D. Kelly and J. E. Parker Ionic States of S,N, and Assignment of its Photoelectron Spectrum W. von Niessen, J.Schirmer and L. S. Cederbaum1499 1521 1537 1543 1563 Crystal Structure and C-C1 Bond Properties of 2,6-Dichloroacetanilide, 2,6- Cl,C,H,NHCOCH,, Phase I and Phase 11. An X-Ray and Cl Nuclear Quadrupole Resonance Single-crystal Study V. Nagarajan, H. Paulus, N. Widen and A. Wiess Computer Simulation of Water between Metal Walls N. G. Parsonage and D. Nicholson Translational Energy Threshold for the Reaction of Oxygen Atoms with Benzene Molecules A. Gonzalez Ureiia, S. M. A. Hoffmann, D. J. Smith and R. Grice lH-Nuclear Magnetic Resonance Studies on Structural Phase Transitions and Molecular Dynamics of Five-membered Rings in Solid Ferrocene, Azaferrocene and Ruthenocene A. Kubo, R. Ikeda and D. Nakamura Spin-exchange Processes in Transition-metal Complexes H.D. Burrows and S. J. Formosinho The following papers were accepted for publication in J. Chem. SOC., Faraday Trans. I during June 1986 51 1634 511665 5/21 58 6/21 1 61264 61290 61328 61432 61532 61584 61599 61643 Bromate Influence of Mixed Iron@) Sulphate Cerium(1v) Sulphate and Ferroin Catalysts on Oscillatory Redox Reaction between Malonic Acid and Bromate F. F. D. Alba and S. Di Lorenzo Molecular-orbital Studies of C-H Bond Scission induced by Ionizing Radi- ation T. Tada Hydrocarbon Formation from Methylating Agents over the Zeolite Catalyst ZSM-5: Comments on the Formation of Methane G. J. Hutchings, M. V. M. Hall and R. Hunter The Kinetics of Solubilisate Exchange between Water Droplets of a Water-in-Oil Microemulsion Using Ion-selective Electrodes to Study the Thermodynamics of Solutions.Part 2.-The Standard Gibbs Free Energies of Transfer of NaCl and KCl from Water to Butanol (Four Isomers) -Water Mixtures Chu Deying, Zhang Qian and Liu Builin Catalytic Reduction of Nitrogen Monoxide with Carbon promoted by Potas- sium T. Okuhara and K. Tanaka An Electron Nuclear Double-resonance Study in Glassy Matrix of Nitroxide Radicals with Delocalized Spin Density M. Brustolon, A. L. Maniero, U. Segre and L. Greci Estimations of Stability Constants by Potentiometry of Some Lanthanum and Erbium Dicarboxylates at Constant Ionic Strength C. B. Monk Concentration Dependence of Spin Friction Coefficients in Suspensions of Parallel Cylinders and Spheres J. H. Masliyah and T. G. M. van de Ven Fourier-transform Infrared Investigation of Structures of Vanadium Oxide on Various Supports H.Miyata, K. Fujii, T. Ono, Y. Kubokawa, T. Ohno and F. Hatayama Kinetics of Reaction with Hydroxide Ions and Solubilities of Iron(I1) Complex Cations in Aqueous Urea Solutions ; Derivation of Transfer Chemical Potentials for Initial and Transition States M. J. Blandamer, J. Burgess, A. W. Hakin, P. Guardado, S. Nuttall and S. Radulovic Absence of Fast HS-Ion Motion in Aqueous Solution of HC1. A Neutron Scattering Study H. Bertagnolli, P. Chieux and H. G. Hertz P. D. I. Fletcher, A. M. Howe and B. H. Robinson (ii)6/645 61673 6/716 61747 61770 61772 5/816 61872 6/909 61980 Investigation of the Mechanism of the Photocatalytic Alcohol Dehydrogenation over Pt/TiO, by using Poisons and Labelled Ethanol P.Pichat, M.N. Mozzanega and H. Courbon Dynamic Kinetics of CO Oxidation over Magnesium Oxide M. Kobayashi, T. Kanno and Y. Konishi The Use of Hydride-forming Rare-earth-Co Intermetallic Compounds in the Dehydrogenation of Propan-2-01 H. Imamura, K. Nukui, K. Yamada, S. Tsuchiya and T. Sakai A Magnetic Resonance Study of the Reactions of the Tetrahydroxyborate Ion with Two Chiral I,3-Diols J. G. Dawber Phosphorus-3 1 Nuclear Magnetic Resonance Studies of Solid Diphosphine Disulphides : Crystallographic Considerations R. K. Harris, L. H. Merwin and G. Hagele Dynamic Properties and Structure of Salt-free Polystyrene Sulphonate Solu- tions H. Vink Fourier-transform Infrared and Catalytic Study of the Evolution of the Surface Acidity of Zirconium Phosphate following Heat Treatments G.Busca, V. Lorenzelli, P. Galli, A. La Ginestra and P. Patron0 Theoretical Analysis of Activation Parameters in Mixed Solvents involving Various Chemical Equilibria. Reaction of Ethyl Iodide with Bromide Ion in N-Methy lace tamide- Ace toni trile and N- Methy lacet amide-N,N-Dime t hyl- acetamide Mixtures Y. Kondo and S. Kusabayashi Kinetics of the Solvolysis of the cis-Dichlorobis( 1,2-diaminoethane) Cobalt(II1) ion in Water and in Water-t-Butyl Alcohol Mixtures G. S. Groves, A. F. M. Nazer and C. F. Wells Chemisorption and Catalysis by Metal Clusters. Hydrogenation of Carbon Monoxide and Carbon Dioxide Catalysed by Supported Ruthenium Clusters derived from Ru,(CO),, and from H,Ru,(CO),, S. D. Jackson, R. B. Moyes, P. B. Wells and R. Whvman 6/ 1 100 The Oxidation of Crystalline UO, studied using X-Ray Photoelectron Spectro- scopy and X-Ray Diffraction 611 130 Spin Trapping Study of the Radiolysis of CCl, A.Halpern 6/ 1 13 1 Biomolecular Dynamics and Electron Spin Resonance Spectra of Copper Antitumour Agent Complexes in Solution R. Basosi, L. Trabalzini, R. Pogni and W. E. Antholine 6/1132 Use of Nitroxides to Measure Redox Metabolism in Cells and Tissues H. M. Swartz 6/ 1 133 Addition-Elimination Paths in Electron Transfer Reactions between Radicals and Molecules: Oxidation of Organic Molecules by the OH Xadical S. Steenken 61 1 142 Radical Production Evidenced by Dimer Analysis in y-Irradiated Amines in Aqueous Solutions and in the Solid State A. C. Dusaucy, J. De Doncker, C. Couillard, M. De Laet and B.Tilquin 611 176 Promotion of Methanol Synthesis and the Water-Gas Shift Reactions by Adsorbed Oxygen on Supported Copper Catalysts G. C. Chinchen, M. S. Spencer, K. C. Waugh and D. A. Whan 6/ 1221 Catalytic Implications of Local Electronic Interactions between Carbon Mon- oxide and Coadsorbed Promoters on Nickel Surfaces J. M. MacLaren, D. D. Vvedensky, J. B. Pendry and R. W. Joyner G. C. Allen, P. A. Tempest and J. W. Tyler (iii)Cumulative Author Index 1986 Abu-Gharib, E.-E. A., 1471 Abuladze, N. A., 2481 Adams, D. M., 1020 Adams, M., I979 Aicart, E., 2977 Aida, M., 1619 Aika, K-i., 2269 Al-Hakim, M., 1575 Albery, W. J., 1033 Allen, G. C., 1367 Alwis, U. de, 1265 Ammann, D., 1179 Anderson, J. A., 1911 Anderson, M. W., 569, 1449, Anderson, S. L. T., 1537 Anderson, T., 767 Andre, O., 2423 Antoniou, A.A., 483 Appleyard, I. P., 2817 Araya, P., 1351, 2473 Atherton, N. M., 3042 Attwood, D., 1903 Augustine, R. L., 3025 Avent, A. G., 1589 Aveyard, R., 125, 1031, 1755, Balasubramanian, K., 2665 Baldwin, R. R., 89 Balk, R. W., 933 Barone, G., 2089 Barouch, E., 2801 Bartlett, J. R., 597 Bartlett, P. N., 1033 Battisti, A. De, 2481 Baur, J., 1081 Becker, K. A., 2151 Beezer, A. E., 2863, 2929 Belton, P. S., 451 Benecke, J. I., 1945 Bennett, C. O., 2155 Berei, K., 3003 Berezin, I. V., 319 Bernstein, T., 1879 Berroa de Ponce, H., 281 1 Berry, F. J., 1023 Berti, P., 2547 Bhattacharyya, S. N., 2103 Bieth, H., 1935 Binks, B. P., 125, 1031, 1755 Biswas, P. K., 1973 Blackburn, G. M., 2965 Blake, P. G., 723 Blandamer, M. J., 1022, 1471, Blesa, M.A., 2345 2851 295 1 2989 Bloemendal, M., 53 Bloor, D., 21 11 B. Nagy, O., 1789 Boelhouwer, C., 1945, 2707 Bond, G. C., 1985, 3043 Booth, B. L., 2007 Booth, C., 1865 Boucher, E. A., 1589 Bozonnet-Frenot, M-P., 2185 Brereton, I. M., 1999 Brett, C. M. A., 1071 Brigandi, P. W., 1032 Brillas, E., 495, 178 1 Brown, 0. R., 3045 Bruckenstein, S., 1105 Buck, R. P., 1169 Bui, V. T., 899 Burch, R., 1985 Burgess, J., 1471, 2989 Busca, G., 3019 Cabani, S., 2547 Cameron, P., 1389 Campos, A., 2781 Canet, D., 2185 Carley, A. F., 723 Carpenter, T. A., 545 Casal, B., 1597 Cass, A. E. G., 1033 Castro, V. Di, 723 Castronuovo, G., 2089 Celda, B., 2781 Cenens, J., 281 Cesteros, L. C., 1321 Champion, J. V., 439 Chang, C. D., 1032 Chao, K-J., 2645 Chapman, D., 3048 Chiou, C.T., 243 Chitale, S. M., 663 Christenson, H. K., 2735 Chung, J. S., 2155 Claesson, P. M., 2735 Clark, B., 1471 Clark, S., 125 Clarke, R. J., 2333 Clewley, J. D., 2589 Clifford, A. A., 2235 Coates, J. H., 2123, 2333 Cochran, S. J., 1721 Cohen de Lara, E., 365 Cohen, H., 2627 Coller, B. A. W., 943 Compostizo, A., 1839 Conti, G., 2547 Contreras Viguria, E., 281 1 Cooney, R. P., 597 Copperthwaite, R. G., 1007 Cortes, J., 2473 Cortes, J., 1351 Corti, H. R., 921 Costas, M., 2977 Covington, A. K., 1209,3042 Craston, D. H., 1033. Craven, J. R., 1865 Crespo Colin, A., 1839 Crilly, J. F., 439 Crowther, N. J., 2791 Crudden, J., 2195, 2207 Dalas, E., 2897 Danil de Namor, A. F., 349, Das, M. N., 1973 Dawber, J. G., 119 de Haas, M. P., 2933 De Schrijver, F. C., 281 Dean, C.E., 89 Dearden, S. J., 1627 Del Vecchio, P., 2089 Delaney, G. M., 2195, 2207 Delannay, F., 2423 Delaval, Y., 365 Delmon, B., 2423 Dharmalingam, P., 359 Dias Peiia, M., 1839 Domen, K., 2269 Domknech, J., 1781 Dore, J. C., 241 1 Duatti, A., 1429 Duce, P. P., 1471 Duplitre, G., 2825 Eagland, D., 2008, 2791 Eastland, G., 2729 Eastland, G. W., 2833 Ebeid, E-Z. M., 909 Eden, J., 2945 Edmonds, R. N., 2515 Edwards, P. P., 2515 Egdell, R. G., 2003 Ekechukwu, A. D., 1965 El-Daly, S. A., 909 Elbing, The Late E., 943 Elia, V., 2089 Elworthy, P. H., 1903 Espenscheid, M. W., 1051 Espinosa-Jimhez, M., 329 Evans, D. F., 1829 Everett, D. H., 2589, 2605, 2915 Ewen, R. J., 1127 Farnia, G., 1885 Feakins, D., 563, 2195, 2207 Fegan, S. G., 785, 801 Fernandez-Prini, R., 921 281 1AUTHOR INDEX Fernandez-Valverde, S.M., 282 Findenegg, G. H., 2001,2691 Fink, P., 1879 Fisher, D. T., 119 Flanagan, T. B., 2175,2589 Fletcher, A. J. P., 2605 Fletcher, P. D. I., 231 1, 2651 Folman, M., 2025 Fouids, N. C., 1259 Fraser, I. M., 607, 2747 Freiser, H., 1217 Freund, P. L., 2277 Fricke, R., 263, 273 Fukuda, H., 1561 Funabiki, T., 35, 707, 1771 Fyles, T. M., 617 Gaboriaud, R., 2301 Gabrys, B., 1923, 1929 Ganghi, N. S., 2367 Garbassi, F., 2043 Garbowski, E., 1893 Garrido, J. A., 1781 Gellan, A., 953 Geoffroy, M., 521 Gervasini, A., 1795 Ghatak-Roy, A. R., 1051 Ghoneim, M. M., 909 Ghousseini, L., 349 Gilbert, R. G., 1979, 2247 Gilhooley, K., 431 Gobolos, S., 2423 Gomez-EstCvez, J. L., 2167 Gonzalez-Caballero, F., 329 Gonzalez-Elipe, A. R., 739 Gonzilez-Fernandez, C.F., 329 Gopalakrishnan, R., 2635 Gormally, J., 157, 2497 Gorton, L., 1245 Gosal, N., 1471 Green, M. J., 1237 Green, N. J. B., 2673 Grieser, F., 1813, 1829 Gritzner, G., 1955 Grzybkowski, W., 1381, 1703, Guardado, P., 1471 Haddad-Fahed, O., 2301 Haggett, B. G. D., 1033 Haines, A. J., 2817 Haines, G. A. J., 2817 Hakin, A. W., 1471, 2989 Hall, D., 21 11 Halle, B., 401, 415 HansCn, O., 77 Harris, R. K., 2817 Harrison, M. R., 2515 Havredaki, V. I., 2531 Heatley, F., 255 Heberger, K., 2621 Hedges, W. M., 179 Hellring, S. D., 1032 Hemfrey, J. P., 1589 Hersey, A., 1271 Hewitt, E. A., 869 Hey, M. J., 1805, 2817 I745 Heyrovsky, M., 585 Hidaka, H., 2615 Higgins, J. S., 1923, 1929, 2004, 3047 Higson, S., 157 Hill, C. A. S., 1127 Hill, H. A. O., 1237 Hill, T., 349 Hitchman, M.L., 1223 Hobert, H., 1527, 2505 Hobson, D. B., 869 Homer, J., 533 Honeybourne, C. L., 1127 Honeyman, M. R., 89 Hooper, A., 11 17 Houghton, J. D., 1127 Howe, A. M., 2411 Howe, R. F., 2887 Hronec, M., 1405 Hsu, W. P., 851 Huang, W-S., 2385 Hubbard, C. D., 1471 Hummel, A., 2933, 2945 Humphrey, B. D., 2385 Humphreys, F. J., 1020, 2006 Hunt, D. J., 189 Hunter, W. H., 2863,2929 Hussian, S. M., 2221 Hutchings, G. J., 1007 Ige, J., 2011 Iizuka, T., 1681, 61 Ikeda, H., 61 Ikeda, O., 1561 Indaratna, K., 2755, 2763 Indelli, A., 1429 Inomata, S., 1733 Inoue, M., 2175 Inoue, T., 168 1 Ishii, T., 2615 Ishikawa, T., 2401 Issa, R. M., 909 Iwamoto, M., 1713 Jackson, S. D., 189, 431, 2719 Jaeger, N., 205 Japaridze, J. I., 2481 Japaridze, S. S., 2481 Jayasuriya, D.S., 457,473 Jensen, M., 1351 Johns, A. I., 2235 Johnson, D. C., 1081 Johnson, J., 1081 Johnston, P., 1007 Jones, W., 545 Jonson, B., 767 Jose, C. I., 663, 681, 691 Kadhum, A. A. H., 2521 Kakuta, N., 1553 Kamat, P. V., 1031 Kaminade, T., 707 Kaner, R. B., 2323 Karaiskakis, G., 2897 Katime, I., 1321, 1333 Katsanos, N. A., 2897 Kavetskaya, 0. I., 319 Kawaguchi, T., 1441 (4 Kawai, S., 527 Kawai, T., 527 Kazusaka, A., 1553 Kelly, H. C., 1271 Kelly, K. P., 3025 Kelly, R. G., 1195 Kemball, C., 3044 Kevan, L., 213 Khan, S. U. M., 2911 Khoo, K. H., 1 Kido, K., 2269 Kinoshita, N., 2269 Kishimoto, S., 2175 Kiss, I., 3003 Kjellander, R., 2735 Kleine, A., 205 Klinowski, J., 569, 1449, 2851 KodejS, Z., 1853 Komatsu, T., 1713 Komiyama, M., 1713 Kondo, S., 2401 Kondo, Y., 2141 Koreeda, A., 527 Koresh, J.E., 2057 Koster, F., 2691 Kowalak, S., 2151 Kremer, M. L., 2133 Krishnasamy, V., 2665 Kuji, T., 2589 Kurotaki, K., 2843 Kusabayashi, S., 2141 Kuzuya, M., 1441 Lamotte, J., 3019 Lancz, M., 883 Lang, J., 109 Langevin, D., 2001 Larkins, F. P., 1721 Larsson, R., 767 Lavalley, J-C., 30 19 Lawless, T. A., 1031, 2951 Lawrence, K. G., 563, 2195, Lawrence, M. J., 1903 Leaist, D. G., 247 Lelikvre, J., 2301 Lionard, J., 899 Lilley, T. H., 2965 Lim, T.-K., 69 Lin, J-C., 2645 Lincoln, S. F., 1999, 2123, 2333 Llars, S., 767 Llinares, A., 521 Lockhart, J. C., 1161 Loewenschuss, A., 993,2873 Logan, S. R., 161 Lomen, C. E., 1265 Lorenzelli, V., 3019 Lowe, B. M., 785, 801 Lowe, C. R., 1259 Lukacs, J., 2621 Lundin, S. T., 767 MacCallum, J. R., 607, 2747 MacDiarmid, A.G., 2323, 2385 Mactaggart, J. W., 1805 Mahnke, R., 1413 2207Malliaris, A., i09 Mandal, P. C., 2103 Manes, M., 243 Marabini, A. M., 2043 Maran, F., 1885 Marchal, J-P., 2185 Marcus, Y., 233,993, 2873 Marczewski, M., 1687 Maroto, A. J. G., 2345 Marshall, W. L., 2283 Martin, C. R., 1051 Maruthamuthu, P., 359 Marx, U., 2505 Mastikhin, V. M., 1879 Matheson, R. A., 2755,2763 Mathieu, M-V., 1893 Matijevid, E., 2801 Matsuda, T., 1357 McCarthy, S., 943 McQuillan, A. J., 2755, 2763 Mead, J., 125, 1031, 1755 Melchor, A., 1893 Miale, J. N., 1032 Miasik, J. J., 1117 Midgley, D., 1187 Milburn, P. J., 2965 Miles, R. J., 2929 Minami, Z., 1357 Mishima, S., 1307 Mishra, S. P., 521 Miura, H., 1357 Miyake, Y., 1515 Miyamoto, A., 13 Mobbs, R. H., 1865 Mol, J. C., 1945, 2707 Mollett, C.C., 1589 Mollica, V., 2547 Molyneux, P., 291, 635 Moore 111, R. B., 1051 Morando, P. J., 2345 Morazzoni, F., 1795 Morgan, H., 143 Mori, K., 13 Moyes, R. B., 189,2719 Mulla, S. T., 681, 691 Murakami, Y., 13 Murata, M., 2615 Muscetta, M., 2089 Nagano, S., 1357 Najbar, M., 1673 Nakajima, T., 1307 Nakamatsu, H., 527 Nakanishi, M., 1441 Nakano, A., 2141 Napper, D. H., 1979,2247 Narayana, M., 213 Neto, M. M. P. M., 1071 Neuburger, G. G., 1081 Nikitas, P., 977 Nitta, S., 2401 Nock, A., 2817 Noyes, R. M., 2999 Nyasulu, F. W. M., 1223 Oakes, J., 2079 Oesch, U., 1179 AUTHOR INDEX Ogino, Y., 1713 ohlmann, G., 263, 273 Okazaki, S., 61 Okuda, T., 1441 Oldfield, M. J., 2673 Oldham, K. B., 1099 Onai, T., 2615 Onishi, T., 2269 Ooe, M., 35 Opallo, M., 339 Orchard, S.W., 1007 Oref, I., 1289 OReilly, P. J., 2195, 2207 Ortiz, A., 495 Owen, A. E., 1195 Parbhoo, B., 1789 Park, C-N., 2589 Parry, D. E., 3051 Parsegian, V. A., 2801 Parsons, B. J., 1575 Patterson, D., 2977 Pease, W. R., 747, 759 Peeters, G., 963 Peeters, S., 963 Penboss, I. A., 2247 Penner, R. M., 1051 Perry, M. C., 533 Pethig, R., 143 Petropolos, J. H., 2459 Petropoulos, J. H., 2531 Pettersson, A., 2435 Pham, H. V., 1179 Phillips, G. O., 1575 Piculell, L., 387, 401, 415 Piekarska, A,, 513 Piekarski, H., 513 Pilarczyk, M., 1703, 1745 Pilling, M. J., 2673 Pimblott, S. M., 2673 Pinna, F., 1795 Pletcher, D., 179 Polta, J. A., 1081 Polta, T. Z., 1081 Porter, S . J., 2323 Pouchlf, J., 1605 Primet, M., 1893 Puchalska, D., 1381 Puttock, S. J., 2773, 3013, 3033 Quintana, J.R., 1333 Radulovic, S., 1471 Rajaram, R. R., 1985 Ramakrishna Rao, D. N., 2367 Ramdas, S., 545 Rao, D. N. R., 2833 Rashid, S., 2235 Rebenstorf, B., 767 Richards, W. G., 3047 Richardson, P. J., 869 Rideout, J., 167 Rigby, S., 431 Rizkallah, P. J., 1589 Roberts, M. W., 723 Robinson, B. H., 1271, 2311, Robinson, P. J., 869 241 1 (vi) Rochester, C. H., 953, 1805, Rodriguez, R. M., 1781 Rooney, J. J., 2005 Rosenholm, J. B., 77, 2435 Rossi, P. F., 3019 Rouw, A. C., 53 Rubio, R. G., 1839 Rudham, R., 2817 Ruiz-Hitzky, E., 1597 Russell, D., 2729 Ryder, P. L., 205 Sacchetto, G. A., 1853 Saez, C., 1839 Saleh, J. M., 2221 Salmon, G. A., 161,2521 Sanchez, F., 1471 Sandonh, G., 1885 Sangster, D. F., 1979 Saris, P., 2435 Sarkhny, A,, 103 Saur, O., 3019 Saville, G., 3041, 3046 Sawada, K., 1733 Scharpf, O., 1923, 1929 Schiller, R.L., 2123 Schlosserovh, J., 1405 Schmelzer, J., 1413, 1421 Schmitt, K. D., 1032 Schoonheydt, R. A., 281 Scott, J. M. W., 2989 Scott, R. P., 1389 Segall, R. L., 747, 759 Seloudoux, R., 365 Sen& M., 2065 Sharma, S., 2497 Shibata, Y., 1357 Shigeto, M., 1515 Shindo, H., 45 Shubin, A. A., 1879 Sidahmed, 1. M., 2577 Siiman, O., 851 Simmons, R. F., 1965 Simon, W., 1179 Sircar, S., 831, 843 Smallridge, M. J., 1589 Smart, R. St C., 747,759 Smith, D. G., 2569 Smith, I., 869 Smith, J. A. S., 2004 Snowdon, S., 943 Soffer, A., 2057, 2627 Sokoll, R., 1527, 2505 Solymosi, F., 883 Somsen, G., 53, 933 Soria, J., 739 Soria, V., 2781 Soriyan, O., 2011 Spiess, B., 1935 Spiro, M., 2277, 3048 Spotswood, T. M., 1999 Stenius, P., 2735 Stephens, A., 2729 Strazielle, C., 1321 191 1, 2569,2773, 3013, 3033 Schulz-Ekloff, G., 205AUTHOR INDEX Strukul, G., 1795 Strumolo, D., 1795 Sugiyama, K., 1357 Suppan, P., 509 Sutherland, I.O., 1145 Suzuki, T., 1733 Swallow, A. J., 1575 Symanski, J. S., 1105 Symons, M. C. R., 167, 2367, 2729, 2833 Szentirmay, M. N., 1051 Tabony, J., 2311 Tadros, Th. F., 3045 Tamura, H., 1561 Tamura, K., 1619 Tanaka, T., 35 Tanaka, Y., 2065 Tang, A. P-C., 108 1 Taniewska-Osinska, S., 1299 Taniewska-Osinska, S., 5 13 Tardajos, G., 2977 Tatam, R. P., 439 Tawarah, K., 21 11 Tear, S. P., 1022 Tejero, R., 2781 Tennakoon, D. T. B., 545 Teramoto, M., 15 15 Thijs, A., 963 Thomas, J. D. R., 1135 Thomas, J. M., 545,2851 Thomson, A. J., 2009 Tiddy, G. J. T., 3043 Tobias, H., 2627 Tofield, B.C., 1117 Toprakcioglu, C., 241 1 Townsend, R. P., 1019 Trasatti, S., 2481 Tunuli, M. S., 2911 Turner, J. C. R., 3052 Turner, P. S., 747, 759 Tyler, J. W., 1367 van de Ven, T. G. M., 457,473 van Lith, D., 2945, 2933 Vansant, E. F., 963 Vasaros, L., 3003 Vekavakayanondha, S., 291,63 Venkatasubramanian, L., 359 Verhaert, I., 963 Veseli, V., 1405 Vidoczy, T., 2621 Vijlder, M. De, 2377 Vink, H., 2353 Viswanathan, B., 2635 Volkov, A. I., 815 Volpe, P. L. O., 2863,2929 Vonk, D., 1945 Waghorne, W. E., 563,2195, Walker, R. W., 89 Wallwork, S. C., 1589 Walton, A. J., 1023 Wang, Z-C., 375 Ward, R. J., 2915 Warhurst, P. R., 119 Warman, J. M., 2933,2945 Warr, G. G., 1813, 1829 Watson, J. T. R., 2235 Watts, P., 1389 2207 Weale, K. E., 1020, 2002 Weiss, E., 2025 Wells, C.F., 2577 Wells, P. B., 189, 2719 Whalley, P. D., 1209 Whyman, R., 189,2719 Wiens, B., 247 Williams, G., 3049, 3050 Wilson, G. S., 1265 Wilson, I. R., 943 Wojcik, D., 1381 Woinicka, J., 1299 Wren, B. W., 167 Wright, K. M., 451 Wright, P. G., 2557, 2565 Wu, E. L., 1032 Wu, Q., 2423 Wuthier, U., 1179 Wyn-Jones, E., 21 11 Wysocki, S., 715 Xiaoding, X., 1945, 2707 Yamashita, H., 707, 1771 Yamazaki, A., 1553 Yatsimirsky, A. K., 319 Yeates, S. G., 1865 Yeo, I-H., 1081 Yoshida, N., 2175 Yoshida, S., 35, 707, 1771 Yoshikawa, M., 707, 1771 You-Sing, Y., 2887 Zana, R., 109 Zanderighi, L., 1795 Ziind, R., 1179 (vii)NOMENCLATURE AND SYMBOLISM Units and Symbols. The Symbols Committee of The Royal Society, of which The Royal Society of Chemistry is a participating member, has produced a set of recommendations in a pamphlet 'Quantities, Units, and Symbols' (1 975) (copies of this pamphlet and further details can be obtained from the Manager, Journals, The Royal Society of Chemistry, Burlington House, London W1 V OBN).These recommendations are applied by The Royal Society of Chemistry in all its publications. Their basis is the 'Systbme International d'Unit6s' (SI). A more detailed treatment of units and symbols with specific application to chemistry is given in the IUPAC Manual of Symbols and Terrninolog y for Ph ysicochemical Quantities and Units (Pergamon, Oxford, 1 979). Nomenclature. For many years the Society has actively encouraged the use of standard IUPAC nomenclature and symbolism in its publications as an aid to the accurate and unambiguous communication of chemical information between authors and readers.In order to encourage authors to use IUPAC nomenclature rules when drafting papers, attention is drawn to the following publications in which both the rules themselves and guidance on their use are given : Nomenclature of Organic Chemistry, Sections A, B, C, 0, E, F, and H (Pergamon, Oxford, 1979 edn). Nomenclature of Inorganic Chemistry (Butterworths, London, 1971, now publis- hed by Pergamon). Biochemical Nomenclature and Related Documents (The Biochemical Society, London, 1978). A complete listing of all IUPAC nomenclature publications appears in the January issues of J. Chem. SOC., Faraday Transactions. It is recommended that where there are no IUPAC rules for the naming of particular compounds or authors find difficulty in applying the existing rules, they should seek the advice of the Society's editorial staff.(viii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM NO. 22 Interaction-induced Spectra in Dense Fluids and Disordered Solids University of Cambridge, 10-1 1 December 1986 Organising Committee: Professor A. D. Buckingham (Chairman) Dr R. M. Lynden-Bell Dr P. A. Madden Professor E. W. J. Mitchell Dr J. Yarwood Dr 0. A. Young Mrs Y. A. Fish Whilst interaction-induced spectra have been studied in the gas phase for many years, their importance in the spectroscopy of condensed matter has been appreciated only relatively recently. At present a considerable number of studies of induced spectra are taking place in what are (nominally) widely separated fields of study.It is highly desirable to bring these communities together so that common issues can be identified and the progress of one field appreciated in another. 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 GENERAL DISCUSSION NO. 83 Brownian Motion University of Cambridge, 7-9 April 1987 Organising Committee: Dr M. La1 (Chairman) Dr J. S. Higgins Dr R. Ball Dr P. N. Pusey Dr E. Dickinson Dr D. A. Young Mrs Y. A. Fish The Faraday Discussion on Brownian Motion will be introduced by Professor J. M. Deutch of MIT and will include contributions from P.Mazur, P. Meakin, R. Jullien, D. A. Weitz, M. Fixman, P. N. Pusey, R. H. OttewiII, A. Vrij, J. A. McCammon, B. J. Ackerson and V. Degiorgio dealing with hydrodynamics, fractals, Brownian dynamics of aggregation processes and photon correlation spectroscopy. There will be a poster session for which contributions are invited in the form of a brief abstract to be sent by 31 January 1987 to: Dr M. Lal, Unilever Research, Port Sunlight Laboratory, Bebington, Wirral L63 3JW The preliminary programme may be obtained from: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBNTHE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 84 Dynamics of Elementary Gas-phase Reactions University of Birmingham, 14-1 6 September 1987 Organising Committee: Professor R.Grice (Chairman) Dr M. S. Child Dr J. N. L. Connor Dr M. J. Pilling Professor 1. W. M. Smith Professor J. P. Simons The Discussion will focus on the development of experimental and theoretical approaches to the detailed description of elementary gas-phase reaction dynamics. Studies of reactions at high collision energy, state-to-state kinetics, non-adiabatic processes and thermal energy reactions will be included. Emphasis will be placed on systems exhibiting kinetic and dynamical behaviour which can be related to the structure of the reaction potential-energy surface or surfaces. Contributions for consideration by the Organising Committee are invited. Titles should be submitted as soon as possible and abstracts of about 300 words by 30 September 1986 to Professor R.Grice, Chemistry Department, University of Manchester, Manchester M13 9PL THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM NO. 23 Molecular Vibrations University of Reading, 15-1 6 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.Contributions for consideration by the Organising Committee are invited. Titles should be submitted as soon as possible, and should be sent before the end of October 1986 to: Professor 1. M. Mills, Department of Chemistry, University of Reading, Reading RG6 2ADTHE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY Marlow Medal and Prize Applications are invited for the award of the Marlow Medal for 1987 and Prize of f 100. The award will be open to any member of the Faraday Division of the Royal Society of Chemistry, who by the age of 32, had made in the judgement of the Council of the Faraday Division, the most meritorious contribution to physical chemistry or chemical physics. The award will be made on the basis of publications (not necessarily in the Transactions) on any subject normally published in J.Chem. SOC., Faraday Transactions / and //, that carry a date of receipt for publication not later than the candidate's 32nd birthday. Candidates should be members and under 34 on 1 January 1987, the closing date for applications, which may be made either by the candidate himself or on his behalf by another member of the Society. Copies of the rules of the award and application forms may be obtained from: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBNJOURNAL OF CHEMICAL RESEARCH Papers dealing with physical chemistry/chemical physics which have appeared recently in J.Chem.Research, The Royal Society of Chemistry’s synopsis+microform journal, include the following: Electron Spin Resonance Study of Anatase-supported Vanadia-Molybdena Catalysts Guido Busca and Leonard0 Marchetti (1986, Issue 5) A Comparison of Some Linear Substituent-free-energy Relationships Martien C.Spanjer and C. Leo de Ligny (1 986, Issue 5) Interception of the Electron-transport Chain in Bacteria with Hydrophilic Redox Mediators. Part 1 . Selective Improvement of the Performance of Biofuel Cells with 2,6-Disulphonated Thionine as Mediator Anna M.Lithgow, Lorraine Romero, lvelisse C. Sanchez, Fernando A. Suoto and Carmen A. Vega (1 986, Issue 5) Ionic Strength Dependence of Complex-formation Enthalpies: a Literature Data Analysis Alessandro de Robertis, Concetta de Stefano, Carmelo Rigano and Silvio Sammartano (1986, Issue 5) Phenanthrene Hydroconversion over Nickel and Molybdenum Sulphides Supported on Alumina: Effect of the Sulphidation Method Jean-Louis Lemberton and Michel Guisnet (1 986, Issue 6) Deposition of Platinum onto CdS Aqueous Supensions under Ultraviolet Illumination Javier Domenech, John Curran, Nicole Jaffrezic-Renault and Robert Philippe (1 986, Issue 6) A Prototype Model for Artificial Photosynthetic Membranes: Water-swollen Chelate Filter Paper with Adsorbed Tris(2,2’-bipyridine)ruthenium(2 +) and Methyl Viologen Yoshimi Kurimura, Noriko Matsuo, Etsuko Kokuta, Yasuyuki Takagi and Yoshiharu Usui (1 986, Issue 7) ln situ Electrochemical Electron Spin Resonance Spectrometry: the Anodic Oxidation of Triphenylmethanol Richard G.Compton, Barry A. Coles and Michael J.Day (1 986, Issue 7) Miguel Pons, Racemization of Peptides. An MNDO Study of the c-(Gly-Gly) Anion Josep M. Bofill and Ernest Giralt (1986, Issue 7) ~~ ~~ ~ FARADAY DIVISION INFORMAL AND GROUP MEETINGS Division Half -day Endowed Lecture Symposium-Chemistry a t Surfaces : Metals, Oxides and Semiconductors including the Tilden Lecture by Professor J. Pritchard and the Meldola Lecture by Dr J. S. Foord To be held at the Scientific Societies Lecture Theatre, London on 4 November 1986 Further information from Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN Colloid and Interface Science Group with Macrogroup UK Polymer-Polymer Interfaces To be held at the Scientific Societies Lecture Theatre, London on 15 December 1986 Further information from Dr R.Aveyard, Department of Chemistry, The University, Hull HU6 7RX (xii)Colloid and Interface Science Group with the Colloid and Surface Group of the SCI Nucleation and Growth in Colloidal Systems To be held at the Society of Chemical Industry, 14 Belgrave Square, London on 16 December 1986 Further information from Dr R. Aveyard, Department of Chemistry, The University, Hull HU6 7RX Neutron Scattering Group Neutron Crystallography To be held at Imperial College, London on 17-19 December 1986 Further information from Dr R. J. Newport, Physics Laboratory, The University, Canterbury, Kent CT2 7NR Electrochemistry Group The Photoelectrochemical Properties of Colloids To be held at the University of Southampton on 7-8 January 1987 Further information from Dr S.P. Tyefield, CEG B Berkeley Laboratories, Berkeley, Gloucestershire Electrochemistry Group with the SCI and the Institute of Corrosion Science Technology Electrochemical Techniques for Corrosion Scientists To be held at St Catherine's College, Oxford on 7-8 January 1987 Further information from Dr S. P. Tyefield, CEG B, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB Division jointly with Perkin Division Half-day Endowed Lecture Symposium on Radical Ion and Carbon Ion Chemistry including the lngold Lecture by F. G. Bordwell To be held at University College, London on 12 March 1987 Further information from Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN ~~ Neutron Scattering Group Neutron Scattering and Phase Transitions To be held at the University of Warwick on 3&31 March 1987 Further information from Dr D.McK. Paul, Department of Physics, University of Warwick, Coventry CV4 7AL Electrochemistry Group Spring Informal Meeting To be held at the University of Bristol on 1-3 April 1987 Further information from Dr A. R. Hillman, School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 1TS Division-Annual Congress The Chemistry and Physics of Intercalation To be held at University College, Swansea on 13-1 6 April 1987 Further information from Professor J. H. Purnell, Department of Chemistry, University College, Singleton Park, Swansea SA2 8PP Polymer Physics Group Fundamental Aspects of Polymer Flammability To be held at Baden Powell House, London on 14-1 5 April 1987 Further information from Dr G.C. Stevens, CERL, Kelvin Avenue, Leatherhead KT22 7SE Division Full-day Endowed Lecture Symposium on Intramolecular Dynamics and Chemical Reactivity including the Centenary Lecture by S. A. Rice and the Tilden Lecture by M. S. Child To be held at the Scientific Societies Lecture Theatre, London on 6 May 1987 Further information from Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN (xiii)Polymer Physics Group Electroactive Polymers To be held at the Geological Society, London on 14 May 1987 Further information from Dr G. C. Stevens, CERL, Kelvin Avenue, Leatherhead KT22 7SE Electrochemistry Group with Macro Group UK Polymer Electrolytes To be held at the University of St Andrews on 18-1 9 June 1987 Further information from Dr C. A. Vincent or Dr J. R. MacCallum, Department of Chemistry, University of St Andrews, St Andrews KY16 9ST Division Xlth International Symposium on Molecular Beams To be held at the University of Edinburgh on 13-1 7 July 1987 Further information from Dr J. F. Gibson, The Royal Society of Chemistry, Burlington House, London W1V OBN 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 10-1 4 August 1987 Further information from Dr F. Franks, Pafra Ltd, 150 Science Park, Milton Road, Cambridge CB4 4GG Polymer Physics Group Biennial Meeting To be held at the 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 14-1 5 September 1987 Further information from Dr R. K. Thomas, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ 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 (xiv)

ISSN:0300-9599    

DOI:10.1039/F198682BP113

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J. Chem. Soc., Faraday Trans. I , 1986, 82, 2621-2625 Limitations of Evaluation Methods for Inhibited Oxidation Processes in the Liquid Phase Karoly He%erger,* Julia Lukacs and Tamas Viddczy Central Research Institute for Chemistry of the Hungarian Academy of Sciences, Budapest P.O. Box 17, H-1525, Hungary The limitations of the different evaluation methods used for liquid-phase oxidation processes in the presence of inhibitors have been investigated using computer simulation techniques. The reaction InH + HROOH has been included in a generally accepted mechanism. According to the calcu- lations the rate of initiation and rate coefficient of the reaction InH+ HROOH should be determined based on inhibition-period data rather than on values of initial rates of oxygen consumption. Using the same data set different formulae have been suggested depending on the parameters to be calculated.The rates of initiation of the oxidation processes of hydrocarbons in the liquid phase are determined, as a rule, either by the measurement of the initial rates of oxygen consumption or by studying the period of inhibition in the presence of suitable inhibitors. Unfortunately, very few papers have been published1 dealing with the limitations and errors faced if using approximations for the calculations of the rates of initiation from experimental data. We have studied the expediency of the various expressions used for the calculations, and in order to avoid the disturbing effects of direct experimental errors we have compared the different methods using simulated data instead of direct experimental Results and Discussion As a model system the oxidation of ethylbenzene (RH,) initiated by 1-phenylethyl hydroperoxide (HROOH) has been chosen.This notation is used to emphasize that the carbon skeleton (R-Ph-y-CH,) remains unchanged during mild oxidation conditions. The initial stages of the overall reaction in the presence of an inhibitor (2,6- di-t-butyl-4-methylphenol; InH) can be represented by a simplified mechanism as referred to in the literature? I (2) HRO; + RH, A HROOH + HRO; HRO', + InH - HROOH +In' (3) HRO', + In' - stable products. (4) 262 12622 r Inhibited L iquid-phase Oxidation Processes Table 1. Rate coefficients used in the simulation value of rate units coefficient ref. kl S-l 1.5 x 8 k, dm3 mol-l s-l 18 9 k, dm3 mol-1 s-l 5 x 105 10 k, dm3 mol-1 s-l 1 x 108 11 k, dm3 mol-l s-l 1 x 10-4 7 [HROOH], = 0.5507 mol dm-,; [RH,], = 6.753 mol dm-,.1 2 3 4 6 7 t/min Fig. 1. Simulated oxygen uptake as. time at different initial inhibitor concentrations at 120 "C [InH],: (1) 0.8, (2) 1.5, (3) 2.3, (4) 3.056, (5) 4.1, (6) 5.0 and (7) 6.0 mmol dm-,. According to our recent report,' process (5) should be also incorporated: 0 2 , RH, InH + HROOH - In' + HRO',. The solution of the differential equations, based on reactions (1)-(5) and on rate constants summarized in table 1, yields plots of rates of oxygen uptake ( Vo,) vs. time for various amounts of inhibitor added to the system as shown in fig. 1 . The corresponding values of the inhibition times (2) have been determined graphically from the curves of fig.1. Calculations based on the Values of the Inhibition Period Usually it is assumed that (i) the rate of initiation is constant during the period of inhibition and (ii) a steady-state treatment can be applied to the radicals. In this case, the following equation is obtained: -- d[lnH1 = wi,O + k, [InH] [HROOH] dt fK. Hiberger, J . Lukacs and T. Viddczy 2623 Table 2. y o and k, and their errors determined with different fitting methods input logarithmic linear quadratic k5/104 dm3 mol-l s-l 1 .OO 0.943 +_ 0.0878a ? 0.7 10 +_ 0.04 1 5" wi, o/ 1 O6 mol dmF3 s-l 1.652 1.665+0.234a 1.662f0.00765 1.690f0.01 la a Uncertainty determined from the square root of the diagonal elements of the covariance matrix. where wi,, and f are the rate of initiation in the absence of inhibitor and the stoichiometric factor (showing the numb( * of radicals scavenged by one molecule of the inhibit or), respectively .Integrating eqn (I) from 0 to z and from [InH], to 0, we obtain the following ' logarithmic' equation: where A = (k,[HROOH])-l and B = f k 5 [HROOH]/wi, ,. yields eqn (111), used widely as a 'linear' :xpression: z = A In (1 + B[InH],) (11) Since B[InH], << 1, the expansion of ekli (11) taking into account the first term only while the first and second terms give a 'quadratic' formula: z = C[InH],+D[InH]E (IV) where C =f/wi, 0 and D = -( f/wi, o)2k5 [HROOH]/2. First, using the data pairs (z, [InH],) obtained graphically, eqn (11)-(IV) have been fitted by the least-squares method and parameters A and B have been determined.The deviation between the graphical and fitted values of z determine the uncertainty of parameters A and B, and the error in wi, , and k, was calculated by the error propagation law (table 2). The difference of input and output data in table 2 originates in the systematic error of the graphic determination of z as discussed earlier in detail.12 In the next step the effect of 'experimental' errors was studied. Therefore normally distributed random numbers (with zero mean and given standard deviation) were added to the z values determined from fig. 1 . With each fixed standard deviation (simulating a given level of experimental error) the procedure was repeated 20-50 times, calculating in each case wi, and k, according to both eqn (11) and eqn (IV).The resulting wi, and k, values were averaged, and their standard deviations were also calculated. These results indicate that with no regard to the level of experimental error, the standard deviation of wi,, is significantly larger when calculated from eqn (11) (the logarithmic equation) than by using eqn (IV) (the quadratic equation). In contrast, for k, eqn (11) gives the more reliable result. Summarizing our results concerning the efficiency of the various fitting methods we find the following. Logarithmic Fitting This method gives acceptable mean values both for k, and wi,,, but the uncertainty in the rate of initiation exceeds by a factor of 2 that of k,, possibly owing to the structure of the logarithmic formula.2624 Inhibited Liquid-phase Oxidation Processes E U *'I 1.5 I ' I ' 500 I I I I I 1000 I ' I I 1500 ' (1 / [ 1nHlo)/dm3 mol-I Fig.2. Initial rate of oxygen consumption us. the reciprocal value of the initial concentration of inhibitor at T = 120 "C. Linear Fitting This procedure does not give any information with respect to k,. In order to determine the value of wi,,, the wi us. [InHI0 relationship was extrapolated to [InH], = 0, yielding acceptable results both for the mean value and the standard deviation of w ~ , ~ . Quadratic Fitting It is interesting that the errors in k, exceed those in wi, *, while the mean value of k, differs considerably (by ca. 20 % ) from the input value of simulation. Thus the quadratic fitting cannot be applied for the calculation of k,.All the calculations have been repeated (a) with k, = 4.3 x lo-, dm3 mol-1 s-l and wi, = 1.24 x mol dm-3 s-l and (b) using a more detailed mechanism outlined in our earlier work.1° However, the results were the same as described. Calculations based on Measurements of the Rate of Oxygen Consumption According to Tsepalov and Shlyapintokh13 the initial rate of oxygen consumption (the very beginning of the curves in fig. 1) in inhibited oxidation can be used to determine the rate of initiation. Namely, processes (1)-(4) yield the following expression: wg2 = Wi,.( 1 + kz[RH1o) f l 3 [InHIo where wg2 is the initial rate of oxygen consumption. According to eqn (V) a plot of wg2 us. l/[InH], gives a straight line (fig. 2) and wi, can be obtained from its intercept.As can be seen from fig. 2, however, the full plot is not linear unless [InH], > 3.0 x Therefore, eqn (V) can be used either at very large initial concentrations of the inhibitor or by using only rates of oxygen uptake in the initial period of oxidation. The latter can be achieved only with computer simulation because woz cannot be measured in such a short time interval. Although the numerical examples are based on a given system (hydroperoxide initiated oxidation of ethylbenzene inhibited by 2,6-di- t-bu tyl-4-methylp henol) the conclusions are independent of the numerical values of the rate coefficients applied. The mathematical structure of the applied equations results from the fact that the experimental error does not influence the accuracy of the estimated parameters (wi,,, k,) in the same manner.These tendencies may be observed for any chemical system provided that the basic assumption that the system can be represented by reactions (1)-(5) holds true. mol dm-3.K. Hiberger, J. Lukacs and T. Vidbczy 2625 Conclusion Our modelling studies suggest that the determination of the rate of initiation should be based on inhibition-period data rather than values of initial rates of oxygen consumption. Further, the evaluation methods should be varied depending on the parameter to be calculated. For the calculation of k , the logarithmic formula is more suitable and wi, ,, can be approximated by the quadratic expression while applying the same data set. References 1 E. Niki, Y. Kamiya and N. Ohta, Bull. Chem. SOC. Jpn, 1969, 42, 3220. 2 F. Hauser and M. Kotva, Nature (London), 1985,313, 732. 3 H. P. Good, A. J. Kallir and U. P. Wild, J. Phys. Chem., 1984,88, 5435. 4 G. H. McKinnon, C. J. Backhouse and A. H. Kalantar, Int. J. Chem. Kinet., 1984, 16, 1427. 5 R. P. L. Absil, J. B. Butt and J. S. Dranoff, J . Catal., 1984, 87, 530. 6 N. M. Emanuel, E. T. Denisov and Z. K. Maizus, Chain reactions of the Oxidation of Hydrocarbons in the Liquid Phase (in Russian) (Nauka, Moscow, 1965). 7 K. HCberger, In?. J. Chem. Kinet., 1985, 17, 271. 8 K. HCberger and I. P. Hajdu, Oxid. Commun., 1983, 4, 171. 9 E. Danoczy, 1. Nemes, T. Vidoczy and D. Gal, J. Chem. Soc., Faraday Trans. I , 1975, 71, 841. 10 J. Lukacs, K. Heberger and D. Gal, Ber. Bunsenges. Phys. Chem., 1983,87, 606. 1 1 L. R. Mahoney and M. A. DaRooge, J. Am. Chem. Soc., 1970,92,4063. 12 T. Vidoczy and D. Gal, Z. Phys. Chem. N.F., 1978,109, 179. 13 V. F. Tsepalov and V. Ya. Shlyapintokh, Kinet. Katal., 1962, 3, 870. Paper 51328; Received 26th February, 1985

ISSN:0300-9599    

DOI:10.1039/F19868202621

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. I , 1986, 82, 2627-2634 The Electrical Conductivity of Carbon-fibre Adsorbents An Attempt to Discriminate between Chemisorption and Physisorption of Chlorine Haim Tobias," Haim Cohen and Abraham Soffer Chemistry Division, Nuclear Research Center Negev, P.O. Box 9001, Beer Sheua, Israel Electrical conductivity measurements have been utilised to discriminate between physisorption and chemisorption of chlorine on carbon. Exposure of oxygen-free carbon filaments to chlorine at low temperatures always increases the conductivity. At high temperatures conductivity rapidly in- creases at first, then drops to a much slower rate. Equilibrium values of the electrical conductivity at high temperatures are lower than those of the bare samples, but increase at higher coverages.The results can readily be interpreted if it is assumed that C1, physisorption increases the conductivity. Electrical conductivity measurements can thus serve as a tool for discrimi- nation between chlorine chemisorption and physisorption. Adsorption of chlorine on carbons and graphite exhibits some unique features, probably due to its chemical reactivity and electron-acceptor properties. Besides reversible physisorption, which is obviously more extensive at low temperatures and which conforms with the available surface area, two general modes of chemisorption had been ~uggested,l-~ namely exchange with chemisorbed hydrogen and addition. While exchange chemisorption can be readily distinguished owing to the release of an equivalent amount of HCl,3 addition chemisorption, which (like physisorption) comprises the net uptake of chlorine, exhibits considerable overlap with physisorption over a wide temperature range.3 This is due to intense physisorption, which is considerable at high temperatures, and to low chemisorption activation energy which, as will be shown in this article, allows the onset of chemisorption at temperatures as low as 23 "C.Discrimination between physisorption and chemisorption on solid adsorbents is relatively facile when the adsorbate is a permanent gas such as hydrogen, nitrogen e t ~ . ~ This is demonstrated in fig. 1, where the adsorption isochore (at constant volume) of hydrogen is presented. A considerable amount of the gas is physisorbed at cryogenic temperatures. On heating, desorption occurs.Upon further heating, activated chemisorption commences. In the case of the heavier chlorine molecule, which is known to chemisorb at high temperatures, the thermally programmed desorption curves are featureless (fig. 2), indicating that deep overlap of physisorption and chemisorption takes place over a wide temperature range. Another method for distinguishing between the two processes is therefore required. Implementation of molecular spectroscopy for this purpose is very difficult because of the opaqueness of well charred carbons over a very wide spectral band. Infrared and Fourier-transform infrared studies were therefore limited to low-rank carbons which, owing to incomplete aromatization, are known to acquire some i.r. transparency.6 In this work an attempt has been made to gain information on various modes of chlorine-carbon interaction by measuring the dependence of the electrical conductivity (e.c.) on chlorine adsorption.Changes in the electrical conductivity of adsorbents go back to Langmuir, who detected chemisorptions on hot tungsten filaments. The electrical conductivity of porous adsorbents is in general not limited to electronic conductivity, since surface ionic conduction may take place in parallel as has been suggested previ~usly,~ or provide the only mechanism in insulating adsorbents such as 26272628 Electrical Conductivity of Carbon-Jibre Adsorbents n u * * 7 2 & W 2 v1 I I 1 I I 1 I I I 4 00 600 800 1000 1200 T/K Fig. 1. Thermal desorption spectrum of chlorine on Continex N- 1 10.Temperature sweep-rate 15 "C min-l [reproduced from fig. 1 of ref. (4) with permission]. 1.0 0.9 4 M .3 0.6 E --- 0 a Q .* +-I 5 0.4 0.2 0 200 400 600 800 1000 T/K Fig. 2. Cyclic H isochore on Continex N-1 10 over the temperature range - 196 to 1000 "C [fig. 9 of ref. (4)]. porous Vycor glass,s, silicalo and zeolites.ll In well carbonised chars and graphites the surface ionic conductivity is completely obscured by the bulk e.c. This, however, still exhibits a considerable dependence on adsorption, owing to the interference of surface electronic states with those of the bulk states. Thus Smeltzer and McIntosh12 had shown that the e.c. of carbon in the presence of varius hydrocarbons if divided by N , the number of carbon atoms in the hydrocarbon molecule, can be presented by a commonH. Tobias, H.Cohen and A . Soffer 2629 plot vs. the amount adsorbed. Dacey et aZ.l3 and Lukaszewicz and Siedewski14 have shown that the e.c. of carbons may increase or decrease upon adsorption, depending on the type of adsorbate. In the present study we also found such dependences in presence of adsorbed chlorine. However, by closely following the trends in e.c. changes upon time lapse, amount adsorbed and temperature we will suggest that the superposition of chemisorption and physisorption is responsible for such behaviour. Experimental A standard volumetric high-vacuum glass sysem Torr)? was used to run the adsorption experiments. A shielded d.c. resistance bridge served for the conductivity measurements. Among the many forms of carbons, the fibrous form is the most convenient for conductivity measurements since it provides a continuous sample with no electrical contact and swelling problems, as is the case with powder samples.15 It also possesses high resistivity which avoids sample overheating, as is the case with granular forms of carbon.A single carbon thread, taken from an activated cloth fabric, served for conductivity measurements (TCM-128, product of Le Carbone Lorraine, France). Also a graphite sample was used in order to distinguish between the edge and basal plane behaviours towards dependence of conductivity on chlorine adsorption. The graphite sample was Papyex brand, product of Le Carbon Lorraine. This is an exfoliated sheet 0.15 mm thick from which a 3 x 25 mm sample was cut.A relatively massive amount of the same carbon or graphite samples was used for determining adsorption. Contained in the same experimental cell both adsorption and electrical conductivity samples could receive the same thermochemical and adsorptive treatment. Furthermore, e.c. changes and adsorption could be studied simultaneously. The samples were prechlorinated, then degassed at 1000 "C prior to measurements, in order to prevent possible interference of chemisorbed ~xygen.~ Both the filament and the massive amount of carbon contained in the measurement cell were evacuated at 1000 "C prior to any successive e.c. experiments. Under these conditions the repeated measure- ments at room temperature of the electrical conductivity of the filament in the presence of helium always reached the same value within < 0.5%, which confirms the standard- ization of the starting material. Nevertheless, to remove any uncertainty we have decided to present the e.c. results as relative conductivity changes 100 (0 - a,)/a, where a is the e.c.in the presence of the adsorbate. Furthermore, this relative presentation also enabled us to compare the results of the carbon sample to those of the graphite, although they had completely different absolute e.c. values at the same temperature. Provisions were made to avoid conductivity changes due to heating the carbon sample; thus a sufficiently low potential was applied to the resistance bridge and helium was introduced to measure the e.c. of the degassed sample prior to exposure to chlorine.Results and Discussion Equilibrium Data In fig. 3-5 the relative changes in the e.c. us. the amount of chlorine adsorbed on the charcoal cloth fibre at several temperatures are presented. At the lowest applied temperature (-44 "C, fig. 3) only an increase in the e.c. is observed upon increasing the amount of adsorbed chlorine, whereas at the highest [650 "C, fig. 5 (c)] a decrease, although to a smaller extent, of the e.c. is observed. At intermediate temperatures [23, 100, 200, 350 and 500 "C, fig. 4 and fig. 5 curves (a) and (b)] initial decreases were followed by increases in the e.c., resulting in distinct f 1 Torr = 101 325/760 Pa.2630 + + +++ + Electrical Conductivity of Carbon-Jibre Adsorbents 60 h g adsorption/mmol g-' Fig. 3. Dependence of carbon-filament e.c.on chlorine adsorption at - 44 "C. 20 E Q) .- U a a, - " 0 adsorption/mmol g-' Fig. 4. Dependence of carbon-filament e.c. on chlorine adsorption at + , 23; 0, 100 and (-)200 "C. minima. This phenomenon is attributed to two different modes of interaction of chlorine with the carbon surface. At high temperatures where only negligible physisorption can take place, the decrease in e.c. should be attributed to activated chlorine chemisorption. CCl,, a compound of similar volatility as that of chlorine, shows no detectible changes in e.c. upon adsorption. It is therefore likely that even physisorbed chlorine acquires some specific interaction with the carbon surface, as has been suggested previously upon analysing adsorption isotherms of chlorine and dichlorodifluoromethane.4 Decreases in the e.c., and the associated minimum, have already commenced at room temperature.This leads to the consequence that chemisorption also occurs at room temperature.H. Tobias, H. Cohen and A . Sofler 263 1 0 Q 0 -4 1 k I 8 L I k I I I 0.2 0.4 0.6 0.8 adsorption/mmol g-' Fig. 5. Dependence of carbon-filament ex. on chlorine adsorption at 0, 350; 0, 500 and +, 650 "C. The following features of the dependence of conductivity on adsorption provide a means of discriminating between physisorption and chemisorption through e.c. changes. (1) Assuming that, for a given temperature, chemisorption predominates at high adsorption values, the initial negative slopes of the curves in fig. 5 should be considered as expressing the first-order constant of the dependence of the e.c.on chemisorption. Analoguously, the final positive slopes represent the constants for physisorption. These constants decrease with temperature, as is evident from fig. 5. Both effects are considered to result from the weaker interaction of the adsorbate with the surface at high temperatures, whereas the molecule-to-surface vibrational levels are higher so that the molecule resides on the average at a greater distance from the surface. (2) The e.c. minimum is displaced to lower adsorption at a given temperature. For a given amount adsorbed, physisorption is relatively greater at lower temperatures. Increases in the e.c. that are due to physisorption therefore come earlier, and acordingly the minimum is shifted towards lower adsorption values.Kinetics The kinetics of e.c. changes, together with adsorption kinetics, were monitored during the exposure of the carbon sample to chlorine (fig. 6). In this experiment the adsorbent was exposed to a limited dose of chlorine so that it was totally adsorbed at all temperatures. While adsorption was complete within a fraction of a second, the e.c. exhibited an immediate increase followed by a slower decrease, which is probably due to reorganization of the adsorbate on the surface. Recalling the suggestion, based on the equilibrium data, that the e.c. increases upon physisorption and decreases upon chemisorption, the kinetic results again confirm the possibility of distinguishing between the two processes: fast physisorption occurs first and increases the e.c.while activated chemisorption brings about a slow decrease. At higher temperatures physisorption is retarded, but activated chemisorption is speeded up. Accordingly, ex. increases are retarded at higher temperatures while the decreases become faster, as shown in fig. 6.2632 Electrical Conductivity of Carbon-jibre Adsorbents - 5 I I 1 I A I L I L 20 40 60 80 100 120 140 t / s Fig. 6. Rate of e.c. changes of the carbon filament upon exposure to a limited amount of chlorine at + , 23; 0, 100 and 0, 200 "C. In all cases chlorine adsorption of ca. 0.06 mmol g-l was completed within a fraction of a second. adsorption/mmol g-' n 150 5 % 24 8 0 0 0.3 0 . 6 0.9 1.2 adsorption/mmol g-' Fig. 7. Dependence of graphite-filament e.c. on chloride adsorption at (a) -44 and (b) 23 "C.Comparison between Carbon and Graphite This two-site hypothesis could be further confirmed if the conductivity changes of graphite were examined upon exposure to chlorine. A well graphitized carbon is expected to expose primarily the low-surface-energy basal planes to the surface, and should not therefore exhibit chlorine chemisorption, which is likely to take place at unsaturated sites or through exchange with C-H bonds on the edge plane. In fig. 7 and 8 the relative ex. changes of the exfoliated graphite Papyex foils that occur upon exposure to chlorine is presented. Only an increase in the ex. takes place over theH. Tobias, H . Cohen and A . Sofer 263 3 0 10 I I 1 I I I 0.02 0.04 0.06 adsorption/mmol g-' Fig. 8.Dependence of graphite-filament e.c. on chlorine adsorption at +, 100 and 0, 200 "C. whole adsorption range. Furthermore, adsorbed chlorine could readily be desorbed at room temperature by degassing through a cold trap, indicating a relatively weak (physical) adsorption interaction. This was unlike the TCM carbon cloth, from which chlorine desorption was completed only after degassing at elevated temperatures. Comparing the conductivity us. adsorption curve of carbon with that of graphite for the same temperature (fig. 3, 4, 7 and 8) reveals that the e.c. increase per unit amount adsorbed on the graphite sample is much greater than than on the carbon cloth. The extent of crystallographic order, namely the average dimension of a graphite-like domain in the graphite, is obviously much greater than that of the carbon sample.Anticipating that the effect of adsorption on the electronic conductivity extends throughout such domains gives a satisfactory explanation of this phenomenon. Mechanistic Considerations How does the e.c. increase with physisorption and decrease with chemisorption? A rigorous answer would demand reliable information on the band structure of carbons, which are highly distorted contaminated semiconductors. Since such information is not available a rather quantilative approach is to be adopted. Considering physisorbed chlorine as an electron acceptor, it may create bulk holes in the carbon/graphite substrate through a charge-transfer interaction. This mechanism closely resembles the charge-transfer mechanism of enhanced conductivity graphite intercalates.16 As to a conductivity decrease due to chemisorption, we may adhere to the Mrozowski interpretation of the e.c.in polycrystalline graphites and condensed aromatic ring systems. l7 The continuity of C-C bond conjugation between graphitic microdomains should be considered responsible for the electronic conductivity in carbon. These chemical bond bridges are on average distorted in terms of bond angle and length and are thus chemically active. As such chlorine should be chemically bonded to these unsaturated sites, destroy the continuity of the conjugation and thus reduce the ex. Desorption of chemibound chlorine would obviously renew these sites and resume the electrical conductivity.2634 Electrical Conductivity of Carbon-fibre Adsorbents Conclusions By monitoring the electrical conductivity changes of a carbon filament upon adsorption of chlorine, it is possible to distinguish between physisortion, which leads to an increase in electrical conductivity, and activated (dissociative) chemisorption, which decreases conductivity.As expected, activated chemisorption prevails at high temperatures, but it also takes place at room temperatures. References 1 B. R. Puri and K. C. Sehgal, Ind. J. Chem., 1967,5, 379. 2 W. 0. Stacy, G. R. Imperial and P. L. Walker, Carbon, 1966,4, 343. 3 H. Tobias and A. Soffer, Carbon, 1985, 23, 28 1. 4 H. Tobias and A. Soffer, Carbon, 1985, 23, 299. 5 A. W. Adamson, Physical Chemistry of Surfaces (Interscience, London, 2nd edn, 1967), 567. 6 M. J. D. Low and C. Morterra, Carbon, 1983, 275. 7 E. Keren and A. Soffer, J . Catal., 1977, 50, 43. 8 S. Levy and M. Folman, J. Phys. Chem., 163, 67, 1278. 9 A. Soffer and M. Folmdn, Trans. Faraday Soc., 1966,62, 3559. 10 V. V. Karasev, B. V. Deryagin and A. V. Bochko, Kolloidn. Zh., 1962, 24,467. 1 1 Stamirees, J. Chem. Phys., 1962, 36, 3 174. 12 W. W. Smeltzer and R. McIntosh, Can. J. Chem., 31, 1239. 13 J. R. Dacey and J. T. Gallagher, Carbon, 1966, 4, 73. 14 J. Lukaszewcz and J. Siedlewski, Pol. J. Chem., 1982, 56, 1417. 15 D. N. Young and A. D. Crowell, Physical Adsorption of Gases (Butterworths, London, 1962), 340. 16 J. E. Fischer and T. E. Thomson. Phys. Today (July, 1978), 36. 17 S. Mrozowski, Phys. Rev., 1952, 85, 609. Paper 5/1177; Received 11 July, 1985

ISSN:0300-9599    

DOI:10.1039/F19868202627

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. I , 1986,82, 2635-2643 Effect of Support and Promoter on the Coadsorption of Carbon Monoxide and Hydrogen on Fischer-Tropsch Cobalt Catalysts Ramasamy Gopalakrishnan and Balasubramanian Viswanathan Department of Chemistry, Indian Institute of Technology, Madras-600 036, India Two cobalt Fischer-Tropsch catalysts of composition Co : kieselguhr = 100 : 200 (A) and Co : Tho, : kieselguhr = 100 : 18 : 200 (B) have been investigated with respect to the adsorption of CO and hydrogen by temperature-programmed desorption (t.p.d.) and infrared (i.r.) tech- niques. Although CO preadsorption is known to inhibit subsequent hydrogen adsorption, a considerable amount of hydrogen (30 pmol g-l on catalyst A and 50 pmol g-l on catalyst B) adsorption has been observed on the CO-presaturated surface of these two catalysts, indicating the possibility of adsorption of hydrogen on support materials by a spillover process and/or the formation of surface complex species.T.p.d. and i.r. studies favour the formation of a surface complex between CO and hydrogen, and such complex formation is highly favoured when hydrogen is preadsorbed. The presence of thoria (a promoter) enhances hydrogen adsorption, making complex formation more favourable on catalyst B than on catalyst A. Studies on supported-metal catalysts have shown that the support materials may have an effect on the catalytic properties of the active metal. Variation resulting from particle size differences1 or from interactions between the metal and support2* can account for the observed alterations in catalytic behaviour.Boudart et aL4 observed that when iron is supported on MgO, the support interacts with iron, stabilizing the formation of small metal particles. Studies by Bartholomew et ~ 1 . ~ 9 and Vannice7’ * provide evidence that CO adsorption stoichiometries are greatly modified by a strong metal-support interaction (SMSI) in well dispersed Ni/SiO, and moderately dispersed Ni/A1203 and Ni/Ti02 catalysts. The number and population of adsorption states at moderate to low coverages and the values of the heat of adsorption have been shown to depend on the nature of the support. Further, the nature of the activated hydrogen adsorption varies with the extent of metal loading on silica.% Cobalt, an efficient catalyst for Fischer-Tropsch (FT) synthesis, is used with kieselguhr and thoria as the support and promoter, respectively.1° The addition of kieselguhr and thoria to cobalt has been reported to increase the selectivity for high molecular-weight hydrocarbons,ll indicating the definite participation of these supporting materials.To gain further insight into the effect of kieselguhr and thoria on cobalt, the present investigation was carried out on the individual adsorption and coadsorption of CO and hydrogen using t.p.d. and i.r. techniques and are compared with studies on polycrystalline cobalt. l2 Experiment a1 Two catalysts, A and B, of the composition Co: kieselguhr = 100:200 and Co : Tho, : kieselguhr = 100 : 1 8 : 200, respectively, were prepared following a procedure reported e1~ewhere.l~ Ca.500 mg of the catalyst was reduced at 573 K for 48 h. The completion of reduction was confirmed by reproducibility in the values of repeated 26352636 Fischer-Tropsch Cobalt Catalysts hydrogen adsorption at the reduction temperature on a clean surface. Each time, prior to the adsorption of CO or hydrogen, the surface was treated with hydrogen at 573 K for 12 h at atmospheric pressure followed by evacuation at 673 K at Torrt for 5 h. For adsorption measurements, gases were admitted to a pressure of 200 Torr at room temperature and allowed to attain equilibrium for 12 h. The unadsorbed gas-phase components and loosely bound surface species were removed by evacuation at lo-, Torr for 2 min, and after 5 min, t.p.d. was followed in a closed system by monitoring the pressure of the desorbed products with respect to temperature.The plot of pressure vs. temperature was further differentiated to obtain the t.p.d. spectrum. The desorbed products could be analysed at any stage by admitting a known amount of the desorbed products into an on-line gas partitioner (Fisher-Hamilton, model 29). Thin pellets of catalysts which were transparent enough for i.r. radiation were used. Such a pellet in a mount was placed in an i.r. cell capable of withstanding a vacuum of up to Torr. Provisions were also available in the cell for heating and for admitting gases. Details of the t.p.d. and i.r. measurements have been described in previous reports.l29 l4 Results and Discussion Studies on Catalyst A Individual Adsorption of Carbon Monoxide and Hydrogen Two desorption maxima were observed in the t.p.d.trace of CO adsorbed at room temperature, one at 350 K and another at 420 K [fig, 1 (a)], indicating the existence of two energetically different surface CO species.12 Desorbed products were found to be pure CO and CO,, which were responsible for the desorption peaks at 350 and 420 K, respectively. Surprisingly, no CH, was noticed. Correspondingly two i.r. absorption bands were observed for CO adsorption at room temperature, on a reduced pellet, at ca. 1987 and 1779 cm-l. This is in agreement with observations made on polycrystalline cobalt and cobalt films.15 In our previous investigations on a polycrystalline cobalt surface,12 the combined t.p.d. and i.r. studies revealed (fig.2) that the linearly adsorbed CO species with an i.r. absorption band at 1990 cm-l desorbed at 350 K and the bridged carbonyl species with an i.r. absorption at 1800 cm-l desorbed at 440 K. Extending the postulates proposed on the basis of similar results on polycrystalline cobalt, it can be stated that on catalyst A the linear type (1987 cm-l) of adsorbed CO species desorb at 350 K while the bridge type of (1 779 crn-l) adsorbed CO species produce CO, at 420 K. Two thermal desorption peaks are observed for room-temperature hydrogen adsorption, one at 350 K and the other around 460 K [fig. 1 (b)]. The appearance of two desorption maxima may be due to the presence of two different adsorbed states of hydrogen. The desorption of hydrogen is found to continue even up to 650 K at a diminished rate.Coadsorption of Carbon Monoxide and Hydrogen Coadsorption experiments were carried out by admitting one of the gases first in a controlled manner to obtain the desired surface coverage (8); subsequently the other gas was admitted to saturate the surface. A series of such coadsorption experiments was made by varying 8 of the preadsorbed gas, and the results are summarised in table 1. Adsorption of hydrogen on a CO-preadsorbed surface decreases steadily with an increase in Oc0, indicating an inhibiting effect of preadsorbed CO. Such an effect has been observed on many metal surfaces.16 Considerable hydrogen adsorption t 1 Torr = 101 325/750 Pa.R. Gopalakrishnan and B. Viswanathan 2637 T/K Fig. 1. T.p.d. traces of (a) CO and (b) hydrogen from catalyst A (adsorption at room temperature). I I 1 I I I 2300 2000 1800 1600 frequency/cm Fig.2. 1.r. spectra of cobalt surfaces under different conditions: (a) CO-adsorbed cobalt surface at a pressure of 20 Torr, (b) surface (a) after evacuation at 350 K for a few minutes, (c) surface (b) after evacuation at 440 K for a few minutes, and ( d ) pure cobalt surface. (30.1 pmol g-l) is observed on the CO-presaturated surface. This hydrogen adsorption can take place on (i) the free sites still available on the CO-preadsorbed surface, which are accessible preferably to hydrogen, the support, owing to a spillover mechanism, or (ii) the same metal sides on which CO is absorbed. However, although there is a slight decrease in CO adsorption initially, on a hydrogen-preadsorbed surface, adsorption increases with increasing OH2.Preadsorbed hydrogen probably enhances the subsequent CO adsorption by creating new adsorption sites, by favouring surface complex formation with CO or by promoting CO adsorption on hydrogen-adsorbed sites.2638 Fischer-Tropsch Cobalt Catalysts Table 1. Amount of H,/CO adsorbed on CO/H,-preadsorbed surfaces of catalyst A at room temperaturea amount of COH, amount of H, amount of amount of CO preadsorbed adsorbed on CO- preadsorbed adsorbed on H,- on bare preadsorbed on bare preadsorbed surface/pmol g-l surface/pmol g--l surface/pmol g-l surface/pmol g-l 0.0 69.4 0.0 106.9 19.0 (0.15) 57.1 14.7 (0.20) 102.6 36.9 (0.29) 45.4 30.7 (0.41) 105.0 49.8 (0.39) 36.9 44.2 (0.59) 125.9 106.9 (0.85) 30.1 69.4 (0.93) 133.9 a Values in parentheses are the degree of surface coverage (0) of the preadsorbed gas (0 = v / V,).The kinetics of CO and hydrogen adsorption obey Langmuir equations and respectively, where u is the volume of hydrogen adsorbed at the equilibrium pressure p , b and a are the adsorption coefficients and V, is the monolayer volume. Thus the V, values for CO and hydrogen adsorption were found by individual adsorption isotherm experiments at room temperature and are found to be 126.2 and 74.6 pmol g-l, respectively. When hydrogen is allowed to adsorb on the CO preadsorbed surface (106.9 pmol g-l), the amount of hydrogen subsequently adsorbed is 30.1 pmol g-l. The total amount of CO and hydrogen adsorbed is hence 137.0 pmol g-l. However, when the adsorption sequence is reversed the total amount of CO and hydrogen adsorbed on the same surface is 203.3 pmol g-l.This difference in adsorption capacity supports the postulate that preadsorbed hydrogen creates additional sites for subsequent CO adsorption and/or that preadsorbed hydrogen favours surface complex formation. The t.p.d. traces obtained for the series of coadsorbed phases are shown in fig. 3 and 4. Two desorption maxima are observed. The first desorption maximum is always found to be around 350 K, irrespective of the sequence of adsorption. At this desorption maximum both CO and hydrogen are found in the desorbed products. The extent of these components in the desorbed products is dependent upon the time of evacuation of the adsorbed surface at room temperature before desorption.The adsorbed hydrogen species may be labile enough to be desorbed by evacuation at room temperature.17 In the case of hydrogen adsorption on a CO-preadsorbed surface, the desorption maximum is observed at 465 K and that of CO adsorption on the hydrogen-preadsorbed surface is at 475 K. In both cases the desorbing species are found to be mainly CO,. After the first desorption maximum the desorption profile shows negative values of the rate of desorption. This can be due to (i) the readsorption of desorbed products such as hydrogen, since hydrogen chemisorption has been found to be an activated process and (ii) the reaction between CO and hydrogen leading to methane formation. However, no detectable methane was found in the gas phase, indicating that the reduction of CO does not take place under the experimental conditions of t.p.d.The readsorbed hydrogen might be responsible for the slow desorption observed at temperatures above 470 K. The position of the second desorption peak is observed at higher temperatures than in the case of individual adsorption [fig. 1 (a)]. There is a ca. 50 K shift (fig. 4) in the secondR. Gopalakrishnan and B. Viswanathan O * O r l r - - 2639 300 400 500 600 T/K Fig. 3. T.p.d. traces following hydrogen adsorption on a CO-preadsorbed (O,,) catalyst surface : (1) e,, = 0.15, (2) e,, = 0.29, (3) eco = 0.39 and (4) e,, = 0.85. O.*O -0.04 J I I 300 400 500 600 T/K Fig. 4. T.p.d. traces following CO adsorption on hydrogen-preadsorbed (OH,) catalyst A surface: (1) OH, = 0.20, (2) OH, = 0.41, (3) OH, = 0.59 and (4) 8& =.0.93* desorption peak owing to coadsorption of CO with hydrogen, probably indicating that the strength of chemisorption for bridge-bonded CO is increased by the presence of hydrogen.Similar observations have been reported on a Ni(l00) surface1* for the coadsorption of CO and hydrogen, and the temperature shift in the thermal desorption spectrum has been attributed to the existence of an interaction between adsorbed CO and hydrogen. The formation of a surface complex due to the interaction between CO and hydrogen has been reported on single-crystal transition-metal surfaces such as Pt,19 Fe20 and W.21 Although there could be complex formation between CO and2640 Fisc her- Tr opsch Cobalt Catalysts hydrogen on catalyst A, only CO, desorption has been observed, which constitutes the second desorption maximum.This indicates that surface carbonyl species alone are responsible for CO, formation and the second desorption maximum. Even if CO, is formed from the dissociation of surface carbonyl through a carbonyl-type intermediate, the hydrogen released from the complex is held strongly on the surface. In the case of hydrogen adsorption on a CO-preadsorbed surface, the second desorption maximum appears at 460 K, resulting in a temperature shift of ca. 40 K compared with the temperature maximum of CO, formation in the case of pure CO adsorption on a bare surface. This shift is less compared with the case in which hydrogen is preadsorbed, indicating that complex formation is more favourable in the latter case.Saturation exposure of hydrogen on a CO-preadsorbed surface does not change any detectable absorption bands in the region 2300-1 600 cm-l. Similarly, no i.r. absorption bands are observed when the sequence of gas admission is reversed. This observation also provides additional support for the presence of a complex formed from adsorbed CO and hydrogen. It is known that the adsorption of CO is stronger and faster than that of hydrogen on the surface of cobalt. Hence when a mixture of CO and hydrogen is admitted on a cobalt catalyst, CO is preferentially adsorbed. This situation exists in normal synthetic conditions. Although there can be complex formation during hydrogen adsorption on a CO-preadsorbed surface, the interaction between adsorbed CO and hydrogen appears to be stronger when CO adsorbs on a hydrogen-preadsorbed surface. Moreover, the total amount of CO and hydrogen adsorbed is more in this sequence. Hence the sequence of adsorption of CO on a hydrogen-preadsorbed surface may increase the catalytic reaction rate.However, it is difficult to cmtrol the nature of a surface with a considerable concentration of hydrogen under reaction conditions. Recently, Vannice,, has shown that the supported-me tal catalysts possessing SM SI characterstics facilitate competitive hydrogen adsorption with CO. Alternatively, foreign materials, usually termed pro- moters, may be added to effect a degree of hydrogen adsorption comparable to that of CO under the reaction conditions. In bimetallic catalysts23 one of the metals preferentially promotes hydrogen adsorption so that a reasonable concentration of surface hydrogen is maintained under the reaction conditions.Studies on Catalyst B Individual Adsorption of Carbon Monoxide and Hydrogen The t.p.d. traces for the individual adsorption of CO and hydrogen are shown in fig. 5. The temperature of desorption maxima for CO and hydrogen are found to be same as in the case of catalyst A, indicating that the energetics involved in the desorption processes for both the catalysts are the same. However, the second desorption peak for the desorption of CO, from adsorbed CO, which appears at 420 K, is broader in the case of catalyst A, indicating that the distribution of energetically similar adsorption sites for GO adsorption in the bridged configuration in catalysts A and B is different.Coadsorption of Carbon Monoxide and Hydrogen The results obtained for the coadsorption of CO and hydrogen are given in table 2, and t.p.d. traces are shown in fig. 6 and 7. Although there is an initial increase in hydrogen adsorption on the CO-preadsorbed surface, further adsorption is found to decrease regularly with an increase in concentration of preadsorbed CO. This indicates the inhibiting effect of adsorbed CO on the subsequent adsorption of hydrogen, as observed on the surfaces of polycrystalline cobalt14 and catalyst A. Unlike polycrystalline cobalt and catalyst A, on catalyst B the preadsorbed hydrogen has the effect of decreasing theR. Gopalakrishnan and B. Viswanathan 264 1 Fig.5. T.p.d. traces of (a) CO and (b) hydrogen from catalyst B (adsorption at room temperature). -0.02 I I I 300 400 500 600 TIK Fig. 6. T.p.d. traces following hydrogen adsorption on a CO-preadsorbed (O,,) catalyst B surface: (I) e,, = 0.16, (2) O,, = 0.28, (3) O,, = 0.43, (4) Oco = 0.59 and (5) Qc0 = 0.98. subsequent CO adsorption. At the initial stages, hydrogen also has an inhibiting effect on CO adsorption. These observations are in agreement with our previous Irrespective of the sequence of adsorption, the total amount of gases adsorbed (CO + H,) is the same, indicating that CO is not preferentially adsorbed, and the ease with which complex formation occurs is not affected by a change in the sequence of adsorption. This behaviour may be due to the presence of Tho,, in which case the amount of hydrogen adsorbed even on the CO-preadsorbed surface is increased.This hydrogen might have been adsorbed on Tho, or kieselguhr owing to the migration of dissociated hydrogen molecules to Tho, or kieselguhr by a spillover me~hanism.,~ The readily available surface hydrogen may be interacting with adsorbed CO on the metal, forming surface-complex2642 0.20 6 0.12 Y .* -2 3 % W L a % 0.04 . - 0. 0L Fischer-Tropsch Cobalt Catalysts 5 TIK Fig. 7. T.p.d. traces following CO adsorption on hydrogen-preadsorbed (OHz) catadst B surface: (1) OHz = 0.16, (2) OHs = 0.30, (3) OHz = 0.41, (4) OHz = 0.47 and (5) 0 ~ 2 = 0.64. Table 2. Amount of H,/CO adsorbed on CO/H,-preadsorbed surfaces of catalyst B at room tempera turea amount of CO amount of H, amount of H, amount of CO preadsorbed adsorbed on CO- preadsorbed adsorbed on H,- on bare preadsor bed on bare preadsorbed surface/pmol g-' surface/pmol g-' surface/pmol g-l surface/pmol g-l 0.0 19.5 (0.16) 35.4 (0.28) 54.3 (0.43) 73.2 (0.59) 122.0 (0.98) 76.1 98.9 88.5 78.1 54.3 50.0 0.0 18.9 (0.16) 36.0 (0.30) 48.8 (0.41) 56.7 (0.47) 76.1 (0.64) 122.0 113.5 102.5 95.8 103.1 100.0 a Values in parentheses are the degree of surface coverage (0) of preadsorbed gas (0 = u/V,, V, values for CO and hydrogen are 125.0 and 119.7 pmol g-l, respectively).species. Hence in the reaction conditions the carbon deposits can easily be removed by this hydrogen on the supporting materials, which might account for the increase in catalytic activity and the lifetime of the catalyst.Conclusions The support (kieselguhr) and the promoter (thoria) have considerable efTect on the adsorption and coadsorption characteristics of the cobalt surface for CO and hydrogen. (1) Kieselguhr and thoria act as surface sites for H, adsorption by a spillover mech- anism, thereby affecting the net adsorption properties of CO on the cobalt surface. (2) Although there is no interaction between CO and hydrogen on a polycrystalline cobalt surface,14 on the kieselguhr-supported and thoria-promoted cobalt catalysts considerable interaction between CO and hydrogen is observed,R. Gopalakrishnan and B. Viswanathan 2643 References 1 M. Boudart, Adv. Catal., 1969, 20, 153. 2 G. M. Schwab, J. Block and D. Schultze, Angew. Chem., 1959,71, 101. 3 R.T. K. Baker, E. B. Prestridge and R. L. Garten, J. Catal., 1979,59, 293. 4 M. Boudart, A. Delbouille, J. A. Dumesic, S. Khammouma and H. Topsae, J. Catal., 1975, 37, 486. 5 C. H. Bartholomew, R. B. Panwell, J. L. Butler and D. G. Mustard, Ind. Eng. Chem. Prod. Res. Dev., 6 C. H. Bartholomew, R. B. Panwell and J. L. Butler, J. Catal., 1980, 65, 335. 7 M. A. Vannice and R. L. Garten, J. Catal., 1979, 56, 236. 8 J. S. Smith, P. A. Thrower and M. A. Vannice, J. Catal., 1981, 68, 270. 9 J. M. Zowtiak and C. H. Bartholomew, J. Catal., 1983, 83, 107. 1981, 20, 296. 10 H. H. Storch, N. Golumbic and R. B. Anderson, The Fischer-Tropsch and Related Synthesis (John Wiley, New York, 1951). 11 R. B. Anderson, Catalysis, ed. P. H. Emmett (Reinhold, New York, 1956), vol. 4. 12 R. Gopalakrishnan and B. Viswanathan, J. Colloid Interface Sci., 1984, 102, 370. 13 B. Viswanathan and R. Gopalakrishnan, J. Catal., in press. 14 R. Gopalakrishnan and B. Viswanathan, Surf. Technol., 1984, 23, 173. 15 F. S. Baker, A. M. Bradshaw, J. Pritchard and K. W. Sykes, Surf. Sci., 1968,12,426; A. M. Bradshaw and J. Pritchard, Proc. R. SOC. London, Ser. A , 1970,316,169; J. Wojtezak, R. Qucau and R. Poilblanc, J. Catal., 1975, 37, 391. 16 G. Wedler, K. G. Kolb, W. Heinrich and G. McElhiney, Appl. Surf. Sci., 1978, 2, 85; G. K. Kok, A. Noordermeer and B. E. Eieuwenhuys, Surf. Sci., 1983, 135, 65. 17 M. E. Bridge, C. M. Comrie and R. M. Lambert, J. Catal., 1979,58, 28. 18 B. E. Koel, D. E. Peebles and J. M. White, Surt Sci., 1981, 107, L367. 19 V. H. Baldwin and J. Hudson, J. Vac. Sci. Technol., 1971, 8, 49; J. H. Craig Jr, Surf. Sci., 1981, 111, 20 J. B. Benziger and R. J. Madix, Surf. Sci., 1982, 115, 279. 21 J. T. Yates, Jr. and T. E. Madey, J. Chem. Phys., 1971,54, 4969. 22 M. A. Vannice, J. Catal., 1982, 74, 199. 23 V. Ponec, Adv. Catal., 1983, 32, 149. 24 R. Balaji Gupta, Ph.D. Thesis (IIT, Madras, 1973). 25 C. K. Rofer De-Poorter, Chem. Rev., 1981,81,447. L695 ; J. H. Craig Jr, Appl. Surf. Sci., 1982, 10, 3 15. Paper 511467; Received 27th August,1985

ISSN:0300-9599    

DOI:10.1039/F19868202635

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1986, 82, 2645-2649 Distribution of Silicon-to-Aluminium Ratios in Zeolite ZSM-5 Jia-Ching Lin and Kuei-Jung Chao* Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan, Republic of China The distribution of silicon-to-aluminium atomic ratios in ZSM-5 crystals has been measured. Particles of ZSM-5 with different sizes may have uniform chemical composition across the particle. In the same batch product, the Si/A1 ratio of each crystal can be different. A number of studies concerning the distribution of aluminium concentration in zeolite ZSM-5 have appeared recently.1-6 By Auger electron spectroscopy (AES) the secondary- ion mass spectroscopy (SIMS), Suib et a1.l and Dwyer et al., obtained a homogeneous aluminium distribution in polycrystalline and in single crystalline (25 pm) materials.Moreover, Si enrichment on the surface of the ZSM-5 cluster and A1 enrichment on the surface of 50-200pm large crystals were observed, respectively, by Hughes et aL3 by using X-ray photoelectron spectroscopy (XPS), and by von Ballmoos and Meier4 from an electron microprobe analysis (EPMA). On the other hand, Derouane et ~ 1 . ~ reported that for large crystals (5-8 pm), surface and bulk Si/A1 ratios were similar; for smaller crystals (< 1 pm), an Al-enriched surface was present. Lyman et a1.6 deduced, by means of transmission electron microscopy (TEM), that particles of ZSM-5 with different Si/Al ratios may have different A1 profiles across the particle. In this paper we report a detailed investigation of the A1 content in ZSM-5 crystals obtained by various synthetic routes, applying surface and bulk characterization analyses to several isolated phases in reaction mixtures.Our results may explain the seeming disparity in the results mentioned above. Experimental Zeolite ZSM-5 of two different sizes (ca. 50-100 pm and ca. 3-5 pm) was prepared by hydrothermal crystallization of aluminosilicate hydrogels in the presence of tetrapropyl- ammonium cations (TPA). ZSM-5 of ca. 3-5pm was synthesized from aluminium sulphate (Merck), waterglass solution of 21.6% SiO, and 8.1 % Na,O, sulphuric acid and tetrapropylammonium bromide (TPABr, WiiKo Chemicals), with Si0,/A120, z 35-140 as previously reported7 at pH 11 and 167 "C for 8-12 days. A high alkalinity was employed for the synthesis of large ZSM-5 crystals.The mixture of sodium aluminate, Ludox HS-40 colloidal silica (Du Pont), sodium hydroxide with TPABr in SiO, : Al,O, : TPABr : NaOH : H 2 0 = 10 : 1 : 30 : 30 : 2000 was reacted at 187 "C for 12 days. The variation of the Si/Al ratio in ZSM-5 was measured by EPMA and AES across an individual zeolite crystal and between crystals in the crystalline products. The bulk compositions of the reaction solution and solid product were analysed by induced- coupling plasma atomic spectroscopy (ICP). Electron microprobe scans were performed on a Joel superprobe 733 instrument at 25 KV, 0.02 pA sample current with a beam diameter of ca. 2-5 pm. Three measurements were taken at each point with an average counting time of 5 s. For scanning Auger electron spectroscopy a Perkin-Elmer PHI 590 26452646 70 60 0 .* w E 0 50,- 7 LO- *g Y > m Distribution of %/A1 in Zeolite ZSM-5 - - a a a a a I I I 1 I I 10 20 30 40 50 distance/pm Fig.1. The profile of %/A1 ratio across a section of a ZSM-5 crystal [plate 1 (b)]. 1 I I I I I 10 20 30 LO 50 distance/pm Fig. 2. The profiles of Si/A1 ratio across a section of two twinned crystals: A, along --- -+ of plate 2(a); A, along- of plate 2(a); 0, along --- -+ of plate 2(b); a, a l o n g - - - + of plate 2(b). AM system was used. Quantitative evaluation of the surface composition from AES data was achieved by recording the peak-to-peak amplitude of respective elements at 3.0 keV and 1.0 ,uA and by calculation using the corresponding sensitivity factors.* A small current from the neutralizer was applied in order to reduce the sample charging.Depth profiles were obtained by repeatedly monitoring the appropriate Auger transitions with simultaneous 3.8 keV Ar+ ion sputtering at an Ar partial pressure of ca. 5 x Torr.? The bulk %/A1 ratio of the sample was examined by ICP emission spectrometry. The solid sample was dissolved in acids and analysed by Plasmakon S35. t 1 Torr = 101 325/760 Pa.J-C. Lin and K-J. Chao 2647 Table 1. Compositional variations across large ZSM-5 crystals crystal size/,um point analysis average Si/A1 ratio 70 x 43 x 22 58 x 40 x 24 93 x 39 x 26 104 x 52 x 26 105 x 30 x 15 1 0 0 x 3 7 ~ 3 3 ~ 50 x 25 x 16b 80 x 41 x 21b 10 10 20 15 10 10 5 5 33f2 40f3 49&2 46f 1 30+ 1 23+2 32+2 45+3 a Twinned crystal of plate 2(a).Twinned crystal of plate 2(b). Table 2. The Si/A1 ratios of the reaction mixtures in ZSM-5 formationa initial reaction solid ZSM-5 solution mixture product cry s t a1 residue 18 19 CU. 18-20 - 35 26 ca. 24-46 - 70 31 CU. 30-120 - 23 ca. 20-30 3.5 x 103 3 5 w 25 - 7.7 x 102 3509 a Bulk Si/Al ratios of solid products and solution residues were determined by ICP. The Si/Al ratio of ZSM-5 crystal was determined by electron microprobe scan of 5-10 crystals. During the growth of large ZSM-5 crystals the crystalline products were contaminated with gel, as observed by SEM. The products were washed with very dilute alkaline solution and de-ionized water. Results and Discussion The scanning electron micrographs of typical single, twinned and powdery crystals are shown in plates 1 , 2 and 3, respectively.Single crystal and powder X-ray diffractions were used to identify the ZSM-5 str~cture.~ The typical A1 concentration profiles of single and twinned crystals are given in fig. 1 and 2. The dispersion of the Si/Al ratio across an individual single crystal is homogeneous. Two types of the twinned crystals were obtained as shown in plate 2(a) and (b). A uniform Si/Al ratio in the crystal of plate 2(a) is observed. The crystal shown in plate 2(b) is composed of two parts with different average Si/Al ratios as shown in table 1 and fig. 2. The variation of aluminium in ZSM-5 crystals produced from the same reaction batch is shown in table 1 . The inhomogeneity of aluminium concentration in ZSM-5 lies between the crystals rather than within a single crystal.Thus, ZSM-5 crystals with different Si/Al ratios can be formed in the same reaction mixture. The crystallization of zeolite from hydrogel includes nucleation and crystal growth. The rate of nucleation is strongly affected by hydroxide ions and by aluminium concentration in the reaction solution. The presence of hydroxide ions accelerates the dissolution of aluminosilicateJ. Chern. SOC., Faraday Trans. I , Vol. 82, part 9 Plates 1 and 2 Plate 1. Scanning electron micrographs of typical large ZSM-5 crystals: (a) crystal for X-ray diffraction; (b) crystal for Si/Al ratio measurement. Plate 2. Scanning electron micrographs of typical twinned crystals. J-C. Lin and K-J. Chao (Facing p . 2648)J .Chem. SOC., Faraday Trans. 1, VoE. 82, part 9 Plate 3. Scanning electron micrograph of typical ZSM-5(35) Plate 3 J-C. Lin and K-J. Chao2648 120- 90- 0 .- c., 2 o 60- 4 0 'S c, m d k m 30 Distribution of %/A1 in Zeolite ZSM-5 - I I I I I I I 1 1 I 2 L 6 8 10 analysis point Fig. 3. The profiles of Si/A1 ratios of small crystals in 0, ZSM-5(18); A, ZSM-5(35); H, ZSM-5(70); one analysis point per crystal. and polysilicate hydrogels. The dissolved silicate and aluminate ions can undergo a polymerization process and regroup around the hydrated cations to form the nuclei of the ordered zeolite. Since the aluminate in solution can form Al(OH),,, which consumes OH- ions in the solution, the quantity of the available OH- ions for depolymerization of gel probably depends on the aluminium concentration in the reaction mixture. Thus, the rate of the crystallization of zeolite ZSM-5 in an Al-rich environment will be slower than that in an Si-rich environment.Large ZSM-5 crystals of Si/Al ratio of ca. 23-49 were formed with analcime (Si/Al = ca. 3-5) and a trace of quartz. The Si/Al ratio of 23 corresponds to the average number of A1 atoms per unit cell being 4 and A1 atoms per channel intersection being 1 in ZSM-5. The negative charge of the aluminate anion resulting from the replacement of Si atoms by A1 atoms in the framework is neutralized by the positive charge of the TPA template ion, The bulk Si/Al ratio of the solid product of the Si02:A120,: TPA: NaOH: H,O = 10: 1 : 30: 30: 2000 batch is 7.7. The aluminium content of the crystalline ZSM-5 is lower than that of the reaction mixture and of the solid product.Zeolite ZSM-5 was produced from the reaction mixture with the Si/Al ratio varying from 18 to 70; it is the only crystalline product in which the bulk Si/A1 ratio is ca. 19-3 1, much lower than those in the reaction mixtures. Crystals of low Si/A1 ratio may also form in an Si-rich environment and these tend to withdraw A1 species from the liquid during growth. Therefore, the aluminium concentration varies during autoclave treatment of the reaction mixture, especially in reaction mixtures with a high Si/Al ratio, such as the %/A1 = 70 batch, in which the distribution of %/A1 ratios between ZSM-5 crystals is more dispersed, as shown in table 2 and fig. 3. The Si/A1 ratio of ZSM-5 crystals formed in the later stages of synthesis may be different from those formed earlier.The A1 content of the crystalline product of the Si/Al = 35 batch was also examined by AES. The Si/Al ratio of ZSM-5 has been plotted against time with Ar+ ion bombardment as shown in fig. 4. Auger electron spectra taken before and after depth profiling yielded an Si/Al ratio of ca. 30-25, indicating that the Si/Al ratio is homogeneous either in the interior or on the surface of crystalline ZSM-5. However, the Si/Al ratio of individual crystals may be different between particles, as shown by EPMA measurements of the gel-free crystals (fig. 3).J-C. Lin and K-J. Chao 2649 5/i LO a I I I I I 20 LO 60 80 100 sputtered time/min Fig. 4. AES measurement on the Ar-ion sputtered ZSM-50(35).Furthermore, we prepared two samples of the same composition. After 8 days at 167 "C, one of the samples was cooled slowly from 167 "C to room temperature in 2 days (S); the other was cooled immediately by quenching the vessel in cold water as reported earlier (F). The average bulk %/A1 ratios of the solid products were 25 for S and 23 for F by ICP. The products were in polycrystalline aggregates of ca. 3-5 pm as observed by electron microscopy. A surface Si/Al ratio of ca. 200-600 was found for sample S and the typical Si/Al ratio of F was ca. 20-30 by analysing five crystals in each case. The silica concentration of the liquid residue of S is lower than that of F, but both have similar aluminium contents. This indicates that the solid cluster of S may be composed either of a thin skin of siliceous material coating the polycrystalline aggregate ZSM-5 or of crystals similar to sample F stacked with small ones of high %/A1 ratio formed during the cooling stage.Perhaps this would explain the different Si/A1 ratios obtained by Hughes et ~ 1 . ~ on their dispersed powder and pelletized ZSM-5. Pelletizing the zeolite breaks up the aggregates and the interior of the aggregates is exposed to the analysis by XPS. Thus, the aluminium distribution of ZSM-5 may be affected by the method of preparation. In summary, we found a homogeneous distribution of aluminium in the individual gel-free ZSM-5 crystals, large or small. In the same batch product, the Si/A1 ratio of each crystal can be different. References 1 S. L. Suib, G. D. Stucky and R. J. Blattner, J . Catal., 1980, 65, 174. 2 J. Dwyer, F. R. Fitch, F. Machado, G. Qun, S. M. Smith and J. C. Vikerman, J . Chem. SOC., Chem. 3 A. E. Hughes, K. G. Wilshier, B. A. Sexton and R. Smart, J . Catal., 1983, 80, 221. 4 R. von Ballmoos and W. M. Meier, Nature (London), 1981, 289, 78. 5 (a) E. G. Derouane, J. P. Gilson, Z. Gabelica, C. Mousty-Desbuquoit and J. Verbist, J . Catal., 1981,71, 447; (b) E. G. Derouane, S. Detremmerie, Z. Gabelica and N. Blom, Appl. Catal., 1981, 1, 20. 6 C. E. Lyman, P. W. Betteridge and E. F. Moran, ACS Sym. Ser., 1983, 218, 199. 7 K. J. Chao, T. C. Tsai, M. S. Chen and I. Wang, J. Chem. SOC., Faraday Trans. 1, 1981, 77, 547. 8 Handbook of Auger Electron Spectroscopy (Physical Electronics Industries, Eden Prairie, Minnesota, 9 K. J. Chao, J. C. Lin and Y . Wang, Zeolite, 1986, 6, 35. Commun., 1981, 422. 1976). Paper 5 / 15 18 ; Received 4th September, 1985 88 FAR 1

ISSN:0300-9599    

DOI:10.1039/F19868202645

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J. Chem. SOC., Furuday Trans. 1, 1986, 82, 2651-2664 The Partitioning of Solutes between Water-in-Oil Microemulsions and Conjugate Aqueous Phases Paul D. I. Fletcher Department of Chemistry, University of Hull, Hull HU6 7RX The partitioning of solutes between an aqueous phase containing sodium chloride and an equilibrium, conjugate, water-in-oil microemulsion phase has been measured. The two-phase system consists of a water phase containing a very low concentration of monomeric surfactant in equilibrium with an upper, oil phase consisting of a water-in-oil microemulsion containing virtually all the surfactant. The surfactant used was sodium bis(2-ethylhexyl) sulphosuccinate (AOT) and the oil was n-heptane. The size of the water-in-oil microemulsion aggregates present in the upper phase was varied by altering the sodium chloride concentration present in the aqueous phase.The solutes investigated were sodium chloride, the cationic dimidium ion, the neutral p-nitroaniline species and the anionic species murexide. The sodium chloride partitions only weakly in favour of the bulk water phase. Dimidium ion partitions strongly to the AOT interface, particularly so at low salt concen- trations. p-Nitroaniline partitions mainly to the AOT interface but less strongly than the DMD. The negative murexide ion partitions between the bulk and dispersed water of the microemulsion phase with a partition coefficient of near unity. The involvement of electrostatic and other forces in determining the partitioning is discussed. The study of partition coefficients in these two-phase systems can yield information about the interaction of the solute with the microemulsion which is relevant to the kinetics of chemical reactions in microemulsions.Water-in-oil microemulsions consist of tiny water droplets (radius 1-20 nm) in a continuous oil solvent, the system being stabilised by a suitable surfactant. Much of the recent interest in these systems arises from their use as novel reaction media, since reaction rates and equilibrium positions may be greatly altered in microemulsions as compared with conventional sol~ents.l-~ This is particularly true for the case of enzyme-catalysed reactions, where the water droplets provide a unique microenvironment for the The effect of the microemulsion on the reaction kinetics and equilibrium is due to two effects.’? * First, reactants and products can partition between the hydrophilic and hydrophobic microdomains of the microemulsion system. Secondly, there can be specific effects upon the reagents caused by the different microenvironment (e.g.polarity, viscosity) experienced by the reagents in the microemulsion as compared with a bulk solvent. For example, the microemulsion dispersed water is known to show reduced a~tivity,~ reduced polaritylO and reduced translational diffusionll in comparison with bulk water. The effect of microemulsification upon the rate of a bimolecular reaction is due to a combination of effects upon the free energy of both reagents and the transition state of the reaction. Measurements of solute partitioning between a microemulsion phase and a conjugate aqueous phase provides a measure of the free-energy difference of a single species dissolved in the microemulsion and in bulk water. The microemulsion system used in this study consisted of water and n-heptane with the surfactant sodium bis(2-ethylhexyl) sulphosuccinate (AOT).This microemulsion system has been extensively investigated in recent years, since AOT-stabilised micro- 265 1 88-22652 1oc R 5a a Yolute Part it ioning in Microemulsions log,, ([NaCl]/mol dm-3) Fig. 1. R value of the microemulsion phase vs. the sodium chloride concentration in the conjugate aqueous phase (open circles) and in the microemulsion dispersed water (filled circles). Temperature = 25.0 "C. emulsions do not require the presence of a cosurfactant (normally a medium-chain-length alcohol) for stability.The water droplet sizes, as measured by ultracentrifugation,12 dynamic light scattering,l3? l4 small-angle neutron scattering15-18 and fluorescence technique^,^^^^^ depend primarily on the molar ratio of water to AOT, R. Changing the AOT and water concentrations together such that R remains constant changes the concentration of water droplets but not their size. The droplet radius as a function of R is given approximately by eqn(1) quoted in ref. (14), in which r is the hydrodynamic radius : r/nm = 0.175 R+ 1.5. Two-phase systems comprising an aqueous phase containing only a very low concen- tration of monomeric AOT in equilibrium with a conjugate water-in-oil microemulsion phase are formed at 25 "C when the water phase contains a concentration of NaCl higher than 0.05 mol dm-3.21 At lower salt concentrations at this temperature, phase separation produces an aqueous phase containing normal micelles of AOT and a conjugate phase of virtually pure n-heptane. At salt concentrations very close to 0.05 mol dm-3, a third, surfactant-rich phase forms with conjugate water- and oil-rich phases.Increasing the salt concentration in the range 0.07-5.0 mol dm-3 decreases the R value of the water-in-oil microemulsion aggregates formed in the upper oil-rich phase and hence their sizes. This is shown in fig. 1. Changing the AOT concentration in the range 0.001-0.5 mol dm-3 alters only the droplet concentration in the microemulsion phase but has no effect on the R values (i.e.at a constant concentration of NaCl, the amount of water present in the microemulsion phase varies in proportion to the AOT concentration such that a constant R value is maintained over this range of AOT concentrations). The effect of salt, alkane solvent variation and temperature on the phase behaviour of AOT has been studied by Shinoda22 and, more recently, by Aveyard et aZ.21f23 For the high NaCl (1)P . D . I. Fletcher 2653 concentration regime, virtually all the AOT is present in the oil phase. The lower aqueous phase contains only monomeric surfactant at concentrations equal to the critical micelle concentration (c.m.c.) in the presence of NaCl and heptane. The c.m.c. values decrease from ca. 0.4 mmol dm-3 at 0.05 mol dm-3 NaCl to ca. 0.1 mmol dm-3 at 0.14 mol dm-3 NaCl.21 For the measurements described here, a low concentration of partitioning solute was shaken with a mixture of a n-heptane solution of AOT and an aqueous salt solution. The mixture was then left to separate into two clear phases. The concentration of solute in each phase was then determined. This was done for different AOT concentrations and different salt concentrations (in order to determine the partitioning as a function of droplet size). The experiments provide a measure of the solute partitioning between the microemulsions and aqueous solutions containing different concentrations of sodium chloride. It is of interest to know, however, the partitioning from some constant, reference state (for example, high dilution in pure water) to the microemulsions.Hence, the solubilities of the solutes in different salt concentrations were also determined to measure the solute activity as a function of salt concentration. The partitioning behaviour was expected to depend strongly on the charge type of the solute. Hence positive, neutral and negative solutes were studied. Also, the partitioning of the salt present was measured. Experimental AOT was supplied by Sigma and used without further purification. This batch of AOT showed no minimum in a plot of interfacial tension as a function of AOT concentration, unlike a Fluka sample tested. Interfacial tension results with Sigma AOT were identical to those measured for a highly purified sample of AOT.24 n-Heptane was Fisons HPLC grade and was run through an alumina column prior to use.Water was distilled, de-ionised and passed through a Milli-Q-Reagent water system. Sodium chloride (BDH AnalaR reagent), Dimidium bromide (Fluka purum), p-nitroaniline (Hopkins & Williams 99 % ) and murexide (ammonium purpurate) (Sigma) were used as supplied. Ultraviolet-visible spectrophotometric measurements at single wavelengths were made using a Perkin-Elmer 550s instrument. The sample cuvettes were thermostatted to +0.2 "C using a water circulating system. Scanning spectra were recorded using a Hewlett-Packard 845 1 A diode-array spectrophotometer at ambient temperature Water concentrations were measured by Karl-Fischer titration using a Baird & Tatlock AF3 automatic titrator. The maximum amounts of water (containing various concentrations of sodium chloride) which could be solubilised in AOT solutions in heptane at 25 "C were determined by addition of aqueous sodium chloride solution to a thermostatted, stirred AOT solution in oil. The limit of solubilisation was detected as the onset of a permanent turbidity of the microemulsion.Chloride ion concentrations in the aqueous phases were measured by Mohr t i t r a t i ~ n . ~ ~ Chloride ion concentrations in the upper, water-in-oil microemulsion phases were calculated from measurements of the chloride concentrations in the aqueous phases at equilibrium and knowledge of the total chloride present and the volume fractions of water in the microemulsion phases. The solubility measurements were made by thermostatting the salt solutions containing excess, solid solute with occasional shaking for a minimum of 24 h.The solutions were then centrifuged and the concentrations determined spectrophotometrically. The procedure used to determine the solute partitioning was the following. The mixtures were contained in stoppered sample bottles and shaken for 5 min. The samples were then centrifuged at ca. 2500 rev min-l for a few minutes to speed up the phase separation. Centrifugation at higher speeds can cause sedimentation of the water droplets. Samples of each phase were then withdrawn and the absorbances measured and used to calculate the solute concentration in each phase. It was checked that equilibrium (21 +2 "C).2654 0.9 0.6 0.3 Solute Partitioning in Microemulsions - - - :. 0 0 0.0 0 0 0 0 0 OO I 20 40 R 60 Fig. 2. Partitioning of sodium chloride between aqueous and microemulsion phases of different R values at 25.0 "C. Data points were determined by turbidity titrations (open circles) and by Mohr titration (filled circles). partitioning was achieved by comparing results obtained from experiments in which the dyes were initially dissolved in the water phase with measurements in which the dyes were initially dissolved in the AOT-containing oil phase. Identical results were obtained for all the systems investigated except for murexide in systems containing > 1 mol dm-3 NaCl in the water phase. In these mixtures the murexide remained in the phase in which it was initially dissolved even after vigourous shaking for several hours. The derived partition coefficients expressed in the various ways described in the text were found to be independent of the solute concentration (which was sub-millimolar) and AOT concentration.Results and Discussion (a) The Two-phase System and Partitioning of the Sodium Chloride Fig. 1 shows the equilibrium R value of the microemulsion phase as a function of the conjugate aqueous phase salt concentration. This date extends measurements by Aveyard et al. on this system.217 23 The R values are also shown as a function of the salt concentration in the dispersed water of the microemulsion phase. The relationship between the two curves can be expressed in the form of a partition coefficient of the salt between the aqueous phase and the dispersed water of the microemulsion phase.Let [NaCl],, be the aqueous phase concentration of salt and [NaCl],, be the concentration of salt in the microemulsion phase expressed as moles of NaCl per unit volume of microemulsion dispersed water. The partition coefficient, P(NaCl)dw,aq is defined by P(NaC1)dw/aq = [NaC1ldw/[NaC1laq- (2) The partition coefficient was calculated from data shown in fig. 1 by comparing the salt concentrations in the dispersed and bulk water components that produce, at equilibrium, the same R value. The partition coefficient was also determined by titration of chloride ion in the equilibrium aqueous phases of the two-phase samples. Comparison of the chloride concentrations before and after equilibration with an AOT solution in heptane allowed the calculation of P(NaCl)d,Iaq.Values of the salt partitioning as a function of R are shown in fig. 2. The salt partitionP. D. I. Fletcher 2655 I I 1 -3 -2 -1 log,, ([AOT],,/mol dm-3) Fig. 3. Partitioning of dimidium ion as a function of the AOT concentration. The sodium chloride concentrations in the aqueous phase were (from right to left) 5.0, 2.0, 0.5 and 0.075 mol dmP3. coefficient P(NaCl),,,,, is virtually constant for R > 20 at ca. 0.35, but rises slightly for R < 20. The salt has slightly less affinity for the dispersed water of the microemulsion phase as compared with bulk water. (b) Partitioning of Dimidium Ion The structure of the cationic dimidium ion (DMD) is shown in (I). Fig. 3 shows the fraction of total DMD that partitions to the oil phase as a function of AOT H I N y N H z concentration at various values of [NaCl],,.DMD shows no solubility in heptane containing no AOT. Increasing the AOT concentration causes an increase in the DMD partitioning to the oil phase. Decreasing the salt concentration (which produces an equilibrium microemulsion phase containing larger, i.e. higher R value, water droplets) also causes an increase in the partitioning to the oil phase. The observed increase with lowered salt concentrations could be explained either by an increasing affinity of the DMD for the larger R value microemulsions or a decreased affinity for the lower salt aqueous phase. Fig. 4 shows the aqueous solubility of DMD as a function of salt concentration. The solubility variation is described by log,, (solubility/mmol dm-3) = 1.80 - 0.5 16[NaCl].(3) The large negative value of the salting constant (= -0.516) shows that the affinity between DMD and the salt solution strongly decreases with increasing salt concentration.2656 Solute Partitioning in Microemulsions 2 i [ NaCl ]/mol dmV3 Fig. 4. Solubility of DMD in aqueous salt solutions at 25.0 “C. Table 1. Partitioning of dimidium “aClI,, K(DMD) [ W M D ) / cl /mol dmP3 R /dm3 mol-1 /dm3 mol-1 P(DMD)i,t,,q/C 0.075 60 > 103 > 103 > 103 0.1 42 > 103 > 103 > 103 0.5 17.2 530 & 80 290 & 50 780f 100 2.0 8.9 120f 10 11*1 29&3 5.0 3.8 34&5 0.09 f 0.01 0.23 & 0.03 Hence, the increased affinity between DMD and the microemulsion at low salt concentrations is the net result of an increased affinity of the DMD for both the oil and water phases.For a particular salt concentration (or R value of the oil phase), an equilibrium constant for the partitioning of a solute X may be defined as in The subscripts oil and aq signify that the subscripted concentrations refer to the oil and water phases, respectively. The concentrations are expressed as moles of solute per total unit volume of the phase indicated by the subscript. Table 1 shows the values of K(DMD) for various salt concentrations. Also shown are values of K(DMD)/C, where C is a correction factor to allow for the changing affinity of the solute for the aqueous phase as a function of the salt concentration. K(DMD)/C may be thought of as the hypothetical partition coefficient of the solute between the actual microemulsion phase and a water phase containing no salt. C is calculated from the solubility data according to C = (solubility at zero [NaCl])/(solubility).( 5 )P. D. I. Fletcher 2657 0.6 0.4 52 5 -2 a -2 0.2 0 I I I I I I wavelengt h/nm Fig. 5. Absorbance spectra of DMD in water and microemulsions of various R values. [DMD] = 9.45 x lop6 mol dm-3, [AOT] = 0.333 mol dm-3. The letters refer to microemulsions of the following R values: (a) 2.8, (b) 5.6, (c) 13.9, (d) 41. Spectrum (e) was recorded in 0.5 mol dm-3 NaCl aqueous solution. The partitioning of DMD [when corrected for the changing affinity of the DMD for the water phase due to changing sodium chloride concentration, i.e. the value of K(DMD)/C] sharply decreases as the salt concentration increases (and hence as the microemulsion water droplet size decreases). Fig.5 shows the u.v.-visible absorbance spectra of DMD in microemulsions of various R values and also in an aqueous solution containing 0.5 mol dm-2 salt. The spectrum of DMD in microemulsion shows a shift towards longer wavelengths and an increase in extinction coefficient as compared to the bulk, aqueous salt solution. The spectra in microemulsions are shifted relative to water but show no wavelength shifts in microemulsions of different R values. This implies the environment of DMD is fairly constant independent of R. Since it is known that the dispersed water properties change as a function of R, it seems likely that the DMD is located in the microemulsions in a region close to or in the annular, surfactant shell at the interface between the oil and dispersed water where it does not experience any large change in environment with changing droplet size.The positive charge on the DMD makes it likely to interact strongly with the anionic AOT interface. The microemulsion phase may be divided into three ' pseudo-phases'. These are locations for solubilised solutesfhat may be treated as if they are separate phases within the microemulsion phase. The pseudo-phases are defined here as the continuous oil solvent, the dispersed water and the interfacial region. The microemulsion is then assumed to behave (for the purposes of analysing and comparing the partition data) as though it consists of three separate phases of volume fractions given by 8dw = O.O18[AOT] R (6) tIint = 0.390[AOT] (7) 8dw, 8int and 8,, are the volume fractions of the dispersed water, the interface and the continuous oil solvent pseudo-phases, respectively. (The last one should not be confused2658 Solute Part it ioning in Microemulsions Table 2.Partitioning of p-nitroaniline in two-phase systems 0.072 65 21 f2 21 + 2 5 5 * 5 0.45 17.6 24+ 1 22* 1 62+3 4.5 4.4 4 6 k 2 18f 1 120+6 with the oil-rich phase with subscript oil.) 0.018 and 0.390 are the molar volumes of water and AOT.26 The dividing lines between the different pseudo-phases are arbitrary. For example, the interfacial pseudo-phases could be defined as containing some water and oil which was assumed to penetrate the surfactant shell. The simple definitions adopted here are useful in that they may be used to compare the partitioning of solutes that partition to different regions of the microemulsion.The definitions (6)-(8) allow the normalisation of the partition coefficients to a standard volume of the particular microemulsion pseudo-phase occupied by the solute. A similar pseudo-phase treatment is adopted in the analysis of chemical reaction kinetics in microemulsions and micellar solutions . 7 6-8 For DMD the equilibrium constant defined in eqn (4) may be redefined as a dimensionless partition coefficient equal to the ratio of concentration of DMD in the microemulsion phase expressed per volume of the interfacial region or pseudo-phase (i.e. the ‘concentration’ in the interfacial pseudo-phase) to the DMD concentration in the bulk aqueous phase. The partition coefficient expressed in this way [P(DMD)i,tIaq] was calculated using the equation Values of P(DMD)int,acl/C are included in table 1.The values of P(DMD)i,t,,q/C refer to partitioning of DMD between a water phase and a microemulsion pseudo-phase consisting of the AOT interface. DMD has a high affinity for the interface at low AOT interfacial film curvature (i.e. large droplet sizes or high R values), but this is sharply reduced at high AOT interfacial curvature (i.e. small droplet sizes or low R values). P(DMD)i,,tI,q = K(DMD)/0.390. (9) (c) Partitioning of p-Nitroaniline (PNA) The previous cases of NaCl and DMD were relatively simple in their partitioning behaviour, since these solutes partition to single microemulsion pseudo-phases (the dispersed water and the AOT interface for salt and DMD, respectively).PNA is a neutral species and shows comparable solubilities in water and heptane. Therefore it is expected to partition between pseudo-phases within the microemulsion phase. This expectation is confirmed by the experimental observations. Table 2 gives the calculated values of K(PNA) for different salt concentrations. In contrast to the DMD results, the PNA partitioning does not change dramatically as a function of sodium chloride concentration. Fig. 6 shows the solubility of PNA as a function of the salt concentration. The behaviour is described by log (solubility PNA/mmol dm-3) = 0.69 - 0.089[NaC1] (10) The solubility data were used to calculate correction factors C for this system. The experimental conditions of spectrophotometer wavelength (360 nm) and relatively high AOT concentrations used for the two-phase partitioning studies were such that the measured oil-phase concentration of PNA corresponded to that located in the AOT interfacial pseudo-phase. Hence the data were used to calculate values of P(PNA)i,t,a4 which are also shown in table 2.P .D. I. Fletcher 2659 *O c 2 4 6 [ NaCl]/mol dm-3 Fig. 6. Solubility of p-nitroaniline in aqueous salt solutions at 25 "C. 14. I I I I I I 1 300 400 wavelengt h/nm Fig. 7. Absorbance spectra of p-nitroaniline in microemulsions of various R values. The letters refer to the following solutions: (a) heptane, (b) 0.333 mol dm-3 AOTIR = 2.8, (c) R = 5.6, ( d ) R = 13.9, (e) R = 30.6, df) R = 55.6, ( g ) water, (h) 1.96 mol dm-3 NaCl in water.Ultraviolet-visible absorbance spectra were recorded for PNA solutions in water, heptane and microemulsions containing various AOT concentrations and R values. Fig. 7 and 8 show typical results. PNA in heptane shows a peak at ca. 325 nm, whereas in water the peak is shifted to ca. 390 nm and further shifted (by a few nm) as the salt concentration in the water is increased. Inspection of the microemulsion spectra show that they contain three overlapping peaks at 325, 360 and ca. 390 nm. These peaks are2660 Solute Part it ioning in Microemulsions 0.8 I I I I I 1 I - ( a ) 300 400 wavelength/nm Fig. 8. Absorbance spectra of p-nitroaniline in microemulsions of various AOT concentrations at an R value of 27.8. The AOT concentrations were: (a) 0, (b) 0.002, (c) 0.004, ( d ) 0.02, (e) 0.2 mol dm-3.Table 3. Partitioning of p-nitroaniline between different pseudo-phases of the one-phase micro- emulsions (determined spectrophotometrically) 1.4 6.9 13.9 27.8 2.8 5.6 13.9 30.6 55.6 750 f 50 - 700 f 60 - 940 f 120 - 780 rf: 60 - - 0.17 f 0.12 - 0.3k0.1 0.24 f 0.04 _. 0.16 f 0.04 - 0.12 & 0.04 - assigned to [PNA],,, [PNAIint and [PNA],,, respectively. The spectrophotometric data were used to calculate partition coefficients for PNA between the different pseudo-phases of the microemulsion. The following partition coefficients were defined : P(PNA)in t / cs = [PNAlint / [PNAI c s P(PNA)dwjint = [PNAldw / [PNAlint. (1 1) (12) The notation used is the same as in eqn (2) and (9), where [XI,, represents the concentration of species X present in the pseudo-phase, ps, expressed per volume of pseudo-phase.Values of P(PNA)intIcs were calculated from spectra recorded for a constant R but varying [AOT] (as in fig. S), whereas P(PNA)dw,i,t was determined by varying R at constant [AOT]. The results are shown in table 3. The collected results for PNA may be clarified by representing the results as a free-energy diagram. Using the (13) equation AG = -RTln PP . D. I . Fletcher 3 x --. P 5 266 1 "i, + -10 o+ 1 + O + + I I I I 0 20 40 60 R Fig. 9. Free-energy diagram for p-nitroaniline partitioning. (a) n-heptane, (b) 5 mol dm-3 NaCl in water, (c) 2 mol dm-3 NaCl in water, ( d ) pure water, (e) dispersed water pseudo-phase, (f) AOT interfacial pseudo-phase. For the AOT interface, the filled-circle data points were calculated from the spectrophotometric measurements, whereas the open-circle data points were calculated from the two-phase partitioning data.and setting the free energy of PNA in pure water arbitrarily equal to zero, the diagram shown in fig. 9 may be constructed using the data of tables 2 and 3. This shows the free energies of transfer of 1 mol of PNA from 1 dm3 of pure water to 1 dm3 of the microemulsion pseudo-phases. The values for the microemulsion pseudo-phases are shown as a function of R. The values for water, salt solutions and heptane are shown as horizontal lines. Several interesting points emerge from fig. 9. First, although PNA has less affinity for the apolar heptane than for water, the PNA has the most affinity for the AOT interfacial region.[Affinity is represented by the vertical distance below the zero (pure water) line.] The affinity of PNA for the AOT interface relative to water is independent of the AOT interfacial film curvature, which is varied by changing the R value. PNA favours the dispersed water relative to bulk water phases containing various amounts of salt to a degree which depends slightly on the R value. Partitioning of Murexide Murexide (11) is a negatively charged metal-complexing agent. The reaction kinetics of nickel-ion complex formation with murexide have been investigated in the microemulsion system used in this study.122662 0.3 a, c 0.15 s: -2 0 Solute Partitioning in Microemulsions Table 4. Partitioning of murexide ~~~~~ ~ “aCII,,, K(mur) /mol dmP3 R /dm3 mol-1 P(mur) dw , aq ~~ ~ ~~ ~~~ ~~~ 0.1 43 0.9+0.1 1.2+0.2 0.1 1 38 0.50 + 0.05 0.7 + 0.2 0.53 16.5 0.29+0.02 1 .o + 0.2 2.0 8.9 equilibrates too slowly 5.0 3.8 equilibrates too slowly ~ ~~ ~ I I I 1 I I I -1 0.3 0.15 I I I I I I I + c 5 00 600 I I I I I 1 I - - I I I 1 I I 500 6 00 wavelength/nm Fig.10. (A) Absorbance spectra of murexide in microemulsions of R values: (a) 2.8, (b) 5.6, (c) 8.3, ( d ) 25.0, (e) 47.2. The AOT concentration was constant at 0.1 mol dmP3. (B) Absorbance spectra of murexide in aqueous solutions containing (f) 0, (g), 0.05, (h) 0.5, (i) 2.0, ( j ) 4.0 mol dm-3 NaCl. Values for the partitioning of murexide are shown in table 4. K(mur) shows a slight decrease with decreasing R value. The measured values of K(mur) were used to calculate P(mur)dw/aq values.It can be seen that the affinities of the murexide for the bulk water and the dispersed water are approximately equal, i.e. P(mur)dwiaq z 1. The spectra of murexide in aqueous solution containing various salt concentrations and in micro- emulsions of various R values are shown in fig. 10. The two series of spectra are very similar supporting the conclusion that murexide is located in the dispersed water of the micr oemulsions. From these results it appears that the murexide ion shows similar interactions with the microemulsion dispersed water as with bulk water. In the metal-ligand complex formation reaction of murexide with nickel ions in AOT-stabilised microemulsions the reaction kinetics are not altered through an effect of the microemulsion on the groundP.D. I. Fletcher 2663 state of the murexide ion. The observed effects12 must be due to changes in the free energy of the nickel ion or the reaction transition state in the microemulsion as compared with water. It was attempted to measure the solubility of murexide in aqueous salt solutions. However, addition of an excess of solid murexide to salt solutions causes the formation of a ‘gel-like’ phase. It was also noted that the partitioning of murexide in two-phase systems containing aqueous phases having > 1 mol dm-3 NaCl was not achieved within an hour. This is very slow when compared to the few minutes shaking found to be sufficient for the other systems studied. It seems likely that the ‘ trapping’ of the murexide in whichever phase it is initially dissolved is related to the formation of the ‘gel’ phase.Conclusions The partitioning of the solutes investigated may be summarised as follows. Sodium chloride partitions between the bulk aqueous phase and the microemulsion-dispersed water with a slight preference for the bulk water. DMD partitions between the water phase and the AOT interfacial region. DMD has a strong preference for the AOT interface at high R values (low interfacial curvature), but this drops off sharply at low R. p-Nitroaniline partitions mainly to the AOT interface (but less strongly than DMD), but does exhibit partitioning to the oil and dispersed water pseudo-phases. The partitioning of PNA to the interface is independent of the AOT interfacial curvature. Murexide partitions between the bulk and dispersed water with a partition coefficient of near unity.The results indicate that the affinities of the solutes for the microemulsion phase containing the negatively charged AOT as surfactant follows the order : DMD (positive) > PNA (neutral) > murexide (negative); as would be predicted on the basis that electrostatic forces dominate the partitioning. However, the results for the partitioning of NaCl show that the simple salt has a nearly equal affinity for the bulk and microemulsion-dispersed water. The near-unity partition coefficient of the negatively charged murexide shows that this ion does not experience any large repulsion although, owing to the small sizes of the microemulsion droplets, it is necessarily located in fairly close proximity to the AOT surface.This implies that specific, non-electrostatic forces are also important in determining partitioning in these systems. A further contributory factor to the partitioning could be the Laplace excess pressure of the droplets. However, since the formation of microemulsions is associated with ultra-low interfacial tensions, this effect might be expected to be relatively small. It is interesting that the affinity between PNA and the interface is independent of the surfactant film curvature, whereas that of DMD is strongly dependent on curvature. This difference may reflect differences in the sites occupied by the two solute species or it may be the solute size that is important. The measurement of solute partitioning in these two-phase systems provides a simple measure of the interactions between solute molecules and the water-in-oil microemulsions.This type of study should yield fundamental information about the interactions responsible for the effects of microemulsions on chemical reaction rates and equilibria. References 1 C. J. O’Connor, T. D. Lomax and R. E. Ramage, Adv. Colloid Znterfuce Sci., 1984, 20, 21. 2 P. D. I. Fletcher and B. H. Robinson, J. Chem. SOC., Furuduy Trans. I , 1984, 80, 2417. 3 J. H. Fendler, Membrane Mimetic Chemistry (John Wiley, New York, 1982). 4 K. Martinek, A. V. Levashov, N. L. Klyachko, V. I. Pantin and I. V. Berezin, Biochim. Biophys. Actu, 5 P. L. Luisi, Angew. Chem., 1985, 24, 439. 6 P. D. I. Fletcher, R. B. Freedman, C . Oldfield, B. H. Robinson and J. Mead, Colloids Surf., 1984, 10, 1981,657,277. 193.2664 Solute Part it ioning in Microemulsions 7 I. V. Berezin, K. Martinek and A. K. Yatsimirski, Russ. Chem. Rev., 1973, 42, 787. I d C. A. Bunton, Pure Appl. Chem., 1977, 49, 696. 9 R. Kubik and H. F. Eicke, Helv. Chim. Acta, 1982, 65, 170. 10 M. Wong, J. K. Thomas and M. Gratzel, J. Am. Chem. SOC., 1976, 98, 2391. 11 J. Tabony, A. Llor and M. Drifford, Colloid Polym. Sci., 1983, 261, 938. 12 B. H. Robinson, D. C. Steytler and R. D. Tack, J. Chem. SOC., Faraday Trans. I , 1979,75,481. 13 M. Zulauf and H. F. Eicke, J. Phys. Chem., 1979,83,480. 14 J. D. Nicholson and J. H. R. Clarke, in Surfactants in Solution, ed. K. Mittal and B. Lindman, 15 C. Cabos and P. Delord, J. Appl. Crystallogr., 1979, 12, 502. 16 B. H. Robinson, C. Toprakcioglu, J. C. Dore and P. Chieux, J. Chem. SOC., Faraday Trans. I , 1984, 17 C. Toprakcioglu, J. C. Dore, B. H. Robinson, A. M. Howe and P. Chieux, J. Chem. Soc., Faraday 18 M. Kotlarchyk, S. H. Chen, J. S. Huang and M. W. Kim, Phys. Rev. A, 1984, 29, 2054. 19 E. Keh and B. Valeur, J. Colloid Interface Sci., 1981, 79, 465. 20 N. J. Bridge and P. D. I. Fletcher, J. Chem. SOC., Faraday Trans. I , 1983, 79, 2161. 21 R. Aveyard, B. P. Binks and J. Mead, J. Chem. SOC., Faraday Trans. I , in press. 22 R. Aveyard, B. P. Binks, S. Clark and J. Mead, J. Chem. SOC., Faraday Trans. I , 1986,82, 125. 23 H. Kunieda and K. Shinoda, J. Colloid Interface Sci., 1980, 75, 601. 24 R. Aveyard, B. P. Binks and J. Mead (University of Hull), unpublished results. 25 A. I. Vogel, Quantitative Inorganic Analysis (Longmans, London, 1961). 26 P. Ekwall, L. Mandell and K. Fontell, J. Colloid Interface Sci., 1970, 33, 21 5. (Plenum, New York, 1984), vol. 3, p. 1663. 80, 13. Trans. 1, 1984, 80, 413. Paper 511714; Received 3rd October, 1985

ISSN:0300-9599    

DOI:10.1039/F19868202651

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

J . Chem. Soc., Faraday Trans. I, 1986,82, 2665-2672 Catalytic Decomposition of Isopropanol over Chromite Spinels MCr,O, (M = Ni, Mn and Mg) Krithivasa Balasubramanian Applied Science Division, Madras Institute of Technology, Anna University, Madras 600 044, India Vengaimuthu Krishnasamy Department of Chemical Engineering, A .C. College of Technology, Anna University, Madras 600 025, India The decomposition of isopropanol over nickel, manganese and magnesium chromite spinel catalysts has been investigated in the vapour phase in an integral reactor. Its decomposition follows first-order kinetics. Kinetic and thermodynamic parameters have been calculated using the Arrhenius and Eyring equations. The activity pattern is found to be NiCr,O, > MnCr,O, > MgCr,O,. The chromite spinels have been characterised by X-ray studies, i.r.spectral analysis, conductivity and thermoelectric potential measurements. All three chromites were found to be p-type semiconductors in the temperature range 150-400 "C. Exclusive dehydrogenation is shown by NiCr,O, and MnCr,O,, whereas MgCr,O, functions as a dehydro- genation and dehydration catalyst. A linear correlation exists between the entropy of activation and the activation energy for electrical conduction for the chromite spinels studied. Spinels are a group of inorganic compounds represented by a general formula AB,0,,1-3 where A and B are bivalent (Mg, Mn, Co, Ni, Cu and Zn) and trivalent (Al, Cr, Fe) metals, respectively. Spinels are thermally stable and they maintain enhanced and sustained activities for a variety of industrially important reactions such as decomposition of nitrous ~ x i d e , ~ hydrodesulphurisation of crude petrole~m,~ oxidation and dehydro- genation of hydrocarbons6? and oxidation and methanation of carbon This study involves the preparation, characterisation and comparison of the catalytic activity of nickel, manganese and magnesium chromite spinels.Experiment a1 Catalyst Preparation A mixture of a 10% solution of the metal nitrates was taken in the ratio of Cr: M = 2: 1 and the mixture was heated to 60-80 "C. To this hot mixture a 5% ammonia solution was added dropwise with constant and uniform stirring. The solution was maintained at pH 9 during the precipitation. The mixture was digested for another 2 h at this temperature to complete precipitation.The precipitate was filtered and dried at 105 "C for 24 h. Calcination of magnesium and nickel chromites was done at 700 "C in a muffle furnace for 8 h in a current of pure dry air and manganese chromite in hydrogen. The purity of isopropanol (AR, BDH) was tested by gas chromatography. 26652666 Catalytic Decomposition of Isopropanol Table 1. X-Ray d spacing data (A) on NiCr,O,, MnCr,O, and MgCr,O, ~ NiCr,O, MnCr,O, MgCr204 plane dlit.b dobs.a dcalc. dobs.a dlit. 111 4.78 w 4.79 (20) - - 4.80 m 4.813 (65) 220 2.90 m 2.93 (30) 3.145 m 2.98 2.94 w 2.95 (14) 31 1 2.49 vs 2.50 (100) 2.542 vs 2.54 2.51 vs 2.51 (100) 400 2.05 m 2.07 (35) 2.11 m 2.1 1 2.10 s 2.08 (55) 422 1.68 w 1.70 (15) 1.72 w 1.72 - - 511, 333 1.58 s 1.60 (60) 1.625 s 1.624 1.587 m 1.603 (40) 440 1.47 s 1.47 (80) 1.496 s 1.492 1.468 s 1.473 (55) a vs = Very strong; s = strong; m = medium; w = weak.Peak intensity in parentheses. Powder diffraction file lattice parameter: NiCr,O, = 8.331 A, MnCr,O, = 8.437 A, MgCr,O, = 8.329 A. Table 2. I.r., conductivity and Seeback potential data on NiCr,O,, MnCr,O, and MgCr,O, ~ metal chromites Cr-0 Cr-0 M-0 M-0 Ua and colour obtained reported obtained reported EJeV /pV OC-l NiCr,O, 575-585 510 630-640 630 1.066 380 MnCr,O, 490-5 10 490 610-630 620 1.054 92 MgCr204 525 525 600-620 650 0.652 6.8 (green) (grey ) (grey-green) a Positive Seeback potential indicates that all three chromite spinels are p-type semiconductors in the temperature range studied. Catalyst Characterization X-Ray Study The spinels were characterised by X-ray powder pattern studies1° using a Philips X-ray diffractometer (PW lOSO), and 'd' spacings and lattice parameter values are given in table 1, along with the reported data for comparison.ll I.R.Study The i.r. spectra of spinels were obtained in a double-beam spectrophotometer (Perkin- Elmer 983). The maxima of the absorption bands for Cr-0 (580-490 cm-l) and M-0 (650-620 cm-l) are given in table 2, along with the reported data for comparison.ll Conductivity and Thermoelectric Potential Measurements Electrical conductivity measurements12 were carried out using a two-probe conductivity cell in the temperature range 150-400 "C. The activation energies for electrical conduction (E,) were obtained from the slope of the plot of log 0 vs.T1/2 and the values are included in table 2. Thermoelectric (Seeback) potential, a meas~rements~~ for all three chromites were also carried out in this temperature range. The nature of charge carriers (holes orK. Balasubramanian and V . Krishnasamy 2667 electrons) was determined by checking the sign of the Seeback potential. For this purpose the following modification in the conductivity measuring apparatus was made. An auxiliary heating element was wound over a silica tube and kept at one end of the conductivity cell containing the catalyst pellet. After equilibrating the sample at each temperature for 15 min, the auxiliary heater was switched on and a temperature difference of ca. 10 K was maintained between the sample ends. After a steady state had been attained the Seeback potential was measured using a d.c.microvoltmeter. In this way, the Seeback potential has been measured at various temperatures. The cold end of the conductivity cell was positive, indicating p-type semiconduction (hole conduction) and the a values are given in table 2. Conductivity data of many spinels have been related to their magnetic properties, both of which in turn depend on the crystal structure.14~ l5 Goodenough,16 using a one-electron energy diagram, has found out that it is the octahedral (B site) cations which are responsible for electrical conduction by virtue of site symmetry in an AB,O, spinel. Neel17 has explained the magnetic behaviour of ferrite spinels on the basis of exchange interactions that occur between the transition-metal ions at A and B sites in the spinel structure.The three possible interactions are A-A, A-B and B-B. A-B interactions can occur through 125" A-0-B super-exchange type, while B-B interactions can be either 90" B-0-B super-exchange type or a direct B-B one. The A-A interaction is usually very weak owing to the large distance between the A-site cations. Thus the relative magnitude of interaction in spinels is in the following order: AB > BB > AA. All three exchange interactions are normally antiferromagnetic and the spin vector would tend to align antiparallel. 18* l9 In NiCr,O, and MnCr,O, all the three exchange interactions are present and the distance between the Cr3+-Cr3+ ions is shortened owing to the higher ionic radii of Ni2+ (0.69 A) and Mn2+ (0.80 A).The resulting antiferromagnetic order thus enhances the activation energy for electrical conduction (table 2). MgCr,O, has a much lower activation energy for electrical conduction owing to the very weak B-B interaction (Mg2+ non-magnetic, radius 0.66 A). Apparatus and Procedure The reactions were carried out in a fixed-bed flow-type integral reactor, 50 cm long with 1.5 cm internal diameter in the temperature range 290-380 "C and at different contact times, W/F (W is the weight of the catalyst and I; is the weight rate of the reactant per hour). Pyrex glass beads (4 mm diameter) were placed above the catalyst bed to a height of 5 cm. The reactor tube was inserted into a cylindrical furnace and heated electrically to the requisite temperature. Using a thermocouple the temperature was monitored along the length of the catalyst bed and the temperature required for a particular run was maintained constant.The liquid products, containing acetone and unreacted isopropanol, were identified and estimated by a CIC gas chromatograph (FFAP column, f.i.d. detector, column temperature 90 "C, injection port temperature 150 "C, detector temperature 90 "C, carrier gas argon, 1.75 kg cm-2, fuel H,, 1.2 kg cm-2, sample size lop3 cm3). The gaseous products consisted mainly of H, with all three catalysts, with a measurable amount of propene over MgCr,O,. Products were estimated using Orsat's gas analyser. At higher contact times, traces of carbon dioxide were noticed and measured. Results and Discussion A plot of logl,[lOO/(lOO-x)] us.contact time (fig. l), where x is the percentage isopropanol converted to acetone, results in straight lines passing through the origin, indicating that the decomposition of isopropanol follows first-order kinetics. The rate2668 Catalytic Decomposition of Isopropanol 0.15 0.0 5 0.5 0.1 5 0.2 contact time/h Fig. 1. First-order plot for the formation of acetone at 290 "C. @, NiCr204; A, MnCr,04; 0, MgCr204* Table 3. Rate constants for dehydrogenation rate constant/h-l catalyst T/"C first-order plot initial rate Guggenheim NiCr,04 290 340 380 MnCr,O, 290 340 380 MgCr204 290 340 380 1.49 2.4 1 4.14 0.69 1.26 2.07 0.46 1.12 2.16 1.33 2.87 4.23 0.77 1.50 2.54 0.46 1.11 1.92 1.11 2.70 4.1 0.63 1.14 1.97 0.37 1.25 2.71 constants calculated from the slopes of these plots are presented in table 3, along with the values obtained by the method of initial rate.The first-order rate constants obtained by Guggenheim's20 finite contxt time method are also included in table 3 for comparison. The formation of acetone as a function of contact time over NiCr,O,, MnCr,O, and MgCr,O, at 340 "C is plotted in fig. 2. The rate of formation of acetone decreases with increasing contact time. Increase of contact time may facilitate the adsorbed acetone to react with lattice oxygen to form CO,. This is evident from the liberation of CO, (table 4). Oxidation of acetone to CO, was confirmed by adding acetone and identifying the liberated CO,. The decrease of acetone may also be due to the occurrence of the reverse reaction, as reported by Daniel and Kuriakose.Over magnesium chromites, dehydration also occurs and the extent of dehydrogenation and dehydration are shown in fig. 3. The effect of temperature on the formation of acetone for the above three catalysts is illustrated in fig. 4. The activation energy (E,) obtained from the Arrhenius plots and thermodynamic parameters Am, AS$ and AG$ evaluated for the activated state2, of the system are given in table 5.K. Balasubramanian and V. Krishnasamy 2669 LO 30 4 2 2 20 ---. E a, Y 20 0.1 0.2 0.3 0.4 contact time/h Fig. 2. Effect of contact time on the formation of acetone at 340 "C. 0 , NiCr20,; A, MnCr,O,; 0, MgCr20,. Table 4. CO, (mol% ) liberated during the decomposition of isopropranol over chromite spinels CO, liberated/mol NiCr,O, MnCr,O, MgCr204 T/"C 0.2a 0.3 0.4 0.2 0.3 0.4 0.2 0.3 0.4 290 0.56 1.1 2.1 0.21 0.64 0.9 0.16 0.4 0.7 340 0.69 1.6 2.7 0.32 0.85 1.4 0.28 0.65 0.9 380 0.9 2.25 3.2 0.42 1.2 1.8 0.4 1 .o 1.3 a Contact time/h.The order of activity, based on the values of activation energy for dehydrogenation, is: NiCr,O, > MnCr,O, > MgCr,O,. The negative ASS values indicate the formation of an ordered activated complex by absorption of isopropanol on the spinel, with resultant loss in the internal degrees of freedom. The higher entropy of activation (- 210 J mol-1 K-l) and lower energy of activation (38.37 kJ mol-l) for dehydration of isopropanol over MgCr,O, compared to the respective values of dehydrogenation shows that activated complex for the former process is relatively stable and easily attainable.This is clear evidence for the prevalence of a different active site over MgCr,O, for isopropanol decomposition. In situ electrical conductivity measurements in ambient atmospheres have been carried out on the three catalysts. The initial conductivities at 340 "C for NiCr,O,, MnCr,O,2670 90 80 70 * E .+ 50 4 0 30 20 z 60 . c 0 Catalytic Decomposition of Isopropanol 0 01 0 -2 0.3 0.4 contact time/h Fig. 3. Effect of contact time on the product distribution over MgCr,04 at 340 "C. A, Unchanged u 20 10 0 isopropanol ; 0, acetone ; 0 , propylene. 1 1 I 290 34 0 38 0 TIo C Fig. 4. Effect of temperature on the formation of acetone. 0, NiCr,O,; A, MnCr,O,; 0, MgCr204.K . Balasubramanian and V. Krishnasamy 267 1 % d --. 0.8 0.7 0.6 Table 5.Activation and thermodynamic parameters at 563 K - - 0 I I Ea A S AGI A S catalyst /kJ mol-1 /kJ mol-l /kJ mol-1 /J mol-l K-I dehydrogenation NiCr,O, 34.46 29.78 130.56 - 175.16 MnCr,O, 37.44 32.76 141.95 - 193.95 MgCr20'4 5 1.06 46.38 149.83 - 183.75 dehydration MgCr!204 38.37 33.69 158.22 -210.2 Fig. 5. Relationship between entropy of activation and activation energy for electrical conduction. 0, CoCr,O,; H, CuCr,O,; 0, ZnCr,O,; A, MnCr,O,; 0, NiCr,O,; 0, MgCr,O,. and MgCr,O, were 6.13 x 2.49 x lop4 and 1.36 x lop3 R-l cm-l, respectively. When isopropanol vapour was introduced the conductivity decreased slowly and attained a constant value of 4.41 x and 0.79 x lW3 R-l crn-l, respec- tively, after 10 min. The decrease in conductivity is attributed to the transfer of electrons from the oxygen of isopropanol to the catalyst during the process of adsorption. This lends further support to the p-type nature of the chromite spinels.The constant value of conductivity may be due to the attainment of adsorption-desorption equilibrium. An exactly similar trend is observed in presence of acetone vapour, except that the conductivity decrease is drastic, while there is no change in conductivity in the atmosphere of hydrogen. The existence of a linear correlation between activation energy for electrical conduction (E,) and entropy of activation (AS$) for Mn, Co, Ni, Cu and Zn chromites is shown 1.83 x2672 Catalytic Decomposition of Isopropanol in fig. 5 (the values for Co, Cu and Zn are taken from our earlier which indicates the exclusive dehydrogenating nature of these spinels, while the dual-function MgCr,O, catalyst does not fit into the linear plot (fig.5). The authors thank the Director of A. C . College of Technology, Dr B. Jaganadhasamy, and the Director of M.I.T., Dr S. Sathikh, for the facilities provided by them to carry out this investigation. References 1 E. W. Corter, Philips Res. Rep., 1954, 9, 295. 2 G. Blasse, Philips Res. Rep., Suppl., 1964, 3, 1. 3 A. B. Van Groeou, P. F. Bongers and A. L. Stuyts, Mater. Sci. Eng., 1968, 3, 317. 4 Reinercker, Gunther, Chem. Tech. (Berlin), 1959, 11, 246. 5 G. K. Boreskov, V. V. Proporskii and V. A. Sezonov, Proc. 4th Int. Congr. Catal., Moscow, 1968. 6 Gillot, Bernard, Bull. SOC. Chim., 1968, 6, 2382. 7 Petro Tex Chemical Corp., Neth. (Pat), Chem. Abs., 1966, 64, 15739d. 8 F. G. Dwyer, Catal. Rev., 1972, 6, 261. 9 P. Schoubye, J. Catal., 1969, 14, 238. 10 R. J. Rennard and W. L. Kehl, J. Catal., 1971, 21, 282. 11 T. M. Yur'eva, G. K. Boreskov, V. I. Zharkov, L. G. Karakchiev, V. V. Poporskii and V. A. Chigrina, 12 V. Krishnasamy, Indian J. Chem., 1979, 17A, 437. 13 R. M. Rose, L. A. Shepard and J. Wulf, The Structure and Properties of Materials (Wiley Eastern Ltd, 14 J. Smit and H. P. J. Wijn, Ferrites (Wiley, New York, 1959), 157. 15 E. J. W. Verwey, P. W. Heayman and F. C. Romejin, J. Chem. Phys., 1947,15, 181. 16 J. B. Goodenough, Magnetism and the Chemical Bond (Interscience, New York, 1963). 17 L. Neel, Ann. Phys., 1948, 3, 137. 18 P. W. Anderson, Phys. Rev., 1959, 115, 2. 19 P. I. Slick, Ferromagnetic Materials, ed. E. P. Wohlfarth (North Holland, Amsterdam, 1980), vol. 2, 20 E. A. Guggenheim, Philos. Mag., 1926, 2, 538. 21 C. Daniel and J. C. Kuriakose, Indian J. Chem., 1969, 6, 648. 22 K. J. Laidler, Chemical Kinetics (Tata McGraw-Hill, Bombay, 1965), p. 89. 23 K. Balasubramanian and V. Krishnasamy, Indian J. Chem., 1982, 21A, 813. Kinet. Catal., 1968, 9, 1063. New Delhi, 1971), vol. IV, p. 169. chap. 3. Paper 511788; Received 15th October, 1985

ISSN:0300-9599    

DOI:10.1039/F19868202665

出版商:RSC    

年代:1986

数据来源: RSC