摘要:

Gas Kinetics Group and Division de Chimie-Physique de la Societe Francaise de Chimie 9th International Symposium on Gas Kinetics To be held in Bordeaux, France on 20-25 July 1986 Further information from Dr R. Lasclaux, Lab. Photophys. Photochim. MolBculaire, Universite de Bordeaux I, 33405 Talence Cedex, France Poiymer Physics Group Biologically Engineered Polymers To be held at Churchill College, Cambridge on 21-23 July 1986 Further information from Dr M. J. Miles, AFRC,Food Research Institute, Colney Lane, Norwich NR4 7UA Polymer Physics Group with the British Rheological Society Deformation in Solid Polymers To be held at the University of Leeds on 9-1 1 September 1986 Further information from Dr J. V. Champion, Department of Physics, City of London Polytechnic, 31 Jewry Street, London EC3N 2EY ~~_____________ ~~~~ Carbon Group Carbon Fibres- P ro pe rt i es and A p p I i cat i o ns To be held at the University of Salford on 1 5 1 7 September 1986 Further information from The Meetings Officer, The Institute of Physics, 47 Belgrave Square, London SW1 X 8QX ~ ~~~~~~~~ ~ Division with the Surface Reactivity and Catalysis Group-Autumn Meeting Promotion in Heterogeneous Catalysis To be held at the University of Bath on 23-25 September 1986 Further information from: Professor F.S. Stone, School of Chemistry, University of Bath, Bath BA2 7AY (viii)Gas Kinetics Group and Division de Chimie-Physique de la Societe Francaise de Chimie 9th International Symposium on Gas Kinetics To be held in Bordeaux, France on 20-25 July 1986 Further information from Dr R.Lasclaux, Lab. Photophys. Photochim. MolBculaire, Universite de Bordeaux I, 33405 Talence Cedex, France Poiymer Physics Group Biologically Engineered Polymers To be held at Churchill College, Cambridge on 21-23 July 1986 Further information from Dr M. J. Miles, AFRC,Food Research Institute, Colney Lane, Norwich NR4 7UA Polymer Physics Group with the British Rheological Society Deformation in Solid Polymers To be held at the University of Leeds on 9-1 1 September 1986 Further information from Dr J. V. Champion, Department of Physics, City of London Polytechnic, 31 Jewry Street, London EC3N 2EY ~~_____________ ~~~~ Carbon Group Carbon Fibres- P ro pe rt i es and A p p I i cat i o ns To be held at the University of Salford on 1 5 1 7 September 1986 Further information from The Meetings Officer, The Institute of Physics, 47 Belgrave Square, London SW1 X 8QX ~ ~~~~~~~~ ~ Division with the Surface Reactivity and Catalysis Group-Autumn Meeting Promotion in Heterogeneous Catalysis To be held at the University of Bath on 23-25 September 1986 Further information from: Professor F. S. Stone, School of Chemistry, University of Bath, Bath BA2 7AY (viii)

ISSN:0300-9599    

DOI:10.1039/F198581FX017

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

xxxij AUTHOR INDEX Singh, Km. S., 751 Sircar, S., 1527, 1541 Slade, R. C. T., 847 Smith, I. G., 1095 Snelling, C. M., 1761 Sobczyk, L., 311 Siiderberg, D., 17 15 Solar, S., 1101 Solar, W., 1101 Soma, M., 485 Somorjai, G. A., 1263 Somsen, G., 1015 Sorek, Y., 233 Souto, F. A., 2647 Spencer, S., 2357 Spichiger-Ulmann, M., 7 13 Spoto, G., 1283 Spotswood, T. M., 1623 Srivastava, R. D., 913 Stachurski, J., 1447, 2813 Staricco, E. H., 1303 Stock, T., 2257 Stockhausen, M., 397 Stokes, R. H., 1459 Stone, F. S., 1255 Strachan, A. N, 1761 Strohbusch, F., 2021 Stuckless, J. T., 597 Su, Z., 2293 Subrahmanyam, V. S., 1655 Sugimoto, N., 1441, 2959 Suminaka, M., 2287 Suprynowicz, Z., 553 Sutcliffe, L. H., 679, 1467, 1215 Suzanne, J., 2339 Suzuki, H., 3117 Swallow, A. J., 1225 Symons, M.C. R., 433, 565, 727, 2131, 2775, 1095, 1963, 242 1 Takagi, Y., 1901 Takahashi, Y., 3 117 Takeshita, H., 2805 Tamilarasan, R., 2763 Tamura, K., 2287 Tanaka, T., 1513 Taniewska-Osinska, S., 695, Tascon, J. M. D., 939, 2399 Taylor, M. J., 1863 Taylor, N., 2357 Tejuca, L. G., 939, 2399, 1203 Teller, R. G., 1693 Tempere, J-F., 1357 Teramoto, M., 2941 Theocharis, C . R., 857 Thomas, J. K., 735 Tielen, M., 2889, 3049 Tindwa, R. M., 545 Tissier, C., 3081 Toi, K., 2835 Tokuda, T., 2835 Torrez-Mujica, T., 343 Townsend, R. P., 1071, 173 1, Trasatti, S., 2995 Treiner, C., 2513 Trenwith, A. B., 745 Trifiro, F., 1003 Troncoso, G., 1631, 1637 Tseung, A. C. C., 1883 Tuck, J. J., 833 Turner, J. E., 1263 Uemoto, M., 2333 Uma, K., 2733 Valencia, E., 1631. 1637 Valigi, M., 813 Vallmark, T., 1389 Van Oort, M.J. M., 3059 Varma, M. K., 751 Vattis, D., 2043 Vecli, A., 433 Veseli, V., 2095 Vink, H., 1677, 1725 Vliers. D. P., 2009 Vukovid, Z., 1275 3081, 1913 3127 Waghorne, W. E., 2703 Ward, A. J., 2975 Watanabe, H., 1569 Waugh, K. C., 3073 Weckstrorn, K., 2947 Weinberg, N. N., 875 Weingartner, H., 1031 Wells, C. F.. 801, 1057, 1401, White, M. A., 3059 Williams, J. O., 271 1 Williams, P. A., 2635 Williams, P. B., 3067 Williams, R. T., 847 Wojcik, D., 1037 Wood, G. L., 265 Wood, R. M., 273 Woolf, L. A., 769, 2821 Wright, C. J., 2067 Wright, J. P., 1471 Wright, T. H., 1819 Wurie, A. T., 2605 Yadav, G. D., 161 Yadava, R. D., 751 Yamaguchi, M., 1513 Yamaguti, K., 1237 Yamasaki, S., 267 Yamashita, H., 2485 Yamatera, H., 127 Yelon, W., 1693 Yoshida, S., 1513, 2485 Yoshikawa, M., 2485 Zambonin, P.G.. 621 zdanov, S. P., 2541 Zecchina, A., 1283 Zelano, V., 2365 Zhan, R. Y., 2083 Zhao, Z., 185 Zhulin, V. M., 875 Zilnyk, A., 679, 1215 Zulauf, M., 2947 Zundel, G., 1425, 2375 1985. 2145, 2475, 3091xxxij AUTHOR INDEX Singh, Km. S., 751 Sircar, S., 1527, 1541 Slade, R. C. T., 847 Smith, I. G., 1095 Snelling, C. M., 1761 Sobczyk, L., 311 Siiderberg, D., 17 15 Solar, S., 1101 Solar, W., 1101 Soma, M., 485 Somorjai, G. A., 1263 Somsen, G., 1015 Sorek, Y., 233 Souto, F. A., 2647 Spencer, S., 2357 Spichiger-Ulmann, M., 7 13 Spoto, G., 1283 Spotswood, T. M., 1623 Srivastava, R. D., 913 Stachurski, J., 1447, 2813 Staricco, E. H., 1303 Stock, T., 2257 Stockhausen, M., 397 Stokes, R. H., 1459 Stone, F. S., 1255 Strachan, A.N, 1761 Strohbusch, F., 2021 Stuckless, J. T., 597 Su, Z., 2293 Subrahmanyam, V. S., 1655 Sugimoto, N., 1441, 2959 Suminaka, M., 2287 Suprynowicz, Z., 553 Sutcliffe, L. H., 679, 1467, 1215 Suzanne, J., 2339 Suzuki, H., 3117 Swallow, A. J., 1225 Symons, M. C. R., 433, 565, 727, 2131, 2775, 1095, 1963, 242 1 Takagi, Y., 1901 Takahashi, Y., 3 117 Takeshita, H., 2805 Tamilarasan, R., 2763 Tamura, K., 2287 Tanaka, T., 1513 Taniewska-Osinska, S., 695, Tascon, J. M. D., 939, 2399 Taylor, M. J., 1863 Taylor, N., 2357 Tejuca, L. G., 939, 2399, 1203 Teller, R. G., 1693 Tempere, J-F., 1357 Teramoto, M., 2941 Theocharis, C . R., 857 Thomas, J. K., 735 Tielen, M., 2889, 3049 Tindwa, R. M., 545 Tissier, C., 3081 Toi, K., 2835 Tokuda, T., 2835 Torrez-Mujica, T., 343 Townsend, R.P., 1071, 173 1, Trasatti, S., 2995 Treiner, C., 2513 Trenwith, A. B., 745 Trifiro, F., 1003 Troncoso, G., 1631, 1637 Tseung, A. C. C., 1883 Tuck, J. J., 833 Turner, J. E., 1263 Uemoto, M., 2333 Uma, K., 2733 Valencia, E., 1631. 1637 Valigi, M., 813 Vallmark, T., 1389 Van Oort, M. J. M., 3059 Varma, M. K., 751 Vattis, D., 2043 Vecli, A., 433 Veseli, V., 2095 Vink, H., 1677, 1725 Vliers. D. P., 2009 Vukovid, Z., 1275 3081, 1913 3127 Waghorne, W. E., 2703 Ward, A. J., 2975 Watanabe, H., 1569 Waugh, K. C., 3073 Weckstrorn, K., 2947 Weinberg, N. N., 875 Weingartner, H., 1031 Wells, C. F.. 801, 1057, 1401, White, M. A., 3059 Williams, J. O., 271 1 Williams, P. A., 2635 Williams, P. B., 3067 Williams, R. T., 847 Wojcik, D., 1037 Wood, G. L., 265 Wood, R. M., 273 Woolf, L. A., 769, 2821 Wright, C. J., 2067 Wright, J. P., 1471 Wright, T. H., 1819 Wurie, A. T., 2605 Yadav, G. D., 161 Yadava, R. D., 751 Yamaguchi, M., 1513 Yamaguti, K., 1237 Yamasaki, S., 267 Yamashita, H., 2485 Yamatera, H., 127 Yelon, W., 1693 Yoshida, S., 1513, 2485 Yoshikawa, M., 2485 Zambonin, P. G.. 621 zdanov, S. P., 2541 Zecchina, A., 1283 Zelano, V., 2365 Zhan, R. Y., 2083 Zhao, Z., 185 Zhulin, V. M., 875 Zilnyk, A., 679, 1215 Zulauf, M., 2947 Zundel, G., 1425, 2375 1985. 2145, 2475, 3091

ISSN:0300-9599    

DOI:10.1039/F198581BX019

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

JOURNAL OF T H E CHEMICAL SOCIETY ~~ FARADAY TRANSACTIONS, PARTS I AND 1 1 The Journal of the ChemicalSociety is published in six sections, of which five are termed Transactions; these are distinguished by their subject matter, as follows: Dalton Transactions (Inorganic Chemistry). All aspects of the chemistry of inorganic and organometallic compounds; including bioinorganic chemistry and solid-state inorganic chemistry ; of their structures, properties, and reactions, including kinetics and mechanisms; new or improved experimental techniques and syntheses. Faraday Transactions I (Physical Chemistry ), Radiation chemistry, gas-p hase kinetics, electrochemistry (other than preparative), surface and interfacial chemistry, heterogeneous catalysis, physical properties of polymers and their solutions, and kinetics of polymerization, etc.Faraday Transactions II (Chemical Physics). Theoretical chemistry, especially valence and quantum theory, statistical mechanics, intermolecular forces, relaxation phenomena, spectroscopic studies (including i.r., e x . , n.m.r., and kinetic spec- troscopy, etc.) leading to assignments of quantum states, and fundamental theory. Studies of impurities in solid systems. Perkin Transactions I (Organic Chemistry). All aspects of synthetic and natural product organic, organometallic and bio-organic chemistry, including aliphatic, alicyclic, and aromatic systems (carbocyclic and heterocyclic). Perkin Transactions II (Physical Organic Chemistry). Kinetic and mechanistic studies of organic, organometallic and bio-organic reactions.The description and application of physicochemical, spectroscopic, and theoretical procedures to organic chemistry, including structure-activity relationships. Physical aspects of bio-organic chemistry and of organic compounds, including polymers and biopolymers. Authors are requested to indicate, at the time they submit a typescript, the journal for which it is intended. Should this seem unsuitable, the Editor will inform the author. The sixth section of the Journalof the Chemical Society is Chemical Communications, which is intended as a forum for preliminary accounts of original and significant work, in any area of chemistry that is likely to prove of wide general appeal or exceptional specialist interest. Such preliminary reports should be followed up eventually by full papers in other journals (e.g.the five Transactions) providing detailed accounts of the work. NOTES I t has always been the policy of the Faraday Transactions that brevity should not be a factor influencing acceptability for publication. In addition however to full papers both sections carry at the end of each issue a section headed ‘Notes’, which are short self-contained accounts of experimental observations, results, or theory that will not require enlargement into ‘full’ papers. The Notes section is not used for preliminary communications. The layout of a Note is the same as that of a paper. Short summaries are required. The procedure for submission, administration, refereeing, editing and publication of Notes is the same as for full papers.However, Notes are published more quickly than papers since their brevity facilitates processing at all stages. The Editors endeavour to meet authors’ wishes as to whether an article is a full paper Or a Note, but since there is no sharp dividing line between the one and the other, either in terms of length or character of content, the right is retained to transfer overlong Notes to the full papers section. As a guide a Note should not exceed 1500 words or word-equivalents. (9NOMENCLATURE 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’ (1975) (copies of this pamphlet and further details can be obtained from the Manager, Journals, The Royal Society of Chemistry, Burlington House, London W I V OBN).These recommendations are applied by The Royal Society of Chemistry in all its publications. Their basis is the ‘ Systeme International d’Unitks’ (SI). A more detailed treatment of units and symbols with specific application to chemistry is given in the IUPAC Manual of Symbols and Terminology for Physicochemical Quantities and Units (Pergamon, Oxford, 1979). Nomenclature. For many years the Society has actively encouraged the use of standard IUPAC nomenclature and symbolism in its publications as an aid to the accurate and unambiguous communication of chemical information between authors and readers. In order to encourage authors to use IUPAC nomenclature rules when drafting papers, attention is drawn to the following publications in which both the rules themselves and guidance on their use are given: Nomenclature of Organic Chemistry, Sections A , B, C, D, E, F, and H (Pergamon, Oxford, 1979 edn).Nomenclature of Inorganic Chemistry (Butterworths, London, 197 1, now published 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.(ii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 80 McMaster University, Hamilton, Ontario, Canada, 23-25 July 1985 Organising Committee : Professor J. A. Morrison (Chairman) Professor W. A. Steele Professor F. S. Stone Dr R. K. Thomas ~ :~2s:orY.i”soles Physical Interactions and Energy Exchange at the Gas-Solid Interface i The programme and application form may be obtained from: Professor J. A. Morrison, Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L8S 4M1 or: Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN, U.K. The discussion will be concerned with certain aspects of current research on the gas-solid interface: elastic, inelastic and dissipative scattering of atoms and molecules from crystal surfaces, and the structure and dynamics of physisorbed species, including overlayers.Emphasis will be placed on the themes of physical interactions and energy exchange rather than on molecular-beam technology or the phenomenology of phase transitions on overlayers. The interplay between theory and experiment will be stressed as they relate t o the nature of atom and molecule surface interaction potentials, including many- body effects. THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM NO. 20 Phase Transitions in Adsorbed Layers University of Oxford, 17-1 8 December 1985 Organising Committee : Professor J. S. Rowlinson (Chairman) Dr E. Dickinson Dr R. Evans Mrs Y. A. Fish Dr N. Parsonage Dr D.A. Young The aim of the meeting is to discuss phase transitions at gas/liquid, liquidliquid and solid/fluid interfaces, and in other systems of constrained geometry or dimensionality less than three. Emphasis will be placed on molecularly simple systems, whereby liquid crystal interfaces and chemisorption phenomena are excluded. The preliminary programme may be obtained from : Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN (iii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 81 Lipid Vesicles and Membranes Loughborough University of Technology, 15-1 7 April 1986 Organising Committee: Professor D. A. Haydon (Chairman) Professor D. Chapman Mrs Y. A. Fish Dr M. J. Jaycock Dr I . G.Lyle Professor R. H. Ottewill Dr A. L. Smith Dr D. A. Young The aim of the meeting is to discuss the physical chemistry of lipid membranes and their interactions, in particular theoretical and spectroscopic studies, polymerised membranes, thermodynamics of bilayers and liposomes, mechanical properties, encapsulation and interaction forces between bilayers leading to fusion but excluding preparation and characterisation methodology. Further information may be obtained from: Professor D. A. Haydon, Physiological Laboratory, Downing Street, Cambridge CB2 3EG Full papers for publication in the Discussion Volume will be required by December 1985. THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION NO. 82 Dynamics of Molecular Photof ragmentation University of Bristol, 15-1 7 September 1986 Organising Committee: Professor R.N. Dixon (Chairman) Dr G. G. Balint-Kurti Dr M. S. Child Professor R. Donovan Professor J. P. Simons The discussion will focus on the interaction of radiation with small molecules, molecular ions and complexes leading directly or indirectly to their dissociation. Emphasis will be given to contributions which trace the detailed dynamics of the photodissociation process. The aim will be to bring together theory and experiment and thereby stimulate important future work. 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 1985, to: Professor R. N. Dixon, Department of Theoretical Chemistry, University of Bristol, Cantock's Close, Bristol BS8 I T S30TH INTERNATIONAL CONGRESS OF PURE A N D APPLIED CHEMISTRY Advances in Physical and Theoretical Chemistry Manchester, S 1 3 September 1985 The Faraday Division is mounting the following symposia as part of the 30th IUPAC Congress: A.B. C. D. Reaction Dynamics in the Gas Phase and in Solution This symposium will examine the ways in which modern techniques allow detailed study of the dynamical motion of molecules which are undergoing chemical reaction or energy exchange. Micellar Systems The symposium will discuss various aspects of micellization, including size and shape factors, micellization in biological systems, chemical reactions in micellar systems, micelle structure and solubilization. Emphasis will also be given to modern techniques of examining micellar systems, including small-angle neutron scattering, neutron spin echo, photocorrelation spectroscopy, N M R and use of fluorescent probes.Surface Science of Solids The symposium will centre on recent advances in the study of kinetics and dynamics at surfaces and of phase transitions in adsorbate layers on single crystal surfaces. Both experimental and theoretical aspects will be reviewed with an emphasis on metal single crystal surfaces. New Electrochemical Sensors (in collaboration with the Electroanalytical Group of the Analytical Division) The symposium will cover such topics as the fundamentals of the subject, new gas sensors based on membrane electrodes and on ceramic oxides, the development of new ion- Iselective electrodes and the synthesis of new guest-host carriers, the development of CHEMFETS and other integrated devices together with the theory of the operation of such devices, and finally the development of biosensors including for instance enzyme electrodes, direct electron transfer to biological molecules and new potentiometric techniques for protein analysis. The full programme and application form may be obtained from: Dr J.F. Gibson, 30th IUPAC Congress, Royal Society of Chemistry, Burlington House, London W1 V OBN~ - FARADAY DIVISION INFORMAL AND GROUP MEETINGS Gas Kinetics Group with SERC Summer School in Gas Kinetics To be held at the University of Cambridge on 26 June to 3 July 1985 Further information from Dr I.W. M. Smith, Department of Chemistry, University Chemical Laboratory, Lensfield Road, Cambridge CB2 1 EP Industrial Physical Chemistry Group with the Food Chemistry Group Water Activity: A Credible Measure of Technological Performance and Phyaiological Viability To be held at Girton College, Cambridge on 1-3 July 1985 Further information from Professor F. Franks, Department of Botany, Downing Street, Cambridge CB2 3EA Polymer Physics Group Biennial Conference : Physical Aspects of Polymer Science To be held at the University of Reading on 11-1 3 September 1985 Further information from Professor Bassett, J. J. Thompson Physical Chemistry Laboratory, University of Reading, Whiteknights, Reading RG6 2AF Statistical Mechanics and Thermodynamics Group Multicomponent Mixtures To be held at the University of East Anglia on 16-1 8 September 1985 Further information from: Dr M.J. Grimson, Food Research Institute, Colney Lane, Norwich NR4 7UA Carbon Group Strength and Structure in Carbons and Graphites To be held at the University of Liverpool on 16-1 8 September 1985 Further information from The Meetings Officer, The Institute of Physics, 47 Belgrave Square, London SW1 X 8QX Surface Reactivity and Catalysis Group with the Catalysis Section of the KNCV Mechanism and Structure in Heterogeneous Catalysis To be held at Noordwijkerhout, The Netherlands on 18-20 September 1985 Further information from: Dr R. Joyner, BP Research Centre, Chertsey Road, Sunbury on Thames TW16 7LN Industrial Physical Chemistry Group A Molecular Approach to Lubrication and Wear To be held at Girton College, Cambridge on 23-25 September 1985 Further information from Mr M.P. Dare-Edwards, Shell Research Ltd, Thornton Research Centre, Chester CH1 3SH Neutron Scattering Group jointly with the Materials Testing Group of the Institute of Physics Industrial Uses of Particle Beams To be K9ld at the Institute of Physics, London on 26 September 1985 further information from Dr J. G. Booth, Department of Chemistry, University of Salford, Salford M5 4WT Division Annual Congress: Structure and Reactivity of Gas-Phase Ions To be held at the University of Warwick on 8-1 1 April 1986 Further information from Professor K. R. Jennings, Department of Molecular Sciences, University of Warwick, Coventry CV4 7ALJOURNAL 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 : Transfer Chemical Potentials for Complex Ions and for Anions: Water to Aqueous Acetone Issue 1) The Production and Photoelectron Spectrum of Propa-I ,2-dien-3-one Donald McNaughton and Roger John Suffoik (1 985, Issue 1 ) Binary lonogenic Equilibria between some Phenols and Bases Geoffrey E.Holdcroft and Peter H. Plesch (1 985, Issue 2) The Radical Cation of Trimethyl Phosphate: E.s.r. Evidence for Bonding to CFCI, Glen D. G. McConnachie and Martyn C. R. Symons (1985, Issue 2) Quantum-mechanical Studies of Catalysis. Part 1. A Model for Nucleophilic Attack on Carbonyl, catalysed by Non-functional Cationic Surfactants Amiram Goldblum and Jehoshua Katzhendler (1 985, Issue 3) Stereochemical Applications of Potential Energy Calculations.Part 4. Revised Cyclopropane Parameters for Molecular Mechanics Pekto M. lvanov (1985, Issue 3) Electron Spin Resonance Studies of the Ammonia-Boryl Radical (H,N -+ BH,.); an Inorganic Analogue of the Ethyl Radical Jehan A. Baban, Vernon P. J. Marti, and Brian P. Roberts (1985, Issue 3) Phase Equilibria Larbi Marhabi, Marie-Chantal Trinel-Dufour and Pierre Perrot (1 985, Issue 3) John Burgess and €22-Eldin A. Abu-Gharib (1 985, The Iron-Vanadium-Oxygen System at I 1 23, 1273, and 1373 K. Part 1. (vii)Arthur Adamson, Editor University of Southern California Arthur Hubbard, Associate Editor University of California at Santa Barbara This new journal published by the American Chemical Society fills the void existing in current literature available today-Langmurr’s broad coverage will bnng together authorltatlve papers from all aspects of this major field of chemistry' Langmulr will include fundamental and applied papers covering ultra-high vacuum surface chemistry and spectroscopy, heterogeneous catalysis, all aspects of interface chemistry involving fluids, and disperse systems Specifically, Langmurr will publish peer-reviewed research in ‘Wet’ Surface Chemistry surface tension spread monolayers wetting and contact angle adsorption from solution nucleation and fundamental aspects of flotation, detergency, emulsions, foams, lubrication, etc 4 ‘UHV’ Surface Chemistry solid surfaces in ultra-high vacuum including surface structure, composition and spectroscopy 0 fundamental papers in heterogeneous catalysis 4 Disperse Systems 4 Electrochemistry colloidal suspensions including aerosols polymeric colloids and membrane systems related to interfacial structure and microemulsions 0 biological and processes In bimonthly issues of Langmuw, you will find experimental and theoretical original papers, letters to the editor, and book reviews.as well as some selected symposium collections Papers having applied aspects will be included And, published by the American Chemical Society, Langrnulr will benefit from the Society’s vast international network of scientists and editorial resources Note to Authors: Langmuir will not have page charges.Editorial Advisory Board N R Armstrong Univ of Arizona G T Barnes Univ of Queensland AUSTRALlA 0 P Biloen Univ of Pittsburgh K S Birdi Technical University of Denmark DENMARK A M Bond Deakin University AUSTRALIA 8 V Derlaguin Academy of Science of USSR 0 D D Eley Univ of Noftmgham ENGLAND 0 G Ertl Unw of Munich GERMANY J Fendler Clarkson College of Technology 0 T Fort Jr California Polytechnic State Univ G Games Jr General Electric W A Goddard Ill California lnstitute of Technology R S Hansen lowa State Univ J Lyklema Agrcultural Univ THE NETHERLANDS R J Madix Stanford Univ J A Mann Jr Case Western Reserve Univ P Mukerjee Univ of Wisconsrn K J Mysels Research Consulting 0 A W Neumann Univ of Toronto CANADA R Ottewill Univ of Br~sfol ENGLAND G D Parfitt Carnegie Mellon Univ H Reiss Univ of Cakfornra at Los Angeles H A Resing Naval Research Laboratory T Rhodin Cornell Univ S Ross Rensselaer Polytechnic Univ 0 J Rouquerol Centre de Thermodynamique et de Microcalorimetrje du CNRS FRANCE R L Rowell Unw of Massachusetts R Rye Sandia National Lab H Sekr IBM K Shinoda Yokohama National Univ JAPAN G A Somorjai Univ of California at Berkley W A Steele Pennsylvania State Unrv Subscription Information 1985 Foreign Rates (Includes Air Service) ACSMembers $ 56 (Personal Use) Nonmembers $308 January-February 1985 Volume 1 No 1 One Volume Per Year ( S I X Issues) ISSN 0743-7463 Cable Address JIECHEM Telex 440159 ACSPUI or 892582 ACS PUBS American Chemical Society 1155 Sixteenth St., N.W. Washington, D.C. 20036 (viii)

ISSN:0300-9599    

DOI:10.1039/F198581FP041

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

J. Chem. SOC., Furaduy Trans. I, 1985, 81, 1113-1119 Heterogeneous Oxidation of Hydrazine by Barium Chromate BY ERWIN BAUMGARTNER, MIGUEL A. BLESA,* RICARDO LAROTONDA AND ALBERTO J. G. MAROTO Departamento Quimica de Reactores, Comision Nacional de Energia Atomica, Avenida del Libertador 8250, 1429, Buenos Aires, Argentina Received 26th March, 1984 The kinetics of the heterogeneous oxidation of hydrazine by barium chromate in aqueous suspensions has been studied. The results obtained on changing the concentration of hydrazine and the mass of barium chromate show that the reaction proceeds through a fast chemisorption equilibrium in which a complex is formed between chromium atoms on the surface of the particles and hydrazine. A Langmuir-type analysis of the data gave an adsorption equilibrium constant of 1.14 x 10, dm3 mol-l and a rate constant k for the decomposition of the adsorption complex of 1.1 x lo-, s-l.A comparison between this heterogeneous reaction and the corres- ponding homogeneous reaction shows that the presence of the interface leads to acceleration by a factor of ca. los. It is shown that this acceleration is due in part to the increased concentration of the complex at the interface ([adsorption complex]/[complex]hom = lo4) and to an increase in its reactivity (khet/khom = 10,). A possible explanation for this enhanced reactivity is given. The mechanism of the oxidation of hydrazine in homogeneous solutions has been the subject of numerous studies and has been reviewed by Audrieth and Oggl and by Bottomley.2 In the case of simple oxidants (e.g.FeIII ions and complexes), the emphasis was on the nature of the intermediate species formed in going from N2H4 to N, and NH3.3-6 In the case of oxidants which undergo a change in oxidation number of two or more, the oxidant species involved have also been studied. In the particular case of CrVT, the current view recognizes the following reactions K , HCrO, + N,H: + N,H,Cr03 + H,O (1) k slow N,H4CrV103---+ CrIV + N,H, + H,O as the first stage. The details of the fast reactions of CrIV and N,H, to give CrlI1 and N, have been reported and involve the reactions CrIV + N,H: -+ CrlI1 ref. ( 7 ) CrIV+CrV1 -+ 2CrV ref. (7)-( 10) 2CrrV --+ CrIII + CrV ref. (9)-( 1 1) N2H, + CrV -+ N, + C P ref. (7) and (8) 2N,H, -+ N, +N,H4 ref. (9)-( 1 1).11131114 OXIDATION OF N2H4 BY BaCrO, The analysis of Haight et aZ.ll suggests that the reactions 2N2H,- N, + N,H, 2CrIV- CrIL1 + CrV fast fast CrV +N2H4- N, + Cr*I* fast (3) (4) are the most likely. We are currently exploring the mechanism of heterogeneous oxidation of hydrazine and we present here the results of a study of the oxidation of hydrazine by an aqueous suspension of barium chromate; we shall report separately a study of the reaction of hydrazine with iron(rI1) oxides. As our main interest is the extent to which heterogeneity affects the reaction rate, our discussion is centred on a comparison of the oxidation of hydrazine by Crvl(aq) and by CrV1(solid). Heterogeneous oxidation has recently become a valuable tool in organic chemistry. Solid permanganate salts have been shown to exhibit remarkable selectivity for the oxidation of alcohols in aprotic solvents.129 l3 The mechanisms remain highly speculative but certainly involve binding of substrate molecules with reactive sites on the solid surface. This is also true for the oxidation of hydrazine by barium chromate in aqueous suspensions.EXPERIMENTAL The kinetics of the reaction was followed by measuring the pressure exerted by the nitrogen formed at constant volume as a function of time using the apparatus depicted schematically in fig. 1. Appropriate amounts of barium chromate were suspended in 85 cm3 of a sodium acetate+acetic acid buffer (pH 4.7). This suspension, contained in reaction flask A, was thermostatted at 30 "C by water circulating through a jacket and stirred magnetically for at least 1 h, as this was the minimum time required to saturate with acetic acid vapour the space above the liquid in flasks A and C and the connecting tube.In order to achieve the initial equilibrium, stopcock D was opened and closed quickly until no further increase in the pressure of the system was detected. To start the reaction, N2H, was poured from the thermostatted tube B into the reaction flask. As nitrogen was produced by the oxidation reaction, pressure was exerted on the manometric liquid in flask C (coloured water) and its magnitude was read on scale E. The volume, or more specifically the cross-section, of flask C was chosen in such a way that the error produced by the transfer of the liquid from flask C to the manometric tube F was minimized. Thus, the initial level in tube F was considered to be constant throughout the reaction.This constant-volume method proved to be superior to the classical gas-burette method, in which the gas volume is measured at constant pressure by adjusting the liquid level and changing the height of the burette. It was found that this procedure gave unreliable results in our case, especially at the beginning of the reaction when nitrogen production was fast, because of fluctuations in the liquid level when changing the height of the burette. Values of the measured pressures were plotted against time. In all cases an initial linear relationship was observed, typically up to 1&15% of the total extent of reaction, calculated from the stoichiometry given by7-11 4CrV1 + 3N,H, + 4Cr111 + 3N2 + 12H+.( 6 ) Beyond this point, the reaction slowed down considerably. In general, the final pressures observed after a reasonably long time corresponded to CQ. 70% of the total reaction. No special effort was put into measuring the actual stoichiometry as several sources of error render this measurement difficult (nitrogen solubility, very slow approach to total conversion, poisoning of the dissolving solid surface etc.).E. BAUMGARTNER, M. A. BLESA, R. LAROTONDA AND A. J. G. MAROTO 11 15 Fig. 1. Schematic diagram of the experimental apparatus. The reaction rates were calculated from the initial slopes Ap/At and expressed as An/At (where n is number of moles of nitrogen produced) by multiplying by the factor V/RT (where V is the volume of the gaseous space in the reaction apparatus, 0.62 dm3).Barium chromate was precipitated by mixing a BaCl, solution, slightly acidified with acetic acid, with a K,CrO, solution. For the present study, the fraction between 230 and 270 mesh (sieve opening between 6.2 x m) was used. Its specific surface area, obtained by nitrogen adsorption in a Micromeritics Accusorb B.E.T. apparatus, was 3.3 m2 g-l. and 5.3 x Mobilities were determined at 30 "C using a Carl Zeiss cytopherometer. Stock hydrazine solutions were prepared by dilution of a concentrated AnalaR (B.D.H.) hydrazine solution. Its concentration was frequently checked by titration with standard iodate. RESULTS AND DISCUSSION Under our experimental conditions, the concentrations of CrOi- and HCrO, were calculated from solubility and protolytic data1,* l5 and found to be 7 x lo-' and 1.08 x mol dmW3, respectively. Hydrazine is ca.100% in the form of N,H;.' Using the data obtained by Haight et aZ.,ll the rate for the homogeneous oxidation of hydrazine under conditions typical of the heterogeneous reaction was calculated to be 2.9 x 10-l' mol dm-3 s-l, whereas our experimental initial rate is 2.35 x mol dm-3 s-l. The large acceleration indicates that a heterogeneous process is taking place.? Measurements were performed at pH 4.7 because of experimental difficulties (a large BaCrO, solubility at lower pH values and low reaction rates at higher pH values, which are probably caused by the strong dependence of chemisorption on pH).18 Fig.2 shows the dependence of initial reaction rate on the total mass of BaCrO,. As expected, the rate increased linearly with increasing available surface area; thus, the fraction adsorbed hydrazine/total hydrazine is low. The adsorption of hydrazine onto barium chromate can be regarded in principle as being similar to the adsorption on binary or ternary oxides such as Fe203 or NiFe,O,. Adsorption of simple amines onto oxides has been shown to be dependent upon the amine protolytic equilibrium, the charge on the oxide surface and the t As pointed out by a referee, the reaction between N,H, and MnO, leads eventually to MnOOH, without further reaction,I6 whereas the homogeneous reduction of N,H, by Mn"' is fast." This indicates that in this case the effect of the surface is the reverse of what has been observed by us.1116 OXIDATION OF N2H4 BY BaCrO, 5 10 15 mass of BaCrO,/g Fig.2. Initial reaction rate, ui, as a function of the mass of BaCrO,. pH 4.7, temperature 30 "C, [N,H,] = 8.7 x mol dmP3. chemical affinity between the substrate and the ~ o l i d . ~ ~ ~ ~ ~ In the case of barium chromate, the charge on the surface is determined both by the concentration of CrOi- and Ba2+ ions (cf. e.g. Ag121,22) and by the concentration of H+ ions (cf. e.g. Fe304231 24). We measured the electrophoretic mobilities of BaCrO, in our suspensions and the results show that at pH 4.7 (acetic acid+acetate) and ionic strength I = mol dm-3, (zeta potential) is slightly negative, [ = - 20 mV, and approaches zero as the ionic strength increases. Thus, electrostatic interactions alone would not lead to appreciable adsorption of N,Ht, which must be regarded as essentially chemical in nature. The Gibbs energy for the chemisorption of complexing molecules or ions onto metal oxides is related to the corresponding Gibbs energy in homogeneous so1utions.18q25 In the present case, complexation in solution is known to take place with formation of CrV1-NH-NH, species;'' we therefore propose the following chemisorption equilibrium for the heterogeneous case : -Cr-OH + H:N-NH2 Cr-NH:-NH, + H,O (7) where -Cr-OH is the Cr-containing part of the surface, as a first, fast pre-equilibrium for the oxidation reaction [adsorption/desorption processes are fast, and they cannot control the rate; this must also be true for the analogous adduct formation, thus making kinetic control of forward reaction (I), as postulated by Gupta et al.,' unlikely].The occurrence of reaction (7) as an adsorption equilibrium is borne out by the dependence of the rate on hydrazine concentration, which shows behaviour typical of an adsorption isotherm of the Langmuir type : where ui is the initial rate of reaction, k is the rate constant corresponding to the decomposition of the adsorption complex and K , is the adsorption equilibrium constant [corresponding to reaction (7)]. When u i l is plotted against [N2H4];i (fig. 3) a straight line is obtained, thus demonstrating the applicability of eqn (8) to our results. From the slope and the intercept, the following values were obtained: k = 5.7 x mol dm-3 s-landK,, = 1.14 x 10, dm3 mol-l.TherelativelylowaffinityE. BAUMGARTNER, M. A. BLESA, R. LAROTONDA AND A. J . G. MAROTO 11 17 t 16 * I 4 j 12 E $ 8 1 4 a d I - 3 1 3 5 7 9 [ N2H4 1 -'/ 1 O2 dm3 mol-' Fig. 3. Reciprocal plot corresponding to eqn (8). pH 4.7, temperature 30 "C, mass of BaCrO, 8 g. of hydrazine for the BaCrO, surface, shown by this low KL value, and the lack of saturation even at 2 x lo-, mol dm-3 N2H4 are in good agreement with the value reported for the equivalent homogeneous equilibrium (Kl = 3.2 dm3 mol-l) between Cr0,H- and N,H:.ll Note that a dissociative adsorption, i.e. N,H,(aq) f 2NH2(ads) (9) at very low coverages also agrees with our data, as can be seen in fig. 4, where the initial rates have been plotted against [N2H,fi. However, it seems unlikely that the acceleratory effect is due to dissociative adsorption.It has been shown that the mechanism of the anodical oxidation of hydrazine does not involve the breakage of N-N bonds; even when ammonia is formed, it is not from NH, radicals but from the decomposition of N4H4.26-28 The acceleration found for the heterogeneous reaction compared with the hom- ogeneous one can be traced back to the increased concentration of the adduct and/or its increased reactivity. The concentration of the adsorption complex can be calculated from [-Cr-NH:-NH,] = KL( 1 - 0) N , Am[N2H4]/ VN (10) where 0 is the fraction of occupied sites, N , is the number of reactive sites, A is the specific surface area, m is the mass of BaCrO,, Vis the volume of the suspension and N is Avogadro's number.At a hydrazine concentration of 1 x mol dmP3 and a coverage 8 of 0.52, a value of 2.7 x mol dm-3 is obtained for [-Cr-NH$-NH,]. In the calculation a value of 1 x 1015 sites cmP2 has been used for N,, as estimated from crystallographic data29 using the assumption that all four chromium atoms in a unit cell lie on the same plane. This is probably an overestimation, and so the concentration of the adsorption complex, as calculated in this way, should be considered as an upper limit. For m and V, the experimental values of 8 g and 0.085 dm3 have been used. For the parallel homogeneous reaction under similar conditions, [N,H,CrO,] = K[HCrO;] [N2H:] = 3.5 x mol dm-3 is obtained. This indicates that there is an increase in the concentration of the reactive species in the heterogeneous reaction as compared with the homogeneous reaction by a factor1118 OXIDATION OF N2H4 BY BaCrO, 0.0 5 0.1 015 [N2H41~/(mol dm-3$ Fig. 4.Dependence of the initial reaction rate, vi, on [N,H,]:. pH 4.7, temperature 30 "C, mass of BaCrO, 8 g. of 7.7 x lo3. The difference between this value and the actual acceleration factor, ca. los, has to be ascribed to differences in the k values [reaction (2)J. Haight et aZ.ll reported khom = 1.1 x lo-, s-l at pH 4.7, whilst our data indicate that khet = 5.7 x s-l by taking into consideration N,, A , rn and V. Thus, the heterogeneous adduct is at least one hundred times more reactive than the homogeneous complex. Note that our calculations yield the upper limit for the intermediate concentration, so that the decomposition rate enhancement factor of lo2 is in fact a lower limit.It is tempting to conclude that neighbouring CrV1 centres play an active role in the decomposition of the adduct, in a manner similar to that proposed by Beck and Durham9 for the reaction in homogeneous solution : dm3 mol-l s-l, which can be converted into khet = 1.1 x N2H5CrO: + HCrOy f Cr03N2H,Cr03 + H20. (1 1) This diester decomposes slowly Cr03N2H,Cr03 -+ 2CrIV + N, slow thus providing another pathway which might increase the overall reaction rate. We thank Lic. J. Lesk for collaborating during the early stages of this research and J. Helzel Garcia for useful suggestions concerning the experimental procedure. L. F. Audrieth and B. A. Ogg, The Chemistry of Hydrazine (Wiley, New York, 1951).F. Bottomley, Q. Rev., 1970, 24, 617. J. W. Cahn and R. E. Powell, J. Am. Chem. SOC., 1954,76,2568. W. C. E. Higginson and P. Wright, J. Chem. SOC., 1955, 1551. D. R. Rosseinsky, J. Chem. SOC., 1957,4685. H. Minato, E. J. Meehan, I. M. Kolthoff and C. Auerbach, J. Am. Chem. SOC., 1959,81, 6168. K. K. Sen Gupta, S. S. Gupta and H. R. Chatterjee, J. Znorg. Nucl. Chem., 1976, 38, 549. V. M. S. Ramanujam, S. Sundaram and N. Venkatasubramanian, Znorg. Chim. Ada, 1975, 13, 133.E. BAUMGARTNER, M. A. BLESA, R. LAROTONDA AND A. J. G. MAROTO 11 19 M. T. Beck and D. A. Durham, J . Inorg. Nucl. Chem., 1970,32, 1971. lo G. P. Haight Jr, T. J. Huang and B. Z. Shakhashiri, J. Znorg. Nucl. Chem., 1971, 33, 2169. * l G. P. Haight Jr, T. J.Huang and H. Platt, J . Am. Chem. Soc., 1974, 96, 3137. l2 N. A. Noureldin and D. G. Lee, Tetrahedron Lett., 1981, 4889. l 3 D. G. Lee and N. A. Noureldin, J. Am. Chem. Soc., 1983, 105, 3188. l4 A. Seidell and W. F. Linke, Solubilities of Inorganic and Metal Organic Compounh (American l5 A. E. Martell and R. M. Smith, Critical Stability Constants (Plenum Press, New York, 1977). l6 W. C. Maskell, J. E. A. Shaw and F. L. Tye, Electrochim. Acta, 1981, 26, 1403. l7 G. Davies and K. Kustin, J . Phys. Chem., 1969, 73, 2248. l8 M. A. Blesa, E. Borghi, A. J. G. Maroto and A. E. Regazzoni, J . Colloid Interface Sci., 1984,98,295. l9 S . L. Swartzen-Allen and E. MatijeviC, Chem. Rev., 1974, 74, 385. 2o S. G. de Busetti, E. A. Ferreiro and A. K. Helmi, Clays Clay Miner., 1980, 28, 149. 21 P. C. Hiemenz, Principles of Colloid and Surface Chemistry (Marcel Dekker, New York, 1977). 22 Colloid Science, ed. H. R. Kruyt (Elsevier, New York, 1949). 23 A. E. Regazzoni, M. A. Blesa and A. J. G. Maroto, J. Colloid Interface Sci., 1983, 91, 560. 24 A. E. Regazzoni, N. M. Figliolia, M. A. Blesa and A. J. G. Maroto, J. Colloid Interface Sci., 1984, 25 L. Sigg and W. Stumm, Colloid Surf., 1980, 2, 101. 26 K. Amolds, J. Heitbaum and W. Vielstich, 2. Naturforsch., Teil A , 1974, 29, 359. 27 S. Karp and L. Meites, J. Am. Chem. Soc., 1962, 84, 906. 28 Y. Fukumoto, T. Matsunaga and T. Hayashi, Electrochim. Acta, 1981, 26, 631. 29 C. W. Pistorius and M. C. Pistorius, Z. Kristallogr., 1962, 117, 259. Chemical Society, Washington, D.C., 1958). 101, 410. (PAPER 4/490)

ISSN:0300-9599    

DOI:10.1039/F19858101113

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. I , 1985,81, 1121-1 132 Electrical Conductivity of Uranium-Antimony Oxide Catalysts BY STANISLAW E. GOLUNSKI~ AND THOMAS G. NEVELL* Department of Chemistry, Portsmouth Polytechnic, White Swan Road, Portsmouth PO1 2DT AND DAVID J. HUCKNALL Department of Chemistry, The University, Southampton SO9 5NH Received 5th April, 1984 The relative ionic and electronic contributions to the electrical conductivity of a uranium- antimony oxide catalyst and of USbO, have been determined from measurements of ax. and d.c. conductance. Under inert atmospheres (390-775 K) conduction in the catalyst (predominantly USb,O,, together with small proportions of Sb,O, and USbO,) is associated with both electronic and effectively charged atomic point defects. Only electronic conduction occurs in USbO,.Under oxygen (1 0-70 kPa, 493-682 K) both materials aren-typesemiconductorsat higher temperatures, but at lower temperatures semiconducting behaviour varies with the pressure of oxygen. Heating USbO, in oxygen induces an ionic contribution to conductivity. Ionic conduction in the catalyst is eliminated by heating in hydrogen or propene at 470 K but is restored by heating in oxygen. It is suggested that both charged oxygen vacancies and interstitial oxide ions are involved in interactions of gaseous components with uranium-antimony oxides. With alkenes, interstitial oxide ions give rise to the products of selective partial oxidation. The uranium antimonates, USb,O,, and USbO,, are regarded as essential com- ponents of highly active U-Sb-0 catalysts1 developed for the allylic oxidation of alkenes.2 Freshly prepared, these catalysts are highly active and selective but their performance can deteriorate rapidly under conditions of continuous ~peration.~ It has been established that certain oxide catalysts operate by the facile release and replenishment of lattice oxygen.Despite various investigations of the U-Sb-0 system, however, the precise role of lattice oxygen in selective allylic oxidation is unclear. Pendleton and T a y l ~ r , ~ for example, have reported that lattice oxygen participates in the oxidation of propene over a U-Sb-0 catalyst at 623-673 K, whereas the results of Keulks and c ~ w o r k e r s ~ ~ ~ indicate a different mechanism for this reaction over USb,O,, at 698 K. Delobel and coworkers6u~ have concluded that, although a redox mechanism is involved in selective oxidation over U-Sb-0 catalysts, in the temperature range 580-640 K the mobility of lattice oxygen is low.In the present work the electrical properties of a U-SbO catalyst (mainly USb,O,, with small amounts of USbO, and Sb,04) and USbO, have been investigated, yielding information concerning the nature of the oxygen involved in allylic oxidation in the presence of binary mixtures of uranium and antimony oxides. Present address: Wispers School, Haslemere, Surrey GU27 1AD. 11211122 ELECTRICAL CONDUCTIVITY OF U-Sb OXIDES EXPERIMENTAL MATERIALS Antimony(II1) oxide and chromium(Ir1) oxide (Aldrich Gold Label, stated purity 99.999 % ), sodium chloride (Fisons, Purity 99.9 ) and uranium(v1) dinitrate dioxide hexahydrate (B.D.H.Chemicals Ltd) were used without further purification. X-Ray diffraction (X.r.d.) and infrared spectroscopy (i.r.) showed that although the antimony(rI1) oxide was mainly the orthorhombic modification, valentinite, some unidentified material was also present. A uranium-antimony oxide catalyst (U: Sb = 1 : 3) was prepared according to the method of Grasselli and Callahan.la The product was shown (by X.r.d. and i.r.) to consist mainly of USb,O,, with relatively small amounts of USbO, and Sb204. Pure USbO, was prepared by the thermal decomposition of USb30,, in air (24 h at 1363 K). In experiments involving flowing gases, oxygen, nitrogen and hydrogen (B.O.C., purity 99.5 % or better) were used without further purification.In experiments with static systems, propene (Cambrian Chemicals, purity 99%) and oxygen were condensed at 77 K and the middle fractions used. Hydrogen and nitrogen were stored after passage through a cold trap (77 K). APPARATUS AND PROCEDURE ELECTRICAL-CONDUCTIVITY MEASUREMENTS Measurements were made on polycrystalline samples, either compacted into discs or deposited on a conductivity probe, using a Wayne-Kerr Autobalance conductivity bridge B642 (1591.5 Hz) and a Keithley 610 C electrometer. m thick and 1.3 x m diameter) in a steel die (compacting pressure 10 tonne per 1.33 cm2). Electrical contact was made between two platinum electrodes to which pressure could be applied until a steady, constant value of conductance was obtained. Measurements were performed on samples heated to a temperature of 950 K under flowing atmospheres.’ In preliminary measurements to assess the reliability of the observations, a.c.and d.c. conductances were measured for well characterised samples of polycrystalline chromium(u1) oxide and sodium chloride. The results were in agreement with the literature*. and established that there were no substantial barrier layers at either the intergrain boundaries or the contacts between the electrodes and the sample. It was also shown that there were no significant temperature gradients in the samples. Conductivity Probe: This devicelo consisted of two platinum wires (3.8 x lo-, m diameter) separated by ca. m and wound concentrically along the length (1 x m) of a piece of woven silica tubing.Catalyst (ca. 0.008 g) was either electrodeposited on the probelo or applied as a suspension of cellulose nitrate in an ethanol+diethyl ether (50/50 v/v) mixture. In the latter method, solvent and cellulose nitrate were removed by gradual heating to 675 K under vacuum. The probe was mounted inside a cylindrical, acid-washed Pyrex reactor (200 cm3) which also contained powdered catalyst (0.78 g, surface area 2.2 m2). The reactor could be evacuated to Pa. Comparable changes in conductivity were observed when similar samples, either deposited on probes or compacted into discs, were heated under similar conditions. Discs: Powdered samples (0.6 g) were compacted under vacuum into discs (2 x X-RAY PHOTOELECTRON SPECTROSCOPY X.P.S. was performed using a VG Scientific ESCA 3 mark I1 spectrometer.Powdered catalysts were mounted in the instrument without further preparation and the spectra were obtained using magnesium Ka radiation. Details of the calibration of the spectrometer are discussed later.-7 - 8 h I d c 2 -9 \ v 80 - 1 c - 1 S . E. GOLUNSKI, T. G. NEVELL AND D. J. HUCKNALL -7 1.4 1 . 8 2 . 2 - 8 a -9 b I I 1.4 1.8 2 . 2 lo3 KIT 1123 1.5 2 .o 2 . 5 Fig. 1. U-Sb-0 catalyst under nitrogen: dependence of (i) a.c. and (ii) d.c. conductivity on temperature. (a) Compacted sample, first heating; (b) compacted sample, sixth heating; (c) sample on probe, after twenty cycles of heating (open points)/cooling (closed points). RESULTS VARIATION OF ELECTRICAL CONDUCTIVITY WITH TEMPERATURE u-sb-0 CATALYST When freshly prepared catalyst was heated in nitrogen [fig.1 (a)] or in oxygen, both a.c. and d.c. conductances increased exponentially with temperature. During initial heating/cooling cycles, the energy of activation for d.c. conduction (Ed,) decreased whilst that for a.c. (EaJ increased, the initial values depending on the method of measurement. However, these differences decreased rapidly with ageing [fig. 1 (b)] and, with the probe, stable behaviour was obtained after 15 cycles [fig. 1 (c)]. It was also observed that Ed, was constant between 293 and 673 K while E,, increased above a clearly defined temperature (q, table 1). USbO, There was no difference between the a.c. and d.c. conductances of polycrystalline USbO, in nitrogen at temperatures between 453 and 823 K. The conductance increased exponentially with temperature [fig.2 (a)] and was reproducible during repeated thermal cycling. These results suggested that conduction was essentially electronic, with a difference in energy between the valence and conduction bands (E, = 2&,) Of 106 kJ m0l-l. Following measurements of the isothermal conductivity of USbO, as a function of oxygen pressure (see below), the system was cooled in oxygen (90 kPa) which was then1124 ELECTRICAL CONDUCTIVITY OF U-Sb OXIDES Table 1. Activation energies for electrical conductivity ~~ ~ U-Sb-0 catalyst USbO, conditions ca. 1% ca. 9% ca. 15% under reduced reduced reduced under N2 (C,H,) (Hz) (HZ) NZ Tt/K 545 575 550 None None E,,/kJ mol-l E,,/kJ mol-1 34 40 37 54 53 61 74 78 67 61 39 54 53 67 74 78 - - - - -6.0 -8.0 1.5 2.0 2.5 Fig.2. USbO, under nitrogen: dependence of (i) a.c. and (ii) d.c. conductivity on temperature. (a) Compacted sample, first heating; (b) sample on probe, after heating/cooling cycles under oxygen. replaced by nitrogen (50 kPa). Subsequent observations revealed, over the temperature range studied, behaviour similar to that of the U-Sb-0 catalyst, with a.c. conductance exceeding d.c. conductance [fig. 2 (b)]. VARIATION OF ISOTHERMAL ELECTRICAL CONDUCTIVITY AS A FUNCTION OF OXYGEN PRESSURE Using materials deposited on probes, measurements were made of conductance, 0, as a function of the pressure of oxygen, Po,. Since changes in conductance were slow following adjustments to the oxygen pressure, a period of 24 h was allowed for equilibration before each reading was taken.Results fitted the general equation 0 K (Po*)+?S. E. GOLUNSKI, T. G. NEVELL AND D. J. HUCKNALL h - I C -s -7.39 v M - -7.40 1 - 7.3 8 . * - 5.82 n -5.84 - c: ’ -5.86 . v 0 00 - 5.88 1125 ~~ 4 .O 4.4 4.8 1% (Po*/Pa) Fig. 3. U-Sb-0 catalyst under oxygen: dependence of a.c. conductivity on partial pressure at (a) 493 and (b) 678 K. u-sb-0 CATALYST Only measurements of as. conductance were made (see Discussion). At 493 K and for pressures of oxygen in the range 10-1 5 kPa the value of q was + 0.035, but at higher pressures (30-70 kPa) the value of q was -0.050 [fig. 3(a)]. At 678 K, q was -0.08 at pressures of oxygen between 10 and 70 kPa [fig. 3(b)]. USbO, Both a.c. and d.c. conductances were measured. At 533 K, oac was characterised by exponents, q, of - 0.040 and + 0.100 for pressures of oxygen between 8 and 45 kPa and 45 and 90 kPa, respectively [fig.4(a)]. The values of q for d.c. conduction over the same ranges of pressure were considerably larger, the respective values being - 0.17 and +0.17. At 673 K, results were similar for oac and ode, giving an exponent of -0.025 [fig. 4(b)].1126 - 6.91 - 6.96 -7.20 n I - c: 2 -7.24 --- w Do - 7 . 2 8 ELECTRICAL CONDUCTIVITY OF U-Sb OXIDES -6.00 - 6 . 0 2 1 I I I 3.6 4.0 4.4 4.8 3.6 4.0 4.1 4.8 log ( P o p ) Fig. 4. USbO, under oxygen: dependence of (i) a.c. and (ii) d.c. conductivity on partial pressure at (a) 533 and (b) 673 K. EFFECT OF REDUCING ATMOSPHERES ON THE CONDUCTIVITY OF THE u-sb-0 CATALYST The electrical conductivity of the U-Sb-0 catalyst in the presence of reducing atmospheres was investigated using the probe over the temperature range 293-673 K.During exposure of the catalyst to propene or hydrogen, conditions were arranged such that, based on stoichiometric USb,O,, and the formation of water and propenal only, a predetermined proportion of lattice oxygen would be removed from the catalyst. After reduction, and in order to obtain repeatable initial values of a.c. and d.c. conductance, the catalyst was reoxidised by heating under oxygen (20 kPa) at 673 K for 24 h. Exposure of the catalyst at 673 K to propene equivalent to 1 % of the lattice oxygen caused the conductivity to increase by ca. 95%. The a.c. and d.c. measurements were identical above 575 K [fig. 5(a')], indicating a negligible ionic contribution to conduction, and the energy of activation for conduction was increased (table 1).Measurements were reproducible on reheating and similar results were obtained when the catalyst was heated under propene equivalent to 2% of the lattice oxygen. On heating the catalyst from 293 K in hydrogen (sufficient to remove 9% of the oxygen in the catalyst), a sharp increase in both a.c. and d.c. conductances occurred at ca. 475 K [fig. 5(b)]. The conductances were identical above 548 K, indicating no contribution from ionic conduction at higher temperatures. Subsequent cooling andS. E. GOLUNSKI, T. G. NEVELL AND D. J. HUCKNALL 1127 -5 -6 h d I c 2 , - 7 v 2 , -8 -9 -5 -6 - 7 - 8 -9 - 5 \P 1.5 2.0 2.5 1.5 2.0 2.5 103 KIT - 6 -7 -8 -9 1.5 2 .o 2.5 Fig.5. U-Sb-0 catalyst under reducing atmospheres: dependence of (i) a.c. and (ii) d.c. conductivity on temperature. (a) Propene equivalent to O,,,, admitted at 675 K (cooling, closed points; reheating, open points); (b) hydrogen equivalent to O,,,, admitted at 293 K, p first heating, q second heating; ( c ) hydrogen equivalent to O,.,, admitted at 675 K. reheating slightly increased a.c. and d.c. conductances over the entire temperature range. Finally, reduction equivalent to 15 % lattice oxygen using hydrogen eliminated the difference between ax. and d.c. conductances at temperatures > 455 K [fig. 5 (c)]. The activation energy for conduction in the reduced catalyst (54 kJ mol-l) was almost identical with that observed for USbO, under nitrogen (table 1).DISCUSSION Ionic point defects, which can contribute significantly to electrical conduction in metal oxides, are believed to play an important role in oxidation catalysis.ll9 l2 These defects may form during the preparation of the catalyst or subsequently as the result of internal or external eq~i1ibria.l~. l4 In addition, free electrons (e-) and electron holes (h+) may participate in electronic rearrangements involving adsorbed species and surface ions.ll According to Blumenthal and Seitz,15 a.c. conduction is associated with both electronic and ionic charge carriers, whereas d.c. conduction is due exclusively to the former. Conductance depends on the charge, mobility and concentration of defects. Ionic conduction may be due to cation or oxygen defects (charged vacancies, interstitial ions etc.) although TulleP suggests that, in oxides, conduction tends to be1128 ELECTRICAL CONDUCTIVITY OF U-Sb OXIDES controlled by the motion of ions in either the cation or oxygen sub-lattice.Electronic carriers can arise intrinsically or from the formation of ionic defects. Consideration of the various equilibria which may be set up involving a solid phase and molecular oxygen15-18 has, in the case of oxides such as Sn-Sb-019$20 and Cu-O,,l * 22 allowed oxygen-excessive and oxygen-deficient phases to be distinguished. An increase in conductance with ambient oxygen pressure, showing p-type semicon- duction, is consistent with the formation of interstitial oxide ions, Of- or OF, or with extension of the lattice and thus the creation of metal vacancies, VM.l69 l7 If equilibrium is assumed then for the former 40,(g) f OF + h+ (1) or +O,(g) f Of-+ 2h+.(2) [h+] = 2[0f-] (3) Using the requirement for electrical neutrality such as for eqn (2), expressions may be obtained which show that defect concentrations vary with oxygen pressure according to and [Or] cc (P02)0.25 [h+] cc (P02)0.25 or [Of-] cc (P02)0.167 ( 5 4 and [h+] oc (P02)0.167 ( 5 b) respectively, for the exclusive formation of either Or or Of-. In the latter case, since both metals in USb301, are reported to be in the oxidation state (v)*~* 6cf 23 then tO,(g) P V$ + 5h+ + 50; where 0; represents a lattice oxide ion; whence [V$] cc (Po2)0.2O8 (7 4 and [h+] cc (Po2)o.208. (7 b) According to these formulations, the concentration of both ionic and electronic defects show the same dependence on oxygen pressure.Opposite trends, showing n-type semiconduction, could be due to oxide ion vacancies or to interstitial metal ions.16* l7 Fot the former, concentrations of vacancies and electrons would be proportional to oxygen pressure to the power of - 0.167, and for the latter (Mf+) the exponent of oxygen pressure would be -0.208. ELECTRICAL CONDUCTION IN THE u-sb-0 CATALYST The catalyst exhibited both electronic and ionic conduction under oxygen or inert atmospheres at temperatures between 293 and 773 K [fig. 1 (b)]. Changes were observed in ionic conduction, however, which were not reflected in the electronic conduction. Since there was no corresponding phase modification,la it is probable that these changes were associated with different mechanisms of ionic conduction.Correspondingly, the measured exponents q in the dependence of conductance on oxygen pressure showed n-type semiconduction above the transition temperature and complex behaviour below this temperature. Numerical values of q were much lower than those deduced above.S. E. GOLUNSKI, T. G. NEVELL AND D. J. HUCKNALL 1129 The simultaneous presence of oxide ion vacancies and interstitial oxide ions has been proposed for several oxides of u r a n i ~ m . ~ , - ~ ~ For U,O, at high temperatures, a decrease in q from 0.25 to -0.167 with oxygen pressure from loF2 to lo5 kPa2' was attributed to the initial formation, at low pressures, of interstitial oxide ions near the surface, despite the high concentration of vacancies.Filling of these vacancies occurred at higher pressures. These defects have also been observed using diffraction techniques.26 The present results indicate that the U-Sb-0 catalyst interacts with oxygen in a similar way, but they do not allow the effective charge of the ionic defects to be determined. The formation of interstitial oxygen species which diffuse only slowly to vacant sites is consistent with the relatively slow rates of reoxidation of the catalyst by atmospheric oxygen after static experiments on the oxidation of alkenes.lo The large increase in conductivity accompanying reduction of the catalyst may be due in part to charge transfer associated with adsorption, but this does not account for the corresponding elimination of ionic conduction.The two observations are, however, consistent with the removal of interstitial oxide ions by processes which increase the concentration of free electrons in the catalyst. Thus, in early stages, the following overall processes could be involved (assuming Of-) H,(g) +Of- e H,O(g) + 2e- CH,-CH=CH,(g) + 0;- + 0; + CH,=CH-CHO(g) + H,O(g) + Vi+ + 4e- (9) where 0; represents a lattice oxide ion and Vi+ an oxide ion vacancy. For hydrogen, the mechanism could involve reaction with superficial lattice oxide ions to leave vacancies which are then filled by interstitial oxide ions. Alternatively, hydrogen could be dissociatively adsorbed. In the allylic oxidation of propene, the antimony ions at which symmetrical adsorbed intermediates are formed1" would be oxide ion vacancies (Vi+) and at least one of the following steps would involve interstitial oxide ions: C,H,(g) + 0; + Vi+ -+ OH(ads) + C,H,(ads) + 2h+ C,H,(ads) + 0; -+ C,H,(ads) + OH(ads) C,H,(ads) + Of- + Vg+ -+ C,H,(ads) + OH(ads) (10) (1 1 4 (1 1 b) C,H,(ads) + Of- -+ C,H,O(g) + Vg+ + 4e- C,H,(ads) + 0; -+ C,H,O(g) + 2Vi+ + 4e- (124 (12b) (13) 20H(ads) -+ H,O(g) + V;+ + 0; + 2e-.ELECTRICAL CONDUCTION IN USbO, Under inert atmospheres, electronic processes were the only means of conduction in freshly prepared USbO, at temperatures between 453 and 823 K. The similarity of values of Eg in USbO, and the reduced U-Sb-0 catalyst indicates that electronic conduction is associated with structural features common to the two antimonates. From d.c. measurements at 533 K it appears that evacuation of USbO, brings about the formation of lattice oxide ion vacancies.Subsequent exposure to low pressures of oxygen allows these to be filled: 0, evac V;++2e-+2O2(g)e0; (14) and under higher pressures interstitial oxide ions and associated positive holes are (1 5 ) formed : iO,(g) s O:-+ 2h+.1130 ELECTRICAL CONDUCTIVITY OF U-Sb OXIDES - 2 Do 1 1 385 390 39 5 4 00 4 0 5 binding energylev I I I I J 5 3 5 5 4 0 5 4 5 5 5 0 55 5 binding energy/eV Fig. 6. X-ray photoelectron spectra of U-Sb-0 active and deactivated catalysts (measured binding energies corrected with reference to C lsl/2 at 285.3 eV). (a) U 4factive (U 4fat 383.7 and 394.4 eV); (b) U 4fdeactivated [U 4fbinding energies (a)]; ( c ) Sb 3d deactivated (Sb 3d5,2 at 534.5 eV and Sb 3d3,2 at 544.0 eV); (d) Sb 3d active (Sb 3d5,, at 533.4 eV and Sb 3d3,, at 542.8 eV).Although changes in ionic conduction would be expected to show the same dependence on oxygen pressure, this was much less marked, which may reflect the relative immobility of atomic defects at this temperature. The value of -0.03 at 673 K for the exponent q (both a.c. and d.c.) is again not consistent with a simple mechanism, indicating the possible presence of both charged oxygen vacancies and interstitial oxide ions which do not interact. That some of these defects are retained on cooling would explain the distinct ionic contribution to the conductivity of USbO, observed subsequently.S. E. GOLUNSKI, T. G. NEVELL AND D. J. HUCKNALL 1131 CATALYSIS BY URANIUM ANTIMONATES The performance of uranium antimonate catalysts depends on the method of preparation, In the absence of gas-phase oxygen, pure USb,O,, reacts only slightly with propene to form propenal,6a whereas the catalyst containing small amounts of Sb,O, and USbO, oxidises alkenes selectively in much larger amounts.la Reoxidation of the impure material is relatively slow and changes in conductivity reflect the extent of reduction.1° The present results show that interstitial oxide ions make a major contribution to the conductivity of the U-Sb-0 catalyst. Although it has been suggestedlC that, in this catalyst, oxygen vacancies provide sites for the adsorption of alkenes during selective allylic oxidation, the possible role of interstitial oxide ions has not been reported previously. The reaction of the adsorbed hydrocarbon with such ions, formed by the interaction of the catalyst with gaseous oxygen, is consistent both with observations indicating a redox mechanismlC9 and results which suggest the involvement of adsorbed oxygen.The progressive deterioration in the performance of the catalyst during continuous use is likely to be caused by the depletion of these ions, the replacement of which from gas-phase oxygen appears to be slow. By implication, interstitial oxide ions in a fresh catalyst are associated with the impurities Sb,O, and/or USbO,. The particular importance of antimony with respect to the catalytic behaviour has also been shown by X-ray photoelectron spectroscopy (fig. 6, spectra uncorrected for surface charging29).Whereas the binding energies associated with U 4f were identical in fresh catalyst and catalyst deactivated by reduction with propene, those for Sb 3d3/, and Sb 3d,,, were increased significantly in the deactivated catalysts. Calculation of the binding energies in insulating or semiconducting samples requires calibration of the spectrometer. At the time, the above results were corrected for charging by reference to the C lsl,2 peak, a technique also used by Delobel et aZ.6c It has been however, that this is an unsatisfactory internal standard since the deposits which give rise to it are in electrical equilibrium with the specimen. Although further work appears to be necessary on X.P.S. of the U-Sb-0 system, the importance of Sb in the catalytic system is clear.Finally, note that the binding energies for the U 4f peaks correspond exactly to those reported by -411en31 for yUO,. This is unexpected and requires further investigation. The mechanisms by which interstitial oxide ions are formed or reformed remain unclear. However, for Sn-Sb-0 catalysts32 evidence points to the significant catalytic effects of superficial antimony ions and to the importance of the impurity Sb,O,. We propose that, for the U-Sb-0 catalyst, Sb3+ ions on the surface trap oxygen, which then forms the interstitial oxide ions involved in allylic oxidation. Allylic oxidation or ammoxidation of propene is relatively slow over USbO,la and competing total oxidation, involving oxide ions from normal lattice sites, is more significant.The present work has shown that atomic point defects are absent from freshly prepared USbO, but may be induced at elevated temperatures by evacuation followed by exposure to gaseous oxygen. Hence there is correspondence between the much lower availability of interstitial oxide ions in USbO, and the reduced selectivity of this compound. (a) R. K. Grasselli and J. L. Callahan, J . Catal., 1969, 14, 93; (b) R. K. Grasselli, D. D. Suresh and K. Knox, J. Catal., 1970, 18, 356; (c) R. K. Grasselli and D. D. Suresh, J. Catal., 1973, 25, 273. J. L. Callahan and B. Gertisser, U.S. Patent 3198759, 1965; U.S. Patent 3308151, 1967. P. W. Grayson, G. H. Lovett, K. B. Watts and M. M. Fontenot, Ger. Offen., 2151539, 1972. P. Pendleton and D. Taylor, J . Chern. Soc., Faraday Trans.I , 1976, 72, 1114.1132 ELECTRICAL CONDUCTIVITY OF U-Sb OXIDES (a) L. D. Krenzke, G. W. Keulks, A. V. Sklyarov, A. A. Firsova, M. Yu. Kutirev, L. Ya Margolis and 0. V. Kyrlov, J. Catal., 1978,52,418 ; (b) E. V. Hoefs, J. R. Monnier and G. W. Keulks, J. Catal., 1979, 57, 331; (c) L. D. Krenzke and G. W. Keulks, J . Catal., 1980, 61, 316. (a) R. Delobel, H. Baussart, M. LeBras and J-M. Leroy, C.R. Acad. Sci., Ser. C, 1978,286, 605. ; (b) H. Baussart, R. Delobel, M. LeBras, D. LeMaguer and J-M. Leroy, J . Chem. Soc., Faraday Trans. 1, 1982,78,485; (c) R. Delobel, H. Baussart and J-M. Leroy, J. Chem. Soc., Faraday Trans. 1, 1983, 79, 879. M. D. Judd and M. I. Pope, J. Appl. Chem., 1970,20, 380. D. B. Meadowcroft and F. G. Hicks, Proc. Br. Ceram. Soc., 1972,23, 33.S . Lanyi, Czech. J . Phys. B, 1978, 28, 547. lo F. J. Farrell, T. G. Nevell and D. J. Hucknall, J . Phys. E, 1979, 12, 1166. l1 V. J. Lee, J. Catal., 1970, 17, 178. l2 G. R. Heal, Annu. Rep. Prog. Chem., Sect. A, 1971, 68, 221. l3 M. Najbar and K. Stadnicka, J . Chem. SOC., Faraday Trans. 1, 1983, 79, 27. l4 I. Brown and W. R. Patterson, J . Chem. Soc., Faraday Trans. I , 1983, 79, 1431. l5 R. B. Blumenthal and M. A. Seitz, in Electrical Conducthity in Ceramics and Glass, ed. N. M. Tallan l6 H. L. Tuller, in Non-stoicheiometric Oxides, ed. 0. T. Sorensen (Academic Press, New York, 1981), l7 P. Ko fstad, Nonstoicheiometry, Dixusion and Electrical Conductivity in Binary Metal Oxides (Wiley- l8 S . E. Golunski, PhD Thesis (C.N.A.A., 1982). lY G. W. Godin, C. C. McCain and E. A. Porter, Proc. 4th Znt. Congr. Catal. (Akademiai Kiado, 2o J-M. Herrmann, J-L. Portefaix, M. Forissier, F. Figueras and P. Pichat, J . Chem. Soc., Faraday 21 B. J. Wood, H. Wise and R. S. Yolles, J. Catal., 1969, 15, 355. 22 J. Maluenda, R. Farhi and G. Petot-Ervas, J. Phys. Chem. Solids, 198 1, 42, 91 1. 23 T. Birchall and A. W. Sleight, J . Catal., 1978, 53, 280. 24 B. T. M. Willis, Nature(London), 1963,197,755; B. T. M. Willis, Proc. R. SOC. London, Ser. A, 1963, 25 G. E. Murch and R. J. Thorn, J. Nucl. Mater., 1978, 71, 219. 26 G. C. Allen, P. A. Tempest and J. W. Tyler, Nature (London), 1982, 295, 48. 27 T. Matsui, T. Tsujio and K. Naito, J. Nucl. Sci. Technol., 1974, 11, 216; 317. 28 R. K. Grasselli and J. D. Burrington, Adv. Catal., 1981, 30, 133. 2y D. J. Hucknall, F. J. Farrell and T. G. Nevell, unpublished work. 30 D. J. Hucknall, B. M. Willatt and R. J. Hockham, in Catalyst Deactivation, ed. B. Delmon and 31 G. C. Allen, J. A. Crofts, M. T. Curtis and P. M. Tucker, J . Chem. SOC., Dalton Trans., 1974, 1296. 32 F. J. Berry, Adv. Catal., 1981, 30, 97; F. J. Berry and B. J. Laundry, J. Chem. SOC., Dalton Trans., (Marcel Dekker, New York, 1974), part A, p. 35. p. 271. Interscience, New York, 1972), p. 22. Budapest, 1971), vol. 1, p. 271. Trans. I , 1979, 75, 1346. 274, 122. G. F. Froment (Elsevier, Amsterdam, 1980), p. 213. 1981. 1441. (PAPER 4/562)

ISSN:0300-9599    

DOI:10.1039/F19858101121

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

.I. Chern. SOC., Furuduy Trans. 1 , 1985, 81, 1133-1 140 Separation of Viscosity B Coefficients into Ionic Contributions Part 4.-Extrapolation Methods Using Tetra-alkylammonium Bromides in Dimethyl sulphoxide and Hexamethylphosphoric triamide BY KENNETH G . LAWRENCE* AND ROY T. M. BICKNELL Department of Chemistry, Birkbeck College, Malet Street, London WClE 7HX AND ANTONIO SACCO AND ANGELO DELL'ATTI Institute of Physical Chemistry, University of Bari, Via Amendola 173, 70126 Bari, Italy Received 15th May, 1984 Viscosity B coefficients of the Jones-Dole equation have been determined with a high degree of precision for Pr,NBr, Bu,NBr, Pe,NBr, Hex,NBr and Hept,NBr in dimethyl sulphoxide and hexamethylphosphoric triamide at 25 and 35 "C. The B coefficients were plotted as functions of the van der Waals volumes, Stokes radii and formula weights of the cations, and the linear portions of the graphs were extrapolated to the zero value of each property tested.The intercepts thus obtained are discussed and compared with the ionic B(Br-) values reported previously using Bu,NBu,B and Ph,PPh,B as reference salts. The reference-salt method is considered to give the best division into ionic contributions. We have previously reported and discussed the division of viscosity B coefficients of the Jones-Dole equation into ionic values using two reference salts, tetrabutylam- monium tetrabutylborate (Bu,NBu,B) and tetraphenylphosphonium tetraphenylbor- ate (Ph,PPh,B), dissolved in dimethyl sulphoxide (DMSO),' hexamethylphosphoric triamide (HMPT)2 and dimethylformamide (DMF).3 The method of division assumes that for each reference salt the cation-solvent and anion-solvent interactions are very similar and that the B coefficient for each salt can be divided into cation and anion contributions in the same ratio as that of the van der Waals volumes of the ions. Having obtained B values for the Bu,N+ and Ph,P+ ions in this way, it is a simple matter to calculate two independent B values for the bromide ion from B coefficients for Bu,NBr and Ph,PBr.The almost identical pairs of values for the bromide ion thus obtained in each solvent provided excellent evidence that the assumptions on which the division had been made were correct. Another method of division involves determining the B coefficients for an hom- ologous series of tetra-alkylammonium salts with a common anion.This method assumes that, if a number of the cations of such a series of salts are unsolvated or interact equally with the solvent and if the B coefficients are a linear function of an independent variable such as their cationic formula weights, extrapolation to zero of the independent variable should give the B value for the anion as intercept. The theoretical justification for this method is based on the fact that a viscosity B coefficient for an ion has the dimensions of molar volume and so its magnitude must be, at least in part, a function of its molar volume. We had previously measured the B coefficients of Bu,NBr in DMSO and HMPT at 25 and 35 "C, so we decided to extend the work to include measurements on DMSO and HMPT solutions of tetrapropylammonium, 11331134 VISCOSITY B COEFFICIENTS tetrapentylammonium, tetrahexylammonium and tetraheptylammonium bromide (Pr,NBr, Pe,NBr, Hex,NBr and Hept,NBr, respectively) to enable us to compare the extrapolation and the reference-salt methods of division.EXPERIMENTAL DMSO SOLUTIONS Tetrapropylammonium bromide (Kodak), m.p. 262-263 "C, was recrystallized from acetone. Hex,NBr (Kodak), m.p. 91-92 "C, was used without further purification. Pe,NBr (Kodak), m.p. 99-101 "C, and Hept,NBr (Kodak), m.p. 87-89 "C, were recrystallized from 60-80 "C petroleum spirit. All of the salts were dried in a vacuum oven at 70 "C. The experimental techniques and the purification of DMSO have been described previously.' HMPT SOLUTIONS The salts were purified and dried in the same way as for the DMSO solutions and had similar melting points.For the purification of HMPT and a description of the experimental techniques see ref. (2). RESULTS AND DISCUSSION Kinetic energy of efflux corrections have been applied to the values for the relative dynamic viscosities shown in table 1. The calculated A coefficients of the Jones-Dole equation shown in table 2 were used in the orthogonal-polynomials method for evaluating the Jones-Dole B coefficients as explained previously.l, Also shown in table 2 are the experimental A coefficients at 25 "C; these agree with the calculated values within 95% confidence limits. The B coefficients for the bromide salts in both solvents at 25 and 35 "C are shown in table 3.Extrapolation of electrochemical quantities to give a single-ion value must be based on evidence that the quantity concerned is a simple, preferably linear, function of some property of the ions. Previous authors have used molar weights, number of carbon atoms in the molecular ion, Stokes radii and van der Waals volumes for a series, or part of a series, of salts with an anion in common. Conway et aL4 used the method to determine the partial molar volume of the anion for a series of homologous tetra-alkylammonium chlorides, bromides and iodides in aqueous solution. They plotted the partial molar volume, V(R,NX), for a series of these salts with a halide ion in common as a function of the formula weight of the cation M(R,N+), and obtained straight-line graphs for each common halide ion.They suggested therefore that their results fitted the equation : V(R,NX) = V ( X - ) + aM M(R,N+) and that extrapolation to zero cationic formula weight gave the partial molar volumes of the halide ions, V(X-). Conway subsequently reviewed5 the division of various parameters into ionic values by the extrapolation and reference-salt methods. Krumgalz* used an extrapolation method for viscosity B coefficients based on the assumption of the ' unsolvation of large tetra-alkylammonium ions in organic solvents'. Of course if the ions were unsolvated they would not dissolve, but what was really meant was that if these ions are sufficiently large, their properties are not influenced by the charge on the nitrogen atom. Literature values of the B coefficients for some tetra-alkylammonium bromides and iodides in five solvents were plotted as functions of their cationic radii and, in most cases (see his correlation coefficients), straight-line plots were obtained for series of salts containing propyl or larger alkyl groups. The cationic radii used in these calculations were the empirical Stokes radii, calculated with the aid of the Stokes equation and values for ion conductances. Although there is no comparable theoretical background to the viscosity BK.G . LAWRENCE, R. T. M. BICKNELL, A. SACCO AND A. DELL'ATTI 1135 coefficients as there is for the partial molar volumes of electrolyte^,^ we tried fitting the B coefficients shown in table 3 to an equation similar in form to eqn (1) : B(R,NX) = b + a,flR,N+) (2) wheref(R,N+) represents some property of the cation and af is the slope of the line.If this property is chosen correctly and the points fit a straight line, the intercept b for the valueflR,N+) = 0 should be interpretable as the viscosity B value for the X- anion. Since we had successfully used van der Waals volumes, V,, in the reference-salt method we calculated these for the cations in the manner described previously1 and plotted the B(R,NX) coefficients against V,(R,N+). We found that for DMSO solutions only the points for Bu,NBr, Pe,NBr and Hex,NBr were collinear at both temperatures. The points representing Pr,NBr and Hept,NBr were ca. 0.05 dm3 mol-1 below and 0.06 dm3 mol-1 above the straight lines, respectively, displacements that are far in excess of the standard errors on the B coefficients (see table 3).We did not expect the tetraheptyl salt to show any marked difference in behaviour from that of the three lower members of the series and the results prompted an analysis of the salt but this showed nothing unusual (calculated: C, 68.54% ; H, 12.33% ; N, 2.85% ; Br, 16.28% ; found: C, 68.80% ; H, 12.42% ; N, 2.86% ; Br, 16.45%); complete re- measurement of the B coefficient confirmed that the viscometric behaviour of this salt was out of line with that of the tetrabutyl-, tetrapentyl- and tetrahexyl- ammonium salts. Using the same procedure with HMPT we found that the points for the four higher homologues were collinear at both temperatures but the points representing Pr,NBr were ca. 0.06 dm3 mol-l above the straight lines.This is the reverse situation to that found in DMSO for the tetrapropyl salt. On extrapolating the best straight line through the points for Bu,N+, Pe4N+ and Hex,N+ in DMSO and through all the points excluding Pr,NBr in HMPT, the intercepts obtained for both solvent systems are shown in table 4. We next tried plots of the B coefficients of the salts as a function of their cationic radii. In order to calculate these radii we chose first the ion-conductance data of Gopals (which did not include a value for Pe,NBr) because these were obtained using transport-number measure- ments, and from these we calculated Stokes radii, rs, for the cations and then plotted the B coefficients against r:; the four points gave a reasonably straight line, bearing in mind the accumulation of errors that arises from the division into ion conductances and the contributory errors of the other experimental parameters used in the calculation steps from ion conductances to Stokes radii. Arrington and Griswold have also published conductance data for all five cations and they used the assumptiong Am(i-Pe),N+ = Am(i-Pe),B- to tabulate ion conductances. Intercept values for both sets of data are shown in table 4.Unfortunately we have not been able to test this procedure with HMPT sol- utions because of a lack of published conductance data for the Hex,N+ and Hept,N+ ions. Before examining the magnitude of the intercepts let us first consider the point for Pr,N+ in DMSO shown in fig. 1. This is the smallest of the cationic series studied and the charge on the N atom is less well screened from solvent molecules by the alkyl chains than the higher homologues.If this results in a stronger attraction between the ion and the solvent molecules creating a relatively larger solvodynamic entity and enhanced B value, we would have a simple explanation for the point for the Pr,N+ ion being located above the line joining Bu,N+ to Hex,N+ in fig. 1 ; however, the point lies below the line and we do not have a simple explanation for this. Possibly its1136 VISCOSITY B COEFFICIENTS Table 1. Concentration, relative density and relative viscosity at 25 and 35 "C for DMSO and HMPT DMSO HMPT conc. relative relative conc. /mol dmP3 density viscosity /mol dm-3 0.006 76 0.009 85 0.014 49 0.019 45 0.026 69 0.032 41 0.037 72 0.047 13 0.006 70 0.009 76 0.014 36 0.019 27 0.026 45 0.032 12 0.037 38 0.046 70 0.006 02 0.009 71 0.012 85 0.019 06 0.029 74 0.033 92 0.044 30 - 0.005 97 0.009 62 0.012 73 0.018 89 0.029 47 0.033 61 0.043 90 - 0.005 16 0.008 72 0.012 06 0.016 85 0.023 61 0.026 76 0.039 41 - 1.000 06 1.000 07 1.000 16 1 .ooo 21 1.000 27 1.000 33 1.000 39 1.000 50 1.000 07 1.000 13 1.000 18 1.000 24 1.000 32 1.000 42 1.000 44 1.000 56 0.999 82 0.999 75 0.999 73 0.999 44 0.999 31 0.999 15 0.998 85 - 0.999 84 0.999 76 0.999 72 0.999 53 0.999 40 0.999 20 0.998 91 - 0.999 77 0.999 62 0.999 48 0.999 24 0.998 97 0.998 80 0.998 36 - Pr,NBr, 25 "C 1.005 84 0.007 53 1.008 35 0.012 49 1.012 36 0.0 17 48 1.016 16 0.022 73 1.021 95 0.026 51 1.026 10 0.032 32 1.030 69 0.034 57 1.038 02 0.039 93 Pr,NBr, 35 "C 1.005 44 0.007 47 1.007 83 0.012 39 1.01 1 46 0.017 33 1.014 99 0.022 55 1.020 34 0.026 28 1.024 21 0.032 06 1.028 37 0.034 29 1.035 15 0.039 60 Pe,NBr, 25 "C 1.007 10 0.005 99 1.010 94 0.009 76 1.014 46 0.014 86 1.020 89 0.020 55 1.032 44 0.029 44 1.036 40 0.038 19 1.047 12 0.044 07 - 0.052 00 Pe,NBr, 35 "C 1.006 68 0.005 94 1.010 21 0.009 68 1.013 58 0.014 74 1.019 49 0.020 38 1.030 18 0.029 19 1.033 92 0.037 87 1.043 85 0.043 72 - 0.051 63 Hex,NBr, 25 "C 1.006 73 0.010 94 1.010 87 0.015 19 1.014 67 0.019 81 1.020 42 0.030 04 1.028 3 1 0.036 01 1.032 05 0.042 98 1.046 33 0.049 56 - 0.058 75a relative relative density viscosity 1.000 43 1.000 55 1.000 69 1.000 83 1.000 93 1.001 23 1.001 30 1.001 47 1.000 61 1.000 67 1.000 74 1.000 80 1.000 89 1.001 33 1.001 43 1.001 62 1.000 13 1.000 16 1.000 20 1.000 11 1.000 30 1.000 17 1.000 24 1.000 08 1.000 14 1.000 23 1.000 06 1.000 20 1.000 22 1.000 41 1 .OOO 19 1.000 36 0.999 97 0.999 90 0.999 90 0.999 74 0.999 67 0.999 59 0.999 24 0.999 24 1.014 20 1.021 53 1.030 74 1.038 87 1.044 07 1.053 94 1.057 56 1.067 50 1.013 31 1.019 96 1.028 12 1.035 76 1.040 74 1.051 28 1.053 57 1.062 76 1.012 70 1.020 97 1.030 23 1.042 5 1 1.060 45 1.077 10 1.087 54 1.102 68 1.011 71 1.019 08 1.027 79 1.039 52 1.055 94 1.071 40 1.081 44 1.094 90 1.025 49 1.034 70 1.044 38 1.065 58 1.078 69 1.094 19 1.109 33 1.132 34K.G. LAWRENCE, R. T. M. BICKNELL, A. SACCO AND A. DELL'ATTI Table 1. Continued 1137 ~~ DMSO HMPT conc. relative /mol dm-3 density 0.005 11 0.008 64 0.01 1 95 0.016 69 0.023 40 0.026 52 0.039 05 - 0.006 48 0.009 84 0.015 35 0.019 98 0.023 64 0.029 68 0.033 11 0.039 92 0.043 19 0.006 42 0.009 75 0.015 21 0.019 80 0.023 42 0.029 42 0.032 81 0.039 56 0.042 80 0.999 80 0.999 61 0.999 50 0.999 27 0.998 93 0.998 94 0.998 45 - 0.999 58 0.999 38 0.999 04 0.998 76 0.998 53 0.998 17 0.997 94 0.997 49 0.997 39 0.999 70 0.999 38 0.999 08 0.998 78 0.998 57 0.998 22 0.997 99 0.997 55 0.997 46 relative conc.relative relative viscosity /mol dmW3 density viscosity Hex,NBr, 35 "C 1.006 25 0.010 85 1.010 22 0.0 15 06 1.013 71 0.019 65 1.018 98 0.029 79 1.026 37 0.035 72 1.030 22 0.042 62 1.043 17 0.049 14 - 0.058 26" Hept,NBr, 25 "C 1.009 24 0.007 06 1.013 60 0.011 05 1.020 89 0.014 34 1.027 50 0.021 37 1.031 97 0.028 40 1.040 17 0.033 99 1.044 38 0.041 13 1.054 82 0.048 27 1.058 61 Hept,NBr, 35 "C 1.008 91 0.007 00 1.012 88 0.010 96 1.019 92 0.014 22 1.025 85 0.021 20 1.030 12 0.028 16 1.037 66 0.033 71 1.042 11 0.040 79 1.051 41 0.047 87 1.055 03 0.999 97 0.999 90 0.999 90 0.999 85 0.999 73 0.999 62 0.999 19 0.999 28 0.999 85 0.999 74 0.999 71 0.999 57 0.999 33 0.999 51 0.999 24 0.999 01 0.999 94 0.999 80 0.999 67 0.999 70 0.999 36 0.999 57 0.999 29 0.999 06 1.022 94 1.031 12 1.039 89 1.061 17 1.073 20 1.088 16 1.100 26 1.122 96 1.018 84 1.027 67 1.035 89 1.051 72 1.067 69 1.081 28 1.098 01 1.116 13 1.017 53 1.025 94 1.033 44 1.048 01 1.063 35 1.075 31 1.091 35 1.107 92 - a Concentrations not included in the calculation of the B coefficients. Table 2.Viscosity A(dm3/2 mol-1/2) coefficients at 25 "C calculated experimental species DMSO HMPT DMSO HMPT Pr,NBr 0.01 1 9" 0.014 7c 0.009 (k0.003) 0.027 (k0.016) Pe,NBr 0.013 5' 0.016 Oc 0.013 (k0.004) 0.021 (f0.012) Hex,NBr 0.013 7" 0.017 Oc 0.013 (f0.003) 0.024 (k0.014) HeptaNBr 0.014 l a 0.020 0 0.010 (f0.005) 0.031 (f0.014) Sources of conductivity data used in Falkenhagen and Vernon equation: " ref.(8); ref. (9); ref. (14). Error limits are 95% confidence intervals. 38 FAR 11138 VISCOSITY B COEFFICIENTS Table 3. Viscosity B (dm3 mol-l) coefficients in DMSO and HMPT DMSO HMPT species 25 "C 35 "C 25 "C 35 "C Pr,NBr 0.749 ( f 0.003) 0.695 ( f 0.002) 1.601 ( k 0.008) 1.492 ( f 0.005) Bu,NBra 0.902 (k 0.003)' 0.842 ( f 0.003)" 1.727 ( f 0.003y 1.606 ( f 0.004)b Pe,NBr 1.002 ( f 0.002) 0.937 ( f 0.002) 1.922 ( f 0.007) 1.789 ( f 0.006) Hex,NBr 1.107 ( f 0.002) 1.039 ( f 0.004) 2.1 14 ( f 0.002) 1.963 ( f 0.008) Hep t,NBr 1.264 (f0.004) 1.199 (k0.003) 2.295 (f0.004) 2.146 (k0.003) Br-a 0.481 ( f 0.002)" 0.451 ( f 0.004)" 0.732 ( f 0.006)b 0.678 ( +0.006)b " Ref.(1); ref. (2). Error limits are standard errors on the fitted B values except for Br- where the standard deviation on two independent results are shown. Table 4. Fitted parameters of eqn (2) intercept, b/dm3 mol-1 flR,N+) T/"C DMSO HMPT slope, a vw 25 35 25 35 e 25 25 M 25 25 ref. (25) salt 35 0.448 (+0.010) - 0.405 (k0.012) - 0.509 ( f 0.027)" - 0.517 (+0.026)b - 0.458 ( f 0.009) - - 0.894 ( f 0.01 5) - 0.816 (k0.006) - 0.91 1 (f0.014) B(Br-)/dm3 molt1 0.481 ( f 0.002)c 0.45 1 ( f 0.004)c 0.732 ( f 0.006)d 0.678 ( f 0.006y 2.53 (f0.04) 2.43 ( f 0.05) 4.67 (f 0.06) 4.42 (f 0.03) 9.1 (f0.5) dm3 mol-l nm-3 8.2 (f 0.4) dm3 mol-l nm-3 1.83 (fO.03) x dm3 g-l 3.38 (k0.04) x dm3 g-l " Ref.(8); ref. (9); ref. (1); ref. (2). Error limits are standard errors on the fitted values except for the reference-salt method where the standard deviations on two independent results are shown. position is caused by the shape of this ion during the viscous-flow process in DMSO making a relatively smaller contribution to its B value [see ref. (l)] than that of the higher homologues. This would result from a more compact arrangement of the alkyl groups around the central nitrogen. The high position of the Hept,N+ point suggests that, because of the length of its alkyl chains, a more open or perhaps even semi-trailing configuration of the chains occurs creating a larger obstruction to the laminar flow process than occurs for the Bu,N+ to Hex," ions.The size, shape, polarity and void space of the solvent molecules may also play important roles here because, by contrast, the corresponding point for Hept,N+ in HMPT is collinear. The molar volumes of DMSO and HMPT are 71.3 and 175.7 cm3 mol-l, respectively, and the larger HMPT molecules probably allow less flexibility to the alkyl chains in the streamlines and restrict the number of configurations available to the cations in the series. We assume that the point for Pr4N+ in HMPT is high and out of line because of slightly enhancedK. G. LAWRENCE, R. T. M. BICKNELL, A. SACCO AND A.DELL'ATTI 1139 2.4 - 2 . 2 - 2.0 - 2 1 . 8 - E mE 1 . 6 - 4 -0 1 h 2 1 . 4 - 1 . 2 1 . o - 0.8 - z, - Q 0.6 Pr4 N+ Bu4N+ Pe4N+ Hex4N+ Hept4N* 100 150 200 250 300 V,,,/cm3 mol-' I I I 1 Fig. 1. Plot of B(R,NBr) as a function V,(R,N+) at 25 "C. (a) HMPT and (b) DMSO. attraction between this ion and the HMPT molecules, which are of comparable size to the ion itself. The experimental evidence to date for the reference-salt method of B-coefficient division is very convincing, and in the following discussion we shall assume that the B(Br-) values obtained in this way1? (shown in table 4) are essentially correct. Let us now examine very critically the intercepts shown in table 4. We notice first that in DMSO the intercept, 6, obtained using V , is smaller than the reference-salt value, whereas in HMPT the intercept is considerably larger. On the other hand the intercepts from extrapolation of rz in DMSO are larger than the B(Br-) value and the agreement is no better if we use molar weights, M , as the extrapolation property in eqn (2).The similarity of the Vw and M intercept values occurs because they are related functions. It is clear that the reason for these discrepancies is that none of the physical properties tested is the correct property to give 6 = B(Br-) and that the intercepts obtained have different physical meanings, which may not become apparent until we have a theoretical basis for the B coefficients. In other words, unless we choosef(R,N+) correctly, eqn (2) becomes B(R,NBr) = B(Br-) + a,V;(R,N+) & Ax] (3) where the subscript x indicates the incorrect property, Ax is a constant and identification of any of the b intercepts with a B(Br-) value is not justified. Conway et al.and PanckhurstlO critically discussed the intercepts obtained when the molar volumes of tetra-alkylammonium halides at infinite dilution are extrapolated as various functions of the cations and showed the importance of choosing a suitable extrapolation function in order to obtain the partial molar volume of the anion. Thompson et al. have also used various methods of estimating ionic B values, including extrapolations of cationic van der Waals volumes and cationic molar masses as well as reference salts for N-methylacetamidell and ethylene carbonate12 solutions. They also found that the various methods gave small but significantly different results without postulating reasons for the differences.38-21140 VISCOSITY B COEFFICIENTS If we are less critical in our comparison of the intercepts shown in table 4 with the reference-salt values, we see that any of the properties examined could be used to obtain an approximate B(Br-) value in DMSO with an estimated error of ca. kO.04 dm3 mol-l, but the same error is clearly not applicable to the HMPT results where +0.2 is more realistic. Another question that arises from the V, intercepts shown in table 4 in the light of eqn (2) and (3) is why do we obtain b < B(Br-) in DMSO whereas b > B(Br-) in HMPT? We believe that these differences in behaviour between DMSO and HMPT are, at least in part, connected with the molar volumes of the so1vents13 but may also include contributions from other factors associated with the solvent.We therefore conclude that an extrapolation method for obtaining ionic B values based on measurements of a series of tetra-alkylammonium salts using van der Waals volumes, molar weights or Stokes radii can give anionic B values of very uncertain accuracy from one solvent to another; values of high precision are best obtained using the reference-salt method. We thank the referees for their courteous criticism and helpful comments. K. G. Lawrence and A. Sacco, J. Chem. SOC., Faraday Trans. I, 1983, 79, 614. * A. Sacco, M. D. Monica, A. D. Giglio and K. G. Lawrence, J. Chem. SOC., Faraday Trans. 1, 1983, 79, 2631. A. Sacco, A. D. Giglio, A. Dell’Atti and K. G. Lawrence, Z. Phys. Chem. (Neue Folge), 1983, 136, 145. B. E. Conway, R. E. Verrall and J. E. Desnoyers, Trans. Faraday SOC., 1966, 62, 2738. B. E. Conway, J. Solution Chem., 1978, 7 , 721. B. S . Krumgalz, J. Chem. SOC., Faraday Trans. I, 1980, 76, 1275. F. J. Millero, in Water and Aqueous Solutions, ed. R. A. Home (Wiley-Interscience, New York, 1972), chap. 3. R. Gopal and J. S . Jha, J. Phys. Chem., 1974,78, 2405. D. E. Arrington and E. Griswold, J. Phys. Chem., 1970, 74, 123. J . Phys. Chem., 3035. lo B. E. Conway, J. E. Desnoyers and R. E. Verrall, J. Phys. Chem., 1971,75,3031; M. H. Panckhurst, l1 P. T. Thompson, M. Durbana, J. L. Turner and R. H. Wood, J. Solution Chem., 1980, 9, 955. l2 P. T. Thompson, B. Fisher and R. H. Wood, J. Solution Chem., 1982, 11, 1. l3 D. Feakins, D. J. Freemantle and K. G. Lawrence, J. Chem. SOC., Faraday Trans. I, 1974, 70, 795. l4 J-C. Bollinger, T. Yvernault, J-Y. Gal and F. Persin, Can. J. Chem., 1976, 54, 3060. (PAPER 4/801)

ISSN:0300-9599    

DOI:10.1039/F19858101133

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

J. Chem. SOC., Furaday Trans. 1, 1985,81, 1141-1 151 Cryoscopic, Infrared Spectroscopic and Dielectric Studies of Associated Cyclohexanol + Benzene Mixtures BY SPELA PALJK, CVETO KLOFUTAR* AND DARJA RUDAN-TASIC ' J. Stefan' Institute, ' E. Kardelj ' University of Ljubljana, 61000 Ljubljana, Yugoslavia Received 18th June, 1984 The practical osmotic coefficients and molal activity coefficients of benzene solutions of cyclohexanol over the concentration range 0.02-0.27 mol kg-' have been determined by the cryoscopic method and infrared spectra of the systems investigated have been recorded in the OH stretching vibration region at 303.65 K. The non-ideal behaviour of the system has been interpreted by the excess Gibbs free energy and on the basis of an associated model including an extended series of multimers.The formation of oligomeric species has been described in term of one independent parameter, i.e. the constant K, which is equal to the stepwise association constants and is related to the self-association constant by p, = K(Q-l). From experimental data obtained by the cryoscopic method, the constant K and the concentration of monomer at the lowest concentration studied have been determined by a curve-fitting method, while the concentration of monomer at any definite concentration has been obtained using Bjerrum's integral. From i.r. measurements the fractions of monomer have been obtained for the con- centration range studied, and thus the integrated band area of the free OH band of the cyclohexanol monomer has been obtained graphically. In the case of i.r.measurements, the constant K has also been obtained by a curve fitting method. The partial molar volumes, partial molar refraction, partial molar polarization and the apparent dipole moment of cyclohexanol in benzene have been determined at 298.15 K and found to be independent of concentration up to 1.30 mol kg-l. The negative solvent effect on the dipole moment of the cyclohexanol molecule in benzene has been elucidated using Higasi's approach. The formation of various oligomeric species of alcohol dissolved in non-polar solvent has been the subject of many investigations, and it has been proposed that at extremely high dilution only the monomers of alcohol molecules exist, while with increasing concentration higher hydrogen-bonded oligomeric species are formed.The nature of the solvent plays an important role [see ref. (l)] in this process. The present work concerns the colligative as well as the i.r. spectroscopic, volumetric and dielectric properties of dilute benzene solutions of cyclohexanol with the aim of elucidating the effects of an aromatic non-polar solvent on the association of cyclohexanol molecules as well as on the dipole moment of the cyclohexanol molecule. EXPERIMENTAL Benzene (Riedel de Haen) was purified as in ref. (2) and cyclohexanol (Riedel de Haen) was dried over anhydrous calcium chloride, purified by vacuum distillation and stored over 0.4 nm molecular sieve in a closed container. Density measurements were performed at 298.15 0.05 K using a digital densimeter of type DMA 10 as previously de~cribed.~ Electric-permittivity measurements were performed at 298.15k0.05 K with a WTW dipole meter (model DM 01), using a DFL 1 cell at a constant frequency of 2 MHz.* Refractive indices were measured at 298.15+0.05 K with a Carl Zeiss 11411142 PROPERTIES OF CYCLOHEXANOL + BENZENE MIXTURES Abbe refractometer ( 3 2 4 110 e) at the wavelength of the yellow sodium line.Cryoscopic measurements were performed as in ref. (5). 1.r. measurements were performed at 303.65 f 0.5 K on a Carl Zeiss UR-20 double-beam i.r. spectrophotometer in the range 3200-3800 cm-' with Irtran I1 cells. RESULTS AND DISCUSSION The practical osmotic coefficient, 4, defined by In a, = -mM4 (1) where a, is the activity of the solvent, m (mol kg-l) is the stoichiometric molality and M , (kg mol-l) is the molar mass of the solvent, was calculated at the freezing point of benzene, B(K), via5 where Ar = rT -re@) is the difference of the thermistor resistances at the temperature of the freezing point of the solution, T(K), and of the pure solvent, respectively, and Kcry is a constant.The values of the practical osmotic coefficient of benzene solutions of cyclohexanol at the freezing point of benzene were fitted into a simple rational functions (see 1+A,m 4=- 1+A,rn (3) where A , and A , are empirical constants. The curve in fig. 1 was drawn on the basis of eqn (3) using the constants A , = -0.237 k0.004 mol-1 kg and A , = 0.940_+0.005 mol-1 kg, obtained by the method of least squares. The standard error of the estimate, s, is 0.01.The values of molal activity coefficient of the solute, y,, at the freezing point of benzene were calculated using Bjerrum's equation' in the form The non-ideal behaviour of the system was characterized by the excess Gibbs free energy, Gex(J kg-l),* at the freezing point of benzene: +- (In ( 1 + A , m) + ____ )]. ( 5 ) Gex = mRT[ ( A , - A , ) 4 4 , 1 + A , m A2 1+A,m In fig. 2 the dependence of Gex on m is shown. The values of Gex lie between - 1.0 J kg-1 (rn = 0.0225 mol kg-l) and - 178.0 J kg-l (m = 0.2710 mol kg-l). The non-ideality of the system was considered to be a consequence of the association of the solute molecules. However, the individual molecular species are assumed to behave i d e a l l ~ . ~ The formation of oligomeric species was described in terms of one independent parameter only, i.e.the constant K. In this case, the values of the step- wise association constant, &, for the successive association reactions B(,-,)+B+B,; q 3 2 (6) where B, B(q-l) and B, denote the mono-, ( q - 1)- and q-meric species of the solute, respectively, are all identical and equal to the constant K :5. PALJK, C. KLOFUTAR AND D. RUDAN-TASIC 1143 0.70 I I 1 I I 0.050 0)OO 0,150 0.200 0.250 rnlmol kg-' Fig. 1. Concentration dependence of the practical osmotic coefficients of benzene solutions of cyclohexanol at the freezing point of benzene. 0 - 40 - '00 -80 Y c, --.. x d -120 - 160 1 1 I I - 0.055 0.110 0.165 0.220 rn/mol kg-' Fig. 2. Concentration dependence of the excess Gibbs free energy of benzene solutions of cyclohexanol at the freezing point of benzene.where the brackets denote the molalities of the species indicated, b is the molality of the free monomer of the solute and /? is the self-association constant. For the self-associa ti on reaction qB + €3,; q 2 2 (8)1144 PROPERTIES OF CYCLOHEXANOL + BENZENE MIXTURES the self-association constant pq is related to the constant K by Considering the adopted model, the stoichiometric molality and the sum of the molalities of solute species present, m,, are given by and Since for an ideal associated solution the practical osmotic coefficient can be considered equal to m,/m,l0 for the association model used, from eqn (10) and (1 1) and for K2 b2 < 1, a simple relation between 0, K and b results: # = 1-Kb.(12) The molality of free monomer at a definite concentration was calculated as in ref. (5). Bjerrum’s integral I was evaluated analytically, expressing the ratio m,/m by mr m i-0 - = E C,(log mr)i. The values of the regression coefficients, obtained by the method of least squares, are : Co = 0.326f0.027, C, = -0.786+0.051 and C, = -0.237f0.022. To obtain the parameters for a description of the association processes occurring in the system investigated, the primary experimental data were analysed by a curve-fitting method.ll The experimental plots of log L = log m-log 1 and log A = log m,-log I against log I were compared with the normalized curves of log L (log I ) and log A (log f) for L = (1 - I)-,, A = (1 - 4-l and I = lb, K, where b, is the free monomer concentration at the lowest molality studied.The normalized curves log L (log I ) and log A (log I ) superimposed on the experimental data log L (log I ) and log A (log I ) for the system are shown in fig. 3. The values of b, = 0.021 mol kg-l and K = 1.42f0.05 mol-l kg were calculated from log L - log L = -log b, log A-log A = -log b, (14) (15) (16) log I - log I = log b, + log K. The values of the left-hand side of eqn (14)-( 16) were obtained from the coordinates of experimental and normalized plots in the position of the best fit. The relevance of the adopted model was confirmed by recalculating the primary data of m and m, using the values determined for b, and K in eqn (1 1) and (1 2) with the first ten terms. The experimental and recalculated values agree within the range (1-2) x mol kg-l.In fig. 4 the distribution diagram of monomeric and dominant oligomeric species of cyclohexanol in benzene solutions at the freezing point of benzene are given. To confirm the adopted model of the association of cyclohexanol in benzene, i.r. measurements were performed. The i.r. spectra were recorded at 303.65 K in the 3200-3800 cm-l range, i.e. in the OH stretching vibration region. In calculations, ideal behaviour of the system was anticipated as was that the absorption band occurring5. PALJK, c. KLOFUTAR AND D. RUDAN-TASIC 1145 -1.500 < C 9 9 8 8 4 4 w w -1.600 419 M M .. .. & I - b ) e ) - 1,700 1 I I y t 0.200 .p' ' 0,100 ' 0.000 - 1,500 - 1.000 - 0.500 '-- I I 1 I 0.000 0:500 inner: log 1 outer: log I 1 .boo Fig. 3.Normalized curves log L (log f ) and log A (log f ) superimposed on the experimental data (0) log L (log r) and (0) log A (log r) for cyclohexanol+ benzene solutions at the freezing point of benzene. 100 0 90 0 80 0 70 q [ B q l 0 60 0 50 0 40 0 30 0 20 0 10 m I I I I I 0 050 0 100 0.150 0.200 0.250 rnlmol kg-' Fig. 4. Distribution of the dominant oligomeric species together with the monomeric species of cyclohexanol + benzene solutions at the freezing point of benzene.1146 PROPERTIES OF CYCLOHEXANOL + BENZENE MIXTURES at the highest frequency, centred at 3605f3 cm-l, results from the OH bond uninfluenced by hydrogen bonding among solute molecules. As the position of this band was found to be independent of concentration, the concentration of end-of-chain OH bonds could be neglected.12 The band of the free OH group was found to be unsymmetrical, as was observed previously for cyclohexanol.The non-symmetry of this band can be ascribed to the conformationally heterogeneous equatorial epimers of the hydroxy group in cyclohexanol molecules. An equatorial hydroxy is more affected by solvent molecules through hydrogen bonds than an axial one. The equatorial conformation of a cyclohexanol molecule is, therefore, more ~tab1e.l~ The position of the free OH band is fairly sensitive to the nature of the solvent. For example, the position of the free OH band of cyclohexanol in benzene is shifted by ca. 20-30 cm-l relative to the location of this band in cyclohexane14 or carbon tetrach10ride.l~ The position of the broad absorption band, the peak of which was centred at 3495 & 5 cm-l, was also found to be independent of concentration.This broad band, which is absent at higher dilution, could be ascribed to the OH group involved in hydrogen bonding between solute molecules forming open dimers.16 In the system studied, the absorption band at lowest frequency (ca. 3350 cm-l), which is attributed to higher oligomeric species, was not observed. Since no significant difference has been reported for the band area of epimers,13 the integrated band area was taken into account instead of the absorption at v, for interpretation of i.r. spectra. The apparent integrated absorption intensity, A , of a band in the frequency region from v' to vN can be given by17 A = J,: log (f), dv = J: E, dv (17) where c (mol dm-3) is the concentration of solute, I (cm) is the cell thickness, and T are the apparent intensities of the incident and transmitted radiation and E , is the molar absorptivity of solute species at frequency v .For an association system in which the free monomer absorbs light in the specified wavelength region, from eqn (1 7) we obtain a3 D = Jv: log ($)v dv = c, I Jz E , , ~ dv = ( c - g--2 C gc, ) q v : E l , " dv (18) where el," is the molar absorptivity of solute monomer at frequency v and cq (mol dm-3) is the concentration of q-meric species of the solute. The value for D was obtained by graphical integration of the free OH band in the range from v' = 3550 to vN = 3670 cm-l. The relation between D and c was found as D = a,c+a,c2 (19) where a, and a2 are regression coefficients.The values of a, = 146f2 and a, = - 84 10 were calculated by the method of least squares. The standard error of the estimate, s, is 0.4. Fig. 5 shows the dependence of D on c. The curve in fig. 5 was drawn on the basis of eqn (19), using the values of the regression coefficients a, and a2. The limit of the derivative dD/dc, when c -+ 0, gives dD lim - = I jv: el," dv = a,. c-0 dcS. PALJK, c. KLOFWTAR AND D. RUDAN-TASIC 1147 c/mol dm-3 Fig. 5. Concentration dependence of D [eqn (19)] at 303.65 K. Thus, the fraction of monomer, a, = c,/c, for the system investigated depends linearly on the molar concentration of the solute: a2 c =I+-. D a, = el Jv: E , , ~ dv a, As the fraction of monomer is independent of the concentration units used, the free monomer concentration, b (mol kg-l), at a definite concentration was obtained as b = alm.For the adopted model, from eqn (10) it follows that (22) m a - = I= qK(q-1) b(Q-1). b 9-1 In the case when P b 2 < 1, the sum in eqn (22) can be given by m b = (1 - Kb)-2. - Eqn (23), normalized with b = Kb, is given byll m - = (1 - b)-2. b (24) The values of m/b = l / a , for the system investigated as a function of log b are plotted in fig. 6. The experimental plot l/al (log b) was superimposed on the normalized plot l/al (log 6). From the difference of the abscissa values of these experimental and1148 PROPERTIES OF CYCLOHEXANOL -k BENZENE MIXTURES I I I I I I -;?so0 -2000 - t 500 -1.1 - 2.000 - 1.500 -1.000 I I I inner: log b outer: log b Fig.6. Normalized curve l/al (log b) superimposed on the experimental data l/al (log b) for cyclohexanol + benzene solutions at 303.65 K. normalized plots in the position of the best fit, the value K = 0.34 f 0.04 mol-l kg was found from (25) log b-log b = log K. The limit of error was found by permissible displacement of the experimental and normalized plots along the abscissa. From the values of the constant K, determined at the freezing point of benzene and 303.65 K, an approximate value of - 39.7 kJ mol-l was calculated via the van’t Hoff relation for the enthalpy change accompanying the stepwise association reactions of cyclohexanol in benzene solutions. The value obtained is close to the enthalpy change for hydrogen bonding of alcohol molecules in non-polar solvents.ls~ l9 For further insight into this associated system, the volumetric and dielectric properties of benzene solutions of cyclohexanol up to 1 .O mol dm-3 were investigated at 298.15 K. The values of the density, dl, (kg dm-3), electric permittivity, E ~ , ~ , and refractive index, n,, 2, were found to be linearly dependent on solute concentration, c (mol dm-3).The above quantities at infinite dilution, d: = 0.8734 f 0.0003 kg dmY3, E: = 2.273 0.003 and ny = 1.4979 0.0001, obtained by the method of least squares, are close to those for pure benzene,20 while the values of the slopes of the respective straight lines are 0.0055 fO.0001 for the density, 0.386f0.005 for the electric permittivity and - 0.0049 0.0001 for the refractive index. The molar polarization, e, (dm3 mol-l), and molar volume, K, (dm3 mol-l), of the system investigated, calculated from eqn (6)4 and (7),* respectively, and the molar refraction, Rl, (dm3 mol-l), from eqn (3),21 were linearly dependent on the mole fraction of the solute.Therefore, the respective partial molar quantities of solvent and solute are independent of concentration and equal to their values at infinite dilution. The partial molar quantities of solvent and solute were obtained using eqn (4).21 The calculated values of = 0.08944+0.00001 dm3 mol-l, = 0.0262f0.00001 dm3 mol-1 at infinite dilution are, within experimental error, equal to the respective molar quantities for = 0.02672+0.00003 dm3 mol-1 and3. PALJK, c. KLOFUTAR AND D. RUDAN-TASIC 2.800 T 2.100 E a - 5 1.400 --.4 1 I I I 1149 0.200 0.400 0.600 0,800 c/mol dm-’ Fig. 7. Experimental values of the quantity D as a function of the concentration of cyclohexanol +benzene at 298.15 K. pure benzene.20 The values of the partial molar quantities of the solute at infinite dilution are = 0.090 3 1 f 0.000 56 dm3 mol-l and = 0.02929+0.00002 dm3 mol-l. For a cyclohexanol molecule in benzene solution, a value for the apparent dipole moment pi of 5.63 x 1 OP3O C m( 1.69 D) at infinite dilution and 298.15 K was obtained using eqn (1 7).22 In calculations, the deformation polarization of solute at infinite dilution, E,.d, was taken as 1.10 x z. The apparent dipole moment of cyclohexanol at infinite dilution was equal to the apparent dipole moment of cyclohexanol in the concentration range studied.= 0.108 35 f 0.00007 dm3 mol-l, The Onsager treatment of electric-permittivity data for liquid mixtures leads where I;s and are the actual concentrations (mol dm-3) of solvent in the solution and in the pure solvent, respectively, and N is Avogadro’s number. For a multicomponent system in which the internal refractive index of all the dissolved species may be considered to be equal to the refractive index nle2 of the solution for the D line of sodium, the following relation is valid where pq is the apparent dipole moment of a solute species q. For the system investigated the concentration dependence of D is given in fig. 7. As can be seen, this dependence is linear over the concentration range studied. Thus, it may be concluded that the apparent dipole moments of the solute species can be related by1150 PROPERTIES OF CYCLOHEXANOL + BENZENE MIXTURES Furthermore, the experimental function s2 is constant and equal to &.The obtained value of & is 3.49 x thus p1 = 5.91 x C2 m2 (3.13 D2); C m (1.77 D). In addition, for the proposed association model, the function Q can be given by where g, is defined as g, = q = 1,2, 3, . . . andg, = 1. From eqn (28) it follows that the correlation coefficients g, for dimers, trimers etc. are one in the system investigated. The effect of solvent on the dipole moment of the cyclohexanol molecule was elucidated following Higasi's 25 Approximate values for the major semi-axis of a = 3.9 x cm for the cyclohexanol molecule were evaluated from its molecular where it was postulated that the OH group occupies an equatorial position and that the point dipole is located on the major axis at a distance of a, = 5.9 x cm from one end of the diameter and that a, is 1.9 x On the basis of the above molecular parameters, the solvent effect was calculated cm and for the minor semi-axis of c = 2.5 x cm from the other end, i.e.2a = a, +a,. using24 &- I- 1+3A(%) E O - 1 PQ 8; + where pi is the dipole moment of the cyclohexanol molecule in the vapour phase and A = (A,+ B,)/2. For calculations of A, and B, the following relations were used: and a, +(a; - c2)i)] -- I C 3 (33) (34) Thus, the value of A = -0.065 was found. From the relation &/pi = 0.94, it may be concluded that a negative solvent effect occurs in the case of cyclohexanol in benzene, i.e.the dipole moment of the cyclohexanol molecule in the vapour phase is higher than in solution. From the results obtained by cryoscopic and i.r. investigations it may be concluded that the extent and degree of association of the cyclohexanol molecule in benzene are depressed by the interactions of the OH proton of the cyclohexanol molecule with 7~ electrons of the aromatic system of the benzene molecule and that the solute-solvent interactions are different in various solvents.'. 149 l5 The concentration independence of the apparent dipole moment of cyclohexanol in benzene might suggest the formation of linear oligomeric species. Also, the evidence of thermodynamic and spectroscopic studies of dilute solutions of alcohols in aromatic3.PALJK, c. KLOFUTAR AND D. RUDAN-TASIC 1151 solvents shows that the ratio of cyclic to open-chain oligomeric species is neg1igible.l The reported dielectric measurements lead to the conclusion that there are no preferential orientations between dipoles in oligomeric species. In addition, the negative effect of the solvent upon the dipole moment of the cyclohexanol molecule in benzene was estimated assuming the cyclohexanol molecule to be composed of two ellipsoids of rotation with a common symmetry axis and with a dipole along the common axis and not at the centre of the m o l e c ~ l e . ~ ~ ~ 25 We thank Mrs J. Burger for her skilful technical assistance and the Slovene Research Community, Ljubljana and the National Science Foundation, Washington D.C. for financial support.R. H. Stokes, Chem. Soc. Rev., 1982, 11, 257. J. H. Richards and S. Walker, Trans. Faraday Soc., 1961, 57, 399. C. Klofutar, s. Paljk and D. Kremser, J. Inorg. Nucl. Chem., 1975, 37, 1729. C. Klofutar and s. Paljk, J. Chem. Soc., Faraday Trans. I , 1983, 79,2377. C. Klofutar and s. Paljk, J. Chem. Soc., Faraday Trans. I , 1981, 77, 2705. N. H. Sagert and D. W. P. Lau, Can. J. Chem., 1982,60,2755. E. A. Guggenheim and R. H. Stokes, Equilibrium Properties of Aqueous Solutions of Single Strong Electrolytes, in The International Encyclopedia of Physical Chemistry and Chemical Physics, ed. D. D. Eley, J. E. Mayer and F. C. Tompkins (Pergamon Press, Oxford, 1969), p. 10. H. L. Friedman, Ionic Solution Theory, in Monographs in Statistical Physics and Thermodynamics, ed. I. Prigogine (Wiley, New York, 1962), vol. 3, p. 195. I. Prigogine and R. Defay, Chemische Thermodynamic (VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig, 1962), pp. 401 and 428. lo H. Buchowski, J. Phys. Chem., 1969,73, 3520. l1 F. J. C. Rossotti and H. Rossotti, J. Phys. Chem., 1961, 65, 926. l2 H. C. Van Ness, J. Van Winkle, H. H. Richtol and H. B. Hollinger, J. Phys. Chem., 1967, 71, 1483. l 3 H. S. Aaron, C. P. Ferguson and C. P. Rader, J. Am. Chem. Soc., 1967, 89, 1431. l4 M. Naray and J. Liszi, Acta Chim. Acad. Sci. Hung., 1974, 81, 1. l5 W. Masschelein, Spectrochim. Acta, 1962, 18, 1557. l6 C. Campbell, G. Brink and L. Glasser, J. Phys. Chem., 1976, 80, 686. D. A. Ramsay, J. Am. Chem. SOC., 1952, 74, 72. W. Weltner and K. S. Pitzer, J. Am. Chem. Soc., 1951, 73, 2606. p. 114. 1970), vol. 11, p. 107. l9 S. N. Vinogradov and R. H. Linnell, Hydrogen Bonding (Van Nostrand Reinhold, New York, 1971), 2o J. A. Riddick and W. B. Bunger, in Techniques of Chemistry, ed. A. Weisberger (Wiley, New York, ** s. Paljk, C. Klofutar and M. Lubej, J. Chem. Soc., Faraduy Trans. I , 1984,80, 1957. 22 W. J. Taylor, J. Phys. Chem., 1975, 79, 1817. 23 P. L. Huyskens, Croat. Chem. Acta, 1982, 55, 55. 24 K. Higasi, Sci. Pap. Inst. Phys. Chem. Res. (Jpn), 1936, 28, 284. 25 N. E. Hill, W. E. Vaughan, A. H. Price and M. Davies, Dielectric Properties and Molecular Behaviour 26 Framework Molecular Models (Prentice-Hall, Englewood Cliffs N.J., 1977). (Van Nostrand Reinhold, London, 1969), p. 253. (PAPER 41 1035)

ISSN:0300-9599    

DOI:10.1039/F19858101141

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

J . Chem. SOC., Faraday Trans. 1, 1985, 81, 1153-1159 The Electronic Factor for Outer-sphere Electron-transfer Reactions BY ERNST D. GERMAN Institute of Electrochemistry, Academy of Sciences of the U.S.S.R., 3 1 Leninsky Prospect, 117071 Moscow, U.S.S.R. Received 18th June, 1984 Electronic matrix elements L have been estimated for symmetrical electon-transfer reactions between transition-metal complexes, based on an analysis of the experimental data in terms of the theory of non-adiabatic transitions. The rate constants calculated using the values of L thus obtained and the cross-relationship for the matrix elements agree well with the experimental data for a wide range of cross electron-transfer reactions. Over the last decade the theory of non-adiabatic electron-transfer (e.t.) reactions in polar media has become widely used when considering redox systems.Theoretical methods1-' for calculating the rate constants of e.t. reactions have led to the following results. If e.t. occurs between two complex ions AL> and BL? in solvent S its rate constant can be written as118 where AF* = @(A& + Up - U,) + AFb*,(8) + AFZ(8) and K , is the electronic transmission coefficient: K , fiWeff - - 2;n(L/kq2 (2nkT/ I a2AF*/a02 1); (3) kT where L is the electronic matrix element (resonance integral). The symmetry factor 8 can be determined by solving the equation A& + Up - U, + aAF,*,(O)/aO + aAFZ(O)/aO = 0. (4) Other symbols in eqn (1)-(3) are as follows: LOeff is the effective nuclear frequency (ca. 6 x 1013 s-l for reactions in water8), U, and Up are work terms for bringing the reactants together and for separating the products, respectively, and A& is the free e_nergy of the reaction. The reaction volume Su is given by ~ X ( R ) ~ SRN/ 1000, where R is the effective distance between the metal ions (in A), which is approximately equal to the sum of van der Waals radii of interacting complexes, SR is the thickness of the reaction layer and N is Avogadro's constant.11531154 OUTER-SPHERE ELECTRON-TRANSFER REACTIONS The outer- and inner-sphere contributions to the free activation energy, AF,*, and AFZ, are given by AFG = a,(@ E, ( 5 ) where @,(@ is a function of the dielectric properties of a solvent and and bB(0) are functions of the frequencies of the normal vibrations of complexes.However, we are mainly concerned with the electronic matrix element L. Numerical computation of the value of L is the most labour intensive way of comparing theory with experiment, especially if e.t. between complex ions is considered. Although quantum-mechanical calculations of L have been carried out for several redox ~ystems,~-ll the results should be treated with care because of the lack of precision of the methods used and because of the neglect of such important effects as modulation of the electronic wavefunctions by a fluctuating phonone field induced by a medium and the ligands. In general, the vibrations of dipoles of a medium and ligands have an important effect on the matrix element. As shown previously,12v13 inclusion of the effect increases L as compared to its gas-phase value.Thus it is reasonable to obtain an estimate of the matrix elements L based on analysis of the experimental data, including using the simple relationship between the vzlues of L for symmetrical and cross e.t. reactions. RESULTS CROSS-RELATIONSHIP BETWEEN THE MATRIX ELEMENTS If it is assumed that e.t. between complex ions follows the Hush me~hanism,~ i.e. involves the ligand orbitals, then in many cases the main contribution to L might be thought to come from the overlap of the wavefunctions of contacting ligand atoms. In other words, if the outer molecular orbitals of the transferable electrons of an oxidant and reductant are where cto and cjLR are the coefficients of the molecular orbitals ryox and ryred at atomic orbitals of the ith andjth contacting ligand atoms and K is the resonance integral between the atomic orbitals.Thus the 1s orbital of a terminal H atom or the 2p orbitals of N or 0 atoms of a contacting ligand (e.g. NH,, H20, en or phen) may provide the atomic functions. For the complexes considered below, the integral K characterizes the exchange interaction between identical or related atoms, and it is assumed that it is approximately constant. The characteristics of the individual ligands (aromatic, ammine or aqua and different amounts of metal-to-ligand and ligand- to-metal charge transfer) are taken into account in the coefficients cko and ctR at the interacting atoms, which are different for different complexes. Hence, the electron densities on the neighbouring atoms of ligands of both complexes play leading roles in this model.After making the assumption about the constancy of the integral K,E. D. GERMAN 1155 Table 1. Outer-sphere reorganization energies E, and other parameters for redox couples A(L1)2/B(L2)2" complexes' distance ligands radii/A of charge transfer, Es U 6 V Ll L, A(Ll), B(L,), RIA /kcal mol-1 /kcal mol-l /dm3 mol-l aq, am aq, am 3.5 3.5 7.0 37 3.6 0.2 en en 4.4 4.4 8.8 29 2.9 0.3 phen, phen, bipy bipy 7.0 7.0 14 18 1.8 0.8 phen, aq,am biPY 7.0 3.5 10.5 30 2.5 0.5 en a?, am 4.4 3.5 7.9 33 3.2 0.25 a E, and U are given for reactions in H20 at 25 "C. For data see ref. (8) and (19). the following relationship between the molecular matrix elements can be obtained from eqn (8): where Lll, L,, and L,, are the matrix elements for symmetrical and cross-reactions. Eqn (9) has been proposed by Sutin,14 who proceeded from an expression for the transmission coefficient but did not consider the relationship between eqn (9) and the molecular structure of the complexes.VALUES OF KINETIC PARAMETERS FOR SYMMETRICAL (THERMONEUTRAL) REACTIONS In accordance with the above, the matrix elements L for symmetrical e.t. reactions were estimated by comparison of experimental rate constants (as extrapolated to zero ionic strength) with those obtained using eqn (1)-(6) with L as an adjustable parameters. The results depend upon the numerical values used in the expression for the rate constant, especially on the values of the reorganization energies and work terrns. L12 = (LllL22)~ (9) OUTER-SPHERE REORGANIZATION ENERGY, E, The values of E, are usually calculated using the Marcus model of conducting spheres,15 which is convenient because of its simplicity but seems inappropriate for complexes of complicated structure.Other models used to calculate E, consider two dielectric spheres and the ellipsoidal dielectric cavity.* The cavity model seems more suitable since it allows one to obtain an exact solution of an electrostatic problem and also appears to provide a more realistic description of the system of two contacting ions within a cage of solvent molecules. The values of Es (for reactions in water) obtained using this model are shown in table 1. The methods used in the calculation of E, and the choice of cavity dimensions are described in ref. (8) and (16).WORK TERM, U The values of U for complexes with charges z1 and z, in a cavity formed by solvent molecules were estimated from the equation U = z1 z ~ / E , ~ ~ R, where R is the distance between the central ions, equal to the sum of the effective radii of the reactants; its * For a review of models for calculating the outer-sphere reorganization energies see ref. ( 1 6).1156 OUTER-SPHERE ELECTRON-TRANSFER REACTIONS Table 2. Inner-sphere reorganization energies Er and electronic matrix elements L for redox couples A(L,)>/B(L,)~ a Er ML,(3 + /2 +) /kcal rnol-1 L/crn-I 2.8 4.4 7.5 1 .o 5.6 6.5 70 34 30 34 30 58 36 31 0 0 66 0 10 50 50 50 50 120 120 50 4 4 4 60 50 50 10 10 120 10 100 - a For data see ref. (8) and (19). values for different ligands are listed in table 1.Using the results for U from models,l7? l8 E , ~ ~ for e.t. reactions in water is taken as equal to E , ~ ; the values of complexes with charges 2 + and 3 + are given in table 1. other U for INNER-SPHERE REORGANIZATION ENERGY, E,. The values of the inner-sphere reorganization energies of the complexes were obtained from ref. (8) and (19), where for some complexes with unidentate ligands they were calculated using X-ray data and the frequencies of the normal vibrations, while for others were estimated indirectly. The values of E,. are listed in table 2 and vary from ca. 0 to ca. 70 kcal mol-l, depending on the complex. ELECTRONIC MATRIX ELEMENTS The electonic matrix elements L for symmetrical systems obtained from comparison of the theory with experiment are presented in the last column of table 2.These are the maximum values of L, from ref. ( I 6); the other models give smaller values of E, than the ellipsoidal cavity model. The values of IC, calculated using these values of L indicate that all the systems considered are non-adiabatic. For the weakly non-adiabatic systems [Ru(bipy)g+’z+ and Cr(H20)i+/2+] the value of IC, is 0.2-0.3. Strongly non-adiabatic systems [Co(bipy)g+/2+, Ru(en)g+j2+ and some others] have Note the values of the matrix elements for bipyridyl complexes of ruthenium, iron and cobalt. As seen from table 2, they decrease in the order: L(Ru) > L(Fe) > L(Co). K , = 10-4.E. D. GERMAN 1157 t This may be interpreted as a decrease, in this order, in the density of the transferable electron on the ligand of the complexes, in qualitative agreement with the result of an analysis20 of the intensities of the charge-transfer bands of Ru”, Fell and Co’ complexes.From the comparison of the matrix elements for ethylenediamine complexes of ruthenium and cobalt it follows that e.t. between ruthenium complexes is substantially more non-adiabatic than e. t. between the respective cobalt complexes (the value of L for the former reaction is ca. lo2 times less than that for the latter). In other words, the low rate of the e.t. between ethylenediamine complexes of cobalt is caused mainly by the high inner-sphere reorganization energy. Note also the comparison between the value of L for the Fe(H20)i+/2+ system1158 OUTER-SPHERE ELECTRON-TRANSFER REACTIONS (ca.50 cm-l) given in table 2 and the results of the non-empirical calculations of Newton,ll where the value of L is ca. 6 cm-l for the ‘face-to-face’ configuration, with the distance between iron ions being ca. 7 A. Such a discrepancy seems quite reasonable as the gas-phase calculations are likely to give a lower estimate of L. DISCUSSION The correlation between theoretical and experimental rate constants (as extrapolated to zero ionic strength) for cross e.t. reactions involving complexes with different ligands is shown in fig. 1. The theoretical values were calculated using the data in tables 1 and 2 and eqn (9). For the great majority of systems considered, the difference A = I log k, -log k, I does not exceed ca. 0.5 for a range of log k, extending across ca.15 units. Only in several cases (3, 20, 21, 24 and 34) is A x 1. This agreement between theory and experiment for a wide range of complexes allows one to suppose that the values of kinetic parameters given above are reasonable, lending support to the validity of the cross-relationship for matrix elements. The values of L given in table 2 for a number of systems are different from those reported earlier,21 since in the present work they have been corrected using all the kinetic data. Note that theoretical rate constants calculated using the tabulated values of L for symmetrical aqua-systems Fe3+/2+ and Cr3+/2+ are lower by ca. 1.8 orders of magnitude than the experimental values. However, if one uses the values of matrix elements giving agreement for the rate constants for the symmetrical redox systems Fe(H2O):+I2+ and CT(H~O);+/~+, then the calculated rate constants for all cross-systems involving aqua-complexes of Fe and Cr are different from the experimental values.Such an anomaly has already been reported21 for aqua-complexes of iron and has been interpreted as an indication that the mechanism of e.t. in the symmetrical Fe3+/2+ system is different from that in a cross-system involving aqua-complexes of iron. It is likely that the symmetrical Cr3+/2+ system also has a different mechanism of e.t. from that adopted in the theoretical consideration. However, the experimental data for this system should be reconsidered and possibly refined. Experimental information on the activation enthalpies could be important in judging the reliability of the quantitative estimates of the kinetic parameters of e.t.reactions. Unfortunately, the available data on AH1 cover a relatively narrow range of reactions, the ionic strength dependence of AH$ being obtained only in a few cases. This is unfortunate as the lack of this information makes comparison of theory and experiment impossible even on those rare occasions when AH$ was measured under conditions of non-zero ionic strength. Therefore, systematic measurements of AH$ as well as studies of its dependence on the ionic strength are required before a more detailed comparison of theory and experiment can be performed. Dr A. M. Kuznetsov is thanked for helpful discussions and critical remarks. R. R. Dogonadze and A. M. Kuznetsov, in Itogi Nauki i Techniki, Kinetika i Kafaliz (Viniti, Moscow, 1973), vol.5. J. Ulstrup, Charge Transfer Processes in Condensed Media (Springer-Verlag, Berlin, 1979). Sh. Efrima and M. Bixon, J . Chem. Phys., 1976, 64, 3639. N. E. Kestner, J. Logan and J. Jortner, J . Phys. Chem., 1974, 78, 2148. L. D. Zusman, Chem. Phys., 1983,80, 29. I. V. Alexandrov, Chem. Phys., 1980,51,449. N. S . Hush, Electrochim. Acta, 1968 13, 1005.E. D. GERMAN 1159 E. D. German and A. M. Kuznetsov, in Itogi Nauki i Techniki, Kinetika i Kataliz (Viniti, Moscow, 1982), vol. 10; E. D. German, Rev. Znorg. Chem., 1984, 5, 123. S. P. Dolin, R. R. Dogonadze and E. D. German, J. Chem. SOC., Faraday Trans. 1, 1977,72, 648. lo V. M. Berdnikov and G. A. Bogdanchikov, Zh. Fiz. Khim., 1979, 53, 273.l1 M. D. Newton, J. Chem. Phys., 1983,78,4086. l 2 A. M. Kuznetsov, Faraday Discuss. Chem. SOC., 1982, 74, 49. l3 A. M. Kuznetsov, Khim. Fiz., 1982, 1469. N. Sutin, Acc. Chem. Res., 1968, 1, 225. l5 R. A. Marcus, J. Chem. Phys., 1956, 24, 966. l6 E. D. German and A. M. Kuznetsov, Electrochim. Acta, 1981, 26, 1595. l 7 S. Levine and D. K. Rosenthal, in Chemical Physics of Ionic Solutions, ed. B. E. Conway, R. G. Barvadas (Wiley, New York, 1966). D. K. Ross, Aust. J. Phys., 1968, 21, 587. l9 E. D. German, Bull. Acad. Sci. USSR, Div. Chem. Sci., 1984,32, 1621; 1779; 2469; 33, 313. 2o S. F. Mason, Inorg. Chim. Acta Rev., 1968, 89. 21 J. T. Hupp and M. J. Weaver, Znorg. Chem., 1983, 22, 2557. 22 J. F. Endicott and H. Taube, J. Am. Chem. SOC., 1964, 86, 1684; Znorg.Chem., 1964, 4, 437. 23 P. V. Manning and R. C. Jarnagin, J. Phys. Chem., 1963,67, 2884. 24 T. Przystas and N. Sutin, J. Am. Chem. SOC., 1973,95, 5545. 25 A. Zwickel and H. Taube, J. Am. Chem. SOC., 1961,83, 793. 26 Ch. A. Jacks and L. E. Bennett, Inorg. Chem., 1974, 13, 2035. 27 W. Bottcher, G. Brown and N. Sutin, Inorg. Chem., 1979, 18, 1447. 28 M. Chou, C. Creutz and N. Sutin, J. Am. Chem. SOC., 1977,99, 5615. 29 A. Miralles, R. Armstrong and A. Haim, J. Am. Chem. Soc., 1977, 99, 1416. 30 R. G. Gaunder and H. Taube, Znorg. Chem., 1970,9, 2627. 31 G. Brown, H. Krentzien, M. Abe and H. Taube, Znorg. Chem., 1979, 18, 3374. 32 T. J. Meyer and H. Taube, Inorg. Chem., 1968,7, 2369. 33 A. Ekstrom, A. McLaren and L. Smythe, Znorg. Chem., 1976, 15, 2853. 34 M. Chou, C. Creutz and N. Sutin, J. Am. Chem. SOC., 1977, 99, 5615. 35 N. Sutin and A. Forman, J. Am. Chem. SOC., 1971,93, 5274. 36 J. Braddock and T. J. Meyer, J. Am. Chem. SOC., 1977, 95, 3158. 37 R. S. Young, F. R. Keene and T. J. Meyer, J. Am. Chem. SOC., 1977, 99, 2468. 38 A. Zwickel and H. Taube, Discuss. Faraday SOC., 1960, 29, 42. 39 Y. Narusawa, M. Kimura and K. Nakano, J. Chem. SOC. Jpn, 1974, 47, 2017. N. Serpone, M. A. Jamieson, S. Emmi, P. Fuochi, Q. Mullazani and M. Z. Hoffman, J. Am. Chem. SOC., 1981, 103, 1091. dl B. M. Gordon, L. L. Williams and N. Sutin, J. Am. Chem. SOC., 1961, 83, 2061. 42 G. M. Brown and N. Sutin, J. Am. Chem. SOC., 1979, 101, 883. 43 J. P. Candlin, J. Halpern and D. L. Trimm, J. Am. Chem. SOC., 1964,86, 1019. 44 J. K. Beattie, R. A. Binstead and M. Broccardo, Znorg. Chem., 1978, 17, 1882. 45 W. F. Prow, S. K. Garmestani and R. D. Farina, Znorg. Chem., 1981, 20, 1297. 46 R. D. Farina and R. G. Wilkins, Znorg. Chem., 1968, 7, 514. 47 R. Berkoff, K. Krist and H. Gafney, Znorg. Chem., 1980, 19, 1 . 48 N. D. Stalnaker, J. C. Solenberg and A. C. Wahl, J. Phys. Chem., 1977,81,601. 4g J. Holzwarth and H. Jiirgensen, Ber. Bunsenges. Phys. Chem., 1974, 78, 526. (PAPER 4/ 1036)

ISSN:0300-9599    

DOI:10.1039/F19858101153

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

J. Chern. Soc., Faraday Trans. I, 1985,81, 1161-1 166 Catalytic Properties of H Mordenite Modified with Fluorine BY KURT A. BECKER Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Grenzflachenreaktionen, Faradayweg 4-6, 1000 West Berlin 33, Dahlem AND STANSILAW KOWALAK* Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland Received 18th June, 1984 H mordenite has been modified using ammonium fluoride solutions and gaseous CHF,. During treatment, some of the acidic OH groups were substituted with fluorine and the acid strength of the remaining hydroxyls was enhanced because of the inductive effect of the fluorine. This was reflected in the higher catalytic activity of the samples for cumene cracking and the higher values of the heats of adsorption for ammonia.Fluorine, the most electro-negative element, is often used as a component or modifier of cata1ysts.l For example, the properties of fluorinated alumina have been Aneke et ~ 1 . ~ 9 * have studied a catalyst consisting of H-Y zeolite, /I-AlF, and Cu, and have found that the presence of fluoride resulted in an increase in the selectivity for toluene disproportionation, Lok et aL99 lo modified zeolites using F, gas, Araya and Dyerll have described the treatment of zeolites with molten fluorides and Sariev and c o w o r k e r ~ ~ ~ - ~ ~ have reported the modification of zeolite catalysts with diluted hydrofluoric acid, which usually increased the catalytic activity. Information concerning zeolite catalysts modified with fluorine can also be found in the patent literature.In our recent investigati~nsl~~ l6 we have dealt with the fluorinated aluminium- containing faujasite. The modified zeolite was more active than the parent A13+ form and sometimes more active than the H form. It is clear, however, that this system is not just a mixture of H zeolite and AlF, in the intracrystalline space and the presence of other Al-F species must also be considered. We believe that on the fluorination of H zeolites we would be able to obtain a less complicated system, in which OH groups would be substituted by fluorine. We have chosen to investigate H mordenite first because of its higher stability; work on H faujasite is in progress. EXPERIMENTAL Commercial H mordenite (Norton, lot 2) was used as the starting material. Its chemical composition (wt %) was as follows: SiO,, 86.14; Al,O,, 13.45; Na,O, 0.41; Si/A1, 5.43.The theoretical formula of the unit cell was H8(A102)8(SiOz)40 .mH20. A 0.1 mol dm-, aqueous solution of NH,F was used for the fluorination, which took place at room temperature in Teflon beakers. During this process the pH of the solution increased, as in the experiment of Breck and Skeels: e.g. after fluorination of sample HMF-2, the final pH of the solution was 5.3, whereas the pH of the suspension of H mordenite in water was 4.5. The samples were separated 11611162 CATALYTIC PROPERTIES OF F-MODIFIED H MORDENITE Table 1. Fluorination procedures and concentration of fluorine in mordenite samples fluorine content (% 1 sample fluorination conditions a b - HMF-0 - - HMF-1 0.43 8.1 HMF-2 0.56 10.1 HMF-3 0.76 14.4 HMF-4 0.80 15.1 HMF-5 1.20 22.7 HMF-G 0.25 4.7 5.0 g of zeolite, 100 cm3 of 0.1 mol dm-, NH,F solution, 20 h 5.0 g of zeolite, 100 cm3 of 0.1 mol dm-3 NH,F solution, 20 h, 5.0 g of zeolite, 500 cm3 of 0.1 mol dm-, NH,F solution, 100 cm3 10 g of zeolite, 500 cm3 of 0.3 mol dmP3 NH,F solution, 20 h 10 g of zeolite, 200 cm3 of 1.2 mol dm-, NH,F solution, 20 h 10 g of H mordenite calcined at 450 "C for 4 h in helium stream (100 cm3 min-l), then CHF, (10 cm3 min-l) added to the gas stream for 20 min, followed by heating in the helium stream for 20 min and finally cooling in the helium stream then 100 cm3 of the same solution for 20 h of NH,F solution changed every 12 h a Wt % of fluorine introduced to the mordenite sample; % of OH groups in zeolite substituted with fluorine.from the solution by centrifugation, dried without prior washing and finally calcined in air at 450 "C for 12 h. Residual NHt cations in the zeolite before calcination were detected by i.r. spectroscopy. The NH; band did not vanish after washing the sample, which means that some cation exchange occurs during fluorination. The method of gaseous fluorination, similar to that used by McVicker et for alumina reactions, was also used. The parameters for the fluorination process and the compositions of the modified samples are summarized in table 1. The amount of fluorine introduced to the mordenite was estimated using an ion-selective electrode. Fluoride anions were removed from the zeolite phase by alkaline hydrolysis with NaOH solution.The presence of aluminium in the solution after the fluorine treatment showed that some aluminium is removed from the mordenite framework. The crystallinity of the modified samples was examined by X-ray diffraction and compared with that of the original H mordenite. The catalytic activity of the modified samples was tested using the cumene cracking reaction. The pulse microreactor was attached directly to a gas chromatograph. The samples (0.01 g) were activated at 450 "C for 0.5 h before being tested. The cumene cracking reaction was carried out at 350 "C in a helium stream (100 cm3 min-l) and 0.5 mm3 pulses were used. Usually only dealkylation products were found in the mixture, but some propene deficiency was seen.The results of the catalytic tests are shown in fig. 1 and 2. Cumene cracking is a well known test for the presence of Brarnsted acid sites. The acid sites were investigated by microcalorimetric measurements of the differential heats of ammonia adsorption using a Calvet twin micro- calorimeter. The method is based on the assumption that the acid strength of active sites is reflected in the amount of the heat liberated by adsorption of a base on this site. The sample (ca. 1 g) was activated at 450 "C under vacuum Torr) for 12 h before measurements were made. Ammonia was then added stepwise in small increments to the sample. The amount of ammonia adsorbed was estimated for the calculation of the differential heats of adsorption. The heats of adsorption for the fluorinated sample are compared with those determined for the initial H mordenite in fig.3. 1.r. measurements were performed with a Perkin-Elmer model 180 spectrometer. The zeolite sample was compacted into an i.r.-transparent wafer and activated in a conventional vacuum cell at a pressure of Torr at 450 "C for 6 h. Pyridine vapour was adsorbed at roomK. A. BECKER AND S. KOWALAK 1163 80 70 $ 6 0 E .g 5 0 . 0, 5 4 0 . - 0 v c W c a2 $ 30 20 10 - - - \ \ I I I I I 0 2 1 6 8 10 pulse number 90 ao 70 n 60 * - ; v 1- 2 50 8 g 40 b W c W 2 30 20 10 0 5 10 1 I I I 1 5 10 15 20 25 OH substituted by F (%> Fig. 1. 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 fluorine content (wt %) Fig. 2. Fig. 1. Cumene conversion for selected samples as a function of pulse number: ., HMF-1; Fig.2. Correlation between fluorine content in the catalyst sample and cumene conversion. v, HMF-G; 0, HMF-0; +, HMF-5. temperature and then desorbed under vacuum at 250 "C for 3 h. 1.r. spectra in the region of the stretching vibrations of OH groups show some decrease in OH band intensity after introducing fluorine. More significant changes occurred in the intensities of the bands originating from the pyridinium ion (1540 cm-l), formed as a result of the interaction of pyridine with acidic hydroxyl groups, and from pyridine coordinatively bound to Lewis-acid centres (1450 cm-l). Results obtained from the i.r. spectroscopic measurements of the samples after chemisorption of pyridine are given in table 2, where the ratio of intensities of the bands at 1540 and 1450 cm-l is taken as a measure of the contribution of Br~rnsted- and Lewis-acid sites, respectively, to catalytic acidity.Such an approach is based on the fact that the ratio of the extinction coefficients of these bands is ca. 1.61164 CATALYTIC PROPERTIES OF F-MODIFIED H MORDENITE 170 - I - z 160- I? 150- 24 1 a 0 .- 140- 8 -0 L 130- z 120- 2 m c U E g 110 - U 100 - 90 - I 1 I I 1 I I I I 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 amount of ammonia adsorbed, nid /mmol g-' Fig. 3. Comparison of the differential heats of ammonia adsorption on H mordenite (--- and 0, HMF-0) and fluorine-modified H mordenite (- and 0, HMF-1). Table 2. Effect of fluorination of the Brsnsted-acid to Lewis-acid ratio ratio of the intensities of bands at 1540 sample and 1450 cm-l HMF-0 5.3 HMF-G 4.1 HMF- 1 2.7 HMF-4 2.0 HMF-5 1.6K.A. BECKER AND S. KOWALAK 1165 RESULTS AND DISCUSSION Both gaseous (using CHF,) and solution (with NH,F) methods of fluorination yield the fluorine modification without noticeably changing the crystallinity of the zeolite. Even concentrated NH,F solutions do not damage the mordenite structure. X-ray diffraction patterns were almost the same for the modified samples and the original H mordenite, with only small differences in intensity. Gas treatment was carried out at temperatures < 450 "C in order to avoid dehydroxylation. Fluorination experiments using NH,F were similar to the experiments of Breck and Skeels,17 who used KF solution to substitute OH groups in zeolite. They observed an increase in pH during this treatment and we have found the same tendency in our experiments.Breck and Skeels did not find any fluorine in the zeolite phase and suggested that it may be present as AlF, in the supernatant solution after fluoride treatment. However, we did find fluorine in the zeolite phase. Breck and Skeels discussed two possible schemes for the fluoride treatment: zeolite OH + F-(aq) + zeolite F + OH-(aq) (1) zeolite Al(OH)& + 3KF (aq) --+ AlF,(aq) + xK+zeolite + (3 - x)KOH(aq) (2) and have suggested that reaction (2) actually occurs. However, the presence of fluorine in our zeolite samples suggests reaction (1). The catalytic activity of fluorine-treated samples increases very sharply; the highest activity was found for samples containing up to 0.4 wt % fluorine, which would mean that ca.8% of the OH groups in the mordenite are substituted by fluorine. A further increase of fluorine content results in a decline of activity because of the decrease in the concentration of Brsnsted-acid sites. The sample richest in fluorine (> 15% of hydroxyl groups substituted by fluorine) was less active than the parent H mordenite. We suggest that the enhanced activity results from the inductive effect of fluorine on the acidity of adjacent hydroxyl groups. Introduction of fluorine reduces the absolute number of OH groups but increases the acid strength of those remaining. It is very likely that fluorine is localized preferentially in the channel sites and that after filling these sites it occupies less accessible positions. The reduced activity of the sample richest in fluorine can result from the deficiency of acid OH groups in the channel positions which are accessible to the cumene molecules (although the total number of OH groups is still high).The results of the microcalorimetric measurements corroborate the results of the catalytic tests. The 'heats of adsorption of ammonia at low surface coverage, particularly for the first adsorption step, are significantly higher for .;.he fluorinated sample (ca. 20 J g-l). This is clear evidence of the creation of stronger acid centres. The spectra confirm our conclusions concerning the substitution of hydroxyl groups with fluorine, since the intensity of the OH bands diminishes with increasing fluorine content. The i.r. spectra of samples covered with chemisorbed pyridine species show a decrease in the Brsnsted-acid to Lewis-acid ratio with increasing fluorine content in mordenite, which is further evidence of the substitution of OH groups (Brsnsted sites) with fluorine resulting in the formation of new Lewis sites (AlF, or other Al-F species).The nature of the fluorine inductive effect is probably the same as it is in fluorinated alumina. The protonic acidity of the alumina hydroxyl groups is very weak, but after partial substitution with fluorine quite strong Brsnsted acidity was l9 In the case of H mordenite, protonic centres already exist, but their strength is increased by fluorine. Because some of the hydroxyl groups in mordenite can be combined with A11166 CATALYTIC PROPERTIES OF F-MODIFIED H MORDENITE cationsz0 it is very likely that after the reaction with fluorine-containing compounds, AlF, or other Al-F species can remain inside the zeolite structure.Therefore the contribution of the hydroxo-aluminium cations to the catalytic activity should be increased by the influence of fluorine. In recent investigations we have studied the A1 form of faujasite modified with fluorine.l5?l6 The catalytic activity of the A1 form was increased after fluorination. If the supposition of Breck and Skeels17 concerning the role of the hydroxo-aluminium cations in the catalytic activity is correct, then the activity of the A1 form should be comparable to that of the H form. In our experiments the activity of the A1Y form is similar to that of the hydrogen form after fluorination.Thus the strength of the hydroxyl groups combined with A1 cations is lower than that of framework OH groups, and we conclude that fluorine is a very effective agent for the modification of zeolitic catalysts for acid-catalysed reactions. reactions . Substitution of the framework OH groups by fluorine is probably the main reaction during the fluorination of H mordenite. However, other reactions, such as cation exchange, dealumination and reactions of fluorine with Al-bearing cations, should also be taken into consideration. We thank Mrs U. Kockeritz and Mr W. Kollmitt for their assistance with the experiments and Dr J. Klinowski, University of Cambridge for his critical reading and helpful discussion of the manuscript. V. R. Choudhary, Znd. Eng. Chem. Prod. Res.Dev., 1977, 16, 12. T. V. Antipina, 0. V. Bulgakov and A. V. Uvarov, in Proc. 4th Znt. Congr. Catal. (Akademiai Kiad6, Budapest, 1971), vol. 2, p. 306. H. J. Reitsma and C. Boelhouwer, J. Catal., 1974, 33, 39. R. Covini, V. Fattore and N. Giordano, J. Catal., 1967, 9, 315. V. C. F. Holm and A. Clark, J. Catal., 1967, 8, 286. F. P. J. M. Kerkhof, J. C. Oudejeans, J. A. Moulijn and E. R. A. Matulewicz, J. Colloid Interface Sci., 1980, 77, 120. L. E. Aneke, L. A. Gerritsen, P. J. van der Berg and W. A. de Jong, J. Catal., 1979, 59, 26. L. E. Aneke, L. A. Gerritsen, J. Eilers and R. Trian, J. Catal., 1979, 59, 37. B. M. Lok and T. P. J. Izod, Zeolites, 1982, 2, 66. 218, 41. A. Araya and A. Dyer, Zeolites, 1981, 1, 35. Sofia, 1979), p. 391. lo B. M. Lok, F. P. Gortsema, C. A. Messina, H. Rastelli and T. P. J. Izod, ACS Symp. Ser., 1983, l2 I. T. Sariev and V. Penchev, in Proc. 4th Znt. Conf. Hetero. Catal. (Bulgarian Academy of Sciences, l 3 V. Penchev, I. T. Sariev and M. Zhelazkova, Kinet. Katal., 1981, 22, 732. l4 M. D. Zhelazkova, I. T. Sariev and S. A. Koralska, in Proc. 5th Int. Symp. Hetero. Catal. (Bulgarian l5 S. Kowalak, React. Kinet. Catal. Lett., in press. l6 K. A. Becker and S. Kowalak, to be published. l7 D. W. Breck and G. W. Skeels, in Proc. 6th Int. Congr. Catal. (The Chemical Society, London, 1977), Academy of Sciences, Sofia, 1983), p. 467. vol. 2, p. 645. G. B. McVicker, C. J. Kim and J. J. Eggert, J. Catal., 1983, 80, 315. S. Kowalak, Acta Chim. Acad. Sci. Hung., 1981, 107, 27. 2o R. M. Barrer and J. Klinowski, J. Chem. SOC., Faraday Trans. 1 , 1975,71, 690. (PAPER 4/1037)

ISSN:0300-9599    

DOI:10.1039/F19858101161

出版商:RSC    

年代:1985

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1985,81, 1167-1 172 Liquidus Measurements and Coupled Thermodynamic-Phase-diagram Analysis of the NaC1-KCl System BY ARTHUR D. PELTON AND ARMAND GABRIEL Ecole Polytechnique, C.P. 6079, Succ. 'A', Montreal, Quebec, Canada H3C 3A7 AND JAMES SANGSTER* Sangster Research Laboratories, Suite M-3, 1270 Sherbrooke Street West, Montreal, Quebec, Canada H3G 1H7 Received 18th June, 1984 The liquidus of the NaCl-KCl system has been measured by a cooling-curve technique. A coupled thermodynamic-phase-diagram analysis of all available thermodynamic and phase- diagram data has been performed to obtain equations for the Gibbs energies of the liquid and solid phases which can be used to generate all the thermodynamic properties and the phase diagram. This analysis has permitted the solidus to be calculated.In a coupled thermodynamic-phase-diagram anal~sisl-~ all reliable thermodynamic and phase-equilibrium data are critically evaluated simultaneously with a view to obtaining a set of equations for the Gibbs energies of the phases which can subsequently be used to generate all the thermodynamic properties and the phase diagram. In this way the experimental data can be smoothed in a thermodynamically correct manner. Furthermore, all available experimental information is utilized. Thermodynamic data are used to shed light upon the phase diagram and the phase diagram is used to calculate thermodynamic properties. Discrepancies among various data sets can often be resolved in this way and error limits can more easily be assigned. Unknown or uncertain phase boundaries can often be estimated with good precision and, conversely, some reported phase boundaries can be rejected as being inconsistent with the thermodynamic properties of the system.All the thermodynamic properties as well as the phase diagram are represented in a very compact form via the coefficients of a small set of equations. This representation is very suitable for computer storage and retrieval. Finally, such a thermodynamic analysis is the first step in estimating ternary and higher-order phase diagrams from binary With regard to the NaCl-KCl system, the liquidus has been investigated by thermal and by the temperature of the first appearance of c r y s t a l ~ . l ~ - ~ ~ The reported minimum varies between 640 and 670 "C.Most of the values lie in the range 655-660 "C. An exception is the value14 of 645 "C. However, this work, like most of the recent measurements, was performed by the inherently less accurate visual method. Points on the solidus curve have been measured by thermal a n a l y s i ~ ~ ~ ' ~ ~ and by visual methods.159 21 These reported solidus curves are in poor agreement, as can be seen from fig. 1, where the solidus points of ref. (13) and (21) are plotted. The limits of solid solubility were investigated several times before 1950 by thermal and optical techniques. Results were not concordant: they indicated a consolute point 11671168 LIQUIDUS MEASUREMENTS OF THE NaCl-KCl SYSTEM I , ' I - I ' I ' I ' I I 1 I 1 I - 800 *80I0C - 660 - 640 - 0 0 0 0 0 I , I .I . I . I , I . I . I . I . - 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 mole fraction NaCl Fig. 1. Liquidus-solidus of the KC1-NaC1 system. Lines are calculated from the thermodynamic equations: 0, liquidus (present study); 0, solidus [ref. (21)] and A, solidus [ref. (13)]. 500 4 5c 4 OC V 350 300 250 20c 0.2 0.4 0.6 0.8 mole fraction NaCl 0 Fig. 2. Solid-solid miscibility gap of the KC1-NaCl system. Curve calculated from the thermodynamic equations: 0, ref. (26) and 0, ref. (27).A. D. PELTON, A. GABRIEL AND J. SANGSTER 1169 near 400 "C. An exception is the work of N a ~ k e n , ~ ~ who measured refractive indices and obtained a consolute point at 495 "C at 65 mol % NaC1. Later investigator~~*-~~ used X-ray techniques either at elevated temperatures or after quenching. Their results are generally concordant within 25 "C over the entire concentration range.Data points from the two most recent studies26T27 are plotted in fig. 2. A consolute point in the range 490-505 "C is indicated at a NaCl concentration between 50 and 70 mol % . The excess enthalpy of the liquid has been measured2* at 810 "C by direct liquid-liquid mixing calorimetry. Excess enthalpies are negative, with a minimum of ca. - 550 J mol-1 near 52 mol % NaCl. Data of ref. (28) are judged accurate to ca. If: 100 J mol-l. The excess enthalpy at 25 "C of metastable solid solutions obtained by quenching has been measured cal~rimetrically.~~~ 29 The results of these two studies agree within 200 J mol-l. Excess enthalpies are positive with a maximum of ca.4400 J mol-1 near 52 mol % NaCl. Finally, the Gibbs energies of fusion of NaCl and KCl are required in the thermodynamic analysis. These were obtained from data compiled in ref. (30) and were expressed as functions of temperature by the following equations : AGiusion (KCl)/J mol-l = 4755+215.399T+(12.734 x AGiusion (NaCl)/J mol-1 = 7735 + 202.091 T T2 -33.581 Tln T+(1.82x lo5) T1 (1) +(11.925x T2-31.824Tln T (2) where Tis in K. EXPERIMENTAL The liquidus was measured by the method of cooling curves. Reagent-grade salts were dried under vacuum and with dry HC1 gas at 700 "C. Samples of ca. 25 g were placed in sealed evacuated fused silica cells. A thermocouple was sheathed in close-fitting fused silica tubes blown into the cells. The cells were placed in a grounded Inconel metal sheath and placed in a vertical electrical-resistance furnace which was cooled at a rate of 1 "C min-l.The melt filled the cells to a depth of ca. 3 cm and the thermocouple sheath extended ca. 2 cm below the surface of the melt. Supercooling was kept to < 2 "C by attaching the cell assembly to a mechanical vibrator. A 24-gauge chromel-alumel thermocouple was used. The manufacturer's calibration was checked against the melting point of Pb, Sn and Zn and was found to agree to within 0.5 "C. RESULTS Three separate measurements of the melting point of pure KCl gave 770.5, 771.2 and 771.8 "C, which agree well with the value of 771 "C given in the most recent ~ompilations.~~ Several measurements of the melting point of pure NaCl gave values within 0.5 "C of the value of 801 "C given in the most recent l i t e r a t ~ r e .~ ~ Measured liquidus points are listed in table 1 and are plotted in fig. 1. Accuracy is estimated as varying from f 1 "C for compositions near each pure component to 2 "C near the liquidus minimum. THERMODYNAMIC ANALYSIS For the liquid phase the calorimetrically measured excess enthalpies2* are well represented by the equation HE(I)/J molt1 = XNaCl A',,,( - 2050 - 272 XNaC1) (3) 39 FAR 11170 LIQUIDUS MEASUREMENTS OF THE NaC1-KC1 SYSTEM Table 1. The NaCl-KC1 liquidus smoothed liquidus from thermodynamic mole fraction NaCl measured points/"C equations/"C 0 0.042 0.1 15 0.127 0.198 0.258 0.314 0.379 0.4 12 0.476 0.513 0.534 0.602 0.674 0.737 0.789 0.8 50 0.933 1 .o 77 1 762.5 745 74 1 721.5 706.5 693 677 669 661.5 658 66 1 673.5 697.5 719 737 758 78 1 80 1 77 1 762 743.5 741.5 722 706.5 692.5 676.5 668.5 658 657.5 660 676 700 720 738 757 782 80 1 where XNaCl and X K C l are mole fractions.Experience with liquid alkali-metal halide solutions shows that excess entropies are generally small in these systems, particularly when the cations are of similar size and the experimental excess enthalpies are small. Hence the assumption that is probably correct to within f0.5 J mob1 K-l. was sought: where a,, a,, a, and b are constant coefficients. Differentiation with respect to Tgives, via the Gibbs-Helmholtz equation, the following expression for the excess enthalpy : s y l ) = 0 (4) For the solid phase an equation for the excess Gibbs energy of the following form GE(s) = XNaCl XKCl + T+ In T , -k bXNaCll ( 5 ) HE(S) = XNaCl XKCl - T , + bXNaCll (6) i.e.the excess enthalpy is assumed to be a linear function of temperature. In view of the wide temperature range over which the experimental data are available (25-800 "C), the inclusion of a temperature dependence of NE(s) is justified. However, it is expected that the coefficient a, should be small. As concerns the composition dependence of GE(s), a ' sub-regular' equation was chosen with, at constant T, two terms in the polynomial expansion in mole fractions. Experience has shown that most alkali-metal halide solutions approximate quite closely to sub-regular behaviour. A third term of the form cPNaC1 could be added in eqn (9, but when this was done in the present case no significant improvement in representing the data was achieved.If a liquidus curve is precisely known and if the thermodynamic properties of theA. D. PELTON, A. GABRIEL AND J. SANGSTER 1171 Table 2. The NaC1-KCl solidus calculated from thermodynamic equations temperature/"C mole fraction NaCl 780 760 740 720 700 690 680 670 660 657 - 0.017 0.052 0.092 0.141 0.172 0.21 1 0.265 0.365 0.983 0.964 0.942 0.9 15 0.877 0.853 0.821 0.772 0.667 0.506 liquid phase are also known, then it has been shown31 that GE(s), averaged over the temperature range of the liquidus/solidus, can be calculated via an exact thermo- dynamic relationship. In the present case the measured liquidus curve, along with eqn (3) and (4), permits GE(s) to be calculated in the range 660-800 "C.From the measurements of the solid-solid miscibility gap2s* 27 values of GE(s) in the temperature range 200-500 "C can be deduced. Finally, the calorimetric 29 at 25 "C give HE(s) at this temperature. By combining all these data the following expression for GE(s) was obtained: GE(S)/J m0l-l = X N ~ C ~ XKcl[(14333 + 32.796T- 5.593T ln T ) + 3287X~,c,]. (7) Equations for the excess enthalpy, excess entropy and excess heat capacity can be deduced from eqn (7): SE(s)/J mol -l K-l = XNaCl XKcl( -27.203 + 5.593 In T ) CpE(s)/J mol-1 K-l = 5.593XNac1 XKcl. (9) The phase diagram, calculated by computer from eqn (1)-(4) and (7), is shown by the lines in fig. 1 and 2. Calculated liquidus and solidus points are listed in tables 1 and 2. The calculated liquidus agrees with the measured liquidus within 1 "C near the pure components and within 2.5 "C near the minimum.The shape of the calculated solidus is similar to that reported in ref. (21). It is estimated that the calculated solidus is correct to within & 5 "C. A minimum at 657 "C at 50.6 mol % NaCl is calculated. The calculated solid-solid miscibility gap in fig. 2 agrees with the measured points within the experimental error limits. The m e a s ~ r e d ~ ~ ~ ~ ~ excess enthalpies at 25 "C are reproduced by eqn (8) to within 250 J mol-l. CONCLUSIONS The liquidus of the NaCl-KCl system has been remeasured by the method of A coupled thermodynamic-phase-diagram analysis of all available reliable data on cooling curves. 39-21172 LXQUXDUS MEASUREMENTS OF THE NaCl-KCl SYSTEM this system has yielded a two-coefficient sub-regular equation for the excess Gibbs energy of the liquid phase and a four-coefficient sub-regular expression for the excess Gibbs energy of the solid phase.These expressions are in agreement with the calorimetrically measured excess enthalpies of the phases. When the phase diagram is calculated from these thermodynamic equations the liquidus and the solid-solid miscibility gap are reproduced within their experimental error limits. 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ISSN:0300-9599    

DOI:10.1039/F19858101167

出版商:RSC    

年代:1985

数据来源: RSC