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An explanation of the isokinetic temperature in heterogeneous catalysis
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as all-out war on fossil fuels and the people who use them. Yet if the politics of global warming require that "something must be done" while we still don't know whether anything really needs to be done - let alone what exactly - let us play to our uniquely American strengths in innovation and technology to offset any global warming by the least costly means possible. While scientists continue research into any global climatic effects of greenhouse gases, we ought to study ways to offset any possible ill effects. Injecting sunlight-scattering particles into the stratosphere appears to be a promising approach. Why not do that?
transmission coefficient. Isokinetic temperature is then defined as the temperature at which [ [ K . K ± = 1.0. Now the corresponding standard free energy summation Z/kG ° + AG ± = 0 and ~/kH ° + AH ± = T(~C/kS ° + AS±). This is in complete accord with the understanding that the Gibbs-Helmoltz equation, AG(=0) = AH - TDS,
An explanation of the isokinetic temperature in heterogeneous catalysis A general, purely physical, theory [1] currently advocated for heterogeneous catalysis is that in the transition state the vibrational frequency of one of the normal modes of the substrate resonates with a vibrational frequency of the solid surface. The widespread observations of isokinetic temperature and the compensation effect [2] for closely related families, substrates or catalyst etc. are then cited [1,3] as evidence for this idea, and equations developed to show that the isokinetic temperature, Tiso, is given by the following where x is a small number, and all the other symbols have their usual significance. Tiso --- (Nhcoc/R) • x However, recently we have argued [4,5] that isokinetic temperature and the compensation effect are explained by the extended Eyring kinetic rate equation. kex p = y - kT/h - t ] K • K ±
~ K is a multiple or quotient of the individual equilibrium constants for all the sequence of steps, chemisorption or complexation, etc., preceding the activation step; kex p is the experimental rate constant and y is the
Applied catalysis A: General
is the basis of all such compensation effects in thermodynamics [6,7]. In like fashion, equilibrium (reversible) thermodynamics are also the cornerstone of an understanding of the Arrhenius and Eyring rate equations in kinetics. T~so is therefore the temperature at which the Eyring equation reduces to the following equation. kex p .:
y
• kTiso/h
Since kexp can be defined as a frequency (kexp -coo), the first equation is identical to the last (x = I/y). There is therefore no need to have recourse to special resonance effects in order to explain the isokinetic temperature and compensation behaviour found in all branches of catalysis. Instead the application of the limited form of the extended Eyring equation is further validated by the physical theory derived by Larrson [1,3]. References [1] Larrson, R., J. Mol. Catal. 55, 70 (1989) [2] Conner, W.C., Jr., J.Catal. 84, 273 (1983) [3] Karpinski, Z. and Larrson, R., J. Catal. 168, 532 (1997) [4] Patterson, W.R. and Rooney, J. J., J. Catal. 146, 310 (1994)
Volume 166 No. 2 - - 8 January 1998
N4
[5] Rooney, J.J., J. Mol. Catal. 96, L1 (1995) [6] Grimwald, E. and Steel, C., J. Am. Chem. Soc. 117, 5687 (1995) [7] Mondieig, D., Espeau, P., Robles, L., Haget, Y, Oonk, H.A.J. and Chevas-Diarte, M.A., J. Chem. Soc. FaradayTrans. 93, 3343 (1997). J.J. Rooney
Jens Weitkamp New President of the International Zeolite Association (IZA) In July 1997, Professor Jens Weitkamp was elected President of the International Zeolite Association, an organization well known to most readers of Applied Catalysis. Before being elected President, Professor Weitkamp served the IZA for three years as its VicePresident. He was the Chairman of the Organizing Committee of the 10th International Zeolite Conference, held 1994 in Garmisch-Partenkirchen, Germany. Jens Weitkamp is known in the catalysis community for his contributions to hydrocarbon conversion (hydrocracking, cracking, isomerization, alkylation etc.), shape selective catalysis and the synthesis, modification and characterization of zeolites. He is a coeditor of the five-volume Handbook of Heterogeneous Catalysis published very recently by Wiley-VCH.
M4 Corridor Catalysis Meeting For many years a regular meeting of the active research groups in Catalysis and Surface Science that reside in the 'M4 Corridor' in the UK has been held. In recent years, this tradition has lapsed slightly, but Professor Mike Bowker has been a driving force in reestablishing these meetings and he acted as host for a meeting at the University of Reading on 30 September 1997. The main aims of these meetings are to provide a forum for the research groups of the 'M4 Corridor' universities active in catalysis in Chemistry and Chemical Engineering departments (Bath, Brunel, Cardiff, Reading, London, Imperial, London University College). A key feature of these meetings is that junior
Applied catalysis A: General
research staff and in particular doctoral students give the presentations and that a realistic time is given to discussion. This meeting was attended by 63 active researchers mainly from Bath, Brunel, Cardiff and Reading. The titles and presenters were: 'Selective alkane oxidation using vanadium phosphorus oxide catalysts,' Johathan Bartley (Cardiff); 'Butane gas sensor catalysis,' Colin Bulpitt (Reading); 'Investigation of nickel antiamides for the ammoxidation of propene,' Tim Cassidy (Reading); 'Design of advanced redox catalysts for three-way catalysts: The CexZqx02 mixed oxides: Paolo Fornasiero (Reading); 'Spillover and catalysis,' Fred Getton (Brunel); 'Recent advances in low temperature CO oxidation,' Nick Hodge (Cardiff); ~,n inelastic neutron scattering study of formate on copper surfaces,' Richard P. Holroyd (Reading); ~ quantum mechanical investigation of chemisorbed imide NH(a) at Cu (100) surfaces,' James Keel (Cardiff); 'A comparison of the (amm)oxidation catalysts bismuth molybdate and iron antimonate,' Colin Weeks (Reading); A study of Ni (110)-O systems and the effect of alkali doping,'James O'Shea (Cardiff); 'Comparisons between CH3OH and 03H8 reductants of NOx in the presence of 02 over AI203,' J.A. O'Sullivan (Reading); 'Sol-gel catalyst preparations,' Tom Salvesen and Jason Leedley (Brunel); 'Kinetics and mechanism of the reduction of NO by 03H6 and C3H 8 over Pt/AI203 under lean-burn conditions,' T.C. Watling (Reading); 'Enantioselective hydrogenation of a-ketoesters using platinum catalysts modified by cinchona alkaloids The importance of liquid phase interaction between substrate and modifier,' Neil McGuire (Cardiff). It is suggested that anybody interested should contact the respective author for further details. It is anticipated that a further meeting will be held in two years time. The key features brought out for this meeting were the diverse systems that are studied, namely catalysts with surface areas ranging from 2 cm 2 to 1000 m 2 gl, with reactions at ambient temperature (CO oxidation) up to 1000C (car exhaust), with small molecules on well defined surface to'loogish molecules'on 'flatish surfaces'. Additionally the interplay between the use
Volume 166 No. 2 - - 8 January 1998
as all-out war on fossil fuels and the people who use them. Yet if the politics of global warming require that "something must be done" while we still don't know whether anything really needs to be done - let alone what exactly - let us play to our uniquely American strengths in innovation and technology to offset any global warming by the least costly means possible. While scientists continue research into any global climatic effects of greenhouse gases, we ought to study ways to offset any possible ill effects. Injecting sunlight-scattering particles into the stratosphere appears to be a promising approach. Why not do that?
transmission coefficient. Isokinetic temperature is then defined as the temperature at which [ [ K . K ± = 1.0. Now the corresponding standard free energy summation Z/kG ° + AG ± = 0 and ~/kH ° + AH ± = T(~C/kS ° + AS±). This is in complete accord with the understanding that the Gibbs-Helmoltz equation, AG(=0) = AH - TDS,
An explanation of the isokinetic temperature in heterogeneous catalysis A general, purely physical, theory [1] currently advocated for heterogeneous catalysis is that in the transition state the vibrational frequency of one of the normal modes of the substrate resonates with a vibrational frequency of the solid surface. The widespread observations of isokinetic temperature and the compensation effect [2] for closely related families, substrates or catalyst etc. are then cited [1,3] as evidence for this idea, and equations developed to show that the isokinetic temperature, Tiso, is given by the following where x is a small number, and all the other symbols have their usual significance. Tiso --- (Nhcoc/R) • x However, recently we have argued [4,5] that isokinetic temperature and the compensation effect are explained by the extended Eyring kinetic rate equation. kex p = y - kT/h - t ] K • K ±
~ K is a multiple or quotient of the individual equilibrium constants for all the sequence of steps, chemisorption or complexation, etc., preceding the activation step; kex p is the experimental rate constant and y is the
Applied catalysis A: General
is the basis of all such compensation effects in thermodynamics [6,7]. In like fashion, equilibrium (reversible) thermodynamics are also the cornerstone of an understanding of the Arrhenius and Eyring rate equations in kinetics. T~so is therefore the temperature at which the Eyring equation reduces to the following equation. kex p .:
y
• kTiso/h
Since kexp can be defined as a frequency (kexp -coo), the first equation is identical to the last (x = I/y). There is therefore no need to have recourse to special resonance effects in order to explain the isokinetic temperature and compensation behaviour found in all branches of catalysis. Instead the application of the limited form of the extended Eyring equation is further validated by the physical theory derived by Larrson [1,3]. References [1] Larrson, R., J. Mol. Catal. 55, 70 (1989) [2] Conner, W.C., Jr., J.Catal. 84, 273 (1983) [3] Karpinski, Z. and Larrson, R., J. Catal. 168, 532 (1997) [4] Patterson, W.R. and Rooney, J. J., J. Catal. 146, 310 (1994)
Volume 166 No. 2 - - 8 January 1998
N4
[5] Rooney, J.J., J. Mol. Catal. 96, L1 (1995) [6] Grimwald, E. and Steel, C., J. Am. Chem. Soc. 117, 5687 (1995) [7] Mondieig, D., Espeau, P., Robles, L., Haget, Y, Oonk, H.A.J. and Chevas-Diarte, M.A., J. Chem. Soc. FaradayTrans. 93, 3343 (1997). J.J. Rooney
Jens Weitkamp New President of the International Zeolite Association (IZA) In July 1997, Professor Jens Weitkamp was elected President of the International Zeolite Association, an organization well known to most readers of Applied Catalysis. Before being elected President, Professor Weitkamp served the IZA for three years as its VicePresident. He was the Chairman of the Organizing Committee of the 10th International Zeolite Conference, held 1994 in Garmisch-Partenkirchen, Germany. Jens Weitkamp is known in the catalysis community for his contributions to hydrocarbon conversion (hydrocracking, cracking, isomerization, alkylation etc.), shape selective catalysis and the synthesis, modification and characterization of zeolites. He is a coeditor of the five-volume Handbook of Heterogeneous Catalysis published very recently by Wiley-VCH.
M4 Corridor Catalysis Meeting For many years a regular meeting of the active research groups in Catalysis and Surface Science that reside in the 'M4 Corridor' in the UK has been held. In recent years, this tradition has lapsed slightly, but Professor Mike Bowker has been a driving force in reestablishing these meetings and he acted as host for a meeting at the University of Reading on 30 September 1997. The main aims of these meetings are to provide a forum for the research groups of the 'M4 Corridor' universities active in catalysis in Chemistry and Chemical Engineering departments (Bath, Brunel, Cardiff, Reading, London, Imperial, London University College). A key feature of these meetings is that junior
Applied catalysis A: General
research staff and in particular doctoral students give the presentations and that a realistic time is given to discussion. This meeting was attended by 63 active researchers mainly from Bath, Brunel, Cardiff and Reading. The titles and presenters were: 'Selective alkane oxidation using vanadium phosphorus oxide catalysts,' Johathan Bartley (Cardiff); 'Butane gas sensor catalysis,' Colin Bulpitt (Reading); 'Investigation of nickel antiamides for the ammoxidation of propene,' Tim Cassidy (Reading); 'Design of advanced redox catalysts for three-way catalysts: The CexZqx02 mixed oxides: Paolo Fornasiero (Reading); 'Spillover and catalysis,' Fred Getton (Brunel); 'Recent advances in low temperature CO oxidation,' Nick Hodge (Cardiff); ~,n inelastic neutron scattering study of formate on copper surfaces,' Richard P. Holroyd (Reading); ~ quantum mechanical investigation of chemisorbed imide NH(a) at Cu (100) surfaces,' James Keel (Cardiff); 'A comparison of the (amm)oxidation catalysts bismuth molybdate and iron antimonate,' Colin Weeks (Reading); A study of Ni (110)-O systems and the effect of alkali doping,'James O'Shea (Cardiff); 'Comparisons between CH3OH and 03H8 reductants of NOx in the presence of 02 over AI203,' J.A. O'Sullivan (Reading); 'Sol-gel catalyst preparations,' Tom Salvesen and Jason Leedley (Brunel); 'Kinetics and mechanism of the reduction of NO by 03H6 and C3H 8 over Pt/AI203 under lean-burn conditions,' T.C. Watling (Reading); 'Enantioselective hydrogenation of a-ketoesters using platinum catalysts modified by cinchona alkaloids The importance of liquid phase interaction between substrate and modifier,' Neil McGuire (Cardiff). It is suggested that anybody interested should contact the respective author for further details. It is anticipated that a further meeting will be held in two years time. The key features brought out for this meeting were the diverse systems that are studied, namely catalysts with surface areas ranging from 2 cm 2 to 1000 m 2 gl, with reactions at ambient temperature (CO oxidation) up to 1000C (car exhaust), with small molecules on well defined surface to'loogish molecules'on 'flatish surfaces'. Additionally the interplay between the use
Volume 166 No. 2 - - 8 January 1998