Universality in Heterogeneous Catalysis

Linear relations between the activation energies and heats of adsorption or heats of reaction have long been assumed to be valid. Such relations are called Bronsted-Evans-Polanyi relations [N. Bronsted, Chem. Rev. 5 (1928) 231 M.G. Evans and M. Polanyi, Trans. Faraday Soc. 34 (1938) 11]. In catalysis such relations have recently been found to hold for the dissociation reactions summarized in Pig. 6.42, and also for a number of reactions involving small hydrocarbon fragments such as the hydro- 

The fact that universal Brondsted-Evans-Polanyi relations appear to exist for these dissociation reactions raises the following questions. Why is the relationship between the activation energy and the adsorption energy of the dissociation products linear Why does it depend on structure Why is it independent of the adsorbates  

All these questions can be answered if we consider the transition states for the dissociation reactions, which are all very similar. The transition state structure for a given substrate geometry is essentially independent of the type of molecule and substrate. Thus the close packed surfaces as well as the stepped surfaces considered in Fig. 6.42 each form a group. Dissociation is furthermore characterized by a late transition state, in which the two atoms have already separated to a large extent and 

Identification of such universal relations between activation energies and heats of adsorption for particular classes of reaction can be seen as a more precise and more quantitative formulation of Sabatier s Principle. It is promising tool in the search for new materials on the basis of optimized interaction strength between relevant intermediates and the surface. 

In this chapter we have largely relied on computational chemistry, in particular on density-functional theory. Quantum mechanical calculations of a macroscopic piece of metal with various species adsorbed on it are as yet impossible, but it is possible to obtain realistic results on simplified systems. One approach is to simulate the metal by a cluster of 3-30 atoms on which the molecule adsorbs and then describe all the involved orbitals. Many calculations have been performed on this basis with many useful results. Obviously, the cluster must be sufficiently large that the results do not represent an artefact of the particular cluster size chosen, which can be verified by varying the cluster size. 

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Nprskov JK, Bhgaard T, Logadottir A, Bahn S, Hansen LB, Bollinger M, Bengaard H, Hammer B, Sljivancanin Z, Mavrikakis M, Xu Y, Dahl S, Jacohsen CJH. 2002. Universality in heterogeneous catalysis. J Catal 209 275. 

Nprskov JK, Bligaard T, Logadottir A et al (2002) Universality in heterogeneous catalysis. J Catal 209 275-278... 

Laboratory, where he worked with John Longo and Allan Jacobson on the synthesis and characterization of mixed metal oxides and their application in heterogeneous catalysis. He joined the chemistry faculty of Northwestern University in 1984 where he is now Professor of Chemistry and an active member of the Center for Catalysis and Surface Science and the Materials Research Science and Engineering Center. Kenneth Poeppelmeier has published over 250 research papers and supervised approximately 40 Ph.D. students in the area of inorganic and solid state chemistry. He is a Fellow of the American Association for the Advancement of Science (AAAS) and the Japan Society for the Promotion of Science (JSPS) and has been a Lecturer for the National Science Council of Taiwan (1991), Natural Science Foundation of China (1999) and Chemistry Week in China (2004), and more recently an Institut Universitaire de France Professor (2003). 

Goodman, D. W., in Heterogeneous catalysis Proceedings of lUCCP Coherence), Texas A M University (1984). 

Ozin, G.A. Baker, M.D. Godber, J. in "Heterogeneous Catalysis" Shapiro, B. Ed. Texas A and M University Press College Station, 1984. See also reference 5. 

The Bodenstein approximation of quasi-stationary behavior, required even by the Christiansen formula, is almost universally (if often tacitly) taken for granted in heterogeneous catalysis. 

Maciel, G. E. In Heterogeneous Catalysis, Proceedings of the Second Symposium of the Industry-University Cooperative Chemistry Program of the Department of Chemistry, Texas A6-M University Shapiro, B. L., Ed. Texas A M University Press College Station, TX, 1984 pp 349-381. 

Satterfield, C.N., "Mass Transfer in heterogeneous catalysis". Cairibridge University Press, Cambridge (1970). 

Firstly, is a kinetic expression, a rate law, such as, e.g., the Langmuir-Hinshelwood-Hougen-Watson rate expressions in heterogeneous catalysis, and as such has no universal applicability. It is derived on the basis of mass action kinetics and does reduce to the fundamental thermodynamic Nemst equation for i = 0, thus q = 0. ° Nevertheless, experimental deviations can be expected as with any other, even most successful, rate expression. 

T.J. Pinnavaia, in Heterogeneous Catalysis (Ed. B. Shapiro), p. 18, Texas A M University Press, College Station, Texas (1985). 

Jan C.J. Bart (PhD Structural Chemistry, University of Amsterdam) is a senior scientist with broad interest in materials characterisation, heterogeneous catalysis and product development who spent an industrial carrier in R D with Monsanto, Montedison and DSM Research in various countries. The author has held several teaching assignments and researched extensively in both academic and industrial areas he authored over 250 scientific papers, including chapters in books. Dr Bart has acted as a Ramsay Memorial Fellow at the... 

An alternative interpretation of some features of the hydroformylation reaction (including the inverse CO dependence), in terms of heterogeneous catalysis by an (unidentified) insoluble cobalt component, has recently been advanced by Aldridge, Fasce and Jonassen (49a). The universal validity of this seems doubtful in the light of the considerable evidence favoring a homogeneous mechanism. 

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