Kinetics of ethane hydrogenolysis over supported platinum catalysts

Results of reaction kinetic, microcalorimetric, spectroscopic, and quantum chemical studies are combined to develop a quantitative description of ethane hydrogenolysis over platinum. This work builds on investigations by John H. Sinfelt and co-workers of ethane hydrogenolysis over Group VIII metals. In the present analysis, quantum chemical methods are used to estimate energetics for interactions of various C2Hx species with platinum that have been observed experimentally in microcalorimetric and spectroscopic studies of ethylene and acetylene adsorption on platinum catalysts. These theoretical methods are then extended to predict energetics for hydrocarbon species and transition states on platinum that can not be observed experimentally. The combined results of these experimental and theoretical investigations provide thermodynamic information about adsorbed C-2 species on platinum as well as transition states for cleavage of the C-C bond in these species. These results were used to refine and constrain kinetic analyses of kinetic data collected for ethane hydrogenolysis over a wide range of conditions. Results of these analyses suggest that the primary reaction pathways for cleavage of the C-C bond take place through activated complexes based on ethyl(C2H5) and ethylidene (CHCH3) species. Furthermore, these analyses suggest that while the more abundant surface species (e.g., adsorbed atomic hydrogen, ethylidyne, and vinylidene species) are not directly involved in the primary reaction pathways, they affect the observed kinetic rates through blocking of sites. (C) 1999 Elsevier Science B.V. All rights reserved.