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 etha ne 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 ene rgetics for interactions of various C2Hx species with platinum that have be en observed experimentally in microcalorimetric and spectroscopic studies o f ethylene and acetylene adsorption on platinum catalysts. These theoretica l methods are then extended to predict energetics for hydrocarbon species a nd transition states on platinum that can not be observed experimentally. T he combined results of these experimental and theoretical investigations pr ovide thermodynamic information about adsorbed C-2 species on platinum as w ell as transition states for cleavage of the C-C bond in these species. The se results were used to refine and constrain kinetic analyses of kinetic da ta collected for ethane hydrogenolysis over a wide range of conditions. Res ults of these analyses suggest that the primary reaction pathways for cleav age of the C-C bond take place through activated complexes based on ethyl(C 2H5) and ethylidene (CHCH3) species. Furthermore, these analyses suggest th at while the more abundant surface species (e.g., adsorbed atomic hydrogen, ethylidyne, and vinylidene species) are not directly involved in the prima ry reaction pathways, they affect the observed kinetic rates through blocki ng of sites. (C) 1999 Elsevier Science B.V. All rights reserved.