Hydrogen transfer in hydrocarbon conversions over transition metal surfaces

Hydrogen-transfer steps are a poorly studied and rarely proposed class of e lementary reactions in heterogeneous catalysis over metal surfaces. In thes e steps, a hydrogen atom that is attached to the carbon in one surface spec ies transfers to a carbon atom of another species. Unity bond index-quadrat ic exponential potential (UBI-QEP) calculations of the activation energies for three model surfaces representing substrates with strong, weak, and int ermediate chemisorption abilities, combined with UBI-QEP/DFT data for the P t(111) surface, suggest that there is no great energetic impediment to thes e steps. Therefore, they should not be arbitrarily ignored when building me chanisms of hydrocarbon conversions over metal surfaces. Moreover, kinetics simulations show that conditions are possible under which one-step hydroge n transfer is faster than the two-step process with the formation of adsorb ed hydrogen. (C) 2001 Elsevier Science B.V. All rights reserved.