Methane dissociation and adsorption on Ni(111), Pt(111), Ni(100), Pt(100), and Pt(110)-(1×2): Energetic study

摘要

We use density functional theory to examine 24 transition states for methane dissociation on fivedifferent metal surfaces. In our calculations, the nonlocal exchange-correlation effects are treatedwithin the generalized gradient approximation using the Perdew–Burke–Ernzerhof functional. In allcases, the minimum energy path for dissociation is over a top site. The barriers are large, 0.66–1.12eV, and relatively insensitive to the rotational orientation of the (nonreacting) methyl group and theazimuthal orientation of the reactive C–H bond. There is a strong preference on the Pt surfaces forthe methyl fragment to bond on the top site, while on the Ni surfaces there is a preference for thehollow or bridge sites. Thus, during the dissociation on Pt, only the low mass H atom needs tosignificantly move or tunnel, while on Ni, both the dissociating H and the methyl fragment moveaway from the top site. For all 24 configurations there is a strong force at the transition state topucker the metal atom over which the reaction occurs. The resulting magnitude of the variation inthe barrier height with the motion of this atom varies a bit from surface-to-surface, but is of the orderof 1 eV/A. We derive a model for the effective reaction barrier height that includes the effects oflattice motion and substrate temperature and compare with recent experiments and other theoreticalstudies.