Microscopic mechanisms in heterogeneous catalysis: H2 dissociation on clean and S covered Pd (1 0 0)

Abstract

Applying methods based on density-functional theory and state-of-the-art computing facilities, it has now become possible to investigate accurately the high-dimensional potential-energy manifolds associated with the interaction of small molecules with crystal surfaces. Hydrogen dissociation on clean and S-covered Pd(100) surfaces is selected as an example in order to discuss the mechanism of non-activated dissociation on transition metals and of the poisoning of the activity of a metal surface by adatoms. We emphasize the importance of incorporating all degrees of freedom into the description of the dynamics of the molecule-surface scattering process. We show that the formation of energy barriers and the restriction of the phase space of possible reaction pathways leads to a strong reduction of the sticking probability in the presence of S-ad-layers. Special attention is paid to the comparison of physical and chemical models of the molecule-surface interaction with our results. In particular, we discuss the predictive power and the limits of local reactivity indices, which aim to describe chemical reactions in terms of the properties of the non-interacting reactants.