CO Oxidation on Pd(100) and Pd(111):  A Comparative Study of Reaction Pathways and Reactivity at Low and Medium Coverages

We have performed density functional theory calculations with the generalized gradient approximation to investigate CO oxidation on a close-packed transition metal surface, Pd(111), and a more open surface, Pd(100), aiming to shed light on surface structure effects on reaction pathways and reactivity, an important issue in catalysis. Reaction pathways on both surfaces at two different coverages have been studied. It is found that the reaction pathways on both surfaces possess crucial common features despite the fact that they have different surface symmetries. Having determined reaction barriers in these systems, we find that the reaction on Pd(111) is strongly coverage dependent. Surface coverages, however, have little effect on the reaction on Pd(100). Calculations also reveal that the low coverage reactions are structure sensitive while the medium coverage reactions are not. Detailed discussions on these results are given.