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 generaliz ed gradient approximation to investigate CO oxidation on a close-packed tra nsition metal surface, Pd(lll), and a more open surface, Pd(100), aiming to shed light on surface structure effects on reaction pathways and reactivit y, an important issue in catalysis. Reaction pathways on both surfaces at t wo different coverages have been studied. It is found that the reaction pat hways on both surfaces possess crucial common features despite the fact tha t they have different surface symmetries. Having determined reaction barrie rs in these systems, we find that the reaction on Pd(lll) is strongly cover age dependent. Surface coverages, however, have little effect on the reacti on 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.