Varying oxygen coverage on Cu55 and its effect on CO oxidation

Abstract

Adsorption of molecular oxygen on a Cu₅₅ cluster and the resulting oxidation effects have been investigated by spin-polarized density functional theory (DFT). The optimal structure for each Cu₅₅O_2N (N = 1–20) complex has been obtained via a sequential addition of O₂ and systematic screening of the preferable adsorption sites. Upon structural optimization, several O₂ molecules dissociate readily on Cu₅₅ at different oxygen coverages, and further DFT molecular dynamics simulations at 300 K confirm the instability (small dissociation barrier) of the remaining O₂ and a spontaneous movement of some oxygen atoms from the surface sites towards the cluster interior. The Cu₅₅ cluster and its oxidized derivatives have been placed on a γ-Al₂O₃(100) surface to study the cluster–support interaction, and furthermore, CO oxidation reactions on both Cu₅₅(O)_2N and Cu₅₅(O)_2N/γ-Al₂O₃(100) have been studied as a function of oxygen coverage. The CO oxidation reaction barrier is rather insensitive to the oxygen coverage regardless of the support, indicating a small increase in activity with the number of surface oxygen atoms.