Varying oxygen coverage on Cu and its effect on CO oxidation.

Adsorption of molecular oxygen on a Cu cluster and the resulting oxidation effects have been investigated by spin-polarized density functional theory (DFT). The optimal structure for each CuO (N = 1-20) complex has been obtained via a sequential addition of O and systematic screening of the preferable adsorption sites. Upon structural optimization, several O molecules dissociate readily on Cu at different oxygen coverages, and further DFT molecular dynamics simulations at 300 K confirm the instability (small dissociation barrier) of the remaining O and a spontaneous movement of some oxygen atoms from the surface sites towards the cluster interior. The Cu cluster and its oxidized derivatives have been placed on a γ-AlO(100) surface to study the cluster-support interaction, and furthermore, CO oxidation reactions on both Cu(O) and Cu(O)/γ-AlO(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.