CO adsorption on monometallic Pd, Rh, Cu and bimetallic PdCu and RhCu monolayers supported on Ru(0Â 0Â 0Â 1)

This work presents a systematic periodic density functional study of the changes in CO adsorption on metallic Rh, Pd, Cu monolayers supported on Ru(0 0 0 1) relative to CO adsorption on their corresponding Rh(1 1 1), Pd(1 1 1), Cu(1 1 1) single metal surfaces. Moreover, CO adsorption on various compositions of bimetallic PdCu and RhCu overlayers, also supported on Ru(0 0 0 1) have been considered. The metallic support affects each metallic crystal surface in a different way. However, the changes in the ability of back-donation from each metal surface to the CO(2π*) antibonding molecular orbital explain the variation of the adsorption energies. On the contrary, the presence of Ru does not affect the CO adsorption geometry. For the supported bimetallic overlayers, the CO-Pd and CO-Rh bond strength is enhanced by the presence of Cu. It is suggested that this effect is due to charge transfer from Cu the other metals thus enhancing their ability to back-donate to CO. The study of adsorption on different sites of the different bimetallic monolayers indicates that the key factor controlling CO adsorption energy is the nature of the metallic atoms constituting the active sites. These findings have been confirmed for two different CO coverage situations.