Interaction of CO with PdCu surface alloys supported on Ru(0001)

The adsorption and desorption of CO on monolayer PdCu surface alloys on a Ru(0 0 0 1) substrate and, for comparison, on Pd/Ru(0 0 0 1), and Cu/Ru(0 0 0 1) monolayer films, have been studied by temperature programmed desorption and infrared reflection absorption spectroscopy, aiming at a detailed understanding of the different effects controlling the chemical properties of bimetallic surfaces, geometric ensemble effects, electronic ligand effects and strain induced effects. The results show that all of these effects are present in these surfaces, acting in a cooperative, synergetic way. Strain effects lead to a destabilization of the Pd-CO and a stabilization of the Cu-CO interaction as compared to CO adsorption on the respective bulk substrates. Geometric ensemble effects are imposed by the highly disperse distribution of the Cu and Pd atoms, reducing the number of otherwise favorable Pd-3 sites, and electronic ligand effects lead to an increasing stability of the Pd-CO bond with increasing Cu content. (C) 2004 Published by Elsevier B.V.