Coadsorption of hydrogen and CO on well-defined Pt(35)Ru(65)/Ru(0001) surface alloys--site specificity vs. adsorbate-adsorbate interactions.

The coadsorption of CO and hydrogen on a structurally well-defined Pt(35)Ru(65)/Ru(0001) monolayer surface alloy and, for comparison, on Ru(0001) were investigated by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). The data reveal distinct modifications in the hydrogen adsorption behavior and also in the CO adsorption properties compared to adsorption of the individual components both on the mono-metallic and on the bimetallic surface. These modifications are discussed on an atomic scale, in a picture that involves adsorbate-adsorbate interactions and site-specific variations in the (local) adsorption properties of the bimetallic surface, due to electronic ligand and strain effects and geometric ensemble effects.