Characterization and Chemical Properties of Pd−Au Alloy Surfaces^†

Abstract

The chemisorptive behavior of CO on Pd−Au alloy films has been studied by infrared reflection−adsorption spectroscopy (IRAS). Geometric (ensemble) and electronic (ligand) effects have been addressed by comparing the results with the corresponding single-component systems. A unique CO vibrational feature at 2088 cm -1 is associated with CO adsorption on isolated Pd sites. Considering the frequency of the CO stretching mode, these data support mainly an influence of an ensemble effect on the chemical properties and contradict any significant contribution from a ligand effect. The surface concentration of isolated Pd sites can be controlled systematically by altering the bulk Pd−Au alloy composition, thus providing a method for studying isolated Pd as an active site for various catalytic reactions.