Surface Alloy Composition Controlled O2 Activation on Pd–Au Bimetallic Model Catalysts

Abstract

Oxygen is an important reactant in several catalytic conversions and partial oxidation reactions on Pd–Au alloy surfaces; however, adsorption and dissociation are not fully understood, especially as a function of the surface alloy composition. In this study, we probe the influence of the atomic makeup of the surface of Pd–Au catalysts regarding control of the catalytic activity toward O2 dissociation and the reactivity of the resulting oxygen adatoms. To experimentally investigate this, we prepared various bimetallic surfaces under ultrahigh vacuum via evaporation of Pd onto a Au(111) surface. Hydrogen molecules were used to characterize the composition of the Pd–Au surfaces, which we simplistically group into two categories: (i) Pd–Au interface sites and (ii) Pd(111)-like island sites. When the Pd coverage is 1.0 ML, which predominantly indicates Pd–Au interface sites, no dissociative adsorption of O2 at 300 K is observed, but dissociation begins to be measurable on the surfaces with larger Pd loadings (...