Dilute Pd/Au Alloy Nanoparticles Embedded in Colloid-TemplatedPorous SiO 2 : Stable Au-Based Oxidation Catalysts

Dilute alloy materials hold great promise for enhancing selectivity in catalytic reactions. A major challenge with such catalytic materials is developing supported alloy nanoparticles (NP) with catalytically optimal composition that are stable with respect to sintering. Here we demonstrate that NP Pd/Au catalysts with minor concentrations of Pd prepared by a colloid templating approach are active for oxygen dissociation and catalytic oxidation, as exemplified by CO oxidation. Using electron microscopic imaging, infrared spectroscopy and X-ray photo electron spectroscopy, we demonstrate that Pd is stabilized within the Au nanoparticle in its metallic state with minor amounts of Pd at the surface. The PdAu nanoparticles are embedded in the colloidally templated silica and are thermally stable catalyst at high temperature. Surface analysis by diffuse reflectance infrared spectroscopy indicates that the Pd atomic distribution at the surface varies with the bulk concentration, forming isolated Pd atoms at 2% P...