The preparation of silica supported, dilute limit PdAu alloys via simultaneous strong electrostatic adsorption

Abstract

Supported, dilute Pd-in-Au alloyed nanoparticles might possess enhanced reactivity due to the altered structural and electronic properties of the Pd atoms isolated in an Au nanoparticle matrix. Simultaneous strong electrostatic adsorption (co-SEA) is a promising approach to synthesize such nanoparticles at high metal dispersion. In this study, Pd sites diluted in Au nanoclusters were achieved via co-SEA with dilute Pd/Au concentration ratios of the impregnating solution. X-ray diffraction, CO chemisorption, and scanning transmission electron microscopy (STEM) demonstrated ultrasmall nanoparticles (∼1.7 nm) with homogenous alloying. Quantitative analysis of CO adsorption with Fourier-transform infrared spectroscopy was used to diagnose the disappearance of contiguous Pd surface ensembles with increasing dilution. Exclusively isolated Pd sites were achieved at or below the ratio of Pd/Au = 0.04. Catalysts comprising completely isolated Pd exhibited turnover frequencies up to two orders of magnitude higher than pure Pd or Au catalysts.