A set of nearly monodisperse Au-Ag alloy clusters (size range 1.6-2.2 nm) with various Ag content (5-30%) was prepared by the co-reduction method in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). The catalytic activities of the Au-Ag:PVP clusters were investigated for aerobic oxidation of p-hydroxybenzyl alcohol as a model reaction to understand the effect of Ag on the catalytic activity of Au clusters. It was found that the rate constants per unit surface area for Au-Ag:PVP clusters with small Ag content (<10%) were larger than those of monometallic Au:PVP clusters of comparable size. The enhancement of the catalytic activity by Ag doping is discussed in light of the electronic structure of the Au-Ag cores probed by X-ray photoelectron spectroscopy. The present results indicate that the partial anionic character of the Au core is important for the aerobic oxidation reactions of Au:PVP clusters.
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