Size effect on the catalysis of gold clusters dispersed in water for aerobic oxidation of alcohol

We prepared a set of nearly monodisperse gold clusters ranging from 1.3 to 10 nm by a seed-mediated growth in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). The seed clusters with a diameter of 1.3 ± 0.3 nm were prepared by reducing AuCl₄^- with NaBH₄ in a low-temperature aqueous solution of PVP. Subsequent reduction of more AuCl₄^- by Na₂SO₃ in the presence of the seed clusters yielded a series of larger Au:PVP clusters. Catalytic activities of the Au:PVP clusters for aerobic oxidation of p-hydroxybenzyl alcohol increased with decrease in the core size. The size dependence is discussed in light of the electronic structures of the cores probed by optical spectroscopy.