Oxidation of ethylene catalyzed by colloidal dispersions of poly(sodium acrylate)-protected silver nanoclusters

Silver nanoclusters protected by poly(sodium acrylate) (PAA) were prepared by UV irradiation of an alcohol–water solution of silver perchlorate in the presence of PAA. Colloidal dispersions of PAA-protected Ag nanoclusters (PAA–Ag nanoclusters) were very stable at room temperature for months and composed of fine particles with an average diameter of 4.2 nm. X-Ray photoelectron spectroscopy data have suggested the 0-valency of Ag in PAA–Ag nanoclusters. Oxidation of ethylene, catalyzed by PAA–Ag nanoclusters, was performed in glycol under 1 atm. of ethylene/oxygen (2/1 v/v). Products were identified as ethylene oxide by analysis with gas chromatography. Ag nanoclusters thus prepared had higher catalytic activity than a commercial silver catalyst. The oxidation rate catalyzed by the PAA–Ag nanoclusters remarkably increased with increasing reaction temperature. PAA-protected Ag nanoclusters had much higher activity than poly(N-vinyl-2-pyrrolidone)-protected ones at high temperature. Addition of both cesium and rhenium ions eminently increased the catalytic activity of PAA–Ag nanoclusters.