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 O-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. (C) 2000 Elsevier Science B.V. All rights reserved.