Size Effect in Ethylene Oxidation over Silver Nanoparticles Supported on HOPG

Abstract

A preparation procedure for a model catalyst – stable silver nanoparticles with a narrow size distribution supported on highly oriented pyrolytic graphite (Ag/HOPG) – is presented. This procedure is carried out under ultra high vacuum conditions and consists of three stages: 1 – surface defect formation by soft Ar+-treatment; 2 – silver deposition; 3 – defect annealing by heating at T = 300 °C. The analysis of oxygen forms on a silver surface was carried out by in-situ X-ray photoelectron spectroscopy (XPS). The simultaneous presence of two oxygen species (electrophilic and nucleophilic) on the silver surface was found to be necessary for high activity of the model catalyst in ethylene epoxidation. An alternative explanation of the size effect in ethylene oxidation has been suggested: size dependence of the reaction rate may result from the existence of a ring-shaped zone at the edge of silver particles in which the surface concentration of nucleophilic oxygen is not uniform. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35147