Ethylene oxide isomerisation on single-crystal Ag(111) in atomically clean and Cs-moderated conditions

Abstract

The isomerisation of ethylene oxide to acetaldehyde has been investigated over a single crystal Ag(111) surface between 300 and 500 K and at pressures of up to 2 Torr. It is found that the nature of the rate-determining step changes at ~410 K; at lower temperatures the rate of isomerisation of the adsorbed reactant is rate limiting, at higher temperatures the rate of adsorption becomes rate controlling. There is qualitative and quantitative agreement between the high-pressure reaction rate data and the measured adsorption/desorption properties of the reactant and product molecules. The rate parameters and reaction order are in satisfactory agreement with data obtained for conventional supported Ag catalysts indicating that it is indeed a metal-catalysed reaction which determines the isomerisation behaviour of such materials. The promoter and moderator actions of dissolved oxygen and preadsorbed Cs are characterised and a model for the observed behaviour is presented.