APPLICATION OF ISOTOPIC TRANSIENT KINETICS TO VINYL-ACETATE CATALYSIS

The isotopic transient kinetics technique has been used to characterise the surface species of Pd/Cd/silica and Pd/Au/silica catalysts for vinyl acetate synthesis. The main feature of both types of catalyst is a substantial film of acetic acid and water equivalent to between two and three molecular layers. Additional temperatureprogrammed desorption experiments have shown that the amount of retained acetic acid is increased by the presence of palladium and the potassium acetate promoter. No reversibly chemisorbed ethylene or oxygen was detected. The major by-product, CO2, was derived equally from ethylene and acetic acid under these conditions. Analysis of the isotopic transients of the vinyl acetate product has allowed an estimate of the active site densities to be calculated. The transients also contain information about product diffusivity. (C) 1994 Academic Press, Inc.