A DFT study on the mechanism of acetaldehyde generation during vinyl acetate synthesis from gas-phase ethylene acetoxylation on Pd/Au (100) surface

Abstract

Acetaldehyde (CH3CHO) is an important by-product in the reaction of ethylene to vinyl acetate (VAC). However, the mechanism of the generation of CH3CHO has been little studied. In this paper, we designed a reaction network for the possible generation of acetaldehyde from intermediate species on Pd/Au catalysts, including three reaction paths. Stable adsorption configurations of the species involved in each elementary reaction were identified by Density Functional Theory (DFT) calculations and the charge changes on the catalyst surface during the adsorption process as well as the structural parameter changes of the adsorption configurations were compared. Based on this, we calculated the kinetic parameters on three reaction paths and combined with Kinetic Monte Carlo (KMC) simulations to found the dominant path and rate-determining step to help understand the mechanism of acetaldehyde generation on the surface of Pd/Au (100). Results suggest that species involved in the reactions are adsorbed mainly on Pd-Au bridge sites, Pd top sites, and Pd-Pd intermediate vacancies and species structure changes after adsorption. CHCH, CH2CH, and CH3CH could all generate CHxCHO by reacting with O species or OH species, and the energy barrier for reactions with O species are all lower than those for reactions with OH species. The dominant pathway for acetaldehyde generation on Pd/Au (100) surface is CH2CH2 → CH2CH→ CH2CHO → CH3CHO and the ethylene dehydrogenation elementary reaction is the rate-determining step.