Kinetics and Mechanism of Vinyl Acetate Monomer Synthesis on Pd(100) Model Catalysts

Abstract

The reaction between ethylene and acetate species on Pd(100) is explored using reflection–absorption infrared spectroscopy and compared with previous results found for a similar reaction on Pd(111). As a consequence of the lower saturation acetate coverage on Pd(100) than on Pd(111), the reaction is much less selective giving rise to carbon monoxide as the predominant product. Carrying out the titration reaction with C2D4 at ~180 K results in a feature at ~1711 cm−1, which has previously been assigned to an acetoxyethyl intermediate indicting that ethylene reacts with adsorbed ethylene on Pd(100) via the Samanos pathway, which involves a direct coupling between ethylene ad acetate species for form vinyl acetate monomer by a β-hydride elimination reaction. Reactions with various ethylene isotopomers suggest that decomposition of the acetoxyethyl intermediate is responsible for the non-selective, carbon monoxide formation. A kinetic model is developed for the reaction between ethylene and acetate species that includes non-selective carbon monoxide formation that reproduces the experimental titration curves.