A first principles analysis of the ensemble effects in the synthesis of vinyl acetate over Pd/Au substrates

The surface ensemble effects on the selectivity and activity of the synthesis of vinyl acetate over Pd/Au substrates were studied. The Au regions separated the active sites such that they were less crowded by other adsorbates. On pure Pd, the surface was covered with ethylene and acetic acid, which hindered adsorption, surface diffusion, and reaction of ethylene and acetate. Either ethylene dehydrogenation or vinyl coupling with surface acetate were similar and may be rate determining, depending on the reaction conditions. The unselective decomposition pathways for ethylene and acetic acid were also considered. The oxidative dehydrogenation and decomposition reactions all appeared to be exothermic and became more favorable at higher oxygen partial pressures. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).