The geometric effect in palladium-gold catalysis. Is the coupling the rate-determining step in the inyl-acetate synthesis?

摘要

First-principles calculations support the hypothesis that the appropriate spacing between Pd monomers controls the catalytic activity of Pd/Au catalysts in the vinyl acetate formation only if a vinyl surface species is involved in the rate-determining step of the reaction, opening new questions on these relevant catalytic systems.rnSince gold catalysis manifests itself only under quite specific circumstances, the interest in the gold catalytic power has dramatically grown only in the last twenty years. For example, gold has demonstrated industrial potential with its use in the production of vinyl acetate monomer (VAM) as a component of bimetallic catalysts due to the ability of Pd-Au catalyst to significantly improve the reactivity in comparison to pure Pd catalysts. Although acetoxylation of ethylene on Pd-Au bimetallic silica-supported catalysts promoted with potassium acetate (KOAc) is a mature commercial process for VAM synthesis, many details concerning the reaction mechanism and the surface reaction site, as well as the promotional role played by gold have not yet been elucidated.