Adsorption and Activation of Methyl Acetate On Pd Surfaces

Esters (ROCOR') are a class of organic molecules frequently encountered in industrial polymer synthesis and biomass feedstock processing. Although reactions of esters catalyzed by transition metals, such as hydrogenolysis and transesterification, have been extensively studied experimentally, the mechanistic details of ester activation remain poorly understood. Therefore we are systematically investigating the reactivity of methyl acetate, a model ester, on palladium, a common hydrogenation catalyst, using density functional theory (DFT) calculations. Based on first-principles thermodynamics, the prevailing surface compositions are determined in the ranges of temperature and hydrogen pressure of practical interest for common Pd surfaces, including the close-packed (100) and (111) terraces and corresponding step edges. The activation of methyl acetate and its derivatives via various C-H and C-O bond scission steps is found to each proceed via similar mechanisms on the different Pd surfaces, but the energetics is sensitive to the extent of coordination of the Pd atoms in the active sites, and the pathway of activation is affected by the extent of hydrogenation of the surfaces. The molecular-level features of methyl acetate activation that our study identifies provide important insights for the selective catalytic conversion of esters in general.