Dimethyl carbonate production via the oxidative carbonylation of methanol over Cu/SiO2 catalysts prepared via molecular precursor grafting and chemical vapor deposition approaches

The influence of catalyst synthesis method and Cu source on the activity and selectivity of Cu/SiO2 catalysts for the gas-phase oxidative carbonylation of methanol to dimethyl carbonate (DMC) is reported. [CuOSi(O tBu)3]4, [CuO tBu]4, and CuCl were used as precursors to produce highly dispersed silica-supported copper. XANES and EXAFS characterization prior to reaction (but after thermal treatment under He) showed that Cu in the catalysts prepared with CuCl and [CuOSi(O tBu)3]4 was present primarily as isolated Cu(I) species, whereas [CuO tBu]4 produced 1-nm Cu particles. During the catalytic reaction, the Cu in catalysts prepared from CuCl and [CuOSi(O tBu)3]4 formed highly dispersed CuO moieties, whereas the Cu in catalysts prepared from [CuO tBu]4 formed a cuprous oxide layer over a Cu(0) core. For comparison, poorly dispersed Cu on silica was prepared via traditional incipient wetness impregnation with Cu(NO3)2. It was found that activity for DMC formation increased with increasing Cu dispersion. The selectivity for DMC formation (relative to CO) decreased with decreasing Cu dispersion when the original state of the Cu was Cu(0) directly preceding reaction conditions.