Hydrogenation of methyl acetate to ethanol over a highly stable Cu/SiO2 catalyst: Reaction mechanism and structural evolution

Abstract

Abstracts A Cu/SiO 2 catalyst with a core-shell structure was found to be highly active and stable for the hydrogenation of methyl acetate to ethanol during 96 h reaction test at 523 K; MA conversion reached at 95% while the selectivity towards the major products (ethanol and methanol) approached ∼95%. Structural analysis revealed that most copper particles in the hydrogen-reduced Cu/SiO 2 catalyst had sizes of 3–7 nm and were coated with a thin layer of silica, forming a core-shell structure. The average size of copper particles and the core-shell structure kept unchanged in the spent catalyst, but the Cu + /(Cu 0 + Cu + ) ratio increased during the course of reaction, probably because of the electronic interaction between copper surface and methyl acetate under the reaction conditions. Mechanistic and kinetic studies have identified that ethyl acetate was formed through trans -esterification of initially produced ethanol with methyl acetate, while the subsequent hydrogenation of ethyl acetate to ethanol proceeded much faster. The Cu + /(Cu 0 + Cu + ) ratio played a crucial role in reaction network; MA could adsorb equally on Cu 0 and Cu + sites while the activation of molecular hydrogen occurs only on the Cu 0 site. Therefore, a rather stable performance could be attained with the increase in the Cu + /(Cu 0 + Cu + ) ratio during the course of reaction as long as the reaction is kinetically controlled by MA adsorption. The outstanding stability of the Cu/SiO 2 catalyst was ascribed to a combination of geometric and electronic effect.