Catalytic Conversion of Carbon Dioxide to Methanol over Palladium-promoted Cu/ZnO Catalysts

Abstract

Methanol synthesis by hydrogenation of CO and CO2 over Cu/ZnO catalysts reduced at various temperatures has been studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Specific activity for CO Hydrogenation decreased with increasing reduction temperature of Cu/ZnO. On the contrary the activity for CO2 hydrogenation increased with the reduction temperature. Structural analysis by means of XRD and TEM indicates the formation of binary Cu-Zn alloy when the Cu/ZnO were reduced at temperatures above 600 K. It was found that the Cu-Zn alloying caused an increase in the activity of methanol synthesis by hydrogenation of CO2. However, the alloying caused a decrease in the catalytic activity by hydrogenation of CO. Doping Cu/ZnO with palladium enabled to prepare either a binary Cu-Zn or a ternary Cu-Zn-Pd alloy at low reduction temperature of 523 K where the formation of the Cu-Zn alloy was hardly observed for the Pd-free Cu/ZnO catalysts. The alloying also enhanced the activity of methanol synthesis by CO2 hydrogenation, but lowered the activity for CO hydrogenation.