Cylindrical shaped ZnO combined Cu catalysts for the hydrogenation of CO2 to methanol

Abstract

Hydrogenation of CO₂ to chemicals is of great importance in the reduction of greenhouse gas emission. And the interaction and/or the boundary between Cu and ZnO played a crucial role in the performance of the Cu-ZnO catalyst for CO₂ hydrogenation to methanol. In this work, cylindrical shaped ZnO was first synthesized via controlled hydrothermal precipitation of Zn(CO₂CH₃)₂·2H₂O, and Cu was further deposited on ZnO via in situ reduction in aqueous solution. Characterizations indicated that the crystallization degree of ZnO decreased with the increasing content of Cu, while the exposed surface area of Cu exhibited a volcano shaped curve. It was found that the cylindrical shaped ZnO combined Cu catalysts were active for the hydrogenation of CO₂, and the space time yield of methanol reached 0.50 g_-MeOH (g_-cat h)^-1 at H₂/CO₂ = 3, 240 °C, 3.0 MPa, and 0.54 mol (g_-cat h)^-1, but the methanol selectivity decreases with the reduction of the (002) polar plane of ZnO. The conversion of CO₂ and methanol selectivity were discussed with the detected exposed Cu surface area and the number of oxygen vacancies.