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 <i>via</i> controlled hydrothermal precipitation of Zn(CO₂CH₃)₂·2H₂O, and Cu was further deposited on ZnO <i>via in situ</i> 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.