Dual active sites over Cu-ZnO-ZrO2 catalysts for carbon dioxide hydrogenation to methanol

CO2 hydrogenation to methanol is a significant approach to tackle the problem of global warming and simultaneously meet the demand for the portable fuel. Cu-ZnO catalysts with various kinds of promoters have received wide attention. However, the role of promoter and the form of active sites in CO2 hydrogenation are still in debate. Here, various molar ratios of ZrO2 were added into the Cu-ZnO catalysts to tune the distributions of Cu0 and Cu+ species. A volcano-like trend between the ratio of Cu+/ (Cu+ + Cu0) and the amount of ZrO2 is presented, among which the CuZn10Zr (the molar ratio of ZrO2 is 10%) catalyst reaches the highest value. Correspondingly, the maximum value of space-time yield to methanol with 0.65 gMeOH/(gcat·hr) is obtained on CuZn10Zr at reaction conditions of 220°C and 3 MPa. Detailed characterizations demonstrate that dual active sites are proposed during CO2 hydrogenation over CuZn10Zr catalyst. The exposed Cu0 takes participate in the activation of H2, while on the Cu+ species, the intermediate of formate from the co-adsorption of CO2 and H2 prefers to be further hydrogenated to CH3OH than decomposing into the by-product of CO, yielding a high selectivity of methanol.