Dual active sites over Cu-ZnO-ZrO_(2) catalysts for carbon dioxide hydrogenation to methanol

摘要

CO_(2) 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 CO_(2) hydrogenation are still in debate.Here,various molar ratios of ZrO_(2) were added into the Cu-ZnO catalysts to tune the distributions of Cu^(0) and Cu+species.A volcano-like trend between the ratio of Cu+/(Cu++Cu^(0))and the amount of ZrO_(2) is presented,among which the CuZn10Zr(the molar ratio of ZrO_(2) 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 CO_(2) hydrogenation over CuZn10Zr catalyst.The exposed Cu^(0) takes participate in the activation of H_(2),while on the Cu^(+) species,the intermediate of formate from the co-adsorption of CO_(2) and H_(2) prefers to be further hydrogenated to CH_(3)OH than decomposing into the by-product of CO,yielding a high selectivity of methanol.