CO2 hydrogenation to methanol over Cu/ZnO/ZrO2 catalysts: Effects of ZnO morphology and oxygen vacancy

Abstract

Cu/ZnO/ZrO2 catalysts with flower, plate, and rod-like ZnO morphologies were prepared by urea hydrolysis method and used for CO2 hydrogenation to methanol. Among these catalysts, Cu/ZnO/ZrO2 with flower-like ZnO (CZZ-flower) exhibits the best catalytic performance (10.7 % yield of methanol and 4.3 mmolMeOH/(gcat·h) STYMeOH). The characterization results show that the CCZ-flower possesses the largest amount of oxygen vacancies. The experimental results reveal that the yield of methanol increases linearly with the increment of oxygen vacancy concentration, suggesting that oxygen vacancy plays an important role in CO2 hydrogenation to methanol. Additionally, the amount of oxygen vacancy can be modulated by changing reduction temperature, reduction time, and reducing gas concentration. It can be seen from DFT (density functional theory) calculations that oxygen vacancy is able to promote CO2 and active hydrogen (H*) adsorption, activate reaction intermediate and reduce the whole energy barriers.