Copper-based catalysts for CO2 hydrogenation: a perspective on active sites

CO2 hydrogenation is regarded as a revolutionized field in heterogeneous catalysis, not only mitigating environmental problems caused by greenhouse gases but also producing valuable chemicals. This Perspective, going over both theoretical and experimental advances, aims to bridge Cu-based catalyst structures, the most important type of CO2 hydrogenation catalyst, and their catalysis applications with varied activity and selectivity. We provide a systematic overview of the catalytic active sites, the reaction mechanism, and their impact on the reaction selectivity, stability, and activity for CO2 hydrogenation. There is a particular focus on the nature of the industrial Cu/ZnO/Al2O3 catalyst, where a large volume of literature is available exploring the reaction energetics on the possible reaction sites, including Cu metal, CuZn alloy, and ZnOxHy overlayers. The recent advances in designing better catalytic active sites, such as the Cu single-atom catalyst, supported Cu cluster catalyst, and bimetallic Cu-M, are then followed to illustrate how the activity and selectivity vary upon changing the active sites. Our perspectives on the future research directions are finally provided, which should benefit the understanding of complex catalytic active sites and the design of better CO2 hydrogenation catalysts.