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 ZnO_xH_y 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.