Relay catalysis in the direct conversion of carbon dioxide to high-value chemicals

Hydrogenation of CO₂ using renewable hydrogen to build block chemicals, such as lower olefins and aromatics, not only mitigates the CO₂ emissions, but also realizes the utilization of CO₂ as a carbon resource. However, it is difficult to activate the inert CO₂ and precisely control the C–C coupling. As a result, the hydrogenation of CO₂ mainly produces C₁ product, and selective synthesis of hydrocarbon chemicals with C–C chains is challenging. In 2016, Chinese scientists first reported the relay catalysis, in which metal oxides and acidic zeolites were integrated together as bifunctional catalysts, for converting synthesis gas to lower olefins and aromatics. Inspired by this, a number of bifunctional catalysts have been recently reported for the hydrogenation of CO₂ to lower olefins and aromatics, using the concept of replay catalysis. In this review, we summarize the recent advances in the transformation of CO₂ to high-value chemicals and try to clarify how to connect two reactions with different characteristics. The key factors that affect the product distribution are also discussed.