Adsorption and activation, active site and reaction pathway of photocatalytic CO2 reduction: A review

Photocatalytic CO2 reduction (PCR) technology is one of the potential strategies to mitigate the greenhouse effect, solve the energy crisis and achieve goals of carbon dioxide emissions peak and carbon neutrality. However, it is extremely difficult to adsorb and activate CO2 due to the high dissociation energy of C = O bond in CO2 molecule (750 kJ·mol−1), resulting in poor performance of PCR. In addition, in the heterogeneous reaction process, adsorbing and activating CO2 are closely related to the active sites on the surface of photocatalyst. Therefore, in-depth and detailed exploration of the adsorption and activation of CO2 on active sites is critical to developing high-performance photocatalysts. Herein, this review firstly explores adsorption modes of CO2 on the active sites of photocatalyst, including physisorption and chemisorption, where chemisorption includes oxygen, carbon and mixed adsorption. Secondly, reaction pathways for the formation of different high value-added chemical products are introduced, including formaldehyde, carbene, glyoxal and mixed pathways. Then, strategies for enhancing the adsorption and activation of CO2 are briefly summarized. Finally, the future prospects and challenges of PCR development are discussed. This work provides insights and references for further designing photocatalysts that can enhance the adsorption and activation of CO2 and improve the performance of PCR.