Unveiling the Mechanism of Photocatalytic CO 2 Cycloaddition over Linker‐Engineered Metal‐Organic Frameworks

Abstract Photocatalytic CO 2 cycloaddition represents a promising route for solar‐driven synthesis of value‐added C 2+ chemicals and simultaneously mitigating anthropogenic CO 2 emissions. However, the pivotal step of direct one‐electron reduction of CO 2 to CO 2 •− requires a very high reduction potential of −1.9 V versus NHE, posing a formidable challenge. In this study, cerium‐based metal‐organic frameworks (MOFs) with linker‐induced defects, specifically Ce‐UiO‐66‐X (X = Me, H, and F), are investigated to elucidate the underlying mechanisms of photocatalytic CO 2 cycloaddition. Among them, Ce‐UiO‐66‐H, which strikes an optimal balance between light absorption and charge separation, demonstrates superior catalytic performance (yield > 90%) when coupled with tetrabutylammonium bromide (TBAB) as a co‐catalyst. In‐situ experiments and theoretical calculations reveal that TBAB stabilizes CO 2 through the formation of [Br − ···TBA + ]∼CO 2 adducts, which lowers the thermodynamic energy requirement for CO 2 •− generation from 0.66 eV (in the direct CO 2 ‐to‐CO 2 •− route) to −0.90 eV. This potential modulation promotes efficient photoelectron transfer from the MOFs to CO 2 , substantially enhancing the overall cycloaddition efficiency.