CsPbBr3 Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

Abstract Due to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi‐hydrogenation/reduction strategy utilizing CsPbBr 3 quantum dots (CPB‐QDs) and Hantzsch ester (HEH 2 ) as a synergistic catalytic system was introduced to reduce the BDE of C β −O−Ar, achieving effective cleavage of the C β −O−Ar bond. This strategy offers a wide substrate scope encompassing various β ‐O‐4 model lignin dimers, preoxidized β‐O‐4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir‐catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH 2 can be activated by CPB‐QDs via single electron transfer (SET), generating HEH 2 ⋅ + as a hydrogen donor while also serving as a hole quencher. Moreover, HEH 2 ⋅ + readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton‐coupled electron transfer (PCET) from HEH 2 ⋅ + to the carbonyl group of the substrate generates a C α ⋅ intermediate.