Lattice Oxygen-Mediated Oxidative Depolymerization of Lignin via Selective C–C Bond Cleavage under Visible Light

Lignin represents the most abundant source of aromatic compounds in nature, and its depolymerization holds great promise for yielding valuable aromatic products. Herein, we demonstrate the photocatalytic oxidative cleavage of β–1 bonds via the the Mars–van Krevelen (MvK) mechanism, and catalytic activity is achieved over lattice oxygen (OL)-rich WO3. A conversion of 99% is reached after reaction for 2 h under visible light, with the selectivity to benzaldehyde and benzoic acid reached 94%, surpassing the most reported catalytic systems. This photocatalytic performance stems from precise modulation of OL and oxygen vacancies (OV) sites in WO3, applicable to diverse β–1 model compounds and industrial lignin. In this MvK mechanism, the substrate adsorbs onto the OL sites, followed by activating the Cβ−H and inserting the lattice oxygen into the C–H bond to form a benzoin intermediate. Then, the desorbed benzoin undergoes a a Norrish Type I-like reaction, breaking the C–C bonds to form benzaldehyde. Concurrently, the adsorbed O2 at OV sites is reduced by photogenerated electrons, replenishing the depleted lattice oxygen and therefore manifesting stability (10 cycles). This in situ removal–regeneration strategy provides an approach for efficient lignin C−C bond cleavage and establishes the rational design principles for interfacial photocatalysts toward lignin valorization.