One-Pot Photocatalytic Cleavage of Lignin β–O–4 Models by Dehydrogenation–Hydrogenolysis

Valorizing lignin into valuable chemicals requires the selective breaking of a large number of C–O bonds found in the β–O–4 structure. In this study, we present a one-pot strategy that utilizes two NiO/TiO2 catalysts for the photocatalytic depolymerization of β–O–4 alcohols. The S-1.6%NiO/TiO2 catalyst is used for the dehydrogenation of β–O–4 alcohols at 450 nm. Then, the L-0.8%NiO/TiO2 catalyst is employed for the hydrogenolysis of β–O–4 ketones at 365 nm. Remarkably, the dehydrogenation–hydrogenolysis tandem reaction can be conducted in one pot, which affords high yields of ketones and phenols (up to 89%) from β–O–4 alcohols. Additionally, the L-0.8%NiO/TiO2 catalyst prepared in this article is the smallest NiO/TiO2 photocatalyst reported to date, and the size of NiO in the S-1.6%NiO/TiO2 catalyst is even small enough to enter the lattice of TiO2. We successfully regulated the reaction selectivity by controlling the loading method and the amount of NiO. Our work offers a promising solution for efficiently cleaving target bonds in lignin and provides insights into the design of efficient photocatalysts.