Photocatalytic Oxidation–Hydrogenolysis of Lignin β-O-4 Models via a Dual Light Wavelength Switching Strategy

Abstract

One of the challenges of depolymerizing lignin to valuable aromatics lies in the selective cleavage of the abundant C-O bonds of beta-O-4 linkages. Herein we report a photocatalytic oxidation hydrogenolysis tandem method for cleaving C-O bonds of beta-O-4 alcohols. The Pd/ZnIn2S4 catalyst is used in the aerobic oxidation of a-C OH of beta-O-4 alcohols to alpha-C=O with 455 nm light, and then a TiO2 NaOAc system is employed for cleaving C-O bonds neighboring the alpha-C=O bonds through a hydrogenolysis reaction by switching to 365 nm light. Interestingly, the oxidation-hydrogenolysis tandem reaction can be conducted in one pot to offer ketones and phenols (up to 90% selectivity) via a dual light wavelength switching (DLWS) strategy. EPR and metal loading experiments elucidate that Ti3+ in TiO2 is hydrogenolysis through electron transfer from Ti3+ to the beta-O-4 ketones. formed in situ and is responsible for the photocatalytic