Nano WO3-Catalyzed One-Pot Process for Mild Oxidative Depolymerization of Lignin and its Model Compounds

Despite challenges related to the robust and irregular structure of lignin, the valorization of this aromatic biopolymer has aroused great interest. However, the current methods exhibit problems such as harsh reaction conditions, complicated operation, and difficult recovery of catalyst. Herein we present a one-pot process for the mild oxidative depolymerization of lignin and lignin model compounds catalyzed by nano WO3, along with tert-butyl hydrogen peroxide (TBHP) as the oxidant and NaOH as the additive, which exhibits advantages of both homogeneous and heterogeneous catalysis. Under the optimized condition, it yielded 80.4 wt % of liquid oil from organosolv lignin with 7.6 wt % of vanillic acid as the main monomer product, accounting for 91.6 wt % monomeric selectivity. Mechanism studies on the model substrate suggest that the reaction proceeds via an oxidation of C-alpha-OH to C=O followed by C-O bond cleavage to afford phenol and ketone products which may undergo further oxidation to produce aromatic carboxylic acids. We have developed an operationally simple procedure for mild fragmentation of lignin and lignin model compounds with excellent yields, which provides the potential to expand the existing lignin usage from energy source to value-added commodity chemicals.

Automated summary

A new one-pot process for the mild oxidative depolymerization of lignin and lignin model compounds has been developed, achieving high yields and monomeric selectivity. The method utilizes nano WO3 as catalyst, tert-butyl hydrogen peroxide as oxidant, and NaOH as additive, providing a potential for transforming lignin into high-value commodity chemicals.