Hydrogen-Free Production of 4-Alkylphenols from Lignin via Self-Reforming-Driven Depolymerization and Hydrogenolysis

Abstract

Lignin is constructed from methoxylated phenylpropanoid with plenty of hydroxys and methoxys. Its conversion to valuable products is extremely attractive but especially challenging without additional hydrogen sources. Herein we report a hydrogen-free production of 4-alkylphenols directly from native lignin via self-reforming-driven depolymerization and hydrogenolysis over Pt/NiAl2O4. This is the first example of acquiring 4-alkylphenols from native lignin. Using this strategy, high yields of 4-alkylphenols, 17.3 wt %, were obtained from birch lignin. Reaction pathway and mechanism studies revealed that this strategy initiates from the reforming of aliphatic hydroxys, followed by the cleavage of C–O linkages, and ends via demethoxylation over Pt/NiAl2O4. Moreover, the subsequent aqueous phase reforming of the as-formed methanol accelerates the whole process. This strategy realizes the one-pot production of 4-alkylphenols from lignin by fully utilizing the structural hydrogen in lignin and H2O, providing a low-cost and safe method of lignin valorization.