Efficient Lignin Depolymerization Process for Phenolic Products with Lignin-Based Catalysts and Mixed Solvents

Abstract

Due to their diverse functional groups and structural composition, carbon-based catalysts exhibit superior performance in various catalytic reaction systems, such as hydrogenolysis, hydrogenation, and oxidation. Herein, we propose an effective strategy of lignin liquid-phase depolymerization by applying the designed lignin-based carbon catalysts to produce aromatic chemicals. A series of Ni–Mo bimetallic carbon-based catalysts were synthesized to explore the effect of different preparation methods on the catalytic activity. The results demonstrate that the embedded Ni–Mo/C-WMO catalyst with multi-active sites of Ni, MoO3, and Mo2C results in a prominent catalytic effect on lignin depolymerization. The Ni–Mo/C-WMO catalyst can achieve a lignin conversion of 87.62% with a 42.25% monophenol yield in the methanol and water system. With the synergistic contribution of multiple active sites of the catalyst and the mixed-solvent system (water, methanol, and 1, 4-dioxane), a remarkably high yield of 62.95% of mono-phenolic compound was achieved at 260 °C and 3 MPa N2 with a reaction time of 4 h. The selectivity of 2-methoxy-4-methylphenol and 2-methoxy-4-ethylphenol in liquid products was 40.85 and 36.42%, respectively. Vanillin, a typical product from lignin depolymerization reported in the literature, was further degraded to monophenol in this system. The outcomes also confirmed that the in situ hydrogen production system of methanol and water coupled with 1,4-dioxane facilitated the lignin depolymerization significantly.