Study on the performance optimization and mechanism of Dawson-type P-W-V polyoxometalate catalyzed oxidative depolymerization of lignin to aromatic monomers

Lignin is the most abundant renewable source of aromatic compounds in nature. However, its complex structure poses significant challenges for efficient depolymerization and catalyst design. In this study, a series of Dawson-type vanadium-substituted phosphotungstic polyoxometalates (POMs) were synthesized and used to catalyze the oxidative depolymerization of natural larch lignin to produce aromatic compounds. The reaction mechanism was investigated in depth. By adjusting the vanadium content, the acidity and oxidation ability of the catalyst were precisely controlled at the atomic level. The results showed that the vanadium content significantly affected the monomer yield. Under the optimal conditions (170 °C, 3 h, 1 MPa oxygen, catalyst-to-lignin ratio 1:1), H₉P₂W₁₅V₃O₆₂ achieved the highest aromatic compound yield of 11.42 %, with the selectivity of vanillin and methyl vanillic acid reaching 93.5 %. During the reaction, the acidic and redox properties of POMs promoted the selective conversion of phenolic hydroxyl groups in lignin to carbonyl structures. This change altered the polarity of the C_α-C_β bond, increased its reactivity, and facilitated bond cleavage. This work achieved precise control over the catalytic activity of POMs and enabled efficient and selective conversion of lignin into high-value phenolic compounds. Additionally, the mechanistic insights obtained in this study provide valuable theoretical and practical support for the high-value utilization of lignin and the development of a sustainable bioeconomy based on biomass resources, which is of significant scientific and economic importance for sustainable development.