Transition metal-substituted phosphomolybdic acid catalysts for selective oxidative depolymerization of lignin to...

Lignin, a complex organic polymer, is an abundant biomass feedstock and among the limited natural aromatic compounds serving as chemical precursors. However, effectively depolymerizing lignin into aromatic compounds remains a significant challenge. In this research, we synthesized a range of transition metal-substituted polyoxometalate (POM) catalysts and investigated their feasibility in the oxidative depolymerization of larch lignin. By optimizing the reaction conditions, we obtained a variety of valuable aromatic compounds, including methyl vanillate and vanillin. Optimization studies identified the PMo₁₁Fe catalyst as achieving maximum efficiency under 150 °C, 1.0 MPa O₂, and 1:1 catalyst-to-lignin ratio conditions, which produced 11.39 wt% monomeric aromatic compounds. The catalyst demonstrated exceptional recyclability through five consecutive catalytic cycles while maintaining a depolymerization efficiency of >85 %. This work establishes polyoxometalate-based catalytic systems as promising solutions for lignin valorization, advancing innovative strategies for sustainable biorefinery operations through selective biomass deconstruction.