Enhanced Depolymerization Performances in Converting Larch Lignin to Monophenolic Compounds by Heterogeneous Catalysts From Transition Metal-Substituted Molybdovanadophosphoric Heteropolyacid and Alkaline Ionic Liquids With Hydrogen Peroxide

The selective preparation of vanillin (Van) and ethyl vanillate (EV) remains a major challenge in depolymerizing lignin. Larch lignin is full of coniferyl alcohol unit, which is preferred to produce Van and EV. In this study, the counterions in H 5 PMo 10 V 2 O 40 were replaced with different metal ions (Cu 2+ , Fe 3+ , and Co 2+ ) to develop the modified polyoxometalates, which were then combined with alkaline ionic liquid (IL) to construct a multiactive catalyst possessing acidic, basic, and oxidizing properties. The incorporation of Cu significantly enhanced the cleavage of C–C and C–O bonds in larch lignin at 160°C for 6 h in an ethanol/water/H 2 O 2 system. Under these conditions, the total yield of monophenol reached 15.62 wt%, Van and EV were dominant with the yield of 5.93 and 9.1 wt%, respectively. The fracture of lignin model compounds showed Cu-based polyoxometalates/IL catalysts are effective in selectively preparing EV and Van. The catalyst can be recycled up to 4 times with excellent stability and recoverability. This study provides a more effective strategy for converting waste biomass into valuable platform chemicals. Graphical The figure illustrates the conversion process of larch lignin being depolymerized into high-value monophenolic products, with vanillin (5.93 wt%) and ethyl vanillate (9.1 wt%), under the mediation of a Cu 2+ -substituted H 5 PMo 10 V 2 O 40 polyoxometalate combined with an alkaline ionic liquid. It visually presents the core pathway for the selective and sustainable valorization of lignin biomass into platform chemicals.