Enhanced Depolymerization Performances in Converting Larch Lignin to Monophenolic Compounds by Heterogeneous...

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 H₅PMo₁₀V₂O₄₀ were replaced with different metal ions (Cu²⁺, Fe³⁺, and Co²⁺) 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/H₂O₂ 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.