Catalytic oxidative depolymerization of lignin to aromatic compounds using transition metal doped ionic Liquid-based polyoxometalate catalysts

Significant attention has been focused on the depolymerization of lignin into monophenolics, as lignin is the most abundant biomass feedstock, and its valorization is considered crucial for a complete biomass refinery. In this study, we investigate catalytic oxidative depolymerization using novel bimetallic transition metal (Ni and Co) doped ionic liquid-polyoxometalate (ILPOM) composites under aerobic conditions. We systematically evaluate various catalysts, including [MIMPS]H₂PW₁₂O₄₀, Ni[MIMPS]PW₁₂O₄₀, Co[MIMPS]PW₁₂O₄₀, [MIMPS]H₂PMo₁₂O₄₀, Ni[MIMPS]PMo₁₂O₄₀, and Co[MIMPS]PMo₁₂O₄₀, assessing their impact on monomer yield and selectivity. Notably, Co[MIMPS]PMo₁₂O₄₀ emerges as a superior catalyst, producing high yields of key aromatic monomers, primarily vanillin and methyl vanillate, under optimized conditions. Additionally, the Co[MIMPS]PMo₁₂O₄₀ catalyst demonstrates effective cleavage of the C-O and/or C_α-C_β bonds within a β-O-4 dimer model compound, indicating potential catalytic cracking capabilities. This investigation elucidates the intricate interplay among transition metals, ionic liquids (ILs), and lignin, providing a novel pathway for lignin transformation.