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

[Display omitted] •The synergistic mechanism of Ni/Co, PMA/PTA and ILs in lignin catalytic oxidative depolymerizationis proposed.•The Co[MIMPS]PMo12O40 catalyst effectively cleaves of the C-O and/or Cα-Cβ bond in a β-O-4 dimer model compound.•The cobalt-doped PMA matrix IL catalyst shows the best catalytic activity for aromatic compound yields.•The interaction of Co/Ni metal ions, POMs and IL leads to high yields of aromatic monomers. 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 Cα-Cβ 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.