Mechanistic Insight into the Acidic/Redox Modulation of Vanadium-Substituted Dawson Polyoxometalates Enabling Overall Conversion of Larch Lignocellulose

Developing structurally well-defined homogeneous catalysts for one-pot lignocellulose depolymerization remains a significant challenge. Herein, V─Mo polyoxometalate (POM) molecules with a Dawson structure have been designed through “metal-to-metal” replacement of addendum MoVI by different amounts of VV to adjust the acidity and redox properties in H6+nP2Mo18–nVnO62 molecules (n = 1–3, H6+nP2Mo18–nVn) via altering the V number, hence studying the activity and mechanism in the aerobic oxidation of the lignin model 2-phenoxy-1-phenylethanol (pp-ol). Experimental and density functional theory results revealed that H9P2Mo15V3 facilitated a unique proton-coupled electron transfer (PCET) mechanism, which was distinct from the electron transfer-oxygen transfer pathway observed in Keggin-type analogues. This PCET process efficiently promoted Cα─OH oxidation to Cα═O and activated β–O–4 bond cleavage by decreasing the C─O bond length in oxidative intermediates. Furthermore, the synergistic effect of protons and redox sites enabled H9P2Mo15V3 to serve as a high-performance homogeneous system for “lignin-first” biorefinery. Through a two-step oxidation–hydrolysis process, raw larch was successfully converted into a suite of value-added products, including aromatic monomers, lignin oligomers, and carbohydrate-derived chemicals (glucose, mannose, glycolic acid, and formic acid), alongside the production of nanosized cellulose. This work provides mechanistic insights into the design of multifunctional POM catalysts for the holistic valorization of native biomass.