A Dual−hydride Channel Strategy for Water−mediated Lignin Depolymerization during Reductive Lignocellulose Fractionation

Reductive catalytic fractionation (RCF) of biomass conventionally employs methanol as a passive solvent primarily for lignin solubilization. Herein, we report a conceptual shift by using water not merely as a green solvent, but as an active catalytic participant. This water-mediated RCF system achieves efficient fractionation of various sawdust feedstocks over conventional catalysts under notably mild conditions (170 °C, 3 MPa H 2 , 5 h), delivering superior efficiency and sustainability compared to methanol-based systems. Combined kinetic and isotopic labeling experiments confirm the essential dissociation of both H 2 O and H 2 , with hydrogen from both sources incorporated into the products. Density functional theory (DFT) calculations reveal a unique dual‑hydride mechanism, wherein water dissociation on the ruthenium catalyst surface generates hydroxyl species that markedly promote H 2 activation, producing additional hydrides. This synergistic dual‑hydride pathway significantly enhances the cleavage of key lignin linkages, enabling efficient depolymerization. Our work fundamentally redefines the role of water in catalytic biorefining and establishes a new paradigm for sustainable RCF, wherein water operates through a concerted catalytic mechanism.