Ligand-Wise Stripping Dictates Metal Ensemble Catalysts for Selective Oxidation of Biomass-Derived 5-Hydroxymethylfurfural

Single-atom catalysts (SACs), with their well-defined active sites, demonstrate remarkable selectivity in biomass platform chemical conversions. However, the feature of single active site fails to synergistically regulate the divergent oxidation pathways of multiple functional groups, thereby restricting multi-step reaction efficiency. Herein, a "stepwise N-stripping" strategy is developed via lignin-derived N-doped carbon matrices, which achieves controlled evolution from isolated Co-N₄ single site to multi-scale atomic/cluster Co synergistic sites by precisely modulating the pyrolysis pathways of lignin-Co precursors. Theoretical and experimental evidence elucidates a synergy-enhanced tandem dual-site catalytic mechanism that single Co atoms with Co-N₂ configuration selectively activate aldehyde groups to drive sequential carboxylation (5-hydroxymethylfurfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) and 5-formyl-2-furoic acid (FFCA) to 2,5-furandicarboxylic acid (FDCA)), while Co clusters enhance oxygen activation for accelerated hydroxymethyl oxidation (HMFCA to FFCA). As expected, the optimized Co-N₂/Co₄ dual-site catalyst achieves 98.76% FDCA yield at 55 °C, surpassing most reported supported metal catalysts, alongside robust cycling stability (6 cycles with > 97% FDCA yield). This work establishes a biomass-tailored paradigm for constructing atomic/cluster hybrid catalysts and unravels the dynamic cooperation mechanism between distinct active sites in multi-step oxidation, advancing the rational design of efficient systems for biomass valorization.