Oriented Conversion\nof HMF to FDCA under Mild Conditions\nover Lignin-Tailored Co Single-Atom Catalyst with Enhanced Co Loadings

Heterogeneous catalysis over single-atom catalysts (SACs)\nhas garnered\nsignificant attention in biomass-derived platform chemical conversion\nowing to the high atomic utilization and reliable selectivity/stability.\nHerein, Co single-atom catalysts (Co–N/F1) derived from fractionated\nlignin were employed for the oriented oxidation of 5-hydroxymethylfurfural\n(HMF), a typical platform chemical derived from glucose, into 2,5-furandicarboxylicacid\n(FDCA) under mild conditions. The Co–N/F1 with enhanced Co\ncontent was obtained using the low-molecular-weight lignin fraction\n(F1) with high functional group contents (e.g., Ph–OH and COOH),\nand the as-prepared catalyst was demonstrated to present a Co–N<sub>4</sub> configuration. Owing to the absence of colored byproduct\nformation from HMF at elevated temperatures, Co–N/F1 realized\nthe highly selective conversion of HMF to FDCA (100% HMF conversion,\n99.20% FDCA yield) under mild conditions (65 °C, 3 bar O<sub>2</sub>), which outperformed most reported non-noble metal-supported\ncatalysts. Density functional theory calculations indicate that the\nCo–N<sub>4</sub> site in Co–N/F1 facilitates the dehydrogenation\nof the α-C position on HMF and its aldehyde intermediates, resulting\nin a significantly enhanced catalytic efficiency. Furthermore, Co–N/F1\nexhibited stable reusability due to the alkaline resistance of the\nCo–N<sub>4</sub> structure. Our study details the insights\ninto the synthesis of Co-SACs using a lignin fractionation strategy\nand further demonstrates its good feasibility for the oriented conversion\nof biomass-derived platform chemicals under mild conditions.