Facile molten salt synthesis of Co@N-C catalysts enables highly efficient HMF-to-FDCA conversion under mild conditions

The transition from petroleum-derived chemicals to sustainable alternatives has intensified interest in 2,5-furandicarboxylic acid (FDCA), a biomass-derived monomer for green polyester production. However, many non-noble metal catalysts for converting 5-hydroxymethylfurfural (HMF) to FDCA still require multistep syntheses and/or harsh oxidation conditions. Here, we report a straightforward molten-salt strategy to prepare nitrogen-doped porous carbon–supported cobalt catalysts (Co@N-C-x). Under ambient air at 90 °C in water, the optimized [email protected] catalyst affords complete HMF conversion and > 99 % FDCA yield, with a productivity of ~1.17 mol FDCA mol Co −1  h −1 , and retains 96.5 % yield in an initial 400-fold scale-up test. Mechanistic and kinetic analyses support a sequential pathway of HMF → HMFCA → FFCA → FDCA, with the FFCA-to-FDCA step being kinetically most demanding under the present conditions. Structure–activity analysis, together with atmosphere-dependent experiments, indicates that Co–Nₓ sites serve as the primary catalytic centers, while adjacent defect-rich surface sites (denoted as O₂-activation sites) promote dioxygen activation and facilitate stepwise oxidation. Density functional theory calculations further show that FDCA binds more strongly to the catalyst surface than the intermediates, which can hinder product desorption and contribute to the observed loss of activity upon recycling.