Chemical Engineering Journal, 528 (2026) 172617.
DOI: 10.1016/j.jcej.2026.172617
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-furan-dicarboxylic acid (FDCA), a biomass-derived monomer for green polyester production. However, many non-noble metal catalysts for converting 5-hydroxyethylfurfural (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 Co@N-C-0.1 catalyst affords complete HMF conversion and >99% FDCA yield, with a productivity of ∼1.17 mol FDCA molCo⁻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 → HMFA → 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 O-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.
EClassical 3100 high-performance liquid chromatography (HPLC) system, equipped with a UV detector and a C18 chromatographic column. The system was used with a mobile phase of 0.5 mM H₂SO₄ in methanol/water (6:4, v/v) at a flow rate of 0.5 mL min⁻¹, detection at 265 nm, and an injection volume of 20 μL.
The EClassical 3100 HPLC system was used to quantitatively analyze the reaction products and determine the conversion of HMF and the yield of FDCA and intermediates (HMFCA, FFCA). It enabled the monitoring of temporal product distribution, the construction of kinetic profiles, and the evaluation of catalyst performance across different conditions and recycling tests. This analytical capability was essential for establishing the reaction pathway, determining activation energies, and confirming the high selectivity and yield of the catalytic system.
