One-Pot Solvent-Free Conversion of Furfural and CO₂ into 2,5-Furandicarboxylic Acid

2,5-Furandicarboxylic acid is an important biomonomer for the synthesis of polyesters, and studies on the synthesis of FDCA mainly focus on the 5-hydroxymethylfurfural and furoic acid routes. The synthetic route starting from furfural has a broader and more economical raw material source than the furoic acid route. In this study, the furfural route was used to develop an energy-efficient and one-pot method for synthesizing FDCA from furfural and CO₂ as raw materials. Under solvent-free conditions, the Co-N-C catalyst and CsOH·H₂O were used as catalyst and base, respectively. Pure furfural was converted to cesium furoate (with a yield of 93%) by mechanical ball-milling. Then, without the need for separation and purification, CsOH·H₂O was in situ-transformed into Cs₂CO₃ at 260 °C under a flowing CO₂ atmosphere, thereby facilitating the carboxylation of furoate to cesium 2,5-furandicarboxylate. The dynamic experiments and Matlab data fitting revealed that it followed the iterative steps of rapid disproportionation (k₁ = 7.53) and slow furfuryl alcohol oxidation (k₂ = 0.13). Single Co sites improved atomic utilization without using any solvent, yielding a fast formation rate of furoic acid (21.6 mol_FA mol_metal^-1 h^-1). The renewable biomass furfural and greenhouse gas CO₂ were comprehensively utilized to form a biobased polyester monomer FDCA via a green and simple strategy.