Recent progress in selective thermal oxidation of 5−hydroxymethylfurfural to 2,5−diformylfuran

5−Hydroxymethylfurfural （HMF）, a key biomass-derived platform molecule, can be selectively oxidized to 2,5−diformylfuran （DFF）, an important intermediate for bio-based polymers, fine chemicals, and functional materials. Compared to the full oxidation of HMF to 2,5−furandicarboxylic acid （FDCA）, the selective formation of DFF requires precise oxidation of the hydroxymethyl group while suppressing overoxidation of the aldehyde group, posing significant challenges in catalyst design and reaction control. This review provides a comprehensive overview of recent progress in the thermal catalytic oxidation of HMF to DFF, with emphasis on the mechanistic pathways, including oxygen source selection, solvent effects, reactive oxygen species generation, and their interplay with active sites. Advances in noble metal catalysts, transition metal oxides, and carbon-based materials are discussed in terms of structural modulation, structure–activity relationships, and catalytic performance. The advantages and limitations of different catalytic systems are critically compared. Finally, key challenges such as selectivity tuning, catalyst stability, mechanistic elucidation, and the development of green, scalable processes are outlined to guide future research on efficient thermal catalytic systems for DFF production.