The selective oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-diformylfuran (DFF) was studied over vanadium phosphate oxide (VPO)-based heterogeneous catalysts in the liquid phase. The selectivity to DFF was highly increased when using intercalated vanadium phosphate oxides under mild conditions (1 atm of oxygen, 110 °C) in an aromatic solvent. We found that the length of the intercalated ammonium alkyl chain had no clear influence on the catalytic performances, and a maximum yield of 83% could be achieved over C14VOPO4 and C14VOHPO4 after 6 h of reaction. Recycling of the catalyst was successfully performed, and we further obtained some insights in the reaction pathway: while the desired oxidation reaction indeed proceeded over the catalyst, the formation of by-products was linked to the presence of free radicals in solution.
