A Carbon Catalyst Co-Doped with P and N for Efficient and Selective Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran

A newly designed N and P co-doped carbon material has been developed to catalyze the conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandialdehyde (DFF) with unprecedented yield and selectivity and demonstrating a synergistic effect between the heteroatoms. The desired catalyst was first synthesized via a pyrolysis method using urea as the nitrogen and carbon source followed by calcination with phytic acid solution as the phosphorus source. The mass ratio of phytic acid to C3N4 and calcination temperature were varied to investigate their effects on catalyst synthesis and microstructure as well as subsequent catalytic activity in simple reaction systems under oxygen. The effect of reaction conditions on the final HMF conversion and DFF selectivity were also investigated systematically. The P−C−N-5-800 catalyst obtained with the optimized annealing temperature of 800 °C and mass ratio of phytic acid/C3N4 of 5 enabled a 99.5 % DFF yield at 120 °C for 9 h under 10 bar oxygen pressure, being the highest among any reported metal-free heterogeneous catalyst to date. The excellent performance of P−C−N-5-800 could be ascribed to the synergy between N and P heteroatoms as well as the high content of graphitic-N and the P−C species within the carbon structure. Reusability studies show that the P−C−N-5-800 catalyst was stable and reusable without deactivation. These results strongly suggest that P−C−N-5-800 is a promising catalyst for large-scale production of DFF in a green manner.