NiO Effectively Regulates the Generation of Oxygen Vacancies in MnO2 Promoting the Selective Oxidation of High-Concentration HMF to DFF

We have developed a highly efficient and stable non-noble metal-based heterogeneous catalyst for the selective oxidation of HMF to DFF. Mixed oxide catalysts with different Mn/Ni molar ratios were synthesized using the urea precipitation method. The Mn 6.6 NiO X catalyst exhibited a 95.33% HMF conversion rate and a 99.39% DFF selectivity under the conditions of 110°C, 2 h, 1 MPa O 2 , and N,N -dimethylformamide. Experimental results indicate that the introduction of NiO can effectively regulate the crystal structure of MnO 2 , forming an amorphous Mn─O─Ni interface, which significantly increases the specific surface area (SSA) of the catalyst while reducing the binding energy of surface lattice oxygen (O L ), promoting the generation of oxygen vacancies (O V ), and thereby enhancing the adsorption and activation capabilities of O 2 . Combined adsorption experiments and kinetic analysis revealed that Ni species preferentially anchor the hydroxymethyl group in HMF molecules, enhancing reaction selectivity. Further experiments demonstrated that the Mn 6.6 NiO x catalyst, under certain conditions, could achieve an HMF conversion rate of 87.52% and a DFF selectivity of 85.81% even at a high substrate concentration of 10 wt% HMF.