The Study On The Selective Oxidation Of Biomass-derived Small Molecule 5-Hydroxymethylfurfural

The selective oxidation of biomass-derived small molecule 5-hydroxymethylfurfural（HMF） is one of the important reactions in the biomass conversion, and it has attracted much interest in recent years. In this dissertation, we investigated a highly efficient heterogeneous supported metal catalyst and a homogeneous catalytic system including general copper salt for the oxidation of HMF into 2,5-diformylfuran（DFF） with various oxidants under mild conditions, respectively. These processes are efficient and selective oxidation under mild conditions. They have very good perspective in the industrial application.Firstly, we studied the catalytic activity of the supported metal catalysts in the selective oxidation of HMF. The catalysts were mainly Co-based catalysts including Co/TiO₂, Co/SiO₂, Co/Al₂O₃, Co/ZnO, etc.. These catalysts were respectively characterized by XRD, BET, FTIR, TEM etc.; it is found that the Co/TiO₂ catalyst showed high catalytic activity in the presence of t-Bu OOH as oxidant, after reaction of 5h in 80℃, the conversion of HMF and the selectivity of DFF are 90.5% and 99.0%, respectively; after that, the effects of used solvent, reaction time, reaction temperature and oxidant on the catalytic activity were investigated. Moreover, after the Co/TiO₂ catalyst was recycled up to five times no significant loss of activity occurs in the reaction. This exhibits good stability of the catalyst.We also developed a homogeneous catalytic system of two components which involves copper salts and nitroryl radicals. The experimental data showed that the simple Cu I-HBT catalytic system was efficient for the selective oxidation of HMF into DFF in the presence of O₂ as oxidant, where a yield of 93.2% was obtained under suitable conditions. Moreover, the effects of various copper salts（CuBr, CuBr₂, CuCl, and CuCl₂）, mediators, oxidants and solvents on the activity and DFF selectivity were examined. Along with a wide range of chemical structure and redox properties, the mediators include 1-hydroxybenzotriazole（HBT）, N-hydroxyphthalimide（NHPI）, 2,2,6,6-tetramethyl piperidine-1-oxyl（TEMPO）, N-methyl mor-philone N-oxide（NMO） and 2,4-dichloro-5,6-dicyano benzo-quinone（DDQ）, etc. Furthermore, the effects of used solvents, reaction time, reaction temperature and different oxidants are tested and optimized in the oxidation reaction. It was found that the CuI /HBT/O₂ catalytic system showed best activity in the oxidation of HMF into DFF. In addition, a possible reaction mechanism was provided based on the obtained data and the corresponding experimental phenomena.