Research On The Catalytic Oxidation Of Biomass Platform Molecule 5-Hydroxymethylfurfural

As a renewable resource wildly existed in nature,biomass provides lots of alternatives to relieve our dependence on fossil energy.5-Hydroxymethylfurfural（HMF）is considered as a versatile biomass-derived platform,which is produced by the dehydration of hexose.The hydroxyl and aldehyde groups in HMF molecule make it prone to form valuable chemicals through selective catalytic process.In this work,the selective oxidation of HMF and oxidation esterification reactions were conducted.Products distribution of 2,5-diformylfuran（DFF）and 2,5-furandicarboxylic acid（FDCA）were investigated during the HMF oxidation reaction.Furan-2,5-dimethylcarboxylate（FDMC）was obtained as the ideal product from the methyl esterification of HMF and reaction pathway was explored.Meanwhile,the catalytic performance of catalysts was examined among the different modifications of HMF.α-Mn O₂ developed by liquid precipitation method was investigated in formation of DFF with isopropanol as a solvent.The lattice oxygen species on theα-Mn O2interface play a vital role in selective oxidation of hydroxyl group andβ-hydride elimination of HMF.The effect of solvents and the formation route of acetal by-product were studied.Under 0.5 MPa O₂,a 93.2%conversion of HMF and 84.3%selectivity of DFF were detected at 140 ^oC for 4 h.After being used for 5 th,α-Mn O2still keeps good stability.La-Mn O₂ catalyst was employed in oxidation of HMF to FDCA.Compared with the undoped Mn O₂catalyst,the mobility of lattice oxygen species on La-Mn O₂is elevated to facilitate the oxidation process.During the HMF oxidation process,the products distribution is influenced by the type of solvents.In isopropanol,95.1%conversion of HMF with 85.8%selectivity of DFF was obtained.In H₂O,germinal diol intermediates formed by the reversible hydration reaction occurred between H₂O and HMF result in the generation of FDCA.Besides,the above hydration reaction was accelerated and the activation energy of FDCA was decreased by NH₃·H₂O additive.A 96.3%conversion of HMF and 95.4%selectivity of FDCA were measured in H₂O solvent and the corresponding reaction mechanism was proposed.A serious of Pd O supported catalysts were examined in the oxidation of HMF without the addition of solvent.Different from the HMF oxidation carried out in H₂O solvent,5-hydroxy-methyl-2-furancarboxylicacid（HMFCA）was not measured as an intermediate under solvent-free condition.The oxidation of HMF to FDCA undergoes three steps,via DFF and FFCA to FDCA without H₂O solvent.A 38.8%conversion of HMF and 83.6%selectivity of FDCA was measured with a Pd O/Al PO₄-5 catalyst at 80 ^oC for 5 h under 0.5 MPa O₂.The effect of hydration process between H₂O and HMF on reaction pathway was discussed.The role of O₂was explored and the reaction pathway was proposed under solvent-free conditions.The catalytic activity of cobalt nanoparticles encapsulated into nitrogen-doped carbon nanotubes catalyst was measured in the oxidative esterification of HMF to FDMC.After the incorporation of N element in carbon nanotubes,the electronic interaction between Co and carbon shell was enhanced and induce the formation of defect sites in C-N material.The synergistic effect between metallic cobalt and nitrogen-doped carbon result in producing the oxygen radical to accelerate the HMF oxidation esterification reaction.According to the experimental results,the esterification of aldehyde group via hemiacetal stage was prior to the oxidation of hydroxyl group on HMF and thus DFF was not detected as the selective oxidation product.A 98.6%conversion of HMF with a 97.2%selectivity of FDMC is achieved at 130 ^oC for 16 h under 1 MPa O₂ and the reaction mechanism is proposed.The catalytic activity of Co-GCN was decreased slightly in recycling tested and the used catalyst can be reactivated after calcination.