The Designation Of Novel Polyoxometalate Based Catalysts In Catalytic Oxidation Of 5-HMF

The depletion of fossil resources and relative environmental problems have caused great attention to the use of renewable energy sources instead of fossil fuels and chemicals.Biomass,as an important carbon-containing renewable resource,can be effectively converted into biofuels and high-value chemicals through various chemical methods,such as lactic acid,levulinic acid,5-hydroxymethylfurfural?5-HMF?and so on.5-HMF is considered as an important chemical intermediate because it has two reactive groups?aldehyde group and hydroxyl group?.2,5-Diformylfuran?DFF?is an important product of 5-HMF selective oxidation,and has potential application value in organic conductors,drugs,polymers,antifungals and so on.Therefore,it is of great significance to study the efficient synthesis of DFF for the development of social economy.Polyoxometalates?POMs?are considered to be a class of acidic and redox catalysts and are widely used in organic conversion,especially in biomass conversion.However,there is a series of competitive pathways in biomass conversion.In order to achieve highly selective synthesis of target products,POMs catalysts often need to be designed as composite materials with multifunctional sites or special environments.Therefore,we have synthesized three novel catalysts by designing polyoxometalates and studied their performance in detail in aerobic oxidation of 5-HMF.1.Trifunctional catalysts H₅PMo₁₀V₂O₄₀@MgnAl-Surf?wt%??abbreviated as HPMoV@MgnAl-Surf?wt%?,n represented the molar ratio between Mg to Al?were synthesized by embedding H₅PMo₁₀V₂O₄₀ into surfactant modified MgAl-layered double hydroxide?LDH?and catalytic activity were evaluated in aerobic oxidation of 5-HMF.HPMoV/Mg_nAl-Surf presented tunable redox potential,Br?nsted acidity,Lewis acidity,and basicity.Meanwhile,the existence of surfactant being covalently bonded on MgnAl-LDH provided a hydrophobic surrounding for concentrating reactants and repelling the product,which promoted the mass transfer among inter-layer gallery.HPMoV@Mg4Al-Surf?23?was found to be most active to give 83.8%DFF yield at 94.6%conversion of 5-HMF in dimethyl sulfoxide?DMSO?at 140? for 12 h with 1.0 MPa O₂,while presented 84.7%2,5-furandicarboxylic acid?FDCA?yield at 93.2%conversion of 5-HMF in water at 120? for10 h with 1.0 MPa O₂.Meanwhile,HPMoV@Mg4Al-Surf?23?showed good stability and duration,because HPMoV was embedded by surfactant and could not be easily leached from Mg₄Al-Surf.2.Mesoporous g-C₃N₄ was prepared by thermal condensation of melamine and combined with?NH₄?₅H₆PV₈Mo₄O₄₀ by ethanol refluxing to synthesize?NH₄?₅H₆PV₈Mo₄O₄₀/g-C₃N₄?NPVMo/g-C₃N₄?,and catalytic activity were evaluated in aerobic oxidation of 5-HMF.NPVMo/g-C₃N₄ showed high catalytic activity due to its Br?nsted acidity,basicity,strong redox potential and large surface area.The optimal conditions were 100 mg of 5-HMF,40 mg of catalyst,6 m L of DMSO at 120? for 10 h with atmospheric O₂ to give 90.6%DFF yield at 97.6%5-HMF conversion.At the same time,NPVMo/g-C₃N₄ showed good recyclability,and still maintained high reactivity after being reused in eight times.3.Choline chloride?ChCl?and?NH₄?₅H₆PV₈Mo₄O₄₀?NPVMo?were used as precursors to prepare a series of POMs-ionic liquid catalysts?NH₄?₅Ch_xH_6-xPV₈Mo₄O₄₀?x=1-6?.The structure and morphology were characterized by infrared spectrum,X-ray powder diffraction,phosphorus nucleus,transmission electron microscope,and the catalytic activity were evaluated in aerobic oxidation of 5-HMF.The optimal conditions were 100 mg of 5-HMF,30mg of catalyst,6 mL of DMSO at 120? for 8 h with atmospheric O₂ to give 92.5%DFF yield at 97.0%5-HMF conversion.The catalytic activity was mainly derived from the Br?nsted acidity and redox potential of NPVMo.In addition,?NH₄?₅Ch_xH_6-x PV₈Mo₄O₄₀0 were stable and easy to be separated,and the catalytic performance did not change significantly after ten cycles.