Fabrication Of Polyoxometalate Nanofiber Materials And Their Catalytic Activity In Oxidation 5-HMF Transformation

5-Hydroxymethylfurfural?5-HMF?as biomass-derived platform chemical is an important intermediate of chemical fuels.The active functional groups of 5-HMF perform high activity and products diversity.The ambiton of 5-HMF oxidation obtained high yield of target product.Nowadays,noble metals immobilized on different supports are widely used for the oxidation of 5-HMF.2,5-dimethyl furan?DFF?,5-hydroxymethyl-2-furan acid?HMFCA?and 2,5-furan dicarboxylic acid?FDCA?are the major oxidation products in the oxidation of5-HMF by O₂ or H₂O₂.The reaction conditions,catalyst composition,acidity/basicity of supports and hydrophobicity affect the conversion of 5-HMF and selectivity of products.In order to avoid the use of the noble metals,it is urgent to develop non-noble metal systems,especially abundant elements.Polyoxometalates?POMs?are a kind of metal oxygen compounds containing W,Mo,V,P and Si.POMs could be widely used in organic synthesis and conversion,due to the properties of strong Br?nsted acidity,Lewis acidity and redox properties.POMs are widely used in the oxidation of biomass instead of noble metals.The applications of POMs are limited,due to the high solubility,low surface area and poor recycleaility.The synthesis of heterogeneous POMs is an important study field.Electrospinning technology as a common method for preparation one-dimensional nano-materials is applied in POM immobilization,which could solve the problems of catalysts recycling and POMs micro-environment.It will be a good way to develop one-dimensional POM catalysts for the effective conversion of5-HMF under aerobic oxidation.The details were as follows:?1?H₅PMo₁₀V₂O₄₀/SiO₂?HPMoV/meso-SiO₂?f??nanofibers with mesoporous structure were successfully fabricated through the combination of electrospinning and surfactant directing pore formation technique.The composition,structure,morphology and porosity of HPMoV/meso-SiO₂?f?were characterized by IR,³¹P MAS NMR,SEM,TEM,Nitrogen adsorption-desorption isotherms and systematically studied the adsorption properties of catalysts.The relationship between HPMoV/meso-SiO₂?f?nanofibers and catalytic activities in oxidition of starch and aerobic oxidation of 5-HMF was investigated.And the reasons of the high catalytic activity of H₂O₂ and O₂ for oxidation reactions were studied.HPMoV/meso-SiO₂?18-f?presented the carboxyl content as 0.58 mol/100g at 70 ^oC,10 h in oxidation of starch,and 92.7%5-HMF conversion,89.2%DFF yield at 120 ^oC,8 h in oxidation of 5-HMF.The stability and recyclability practicability of HPMoV/meso-SiO₂?f?were evaluated by recyclability experiments.?2?The HPMoV/sillica-NH₂ precursor was prepared by coupling agent?3-aminopropyl triethoxysilane,APTES?and pore template sol-gel copolymerization.One-dimensional HPMoV/SiO2-NH2 mesoporous nanofibers?abbreviated as HPMoV/meso-SiO2-NH2?f??were synthesized by electrospinning.The composition,structure,morphology and other physical and chemical properties of catalysts were characterized by IR,³¹P MAS NMR,SEM and TEM.And the adsorption properties of substrate and oxygen were investigated.The properties of acidity-basicity of HPMoV/meso-SiO2-NH2?f?for 5-HMF oxidation were systematically studied.The results showed that HPMoV/meso-SiO2-NH2?f?introduced amino groups to reduce the acidity of the catalyst to avoid over-oxidation of 5-HMF and increase the yield of DFF.As the acid-base ratio was 2.4,93.2%5-HMF conversion and 90.0%DFF yield were obtained under 120 ^oC,8h and the stability and reuse of HPMoV/meso-SiO₂-NH₂?f?were evaluated by recyclability experiments.?3?HPMoV/ZrO2 nanofibers?HPMoV/meso-ZrO2?f??with mesoporous structure were fabricated through combined electrospinning and surfactant directing pore formation technique.The composition,morphology and porosity were characterized by IR,XRD,SEM,TEM and Nitrogen adsorption-desorption isotherms.And the adsorption performance was systematically studied.In the oxidation of 5-HMF by oxygen,the effect of the catalyst structure and the reasons of high activity were studied.The results show that the introduction of Lewis acidity increases the total acidity of HPMoV/meso-ZrO2?f?,which was promoted the conversion of 5-HMF to DFF.As the Lewis/Br?nsted=0.24,96.2%5-HMF conversion and89.9%DFF yield was obtained under 120 ^oC,8 h.The stability and recyclability of HPMoV/meso-ZrO2?f?were evaluated by recyclability experiments.?4?HPMoV@lipid?n?/CeO₂?n=2,4,6,8,10?nanofiber with lipid-like bilayer was fabricated through the combination of electrospinning and covalent bond method in this chapter.The composition,structure,morphology,hydrophobicity and other physical and chemical properties of catalysts were characterized by IR,³¹P MAS NMR,SEM and TEM.The adsorption properties of different surfactant layers on 5-HMF were systematically studied.In the 5-HMF/O₂ reaction system,the influence of catalyst structure on the catalytic activity was studied.The reaction conditions of oxygen oxidation of 5-HMF were optimized.Studies had shown that HPMoV@lipid?n?/CeO2 with controllable surfactant structure providesed a micro-environment similar to an enzyme reaction for catalytic reactions and promoted the conversion of 5-HMF to DFF.100%5-HMF conversion and 95.3%DFF yield was obtained by HPMoV@lipid?4?/CeO₂ at 120 ^oC,6 h.And the stability and recycling of the catalyst were investigated through recyclability experiments.