Synthesis And Oxygen Oxidation Activity Of Functionalized Polyoxometalates Hybrid Materials

Oxidation reaction is a very important kind of reaction in chemistry and plays an important role in the field of production,life and petrochemical industry.In recent years,oxygen or air as an oxidant has been paid more attention and developed in the field of catalytic oxidation owing to its advantages,which are wide source,bargain price,easy access and environment protecting.Polyoxometalates（POMs）,as a kind of common oxidation/acid catalysts,has been widely used in the field of catalysis.The functionalized POMs by organic carrier not only endue its unique structure and physicochemical properties,but also improve catalytic activity and solve the problem that POMs is difficult to recycle as homogeneous catalyst.Therefore,the design of carrier is of great significance to the synthesis of catalyst and the improvement of reactivity.In this paper,two kinds of composite catalysts were synthesized by Porous Aromatic Frameworks or dibinudeate phthalocyanine cobalt sulfonic acid ammonium sulphate as organic precursors and POMs as active center.The porous structure,high specific surface area or planar conjugated macroring structure of the organic precursors promoted the electron transfer and delocalization of the composite catalyst in the catalytic reaction and enhanced the catalytic activity.Using oxygen as oxidant,the activity and synergistic mechanism of the composite catalyst in the reaction of alcohol oxidation and esterification and oxidation desulfurization were investigated.It mainly includes the following aspects:1.A series of Keggin type（NH₄）₅H₆PV₈Mo₄O₄₀,H₅PV₂Mo₁₀O₄₀,H₅PMo₁₂O₄₀,H₃PW₁₂O₄₀,K₇PW₁₁O₃₉,and POMs substituted by different transition metals K₅PW₁₁MO₃₉（M=Co,Fe,Mn,Ni and Cu）were synthesized and evaluated as homogeneous catalysts for the oxidation and esterification of ethanol as a model reaction.The influence of Lewis acid metals as substituted atoms on the total acidity and redox properties of POMs was studied.The one with the best catalytic activity to ethanol and highest selectivity to ethyl acetate was selected.2.In numerous POMs compounds,K₅PW₁₁CoO₃₉(PW₁₁Co)showed the highest catalytic activity in the oxidation and esterification of ethanol and selectivity of ethyl acetate.PW₁₁Co@iPAF-2 took PW₁₁Co as its inorganic precursor and Porous Aromatic Frameworks（PAFs）iPAF-2 as its organic carrier.The structure-activity relationships,synergy mechanism and optimal reaction conditions in oxidation and esterification reaction of ethanol with PW₁₁Co@iPAF-2 as catalyst were investigated.The effects of Lewis acidity and redox properties of PW₁₁Co@iPAF-2 on the oxidation and esterification of ethanol was studied.The stability and recyclability of PW₁₁Co@iPAF-2 were investigated in repetitive experiments.3.According to the research in（1）and（2）,the type of Lewis metal not only affects the acidity and oxidation reduction of POMs,but also has a certain effect on the selectivity of ethyl acetate.Introduction of transition metal Co in composite material showed the best reaction activity,therefore PW₁₁Co/Co-Pc（Ⅰ）took PW₁₁Co as its inorganic precursor and phthalocyanine cobalt（Co-Pc）which containing transition metal Co²⁺as its organic carrier.The structure-activity relationships,synergy mechanism and optimal reaction conditions in oxidation and esterification reaction of ethanol with PW₁₁Co/Co-Pc（Ⅰ）as catalyst were investigated.The stability and recyclability of PW₁₁Co/Co-Pc（Ⅰ）were investigated in repetitive experiments.4.According to the research of（2）and（3）,the combination of POMs and organic carriers can activate oxygen and improve the catalytic activity.Based on this conclusion,the performance of functional POMs in aerobic oxidation desulfurization is worth to investigating.A[PV_xMo_12-xO₄₀]^（3+x）-series of Keggin type POMs(H₃PMo₁₂O₄₀,H₄PVMo₁₁O₄₀,H₅PV₂Mo₁₀O₄₀,H₆PV₃Mo₉O₄₀ and（NH₄）₅H₆PV₈Mo₄O₄₀ were evaluated in the aerobic oxidation desulfurization.It was found that V content of POMs was positively correlated with the effect of aerobic oxidation desulfurization.Therefore,PMoV/co-pc composites were prepared by taking（NH₄）₅H₆PV₈Mo₄O₄₀（abbreviated as PMoV）as the active center and Co-Pc as the organic carrier.The catalytic activity of the composites was investigated in the reactions of aerobic oxidation desulfurization of model oil,actual oil and inorganic sulfur.The structure-activity relationships,synergy mechanism,optimal reaction conditions,adsorption performance of the composites and the reaction mechanism in the aerobic oxidation desulfurization were studied.The stability and recyclability of PMoV/Co-Pc（Ⅰ）were investigated in repetitive experiments.5.According to the research in（4）,the stronger oxidation and adsorption of composite materials,the more conducive to the aerobic oxidation desulfurization.IMo₆@iPAF-1 or PMoV@iPAF-1 was designed and synthesized by using strong oxidizing Anderson type Na₅IMo₆O₂₄（abbreviated as IMo₆）or Keggin type PMoV as the active center and Porous Aromatic Frameworks iPAF-1 which has the excellent performance in adsorbing the substrate as organic carrier.The catalytic activity of the composites was investigated in the reactions of aerobic oxidation desulfurization of model oil and actual oil under O₂ or air.The structure-activity relationships,synergy mechanism and optimal reaction conditions in the aerobic oxidation desulfurization reaction with IMo₆@iPAF-1 as catalyst were studied.It was found that the appropriate porosity,specific surface area and aromatic ring structure of iPAF-1provided a microenvironment conducive to the aerobic oxidation desulfurization reaction.The substrate which was adsorbed and limited around the active site and product precipitation increased the reaction rate.The stability and recyclability of IMo₆@iPAF-1 were investigated in repetitive experiments.