Synthesis And Catalytic Oxidation Properties Of Keggin Type Polyoxometalates Based Composite Catalysts

Polyoxometalates(POMs)are a kind of metal-oxides cluster compounds and there exist rich Mo,W,V and other transition metal elements in the skeleton structures.POMs usually have particular structures,which result in outstanding properties,such as photoelectricity,electricity,agnosticism and strong acidity.Derived from those metal atoms with highest oxidation state,POMs also have great oxidoreduction properties.Its strong acidity comes from its Bronsted acid,especially in non-polarity organic solvents.Thus it is promising for POMs to replace the traditional acids including sulfuric acid in organic catalyst reactions.It is soluble in water,but it is not easy to recycle.In the catalysis reactions it is urgent to immobilize POMS to a reliable carrier,such as oxides,zeolites,active carbon and hydrotalcite.Here we chose ZnO,SiO2,graphite oxide(GO)and graphene sheets(GS)as the carriers to form the loaded catalysis materials whose structures and catalysis properties were then characterized measured.The main works are as follows:1.Synthesis,characterization and catalysis performance of Keggin-type POMs/ZnO complexes.The Keggin-type POMs/ZnO were prepared by dipping method with ZnO,Keggin-type POMs and nickel nitrate.The complexes were characterized by infrared(IR),X-ray powder diffraction(XRD)and thermo gravimetric(TG).The results demonstrated that the Kiggin skeleton structure kept well and there existed some chemical actions between POMs and ZnO.The complexes were tested and evaluated by catalytic oxidative desulfurization performance test and the experiments data show that the Keggin-type POMs/ZnO synthesized above represent high catalytic desulfurization performance.The catalytic effect of the composite was not obviously attenuated after the catalyst has been used circularly for five times.2.Synthesis,characterization and catalysis performance of Keggin-type POMs/GO-SiO2.A series of new catalysts including POMs/GO-SiO2 were synthesized by GO,TEOS,ethanol,and Keggin-type acid.And these composites were characterized by IR,XRD,TG and Raman.The measurement data confirmed a layer structure in POMs/GO-SiO2 and the well kept POMs structure had been inserted POMs in GO-SiO2.The catalytic activity of POMs/GO-SiO2 to epoxidation reaction ofalkenes was investigated with styrene as the reactant.The results show that POMs/GO-SiO2 is synthesized above represent high catalytic activity and selectivity to the epoxidation of styrene.The catalytic effect of the composite was not obviously attenuated after the catalyst has been used circularly for five times.It is also proved that there is a strong chemical interaction between the GO-SiO2 and POMs and the POMs anion is difficult to dissolve.3.Synthesis,characterization and catalysis performance of Keggin-type POMs/GS.GO was first prepared through Hummers and then POMs/GS complex was synthesized by hydrazine with GO and POMs as the construction units.The complex was characterized by IR,XRD,TG,Raman,scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results confirmed the GS and Keggin-type POMs unit structures in the complex.There existed great chemical bond effect between them.The POMS in the new catalyst was not easy to be split by dissolving.The catalytic activity of this new POMs/GS catalyst to epoxidation reaction of alkenes was investigated with styrene as the reactant.