Study Of Synthesis And Catalysis Performance Based On Polyoxometallates

Polyoxometallates(heteropolyacids) have been widely employed as oxidationcatalysts in various homogeneous and heterogeneous reactions. One of the greatadvantages of polyoxometallates catalysts is that their oxidation catalyticproperties can be controlled in a systematic way by changing the identity ofcharge compensating counter-cations heteroatoms, and framework polyatoms.However, there are some problems for polyoxometallates in the application,ashomogeneous catalyst, it is difficult to recover the catalyst from the system andas heterogeneous catalyst, their surface area is very low. So it is very importantto resolve above mentioned problems for the application of polyoxometallates.Based on the investigation of literatures, this thesis was focused on theresearch of some organic reactions catalyzed by Keggin type multicomponent HPCcatalytic systems. The main progress and research results have been obtained asfollows:1. Oxidation of benzyl alcohol to benzaldehyde over Keggin-type phosphorustungsten supported heteropoly compounds.A series of heteropoly acid (salt) were synthesized and characterized by IR.The catalytic activity of the synthesized heteropoly acids (salts) for the oxidationreaction of benzyl alcohol were estimated. The effects of the solvent type,reaction temperature, reaction time, catalyst dosage and the dosage of H₂O₂on theoxidation reaction of benzyl alcohol over phosphotungstic acid were investigatedand the mechanism of the reaction were preliminary discussed. The resultsrevealed that all the five heteropoly acids(salts) possessed the Keggin-typestructure and better catalytic activity in the oxidation of benzyl alcohol tosynthesize benzaldehyde with water as solvent, in which phosphotungstic acid wasthe best. Under the reaction conditions of the amount of catalyst is0.04mmol,reacting at90℃for3.5h, the conversion of benzyl alcohol was95.59%and theyield of benzaldehyde could reach91.62%. It follows that H₃PW₁₂O₄₀/H₂O₂/H₂Ois the environment friendly high efficient catalyst system, will have the industrialapplication prospect.2. Phosphotungstic acid supported on silylated activated silica for thecondensation of cyclohexanone with glycerol.The catalyst (HPW/APTES-SiO₂) of heteropoly acid supported on acidactivated and silanizing silica(APTES-SiO₂) by3-aminopropyl triethox-ysilane (APTES) was prepared via chemical bonding. The properties of the catalyst wascharacterized by infrared spectroscopy, X-ray diffraction,Brunauer–Emmett–Teller (BET) specific area measurement and thermogravimetricanalysis(TG-DTA).The catalytic activity of the catalyst was determined by thecondensation of cyclohexanone with glycerol. The highest conversion ofcyclohexanone and the selectivity of1,4-dioxasp iro[4,5] decane-2-methanolreached92.7%and97.8%, respectively, by using HPW/APTES-SiO₂as thecatalyst under the optimum reaction conditions.The recycling tests show that thecatalyst can be easily separated from the reaction system and to be reused fourtimes.3. Oxidation of alcohols with hydrogen peroxide catalyzed by a reusabletrilacunary keggin Polyoxometalates.A trilacunary keggin Polyoxometalates reaction-controlled phase-transfercatalyst (TMBAC)6[PW9O34Fe3] was synthesized, and characterized by IR, XRDand TGA. The results of analysis indicated that the catalyst structure was keptwell after the reaction, and the catalyst during the reaction had the feature ofreaction-controlled phase-transfer catalysis. The catalyst was used for the nextcycle from the organic product by separation. Different kinds of alcohols wereefficiently transformed into corresponding carbonyl compound catalyzed by atrilacunary Keggin polyoxometalate of (TMBAC)₆[PW₉O₃₄Fe₃] in acetonitrilewith30%hydrogen peroxide. High yields of carbonyl compound obtained inoxidation such as benzyl alcohol was converted to benzaldehyde in highconversion and selectivity.