Synthesis, Characterization And Catalytic Performance Of Heteropoly Tungstosilicate

Polyoxometalates are a kind of inorganic compounds which are well known by people. The compounds have been received more and more attention in the area of catalysis in recent years, because they are economical and environmentally friendly catalysts with high catalytic performance and selectivity. Their acidic and redox properties can be controlled at atomic or molecular levels. Therefore, polyoxometalates are capable of catalyzing oxidation reaction. The main progress and research results in the paper have been obtained as follows:1. Peroxotungstate [DDA]3[(OH)SiO3{WO(O2)2}3] as catalyst for epoxidation of alkenesThis paper reported a new peroxotungstate [DDA]3[(OH)SiO3{WO(O2)2}3] (Ⅰ), which was synthesized and used as reaction-controlled phase-transfer catalyst for epoxidation of alkenes with H2O2 as the oxidant and ethyl acetate as the solvent epoxidation systems. This system can be used for catalytic epoxidation of olefins and exhibits high conversion and selectivity. In an H2O/ethyl acetate biphasic system, catalyst I itself was not soluble in the ethyl acetate phase, but it dissolved slowly with the increase of reaction temperature and action of hydrogen peroxide and olefin, which subsequently led to homogeneous catalytic epoxidation of olefins. When the reaction stopped, the structure of catalysts had changed with the transfer of active oxygen of catalyst and consumption of hydrogen peroxide. With temperature dropping, catalyst I precipitated gradually. This new system not only catalyzed homogeneous epoxidation of alkenes with unique reaction-controlled phase-transfer catalyst character, but also avoided the using of toxic solvents. The catalyst could be easily recovered and reused after reaction, and the epoxidation of cyclohexene was recycled twenty times without activity loss. The fresh catalyst, used one were characterized by ICP, IR, UV-vis,183W NMR and 29Si MAS NMR.2. Substituted Keggin-polyoxometalate complexes as catalyst for the selective oxidation of alcohols.In this study, a series of dimetal-substituted Kiggin-type POMs were synthesized. The results indicated that dialuminum-substituted Keggin-polyoxometalate was more efficient than others for oxidation of alcohols to ketones. The high yields of ketones and good selectivity were obtained in oxidation of alcohols in water at 90℃. Compared with other dimetal-substituted POMs catalysts, aluminum was introduced into polyoxometalate that had the advantage of the selective oxidation of alcohols. This could be due to Al introduced into polyoxometalate that changes distribution of charges in different pattern and changes its redox in reaction system.3. Dilacunary silicotungstate as calalyst for the selective oxidation of alcohols with hydrogen peroxide in biphasic system.A dilacunary silicotungstate, K8 [γ-SiW10O36]·13H2O, catalyzed the selective oxidation of alcohols with 30% aqueous hydrogen peroxide. The reaction was carried out in an aqueous/oil biphasic system, which allowed easy recovery of catalyst under relative mild conditions. The high yields of ketones were obtained in oxidation of alcohols by the dilacunary silicotungstate and the catalyst was recycled five times without activity loss in the oxidation of cyclohexanol to cyclohexanone at room temperature.