Preparation And Catalytic Application Of Lacunary Heteropolyoxometallates In The Reactions Of Alcohol

The polyoxometalates(POMs) are widely used and versatile in acid catalyzed reactions due to their several advantages such as high catalytic activity and selectivity, reusable and adjustable, lower volatility and pollution, little corrosion and fine thermal stability. A lacunary polyoxometalate is a ―defect‖ polyacid anion by losing a certain number of{MOn}octahedral units based on the basic configuration of polyacids. These compounds show excellent performance because structures of the active sites can be designed at atomic and molecular levels and they are highly regulated in size, charge, acidity and redox properties. So they have attracted much attention of many researchers.The thesis consists of four chapters as follows:Chapter 1. ReviewsThis chapter mainly reviewed the following three subsections including(1) The heteropoly acid. The history of the polyoxometalate were introduced, the structure and property as well as the catalytic performance of the polyoxometalates and the substituded polyoxometalates were also introduced in this part;(2) The oxidation of alcohols. The progress of the nonmetal catalysts and metal catalysts used in the oxidation of alcohols were introduced in this part, respectively.(3) The acetalization and ketalization reactions. The commonly acepted mechanisms of the acetalization and ketalization reactions were well introduced, and the progress of the catalysts in the condensation were also discussed.Chapter 2. The synthesis, characterization and catalytic property of dizirconium(IV) substituted divacant lacunary γ-Keggin silicodecatungstate in the oxidation of alcoholsIn this chapter, a Keggin-typed dizirconium-substituted silicodecatungstate, TBA4[γ-H2 Si W10O36Zr2(μ-OH)2](TBA-I, TBA=tetra-n-butylammonium bromide) derived from a divacant lacunary γ-Keggin silicodecatungstate, was synthesized and characterized by Fourier transform infrared spectroscopy(FT-IR), powder X-ray diffraction(XRD) and ultraviolet visible spectroscopy(UV-Vis) techniques. The results suggest that the Keggin-typed structure of the synthesized catalyst was well kept, and it was hydrolytically and thermally stable in the oxidation. TBA-I was then used as catalysts for the oxidation of alcohols in homogeneous reaction media using hydrogen peroxide as oxidant. The optimum oxidation condition was well concluded through the investigation of the effect of the temperature, the time, the dosage of the catalyst, the mount of the oxidant, as well as the solvent on the oxidations. It showed that many of selected alcohols, including aromatic as well as aliphatic alcohols, were efficiently converted to the corresponding carbonyl products with the catalysis of the prepared zirconium-containing silicodecatungstate. High substrate conversions as well as product selectivities were obtained in these oxidation reactions. Only a single byproduct of water was produced in these oxidations, and the catalytic systems were considered to be accorded with the requirement of green chemistry.Chapter 3. The synthesis, characterization and catalytic property of iron(III) monosubstituted lacunary α-Keggin phosphotungstate for the acetalization and ketalization reactions.A Keggin-typed iron monosubstituted phosphotungstate of K5PFe(OH)2W11O39?n H2O(PW11-Fe), derived from a lacunary α-Keggin phosphotungstate, was synthesized and characterized by Fourier transform infrared spectroscopy(FT-IR), powder X-ray diffraction(XRD) and ultraviolet visible spectroscopy(UV-Vis) determing techniques. The results showed that the Keggin-typed structure of the synthesized catalyst was also well kept in the prepared sample, and it was hydrolytically and thermally stable in the oxidation. The prepared PW11-Fe polyacid was then used as catalyst for the acetalization and ketalization reactions between some selected ketones/aldehydes and alcohols. The effects of the temperature, the time, the dosage of the catalyst as well as the proportion of the reactants on the condensations were well investigated, and the optimum oxidation conditions were concluded. The results suggested that the synthesized catalyst showed excellent catalytic reactivity in these condensation reactions, and the simple product of ketal/acetal was provided in these conversions.Chapter 4. Synthesis, characterization and catalytic property of the WellsDawson-typed phosphotungstic acid of H6P2W18O40 for the acetalization and ketalization reactions.A Wells-Dawson-typed phosphotungstic acid of H6P2W18O62 were synthesized and characterized by Fourier transform infrared spectoscopy(FT-IR), ultraviolet visible spectroscopy(UV-Vis) and powder X-ray diffraction(XRD). The prepared acid was used as catalyst for the acetalization and ketalization reactions. The reaction condition was well optimized through varying the factors such as the dosages of the catalyst, the reaction time, the temperature, respectively. It was found that the prepared Wells-Dawson-typed phosphotungstic acid showed high catalytic and selectivity in these condensation systems.