Synthesis, Characterization And Catalytic Performance Of Transition Metal-Substituted Keggin Heteropoly Compounds

The Keggin type of heteropoly compounds(HPC) are a catalyst of new and efficient catalysts that have simple composition, clear structure and possess of unique properties:the double-functional property of acidity and redox, and the pseudoliquid-phase characteristic. Their distinctive acidity and redox property, which can be controlled by changing element composition on the atom or molecular level and by modifing the heteroatom or the framework transition-metal atoms. They have been investigated extensively in catalytic field and material chemistry for their high catalytic performance and selectivity, moderate reaction conditions, their easy synthesis, non-corrosion, low cost and good thermal stability. Therefor, it has important research and industrial significance to develop their applied research in organic synthesis and catalytic field.A series of common transition metal substituted phosphotungstic heteropoly compound catalysts (Cpyr)4/5[PW11M(II/III)O39](M=Fe, Co, Ni, Cu, Mn)(TMSPs) with Keggin structure, in which the counter ion were modified by bromohexadecyl pyridine as phase-transfer catalysts, were synthesized and characterized by FT-IR and XRD. The catalytic activities of the as-synthesized heteropoly compounds for the epoxidation of styrene were evaluated. The main progress and research results have been obtained as follows:1. Catalytic Oxidation of styrene to epoxyethylbenzene over Keggin-type transition metal substituted phosphotungstic heteropoly compound catalysts.Take TBHP as oxidant, different catalytic activities of a series of transition metal substituted heteropoly compound catalysts for the catalytic oxidation of styrene to epoxyethylbenzene were compared. The effects of the reaction temperature, reaction time, catalyst dosage and the dosage of tert-butyl hydrogen peroxide on the oxidation reaction of styrene over (Cpyr)5PW11Co were investigated. The results show that among various transition metals, Co exhibited the highest conversion of styrene (89.29%) with the selectivity of epoxyethylbenzene of77.41%at353K for8h in styrene catalytic oxidation to epoxyethylbenzene with TBHP (25mmol) in 1,2-dichloroethane (10ml) solvent, the amount of catalyst is0.04mmol.2. Catalytic Oxidation of styrene to benzaldehyde over Keggin-type transition metal substituted phosphotungstic heteropoly compound catalysts.With molecular oxygen as oxidant and tert-butyl hydrogen peroxide oxidation as co-oxidant, different catalytic activities of a series of transition metal and different counter-ion substituted heteropoly compound catalysts for the catalytic oxidation of styrene to benzaldehyde were evaluated. The effects of the reaction temperature, reaction time and catalyst dosage on the oxidation reaction of styrene over (Cs)5PW11Co were investigated. The results show that the conversion of styrene (35.1%) with the selectivity of benzaldehyde of88.1%at353K for8h in100mmol styrene catalytic oxidation to benzaldehyde with latm O2,TBHP (0.2mmol), the amount of catalyst is25mg.3. Benzaldehyde glycol acetal with Heteropoly Acid Immobilized on Silylated PalygorskiteThe surface of acid-activated palygorskite was modified by grafting3-aminopropyl-triethoxysilane for immobileizetion of molybdovanadophos-phoric heteropoly acids. The samples were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and BET specific area measurement. The catalytic activity of the catalyst thus prepared was tested for the acetal of benzaldehyde with ethylene glycol. under the optimal reaction conditions, i.e., ethylene glycol:acetophenone=1.75:1,8mL of cyclohexane as the water-carrying agents, with0.1g of PMoV/PaAPTES catalyst at115℃, and the selectivity of99.2%for benzaldehyde cylic ethylic acetal at a benzaldehyde conversion of95.5%was achieved within120min. The recycling tests show that the PMoV/PaAPTES catalyst can be easily separated from the reaction system and can be used for many times.