The Immobilization Of Molybdovanadophosphoric Acid And Relevant Catalytic Applications In Selective Oxidations

Owing to their moderately high thermal stability in solid state, high catalytic activity in low temperature, and ability to form pseudo-liquid phases, heteropoly acids(HPAs) have been shown to be promising catalysts in the field of organic catalysis. Of HPAs, phosphomolybdic acids, in particular, vanadium-containing phosphomolybdic acids have been recognized as oxidation catalysts with superior redox performance. It should be noted that pristine HPAs have high solubility in polar solvents, which often leads to recovery and reuse problems. In this context, ‘‘heterogenization’’ of HPAs appear to be one of efficient solutions to solve the aforementioned problems. In this dissertation, a series of supported molybdovanadophosphoric acids were prepared via a one-pot procedure, which significantly simplifies the synthetic processes of the relevant catalysts. Moreover, introducing both imidazolium cation-based bridged silsesquioxane and mesostructure into the catalysts endow synergistic properties of salification and immobilization to our catalysts, which improves the catalytic performance of the molybdovanadophosphoric acids.(1) Keggin-type molybdovanadophosphoric acid(H4PMo11VO40) was synthesized and used as catalytically active component. Combining imidazolium cation-based bridged silsesquioxane as structure promoter and mesoporous silica as base support, a series of immobilized H4PMo11VO40 catalysts were prepared via the one-pot procedure and the effects of the occasion of adding H4PMo11VO40 during the synthesis of the catalysts on ultimate catalytic performance were investigated primarily. The resultant catalysts were characterized by FT-IR, ICP-AES, SSNMR, nitrogen adsorption-desorption, XRD and TEM techniques. Using air-mediated selective oxidation of benzyl alcohol as test reaction, K-MPV1A-IL-PMO-15/5min was selected as an optimum catalyst to investigate the effect of operational variables. Under optimum operational variables(1 ml of benzyl alcohol, 10 ml of DMSO, 150 mg of catalyst, 150 oC, 6 h), the conversion of benzyl alcohol was as high as 94%, meanwhile, the selectivity to benzaldehyde was near 100%. It should be noted that the catalyst could be reused for 6 times without significant loss of activity.(2) Four Keggin/Dawson-typed molybdovanadophosphoric acids of H5PMo10V2O40, H6PMo9V3O40, H7P2Mo17VO62, and H8P2Mo16V2O62 were synthesized as catalytically active components, leading to immobilized catalysts of K-MPV2A-IL-PMO-15, K-MPV3A-IL-PMO-15, D-MPV1AIL-PMO-15 and D-MPV2A-IL-PMO-15, respectively. Using hydrogen peroxide-mediated selective oxidation of cyclohexane as test reaction, the catalysts were investigated in terms of catalytic performance. Under optimum operational variables(2 ml of cyclohexane, 10 ml of isobutanol, 150 mg of catalyst, 2.5 ml of 30% hydrogen peroxide, 85 oC, 21 h), D-MPV2A-IL-PMO-15 achieved a cyclohexane conversion of 7.2% with 99% selectivity to cyclohexanol/cyclohexanone. After the catalyst was reused for three times the conversion decreased obviously whereas unchanged selectivity was observed.