The Synthesis And Catalytic Epoxidation Performance Of W/Mo-based Catalysts Modified By Ionic Liquid

Epoxidation of alkene is an important reaction in organic chemical synthesis and epoxides are important raw materials of chemical industrial production in epoxy resin, surfactant, pigment and drug. Traditional epoxidation processes containing peracids, epichlorohydrin and Haakon present serious problems such as equipment corrosion, high cost and environmental pollution. Consequently, various environment-friendly and efficient green epoxidation catalysts have been induced to displace the traditional methods. As a kind of green catalytic materials, ionic liquids(ILs) have been extensively investigated in various fields for its unique physical and chemical properties. Due to their highly adjustable cations and ions, they have become a new favorite in catalysis system. The paper targets on the synthesis of heterogeneous epoxidation catalyst by using ionic liquid to decorate metal active center, which can synthesize the catalysts contaning metal with empty outer electron orbit such as Mo and W. And the catalysts were applied in selective epoxidation in favour of electron transfer.(1) The cationic moiety of heteropolyacid-based ionic catalyst has an important influence on the catalytic activity and performance in the reaction system. Therefore, phosphotungstate-based catalysts modified by unsymmetrical dicationic cations [DnmimN]1.5PW4O16 had been synthesized and characterized by FT-IR, SEM, TG, 1H NMR and CHN element analyses. The catalytic activities of the catalysts were measured for the epoxidation of cyclohexene with hydrogen peroxide(H2O2) in acetonitrile. These catalysts were proved to be high catalytic activities. In particular, the phase condition was determined by the amount of H2O2. When the amount of H2O2 was more than substrate, the system would get homogeneous. So the copolymer heterogeneous catalyst DIM-NIM-PW4O16 was also synthesized and showed high activity compared to the former. The conversion of cyclohexene and selectivity for epoxycyclohexane were 93.9% and 91.4%, respectively, at 70 oC in 4 h. After the reaction, the catalyst could be recovered simply by centrifugation. And the conversion of cyclohexene and selectivity for epoxycyclohexane were still 83.8% and 80.7%, respectively, after recycling the catalyst five times.(2) Ionic liquid was first covalent-grafted on nano-SiO2 and followed by coordination to introduce Mo complex. Characterization methods of FT-IR, TG, SEM, BET, etc. were carried out to have a comprehensive insight into the catalyst. The catalytic activities of the catalyst were measured for the epoxidation of cyclooctene with H2O2 in acetonitrile. The catalyst showed high catalytic activities but with poor recycling performance. Subsequently, an inorganic-organic porous silica network catalyst was prepared by linking silica nanoparticles using ionic liquid and followed by anion-exchange with phosphotungstate. Various characterizations were also carried out to confirm the succfully synthesis of the catalyst. The catalyst was used for catalyzing cyclooctene epoxidation with higher catalytic activity and more convenient recovery than the former. The conversion and selectivity of epoxy-cyclooctene could both reach over 99% at 70 oC for 8 h using H2O2 as oxidant and acetonitrile as solvent.(3) Phosphotungstic acid was immobilized onto graphene previously non-covalent functionalized by polymeric ionic liquid. Characterization methods of FT-IR, TGA, CHN element analysis, EDX, XPS, Raman and ICP-AES were carried out to confirm the successful incorporation of ionic liquid and heteropolyacid onto the graphene. SEM and Nitrogen adsorption-desorption displayed the structure of the prepared catalyst. The catalyst was used in catalytic epoxidation of cyclooctene and the results showed that amino ionic liquids and RGO both had obvious improvement on catalyst activity. The conversion of cyclooctene and selectivity of epoxy-cyclooctene could both reach 98.5% and 99.1% at 70 oC within only 2 h using H2O2 as oxidant and acetonitrile as solvent. Moreover, because of the strong cation-π and π-π interactions between PIL and RGO, the phosphotungstic acid-based ionic liquid was not so easy to fall off, resulting in a good recovery performance.