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Preparation, Characterization And Catalytic Properties Of Phosphotungstic Acid Supported On M41S And SBA-15 Mesoporous Molecular Sieves

Posted on:2016-02-03Degree:MasterType:Thesis
Country:ChinaCandidate:Y ChenFull Text:PDF
GTID:2191330461451143Subject:Physical chemistry
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As a typical kind of heteropoly acid, silicotungstic acid(HSi W) exhibited excellent catalytic properties in many reactions because of its character of strong acidity and oxidization. However, bulk HSi W had obvious shortcoming including low surface area, weak thermal stability, and separation problems from reaction mixture due to its high solubility in polar reaction media, which limited its practical application. Such problems could be overcome by supporting or encapsulating it on suitable mesoporous molecular sieves supports to improve its specific surface area, tenrmal stability and mechanical strength. And this may be helpful for the the industry applications of HSi W.On the other hand, the new clean energy development has become an urgent need for the sustainable development of the world in consideration of the limited stock of fossil fuels and environmental pollution ascribed to the uses of these fuels. Up to now, biodiesel has attracted extensive attention because of the advantages of its renewable and environmental friendly properties. Therefore, the preparation of methyl oleate over the environmental friendly catalysts with excellent catalytic performace and wide universality had great significance since it was one of the main components of biodiesel.In this thesis, several kinds of M41 S and SBA-15 mesoporous molecular sieves were prepared and then used as supports to prepare the supported HSi W catalysts, respectively. Meanwhile, HSi W-SBA-15 catalysts were synthesized with a one-pot hydrothermal method. The samples were characterizatized by various physicochemical techniques such as XRD, FT-IR, DR UV-Vis, SEM, TEM, NH3-TPD, and N2 adsorption-desorption. The esterification of oleic acid with methanol was utilized to evaluate the catalytic performance of the resulting catalysts. The primary conclusions were as follows:(1) Mesoporous molecular sieves SBA-15 were prepared by hydrothermal method and M41 S including MCM-41, MCM-48 and Al-MCM-48 was prepared with a non-hydrothermal process, respectively. The supported 12-silicotungstic acid catalysts with different HSi W loadings(5-45 wt.%) were prepared via an impregnation method. HSi W-SBA-15 catalysts were directly synthesized with a one-pot hydrothermal method.(2) The characterization results suggested that the Keggin structure of HSi W and the mesoporous structure of the supports were both preserved in the resulting catalysts. Even so, the long-range order of the mesoporous structure was destroyed with the increasing incorporation of HSi W while the Br?nsted acid sites and total concentrations of acid sites increased gradually. The destruction may be resulted from the interaction between HSi W and Si-OH on the surface of the support, which damaged the framework structure of the mesoporous molecular sieves to some extent.(3) The resulting catalysts were used in the esterification of oleic acid with methanol without any other solvent. The catalytic results showed that their catalytic activity changed in regular with the variations of the structure parameters and HSi W loadings. Among the resulting catalysts, HSi W/SBA-15 catalysts exhibited the highest catalytic activity and the maximum yield of methyl oleate was 89.7%. While the HSi W-SBA-15 catalysts showed the most excellent cycling stability.
Keywords/Search Tags:12-silicotungstic acid, mesoporous catalysts, biodiesel, methyl oleate, esterification
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