New tungsten-sulphate modified silica-titania as oxidative-acidic bifunctional catalyst for diol formation
DOI:
https://doi.org/10.11113/mjcat.v1n1.11Keywords:
bifunctional catalyst, oxidative, acidic, tungsten oxide, sulphuric acidAbstract
A series of new tungsten-sulphate modified silica-titania bifunctional catalysts were successfully synthesized and characterized. The effect of two parameters, namely tungsten oxide loading and sulphuric acid content was studied. SiO2-TiO2 was prepared via sol-gel method, followed by impregnation with tungsten oxide (WO3) and sulphate group (SO42-). XRD results demonstrated that monoclinic WO3 appeared in samples of high tungsten loading. A drastic decrease of ~70% in surface area of solid catalyst from 725.8 to 215.3 m2/g was observed after loading with both WO3 and SO42-. Existence of both WO3 and hydrated tetrahedral Ti in the materials was crucial to generate oxidative sites. Further modification with SO42- has significantly improved both oxidative ability and acid strength of solid catalyst, producing several folds higher of epoxides and diols. Since Brønsted acid sites are needed for transformation of epoxides to diol, it was believed that the current materials possessed Brønsted acidity. Evidently, the coexistence of WO3 and SO42- were vital to generate both oxidative and acidic sites in SiO2-TiO2. The results suggested that 0.5M_SO42-/W/SiO2-TiO2 was a promising bifunctional catalyst in diol synthesis which yielded 1217 μmol 1,2-epoxyoctane and 246 μmol 1,2-octanediol after 24 h reaction.Â
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