Preparation, Characterization And Catalytic Oxidation For Cyclopentene Of WO_x Catalysts

In this dissertation, the WO₃/SiO₂ catalyst was prepared by sonication-impregnation combination approach using commercial silica gel as support. Combining with some modern physical methods used to study the crystalline structure, the interaction between support and active constituent, the state of the active constituents on the surface of support, such as X-ray diffraction (XRD), laser Raman, Fourier transformed infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS), and so on. The results indicate that the loading amount of the active constituent and the calcination temperature will influence the crystalline structure, the interaction between the support and the active constituent as well as the state of the active constituent. When the loading amount of the catalyst was more than 15 wt%, or the calcination temperature was higher than 723 K, WO₃ crystals would emerge on the surface of support with weakened interaction between the catalyst and the supporter. Besides, low-valenced ion of W⁵⁺ existed in the active constituent on the surface of the catalyst.Uniform and micrometer-scaled spherical TiO₂ particles were fabricated through the hydrolysis of TiCl₄, which was utilized as supporter to prepare highly-dispersed WO₃/TiO₂ by ultrasonic-impregnation method. Characterizations by SEM, TEM, XRD, laser Raman and XPS were applied to analyze the as-prepared TiO₂ and WO₃/TiO₂.The results show that the TiO₂ micro-balls are of anatase crystalline type with diameter of about 3μm. The core-shell structure of WO₃/TiO₂ possesses a WO₃ shell of about 150 nm thickness. After the loading of WO₃, the crystalline type and the structure of TiO₂ as the supporter did not change. When the loading amount was less than 15 wt%, the tungsten oxide was amorphous. When the loading amount was between 15 wt% and 20 wt%, the tungsten oxide existed in the form of tetrahedron WO₄^2-. But in the case of high loading amount of larger than 20 wt%, the WO₃ crystals in octahedron were formed on the surface of TiO₂.Cyclopentene was chosen as degradation substrate to investigate the catalytic oxidation activity of WO₃/SiO₂ and WO₃/TiO₂. The experimental results show that the catalytic activities of these two systems are similar and both of them can effectively oxidize cyclopentene catalytically. The main factors that affect the degradation of cyclopentene by the tungsten oxide have been analyzed, such as reaction temperature, reaction time, the amount of hydrogen peroxide, solvent species, cocatalyst, silicon gel type, the loading amount of catalyst, the calcination temperature of the catalyst, etc. Meanwhile, the reuse and the regeneration of the WO₃/SiO₂ catalyst were also examined. At least 5 times of repeated operation could be realized for this catalyst, as confirmed by our experiment.