The Preparation Of W-base Catalysts And Its Application In Oxidative Desulfurization

As the environmental pollution caused by SOx enter the atmosphere has become more and more severe which was produced along with the sulfur-contain oil combustion, various countries have legislation to strictly limit the diesel oil of sulfur content. Although the conventional hydrodesulfurization (HDS) process can remove most of organic sulfur compounds from fuels, but the HDS process is less effective for removing aromatic thiophenes such as benzothiophene, dibenzothiophene, and their alkyl derivatives. Therefore, researchers have committed to develop new desulfurization process. Oxidative desulfurization (ODS) is drawing significant research interest because of its high desulfurization efficiency, low operating cost and simple technical process.In this paper, WO3/SiO2, WO3/Al2O3and WO3/MCM-41catalysts were prepared by impregnation method and the catalysts were characterized by X-ray diffraction (XRD), ultraviolet-visible diffuse reflection spectrum (UV-vis), nitrogen adsorption isotherm method, inductively coupled plasma (ICP) and UV Raman spectroscopy. The catalytic performance in the oxidative desulfurization (ODS) of dibenzothiophene (DBT) with cumene hydroperoxide as the oxidant in toluene was investigated at50℃and atmospheric pressure. The experiment result indicated that WO3is a good active species. The DBT conversion was60%when SiO2supported20wt.%of WO3. The DBT conversion was only38%when Al2O3supported20wt.%of WO3, but the catalyst had well stability and the activity had no change after6hours reaction. The DBT conversion was54%when MCM-41supported20wt.%of WO3but the activity had significantly decrease after6hours reaction. The catalyst activity of20wt%WO3/SiO2was investigated by long time reaction. The DBT conversion is about60%in the first10hours, and then it decreases with the reaction time increasing. The DBT conversion was20%after90hours reaction. Shown by XRD, UV-vis and UV Raman characterization results, the results indicated that tungsten oxides interacted strongly with γ-Al2O3. As a result, the W species were in the highly dispersed tetrahedrally coordinated state. When tungsten oxides were deposited on SiO2, the octahedrally coordinated WO3were detected. All the SiO2supported catalysts showed higher ODS activity than their γ-Al2O3supported counterparts, suggesting that the octahedrally coordinated WO3is intrinsically more active than the tetrahedrally coordinated W species bound on the surface of γ-Al2O3. ICP results showed that most of the tungsten species are loaded on the support and the W content nearly without loss after reaction, which suggested that the decreased of activity was not caused by the loss of active centers, probable due to oxidation products deposited on the catalyst.In addition, The SiO2was modified with1-propyl-3-triethoxysilyl3-methylimidazolium chlorid by grafting method. The phosphotungstic was immobilized onto SiO2and the modified SiO2to prepare the PW/SiO2and PW/ILSiO2catalyst and used to catalyze the sulfur-containing compounds in model oil with30wt.%H2O2as the oxidant. Maximum oxidation activity was observed at a loading of30wt.%H3PW12O40which can complete oxidation0.2wt.%of DBT at50℃and an O/S molar ratio of3.0in40min. The PW/ILSiO2catalyst could be easily separated by centrifugation and reused for seven times without any deactivation.