Oxidative Desulfurization Over MoO₃-based Catalysts

With the increasing severe environmental pollution and stringent environmental regulations, it was urgent to solve the problem caused by SOx-Oxidative desulfurization (ODS) was drawing significant research interest, due to its simple technical process, high desulfurization efficiency and low operating cost, The focus of this thesis was to study the ODS over MoO3-based catalysts and to explore the reaction mechanism.In this work, MoO3/?-Al2O3, MoO3/8-Al2O3 and MoO3/La-Al2O3 catalysts were prepared by impregnation method. The obtained catalysts were fully characterized by X-ray powder diffraction (XRD), ultraviolet-visible diffuse reflection spectrum (UV-vis), UV Raman spectroscopy and nitrogen adsorption isotherm(77K). The catalytic performance in the ODS of DBT with CHP as the oxidant in toluene was investigated in a fixed bed reactor at 40? and atmospheric pressure. Shown by XRD, UV-vis, UV Raman spectroscopy results, molybdenum oxides interacted strongly with y-Al2O3, formed four-coordinate molybdenum oxide tetrahedrons highly dispersed on the support. The octahedrally coordinated MoO3 were observed when molybdenum oxides deposited on ?-Al2O3. The results showed that lanthanum oxide can be used to modify Al2O3. The ?-Al2O3 supported catalysts showed higher ODS activity than their ?-Al2O3 supported counterparts, suggesting that the octahedrally coordinated MoO3 is intrinsically more active than the tetrahedrally coordinated Mo species. The catalysts activity of ODS are in the sequence of MoO3/La-Al2O3>MoO3/?-Al2O3> MoO3/?-Al2O3.With MoO3/La-Al2O3, MoO3/SiO2 as catalysts, isopropyl alcohol and benzoquinone as free radical scavengers, hydroperoxide (CHP) and tert-butyl hydroperoxide (TBHP) as oxidant, the ODS reaction mechanism was explored. It was found that the participation of isopropanol leads to a significant decrease on the reaction rate and and extension on the induction period. Thus, we concluded that the reaction mechanism of the oxidation with CHP or TBHP is hydroxyl free radical mechanism.USY and different types of Al2O3 were used to adsorb dibenzothiophene sulfone (DBTO2) which formed after ODS. The results showed that Al2O3(2) has better adsorptive and regenerative performance. In addition, the nitride from the diesel can seriously affect the catalytic process and the efficiency of diesel, and can directly produce nitrogen oxides by burning which can lead to acid rain. Removal of nitrogen compounds from diesel was studied using resin, activated carbon, Al2O3, HY, USY as well as solid super acid SO42-/TiO2 modified by USY in dynamic adsorption. After overall consideration, Al2O3 and USY were selected as optimal adsorbent which have better adsorptive performance than others. The regeneration result showed the employed USY could recover most adsorptive active sites after regeneration.