Study On Properties Of Ni Supported On ZnO-based Mixed Oxides For Hydrodesulfurization Of Thiophene

As the continuously increase of petroleum consumption, the oil becomes heavy and environmental pollution caused by waste gas from incomplete combustion of oil is increasing severely. So deep processing of heavy oil and residue becomes more and more important. It has a great important economic and realistic significance to study on hydrodesulfurization(HDS) of oil. Among the factors of influence on HDS, improvement of catalyst performance is one cheap selection for production of low sulfur fuel.In the first part of the thesis, mixed oxides ZnO-Al₂O₃, ZnO-ZrO₂ and ZnO-TiO₂ were prepared by solid state combustion method, hydrodesulfurization of thiophene (HDS) was selected as probe reaction to study their catalytic property with Ni as active component. The results of HDS indicated that the activities of the catalysts supported on the mixed oxides were higher than that of Ni/ZnO; Ni/ZnO-ZrO₂ exhibited the highest activity among the three catalysts supported on the mixed supports, and the conversion of thiophene over it was 74% at 400℃. The results were attributed to the relatively high surface areas of mixed oxides, which was favored of dispersion of active component. As a result, NiO over the mixed oxides was reduced to active Ni°more easily, and more adsorption sites existed over the surface of Ni/mixed supports, leading to the better performance for HDS of thiophene.In the second part of the thesis, mixed oxides ZnO-ZrO₂ were prepared by solid state combustion method, precipitation method and microemulsion method. Effect of the methods of preparating ZnO-ZrO₂ on the properties of Ni/ZnO-ZrO₂ for hydrodesulfurization of thiophene was studied. The results indicated that Ni/ZnO-ZrO₂ exhibits relatively good activity for HDS when support was prepared by solid state combustion method, the conversion of thiophene over it was 74% at 400℃. However the activity of the catalyst was lowest if ZnO-ZrO₂ was prepared by precipitation method, the conversion of thiophene was only 51%. This was attributed to relatively high surface area of ZnO-ZrO₂ prepared by solid state combustion method, which was favored of dispersion of active component. As a result, NiO over the support was reduced more easily, more adsorption sites existed over the surface of Ni/ZnO-ZrO₂, and the acid strength of it was higher, which resulted in the better performance for HDS of thiophene.Furthermore, Co and Mo selected as the second components were add to Ni/ZnO-ZrO₂. Effect of Co and Mo dopant on the properties of Ni/ZnO-ZrO₂ for hydrodesulfurization of thiophene was studied. The results indicated that the doping of Co improved the properties of Ni/ZnO-ZrO₂, the conversion of thiophene over it was 97.3% at 400℃.On the contrary, the doping of Mo reduced the properties of Ni/ZnO-ZrO₂.Because of the doping of Co, active component was highly dispersed, and then its reducing temperature was reduced, so there had more active center on the catalyst surface. But the active component of MoNi/ ZnO-ZrO₂ could not be reduced completely, part of it existed in form of NiO, there existed fewer active sites, resulting that it had bad performance for HDS of thiophene.