Study On The Catalytic Properties Of Supported Amorphous Ni-B And Ni-Mo-B Alloy Catalysts For Hydrodesulfurization Of Thiophene

With the petroleum becomes heavy, inferior degree deepen and the environmental laws become more and more strict, the fuel quality, especially the sulfur content was strictly limited in the world. The sulfur content of petroleum is mainly distributed in the heavy distillate, and thiophene sulfides take up mostly. Deep hydrodesulfurization of oil is one of the most effective means to product clean fuel. Therefore, the development of more high-performance hydrodesulfurization catalyst has important and practical significance.In this paper, a series of Ni-B amorphous alloy catalysts with different support were prepared by the impregnation-chemical reduction method. Thiophene hydrodesulfurization (HDS) was chosen as probe reaction to investigate activity of the catalysts. The catalysts were characterized by X-ray diffraction, differential scanning calorimetry, inductive coupled plasma, temperature-programmed reduction, temperature-programmed desorption, X-ray photoelectron spectroscopy and transmission electron microscope.In the first part of this thesis, Ni-B/boehmite (marked as Al2O3) amorphous alloy catalysts were prepared, modified with with the third component Mo, and were applied to HDS of thiophene. The results indicated that the addition of Mo improved the thermal stability of Ni-B/Al2O3, decreased the reduction temperature, weakened the strength of Ni-H bonds, increased acidity, and therefore promoted catalyst activity dramatically. At low temperature of220℃, when the Mo content was12wt%of Ni, the conversion of thiophene is the highest, up to73.9%.In the second part, the surface of boehmite support was modified by high molecular compound of chitosan (CS), then Ni-B/CS-Al2O3catalyst were prepared by the impregnation-chemical reduction method. At the same time, Ni-B/CS-Al2O3was modified by different content of Mo for thiophene hydrodesulfurization. The results showed that the chelate and adsorption effect of chitosan made the active component better dispersion on the surface of the carrier, inhibited the amorphous particles reunite to crystalline, improved the thermal stability of catalyst, while increased the active component Ni load. XRD results showed that addition of the chitosan and Mo did not change the amorphous catalyst structure, TPR and TPD results showed that chitosan modification on carrier surface and Mo addition made the reduction of catalyst active species easier, increased the adsorption center, enhanced acidity, significantly improved the activity of the catalyst. When the Mo content was15wt%of Ni, the thiophene conversion rate reached at84.7%.In the third part of this paper, combined the unique acid of Nb2O5and high specific surface of γ-Al2O3, the composite oxide carrier Nb2O5-γ-Al2O3(marked as Nb-Al) was prepared, then Ni-B/Nb-Al catalysts were prepared with different content of Nb2O5for thiophene hydrodesulfurization. NH3infrared spectroscopy results showed that both Broensted and Lewis acids exist in the catalysts after the Nb2O5addition in the carrier. With the synergistic effect of suitable content of both Broensted and Lewis acids, catalyst has high desulfurization activity. when the content of Nb2O5is30wt%of the support, catalyst activity was the highest. Different content of Mo modified the Ni-B/30%Nb-Al catalysts, and the results showed that the Mo addition improved the thermal stability of catalyst, decreased the reduction temperature, formed amorphous alloy more easy, increased the adsorption center, enhanced acidity of the catalyst surface, which were conducive to the improvement of catalyst activity. When the Mo content was8wt%of Ni quality, the thiophene conversion rate reached100%.