Preparation And Hydrodesulfurization Properties Of Ni₂P/SBA-15 Catalysts With Boron And Aluminum Promoter

Hydrodesulfurization (HDS) technology of fuel oil is becoming to develop the deep hydrodesulfurization because the environmental regulations have become more and more strict. Hydrodesulfurization (HDS) catalysts have been playing vital roles in producting clean fuel. Traditionally, hydrotreating catalysts are based on molybdenum or tungsten sulfide, which have some difficultion on removing the dibenzothiophene (DBT) and aromatic alkyl substituents, hardly meet to severe requirements of legislative restructions of sulfur content in petroleum products. Therefore, it is necessary to develop novel hydrotreating catalysts.Transition metal phosphides, especially Nickel phosphides(Ni2P), have showed excellent desulfurization performance, which is considered as new generation of HDS catalysts in the hydrodesulfurization process. In addition, Mesoporous molecular sieves have been recognized as the good catalytic supports for their high specific area and pore volume as well as the uniform pore size distribution. In our recent work, Ni2P/SBA-15 catalysts and had been prepared, and had showed deep HDS activity. In order to study comprehensively the catalytic performances of Ni2P/SBA-15 catalysts, a series of B-Ni2P/SBA-15 precursors with B promoter and Al-Ni2P/SBA-15 precursors with Al promoter were prepared; these particle precursors were coated to the pretreated cordierite and B-Ni2P/SBA-15/cord and Al-Ni2P/SBA-15/cord monolithic recursors were obtained. Then, Ni2P/SBA-15,B-Ni2P/SBA-15,Al-Ni2P/SBA-15,B-Ni2P/SBA-15/cord and Al-Ni2P/SBA-15/cord catalysts with initial P/Ni molar ratio of 0.8 and Ni2P content of 40 wt% were prepared by temperature-programmed reduction method in H2 flow. The structure of catalysts was characterized by X-ray diffraction (XRD), N2 adsorption-desorption, Transmission electron microscopy (TEM) and NH3 temperature-programmed desorption (NH3-TPD). The catalytic performances of HDS were evaluated in a fixed-bed micro-reactor using dibenzothiophene as model compound. The effect of B and Al on the hydrodesulfurization catalytic performance was respectively investigated.The hydrodesulfurization of dibenzothiophene DBT was performed for B-Ni2P/SBA-15 catalysts. The B-Ni2P/SBA-15 catalysts still maintained the mesoporous structure. The Ni2P phase was mainly observed in all the catalysts. The proper addition of boron reduced the active particles of Ni2P, but increased specific surface area of the catalysts. Acid amount of B-Ni2P/SBA-15 was also increased by the addition of boron. When the temperature was increased from 300℃to 360℃, the HDS conversion of DBT over the catalyst was clearly changed by the content of boron, the B-Ni2P/SBA-15 catalyst with boron content of 1.40wt% had the best catalytic activity. The mechanism of the HDS of DBT was the main direct desulfurization (DDS) over the B-Ni2P/SBA-15 catalysts.The hydrodesulfurization of DBT was performed for Al-Ni2P/SBA-15 catalysts. The promoter of Al produced some effect on both the structure and activity of catalysts. The Ni2P phase was mainly observed in the Al-Ni2P/SBA-15 catalysts when Al content was less than 5.29wt%. The Ni2P phase and Ni12P5 phase were found when Al content was from 5.29wt% to 6.35wt%. The catalysts modified by Al still maintained the mesoporous structure. The HDS activity kept constant up to Al content of 4.24wt% and decreased with a further increase in Al content. For all the Al-Ni2P/SBA-15 catalysts, the reaction route for HDS of DBT is mainly DDS.Finally, the hydrodesulfurization of dibenzothiophene was performed for B-Ni2P/SBA-15/cord and Al-Ni2P/SBA-15/cord monolithic catalysts. The activity of the two monolithic catalysts was improved with increasing the content of promoters (B and Al). Further increasing the content of promoters led to decrease in catalytic activity. For B-Ni2P/SBA-15/cord monolithic catalysts, the best content of B is 1.75wt%; for Al-Ni2P/SBA-15/cord monolithic catalysts, the best content of Al is 4.24wt%. The mechanism of the HDS of DBT was the main direct desulfurization (DDS) over the monolithic catalysts.