Preparation Of Phosphide Catalysts And Their Performance Of Hydrodesulfurization

Recently, many countries enact severe regulations to limit the sulfur contents in fuel. It has stimulated the investigation and development of high performance hydrodesulfurization (HDS) catalysts. Transition metal phosphides exhibit very good catalytic performance in some catalytic reactions, especially for HDS reaction. Transition metal phosphides are considered as new generation of HDS catalysts due to excellent desulfurization performance. Monolithic catalysts have obvious advantages, such as low-pressure drop over the catalyst bed, favorable heat and mass transfer properties, and uniform profiles of concentration and temperature in comparison with the conventional fixed-bed catalytic reactors. Therefore, monolithic catalysts have been extensively applied to the control of emissions. However, the applications of monolithic catalysts in petroleum and chemical industry are being explored.In previous research work, Ni2P/SBA-15 catalysts had showed good activity for HDS of thiophene and dibenzothiophene. The activity for HDS of DBT over Ni2P/SBA-15/cordierite monolithic catalyst is not investigated. In this paper, Ni2P was introduced into SBA-15 by impregnation method, and then promoters (Co, W, La, and Ce) were introduced into Ni2P/SBA-15 precursor. A series of Co-Ni2P/SBA-15,W-Ni2P/SBA-15,La-Ni2P/SBA-15,Ce-Ni2P/SBA-15 catalysts were prepared by TPR. Addition, NixP/SBA-15 precursors were coated onto the pretreated cordierite and NixP/SBA-15/cordierite monolithic catalysts with different NixP content (NixP=6%-31%) and P/Ni ratio (P/Ni= 1/3,1,2,3) were obtained by TPR. Co-Ni2P/SBA-15/cordierite and La-Ni2P/SBA-15/cordierite catalysts were also prepared using cordierite as support and Co-Ni2P/SBA-15 and La-Ni2P/SBA-15 precursors as active washcoat. Then, the prepared catalysts were characterized by XRD, N2 adsorption-desorption isotherms, HRTEM, SEM, TEM, NH3-TPD, and XPS. The catalytic performances of the catalysts were evaluated by HDS of dibenzothiophene (DBT).For NixP/SBA-15/cordierite monolithic catalysts with different NixP content and P/Ni=0.5, Ni2P and Ni12P5 were the active phases. Surface area of cordierite increased when NixP/SBA-15 was coated onto cordierite and the thickness of washcoat was about 90μm. The 31%NixP/SBA-15/cordierite monolithic catalyst had the highest HDS activity, which DBT conversion can reach 99% at 360℃. For NixP/SBA-15/cordieritemonolithic catalysts with different P/Ni ratio, the active phase is Ni3P for NixP/SBA-15/cordierite (P/Ni=1/3), whereas the active phase is Ni2P for the catalysts with P/Ni of 1,2, 3. The surface area and pore volume of NixP/SBA-15/cordierite decreased with increasing P/Ni ratio. The catalytic activity over Ni2P for HDS of DBT was higher than that of Ni12P5 and Ni3P. NixP/SBA-15/cordierite with P/Ni of 1 had the highest HDS activity, which DBT conversion can be reach 95% at 360℃.For Co-Ni2P/SBA-15 catalysts with different Co content, Ni2P existed in Co-Ni2P/SBA-15 catalysts. All obtained samples have mesoporous structure. The addition of Co to Ni2P/SBA-15 catalyst can increase surface area and pore volume of samples; 4%Co-Ni2P/SBA-15 catalysts had the best HDS activity, which DBT conversion can reach 99% at 360℃. The addition of Co can improve BP selectivity. Compared to N2P/SBA-15 catalyst, BP selectivity over Co-N2P/SBA-15 catalysts was increased by 9%. In case of Co-N2P/SBA-15/cordierite monolithic catalyst, the active phase was Ni2P. The surface area and pore volume increased due to the addition of Co. The additions of 0.55%Co to Ni2P/SBA-15/cordierite monolithic catalysts can promote Niδ+ relative concentration. Excess P existed on the surface of monolithic catalyst.0.55%Co-Ni2P/SBA-15/cordierite monolithic catalyst had the best HDS activity, which DBT conversion can reach 95%.For La-Ni2P/SBA-15 catalysts with different La content, Ni2P was active phase. The size of Ni2P particles decreased when La was introduced into Ni2P/SBA-15 catalyst. La, Ni and P existed as the form of La3+, Niδ+and Ni2+, Pδ+ and P5+ respectively on the surface of catalysts. The 4%La-Ni2P/SBA-15 catalyst had the best HDS activity, which DBT can reach 94% at 340℃. In case of La-Ni2P/SBA-15/cordierite monolithic catalysts with different La content, the value of the surface area and pore volume of samples first increased, and then decreased with increasing La content. The 1.5%La-Ni2P/SBA-15 catalyst had the best HDS activity, which DBT conversion can reach 94%.In case of W-Ni2P/SBA-15 catalysts with different W content, the values of the surface area and pore volume of W-Ni2P/SBA-15 catalysts increased when W was added to Ni2P/SBA-15 catalysts. The acid properties of the samples were affected when W was added to Ni2P/SBA-15 catalyst. The strength of acid and the amount of total acid increased with increasing W content. The addition of W to Ni2P/SBA-15 catalyst decreased the Niδ+ concentration in Ni2P. BP selectivity over W-Ni2P/SBA-15 catalyst was increased by 18% at 360℃-380℃.For Ce-Ni2P/SBA-15 catalysts with different Ce content, Only Ni2P phase was formed in Ce-Ni2P/SAB-15 catalysts with Ce≤5%. Ni2P and Ni12P5 phases existed in 7%Ce-Ni2P/SBA-15 catalyst. The surface area and pore volume increased when Ce was added to Ni2P/SBA-15 catalyst. Ce-Ni2P/SBA-15 gave a higher the strength of the acid sites and total acid amount. The addition of Ce to the Ni2P/SBA-15 catalyst decreased the amount of active sites in Ni2P/SBA-15. BP selectivity over Ce-Ni2P/SBA-15 catalyst was increased by 13%.