Hydrodesulfurization Properties Of Nickel Phosphide Monolithic Catalysts With Molybdenum Promoter

Recently, the oil hydrodesulfurization(HDS) technology needs a high development with the improving of environmental requirements in the world. Nickel phosphides(Ni2P) as the active component in the hydrodesulfurization process which have showed excellent desulfurization performance is considered as new generation of HDS catalysts. As a new-type catalyst, monolithic catalysts have better mass transfer performance and lower pressure drop.In previous research work, Ni2P/SBA-15 catalysts and Ni2P/SBA-15/cord monolithic catalysts had showed deep HDS activity, but the effect of promoters has not been studied. Therefore, in this paper, molybdenum was added into Ni2P/SBA-15 and Ni2P/SBA-15/cord monolithic catalyst as promoters. Then, the prepared catalysts were characterized by XRD, N2 adsorption-desorption isotherms, SEM and XPS. Finally, the catalytic performances of the catalysts were evaluated by HDS of dibenzothiophene (DBT).A series of Mo-Ni2P/SBA-15 precursors that varied the Mo contents were prepared by co-impregnation method using mesoporous molecular sieve SBA-15 as support. Then, the Mo-Ni2P/SBA-15 catalysts were obtained by temperature-programmed carburization (TPC) method(w(Mo)=0%,1.0%, 3.0%,5.0%,7.0%,10.0%). All obtained samples had well mesoporous structure. When w(Mo)≤7.0%, the active phase was Ni2P; when w(Mo)=10.0%, the active phase were mixtures of Ni2P and MoNiP2. Mo-Ni2P/SBA-15(w(Mo)=1.0%) had the best DBT HDS activity at 380℃while the conversion had reached 99.0%.Mo-Ni2P/SBA-15 precursors were coated to the pretreated cordierite and Mo-Ni2P/SBA-15/cordierite monolithic catalysts(w(Mo)=0%,0.6%,1.8%, 3.0%,4.2%,6.0%) were obtained by TPR. All the samples had mesoporous structures, the active phase was Ni2P. Ni, Mo, P elements were found to be Niδ+, Moδ+, Pδ- valence in the transition metal phosphides. When w(Mo)=4.2%, the DBT conversion was 99.0% at 380℃, the selectivity of CHB increased with the improving of temperature, DDS and HYD mechanism both played an important role.In the stability tests of different DBT concentrations, the best DBT conversion remained at 86% when w(DBT)=1.0% on Ni2P/SBA-15 cordierite monolithic catalyst.After the experiment, the surface area and pore volume had increased, the pore size distribution of 6nm increased. Niδ+ and Pδ- of the catalyst decreased greatly. In the 100h stability test of Mo-Ni2P/SBA-15 cordierite monolithic catalyst for w(DBT)=1.0%, DBT conversion remained at 90%. The sample surface area, pore volume and pore diameter changing little and Niδ+, Moδ+ and Pδ- few loss indicated Mo-Ni2P/SBA-15 cordierite monolithic catalyst had excellent HDS activity and stability.