Preparation And Hydrodesulfurization Properties Of Phosphide Catalysts With Electronic Promoters

With the increasingly strict environmental legislation of countries and heavy crude oil of worlds, more and more people began to study and explore new hydrotreating catalysts to fulfill the challenge of producing clean fuel from petroleum. As the new type of catalytic material, transition-metal phosphides with high activity and stability in hydrodesulfurization reaction have been considered as a hot spot in current catalytic research. Nickel phosphides with potential application which have showed efficient desulfurization performance are proven to become new generation of HDS catalysts. Recently, monolithic catalysts are given more and more attention by their 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 excellent deep HDS activity. In this paper, Alkali metals (Li, Na, K) and alkaline earth metals (Mg, Ca, Sr, Ba) were considered to add into Ni2P/SBA-15 catalyst and Ni2P/SBA-15/cord monolithic catalyst as electronic promoters. Then, the prepared catalysts were characterized by XRD, N2 adsorption-desorption isotherms, HRTEM, NH3-TPD and XPS. Finally, the catalytic performances of the catalysts were evaluated by HDS of dibenzothiophene (DBT). We compared the structural and textural properties of catalysts with different electronic promoters (Li, Na, K, Mg, Ca, Sr and Ba), different Ni2P loadings and different P/Ni molar ratios as well as their catalytic performance in dibenzothiophene HDS.A series of M-Ni2P/SBA-15(M=Li, Na, K, Mg, Ca, Sr or Ba) precursors with different metals and Ca-Ni2P/SBA-15 precursors with different Ca contents were prepared by co-impregnation method using mesoporous molecular sieve SBA-15 as support. Then, the M-Ni2P/SBA-15 catalysts and Ca-Ni2P/SBA-15 catalysts were obtained by temperature-programmed reduction(TPR) method(w(M)=3.0%; w(Ca)=0%,0.7%,2.1%,3.5%,5.0%, 6.4%,8.5%,10.7%). The prepared samples all had well mesoporous structure. Ni2P particles were the active phase for M-Ni2P/SBA-15 catalysts, among which the alkaline earth metal Ca significantly improved the HDS activity of catalysts. When w(Ca)≤6.4%, the active phase was Ni2P; when w(Ca)= 8.5% and 10.7%, the active phase were the mixtures of Ni2P and Ni12P5. Ca-Ni2P/SBA-15(w(Ca)=3.5%) catalysts had the best dibenzothiophene HDS activity while the conversion had reached above 99.0% at 380℃.The prepared Ca-Ni2P/SBA-15 precursors were coated to the pretreated cordierite and Ca-Ni2P/SBA-15/cordierite monolithic catalysts(w(Ca)=0%, 0.7%,2.1%,3.5%,5.0%,6.4%) were obtained by TPR. All the obtained samples had mesoporous structures, the active phase was Ni2P. When w(Ca)=2.1%, the conversion of DBT was 99.0% at 380℃, the CHB selectivity increased with the improving of temperature, DDS and HYD mechanism both played an important role at 380℃.The obtained Ca-Ni2P/SBA-15 precursors with different Ni2P loadings and different P/Ni molar ratios were coated to the pretreated cordierite and Ca-Ni2P/SBA-15/cordierite monolithic catalysts with different Ni2P loadings (w(Ni2P)=10%,20%,30%,40%) and different P/Ni molar ratios(P/Ni=0.5, 0.8,1.0,1.25 and 1.5) were obtained by TPR. All prepared samples had mesoporous structures. For different Ni2P loadings monolithic catalysts, the active phase was Ni2P, and the catalytic activity increased with the improving of Ni2P loadings. For Ca-Ni2P/SBA-15/cordierite monolithic catalysts with different P/Ni molar ratios, When P/Ni=0.5, the active phase were the mixtures of Ni2P and Ni12P5; When P/Ni≥0.8, the active phase was Ni2P; The activity of Ni2P is higher than Ni12P5, the HDS activity of catalysts would be affected when P/Ni molar ratio was too high or too low; The catalyst of P/Ni=0.8 had the best DBT HDS activity, the DBT conversion was 95.3% at 360℃, the CHB selectivity increased with the improving of temperature, DDS and HYD mechanism both played an important role after 360℃.