Preparation And Hydrodesulfurization Performance Of Al-MCM-41-Supported Nickel Phosphide Catalysts

Al-MCM-41 mesoporous molecular sieves was prepared by the azeotropic distillation and ultrasonic dispersive technology using sodium aluminum sulfate as aluminum source, silicate as silica source and cetyltrimethyl ammonium bromide as structure-directing agent. Al-MCM-41 was characterized by BET, BJH, XRD, SEM and FTIR. Studied the factors such as the methods of calcination, ultrasonic oscillation, Si/CTAB, crystallization time on the effects of preparation of Al-MCM-41. By using nickel nitrate and diammonium hydrogen phosphate as raw material,Al-MCM-41 as support,a series of supported Ni₂P and Ni₂P/Al-MCM-41 were prepared via the method of temperature-programmed reduction under ultrasonic oscillation. Ni₂P/Al-MCM-41 was characterized by BET, BJH, XRD, SEM. Studied the factors such as Ni/P, dehydration, gas flow velocity, temperature-programmed reduction speed, ultrasonic oscillation, loading, supports, reaction pressure, reaction temperature and reaction time.During the preparation process of supports, Al-MCM-41 prepared by temperature-programmed calcination had a higher specific surface area, pore volume and pore diameter than that prepared by direct calcination. Al-MCM-41 prepared by ultrasonic dispersive technology had a much higher specific surface area,pore volume and pore diameter than that prepared by conventional mechanical mixing. And Al-MCM-41 prepared by azeotropic distillation and ultrasonic dispersive technology was also better than that using only ultrasonic dispersive technology. The appropriate ratio of Si/CTAB and appropriate crystallization time were conducive to the formation of framework of Al-MCM-41.It was found that nickel phosphide catalysts with nickel phosphides atomic ration (Ni/P=1/2, 3/4, 1, 5/4) were evaluated on the reactivity of hydrodesulfurization on thiophene. The catalyst with Ni/P=3/4 presented the best reactivity of hydrodesulfurization on thiophene, and the conversion reached 99.77% at 598K. The dehydration at 473K and high H₂ flow velocity could increase the activity of catalysts of hydrodesulfurization on thiophene. The reduction temperature was the key factor for synthesizing high activity catalysts, and 923K was best. Using ultrasonic oscillation in the process of synthesis of catalysts could greatly improve the hydrodesulfurization activity of Ni₂P and Ni₂P/Al-MCM-41 catalysts. The best loading on Al-MCM-41 was observed to be 30% among 20%, 30%, 40%, 50%, and the hydrodesulfurization conversion of thiophene reached 100% at 548K. As different supports, such asγ-Al₂O₃, MCM-41, Al-MCM-41(A10), Ni₂P/Al-MCM-41(A10) had best activity. The Ni₂P/Al-MCM-41 catalysts hydrodesulfurization conversion of thiophene nearly reached 100% at the reaction time 5h, and reaction pressure 3.5 MPa, reaction temperature 548K.