MCM-41 Supported Molybdenum/Tungsten Phospides Catalysts For Deep Hydrodesulfurization

Interest in the development of novel catalysts for hydrodesulfurization has been spurred by the need to meet stringent environmental regulations that have recently been enacted throughout the world. More recently, transitional metal phosphides were reported to have superior activities to traditional Mo sulfide catalysts in hydrotreating processes. Among them, molybdenum phosphides and tungsten phosphides show high HDS activities and in some cases even exhibit good property of resistant sulfur.MCM-41 supported molybdenum phosphides and tungsten phosphides with different weight loadings were prepared by in-situ TPR reduction from molebdenum and tungsten phosphate precursors and characterized by XRD. The precursors were obtained by incipient wetness impregnation of the support with aqueous solution and characterized by TPR. The HDS performance of the prepared phospides catalysts was evaluated in a fixed bed reactor using 0.8 wt% dibenzothiophene in decalin as the feed. The best loading is observed to be 40 wt%.The MoP/MCM-41 catalysts prepared using basic or neutral impregnation solution exhibit higher HDS activity than those prepared using acidic solution.It was also observed that the MoP/MCM-41 catalysts prepared by co-impregnation and two-step impregnation show the same HDS activities.The precursors can be reduced to MoP/MCM-41 absolutly within 2 hours at 650℃.The catalysts prepared at 650℃ show high activity than the catalysts prepared at other temperature. Compared with MOP/Al₂O₃, MoP/MCM-41 shows higher HDS activity. The distribution of HDS products suggests that hydrodesulfurizations of DBT predominately takes the route of direct desulfurization over MoP/Al₂O₃ but that both hydrogenolysis and hydrogenation play important rule in the hydrodesulfurization of DBT catalyzed by MoP/MCM-41.MoP/MCM-41 prepared by different activation ways was valuated for DBT HDS.It is indicated that the catalysts prepared by sulfidation-reduction have higher activity of DBT HDS than that prepared by reduction.The effect of different activation ways on the activity of DBT HDS is more obvious when the catalysts were prepared at lower final temperature. The distribution of HDS products suggests that the activity of hydrogenolysis and hydrogenation in the hydrodesulfurization of DBT catalyzed by MoP/MCM-41 prepared by sulfidation-reduction is higher than that prepared by reduction. MoP/MCM-41 (Mo:P=2:l) prepared by different activation ways was also valuated for DBT HDS.It is indicated that thecatalysts prepared by sulfidation-reduction have higher activity of DBT HDS than that prepared by reduction.The precursors of MoP/MCM-41 with different Mo/P ratio sulfided at 400 °C exhibit lower activity of DBT HDS than MoS2/MCM-41.WP/MCM-41 prepared by different activation ways was also valuated for DBT HDS.lt is indicated that the catalysts prepared by sulfidation-reduction have higher activity and selectivity of cracking of DBT HDS than that prepared by reduction. Compared with MoP/MCM-41, the effect of different activation ways on the activity of DBT HDS catalyzed by WP/MCM-41 is more obvious.