Hydrodenitrogenation of quinoline catalyzed by MCM-41-supported nickel phosphides

A series of MCM-41-supported nickel phosphides with an initial Ni/P atomic ratio of 0.5-2 in the oxidic precursors were prepared by an in situ reduction method and characterized by X-ray diffraction (XRD), CO chemisorption, N-2 adsorption, and transmission electron microscopy. Their catalytic performances were evaluated in the hydrodenitrogenation (HDN) of quinoline and compared with MCM-41-supported Ni-Mo sulfide. The supported nickel phosphides with initial Ni/P ratios of 1 or 1.25 exhibited much higher HDN activity than the supported Ni-Mo sulfide. XRD patterns of both high-performance phosphide catalysts revealed that the active phase was Ni2P. It is indicated that the HDN of quinoline on the MCM-41-supported nickel phosphides exclusively proceeds via a pathway, which involves fully saturated intermediates. The cleavage of the C-N bond in the decahydroquinoline is the rate-determining step in the HDN of quinoline on the supported nickel phosphides. In addition, the effects of H2S (CS2 as the precursor) on HDN and the performances of the prepared nickel phosphide catalysts in the simultaneous HDN of quinoline and hydrodesulfurization (HDS) of dibenzothiophene (DBT) were investigated. The presence of H2S dramatically reduced the hydrogenation of 1,2,3,4-tetrahydroquinoline to decahydroquinoline, altering unfavorably the reaction pathways involved in the HDN of quinoline. The simultaneous HDN and HDS indicated that the HDN activity of Ni-Mo sulfide was hardly affected in the presence of DBT. Whereas, the supported nickel phosphide was sensitive to the presence of DBT at low temperatures. It is favorable to perform HDN at high temperatures because the inhibiting effects of H2S and DBT on HDN were dramatically reduced at elevated temperatures.