Hydrodesulfurization of dibenzothiophene over siliceous MCM-41-supported nickel phosphide catalysts

Siliceous MCM-41-supported nickel phosphides from a precursor with a Ni/P atomic ratio of 3, 2, 1.25, 1, 0.5, or 1/3 were prepared by in situ reduction. A high heating rate and a multistep program were used to prepare the supported nickel phosphides. The in situ reduction method proved superior to the traditional reduction-passivation-rereduction method. The timely removal of local moisture from the surface during reduction is crucial to obtaining a high hydrodesulfurization (HDS) performance of the phosphide catalysts. The precursors were characterized by TPR to investigate the reactions involved in phosphide preparation, and the structures of the resulting nickel phosphides were characterized by means of 31P NMR and XRD. Nickel phosphide formation may start with the reduction of NiO to Ni, and the Ni metal may assist phosphide formation in the reduction of nickel-rich precursors. Nickel-rich phosphides exhibited much higher HDS activity than phosphorus-rich phosphides prepared by the in situ reduction method. Reduction of the precursor with Ni/P = 2 yielded Ni12P5/ MCM-41, whereas reduction of the precursor with Ni/P=1.25 produced Ni2P/MCM-41. As in the traditional reduction-passivation-rereduction method, a small excess of phosphorus in the precursors is also needed to obtain the desired nickel-rich phosphides by the in situ reduction method. Ni2P/MCM-41 was the most active catalyst in the HDS of dibenzothiophene among all of the supported nickel phosphides prepared by the in situ reduction method.