Synthesis, Characterization, and Hydrotreating Activity of Several Iron Group Transition Metal Phosphides

A series of iron, cobalt, and nickel metal phosphides of chemical formula Fe2P, CoP, and Ni2P with specific surface areas of around 3 m2 g−1 were synthesized by means of temperature-programmed reduction (TPR) of the corresponding phosphates. These phosphides were also successfully prepared in dispersed form on a silica support (90 m2 g−1) for use as catalysts. The phase purity of these materials was established by X-ray diffraction (XRD), and surface properties were determined by N2 BET specific surface area (Sg) measurements and CO uptake determinations. The activity of the silica-supported catalysts in hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) was evaluated in a three-phase trickle-bed reactor using a model liquid feed containing 2000 ppm nitrogen as quinoline, 3000 ppm sulfur as dibenzothiophene, 500 ppm oxygen as benzofuran, 20 wt% aromatics as tetralin, and balance aliphatics as tetradecane. The reactivity study showed that the HDS activity sequence for the three samples was Ni2P/SiO2>CoP/SiO2>Fe2P/SiO2, while the HDN activity followed the sequence CoP/SiO2>Ni2P/SiO2>Fe2P/SiO2. Compared with a commercial Ni–Mo–S/γ-Al2O3 catalyst, Ni2P/SiO2 had a higher HDS activity (90 vs 76%), but a lower HDN activity (14 vs 38%), based on equal sites loaded in the reactor. The sites were determined by CO chemisorption for the phosphide and low-temperature O2 chemisorption for the sulfide. XRD and X-ray photoelectron spectroscopy characterizations of the spent catalysts indicated that the Ni2P/SiO2 catalyst was tolerant of sulfur.