Controllable synthesis of nanostructured nickel phosphosulfide by reduction of mixtures of Na4P2S6 and NiCl2 with low P/Ni ratios in hydrogen plasma

Abstract

Transition-metal phosphides and phosphosulfides constitute a class of versatile and promising catalysts in the field of enery production. The preparation of nanostructured phosphides and phosphosulfides is chanllenging because the thermal reduction of phosphate precursors requires high temperatures. In the present work, nanostructured nickel phosphosulfide catalysts composed of Ni2P particles surrounded by a distinct sulfur-containing layer were prepared by reduction of mixtures of Na4P2S6 and NiCl2 in H2 plasma. The minimum P/Ni ratio needed for the formation of nickel phosphosulfide was between 4/7 and 2/3, and the input voltage of the plasma generator (Vin) should be higher than 40 V. The control of the particle sizes of the nickel phosphosulfide catalysts was realized by simply regulating Vin. Another minor factor affecting the particle size was H2 flow rate. The actual precursor for the formation of nickel phosphosulfide can be Ni2P2S6, which underwent fast reduction in H2 plasma to yield NiS. In the hydrodesulfurization of dibenzothiophene, the nanostructured nickel phosphosulfide catalyst exhibited higher activity and hydrogenation pathway (HYD) selectivity than the one with large particle size. The optimal P/Ni ratio of the nickel phosphosulfide catalysts was found to be 4/5, and the HYD pathway was more favored by the increase in the P/Ni ratio than the direct desulfurization pathway.