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

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 Ni 2 P particles surrounded by a distinct sulfur-containing layer were prepared by reduction of mixtures of Na 4 P 2 S 6 and NiCl 2 in H 2 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 (V in) should be higher than 40 V. The control of the particle sizes of the nickel phosphosulfide catalysts was realized by simply regulating V in. Another minor factor affecting the particle size was H 2 flow rate. The actual precursor for the formation of nickel phosphosulfide can be Ni 2 P 2 S 6 , which underwent fast reduction in H 2 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. [Display omitted] • Mixtures of Na 4 P 2 S 6 and NiCl 2 were used as catalyst precursors. • Preparation of nickel phosphosulfide (NiPS) by H 2 plasma reduction of the mixtures. • The control of the particle size of NiPS by regulating the input voltage. • The minimum P/Ni ratio of the mixture for the formation of NiPS was 2/3. • Large NiPS particles showed lower hydrodesulfurization activity than nanoparticles. [ABSTRACT FROM AUTHOR]