Synthesis, Characterization and HDS Activity of Carbon-Containing Ni–Mo Sulfide Nano-Spheres

Ni-promoted tetramethylammonium tetrathiomolybdate precursor was prepared by the aqueous solution precipitation method using (NH4)2MoS4, (CH3)4NBr and NiCl2.6H2O as raw materials. Carbon-containing Ni–Mo sulfide nanospheres, namely Ni/C1–MoS2, were obtained by ex situ thermal decomposition of the precursor under N2 atmosphere. Energy dispersive X-ray spectroscopy (EDS), low temperature N2 adsorption (BET method), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) techniques were employed to characterize these as–synthesized sulfide particles. The results showed that the average size of solid Ni–Mo sulfide nanospheres, with surface composition MoNi0.40S0.73C1.43, is 75 nm and the solid structure leads to low surface area of Ni/C1–MoS2. In addition, the introduction of methyl chain improved the dispersion of nickel phases and resulted in C/Mo ratio, 1.4. By comparison with catalytic performance of the Ni/MoS2 catalyst counterpart, Ni/C1–MoS2 revealed lower HDS activity but higher direct desulfurization (DDS) selectivity. Lower stacking number of MoS2 slabs (5 layers) and shorter slabs length of MoS2 slabs (6 nm) explained higher DDS selectivity satisfactorily. The formation of carbon-containing Ni–Mo sulfide nanospheres was possibly due to surfactant effect of tetramethylammonium cations and the potential measure to increase their surface area was discussed as well in this work.