Uniform 3D NiMoS nanoflowers with self-assembled nanosheets were successfully synthesized via a simple hydrothermal growth method using cheap and nontoxic elemental sulfur as sulfur sources. The structure and morphology of the nanomaterials were characterized by SEM, TEM, XRD, Raman and XPS analyses, revealing that the NiMoS nanoflowers were composed of ultrathin nanosheets with a thickness of approximately 6–12 nm. The HRTEM results indicate that the curve/short MoS₂ slabs on the nanosheets possess the characteristics of dislocations, distortions and discontinuity, which suggests a defect-rich structure, resulting in the exposure of additional Ni–Mo–S edge sites. The obtained NiMoS nanoflowers exhibited an excellent activity for thiophene hydrodesulfurization (HDS) and 4,6-dimethyldibenzothiophene deep HDS due to their high density of active sites. The outstanding HDS performance suggests that these NiMoS composites with a unique flower-like nanostructure could be useful as promising catalysts for deep desulfurization of fuel oils.

After partial dealumination and desilicification caused by Mg doping and alkali treatment, Mg substituted hydroxyl group in the structure of HZSM-5. The increase in the number of Lewis acid sites led to a strong interaction of Mg (OH)⁺ with EFAL.

The findings in this study provide new insight into the NiMoS model, revealing that there is a sulfur dynamic equilibrium between the NiMoS edge and the gas phase. Since the evolution of non-stoichiometric sulfur proceeds rapidly at the initial stage of hydrodesulfurization reaction, the sulfur dynamic equilibrium does not draw so much attention. The results indicate that excess sulfur on the Ni–Mo–S edge can be reduced by hydrogen to form SH groups and release H₂S, which lead to a low sulfur-covered NiMoS edge and a significant increase in coordinatively unsaturated sites (CUS), resulting in an outstanding HDS activity. Apart from elucidating the effect of non-stoichiometric sulfur on the NiMoS structure, the relationship among H₂S partial pressure, S_x and HDS activity has been quantitatively studied. It is expected that these results will be used to deepen the understanding of HDS reaction over promoted MoS₂ catalysts, as well as to guide the research on ultra-deep HDS of fuel oils.