Synergistic IntermetallicEffect on the Sulfurizationof the NiWMo/Al₂O₃ Catalyst to Enhance the HydrodesulfurizationPerformance

The trimetallic NiWMo catalyst exhibits higher hydrodesulfurization activity compared with the bimetallic NiMo(W) catalyst. However, the nonsynchronous sulfurization of Mo and W during sulfurization leads to either an increase in slab size or incomplete sulfurization. This limitation hinders further improvement of the NiMoW catalyst’s performance. Therefore, it is essential to investigate factors influencing the sulfurization process of the trimetallic NiWMo catalyst, achieving synchronous sulfurization of Mo and W. Herein, the trimetallic NiWMo/Al₂O₃ catalyst is prepared by the impregnation method. During sulfurization, the interaction between additive Ni with main metals W and Mo reduces the sulfurization temperature while increasing the degree of sulfurization for the main metals. Additionally, the interaction between W and Mo reduces the sulfurization temperature difference. As a result, the highest sulfurization rates for Ni, Mo, and W are observed within 290–375 °C, where close contact between Mo and W species inhibits unrestricted growth of Mo(W)S₂ slab length and forms a Ni–Mo–W–S active phase. Consequently, the Mo(W)S₂ lamella exhibits a higher stacking number and reduced slab length, which results in increased exposure to edges where Ni–Mo–W–S is present and an enhanced number of active sites on the catalyst. This enables higher hydrodesulfurization activity for NiWMo/Al₂O₃ and the 4,6-dimethyl-2-benzothiophene conversion reaches 100% at 320 °C.