Characterization of the active phase of NiMo/Al2O3 hydrodesulfurization catalysts

The active phase of the NiMo/Al₂O₃ catalyst for hydrodesulfurization reactions has been investigated in this work. Special attention has been focused on the effect of the order of metal impregnation on the formation of the active phase in the reaction. The Mo and Ni oxides and their sulfides on the alumina were investigated by XPS and DRS analyses. The Ni-Mo oxides or precursor of the active phase which are chemically bonded between Mo and Ni were also confirmed from the binding energy shifts of the XPS peaks. The amount of Ni-Mo oxides was determined after the formation of metal oxides during calcination. The Ni-Mo sulfide (active phase) was then induced through sulfidation. It was important that Mo should be located at the tetrahedral sites on the alumina with a high Mo dispersion. These results indicated that there are two important factors in preparing highly efficient Ni-Mo catalysts; one is that Mo should be located at the tetrahedral coordination on Al₂O₃ in high dispersion (Mo/Al₂O₃) and the other is that the Ni species should be supported on MoAl₂O₄ to form Ni-Mo oxides which change into the Ni-Mo sulfide active sites by sulfidation.