The role of nickel in the initial transformations of hydrodesulfurization catalysts

The initial hydrodesulfurization activity behavior of supported nickel molybdate catalysts has been found to be markedly influenced by the presence of the promoter (nickel). The promoter diminished both the rate and the extent of deactivation of the fresh catalyst when exposed to a mixture of hydrogen and thiophene at atmospheric pressure. Presulfidation of the catalysts with pure H₂S did not affect the optimum nickel concentration but increased the optimum molybdenum concentration. These results together with those obtained on surface acidity, carbon deposition, and sulfidation extent seems to support the idea that the positive influence of the promoter on the initial transformation of the catalyst is to maintain the dispersion of molybdenum during the sulfidation of the catalyst and to diminish carbon deposition.