Hydrodesulfurization and hydrogenation on alumina-supported tungsten and nickel-promoted tungsten catalysts

Abstract

Hydrodesulfurization (HDS) of radioactive ³⁵S-labeled dibenzothiophene was carried out over a series of alumina-supported W-based catalysts containing ca. 10–35 wt.% WO₃ and 0–9 wt.% NiO at temperatures in the range 220–400°C and under a reaction pressure of 50 kg cm^-2. The catalytic activities of the catalysts changed depending on the W loadings and sulfidation temperature for W–Al₂O₃ catalysts. Moreover, the HDS and hydrogenation (HYD) activity of W–Al₂O₃ catalysts were remarkably enhanced with the addition of nickel. Further, the amount of labile sulfur (S₀) on the W–Al₂O₃ catalyst was much less than that on the corresponding Mo catalyst although the strength of the W–S bond is weaker than that of Mo–S. This is attributed to the fact that the sulfidation of the W–Al₂O₃ catalyst and the formation of the W–S bond are more difficult. On the other hand, S₀ and the rate constant of H₂S release (k_RE) increased significantly on addition of nickel, as in the case of the Co–Mo catalyst. Moreover, the Ni-promoted W–Al₂O₃ catalyst with higher Ni/W ratio (0.6) also showed S₀ and k_RE comparable to those of the corresponding Co–Mo catalyst. These results suggested, therefore, that the promoting effect of nickel enhanced the relative ease of sulfidation of W catalysts and resulting in formation of more active sites simultaneously.