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

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 (kRE) 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 kRE 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.