Hydrodesulfurization of dibenzothiophene over Mo-based catalysts supported by siliceous MCM-41

Deep hydrodesulfurization (HDS) catalysts were prepared by depositing Co-Mo or Ni-Mo species over siliceous MCM-41. The extremely high surface area of MCM-41 favors the dispersion of the active species, resulting in a very high reactivity in desulfurizing dibenzothiophenes. A maximum HDS activity was observed at Co/Mo or Ni/Mo molar ratio of 0.75 for the supported catalysts, higher than that of the conventional gamma-Al2O3 supported catalysts. A S-35 isotope tracer technique was used to investigate the HDS reaction mechanism. It was revealed that sulfur atoms retained on the surface could be removed only by the introduction of a sulfur-containing compound, indicating that sulfur atom exchange between sulfur-containing compounds and the active sites is involved in the HDS reaction. Accordingly, a reaction mechanism for HDS is proposed.