Characterization of Carbon- and Alumina-Supported NiW and CoW Sulfided Catalysts

Sulfided NiW and CoW catalysts supported on activated carbon and alumina were characterized with ⁵⁷Co Mössbauer emission spectroscopy (MES) and EXAFS at the W–L_III edge. NiW catalysts were studied with MES by probing the Ni atoms with ⁵⁷Co. MES results demonstrate that the Ni–W–S phase is present in sulfided NiW catalysts. Formation of Co₉S₈-type phases could be related to the lower thiophene HDS activity of CoW catalysts. W EXAFS showed that addition of Co or Ni to a W/Al₂O₃ catalyst results in a higher W sulfidation degree. No structural differences were found for carbon- and alumina-supported catalysts, in spite of the two times larger thiophene HDS activity of carbon-supported NiW.     

Ni-sulfide particles in NaY-zeolite for combined hydrodesulfurization and hydrocracking purposes

The influence of physisorbed water on the formation of nickel-sulfide species in a ⁵⁷Co doped ion exchange type ⁵⁷Co:NiNaY catalyst is studied by Mössbauer Emission Spectroscopy. The absence or presence of physisorbed water during sulfidation seems to have no influence on the local nickel environment of the formed Ni-sulfide species. This result is confirmed by EXAFS measurements. In spite of the resemblance found in MES and EXAFS a large difference is found for the initial HDS activities, which is explained by the different particle sizes (HREM) found at the outer surface of the zeolite.