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–LIII 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

The sulfidation mechanism of NiW/gamma-Al2O3 as a function of the calcination temperature studied with Fe-57-MAS and temperature programmed sulfidation

Currently the production of low sulfur diesel fuel (< 0.05 wt.% S) is an important topic in oil refineries due to new environmental legislation. Consequently, alternative catalysts for deep HDS processes are required and NiW/gamma-Al2O3 catalysts are a promising option. An important issue in the application of NiW/gamma-Al2O3 catalysts is their activation. In this work a quantitative description of the sulfidation mechanism of W in NiW/gamma-Al2O3 catalysts, as obtained from temperature programmed sulfidation measurements, is presented. It is shown that the calcination temperature has a great influence on the relative importance of the different sulfidation reactions. Especially the WS2 formation at sulfidation temperatures below 600 K is strongly decreased after calcination above 673 K. Fe-57-MAS shows that re-dispersion of Ni-sulfide species occurs after sulfidation at 573 K for a dried catalyst to form the so-called NiWS phase. The NiWS phase is also formed on calcined catalysts but only at sulfidation temperatures of 673 K. It is demonstrated that the formation of WS2 slabs is a prerequisite for the re-dispersion of Ni-sulfide species. (C) 1999 Elsevier Science B.V. All rights reserved

The sulfidation mechanism of NiW/gamma-Al2O3 as a function of the calcination temperature studied with Fe-57-MAS and temperature programmed sulfidation

Currently the production of low sulfur diesel fuel