On the structure and hydrotreating performance of carbon-supported CoMo- and NiMo-sulfides

The sulfiding behaviour and hydrotreating performance of CoMo and NiMo on carbon catalysts wereinvestigated, with a view to establishing the suitability of an active-carbon carrier for industrialhydrotreatment purposes. The sulfidation process (H2/H2S at 0.1 and 4 MPa) was followed with57CoMössbauer emission spectroscopy, and X-ray absorption spectroscopy (Mo- and Co-edge). It turns outthat the structural evolution of the CoMo/C catalyst is in broad terms very similar to that of a CoMo/Al2O3one, including the type I ¿ II phase transition at increased sulfiding pressure, albeit that some sinter-ing takes place concomitantly. In the hydrotreating part a NiMo/C catalyst was employed, sulfided at1 or 4 MPa, in trickle-flow conditions at 3.5 (HDS) and 6 (HDN) MPa. It transpires that the adsorptionproperties of NiMo/C are quite different from those of a NiMo/alumina, in that dibenzthiophene, quino-line, and polyaromatics are much stronger adsorbed on the carbon-supported catalyst. This leads to veryhigh dibenzothiophene HDS and quinoline HDN activities, but to a disappointing performance in thehydrotreatment of a heavy gasoil, where the polyaromatics can compete effectively for adsorption onthe active HDS/N sites.