A refinement on the notion of type I and II (Co)MoS phases in hydrotreating catalysts

The influence of Mo content on thiophene hydrodesulfurization for alumina- and carbon-supported (Co)Mo catalysts is investigated by TPR, XPS and H2-D2 equilibration. Activity trends for alumina-supported catalysts are explained by a gradual change of the type I MoS2 active phase from a large to a small number of Mo-O-Al anchors. A pure type II phase without such anchors and a high HDS activity is only obtained employing chelating ligands or a carbon support. At low Mo loading a separate oxysulfidic Mo species in strong interaction with alumina exhibits an unexpectedly high HDS activity, which, however, is difficult to promote by Co.