Origin of the dispersion limit in the preparation of Ni(Co)Mo/Al2O3 and Ni(Co)Mo/TiO2 HDS oxidic precursors

Conventional alumina and titania oxidic precursors have been characterized by Raman spectroscopy after maturation, drying and calcination. The evolution of the impregnating solution has been followed and the nature of the precipitates has been determined. After impregnation of alumina 6molybdoaluminate entities (well dispersed or not) are characterized for both the NiMo and CoMo based solids. At high Mo loading, the formation of a CoMo oxyhydroxide that yields bulk cobalt molybdate upon calcination is also observed. In counterpart on TiO(2) surface of the NiMo precursor, the formation of 6molybdonickelate leading to bulk nickel molybdate upon calcination is observed. The formation of well defined phases i.e. CoMoO(4) and NiMoO(4) was not observed on respectively titania and alumina supports, but well dispersed polyoxomolybdate was characterized at the same Mo loading.