Al-pillared montmorillonite-based Mo catalysts: effect of the impregnation conditions on their structure and hydrotreating activity

The effects of the pH and medium of the impregnation solution on the surface structure and activity for gas oil hydrodesulfurization (HDS) of molybdenum catalysts supported on an Al-pillared montmorillonite have been studied. Catalysts were characterized by using X-ray diffraction, nitrogen and ammonia sorption measurements, temperature-programmed reduction, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that impregnation at basic pH leads to the incorporation of molybdenum mainly in form of monomeric and polymeric species, with a substantial part of Mo species in the interlayer space of the Al-pillared clay, probably in interaction with the alumina pillars. Whereas, formation of small particles of bulk MoO3 deposited on the external surface of the Al-pillared clay was favoured by impregnation at acid pH. The impregnation at pH 8.5 in a H2O2 solution produced abundant formation of incipient MoO3 crystallites relatively well dispersed, partially located inside the porous system. The catalysts prepared at basic pH values had slightly higher HDS activity than those prepared at acid pH values.