Carbon-supported Mo catalysts prepared by a new impregnation method using a MoO3/water slurry: saturated loading, hydrodesulfurization activity and promotion by Co Original Research Article

MoO3/activated carbon catalysts were prepared by a new impregnation method: Mo species were adsorbed from a MoO3/water slurry. The maximum achieved loading was 27–34 wt.% MoO3 for various carbons and the deposited phase was X-ray amorphous. The surface area and volume of micropores of the carbon supports dropped by about 40% after saturation of the supports with molybdenum trioxide. For the support Norit RX, the point of zero charge decreased from an initial 8.2 to about 2.6 as the MoO3 loading increased up to about 15% and then levelled off. The catalytic activity for the hydrodesulfurization of thiophene increased linearly with loading up to about 15% and then almost levelled off. A strong synergistic effect in activity was achieved by addition of Co to the 15% MoO3/C catalyst; however, the synergism observed when adding Co to a saturated 33% MoO3/C catalyst was small. It was concluded that molybdenum trioxide is chemisorbed in a highly dispersed ‘monolayer’ form up to a loading of about 15% MoO3. Further adsorption between about 15% and the saturation loading occurs by ‘physisorption’ in micropores and leads to a ‘multilayer’ form. The ‘multilayer’ form does not contribute to the surface properties (e.g. catalytic activity) and is not accessible to promotion by cobalt. Carbon-supported catalysts were much more active than their alumina-supported counterparts.