XPS STUDY OF THE SUPPORTED PHASE-SIO2 INTERACTION IN MO-SIO2 AND COMO-SIO2 HYDRODESULPHURIZATION CATALYSTS IN THEIR OXIDIC PRECURSOR FORM

XPS results on two series of catalysts, namely Mo/SiO2 and CoMo/SiO2 in the oxidic form, are reported. In the first series the molybdenum oxide content deposited on SiO2 ranges from 2.8 to 20.6 weight %. The second series was obtained by cobalt impregnation of the first series; in this case the atomic ratio Co/(Co + Mo) was fixed at 0.36. XPS binding energy and intensities measurements enable estimation of the interaction and dispersion between the oxide phase and the support to be made. In the case of molybdenum deposited alone on the support, the binding energies of the Mo and O levels both increase with MoO3 content. When cobalt is also present on the support, the binding energies of the Mo and O levels remain constant. The relative intensities IMo/ISi and ICo/ISi remain constant up to 12% active phase and then drastically increase for higher amounts of oxide. These results confirm the existence of a relatively strong Mo/SiO2 interaction. This interaction is substantially weaker when Co is supported on the MoSiO2 solid, leading to the formation of CoMoO4 at the expense of the Mo/SiO2 interaction. Furthermore, it is shown that at high content of oxide the active phase is deposited on the outer surface of the particle and not inside the pores. © 1979.