PHYSICOCHEMICAL CHARACTERIZATION OF THE INTERACTION BETWEEN COBALT MOLYBDENUM OXIDE AND SILICON DIOXIDE .2. INFLUENCE OF THE AMOUNT OF OXIDE PHASE

Silica is a relatively inert support in comparison with alumina. For the same amount of active phase, it has been shown that the nature of the compound present on these two supports is very different in the range of composition from 0 to 1 cobaltmolybdenum atomic ratio. We have determined the influence of the amount of oxide phase present on the support on the structure of Mo/SiO2 and CoMo/SiO2 catalysts by using X-ray diffraction, DRS measurements, and a gravimetry study of the reduction by hydrogen. In the first series of catalyst, the molybdenum oxide content ranges from 2.8 to 20.6 wt %. In the second one, the amount of active phase (Co3O4 + MoO3 ranges from 3.7 to 27.7 wt %. In the latter case the atomic ratio Co/(Co + Mo) is constant and equal to 0.36. When only molybdenum is supported on silica both attached Mo(VI) interacting with SiO2 and bulk MoO3 are present in proportion which depends on the amount of molybdenum oxide phase. The addition of cobalt on Mo/SiO2 catalyst brings about a detachment of molybdenum oxide in interaction with SiO2 and formation of CoMoO4. Furthermore, there is no evidence of cobalt oxide formation. © 1979 American Chemical Society.