A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 3. Drying process

In the present part of the group study on the preparation of 13 wt% MoO3/Al2O3, the effects of drying processes were investigated on the physicochemical and catalytic properties. Two series of catalysts were prepared by a conventional impregnation technique and by an equilibrium adsorption method using a common extrudate support. XPS and EPMA results demonstrated that the distribution of Mo oxide species in extrudates was strongly affected by drying processes. A rapid drying, in particular at a reduced pressure, was found to induce a strong segregation of Mo oxides on the outer surface of the extrudates, forming a sharp egg shell type distribution of Mo. On the other hand, drying under static conditions produced a moderate egg shell type distribution, suggesting that a slow drying rate is favorable for a homogeneous distribution of Mo. The equilibrium adsorption technique was found to provide considerably flat Mo profiles inside the extrudates except for the utmost surfaces where Mo concentrations increased steeply.