Influence of preparation method on the acidity of MoO3(WO3)/ZrO2 catalysts

Zirconia-supported Mo and W oxides have been prepared by three methods: a conventional impregnation technique, a molten salt method and calcination of zirconium hydroxide impregnated with Mo(W) salt. The state of the Mo(W) and the acidity of the solids were studied, versus Mo(W) loading and calcination temperature. It has been shown that superficial acidity depends strongly on the preparation method used. Among the systems studied, solids prepared by calcination of impregnated zirconium hydroxide manifested the strongest Lewis and Bronsted acidity. The latter was, however, lower than the acidity of sulfated zirconias, as revealed by catalytic tests. A model of the structure of the acidic centres was proposed.