Surface area determination of supported oxides: WO3/Al2O3

The concept that the variation in the point of zero charge (pzc) of physical mixtures of pure oxides can serve as a 'calibration curve' to evaluate the surface areas of the individual phases of composite oxides is now applied to the WO{sub 3}/Al{sub 2}O{sub 3} system. The results of the previously reported model, which assumes the surface area of each component in a composite oxide is a surface area weighted sum of the pzc's of the pure components, are compared to another model that accounts for variations in the measured BET area due to the increased loading of the second phase. The parameters of the models are the number of dispersed clusters and their size, and results from both models show the same qualitative trends. They become quantitatively the same as the second-phase loading decreases.