Effect of F and Mg on the Dispersion of Mo/Al2O3 and W/Al2O3

Samples containing 8% Mo and l5% W supported on magnesium- and fluoride-modified aluminas were prepared by incipient wetness impregnation and examined in the dried and calcined states using X-ray photoelectron spectroscopy (XPS, ESCA). The presence of fluoride as an additive decreased the dispersion of the Mo and W phases for dried samples. The opposite effect was observed for dried Mg-modified samples. The effects of F and Mg addition largely disappeared when the samples were calcined. The results are interpreted in terms of the interactions between Mo and W species and the basic hydroxyl groups of the alumina.