XPS QUANTITATIVE-EVALUATION OF THE OVERLAYER SUPPORT INTENSITY RATIO IN PARTICULATE SYSTEMS

The XPS intensity ratios M(M)/I(Zr) were measured for supported MOx/Zr O2 SYStems (where M is Cr, Mo, Na, K, Re, designated as the ''promoter '') and compared with the intensity values calculated for different mo dels. When the support is the high surface area (about 300 m2 g-1) hyd rous zirconia (HZ) treated at 383 K, the Kerkhof and Moulijn model fit s the data very well. If the zirconia support is heated at T between 7 73-923 K before promoter adsorption, the observed intensity ratios are roughly twice as high as those predicted by a non-attenuating overlay er on a semi-infinite support (referred to as ''planar'') model. To ac hieve a correct fit for the experimental data, the contribution of eje cted electrons from low angles must be taken into account. A model has accordingly been tested, which can fit the observed intensity ratios independently of the nature of the promoter.