XPS STUDIES ON CE AL2O3 AND ON CO-RH/NB2O5 CATALYSTS/

The surface properties of supported catalysts are studied. XPS data ar e used to identify the different surface species but, alone, it is not sufficient to provide enough information to describe the correct form and distribution of these species and phases on the surface. However, XPS supported by an accurate mathematical formalism to model catalyst s surface structure, may become a powerful tool to help understanding surface properties. First, a new mathematical model for supported bime tallic Co-Rh/Nb2O5 catalysts is proposed based on quantitative analysi s of XPS intensities assisted only by TPR data XPS peak intensities ar e compared to the values predicted from different structural models of the oxide particles. Secondly, the Ce/Al2O3 system generated from dif ferent precursors of cerium salts and contents is examined using diffe rent techniques. XPS results show the effect of the precursor on the C e/Al ratio while TEM the morphology. In addition, the EPR data show th e Ce3+ species distributed in regions underneath the topmost surface l ayer. Then, an improved model is proposed based on quantitative analys is of XPS intensities, XRD, and TEM results.