XPS studies on Ce/Al2O3 and on Co-Rh/Nb2O5 catalysts

The surface properties of supported catalysts are studied. XPS data are 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 catalysts surface structure, may become a powerful tool to help understanding surface properties. First, a new mathematical model for supported bimetallic Co-Rh/Nb2O5 catalysts is proposed based on quantitative analysis of XPS intensities assisted only by TPR data XPS peak intensities are compared to the values predicted from different structural models of the oxide particles. Secondly, the Ce/Al2O3 system generated from different precursors of cerium salts and contents is examined using different techniques. XPS results show the effect of the precursor on the Ce/Al ratio while TEM the morphology. In addition, the EPR data show the Ce3+ species distributed in regions underneath the topmost surface layer. Then, an improved model is proposed based on quantitative analysis of XPS intensities, XRD, and TEM results.