X-ray photoelectron spectroscopy (XPS) for catalysts characterization

The general principles of X-ray photoelectron spectroscopy (XPS) as applied in the field of heterogeneous catalysis are reviewed. In particular, the use of this technique in the determination of chemical and physical changes of catalysts upon exposure to gaseous molecules and upon different thermal treatments is examined. Furthermore, examples of methods useful in obtaining the dispersion of supported catalysts are described and, for this purpose, theoretical models of the particle-support distribution are also discussed. The XPS characterization of supported Pd-Ag catalysts is reported, emphasising the advantages of using XPS to investigate surface segregation processes. In the case of supported Pd/Pt bimetallic catalysts it is shown how both, Auger and photoelectron peaks, characterized by different kinetic energies, allow to get depth profile non-destructive analysis. Finally the surface behaviour of CoMo catalysts, used for hydrodesulfurization reactions, is investigated on different supports and under different pre-treatment and reaction conditions. (C) 2002 Elsevier Science B.V. All rights reserved.