Pd-Ni catalysts supported on Al2O3, (Ce,Zr)O-X/Al2O3, and (Ce.Zr)O-X are characterized at a nanoscopic level using mainly electron microscopy-related techniques (HREM images, XEDS, and Z-contrast images/EELS spectra done with TEM and STEM instruments). The presence of rather homogeneous Ce-Zr mixed oxide nanostructures is revealed from analysis of HREM pictures. Analysis of the Pd-Ni/(Ce,Zr)O-X/Al2O3 system shows the existence of preferential interactions of Pd and Ni with the (Ce,Zr)O-X and Al2O3 components, respectively, as evidenced mainly by XEDS and confirmed by FMR. Dispersion states of the metals and particle size distributions of palladium are inferred from analysis of Z-contrast images and EELS spectra. The results are complemented by XPS and XAFS results used to analyse the chemical state of the metallic components in the catalysts and their dispersion over the different supports. (c) 2005 Elsevier Inc. All rights reserved.