The morphology of rhodium particles in a 5 wt% Rh/Ce0.5Zr0.5O2 catalyst subjected to different treatments is investigated by EXAFS, HREM, and H-2 chemisorption. Despite the high Rh loading highly dispersed metal particles are observed in the sample. In the presence of NO and CO, the Rh particles are easily oxidized to give small Rh oxide clusters, and the high rhodium dispersion is retained even after a further reduction at 773 K. Comparison with an Rh/Al2O3 prepared under identical conditions clearly suggests that the presence of the Ce0.5Zr0.5O2 support favors high dispersion of rhodium particles. Despite the fact that RhCl3. nH(2)O has been employed as precursor, no chloride could be detected in the Rh nearest-neighbor shell, suggesting its migration over the support. (C) 2000 Academic Press.