The present work has provided new fundamental information on the effects of aging (mileage, kin) of a commercial Pd-Rh (9: 1, w/w) three-way catalyst (TWC) on (a) the H-2 chernisorption, (b) the redox properties of washcoat material, and (c) the dynamic oxygen storage and release properties of TWC. Hydrogen chemisorption in the 25-400degreesC range was found to decrease with increasing aging of TWC. On the other hand, H, chemisorption performed at 200 and 400degreesC resulted in a significantly larger amount of chentisorbed hydrogen (exceeding the monolayer value based on the noble metals) compared to that obtained after chernisorption at 25degreesC. This is due to the onset of a hydrogen spill over process in the 200-400degreesC range. The features of H-2-TPD spectra were found to strongly depend on the aging of TWC. Hydrogen chemisorption at 25degreesC followed by TPD after a given pre-treatment of the catalyst surface might be considered as a procedure for a good estimate of the metal dispersion of a commercial Pd-Rh TWC. The redox properties of the oxygen storage components of the washcoat of a commercial Pd-Rh TWC were found to drastically change with increasing aging of TWC. It was found that the oxygen storage capacity (OSC) of the TWC investigated decreases significantly with catalyst aging in the 0-56,000 km range and in the temperature range of 500-750degreesC. In the case of fresh TWC, the presence of 20 ppm SO2 Or 10% CO2 in a 1.5% O-2/He gas mixture used for oxygen storage (oxidizing gas) was found to result in a large decrease in the amount of dynamic OSC measured by alternating switches between oxidizing and reducing feed gas compositions. The shift in time of the peak maximum of the transient response Of CO2 obtained during the switch O-2/He --> He --> CO/He (t) can be ascribed to the alteration of the kinetics of the oxygen back-spillover process and not to the kinetics of CO oxidation on the metal surface. (C) 2004 Elsevier B.V. All fights reserved.