Oxygen storage capacity (OSC) measurements at 450 • C were carried out on 10 different alumina and ceria-alumina supported Pd, Pt, Rh, PdRh and PtRh catalysts. Experiments were performed under both transient (0.5 and 1 Hz) and stationary reaction conditions using a mass spectrometer for the gas phase analysis every 100 ms. OSC was shown to be strongly dependent on the metal nature -oxidized or reduced. Rh appeared to be the best OSC promoter. Furthermore, ceria addition to the alumina support strongly enhances the OSC. In fact looking at the OSC values, a factor of 3 was evidenced between Pt/Al 2 O 3 and Rh/Al 2 O 3 and an additional factor of about 12 between Rh/Al 2 O 3 and Rh/CeO 2 -Al 2 O 3 . The metal oxides relative stability as well as the metal electronic configuration were shown to be strongly influent on the overall reactivity of the catalyst. Additional kinetic studies showed that the oxide reduction rate under CO is slower than the oxide oxidation rate under O 2 . Finally a general scheme for the oxygen storage process is proposed and discussed.

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