Abstract
Two series of metal catalysts (Rh, Pt, Pd, Ru and Ir) supported over CeO 2 and Ce 0.63Zr 0.36O 2 were prepared. Catalysts were pretreated at 500 °C (fresh) and further sintered either in H 2 or in air at 700–900 °C. All catalysts were characterized by H 2 chemisorption at −85 °C and/or by transmission electron microscopy (TEM). The 16O 2+ 18O 2 homoexchange reaction was carried out in the 200–500 °C temperature range. Rh, Ru and Ir showed the highest homoexchange rate R (per m 2 metal) while Pd and to a lower extent Pt were less active. Sintering affected the metal performances differently: while R is higher on small Rh particles (fresh catalysts), the reverse situation could be observed for Ru and Ir where the sintered catalysts were more active than the fresh ones, especially in the case of CeO 2.
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