16O/18O isotopic exchange: A powerful tool to investigate oxygen activation on M/CexZr1−xO2 catalysts

Two series of metal catalysts (Rh, Pt, Pd, Ru and Ir) supported over CeO2 and Ce0.63Zr0.36O2 were prepared. Catalysts were pretreated at 500 °C (fresh) and further sintered either in H2 or in air at 700-900 °C. All catalysts were characterized by H2 chemisorption at −85 °C and/or by transmission electron microscopy (TEM). The 16O2+18O2 homoexchange reaction was carried out in the 200-500 °C temperature range. Rh, Ru and Ir showed the highest homoexchange rate R (per m2 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 CeO2.