Abstract
Oxygen (site and isotope) exchange reactions over well-outgassed and partially reduced cerium oxide were examined in the temperature range 200–373 K by means of Fourier-transform infrared (FT-IR) spectroscopy. Isotopic exchange between gaseous O 2 and lattice oxygen of the cerium oxide does not occur at the temperature below 373 K. Site exchange via gaseous O 2 with adsorbed superoxide (O 2 − ads) species was found to be very fast on both the outgassed and partially reduced surfaces even at 200 K, but site exchange between gaseous O 2 and adsorbed peroxide (O 2 2− ads) species does not take place in the temperature range 200-373 K. The isotopically exchanged superoxide species ( 16O 18O ads −) with characteristic IR bands at 2175 and 1095 cm −1 are readily formed from a mixture of 1602 + 1$02 adsorption over well-outgassed and partially reduced cerium oxides. It is concluded that isotope exchange reactions proceed via adsorbed superoxide species and the exchange reaction is presumed to involve a tetraoxygen intermediate as the result of the reaction of gaseous O 2 with adsorbed superoxide species.
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