OXYGEN-EXCHANGE REACTIONS OVER CERIUM OXIDE - AN FT-IR STUDY

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 O2 and lattice oxygen of the cerium oxide does not occur at the temperature below 373 K. Site exchange via gaseous O2 with adsorbed superoxide (O2-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 O2 and adsorbed peroxide (O22-ads) species does not take place in the temperature range 200-373 K. The isotopically exchanged superoxide species (16O18Oads-) 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 O2 with adsorbed superoxide species. © 1990.