Isotopic investigations into oxygen activation on Co3O4|CeO2 heterojunctions – Mechanistic role of the interface and the spinel-ceria ratio

Cobalt spinel-ceria catalysts of various compositions were tested for isotopic 16O2/18O2 and 18O2/16Osurf exchange. The onset of the exchange was dramatically decreased down to 140 °C, compared to 310–350 °C observed for the single components. The temperature evolution of the 16O2, 16O18O and 18O2 profiles implied competing homogeneous (R0) and heterogeneous, R1 and R2, exchange processes. Their relative contributions were changing with the Co/Ce ratio and temperature. The isotopic exchange processes are spatially separated, with R0 occurring preferentially on the cobalt spinel component, whereas the single (R1) and double (R2) exchange on the ceria moiety.