Ceria-supported Au-CuO and Au-Co3O4 catalysts for CO oxidation: An O-18/O-16 isotopic exchange study
Résumé
In this work isotopic exchange of O-18(2) with O-16 and oxidation of (CO)-O-16 were investigated at 130 degrees C on ceria-supported Au-CuO and Au-Co3O4 catalysts. Oxygen storage capacity (OSC) was measured at 400 degrees C to check the influence of the metals in the catalysts, resulting in an enhancement of OSC for gold-containing catalysts compared to monometallic catalysts. The reactivity of surface oxygen atoms and the oxygen availability from the samples were studied by two isothermal experiments, both feeding (CO)-O-16 (anaerobic oxidation (CO)-O-16/Ar and aerobic oxidation (CO)-O-16/O-2) to the O-18 pre-exchanged samples. Exchange leads to (CO)-O-18 formation and oxidation leads to (CO2)-O-16, (COO)-O-16-O-18 and (CO2)-O-18 formation. In anaerobic conditions the predominant reaction at the beginning is the exchange: a rapid exchange of (CO)-O-16 with the surface can be observed for all the samples except for CoCe that inhibits the exchange and the CO oxidation. In aerobic conditions, the predominant reaction is CO oxidation with the rapid increase of (CO2)-O-16 due to the relatively high O-16 coverage in reaction as a result of the (CO)-O-16 exchange and from exchange between O-18 surface species and O-16 bulk atoms. At 130 degrees C, bare ceria shows null activity in both aerobic and anaerobic oxidation.