The oxygen exchange mechanism between (CO2)-O-18 and Ceo(2) and the role of Pt in this process have been studied in an advanced TAP reactor in the 200-600 degrees C temperature range. For bare and Pt-containing CeO2, the exchange of the oxygen atoms Of (CO2)-O-18 takes place in the whole temperatures range studied, and the oxygen exchange rate increases with temperature. The proposed mechanistic pathway consists of the exchange of the oxygen atoms in the (CO2)-O-18 Molecule in two consecutive steps. In the case of bare CeO2, only one of the oxygen atoms Of (CO2)-O-18 is exchanged between 200 and 300 degrees C, and temperatures above 300 degrees C are required for the exchange of the second oxygen atom of the (CO2)-O-18 molecule. Pt accelerates the exchange rate between 200 and 400 degrees C, mainly favouring the exchange of the second oxygen atom of the (CO2)-O-18 molecule. The effect of Pt cannot be resolved at higher temperature (above 400 degrees C), since at high temperature the direct exchange over bare CeO2 is already fast. (c) 2008 Elsevier B.V. All rights reserved.