In Figure In general, these results are consistent with those reported by Guerrero-Ruiz et al. , Yan et al. and by Mansour and Iglesia for reaction at significantly higher temperature (300 °C -450 °C). Hence, although reversible formation and re-oxidation of CO as possible intermediate can be excluded under present reaction conditions, exchange of oxygen is possible at 190 °C. Most simply, this can be explained by a reaction of CO2 with surface lattice oxygen of Al2O3 to form weakly bound carbonate species, which even at 190°C can subsequently decompose and release CO2 under exchange of oxygen. Oxygen exchange is possible if the previous surface lattice oxygen species in the surface carbonate can be incorporated into the desorbing CO2, while an oxygen atom from the previous CO2 is incorporated into the Al2O3 surface lattice instead. For bi-or tridentate carbonates this requires that a bond between former surface lattice O and Al can be broken comparably easy as one between 18 O from the former C 18 O2 molecule and Al. This would agree with findings from a combined experimental and theoretical study by Casarin et al. , who reported that CO2 interaction with -Al2O3 leads to the formation of a bidentate surface carbonate, which can reversibly decompose and release CO2 at higher temperatures. Comparable results were reported also by Szanyi and Kwak . Investigating the interaction of CO2 with -Al2O3, they observed the formation of bicarbonates and weakly held surface carbonates, together with linearly adsorbed CO2, where the latter can be readily removed by evacuation at room temperature. We will continue the mechanistic discussion and present a more quantitative discussion of the oxygen exchange behavior in section 3.4, after the presentation of additional O exchange data in the next two sections.