Similar to H2 desorption it also continues during the time at 500 °C, indicating that additional CO2 formation can be expected at higher temperatures. Considering the rather weak interaction of CO2 with solids, we also attribute the evolution of CO2 to the decomposition of surface species such as (bi-)carbonate or formate adspecies, which were formed during the preceding pulse experiments. This would agree with the IR spectroscopic detection of such species during interaction of CO or H2/CO2 with Ru/Al2O3 at 175 °C and 230 °C . The different shapes of the H2 and CO2 desorption curves indicates that they cannot result from the decomposition of a common species only. The present CO2 peak is somewhat higher in temperature than obtained during desorption from a CO pulse-reduced catalyst, where two well-separated peaks appeared with maxima at 276 °C and 407 °C . On the other hand, a TPD measurement performed after O150 pretreatment and CO2/Ar pulsing, without H2 in the pulses, showed a shoulder at about 315 °C and the intensity further increasing up the maximum temperature at 450 °C . Obviously, the surface species resulting from the different pulse treatments differ significantly in their stability, which is especially apparent in the low-temperature regime. In all three cases, however, CO2 evolution starts between 210 °C and 235 °C, i.e., rather close to the temperature of the preceding pulse experiment. This supports our previous assumption of a steady-state situation in the pulse experiments where less stable surface carbonates etc. can be continuously formed and decomposed at 190 °C.