(1120) , and molecularly adsorbed CH4 would be bound very weakly, also this peak must result from decomposition of adsorbed species such as CHx, ad species rather than from CH4,ad desorption. Interestingly, it starts at higher temperature than the onset of CHx and finally CH4 formation in a H2/CO2 atmosphere over Ru/Al2O3, which was detected at about 200 °C in an in situ IR study . This indicates that purely thermal decomposition of such adsorbed species cannot be rate limiting during the CO2 methanation reaction. Finally, we detected a small amount of water (5.4•10 18 molecules gcat -1 ), which could have been formed, e.g., by recombination of hydroxyl species. Based on the significant amount of H2 desorption, but almost no H2O desorption, the barrier for water formation from the surface species must be significantly higher than that for H2 formation. This result also agrees at least qualitatively with previous findings for a O150 + CO pulse reduced catalyst surface and a O150 + H2/CO2 pulsed catalyst surface. Main results of this measurement are that decomposition of adsorbed species formed before or during the H2/CO2 multipulse sequence leads mainly to the formation of CO2, while CO is formed only in small amounts and at higher temperatures. The formation of these gaseous species, in particular that of CO, must result from decomposition processes that are slow during the pulse temperature of 190 °C, indicating that reversible formation -decomposition processes via the surface species detected here can contribute only little to the reaction at 190 °C. Nevertheless, reversible CO2 consumption and formation must be possible at 190 °C, by formation and decomposition of less stable (bi-)carbonate species, while there is no indication for CO formation at or slightly above 190°C from the TPD data. Furthermore, while there are differences in the exact peak shapes and relative amounts of CO2 formation for differently treated catalysts (CO pulse reduction, H2/CO2 pulsing, CO pulse reduction followed by H2/CO2 pulsing), the general features of the CO2 and CO spectra are maintained. Finally, H2/CO2 pulsing results in a large amount of H-containing adsorbed species, whose decomposition leads to H2 formation rather than H2O formation. The latter would be favored, e.g., for recombination of adsorbed hydroxyls, while H2 formation may be favorable for decomposition of adsorbed formate, bicarbonate, or CHx species.