8. TAP-TPD measurements indicate the presence of more stable surface species on the surface after exposure to H2/CO2 pulses, which start decomposing and evolving CO2 only at higher temperature (260 °C). Most likely, less stable species decomposed already before the TPD measurement, while holding the temperature at 190°C. Exposure to CO2 pulses leads to adsorbed carbonate-like species which start decomposing to CO2 at temperatures slightly above the temperature during CO2 pulsing, at between 210 °C and 230 °C. and C 18 O2, with preferential C 18 O2 formation in a low-temperature peak, can be rationalized by kinetic limitations, due to a decreasing probability for oxygen exchange with C 18 O2 with increasing stability of the surface species. Based on the similar isotope composition as obtained at the end of the C 18 O2 pulse sequence, the low-temperature peak can be associated with species whose exchangeable oxygen composition was equilibrated. CO2 evolution at higher temperatures must result from species that were present on the surface before C 18 O2 pulsing, and that were little active for oxygen exchange due to kinetic limitations, reflecting a decreasing probability for oxygen exchange with C 18 O2 with increasing stability of the surface species.