The consumption of C 18 O2 molecules, the remaining release of C 18 O2 and the formation of the possible oxygen exchange products C 16 O 18 O and C 16 O2 are presented in Figure . Also here, the general trends are comparable to those in Figure . As expected from the much faster increase of the C 18 O2 pulse intensities in Figure , the consumption of these species decays much faster than in Figure . The C 16 O 18 O signal intensity (Figure and S6b) was maximal after approx. 60 pulses, thus, significantly earlier than in the previous experiment. Also this can be explained by the larger pulse size, which leads to a faster exchange of the exchangeable surface oxygen species. The subsequent decay was again comparable to that in Figure . It is important to note that this decay is not exponential, at least, it does not seem to exponentially decay to zero, which will be discussed more in section 3.3.4. The formation of C 16 O2 (Figure , dark green) occurred rather similarly as described for Figure , with an initial maximum followed by an about exponential decay. Similar to the increase in the C 18 O2 pulse intensity (Figure ), the loss in C 16 O2 pulse intensity (Figure ) and thus in C 16 O2 formation (Figure ) is much faster than in the previous experiment. In this case, the decay to about 50% of the maximum intensity takes only about 20 pulses. The accumulated formation and consumption of the different CO2 isotopologues (Figure ) differed mainly by the higher number of exchanged oxygen species from the previous experiment (for details see section 3.4). Accordingly, the exchange probability (red dots in Figure ) decays also to a lower value than in the previous experiment (see Table ). Most easily this could be explained by a higher number of exchangeable oxygen species on the catalyst surface, so that despite of the 2.5 times larger C 18 O2/Ar pulse size the relative concentration of 18 O species in the surface carbonates is only somewhat smaller at the end of the pulse sequence than in the previous experiment. This explanation agrees perfectly also with the larger number of consumed C 18 O2, which is 1.9•10 21 molecules gcat -1 in the present experiment instead of 1.33•10 21 molecules gcat -1 in Figure . This will be discussed further after the presentation of the next data set in section 3.4.