Finally, we explored the oxygen exchange behavior on a freshly O150 treated catalyst, without any reduction and re-oxidation procedures. Figure shows integrated C 18 O2 pulse intensities and the related initial pulse intensities, before passing through the catalyst bed. The integrated pulse intensities of all species are plotted in Figure . Also in this case, the general characteristics of the C 18 O2 pulse evolution closely resemble those obtained in the previous experiments. The pulse size is of similar magnitude (94 %) as that after pre-oxidation by H2/CO2 pulsing (section 3.3.1). Accordingly, the initial increase of the C 18 O2 pulse intensity with number of pulses is slower than in Figure , and comparable to that in Figure . Different from the previous cases there is a small decrease in the incoming C 18 O2 pulse size with increasing number of pulses, but the effect is rather small.