After subtraction of the background signal we integrated the signal area under each pulse for the respective species. The amount of consumed reactant was calculated from the difference in pulse size between the incoming pulse and the effluent measured pulse, where the former was determined from the measured pulse size of the Ar standard and the average ratio of the reactive gas to Ar, which was determined in a blank measurement on an inert α-Al2O3 catalyst bed. From the amount of reactant consumed or product produced in each pulse we calculated the accumulated amount of consumed / produced species during the pulse sequence. For the quantification of CO and CO2 we considered the fragmentation of CO2 in the QMS to CO by correcting the measured signal intensities of CO and CO2 by a fragmentation probability of 13% (measured CO intensity relative to the measured CO2 intensity), which we had determined in a blank measurement. Finally, from experimental reasons we had to separate the pulse sequences into subsequences of 180 -200 pulses each, due to size limitations in the resulting data files. This resulted in breaks between subsequences of approx. 5 min. More important, these breaks may also lead to a sudden change in the incoming and thus also effluent pulse size, (see ref. ), which could be quantified and corrected for via the pulse size of the Ar standard.