The main features of the individual pulses are a steep initial increase of the intensity, followed by an about exponential decrease. The latter was tested in plots of the logarithmic intensity in representative pulses vs. time. For the Ar pulses, pulse broadening should only result from transport processes through the catalyst bed due to the inert nature of Ar, while contributions from adsorptiondesorption processes can be neglected. Indeed, the Ar pulses are rather narrow (Figure ) and do not vary in width from the initial to the final pulses (Figure ). Over the whole sequence, the measured Ar pulse intensity decreases continuously, which will be quantified and discussed in more detail in the following section 3.2. As we can exclude intensity losses due to Ar adsorption, this reflects a slight intensity decay of the incoming pulses.