Finally, the pulses of the H2O product are significantly broader than the other signals (Figure ). Such broadening is generally attributed to a strong interaction of the respective species with the catalyst surface, leading to rather long lifetimes of the adsorbed species during adsorption -desorption processes occurring during the passage through the catalyst bed, or to slow formation in the catalyst bed. Due to the pronounced pulse broadening the pulses do not have enough time to return to the background signal before the next pulse (Figure ), leading to an increase of the apparent background signal already during the initial pulses 1 to 5 (Figure , Figure (see next section). H2O can be generated as a final product of the methanation reaction on the one hand, but also by the reactive removal of active oxygen (Oact) by H2 from the catalyst surface or as a product of the decomposition of surface species on the other hand.