Due to the high time resolution of the TAP reactor pulse experiments, we could resolve an initial rapid increase in the formation of CH4 and H2O during the first 6 -8 pulses (i.e., up to 150 s), which we associate with an increasing formation of adsorbed intermediates that can react with H2 to CH4 in the presence of gaseous H2. These are sufficiently stable that they can accumulate during the first pulses, and then react also with H2 in subsequent pulses. After reaching this maximum, CH4 formation decreases slowly. Parallel to the initial build-up of these reactive intermediates, also little reactive or non-reactive adsorbed species are formed, which is responsible for most of the CO2 consumption. These species and the active sites for their formation must be different from the adsorbed reaction intermediates and the active sites for their formation, otherwise the rapid increase of the amount of non-reactive species on the surface would reduce the activity for CH4 formation much faster than observed experimentally.