3. Transient TAP measurements, exposing the pre-reduced catalyst to H2/CO2/Ar pulses with stoichiometric H2 : CO2 ratio (4 : 1) at 190 °C, demonstrate that the activity for the formation of CH4 and H2O on the one hand and of rather stable carbon containing adsorbed species on the other hand is highest at the very beginning of the sequence, directly after the onset of the multipulse sequence. An initial, rapid increase in the formation of CH4 and H2O during the first 6 -8 pulses is associated with an increasing formation of adsorbed intermediates that can react with H2 to CH4 in the presence of gaseous H2. These intermediates are sufficiently stable that they can accumulate during the first pulses and can react also with H2 in subsequent pulses.