At high O 2 pressures (Figure , left) a transition can be observed to the CO poisoning-free regime. Higher O 2 pressures seem to be beneficial, regardless of the temperature, as expected. O 2 adsorption becomes more favorable than CO, which then converts to O* via O 2 dissociation and CO* + O 2 *. From 100 K to 275 K the surface composition is 0.4 ML CO 2 *, ~0.5 ML O* and ~0.1 ML O 2 *. At higher temperature, O 2 dissociation becomes more favorable and O* coverage increases at the cost of O 2 * sites. The presence of CO 2 * indicates that the LH channel is not hindered by CO poisoning. However, CO 2 * limits the availability of active sites for LH and ER pathways, so the efficiency of CO 2 production is compromised. The TOF CO2 decreases linearly with temperature from 10 -1 to 10 -2 s -1 . We anticipate that CO 2 poisoning can cause a drop in the TOF CO2 by two orders of magnitude, although the effect is milder than for CO poisoning.