A CO-rich feed (Figure , right) has an extremely detrimental effect on the performance of the monometallic cluster at low temperatures; Pt 4 becomes almost completely poisoned by CO (θ CO 0.8 ML). In this regime there is a scarcity of O 2 * and O* sites for LH and ER paths and thus the oxidation rate decreases drastically. This behavior can be understood in terms of DFT binding free energies that show the strong adsorption of CO on pure Pt clusters. The TOF CO2 increases with temperature until it is stabilized in the 225-325 K window. CO* nearly disappears but CO 2 * coverage becomes more pronounced (θ CO2 ~0.6 ML). Nonetheless, there is still a fraction of O* and O 2 * which can oxidize CO at rates similar to P O2 > P CO . As the temperature increases, CO* coverage starts increasing at the expense of CO 2 * and the TOF CO2 is slightly reduced.