Pure Pt 4 presents small barriers for the first (0.19 eV) as well as the second step (0.50 eV). Regarding the bimetallic counterparts, the first step for Pt 4 Ge and Pt 4 Ge 2 are also rather small (0.29 and 0.52 eV), whereas the second barrier becomes significantly large (> 1.5 eV), while O* has to migrate from one very stable bridge position to the adjacent one. In Pt 4 Ge 3 the first CO 2 formation shows a barrier of 0.78 eV, while in Pt 4 Ge 4 both barriers are around 0.55 eV. The first step is always more exothermic than the second as the O-O scission releases extra energy. CO 2 desorption is found to be endothermic with a BE of around 0.10 eV and 0.30 eV in the first and second steps, respectively.