To search for the most suitable starting point a screening of the most stable co-adsorption complexes was done by adsorbing CO with multiple orientations on adjacent sites to O 2 * or O* in Pt 4 Ge n O 2 and Pt 4 Ge n 2O. We begin with the CO* + O 2 * reaction (Figure ). As the reactants approach each other the O-O bond is elongated and the reaction proceeds via the first TS to an intermediate (IM). It should be mentioned that in many cases this first step involves the formation of a OCOO* species in the IM. However, our calculations for PtGe reveal that the cleavage of O-O and formation of C-O occurs simultaneously in the first step, so CO 2 * is already formed in the IM. Apart from Pt 4 Ge, oxygen is already dissociated in the TS. The charge of the reacting O increases up to ~1.0 |e|. In the IM complex CO 2 is usually bonded from the C atom to Pt with a Pt-C distance of ~2.05 Å and has an internal angle of ~130º. When the reaction occurs close to the interface, CO 2 also binds to a substrate Mg atom via one of the oxygens. Subsequently, there is a barrierless release of the formed CO 2 molecule to the environment, leaving an O* on the surface to further oxidize another CO molecule.