Control of CO emissions raises serious environmental concerns in the current chemical industry, as well as in nascent technologies based on hydrogen such as electrolyzers and fuel cells. Pt remains one of the state-of-art catalysts for the CO oxidation reaction, but suffers from CO self–poisoning. Recently, PtGe alloys were proposed as an excellent alternative to reduce CO poisoning. In this work we investigate the impact of Ge content on the CO oxidation kinetics of P4Gen subnanoclusters supported on MgO. Pt−Ge nanoalloys act as a bifunctional catalyst by displaying dual adsorption sites; i.e., CO is adsorbed on Pt whereas oxygen binds to Ge, forming an alternative oxygen source GeOx. Besides, Ge alloying modifies the electronic structure of Pt (ligand effects) and reduces the affinity to CO. In this way, the competition between CO and O2 adsorption and the overbinding of CO is alleviated, achieving a CO poisoning−free kinetic regime. Our calculations suggest that Pt4Ge3 is the optimal catalyst, evidencing that alloying composition is a parameter of extreme importance in nanocatalyst design. The work relies on global optimization search techniques to determine the accessibility of multiple structures at different conditions, mechanistic studies and microkinetic modelling.