On Pt 4 Ge x no spontaneous dehydrogenation of ethylene is found, suggesting an improved selectivity as compared to the monometallic clusters. In the cluster alloys, ethylene always binds to Pt atoms, rather than Ge. On Pt 4 Ge, Pt 4 Ge 3 and Pt 4 Ge 4 ethylene only binds in the less reactive 𝜋-mode. On Pt 4 Ge 2 , conversely, the most stable adsorption mode is di-𝜎, suggesting a higher reactivity. It should be highlighted that the presence of ethylene has a substantial impact on the relative population of these clusters in the ensemble. The most dramatic cases are Pt 4 Ge 2 and Pt 4 Ge 3 , where the third most stable isomers (isomers III with 17% and 10% initial populations, respectively) become predominant upon ethylene adsorption (configurations 1 with 64% and 57% populations, respectively). Moreover, isomer II of Pt 4 Ge, with the initial population of 21%, becomes a negligible minority upon ethylene adsorption.