Secondly, alloying Pt with Ge increases the dehydrogenation reaction barriers. The most selective catalysts are predicted to be Pt 4 Ge and Pt 4 Ge 3 , which exhibit the largest barriers for the undesired ethylene dehydrogenation. The presence of unpaired electrons appears to be key for this step. In fact, Ge quenches spins on Pt atoms. Fig. (bottom panel) shows the singlet-triplet gaps for the most relevant isomers. While most of Pt 4 isomers have an open-shell electronic configuration (and the one with all the electrons paired has a small singlet-triplet gap of 0.11 eV), all the Pt 4 Ge x (x = 1-4) nanoclusters have a closed-shell electronic configuration. Moreover, one Pt 4 Ge 2 isomer features a smaller gap as compared to other compositions, making it less selective than other PtGe alloys. On such Pt 4 Ge 2 isomer ethylene binds in the di-𝜎 fashion, and the activation energy for the first dehydrogenation, although much improved with respect to pure Pt, is smaller than that in other PtGe compositions. Finally, it must be highlighted that on Pt 4 Ge the energy barrier for the ethane dehydrogenation, related to the catalytic activity, is also increased with respect to pure Pt, but such barrier is significantly smaller than that for dehydrogenating ethylene, related to the selectivity. Therefore, a low Ge content will provide more resilient catalysts, while maintaining the activity.