In summary, from the TPD, XPS, and DFT results, we found that Pt4Ge/alumina promotes intact desorption of ethylene in ethane dehydrogenation, largely, but not completely preventing carbon deposition. There is one minority isomer of Pt4Ge/alumina (LM2, or LM') that acts as a gateway to carbon deposition on Pt4Ge/alumina, gradually resulting in all the Pt4Ge clusters becoming coked. However, defying expectations, coking is not detrimental to catalytic activity, and instead preserves the desired catalytic properties while dramatically enhancing cluster catalyst stability. The coking is self-limiting: once Pt4GeC2/alumina forms, it dramatically decreases the further deposition of carbon by ethylene dehydrogenation via increased barriers for ethylene desorption, eventually reaching a steady-state catalyst where no further changes in the ethylene binding sites or D2 desorption are observed experimentally. Furthermore, Pt4GeC2/alumina still binds ethane strongly, with low activation barriers for ethane-to-ethylene conversion. Thus, the self-limiting coking of Pt4Ge improves the selectivity of the catalyst without degrading the activity. The Ge atom in the cluster interacts with the carbon in the coked cluster, stabilizing the cluster significantly, and prevents deactivation of the cluster via either physical blocking of sites, or dramatic change in electronic structure. This moderates the tendency of the cluster to coke, enabling the self-limiting behavior. The synergy between alloying and selective coking could be a way forward in creating ultra-stable sub-nano cluster catalysts for other reactions, solving the main limiting factor hampering wide-spread use of subnano clusters in catalysis.