The next question posed by the experiments is how Pt4Ge/alumina retains its hightemperature ethylene binding sites after 21 TPDs, even though the C 1s XPS and ISS results indicated significant carbon deposition. The DFT results indicate that once dehydrogenation has gone beyond ethylene, it should proceed to completion, depositing a pair of C atoms. Therefore, we study the Pt4GeC2/alumina system with DFT, finding, surprisingly, that only a single Pt4GeC2 isomer was thermally accessible (Fig. ). This structure is recognizably a relative of LM' that has incorporated two carbon atoms as an intact C2 unit into the middle of the cluster, maximizing the number of Pt-C bonds. Theory thus predicts that all the Pt4Ge clusters will eventually reach this single Pt4GeC2 structure as they coke via the LM' gateway isomer. Because the carbon is located in the center of the Pt4 ring, it does not physically block any Pt sites, in agreement with the observed minimal Pt ISS attenuation.