For ethylene on Pt4Ge/alumina, DFT suggested an interesting mechanism to account for the gradual and self-limiting coking observed. The GM and most LM isomers were found to bind C2D4 in π-mode, with barriers for decomposition exceeding the energy for intact C2D4 desorption. The small amount of D2 observed in the first TPD (see also Fig. ) was attributed to a small population of a "gateway" LM isomer that supports strong di-σ ethylene bonding, favoring decomposition to produce D2, and converting Pt4Ge to Pt4GeC2, which was predicted to be stable against further coking. The continued, but slowly decreasing D2 signal over multiple TPD runs is an effect of cluster isomerization, ensuring that the decreasing population of un-coked Pt4Ge has a fraction with the gateway structure, resulting in additional D2 desorption and coking, and gradually converting all the Pt4Ge to Pt4GeC2.