S9 and S10), and then the barriers for C-H dissociation calculated. We again found that the barriers to ethane C-H activation were generally lower than the desorption energies for ethane from the cluster, suggesting that the Pt4GeC2 cluster should still be highly active for ethane to ethylene dehydrogenation. To be stable with respect to further carbon deposition, it is necessary that the resulting ethylene desorb instead of dehydrogenating further. For ethylene on Pt4GeC2/alumina (Figs. and), some configurations were calculated to have highly endothermic (>1.2 eV) dehydrogenation, and in others, the activation barriers were high (>2 eV). Some structures showed the possibility for dehydrogenation of ethylene, with barriers between 1.3-1.5 eV to access structures that are not highly endothermic, however, we note that these barriers are higher than those for the dehydrogenation of ethylene on the Pt4Ge cluster, indicating that the Pt4GeC2 cluster is even more selective than the initial Pt4Ge catalyst. Acetylene dehydrogenation by Pt4GeC2 (Fig 6D ) either retains very high barriers (>2 eV), or has such low barriers for the reverse reaction of re-hydrogenation that dehydrogenation remains unlikely. We note that there is only one thermally accessible acetylene binding mode (Fig 6D, left-most inset), which involves the binding of acetylene to two Pt atoms, in a mixed π-/σ-fashion, as well as binding to a C in the C2 unit. This collapse of accessible modes is reminiscent of that of Pt4Ge to Pt4GeC2, which is likewise likely attributable to the formation of multiple Pt-C bonds, as well as an additional C-C bond. It is therefore possible that the cluster cokes further, albeit at an even slower rate once coke has begun to form, based on the heights of C-H activation barriers for ethylene and acetylene on the Pt4GeC2 cluster.