We previously reported detailed DFT studies examining Ptn/alumina (n = 4, 7, 8), including ethylene binding strengths on the thermally accessible cluster isomers and the effects of ethylene binding on cluster structures. For Pt4Ge/alumina and Pt4GeC2/alumina we reported DFT for all thermally accessible isomers of the bare clusters, the binding of one or more ethylene molecules, and the activation energies for dehydrogenation reactions of adsorbed ethane, ethylene, and acetylene. An excited cluster isomer was found to be responsible for the observed self-limiting coking of Pt4Ge, i.e., including the energetically accessible isomer ensemble was critical to understanding the chemistry of the n=4 clusters. Unfortunately, the numbers of potential cluster isomers, of cluster-support binding geometries, and of possible C2H4 or CO adsorption geometries on the clusters all increase rapidly with cluster size, as does the cost per calculation, making such exhaustive studies infeasible for the larger Ptn, PtnGem and PtnGemCn systems. We did a more limited C2H4 and CO binding study for the Pt7-based systems, described below, including only the cluster global minimum (GM) and the two lowest energy local minimum isomers, LM1 and LM2. Even with this limitation, the computational cost was ~4 million CPU hours, and we estimate that the cost for a similar, limited computational study of the Pt11-based systems would exceed 50 million CPU hours. Fortunately, many aspects of the experimental results are quite similar for all three cluster sizes studied, including the observation that coking self-limits at ~2 C atoms/PtnGem cluster for all sizes. The DFT results for the Pt7-and Pt4-based systems also show many similarities, thus, we feel that the insights from the Pt4-and Pt7-based calculations can reasonably be applied to understanding the Pt11-based clusters as well.