This value corresponds to the Pt-free alumina peak observed below 250 K in the experimental data. For all the stable binding modes of all three clusters, ethylene is found to bind only to Pt atoms, consistent with the interpretation of the TD-ISS results in Fig. electronic energies relative to the GM for Pt7-ethylene (ΔE) and the ethylene binding energies (ΔEC2H4) in each structure. We note that the binding energies are electronic, rather than free energies, and therefore cannot be directly compared to the energetics estimated from TPD. However, the entropic corrections for different clusters/isomers should be similar, thus the trends of binding vs. cluster composition should be reliable.