These studies suggest several points that may also apply to sub-nano Ptn on alumina. Because the TPD experiments below all started with the samples saturated with ethylene, the bulk Pt TPD behavior suggests that we might expect the initial desorption to be dominated by intact ethylene, but that as desorption creates empty sites, the remaining molecules should tend to decompose, with hydrogen desorbing and carbon depositing. Furthermore, our previous DFT work for C2Hx bound to Ptn/alumina showed that C-C bond scission occurred only after dehydrogenation with hydrogen loss, resulting in bound acetylene, which further decomposed yielding 2 C, with the hydrogen desorbing. In addition, the previous studies suggest a correlation between ethylene bonding configuration (di-σ vs. π) and its reactivity. Ethylene in π-bonded, sp 2 configurations tended to desorb intact (or hydrogenate if H2 was co-adsorbed), while di-σ bonded, sp 3 ethylene tended to decompose, depositing carbon and liberating hydrogen. For our system, no hydrogen was added and no hydrogenation products were observed, thus the correlation would be decomposition from di-σ bonded ethylene, v.s. intact desorption of π-bonded ethylene.