Before presenting the results, we briefly review the literature for ethylene adsorption/decomposition on Pt and Pt alloy surfaces to provide context. Ethylene binding and hydrogenation/dehydrogenation reactions on well-defined Pt surfaces have been well studied, and for brevity we focus on just a subset of particularly relevant work. At low temperatures ethylene adsorbs in a di-σ arrangement on Pt(111) and Pt(100) , but forms π-bonds to lower-coordination Pt atoms on surfaces like Pt(210) and Pt(110). For high coverages on Pt(111), desorption of intact ethylene starts at 235 K, but as desorption creates empty sites, the remaining ethylene decomposes, resulting in some ethane desorption at ~285 K, but with most of the decomposition resulting in H2 desorption with carbon deposition. TPD of C2D4 and C2H4 co-adsorbed on Pt(111) yielded mixed species like C2D3H and C2H3D, indicating that recombinative desorption of dissociatively chemisorbed ethylene also contributes to the "intact" ethylene desorption signal. Dehydrogenation proceeds through various intermediates, including ethylidyne (-CCH3), , which undergoes further dehydrogenation to H2 plus adsorbed carbon, going to completion by ~ 700 K. For Pt(210), some π-bound ethylene desorbs intact at ~ 250 K, but most dehydrogenates, ultimately resulting in H2 desorption above ~300 K, again going to completion by ~700 K. For π-bound ethylene on Pt(110)-(1x1), desorption of some methane and H2 was also observed between 270 and 330 K, but most of the carbon deposited, liberating H2 below 700 K. For alumina-supported Pt nanoparticles, ethylene was found to adsorb below 180 K as a combination of π-bound ethylene, di-σ bound ethylene, and ethylidyne. The π-bound ethylene desorbed intact below 300 K, while the di-σ ethylene decomposed at higher temperatures, generating H2 and depositing carbon.