Figs. and show that repeated C2D4 TPD runs on Ptn/alumina decreased the numbers of strong (Tdesorption>260 K) Pt-associated C2D4 binding sites and the fraction of adsorbed C2D4 that decomposed, but also increased the number of weak C2D4 binding sites. Ge addition reduced the initial number of strong C2D4 binding sites; however, it also stabilized these sites against the effects of carbon deposition and sintering. One obvious question is whether the effects of carbon or Ge addition are geometric, due to site blocking by C or Ge atoms, or if the main effects are electronic, changing the nature and strength of C2D4-cluster binding. For PtnGem/alumina, another question is whether the high stability simply results from reduced carbon deposition or if Ge also suppress sintering, as seems to be implied by the TPD results.