For comparison, the figure also shows the desorption signals observed from the alumina and Ge-treated alumina (Ge/alumina) supports with no Pt/PtGe clusters. For both supports, C2D4 corresponding to a few percent of a monolayer adsorbed during the 150 K dose, desorbing below 250 K when heated. This support-bound C2D4 might be bound at defects in the alumina film, for example. No D2 desorption was observed, showing that neither the alumina nor Ge/alumina supports were active for ethylene dehydrogenation, and as might be expected, the desorption signals in repeated runs were unchanged.