During the 1 st TPD from the Pt4/alumina sample, there was substantial C2D4 desorption in the 250 -450 K range, corresponding to ethylene binding to the Pt4 clusters, in addition to a lower temperature feature attributed primarily to weak binding to the alumina support. D2 desorbed in a broad feature extending from 250 K to 750 K, implying that many of the C2D4 molecules dehydrogenated, liberating D2 and depositing carbon. During the 2 nd run there was substantially less C2D4 desorption above 250 K and a general shift to desorption at lower temperatures, implying fewer and weaker C2D4 binding sites. The amount of D2 desorption also decreased, suggesting that dehydrogenation occurs primarily for strongly bound C2D4, but the number of such sites was much smaller in the 2 nd TPD cycle. As additional cycles were carried out, the decrease in C2D4 desorption at high temperatures, and the reduction in D2 desorption continued, with the rate of change slowing as the clusters were mostly deactivated.