The binding and reactivity properties of Ptn/alumina (n = 4, 7, 11) model catalysts were studied by ethylene temperature-programmed desorption (TPD), using C2D4 to avoid high background for the hydrogen-desorption channel. Select experiments with C2H4 were used to show that there was no significant acetylene desorption. As noted above, new experiments for Ptn/alumina (n = 4, 7) were done so that Fig. and the tables summarizing the analysis could be based on data taken under conditions identical to those used for Pt11 and for the PtnGem clusters discussed below. The dotted curves show the desorption observed in the 1 st TPD run for a Pt-free alumina sample.