METHANE ACTIVATION ON UNSUPPORTED PLATINUM CLUSTERS

We report the first observation of size-selective methane activation by unsupported platinum clusters. Platinum dimer through pentamer are the most reactive. The other small clusters, Pt6-24, are less reactive. A factor of 4 drop in reactivity occurs in going from Pt5to Pt6. The dominant products observed are of the form PtnC1.2HyAs the clusters increase in sizsse, the number of hydrogens retained also increases. The reactivity tends to decrease with increasing cluster size, in contrast to the trends observed for dihydrogen chemisorption on several transition metals. A mild correlation is found between reactivity and the ability of certain size clusters to form compact structures and the number of ≤ 3-coordinated surface atoms in close-packed structures found to be most stable from theoretical calculations. These results suggest that, as in organometallic chemistry, coordinative unsaturation is critical for methane activation by naked metal clusters. © 1990, American Chemical Society. All rights reserved.