Platinum particles, approximately 1.6 nm in size, were formed on gamma-Al2O3 following impregnation with a Pt-40-dendrimer precursor solution. These Pt particles are not catalytically active, since they are covered by the dendrimer component. Treatment in O-2 plasma at room temperature removes the dendrimer without affecting metal dispersion. Subsequent treatment in H-2 at 300 degrees C leads to partial aggregation of Pt, although the degree of such aggregation is relatively small, as the average size of the Pt particles remains approximately 2 nm. In contrast, when a high temperature oxidation/reduction treatment is used to activate the Pt-40-dendrimer/gamma-Al2O3 material, sintering of Pt is observed and the average Pt particle size increases to approximately 4 nm. Kinetic data obtained with Pt/gamma-Al2O3 catalysts activated under both protocols for the structure-insensitive CO oxidation and the structure-sensitive ethane hydrogenolysis reactions underline the differences in the sizes of the Pt particles in these materials, consistent with previous literature reports. (c) 2012 Elsevier Inc. All rights reserved.