Well-defined platinum-based catalysts were prepared using fourth-generation hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers as templates. Nanoparticles with an average of 40 Pt atoms and an average diameter of 1.5 nm were produced this way, and dispersed on a homemade sol-gel silica support. Different treatments were tested for the activation of the resulting catalyst, including heating in vacuum or in oxygen or hydrogen atmospheres. A combination of electron microscopy, infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and catalytic kinetic measurements were used to investigate the effect of those treatments on the decomposition and elimination of the material associated with the dendrimer and on the activity and selectivity of the resulting catalysts. Neither heating in vacuum nor burning with oxygen was deemed acceptable, because much graphitic material is deposited with the former treatment and metal oxidation is induced by the latter. Hydrogen pretreatments, on the other hand, lead to fairly active catalysts with high selectivity for the conversion of trans olefins to their cis counterparts. (C) 2010 Elsevier B.V. All rights reserved.