Sintering, the growth of large particles at the expense of smaller ones, is one of the main causes of catalysts deactivation, since the physicochemical properties of a nanoparticle may depend strongly on its size, shape and composition. For application as heterogeneous catalysts, the nanoparticle kinks and edges often play an important role for the catalytic activity. In order to preserve these sites, it is important to stabilize the supported nanoparticles with sizes of a few nanometers during operational conditions at often high temperatures and in the relevant gas environments. A prototypical nanocatalyst system for studying coarsening consists of Pt nanoparticles supported on an Al2O3 material which is relevant as an oxidation catalyst in diesel and lean-burn engine exhaust after-treatment technologies. In this study we address the effect on sintering of the shape of Pt nanoparticles supported on planar, amorphous Al2O3. Characterization of the size and shape of the Pt nanoparticles has been done by combining transmission electron microscopy (TEM) and non-contact atomic force microscopy (NC-AFM), because of the great complementarity between these techniques. TEM measurements very accurately give the nanoparticle diameters while AFM measurements give the height. It is suggested that the Al2O3-supported nanoparticles adopt size-dependent 3D geometrical shapes after thermal aging and additionally, it is suggested, that the height-diameter ratio exhibits a surprising decrease with the nanoparticle size. This size-dependence of the shape may influence the ripening process in several ways.
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14th International Conference on non-contact Atomic Force Microscopy, 2011