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The structure of Au heterogeneous catalysts on the anatase form of TiO2 has been characterized by high-resolution electron microscopy (HREM) and quantitative Z-contrast scanning transmission electron microscopy (STEM). These materials are prepared by deposition of highly monodisperse Au13[PPh3]4[S(CH2)11CH3]4 (8-A diameter) ligand-protected clusters on anatase, followed by reaction with ozone or a rapid oxidative thermal treatment to remove the ligands. The materials obtained differ markedly in each case. For the thermal treatment at 400 °C in air, the supported particles grow to an average size of 2.7 nm ( ± 0.6 nm ) in diameter, and the larger particles in the distribution are found to adopt a spherical geometry. Particle growth is greatly inhibited when ozone is used to remove the ligands (average diameter 1.2 ± 0.5 nm ). These particles assume a more oblate geometry, consistent with a truncated hemispherical shape. It was found that subsequent thermal treatments of the ozone-derived supported nanoparticles at 400 °C in air did not induce additional growth, indicating that sintering is strongly affected by the particle–support interactions developed by the ozone-based low-temperature ligand removal step. These materials exhibit catalytic activity and high stability for the oxidation of CO at elevated temperatures, with the level of activity dependent on catalyst preparation. |
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