Preparation of TiO2-supported Au nanoparticle catalysts from a Au13 cluster precursor: Ligand removal using ozone exposure versus a rapid thermal treatment

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-Å 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±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 nm1.2±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.