Synthesis of a sinter-resistant, mixed-oxide support for Au nanoclusters

Following the discovery that small gold clusters highly dispersed on metal oxide supports are active catalysts at low temperature for a variety of reactions, a number of studies have been carried out to determine the structure of the clusters and the mechanism leading to their activity. A major deterrent to the use of these catalysts, however, is that under reaction temperatures and pressures, the clusters tend to sinter, or agglomerate, leading to a dramatic decrease in activity. In an attempt to make these highly active Au catalysts more stable, mixed-oxide supports have been developed by substituting Ti atoms for Si in a silica thin film network. Depending on the amount of Ti deposited, the TiO ₂-SiO ₂ surface consists of substituted Ti atoms and/or TiO _x islands. With deposition of Au onto these TiO ₂-SiO ₂ surfaces (at low and high Ti coverages), the substituted Ti and/or TiO _x islands act as Au cluster nucleation sites, leading to a marked increase in the cluster number density compared to the Ti-free SiO ₂ surface. Furthermore, upon exposure of Au clusters nucleated on surfaces with TiO _x islands to reaction temperatures and pressures, the clusters do not sinter. These results demonstrate that it is possible to produce a supported Au catalyst where metal agglomeration is significantly inhibited, allowing the unique properties of Au nanoclusters to be fully exploited.