Synthesis of a sinter-resistant, mixed-oxide support for an 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 TiO2-SiO2 surface consists of substituted Ti atoms and/or TiOx islands. With deposition of Au onto these TiO2-SiO2 surfaces (at low and high Ti coverages), the substituted Ti and/or TiOx islands act as Au cluster nucleation sites, leading to a marked increase in the cluster number density compared to the Ti-free SiO2 surface. Furthermore, upon exposure of Au clusters nucleated on surfaces with TiOx 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.