Synthesis, characterization, and testing of supported Au catalysts prepared from atomically-tailored Au38(SC12H25)24 clusters.

Nearly monodispersed Au(38)(SC(12)H(25))(24) clusters (1.7 ± 0.2 nm) were synthesized using a modified Brust process while utilizing a "thiol etching" approach for the ligand exchange. HRTEM, MALDI, FTIR, and XAS analysis confirmed the formation of the 38-atom clusters in solution. This solution was used to impregnate a microporous TiO(2) support to give 0.7% Au(38)/TiO(2) catalyst. Subsequent drying in air and treatment with H(2)/He at 400 °C removed most of the sulfur ligands, and also increased the Au cluster size to 3.9 ± 0.96 nm. XPS and EXAFS analysis of this supported catalyst showed trace levels of residual sulfides, apparently located at the Au-TiO(2) interface. CO oxidation tests on these supported clusters show an activation energy and range of TOFs comparable to those reported by others. These results suggest that supported Au clusters of controllable size can be prepared with this thiol-ligated solution-based method, providing a new approach to the synthesis of these catalysts.

Size evolution of gold nanoparticles in a millifluidic reactor.

The size evolution of gold nanoparticles in a millifluidic reactor is investigated using spatially resolved transmission electron microscopy (TEM). The experimental data is supported by numerical simulations, carried out to study the residence-time distribution (RTD) of tracers that have the same properties as Au ions. Size and size distribution of the particles within the channels are influenced by the mixing zones as well as the RTD. However, the Au nanoparticles obtained show a broader size distribution even at the shortest investigated residence time of 3.53 s, indicating that in addition to surface growth reaction kinetics also plays an important role. The comparison of time resolved particle growth within the millifluidic channel with flask-based reactions reveals that the particle size can be controlled better within millifluidic channels. Overall, the results indicate potential opportunities to utilize easy to fabricate millifluidic reactors for the synthesis of nanoparticles, as well as as for carrying out time resolved kinetic studies.