| dc.description.abstract | Conventional nanocatalysts have a nonuniform particle size distribution, while catalytic activity of nanoparticles is size dependent. This is also the case for gold as the intrinsic chemical properties of very small gold particles (called Au clusters) are strongly dependent on its size and composition. It is, however, unknown how the catalytic activity evolves in this nanosized regime. Sintering of these clusters could be prevented by using a suitable support material and without calcination at high temperatures. In this research, the activity and stability of various Au nanoclusters are investigated. In order to do this, CeO2 rods, cubes and polyhedra are synthesised as support material exhibiting ({110} and {111}), {100} and ({100} and {111}) exposed surface planes respectively because these tend to have different stabilising properties. After deposition of Au9 clusters on each CeO2 material and heat treatment, the rods and cubes showed least nanoparticle formation. Hereafter, Au8, Au6Pd are deposited and Au nanoparticles were grown on CeO2 rods because this material seemed to prevent sintering. These catalysts were subsequently tested in the gas phase oxidation of ethanol using O2. The Au nanoparticles showed the highest activity, but its higher selectivity towards CO2 also resulted in possible polycarbonate species bound to the CeO2 surface which lead to deactivation. Furthermore, a decrease of cluster size by only one atom (Au9 Au8) resulted in a decrease in oxidation activity, while a bimetallic cluster (Au6Pd) did not show a much higher activity contrary to previous believes. Next to this, Au9 clusters deposited on SiO2 are treated with BCl3 to chemically remove its protecting ligands. This resulted in growth of the Au nanoparticle size and Au leaching. This makes BCl3 treatment an unsuitable method for chemical ligand removal to investigate the properties of various Au clusters on inert supports. | |
