Model Catalysts Based on Au Clusters and Nanoparticles

Small Au particles have been shown to exhibit interesting catalytic properties. In an attempt to parallel catalytic studies on powder supports we have undertaken a series of model studies using oxide films as support. We address the formation of Au aggregates as a function of size starting from Au atoms to clusters and islands of larger size and as a function of the support. In addition we have studied different support materials such as alumina and iron oxide and we compare ultrathin and thicker oxide films of the same material (MgO). From a comparison of charge transfer through ultrathin films with the situation encountered in thicker films, we propose the use of dopants in bulk materials to control particle shape.We include the study of carbon monoxide adsorption on Au clusters of varying size. It is demonstrated how chemical modification (hydroxylation) of oxide supports influence particle growth and properties. Finally, we report on effects to study the processes involved in particle growth by wet impregnation in order to bridge the gap to catalyst preparation under realistic conditions. On that basis one may now compare properties of supported particles prepared in ultrahigh vacuum using physical vapor deposition with those prepared by wet impregnation