Chemistry Reference
In-Depth Information
Model Catalysts Based on Au Clusters
and Nanoparticles
Niklas Nilius, Thomas Risse, Shamil Shaikhutdinov, Martin Sterrer,
and Hans-Joachim Freund
Abstract 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 influ-
ence 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.
Keywords Adsorption
Au clusters
Chemical modification
Dopants
Electronic
properties
Oxide films
Wet impregnation
Contents
1
Introduction ..................................................................................
92
2 Binding of Single Metal Atoms and Small Clusters to Oxide Surfaces ...................
93
2.1 General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
93
2.2 Role of Charge Transfer for Binding Single Adatoms to Oxide Thin Films . . . . . . .
95
