The
structure sensitivity of gold-catalyzed CO oxidation is presented
by analyzing in detail the dependence of CO oxidation rate on particle
size. Clusters with less than 14 gold atoms adopt a planar structure,
whereas larger ones adopt a three-dimensional structure. The CO and
O2 adsorption properties depend strongly on particle structure
and size. All of the reaction barriers relevant to CO oxidation display
linear scaling relationships with CO and O2 binding strengths
as main reactivity descriptors. Planar and three-dimensional gold
clusters exhibit different linear scaling relationship due to different
surface topologies and different coordination numbers of the surface
atoms. On the basis of these linear scaling relationships, first-principles
microkinetics simulations were conducted to determine CO oxidation
rates and possible rate-determining step of Au particles. Planar Au9 and three-dimensional Au79 clusters present the
highest CO oxidation rates for planar and three-dimensional clusters,
respectively. The planar Au9 cluster is much more active
than the optimum Au79 cluster. A common feature of optimum
CO oxidation performance is the intermediate binding strengths of
CO and O2, resulting in intermediate coverages of CO, O2, and O. Both these optimum particles present lower performance
than maximum Sabatier performance, indicating that there is sufficient
room for improvement of gold catalysts for CO oxidation.