Nanoassembled model catalysts

The present review outlines, on the basis of specific examples taken from o ur laboratory, the most important steps in (i) preparing supported nanoasse mbled model catalysts and (ii) investigating their size-dependent catalytic properties. We describe the cluster generation and present evidence for so ftlanding of the clusters onto solid surfaces. Subsequently, the growth and the characterization of the cluster support material, thin magnesium oxide films, are discussed, including the role of surface defects. Then the ther mal stability of Cu clusters and the individual electronic structure of sma ll Ag and Cu clusters on MgO are addressed. Finally, two examples of cluste r size-dependent heterogeneous catalytic reactions are presented, (i) the c yclotrimerization of acetylene on nanoassembled Pd catalysts, and (ii) the CO oxidation on nanoassembled Au catalysts. We show experimentally and toge ther with first-principle calculations that the interaction of such small m etal clusters with the oxide surface strongly changes their catalytic prope rties. In contrast to large particles an additional electron in localized v alence states of small clusters represents a major change. It is this charg e transfer which turns inactive gold and palladium clusters into active mod el catalysts opening new perspectives to tune catalytic processes on the na noscale.