Chemical and Catalytic Properties of Size-Selected Free and Supported Clusters

Clusters reveal unique physical and chemical properties as their dimensions are reduced to the nanoscale. Their properties are not scalable from those of bulk materials. Clusters are thus building blocks for nanocatalytic materials. Since the early days of cluster science, it has been speculated about strong size-dependent catalytic activity of metal clusters just a few or few tens of atoms in size. It was proposed that tuning reactivity and selectivity is feasible by simply changing cluster size [1] because intrinsic cluster properties relevant for catalytic behavior, like the electronic spectrum, the symmetry, or the spin multiplicities, can thus be tuned for obtaining the desired activation of the reactant molecules relevant in a catalytic process. It has been possible only in recent years, through the development of new experimental schemes, to show that model catalysts made of such small clusters indeed reveal variations in the catalytic activity when cluster size is changed just by a single atom.