Fundamental aspects of catalysis on supported metal clusters

In this review, we examine the role of oxide support defects, cluster size-dependence, cluster structural fluxionality, and impurity doping on the catalytic properties of size-selected metal clusters on surfaces. By combining experimental results from the oxidation of CO on sizeselected gold clusters with ab-initio calculations, a detailed picture emerges of the electronic and structural dynamics of this process. For Au8, Au4, and Au3Sr clusters on F-center defects on MgO(100), optimized atomic structures and local density of states calculations support the experimental results for the oxidation of CO. Fundamental aspects such as charge transfer from oxide defect sites and the adsorption and activation of reactant molecules are elucidated. Using a pulsed molecular beam set up, turnover frequencies for the oxidation of CO and the reduction of NO on Pd clusters were determined. This new experimental scheme allows for the determination of mechanistic details of much greater sophistication than with one-cycle experiments. Isolating known catalytic phenomena such as spillover, reverse spillover, and adlineation should be attainable at the atomic level using these pulsed molecular beam experiments on size-selected metal clusters on surfaces.