Bonding supported metal nanoclusters

The importance of supported metal nanoclusters and nanoparticles in catalysis and the rough analogy between supported nanoclusters and organo-metallic cluster compounds (those with metal-metal bonds) in catalysis have motivated researchers to find connections between these two classes of materials. Thus, an obvious synthetic goal has been size-selected metal nanoclusters on supports. 

There is good agreement between EXAFS data and theoretical results characterizing structure and bonding in supported metal nanoclusters and the metal-support interface. 

The methods of structure determination of supported nanoclusters are essentially the same as those mentioned previously for supported metal complexes. EXAFS spectroscopy plays a more dominant role for the metal clusters than for the complexes because it provides good evidence of metal-metal bonds. Combined with density functional theory, EXAFS spectroscopy has provided much of the structural foundation for investigation of supported metal clusters. EXAFS spectroscopy provides accurate determinations of metal-metal distances ( 1-2%), but it gives only average structural information and relatively imprecise values of coordination numbers. EXAFS spectroscopy provides structure data that are most precise when the clusters are extremely small (containing about six or fewer atoms) and nearly uniform (Alexeev and Gates, 2000). 

Summary on Sn-Ru/AkO Catalysts. - In the last decade supported tin-ruthenium catalysts have been extensively studied because of their activity and high selectivity in the hydrogenation of unsaturated aldehydes, esters or acids into the corresponding alcohols. The increased performance of metal catalysts with the addition of promoters such as tin is attributed to the presence of promoter-cations on the surface or at the periphery of metal nanocluster, which activate the C=0 bond through the interaction with the lone electron pair of the carbonyl group oxygen. 

Ricci D, Bongiorno A, Pacchioni G, Landman U. Bonding trends and dimensionality crossover of gold nanoclusters on metal-supported MgO thin films. Phys Rev Lett. 2006 97 036106. 

---