Reactivity of metal clusters

Reactivity of metal clusters can be studied using spectroscopic techniques. By means of single molecule luminescence spectroscopy, we can observe individual clusters. Photoreactivity of gold clusters synthesized using a photochemical method... 

The difference in reactivity of metal clusters and metal surfaces has also been well illustrated in these iridium-based systems [205]. A lack of reactivity of alkyli-dyne species on Ir4/y-Al203 with H2 is observed meanwhile, the chemisorption of H2 is not hindered. This behavior contrasts with that of metallic surfaces, which allow the reaction between alkylidyne species and H 2. It is inferred that over metallic clusters the reaction of H2 with alkyklidyne is not allowed because of the lack of available adjacent metal sites, which are necessary for the formation of the intermediates [205]. 

Radiation chemical methods have been proven to have a potential to induce and to study the dynamics of nucleation and growth and of the reactivity of metal clusters from the monomer to the stable nanoparticle. 

Another quite different area where ECP s have proven to be very useful for the development of transition metal cluster models. By using a very simplified description of the metal atoms, where all electrons including the d-electrons are considered as core, certain properties of the solid material such as chemisorption on metal surfaces or the reactivity of metal clusters has been studied theoretically with considerable success. 

A. Ship-in-Bottle Synthesis of Metal Clusters in Zeolites and Clay Minerals Structures and Reactivity of Metal Clusters in Zeolites... 

G. Synthesis and reactivity of metal clusters G1. Synthesis of metal cluster complexes G2. Dynamic processes in metal clusters... 

Chemistry and reactivity of metal cluster carbonyl radical anions... 

We have been interested in investigating the size-dependent electronic structure and reactivity of metal clusters deposited on solid substrates. Thus, we have shown that when the cluster size is small (SI nm), an energy gap opens up. Bimetallic clusters show additive effects due to alloying and cluster size in their electronic properties. Small metal clusters of Cu, Ni and Pd show enhanced chemical reactivity with respect to CO and other molecules. Metal clusters and colloids, especially those with protective ligands, have been reviewed in relation to nanomaterials. We have recently developed methods of preparing nanoparticles of various metals as well as nanocrystalline arrays of thiolized nanoparticles of Au, Ag and Pt. In Fig. 16, we show the TEM image of thiol-derivatized Au... 

The chemical hardness of a metallic cluster can be expressed in terms of the ionization potential I and the electron aflinity A. In this paper we analyze the variation of I and A with cluster size, for the case of simple metals. The behavior of I and A shows interesting size effects, which manilcst themselves also in the behavior of the hardness. The chemical reactivity of metal clusters is sensitive to these size effects. 

Understanding the reactivity of metallic clusters is a complicated subject. With regard to the kinetics of reaction, there is a wide variability in reactivity as a function of the nature of the metal as well as cluster size. Some insight into the effect of the geometry and electronic structure on the reactivity can have tremendous impact on such diverse areas as thin film coating and catalysis. In this final Section we only intend to illustrate, with selected examples, how the reactivity indices studied in previous Sections can help us to explain some reactivity trends. 

The next physical quantities of interest are the size dependence of the ionization potential and of the electron affinity because these quantities can be related to the chemical reactivity of metal clusters. Within the DFT jellium model the size dependence of the ionization potential is easily obtained from two total energy calculations ... 

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