Catalytic relay, metal cluster

Figure 14 Mechanism of catalytic electron transfer involving metal clusters as relay. The thermodynamic conditions to be fulfilled are that the cluster redox potential be higher than the donor D and lower than the acceptor A potential, which implies that the cluster itself is a size range that offers the efficient redox potential. (From Ref. 63.)...

Important consequences result from the increase of the redox potential of metal clusters with their nuclearity. Indeed, independently of the metal, the smaller clusters are more sensitive to oxidation and can undergo corrosion even by mild oxidizing agents. Moreover, size-dependent redox properties explain the catalytic efficiency of colloidal particles during electron transfer processes. Their redox potentials control their role as electron relays the required potential being intermediate between the thresholds of the potentials of the donor (more negative) and of the acceptor (more positive). Catalytic properties of the nanoparticles are thus size-dependent. Haruta and co-workers reported that gold nanoparticles smaller than 5 nm have potential applications in catalysis as they are very active in... 

Figure 9 Scheme ofthe mechanism ofa catalytic electron transfer Involving metal clusters as a relay. The... 

One of the important applications of mono- and multimetallic clusters is to be used as catalysts [186]. Their catalytic properties depend on the nature of metal atoms accessible to the reactants at the surface. The possible control through the radiolytic synthesis of the alloying of various metals, all present at the surface, is therefore particularly important for the catalysis of multistep reactions. The role of the size is twofold. It governs the kinetics by the number of active sites, which increase with the specific area. However, the most crucial role is played by the cluster potential, which depends on the nuclearity and controls the thermodynamics, possibly with a threshold. For example, in the catalysis of electron transfer (Fig. 14), the cluster is able to efficiently relay electrons from a donor to an acceptor, provided the potential value is intermediate between those of the reactants [49]. Below or above these two thresholds, the transfer to or from the cluster, respectively, is thermodynamically inhibited and the cluster is unable to act as a relay. The optimum range is adjustable by the size [63]. 

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