Alloyed cluster development

One of the important applications of metal clusters is to be used as catalysts. The cluster potential and its dependence on the nuclearity or adsorbed molecules play a crucial role in the catalysis of electron transfer. The cluster is able to relay efficiently electrons from a donor to an acceptor, provided the potential value is intermediate between those of the reactants. This optimum range is adjustable by the size.  

concerning the electron transfer from radiation-induced free radicals such as COj or (CH3)2C OH to a substrate, after the complete reduction of the metal ions, has been demonstrated. Electrons donated from the radicals are first stored on clusters as charge pools and then are transferred again for example pairwise to water producing molecular hydrogen  

Pulse radiolysis allows one to observe directly some catalytic electron transfer reactions other than the autocatalytic growth (reactions (25-27). Indeed the clusters are so small that they may be considered as diffusing molecular systems. The electron transfer from MV to protons in water requires the presence of a catalyst, for example radiolytically formed gold or platinum clusters  

For a given metal amount, the transfer rate increases linearly with the particle concentration. The initial electron transfer step (41) between one MV radical and one Pt cluster of n = 35-50 atoms is diffusion controlled and the rate determining step of the process is clearly, as on Au , the desorption step after the intra- or inter-particle formation (43) of the molecular hydrogen. 

The catalytic role of the metal clusters may be explained again by their influence on the reaction thermodynamics. Actually, the direct electron transfer from MV (E°(MV /MV ) = - 0.41 Vn e) to H3O (E°(H30 /H) = -2.3 Vnhe) is thermodynamically unfavored if they are both in solution, and in contrast the reverse reaction from H to MV is fast. However, the redox potential of HjO /H when adsorbed on a nanometric cluster E°(H30, Pt /H, Pt ) is shifted to values higher than that of E°(MV /MV ) and the transfer (39-41) becomes possible. The evolution of molecular hydrogen catalyzed by clusters from radicals such as COz or (CH3)2COH which are also in solution less strong reducing agents than H radicals may be similarly explained. 

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Very important in current and prospective electrochemical technology are dispersed electrocatalysts on high-area supports. Opportunities exist for developing new catalysts, such as alloy clusters, improved dispersion techniques, superior supports (especially among the oxides, carbides, and nitrides), and new binding polymers for composite electrodes. 

The synthesis of different doped carbon nanotubes has been achieved using the Dopant Encapsulation method we developed. This method was used to dope the tubes not only with metals, but also with alloyed clusters of different metals. The Dopant Encapsulation method was utilized to produce large quantities of metal doped carbon nanotubes of consistent structure (see Figures 1 and... 

Special processes of diffusion transfer in silver photographic emulsions require diffusion of silver ions of the positive image and their catalytic reduction around added development centers such as metal clusters, small enough to ensure a high resolution and no loss of transparency. Added y-induced silver clusters have a strong efficiency. However, alloyed clusters of Au-Cu and Ni-Pt and mostly of Ag-Au, Ag-Cu, and Ag-Cu-Pd, prepared under... 

The atom-exchange method was developed by Tsai, Abraham, and Pound to speed barrier crossing in binary (two types of atoms) alloy cluster simulations. During the Metropolis walk two different types of atoms are periodically chosen, and their positions are exchanged. The exchange is accepted or rejected by the standard Metropolis acceptance probability. The utility of this method is naturally limited to systems of this particular type, namely, binary atomic clusters and liquids. 

We have developed a theory that allows to determine the effective cluster interactions for surfaces of disordered alloys. It is based on the selfconsistent electronic structure of surfaces and includes the charge redistribution at the metal/vacuum interface. It can yield effective cluster interactions for any concentration profile and permits to determine the surface concentration profile from first principles in a selfconsistent manner, by... 

Cryophotochemical techniques have been developed that (i) allow a controlled synthetic approach to mini-metal clusters 112), Hi) have the potential for "tailor-making small, bimetallic clusters (mini-alloy surfaces) 114,116), Hi) permit the determination of relative extinction-coefficients for naked-metal clusters 149), and iv) allow naked-cluster, cryophotochemical experiments to be conducted in the range of just a few atoms or so 112,150,151). 

The development of the synthesis concept described here for metalloid clusters should ultimately be capable of extension to element combinations and therefore molecular nanostructured alloys, as several results on metalloid SiAl and SiGa clusters have shown [114, 88, respectively]. Such mixed clusters resemble the Zintl-type compounds that are under intense investigation by Corbett et al. [115, 124-126],... 

Physical properties and detection of liquid Zintl compounds have been discussed and problems of gradual development of stoichiometries in non-clustering liquid ionic alloys, and their agreement with those persisting in the solid, have been considered. Neutron diffraction techniques and the results of their applications (Ga, Tl, alkali alloys) have been described. 

Abstract This review highlights how molecular Zintl compounds can be used to create new materials with a variety of novel opto-electronic and gas absorption properties. The generality of the synthetic approach described in this chapter on coupling various group-IV Zintl clusters provides an important tool for the design of new kinds of periodically ordered mesoporous semiconductors with tunable chemical and physical properties. We illustrate the potential of Zintl compounds to produce highly porous non-oxidic semiconductors, and we also cover the recent advances in the development of mesoporous elemental-based, metal-chalcogenide, and binary intermetallic alloy materials. The principles behind this approach and some perspectives for application of the derived materials are discussed. 

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