Nanostructured metallic systems

In this chapter the potential of nanostructured metal systems in catalysis and the production of fine chemicals has been underlined. The crucial role of particle size in determining the activity and selectivity of the catalytic systems has been pointed out several examples of important reactions have been presented and the reaction conditions also described. Metal Vapor Synthesis has proved to be a powerful tool for the generation of catalytically active microclusters SMA and nanoparticles. SMA are unique homogeneous catalytic precursors and they can be very convenient starting materials for the gentle deposition of catalytically active metal nanoparticles of controlled size. 

Abstract Investigations on nanostructured metallic systems have shown that exceptional... 

Key words nanostructured metallic systems/microstructural stability/structure-property relationships/metallic nanostructures/nanostructured multilayers... 

In Volume 6, various topics related to nanotechnology and nanostructured materials are discussed. The topics include electrochemically self-assembled ordered nanostructured arrays (quantum dots, dashes and wires), mechanical spectroscopy of nanostructured metallic systems, soft amorphous and nanociystalline magnetic materials, nanoporous materials for microlasers and microresonators, nanoporous materials for optical applications, optical properties and impurity states in nanostructured materials, and confined systems and nanostructured materials. 

Chapter 2. Mechanical Spectroscopy of Nanostructured Metallic Systems Luca Pasquini... 

Oxide surfaces, and in particular oxide films, are versatile substrates for the preparation of model catalysts. Quite a few of these systems show nanoscale reconstructions, which can be employed as templates for the growth of ordered model catalysts of reduced complexity. In order to efficiently control the growth of nanostructured metal particle arrays, two conditions have to be met. First, the template must provide sites of high interaction energy that trap the deposited metals. Second, the kinetics of the growth process must be carefully controlled by choosing... 

Quantum chemistry has so far had little impact on the field of photoelectrochemistry. This is largely due to the molecular complexity of the experimental systems, which has prevented reliable computational methods to be used on realistic model systems, although some theoretical approaches to various aspects of the performance of nanostructured metal oxide photoelectrochemical systems have appeared in the last 10 years, see e.g. [139, 140, 141]. Here we have focussed on quantum-chemical cluster and surface calculations of a number of relevant problems including adsorbates and intercalation. These calculations illustrate the emerging possibilities of using quantum chemical calculations to model complicated dye-sensitized photoelectrochemical systems. 

We have studied photocatalytic properties of nanostructured metal-semiconductor composites, made from mesoporous samples of Ti02 and a number of metals (Cu2+, Ni2+, Co2+, Cd2+, Fe2+, Ag+, Zn2+, Pb2+) in hydrogen evolution from water-ethanol solutions. Correlations between the quantum yields of the photoreaction and various parameters of the reacting system (such as the metal nature and concentration, photocatalyst quantity, light intensity, temperature) have been found and discussed. It has been shown, that maximal quantum yield of hydrogen production (y = 0.44) could be achieved in case of Ti02/Cu composite. 

The reversibility is a major characteristic feature of the SMSI effect (300-302). In the case of NM/TiOj, reoxidation at about 773 K, followed by a reduction at low temperature, 473 K, is known to be effective for recovering the catalysts from the SMSI state (300-302,323). Probably by analogy with these earlier studies on titania-supported noble metal systems, similar reoxidation temperatures (773 K) have also been applied to NM/Ce02 catalysts for recovering their chemisorptive and/or catalytic properties from the deactivated state (133,144,221). Data commented below, in which the nanostructural changes of Rh and Pt catalysts in a redox cycle have been followed, prove, nevertheless, that drastic differences are also observed in the reversibility behaviour of ceria based systems, and also that more severe treatments are required to recover this family of catalysts from their corresponding interaction states. 

Schoiswohl J, Sock M, Chen Q, Thornton G, Kresse G, Ramsey MG, et al. (2007). Metal supported oxide nanostructures model systems for advanced catalysis. Top Catal, 46, 137... 

DEVELOPMENT OF NANOSTRUCTURED AND NANOPARTICLE DISPERSION-REINFORCED METALLIC SYSTEMS... 

Development of nanostructured and nanoparticle dispersion-reinforced metallic systems... 

After having exploited the use of reconstructed metal surfaces and vicinal surfaces as templates we will now turn to metal films. Since it has been shown that the nanopatterns of the above mentioned surfaces are in many cases excellent templates for overlayer growth the same can be expected for nanostructured metal films. Indeed a number of such systems have been investigated in terms of their potential use as templates. As the first example we refer to the homoepitaxial growth of Ag on the reconstructed 2 ML thick Ag film on Pt(l 11) (see Fig. 10). Already in 1995 Brune et al. were able to show that further Ag deposition at 100 K on this specific surface leads to the ordered growth of Ag islands [169,170]. Later it was reasoned that the ordering occurs due to the confined nucleation of adatoms within the superstructure cells of the periodic surface dislocation network [171]. The same effect is also present for the deposition of mass select Ag7 clusters [172] and Fe film growth on 2 ML Cu on Pt(l 1 1) [170]. 

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