Nanoparticles Catalytic agents

An example of a possible system for photocatalytic water decomposition is shown in Fig. 6. The photocatalyst in Fig. 6 is a CdS nanoparticle, which is located, e.g., in the inner aqueous phase. A sacrificial electron, donor (D) is also located in the inner phase. In the presence of a suitable water oxidation catalyst, the role of the donor could be served by the molecules of water. The molecular carriers of electrons (C in the figure) are built into the lipid membrane by the principle of a cascade, providing a certain gradient of redox potentials. In the outer aqueous phase, an electron acceptor and a catalytic agent of water reduction to hydrogen are placed. Thus, at light quantum absorption by the semiconductor PhC, the charge separation derives an electron hole which passes to the catalyst of... 

When Au-NP labels are present near an electrode they can act as (electro)catalytic agents. However if the electrocatal3Aic reaction is not reproducible, which jeopardizes the achievement of low detection limits, the electrocatal3Aic reaction should be minimized and the electrochemical signal should arise only from the catalytic reaction [7]. The latest can be done by limiting the electron transfer between nanoparticles and the electrode through the use of nonconductive spacers like other particles, organic monolayers, etc. [11,27,28]. 

The durability of the catalytic system was investigated by employing it in five successive hydrogenations. Similar TOFs were observed due to the water solubihty of the protective agent which retains nanoparticles in aqueous phase. The comparative TEM studies show that (i) the average particle size was 2.2 0.2 nm (ii) the coimter anion of the surfactant does not allow a major influence on the size and (iii) nanoparticle suspensions have a similar size distribution after catalysis. 

Finally, Jessop and coworkers describe an organometalhc approach to prepare in situ rhodium nanoparticles [78]. The stabilizing agent is the surfactant tetrabutylammonium hydrogen sulfate. The hydrogenation of anisole, phenol, p-xylene and ethylbenzoate is performed under biphasic aqueous/supercritical ethane medium at 36 °C and 10 bar H2. The catalytic system is poorly characterized. The authors report the influence of the solubility of the substrates on the catalytic activity, p-xylene was selectively converted to czs-l,4-dimethylcyclohexane (53% versus 26% trans) and 100 TTO are obtained in 62 h for the complete hydrogenation of phenol, which is very soluble in water. 

There are different ways in which the nanoparticles prepared by ME-technique can be used in catalysis. The use of ME per se [16,17] implies the addition of extra components to the catalytic reaction mixture (hydrocarbon, water, surfactant, excess of a metal reducing agent). This leads to a considerable increase of the reaction volume, and a catal5fiic reaction may be affected by the presence of ME via the medium and solubilization effects. The complex composition of ME does not allow performing solvent-free reactions. 

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