Rh and Ru Nanoparticles

Chaudret s team has developed the use of organometallic complexes as precursors for the synthesis of metal nanoparticles. The main advantage of this organometallic approach is the mild reaction conditions followed, the synthesis being mostly performed at room temperature and under low gas pressure (1-3 bar H2 for example). Ideal precursors are complexes bearing olefins as ligands since 

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Soluble Rh and Ru nanoparticles are commonly used as catalysts in olefin and alkyne hydrogenation reactions. Various catalytic systems are investigated, depending on the metal precursor and the stabilizer. 

Rh and Ru Nanoparticles as Catalysts in Hydrogenation Reactions 361 Table 11.6 Selected results for hydrogenation of various arenes under biphasic conditions. ... 

This chapter gives a nearly exhaustive overview of the performance of Rh and Ru nanoparticles as soluble catalysts. Rh and Ru nanoparticles are mainly used in traditional hydrogenation reactions, in particular in the hydrogenation of carbon-carbon multiple bonds and aromatic compounds, but a few examples of other substrates containing carbonyl groups or other reducible functions such as the nitro group are also reported. Finally, in the main fields of homogeneous... 

Recently five monometallic (Au, Pd, Pt, Ru, Rh) nanoparticles were investigated as electron mediators together with four core/shell bimetallic (Au/Pd, Au/Pt, Au/Rh, Pt/ Ru) nanoparticles [53,194-196]. The linear relationship was observed between the electron transfer rate coefficients and the hydrogen generation rate coefficient as shown in Figure 15. 

PAMAM dendrimer-templated synthesis of metal nanoparticles has been demonstrated for many metals, such as Cu, Pt, Pd, Au, Rh, and Ru [42]. Most of the syntheses were carried out in aqueous solution at an appropriate pH. For amine-terminated PAMAM dendrimers, the pH of the solution needs to be adjusted to 3 to protonate the terminal amine groups and prevent dendrimer cross-linking [61, 62]. Metal ions cannot bind to protonated amine groups instead, they bind to the tertiary amines inside the PAMAM dendrimer. 

In 1999, Albach and Jautelat described in a patent the use of a sulfobetaine as the surfactant to stabilize Ru, Rh, Pd, Ni nanoparticles and bimetalUc mixtures [77]. Benzene, cumene and isopropylbenzene are reduced in biphasic media under various conditions 100-150 °C and 60 bar of H2. 250 TTO are... 

These were prepared by tethering Rh and Pt complexes to silica-supported metal catalysts (metal = Pd, Ni, Ru, Au). The catalysts are very active in the hydrogenation of benzene derivatives to the corresponding substituted cyclohexanes under mild conditions. The activities are higher than those of the separate homogeneous complexes, complexes just tethered to silica, or the silica-supported heterogeneous catalysts. When the sol-gel-entrapped [Rh2Co2(CO)12] complex was heat-treated at 100°C, immobilized metallic nanoparticles were formed.425 The catalyst thus prepared efficiently catalyzed substituted benzene derivatives. 

The best known heterogeneous catalysts are oxide-supported Ru, Rh, and Ni, and Ru exhibits the highest selectivity. Marked support effects are observed and Ti02 is usually found to be the best support material. Pd on zirconia and Ni on zirconia are particularly effective catalysts when prepared using amorphous Pd-Zr, Ni-Zr, and Ni-containing multicomponent alloys by controlled oxidation-reduction treatment240-242 or generated under reaction conditions.243-245 Stabilized metal nanoparticles of uniform dispersion embedded into the oxide matrix are the... 

Ceria/noble metal (such as Ru, Rh, and Pd) catalysts are composed of noble metal species such as nanoparticles and clusters dispersed on the ceria supports. The catalysts show typical strong metal-support interactions (SMSI) (Bernal et al., 1999), that is, the catalysts exhibit a number of features for SMSI effects including (1) reducible supports (2) "high temperature" reduction treatments (3) heavily disturbed chemical properties and significant changes in catalytic behavior of the dispersed metal phase (4) reversible for recovering the conventional behavior of the supported metal phase. In these cases, the reducibility of ceria NPs is greatly enhanced by the noble metal species and the catalytic activities of the noble metals are enhanced by ceria NPs. 

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