Solvated metal atom

In both cases, the Au nanoparticles behave as molecular crystals in respect that they can be dissolved, precipitated, and redispersed in solvents without change in properties. The first method is based on a reduction process carried out in an inverse micelle system. The second synthetic route involves vaporization of a metal under vacuum and co-deposition of the atoms with the vapors of a solvent on the walls of a reactor cooled to liquid nitrogen temperature (77 K). Nucleation and growth of the nanoparticles take place during the warm-up stage. This procedure is known as the solvated metal atom dispersion (SMAD) method. 

After co-deposition the frozen matrix is allowed to melt (Scheme 1(B)). This generates solvent-stabilized metal microclusters (Solvated Metal Atoms, SMA), which are soluble in the excess of ligand and can be recovered and handled at low temperature (—50 to -30 °C) under an inert... 

Solvated Metal Atoms as Homogeneous Catalytic Precursors... 

Table 1. Catalytic reactions promoted by solvated metal atom solutions.

Hydrofromylation of 1,3-Dienes with Rhodium-Solvated Metal Atoms Catalyst A... 

Living Colloidal Metal Particles from Solvated Metal Atoms Clustering of Metal Atoms in Organic Media... 

A review of preparative methods for metal sols (colloidal metal particles) suspended in solution is given. The problems involved with the preparation and stabilization of non-aqueous metal colloidal particles are noted. A new method is described for preparing non-aqueous metal sols based on the clustering of solvated metal atoms (from metal vaporization) in cold organic solvents. Gold-acetone colloidal solutions are discussed in detail, especially their preparation, control of particle size (2-9 nm), electrophoresis measurements, electron microscopy, GC-MS, resistivity, and related studies. Particle stabilization involves both electrostatic and steric mechanisms and these are discussed in comparison with aqueous systems. 

Solvated metal atoms can be dispersed in excess organic solvent at low temperature and used as a source of metal particles for the preparation of both unsupported metal powders and supported metal catalysts158,161. Alternatively, metal vapor is condensed into a cold solution of a stabilizing polymer to form crystallites of the order 2-5 nm in diameters159. Equation 17 illustrates the unique activity of a colloidal Pd catalyst in the partial hydrogenation of acenaphthene. 

Solvated Metal Atom Dispersed (SMAD) Bimetallic Catalysts... 

Platinum—Tin and Gold—Tin Bimetallic Particles Prepared from Solvated Metal Atoms... 

Solvated metal atom dispersion or impregnation (SMAD or SMAI)... 

This method of preparation of supported metal catalyst requires a closed reactor to perform the preparation in the absence of water, so both the organic solvent and the oxide support must be carefully dehydrated. The method is based on the following principle the metal is evaporated and co-condensed with the organic to 77 K on the walls of the reactor. Under dynamic vacuum, the co-condensate is then warmed up to 195 K, and melted. The oxide support is impregnated with the solvated metal atom (cluster) at the same temperature, After a given time of contact, the slurry is warmed up to ambient temperature, and the solvent is eliminated, after which the sample can be dried. 

SOLVATED METAL ATOM DISPERSION (SMAD) METHOD FOR THE PREPARATION OF NANOPARTICLES... 

Fig. 9.1. Apparatus used for the preparation of nanoparticles by the Solvated Metal Atom Dispersion Method (SMAD). (Reprinted with permission from Klabunde, K. J Acc. Chem. Res., 1975, Fig.1, copyright (1975) American Chemical Society.)...

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