Solvated metal atom dispersion SMAD

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. 

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

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

Figure 5 shows high-resolution electron microscope images of several gold nanoparticles formed by this metal vapor synthesis method, often called Solvated Metal Atom Dispersion (SMAD). 

In solvated metal atom dispersion (SMAD) method solvated atoms prepared at very low-temperature are used as transient, highly reactive organometallic reagent for the deposition of Sn-Pt bimetallic particles onto different supports. In another approach chemical vapor deposition (CVD) using tin organometallic compounds was applied. For example, the selective reaction of Sn(CH3)4 vapour with Pt nanoparticles supported on Si02 appears to be very promising preparation method. 

In order to discriminate between the activity of the different gold species on ceria, our group prepared ceria-supported gold catalysts by classical deposition-precipitation (DP) followed by drying at 393 K, and by the solvated metal atom dispersion (SMAD) technique... 

Because they have low vapor pressures, transition metals cannot be loaded by direct adsorption, but their adsorption can be mediated by transient organo-metallic complexes formed between zerovalent metal atoms and solvent molecules. This is the basis of the solvated metal atom dispersion (SMAD) method developed by Klabunde and Tanaka [72]. Metal vapors condensed in Hquid hydrocarbons at low temperatures form weak complexes that are easily decomposed even below room temperature. Microporous supports impregnated with solutions of metal complexes at low temperatures are warmed up to decompose the complex and liberate zerovalent metal atoms which nucleate into clusters. Preparation of Ni- and Co-clusters in HY and HZSM-5 was reported [72]. In the same way, Nazar et al. [64] condensed iron and cobalt vapors in a slurry of dehydrated NaY zeolite in toluene at -120 °C, then the mixture was rotated at-78°C. The bis-toluene complex thus formed and adsorbed in the zeoUte was decomposed by warming to room temperature yielding clusters small enough to fit into supercages. 

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

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.)...

---