Nanoparticles facetted

Nanoparticle-faceted terraces, comers, and edges presence (a) Third-body effect... 

Fig. 11 Formation of crystalline 3D super-lattices of tin nanoparticles a TEM view of a facetted super-crystal b SEM image showing particles included into a super-crystal as well as the organic surrounding c High resolution micrograph showing the alignment of the tin atomic planes inside the super-structure...

The synthesis of Pt nanocrystals with controlled morphology must have interesting applications in practice, since the catalytic activity for structure-sensitive reactions depends on the orientation of the crystalline facets. Using the obtained morphologically controlled Pt nanoparticles, Pt/Al203 catalysts were prepared and applied for a structure-sensitive reaction, i.e., NO reduction by CH4. 

By using thermosensitive poly-acrylamides, it is possible to prepare cubic Pt nanocrystals (with predominant (1 0 0) facets) and tetrahedral Pt nanocrystals (rich in (111) facets). These Pt nanocrystals can be supported on oxide (alumina) and used as a catalyst in structure-sensitive reaction, NO reduction by CH4. The results proved that morphologically controlled metal nanoparticles supported on adequate support give us a novel tool to connect the worlds of surface science with that of real catalysis. 

The potential of morphologically controlled metal nanoparticles should be expanded by further improvement of their preparation method. It is highly required to develop preparation methods to obtain a better morphological control, i.e., perfect facet control on the particles of optional size. Better morphological control of metal nanoparticles is expected to be achieved in near future and the obtained metal particles will find new exciting applications, not only in catalysis but also in other technically important fields. 

Figure 1. Change of concentration during the nucleation and growth of faceted nanoparticles.

Figure 4. Representative TEM image showing different shapes of faceted Pt nanoparticles.

Figure 15.4 Schematic representation of the Langmuir-Hinshelwood reaction between two adsorbates mobile X (black) and immobile Y (white) on a stepped single-crystalline surface (a) and a facetted nanoparticle (b).

A key feature of this study was the structural information available on the model palladium nanoparticle catalyst. The mean particle size is 5.5 nm, containing on average 3000 atoms the majority of the particles are well formed with a (111) orientation and terminated by (111) facets with only a small fraction of (100) facets exposed. 

The structure of 3 was confirmed by X-ray crystallography (Fig. 1). The morphology of the nanoparticles was examined by transmission electron microscopy (TEM). The two sp2-C palladacycles 1 and 4 gave what appeared to be triangular nanoparticles, in 2D, from 2-12 nm in size while the sp3-C PdCys 5 and 6 and Pd(OAc)2 exhibited more conventional morphology and were faceted palladium particles from 3-10 nm (Fig. 2). 

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