Catalyst particles, ultra-fine

We have employed this method to prepare a highly dispersed metal support catalyst and ultra-fine particle support catalysts were obtained[4]. 

VGCFs have typical diameters of 100 nm - 100 pm with hollow cores [9]. Thus VGCFs are 10 - lO times thicker than CNTs. A preparation method for VGCFs was first developed by Endo [10,11] wbo decomposed benzene at 1150-1.300°C in an electric furnace in the presence of H2 (99.9% pure) as the carrier gas (see Fig. 1). Ultra-fine particles of Fe (ca. 10 nm diameter) or its compounds, such as Fe(N03)3 or ferrocene, were introduced into the chamber as a catalyst. 

One of the excellent characteristics of Raney catalyst is a porous skeletal structure composed of ultra fine particles. 

Through the combined use of catalytic probe reactions, Mossbauer, EXAFS, XPS, XRD, it has been demonstrated that the anticipated particle structures for the half-SMAD and full SMAD procedures are close to reality.(40-42) Thus, 119Sn Mossbauer, a bulk solid analysis technique, revealed the relative amounts of Sn, Pt-Sn alloy, SnO, and Sn02 present in the catalysts. It was possible to differentiate Sn° from Pt-Sn alloy through supporting evidence of XPS and selective oxidation, since it was found that ultra-fine Sn° particles were much more susceptible to oxidation than Pt-Sn alloy particles. Also, since the full SMAD Pt°-Sn°/Al203 catalysts behaved much differently than Pt°/Al203, it is clear that the SMAD catalysts are not made up of separate Pt° and Sn particles. 

The methodology was first reported by Boutonnet et al.. They obtained a supported metal catalyst by depositing ultra-fine particles synthesized in a w/o microemulsion on pumice. The activity of this catalyst was tested in the but-1-ene hydrogenation reaction and compared with the activity of similar catalysts prepared by the traditional impregnation method both from aqueous and alcoholic solutions. The particle size was found to be in the 20-30 A range for the particles prepared from microemulsions and above 200 A for the classical impregnation counterparts. The behaviour of the Pt-based catalyst was found to depend on the preparation method. However, such a correlation between the activity and the preparation method could not be established in the case of Rh and Pd-based catalysts. 

A preparation of designed catalyst is one of the interest subjects to understand the catalysis. Efforts have been paid for the development of unique preparation method[1] those are metal cluster catalysts derived from metal carbonyls, tailored metal catalysts through organometallic processor and ultra-fine metal particle catalysts prepared by metal alkoxides, etc. These preparation methods are mainly concentrated to design the active sites on support surfaces. However, the property of support itself is also a dominant factor in order to conduct smoothly the catalytic reaction. It is known that some supports are valuable for the improvement of selectivity. For example, zeolites are often used as catalysts and supports for their regular pore structures which act effectively for the shape selective reaction[2]. In order to understand the property of support, the following factors can be pointed out besides the pore structure structure, shape, surface area, pore size, acidity, defect, etc. Since these are strongly correlated to the preparation procedure, lots of preparation techniques, therefore, have been proposed, too. Studies have been still continued to discover the preparation method of novel materials as well as zeolites[3]. 

Chen et al. [37] studied a series of complexes of styrene-4-vinylpyridine copolymers or poly(4-vinylpyridine) and transition metal chlorides. The transition metal-polymer complexes were used to prepare ultra-fine metallic particles dispersed in a polymer matrix by chemical reduction. Upon reduction, the metal ions were transformed into the corresponding nanometer scale metal particles with the protective polymers preventing the metal particles from oxidation and excessive aggregation. Ohtaki et al. reported the effects of polymer support on the substrate selectivity of covalently immobilized ultra-fine rhodium particles as a catalyst for olefin hydrogenation [38]. 

Enhanced capacitances have been achieved by preparing extremely fine RuOj particles with a porous network in a coated-oxide layer with the addition of salts or rare-earth elements in the dip-coating procedure on Ti substrates, or by preparing ultra fine RuOg particles with the addition of a salt catalyst in a sol-gel process [58]. 

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