Metal catalysts crystal properties

Meanwhile, development of coordination catalyst was proceeding full scale. The polyisoprene prepared using this coordination catalyst (TiClj, AIR ) proved to be more suitable in physical properties than the one made by lithium metal or organolithium compounds in hydrocarbon media. The Ziegler polyisoprene, as it was called, has greater stereoregularity and stress-induced crystallization properties than polyisoprene made by the alkyl lithium catalyst. How-... 

When the catalytic properties of metals are examined, the importance of the non-uniformity of sites depends on the reaction under study. For some reactions, the activity of the metal catalyst depends only on the total number of sites available and these are termed structure-insensitive reactions. For other reactions, classified as structure-sensitive reactions, activity may be much greater on sites associated with a particular crystal face or even with some type of defect structure. The alternative names of facile or demanding have been used to describe structure-insensitive or structure-sensitive reactions, respectively. 

Concerning the first advantage, one can as easily study reactions on a single crystal metal surface as on a planar surface generated to duplicate the properties of a supported metal catalyst, as described above. Furthermore, with planar surfaces, LEED, Auger and photoelectron spectroscopies, along with many other analytical methods of surface science, can provide characterization of the surface composition and structure. 

On the other hand the carbon materials are widely known supports of metal catalysts from of old. It has been shown, that the carbon supports increase the dehydrogenative properties of the metal catalysts due to the epitaxial changing of metal crystal structure providing their structural relevance with reacting molecules [8],... 

Rapid crystallization would overcome the disadvantages of slow crystallization and, more significantly, hetero elements could be incorporated inside the crystals. Metal-incorporated zeolitic materials serve as bifunctional catalysts, exhibiting properties of both metal catalysts and zeolite catalysts. 

One of the most active current research areas in metal oxide surface science is oxide-solid interfaces. Work to date falls into three broad categories. The earliest work was the growth of metal films on single-crystal oxide substrates. One of the motivations there was to produce model systems to study the basic properties of oxide-supported metal catalysts. Quite a few groups have been involved in that work, and several papers have reviewed parts of the field [35-37]. An example of this approach is presented in Chap. 9 here. 

A heterogeneously catalyzed reaction takes place at the surface of a catalyst. Catalysts, their properties, and the nature of catalytic surfaces are discussed in Chapter 7. For this discussion, we approximate the surface as a single crystal with a known surface order. The density of atoms at the low-index planes of transition metals is on the order of. 10 cm 2. Figure 5.16 presents the atomic arrangement of low-index surfaces for various metals. This figure illustrates the packing arrange-... 

There are other types of active sites. In 1955 Kobozev (17) pointed out that sometimes—especially with certain metals—the catalytic properties could be due to the properties of atoms, but that in other cases—as with some metal oxides—the catalytic property might be associated with the entire crystal We showed later (j ) that in at least one case, silica-alumina catalyst, it is very easy to err concerning the nature of the site Thus, evidence for Bronsted acidity could be interpreted as evidence for the presence of aluminum which can be ion-exchanged when the catalyst is placed in salt solution Looking at all these examples, we conclude that that there are many different sources of activity on the solid catalyst surface. 

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