Catalytic graphitization

Figure 4.12 Micrograph (A) and a schematic (B) of catalytic graphitization of amorphous carbon in the presence of metal nanoparticles. The top arrow indicates the streamline of the fluidized particle [4]. (Courtesy of K. I. Zamaraev )...

When the formation of graphite particles from the metal-dissolved carbon is the rate-limiting step of the catalytic graphitization, then... 

Figure 4.14 A very simplified melting diagram of the Fe-C system where a stationary metastable phase can form during the catalytic graphitization of amorphous carbon. FesC (cementite) and Fe2C are stoichiometric iron carbides. A is the equilibrium eutectic point (T = 1420 K, x = 0.173), and B is the stationary oversaturated state (T = 920 K).

Polyarylacetylene, formed from the polymerization of diethynylbenzene [62,63] is non-graphitizing, but does have a char yield of 88% and can be catalytically graphitized at lower temperatures using carborane (C2B10H12), a boron containing compound. 

Figure 10.4. XRD patterns for the graphitized carbons (a) before and (b) after metal removal [35]. (Reproduced from Carbon, 44(3), SeviUa M, Fuertes AB. Catalytic graphitization of templated mesoporous carbons, 468-74, 2006, with permission fi om Elsevier.)...

Hyeon et al. [116] successfully synthesized carbon nanoeoils composed of nanometer-thiek graphitic fibers by the catalytic graphitization of a resorcinol-formaldehyde gel. The carbon nanocoils were applied as eleetrode materials for direct methanol fuel cells. The SEM image reveals that the carbon materials consisted of partieles approximately 100 mn in diameter (Figure 10.14(a)). The TEM image (Figure 10.14(b)) shows that each individual particle is composed of... 

Manivannan et al. (1999) also report on the presence of magnetic inorganic impurities of size too small to be detected by WAXD. Such impurities can have significance in terms of catalytic gasification (during physical activation) and in terms of catalytic graphitization (during carbonization processes). 

Apart from the rather unusual phenomenon of catalytic graphitization, graphitic structures never appear at temperatures below about 2500 °C. The crystallite theory for carbon structure has hindered a realistic understanding of what makes an activated carbon for too long a time. 

Catalytic graphitization refers to a transformation of non-graphitic carbon into graphite by heat treatment in the presence of certain metals or minerals. 

Catalytic graphitization gives a fixed degree graphitization at lower temperature and/or... 

Hong SE, Kim DK, Jo SM, Kim DY, Chin BD, Lee DW (2007) Graphite nanofibers prepared from catalytic graphitization of electrospun poly(vinylidene fluoride) nanofibers and their hydrogen storage capacity. Catal Today 120(3-4) 413-419. doi 10.1016/j.cattod.2006.09.013... 

Solid Superacids. Most large-scale petrochemical and chemical industrial processes ate preferably done, whenever possible, over soHd catalysts. SoHd acid systems have been developed with considerably higher acidity than those of acidic oxides. Graphite-intercalated AlCl is an effective sohd Friedel-Crafts catalyst but loses catalytic activity because of partial hydrolysis and leaching of the Lewis acid halide from the graphite. Aluminum chloride can also be complexed to sulfonate polystyrene resins but again the stabiUty of the catalyst is limited. 

As was found in Ref. [13], the method of catalytic decomposition of acetylene on graphite-supported catalysts provides the formation of very long (50 fim) tubes. We also observed the formation of filaments up to 60 fim length on Fe- and Co-graphite. In all cases these long tubules were rather thick. The thickness varied from 40 to 100 nm. Note that the dispersion of metal particles varied in the same range. Some metal aggregates of around 500 nm in diameter were also found after the procedure of catalyst pretreatment (Fig. 2). Only a very small amount of thin (20-40 nm diameter) tubules was observed. 

As in the case of graphite-supported catalysts, some metal particles were also encapsulated by the deposited carbon (Fig. 4). However, the amount of encapsulated metal was much less. Differences in the nature of encapsulation were observed. Almost all encapsulated metal particles on silica-supported catalysts were found inside the tubules (Fig. 4(a)). The probable mechanism of this encapsulation was precisely described elsewhere[21 ]. We supposed that they were catalytic particles that became inactive after introduction into the tubules during the growth process. On the other hand, the formation of graphite layers around the metal in the case of graphite-supported catalysts can be explained on the basis of... 

In a common method for the production of tubular carbon fibers, the growth is initiated by submicrometer size catalytic metal particles[19]. Tube growth out of a graphite rod during arc-discharge might also be related to nanoparticle-like seeds present... 

The inner (outer) diameter of the observed curved or coiled nanotubules produced by the catalytic method[8] varies from 20 to 100 A (150 to 200 A), which corresponds to the graphite layer order 3< <15 (Table 1). 

From the observation of the early stage of nanotube production by the catalytic decomposition of acetylene, it is concluded that steric hindrance arising from the surrounding nanotubes, graphite, amorphous carbon, catalyst support and catalyst particle itself could force bending of the growing tubules. 

Allylic sulfones and a, /5-unsaturated sulfones are known to be in equilibrium314-319. Allylic sulfones, such as 242, isomerize to a, /5-unsaturated sulfones 243 upon treatment with a catalytic amount of potassium t-butoxide in dry THF. The a, /5-unsaturated sulfones can be converted to the corresponding olefins upon desulfonation with sodium amalgam320 or aluminium amalgam294,321. Since treatment of allylic sulfones with potassium-graphite gives 2-alkenes, alkylation of allylic sulfones and subsequent desulfonation is a useful process for the synthesis of olefins, as shown in Scheme 6. 

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