Carbon nanofibers methods

The multiwalled nanotubes as well as the herringbone type carbon nanofibers were synthesized in-house in a quartz glass fluidized bed reactor via chemical vapor deposition (CVD). The method is described in detail elsewhere.19 The platelet nanofibers, in contrast, were purchased from the company FutureCarbon GmbH (Bayreuth, Germany). 

Thus, for the first time it is shown that carbonic nanomaterials (fullerene, single-and multiwall nanotubes, nanofibers) demonstrate high activity at cryogenic conditions (77K) in reactions of chain halogenation (F2, Cl2) with kinetic chain length up to 104 -105. The ESR spectra of active free- radical intermediates were recorded. The presence of vibration bands of C-Cl bonds in products has been indicated by IR method. For the first time chain fluorination of carbonic nanofibers, mono- and multiwall nanotubes has been performed at low temperatures. 

One of the features of the catalysts for production of carbon nanofibers and especially nanotubes consists in a big role of catalyst particle size besides the catalyst chemical composition. The size can not be assigned in advance, and only the change of synthesis method or synthesis condition allows to produce the most active particles. Chemical composition of the catalyst can be changed during pyrolysis. 

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

For different electrochemical applications such as batteries, supercapacitors, fuel elements porous carbon nanomaterials are used. We have obtained porous carbon nanofibers by CVD method from acetylene with use of new (Fe,Co,Sn)/C/Al203-Si02 catalysts prepared by mechanochemical method [13, 14]. The porous nanostructures formed (Fig. 4) somewhat resembles structures, synthesized in [15] on titania-containing catalyst. 

Surface area of as-obtained CNF is nearly 300-500 m2/g. One of the effective methods of activation of different carbon materials is treatment with melted KOH at 400-900°C. High surface area (up to nearly 3000 m2/g) carbon materials were obtained [16, 17]. This method was also applied to carbon nanotubes. Significant development of surface was observed, from 465 m2/g for starting MWNT to 1184 m2/g after activation [18], Also, KOH activation of carbon nanofibers resulted in increase of surface area from initial 174 m2/g up to 1212 m2/g [19]. When activated our nanofibers, we obtained for some samples very high effective surface area, nearly 2000-4000 m2/g and in some experiments even 6000 m2/g (measured by argon desorption method). In electron image of activated material (Fig. 7) fiber-like structure is observed. 

Yanchenko V.V., Sementsov Yu.I., Melezhyk O.V. Method of obtaining of catalysts for CVD of carbon nanofibers. Ukrainian Patent 69291A, 2004. 

Brunauer-Emmet-Teller (BET) estimated surface areas [23], For example, from Figure 5.9, graphite felt electrodes show poor volume-normalized ORR current density compared to carbon nanofibers and multiwaUed carbon nanotube (MWCNT)-based electrodes. However, the results also reveal that CNTs and porous carbon tubes exhibit dramaticaUy lower ORR current densities when normalized to B ET surface area, while graphite felt electrodes perform better, perhaps indicative of agglomeration of the carbon tubes, preventing enzyme adsorption over the entire area. Further research on methods to permit dispersion of nano-tubes, while retaining electrical conductivity and adsorption of enzymes oriented for DET, is warranted. 

The carbon nanofiber (CNF) synthesis was performed at atmospheric pressure at temperatures ranging from 550 to 650 °C and under various matures of ethane and hydrogen. After synthesis the material was cooled to room temperature under the synthesis mixture and then discharged. Due to the high carbon nanofiber yield no post-treament was needed as usually encountered with other preparation methods such as acidic treatments in order to remove the metal catalyst from the final product. 

The hydrogenation of nitrobenzene was carried out on palladium supported on the carbon nanofibers prepared according to the preceding method without further purification and compared to a commercial palladium catalyst supported on a high surface area activated charcoal (Aldrich, 970 m /g). 

The preparation is achieved using the floating catalyst method. The precursor of the catalyst (in this case ferrocene or Fe(CO)5 with H2S as cocarbon source (natural gas mainly consisting of methane here). The resulting carbon nanofibers then may be graphitized at about 3(X)0 C. 

Another method that is becoming increasingly important is the application of carbon on a ceramic surface, as is the growth of carbon filaments over deposited metal particles (the CVD method) [12-14]. Carbon nanofibers (CNFs) have long been known as a nuisance that often emerges during catalytic conversion of... 

Even more spectacular results in terms of the increasing importance of nanocatalysis for bulk industrial processes have recently been reported by Kuipers and de Jong [32, 33]. By dispersing metallic cobalt nanoparticles of specific sizes on inert carbon nanofibers the authors were able to prepare a new nano-type Fischer-Tropsch catalyst. A combination of X-ray absorption spectroscopy, electron microscopy, and other methods has revealed that zerovalent cobalt particles are the true active centers which convert CO and H2 into hydrocarbons and water. Further, a profound size effect on activity, selectivity, and durability was observed. Via careful pressure-size correlations, Kuipers and de Jong have found that or cobalt particles of 6 or 8nm are the optimum size for Fischer-Tropsch catalysis. The Fischer-Tropsch process (invented in 1925 at the Kaiser-Wilhelm-Institute for... 

In this paper, oxidation of carbon nanofibers by nitric acid in combination with a deposition precipitation method was investigated as a modus operandi for the preparation of highly dispersed carbon nanofiber supported, cobalt oxides. A variety of thermal and spectroscopic techniques such as thermogravimetric... 

Carbon nanofiber supported cobalt catalysts were prepared according to a deposition precipitation method utilizing urea as precipitating reagent. XPS,... 

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