Catalysts nanotubes

When the same approach is used to simulate thermal conductivity, quantum theory might be needed again to predict the resulting thermal properties of composite structures. On the other hand chirality, diameter, and the thickness of, for example, multi-walled carbon nanotubes, as well as morphology (both non-aligned and random - whiskers or straight and curved nanotubes), may play an important role in how to approach the effective determination of properties. Finally, the conductance at the metal catalyst-nanotube junction in the catalyst layers may be different... 

Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

Whereas multi-wall carbon nanotubes require no catalyst for their growth, either by the laser vaporization or carbon arc methods, catalyst species are necessary for the growth of the single-wall nanotubes [156], while two different catalyst species seem to be needed to efficiently synthesize arrays of single wall carbon nanotubes by either the laser vaporization or arc methods. The detailed mechanisms responsible for the growth of carbon nanotubes are not yet well understood. Variations in the most probable diameter and the width of the diameter distribution is sensitively controlled by the composition of the catalyst, the growth temperature and other growth conditions. 

Fig. 11. The loss of carbon rapidly increases with the increase of temperature. Heating of the catalysts in open air for 30 minutes at 973 K leads to the total elimination of carbon from the surface. The gasification of amorphous carbon proceeds more rapidly than that of filaments. The tubules obtained after oxidation of carbon-deposited catalysts during 30 minutes at 873 K are almost free from amorphous carbon. The process of gasification of nanotubules on the surface of the catalyst is easier in comparison with the oxidation of nanotubes containing soot obtained by the arc-discharge method[28, 29]. This can be easily explained, in agreement with Ref [30], by the surface activation of oxygen of the gaseous phase on Co-Si02 catalyst.

Fig. 5. Diameter distributions of nanotubes produced via different methods (a) Fe catalyst in an Ar/CH4 atmosphere, adapted from Ref. 2 (b) Co catalyst in He atmosphere, adapted from Ref. 5 (c) Co catalyst with sulfur, about 4 at. % each, adapted from Ref. 5.

A POSSIBLE MECHANISM FOR THE GROWTH OF NANOTUBES ON A CATALYST PARTICLE... 

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. 

Small diameter, single-wall nanotubes have been synthesized with metal catalysts by maintaining a dc arc (30 V, 95 A) between two electrodes in —300 Torr of He gas.[21,22] The metal catalyst (cobalt[22] or... 

Case - Use of Carbon Nanotube-Based Catalysts in Hydrogen Production... 

Carbon nanotubes (CNTs) are a set of materials with different structures and properties. They are among the most important materials of modern nanoscience and nanotechnology field. They combine inorganic, organic, bio-organic, coUoidal, and polymeric chemistry and are chemically inert. They are insoluble in any solvent and their chemistry is in a key position toward interdisciphnary applications, for example, use as supports for catalysts and catalytic membranes [20, 21]. 

The potential for the use of catalysis in support of sustainability is enormous [102, 103]. New heterogeneous and homogeneous catalysts for improved reaction selectivity, and catalyst activity and stabihty, are needed, for example, new catalytic materials with new carbon modifications for nanotubes, new polymers. 

Screening of metal oxide catalysts for carbon nanotubes and hydrogen production via catalytic decomposition of methane... 

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