Catalysts for vapor-phase deposition of multi-walled carbon nanotubes are considered. A method for synthesis of iron-containing catalyst by coprecipitation of aluminum, magnesium, and iron(II) hydroxides is suggested.Carbon nanotubes (CNT), which were only available in milligram amounts several years ago, are gradually becoming a product of large-tonnage synthesis. Simultaneously with the increase in the production scale, new application fields of CNT are being revealed. For example, Hyperion Catalysis International Co. (USA) manufactures CNT 10315 nm in diameter and CNT-containing polymeric formulations. Introduction of 235% CNT into polymeric materials makes them electrically conducting and thereby hinders accumulation of static electricity [1]. Mechanical properties of CNT-filled polymeric materials have been studied [23 4]. CNT and CNT-based composites are under intensive scientific and technological development in China [5310].According to the results of [9], the most valuable are fine CNT less than 20 nm in diameter. In the best variants reported in numerous publications devoted to synthesis of multi-walled CNT by the chemical vapor deposition technique, the CNT diameter is 10 320 nm. The authors of the present study are not aware of any method for obtaining multi-walled CNT with an average diameter of less than 10 nm.It is commonly believed, even though this issue remains insufficiently studied, that the diameter of a growing nanotube is determined by the size of the cluster of a catalytically active metal, e.g., iron, cobalt, or nickel. Presumably, the most efficient way to obtain and stabilize nanosize clusters of catalytically active metals is their immobilization on some highly dispersed or porous support, e.g., aluminum oxide, silicon, magnesium, or carbon. For this purpose, a dispersed support is impregnated with solutions of metal compounds (nitrates, acetylacetonates, salts of organic acids, etc.) On being introduced into a hot reactor, these compounds decompose to give, commonly, metal oxides, from which catalytically active metal clusters are formed in a reducing atmosphere (as a rule, a mixture of hydrogen and hydrocarbons). Such a procedure for fabrication of catalysts for synthesis of multi-walled CNT was described, e.g., in the patent [11]. Aluminum oxide with a particle size of about 10 nm was used as a highly dispersed support, and nitrates and acetylacetonates of iron, molybdenum, manganese, and chromium, and mixtures of these, as compounds of catalytically active metals. Ethylene mixed with hydrogen served as a source of carbon. The mass of the multi-walled CNT obtained was tens of times that of the catalytically active metals, and the diameter of the resulting CNT was in the range from 3.5 to 70 nm. The method described has the following disadvantage. As a result of impregnation and drying, particles of the material undergo aggregation and the size of metal oxide clusters formed in pyrolysis may markedly exceed the particle size of the highly dispersed support. Thus, the nanotubes obtain...
