Synthesis of Carbon Nanofibers via Catalytic Chemical Vapor Deposition of Halogenated Hydrocarbons
Статья (Full article),
||Carbon Nanofibers: Synthesis, Applications and Performance
Nova Science Publishers. 2018.
319 c. ISBN 9781536134339.
||Catalytic chemical vapour deposition (CCVD), catalytic decomposition, chlorinated hydrocarbons, carbon nanofibers, nanostructured carbon product, Ni-based catalysts, metal dusting, carbon erosion, disintegration, induction period, bulk metals and alloys, Ni and Ni-based alloys, mechanical alloying, mechanism of CNF growth, organochlorine waste, utilization, recycling, processing, valorization, structure and morphology of CNF, texture of CNF product
Институт катализа им. Г.К. Борескова СО РАН
Национальный исследовательский Томский политехнический университет
Институт неорганической химии им. А.В. Николаева СО РАН
Новосибирский национальный исследовательский государственный университет
Nanostructured carbon materials, due to the variety of their unique properties, attract wide attention in different fields of science and industry. Among these materials, carbon nanofibers (CNF) occupy a special place, drawing a heightened interest. The catalytic chemical vapor deposition (CCVD) method is considered as a scalable approach allowing to obtain the carbon product with desired controllable characteristics. As usual, catalysts used for this purpose are based on transition metals.
On the other hand, the presence of heteroatoms in the composition of organic compounds is well known as a factor significantly affecting the textural and morphological properties of the carbon nanofibers being prepared. Such effects were shown by numerous studies for oxygen-, nitrogen- and sulfur-containing precursors. In the case of chlorinated hydrocarbons, the situation is more complicated. Depending on reaction conditions (mostly temperature and hydrogen concentration in the gas phase), released chlorine is capable of interacting with metal particles, thus causing their bulk chlorination with subsequent deactivation. At the same time, the presence of halogen atoms in the composition of substituted hydrocarbon influences the overall mechanism of CNF formation and consequently, has the significant effect upon morphology, structure and textural characteristics of carbon products. Nevertheless, the catalytic decomposition of chlorinated hydrocarbons is now considered as a very promising method for the utilization of hazardous organochlorine waste products represented by a complex mixture of chlorinated hydrocarbons.
In terms of resistance towards chlorination, nickel should be mentioned as the most stable among the metals of the iron subgroup (Ni, Co, Fe). Doping of Ni with some other metals allows one to enhance catalytic activity and stability with respect to CCVD of unsubstituted hydrocarbons.
In order to make the catalyst more effective in the CCVD process, the high dispersion of active components has to be provided. In this turn, impregnation and coprecipitation are known as conventional methods used for preparation of dispersed Ni-containing particles. One-step synthesis of the catalysts by mechanochemical activation of oxides looks more preferable from technological and environmental points of view. Alternatively, dispersed metal particles can be obtained via the metal dusting process which implies the spontaneous disintegration of bulk nickel-based alloys in a strongly carburizing atmosphere. This process, extremely undesirable in the chemical industry, is now considered as a new promising way for the purposeful synthesis of carbon nanostructures. The main problem assigned to this process is the existence of a prolonged induction period. In the case of chlorinated substrates, the presence of chlorine accelerates greatly the slow process of metal dusting and shortens the duration of the induction period from hours to tens of minutes. Usage of commercial Ni-containing alloys for CCVD of halogenated hydrocarbons requires additional activation treatment procedures to initiate the metal dusting process and reduce the induction period down to a few minutes. On the other hand, mechanical alloying of metal powders (nickel and required additives) allows one to obtain bulk Ni-based alloys which undergo metal dusting followed by CCVD without an induction period.