Kinetic model of carbon nanotube production from carbon dioxide in a floating catalytic chemical vapour deposition reactor

Abstract

The production of carbon nanostructures, including carbon nanotubes (CNTs), by chemical vapour deposition (CVD) occurs by thermally induced decomposition of carbon-containing precursors. The decomposition of the feedstock leading to intermediate reaction products is an important step, but rarely incorporated in rate equations, since it is generally assumed that carbon diffusion through or over the catalyst nanoparticles is the rate-limiting step in the production of CNTs. Furthermore, there is no kinetic model to date for the production of CNTs from carbon dioxide. These aspects are addressed in this study with the aid of a series of experiments conducted in a floating catalytic CVD reactor in which the effects of reactor temperature, concentration and flow rate of CO 2 were investigated. A simple rate equation for the reductive adsorption of CO 2 onto the catalyst surface followed by carbon diffusion leading to the production of CNTs is proposed as follows:, where K is proportional to the diffusion coefficient of carbon. The derived kinetic model is used to calculate the amount of CNTs for a given concentration of CO 2 , and the experimentally measured data fits the simple rate equation very well at low carbon dioxide concentration.

Carbon Nanotube Synthesis Using Coal Pyrolysis

“…The following reaction typically proceeds due to lower activation energy than the dry reforming reaction itself given in reaction . However, the side reaction of reforming also occurs via the intermediate reaction steps shown below: The first reaction among these two is the rate-limiting, implying that the overall rate is governed by the concentration of methane and adsorbed carbon in the forward and reverse directions, respectively. Introducing an equilibrium constant K 1 results in In addition to the methane acting as a carbon source for the formation of CNTs, the CO produced during coal pyrolysis also serves this function in a secondary manner. However, the procedure by which CO forms the adsorbed carbon suitable for CNT formation is more complex than that of methane, and the kinetics of this approach has been discussed previously . It has been deduced that CO will split in one of the two possible reactions as shown below: Reaction is unlikely to take place due to the extremely high temperatures required, and therefore only the Boudouard reaction is considered here.…”

“…However, the procedure by which CO forms the adsorbed carbon suitable for CNT formation is more complex than that of methane, and the kinetics of this approach has been discussed previously . It has been deduced that CO will split in one of the two possible reactions as shown below: Reaction is unlikely to take place due to the extremely high temperatures required, and therefore only the Boudouard reaction is considered here. It is well-known that the Boudouard reaction produces CNTs and has therefore resulted in CO becoming one of the most common sources for CNT production in the literature.…”

“…It is well-known that the Boudouard reaction produces CNTs and has therefore resulted in CO becoming one of the most common sources for CNT production in the literature. However, this reaction cannot be represented by elementary kinetics as it is a catalytic reaction . Before CNT synthesis can take place, a number of intermediate surface reactions must take place in order for elemental carbon to be deposited on the catalyst surface.…”

Synthesis of CNTs via chemical vapor deposition of carbon dioxide as a carbon source in the presence of NiMgO

“…In other words, a large energy input is required to transform CO 2 [9]. Thus, recently, efforts have been made to explore the possibility of thermally splitting CO 2 [10].…”

Post-Treatments for Multifunctional Property Enhancement of Carbon Nanotube Fibers from the Floating Catalyst Method

“…Alternatively, the direct growth method, on the basis of the aerogel technique, has been considered a significant step toward scalable fiber production . While this method is widely used to synthesize aligned CNTs, , it has been reported that the CNT fibers directly spun from this method commonly possess high mechanical properties with good electrical conductivities . When the effects of gauge length (GL) are neglected, their strength and Young’s modulus could reach up to 3.24 and 357 GPa (at a 1 mm GL), respectively, after a simple acetone densification, whereas their electrical conductivities are on the order of ∼10 3 S/cm. ,,, Recently, Gspann et al reported a comprehensive study of the floating chemical vapor deposition (CVD) process, in which purity issues and the roles of sulfur were highlighted.…”