High-Quality Multiwalled Carbon Nanotubes from Catalytic Decomposition of Carboneous Materials in Gas−Solid Fluidized Beds

Abstract

The effects of reaction temperature (873-1223 K), carbon sources (CH 4 , C 2 H 2 , C 2 H 4 , and C 2 H 6 ), and the amount of catalyst (2.5-20 g) on the physical properties (tube diameter, conversion, volume expansion, intensity ratio of the D-and G-band peaks (I D /I G )) of multiwalled carbon nanotubes (MWCNTs) in a gas-solid fluidized bed reactor (with an inner diameter (id) of 0.056 m and a height of 1.0 m) have been determined. The MWCNTs synthesized by the catalytic decomposition of methane produce the smallest tube diameter and the highest intensity ratio (I D /I G ) among the carbon sources (acetylene, ethylene, and ethane). Although the tube diameter of MWCNTs that have been synthesized from the decomposition of methane and ethane at 1073 K are similar, the volume expansion of the carbon nanotubes (CNTs) agglomerate from ethane is higher than that from methane. Both the tube diameter and the I D /I G ratio of the MWCNTs synthesized from the decomposition of methane decrease as the reaction temperature increases (in the temperature range of 1073-1223 K). The amount of catalyst does not affect the mean tube diameter of the synthesized CNTs; however, CNTs with a bamboo structure are synthesized when the carbon decomposition rate is higher than the CNT growth rate.

Fluidized bed catalytic chemical vapor deposition synthesis of carbon nanotubes—A review

“…In accordance with their comment, See and Harris [132] also applied 40 g pure CaCO 3 in addition to the 70 g catalyst (Fe-Co supported) on CaCo 3 . In contrast, some researchers insist on a small initial bed heights are sufficient for effective synthesis of CNTs in FBCVD because of the significant decrease in bed density and rapid bed expansion [65,131,132]. Moreover, large amount of catalyst demands a very high flow rate of gas for organization of homogeneous condition in the reactor and for its transportation into the reactor.…”

“…In the CCVD process, there is an optimum time that beyond this, nucleation becomes more difficult and a progressive deactivation of the catalytic nanoparticles starts to occur. However, there is a great disparity in the proposed optimum time of CCVD with respect to process parameters and nature of catalyst as well as carbon source [10,19,58,65,75,94,100,106]. To nucleate CNT, accumulated carbon atoms must reach a critical concentration inside the catalyst particles, which is related to the deposition rate.…”

“…Kim et al [71] failed to observe any significant effects of temperature on average diameter of MWCNTs but observed that elevating the temperature had increased the length as well as the crystallinity of the nanotubes. Son et al [65] concluded that the CNT diameters synthesized from methane in fluidized bed decreases as the reaction temperature increases. Nevertheless, the effect of temperature was evident on the growth rate, purity and the crystallinity of CNTs in all mentioned studies.…”

“…The starting temperature of CCVD synthesis of CNTs has been mostly reported higher than 500 • C but there is a conflicting result for maximum temperature. Early on, it was believed that a very high temperature (e.g., 1000-2000 • C) favors the formation of SWCNTs over MWCNTs [5], however, with the advent of new CVD methods, especially FBCVD, this opinion is changing as the SWCNT growth temperature keeps getting lower [62][63][64][65][66][67]. Some investigated conditions for the CVD growth of CNTs are displayed in Table 1.…”

Effect of operating variables on synthesis of multi-walled carbon nanotubes in fluidized beds

“…Under a given set of conditions, carbon yield increases as the reaction temperature is increased but decreases once the temperature exceeds the threshold. In systems using a different carbon source, carbon yield with respect to reaction temperature shows the same trend, but optimal reaction temperatures vary (Morancais et al, 2007;Philippe et al, 2009;Son et al, 2008). In addition, CNT diameter and crystallinity vary depending on the reaction temperature (Muataz et al, 2006;Andrews et al, 2002;Kim et al, 2005;Nourbakhsh et al, 2007;Xiong et al, 2005;Yao et al, 2004).…”