Rate-controlled growth of carbon nanotubes (CNTs) and catalyst design are considered efficient ways for the preparation of CNTs with specific structures and properties. However, due to the difficulties in capturing the growth process of the CNTs with tiny size under a complex growth environment, the growth kinetics of CNTs and their correlation with the catalyst seed have been seldom revealed. Here, we investigated the growth process of CNTs from Ni nanoparticles (NPs) in real-time under atmospheric pressure using transmission electron microscopy equipped with a closed gas cell. It was found that the growth rates of CNTs fluctuated, and a phase transition from Ni₃C to Ni, and a reshaping of the catalyst NPs occurred during the growth process. We demonstrated that CNTs dynamically interacted with the connected catalyst NPs and the fluctuated growth rates of CNTs were correlated with the structure change of catalyst NPs. The origin of the growth rate fluctuation is attributed to the change of carbon concentration gradient in catalyst NPs.

The chirality structure of a single-walled carbon nanotube (SWNT) strongly depends on the composition of catalyst used in the chemical vapor deposition process. In this study, we develop a porous magnesia supported manganese-rhenium (MnRe/MgO) catalyst for chirality-selective synthesis of SWNTs. Detailed characterizations reveal that (6,5) tubes with a selectivity higher than 70% are grown from the Re-rich MnRe/MgO catalyst. By comparing the SWNT growth results with those of monometallic Mn or Re, the formation of sigma phase, an intermetallic compound occurring in transition-metal alloy systems, is revealed to be crucial for the dominant synthesis of (6,5) SWNTs. This work not only extends the application of sigma phase alloy for catalytic synthesis of SWNTs, but also sheds lights on the growth of SWNTs with a high chirality selectivity.