Mechanism of K-catalyzed transformation of solid carbon structure into carbon nanotubes in coal

In this paper, the changes in solid-phase carbon structure and the formation of carbon nanotubes in the process of K-catalyzed pyrolysis of bituminous coal were investigated. The results showed that the content of carbon nanotubes in K-catalyzed coal pyrolysis products increased with the extension of residence time. When the residence times were 0, 30 and 90 min, the yields of carbon nanotubes in the coal pyrolysis products were 1.98 wt%, 6.85 wt% and 10.16 wt%, respectively. It was found that the aromatic carbon CC, CH and ether carbon C-O-C structures in coal were the main carbon sources for the growth of carbon nanotubes. The probable growth mechanism of carbon nanotubes in the process of K-catalyzed coal pyrolysis was proposed to be as follows: aromatic CC and CH structures in coal convert K components such as K2CO3 and K2O into metal K, and then metal K converts carbon atoms in the ether bond C-O-C structure into carbon atoms or clusters, which generate carbon nanotubes under the action of Fe catalyst particles in coal. This method provides a new strategy for the simultaneous high-value utilization of coal resources and macroscopic, low-cost preparation of carbon nanotubes. [Display omitted] •Carbon nanotubes were directly synthesized from K-catalyzed coal or coke pyrolysis.•Type of carbon structure in coal required for carbon nanotubes growth was determined.•Formation mechanism of carbon nanotubes from K-catalyzed coal pyrolysis was proposed.