Preparation and Formation Mechanism of Carbon Nanotubes via Coal Pyrolysis Using Alkaline Potassium Catalysts

In this study, two potassium-based alkaline compounds, KOH and K₂CO₃, were utilized as catalysts for the pyrolysis of bituminous coal to directly synthesize carbon nanotubes (CNTs). During the conventional reaction process, CNTs were observed as unusual products, with respective contents reaching 9.43 and 8.98 wt.% in the pyrolysis products. The results indicate that at temperatures exceeding 600 °C, KOH undergoes complete conversion into K₂CO₃. The melting point of K₂CO₃ (890 °C) serves as the critical temperature for the formation of CNTs. Under the reducing atmosphere provided by -CH₂- and aromatic C-C structures in coal, the transformation process K₂CO₃ → K₂O → K occurs. At high temperatures, highly etching K reacts with the C-O-C structures in coal, converting them into carbon atoms and exposing the iron (Fe)-containing minerals in coal to the particle surface. Finally, the carbon atoms derived from the ether bonds form CNTs under the action of the native Fe catalyst in coal. The resulting product is a mixture of activated carbon and CNTs. This method fundamentally alters the composition of traditional coal-based activated carbon and provides a new approach for the cost-effective, large-scale production of high-value CNTs.