A mechanistic study on the growth of multi-walled carbon nanotubes by methane decomposition over nickel–alumina catalyst

Multi-walled carbon nanotube growth by catalytic decomposition of methane over Ni–Al2O3 catalyst has been carried out using a riser simulator (mini-fluidized bed batch) reactor. The catalyst was prepared by incipient wetness impregnation and characterized by nitrogen adsorption, powder X-ray diffraction, Raman spectroscopy and temperature programmed reduction (TPR). The multi-walled carbon nanotubes (MWCNTs) formed were characterized by transmission electron microscopy and Raman spectroscopy. The observed degree of MWCNT graphitization increased with temperature and time leading to better quality MWCNTs. Measured methane conversion against time data was used to find the reaction order for methane decomposition. A first order rate with respect to methane was obtained. The calculated activation energy for methane decomposition on Ni–Al2O3 catalyst was 37.1 ± 3.5 kJ/mol.

► MWCNT growth was conducted in a riser simulator by methane decomposition.
► First order decomposition of methane during MWCNT growth.
► Deactivation of the Ni–Al2O3 catalyst was minimal during carbon nanotube growth.
► Activation energy for methane decomposition on the catalyst was 37.1 ± 3.5 kJ/mol.