Kinetic study of multi-walled carbon nanotube synthesis by thermocatalytic decomposition of methane using floating catalyst chemical vapour deposition

Abstract

Multiwalled carbon nanotubes (MWCNTs) have been synthesized using methane in a floating catalyst chemical vapour deposition reactor at atmospheric pressure. The catalyst concentration, partial pressure of methane and synthesis temperature have been varied in order to understand their effects on the rate formation of MWCNTs, purity and size of MWCNTs. Reaction mechanism, rate controlling step and overall rate of reaction have been deduced using chemical reaction engineering approach. A systematic study was carried out in order to obtain the kinetic expression based on Langmuir-Hinshelwood type model. The kinetic model was based on the dissociative adsorption pathway of methane and subsequent removal of hydrogen from the adsorbed methyl group with two different active sites. The activation energy for the overall reaction was 46.1 kJ mol−1 in the temperature range of 1073–1273 K. The products have been characterized by transmission electron microscopy, thermogravimetry, BET and Raman spectroscopy. The BET surface area of purified MWCNTs were found to be 157 m2 g−1 with pore volume of 0.176 cc g−1.