Kinetic study of double-walled carbon nanotube synthesis by catalytic chemical vapour deposition over an Fe-Mo/MgO catalyst using methane as the carbon source

Abstract

A kinetic study was performed to describe experimental reaction rates of double-walled carbon nanotube (DWNT) synthesis by catalytic chemical vapour deposition (CCVD) over an Fe-Mo/MgO catalyst using methane as the carbon source. Initial reaction rates were determined by mass spectrometry for methane partial pressures ranging from 0.01 atm to 0.9 atm and for three temperatures: 900 °C, 950 °C and 1000 °C. Mass transfers from the bulk of the fluid to the external surface of the catalytic bed and through the catalytic bed were negligible as determined experimentally and confirmed by the methane mass balance. A detailed kinetic study was carried out to discriminate between phenomenological kinetic models and to validate the good agreement between the chosen model and the experimental data. The best model was found to involve the irreversible dissociative adsorption of methane followed by the irreversible decomposition of the adsorbed methyl group, which is the rate-determining centre. Activation energy of adsorbed methyl decomposition was found to be equal to 58 kJ mol −1. The catalytic deactivation by coking was expressed by a decreasing function of coke content, which leads to a sigmoid equation.