Growth rate of carbon filaments during methane pyrolysis on an iron catalyst with analysis using a kinetic–thermodynamic approach

Optical microscopy has been used to determine the Arrhenius parameters of the linear growth rate for nano- and microfilaments of about ∼100 nm and larger in diameter. The quasi-steady state linear growth rates of carbon filaments in methane/hydrogen pyrolysis on an iron catalyst have been measured for filaments grown in a gas flow reactor at temperatures of 950–1050 °C. The filament growth rate as a function of the carbon activity of the feedstock CH4/H2 mixtures was shown to have both a local maximum at the carbon activities of about 200–300 and a local minimum at higher carbon activities, followed by another sharp increase at richer methane mixtures. The magnitude of the maximum was determined by the contribution of gas phase pyrolysis products to filament growth. A sharp increase in the growth rate after its local minimum was explained by changes in the growth mechanism mode, which, in turn, might be caused by melting of a catalyst particle. To analyze the kinetic data, a combined kinetic–thermodynamic approach was used.