Suppression of methane formation as catalytic converting light hydrocarbons into H₂ and carbon nanotubes

Conversion of C-2-C-5 hydrocarbons using the nanosized Fe catalyst at 700-800 degrees C was studied, with the purpose of simultaneously producing H-2 and carbon nanotubes and suppressing the formation of CH4. The ratio of CH(4 )as a byproduct increased with the increase of reaction time and the defect degree of the carbon products, which was a product thermodynamic favorable as calculated. Thus, the critical factors of increasing the selectivity of H-2 and suppressing the formation of CH4 lay in maintaining the fast growth and full growth trend (kinetically) of carbon nanotubes. Related measures including the variation of the type of hydrocarbons, the addition of water in small amounts, the particle sizes of the catalyst, and the agglomerates of the synthesized CNTs were fully investigated quantitatively. It validated that any measures of increasing the carbon diffusion and precipitation or recovering active sites on the catalyst surface would enhance the stepwise dehydrogenation of intermediates to be CNTs, which naturally suppress the hydrogenation of intermediates to be CH4. Under optimal operating conditions, the carbon elements in hydrocarbons were fixed as carbon nanotubes with a yield of 69 % (carbon atoms base), and the selectivity of H-2 in the gaseous product was 71-95 % (volume base).