Influence of the composition of a H2-CH4 gas mixture on the catalytic synthesis of carbon nanotubes-Fe/Fe3C-Al2O3 nanocomposite powders

Abstract

C _NTs -Fe/Fe ₃ C-Al ₂ O ₃ nanocomposite powders have been prepared by selective reduction of an α-Al _1.9 Fe _0.1 O ₃ solid solution in H ₂ -CH ₄ gas mixtures (0, 1.5, 3, 4.5, 6, 9, 12, 14, 16, 18, 24, 30 and 45 mol% CH ₄ ). The powders have been studied using macroscopic and microscopic techniques. The C _NTs are arranged in very long bundles homogeneously dispersed in the composite powder. Most C _NTs have less than four walls and are free of pyrolytic or amorphous carbon deposits. The inner diameter is in the range 1-6 nm, which could indicate that the catalyst particles active for C _NTs formation are in this size range. The reduction of the Fe ³⁺ ions to metallic Fe is highly favoured by the presence of CH ₄ in the reduction atmosphere. There are more Fe ₃ C than α-Fe particles located at the surface of the matrix grains for CH ₄ contents higher than 4.5 mol%, however, the exact nature of the catalytically active particles remains an open question. Compositions in the range 9-18 mol% CH ₄ give the best results.