Decomposition of Methane over Iron Catalysts at the Range of Moderate Temperatures: The Influence of Structure of the Catalytic Systems and the Reaction Conditions on the Yield of Carbon and Morphology of Carbon Filaments

摘要

Decomposition of high-purity methane in the presence of #alpha#-Fe- based catalysts to produce filamentous carbon was investigated. The reaction was studied in the temperature range of 650 to 800degC. Filamentous carbon was demonstrated to form at temperatures not lower than 680degC in the presence of both bare a-Fe and catalysts based thereon with admixtures of various hard-to-reduce oxides (SiO_2, A1_20_3, ZrO_2, and TiO_2). The maximal carbon yield, 45 9 per 9 of iron, was obtained with the Fe/SiO_2 catalyst comprising silica in amounts of 15 wt%. XRD and high-resolution electron microscopy were used for studying the carbon deposits. The data obtained allowed the conclusion on the essential influence of the chemical na- ture ofthehard-to-reduce oxide admixture in the iron catalyst on the microstructure and morphology of the carbon filaments. Depend- ing on the admixture, specific shapes of filaments and nanotubes predominated. Carbon nanotubes with thin walls built up by coax- ial cylindrical graphene layers were formed in large amount over the Fe/Al_2O_3 catalyst. Centers of growth of octopus-like nanotubes were observed.