Growth of carbon nanotubes from butadiene on a Fe-Mo-Al₂O₃ catalyst

Abstract

The MoO₃-Fe₂O₃-Al₂O₃ catalysts were prepared from metal nitrates using a coprecipitation method. It was found that the modification of an alumina-iron catalyst with molybdenum oxide resulted in the formation of a solid solution based on hematite, in which a portion of iron ions was replaced by aluminum and molybdenum ions. The MoO₃-Fe₂O₃-Al₂O₃ catalyst was reduced with a reaction mixture at 700°C. Under the action of 1,3-butadiene diluted with hydrogen, the solid solution based on hematite was initially converted into magnetite and then into an Fe-Mo alloy. The modification of an alumina-iron catalyst with molybdenum oxide considerably changed its properties in the course of carbon nanotube formation. As the Mo content was increased, the yield of carbon nanotubes passed through a maximum. The optimum catalyst was 6.5% MoO₃–55% Fe₂O₃-Al₂O₃. The addition of small amounts of MoO₃ (to 6.5 wt %) to the aluminairon catalyst increased the dispersity and modified the properties of active metal particles: because of the formation of an Fe-Mo alloy, the rate of growth decreased but the stability of carbon nanotube growth and the yield of the nanotubes increased. A further increase in the molybdenum content decreased the yield because molybdenum is inactive in the test process.