CaCo 3 supported Co‐Fe catalysts for carbon nanotube synthesis in fluidized bed reactors

The synthesis of carbon nanotubes (CNTs) on a cobalt‐iron (Co‐Fe) catalyst supported on a calcium carbonate (CaCO 3 ) substrate, contained within a fluidized bed was investigated for the first time. CaCO 3 supported catalysts, prepared using traditional wet impregnation techniques result in a soft and sticky powder requiring special arrangements to ensure satisfactory fluidization. A modified method developed using citric acid complex resulted in CaCO 3 supported catalysts that can be classically fluidized without special arrangements. The issue of Fe 3+ (aq) hydrolysis above its critical pH of ∼3.5 was also addressed. A carbon yield consistently greater than 10 times the weight of the catalyst metal loading was obtained. Thermogravimetric analysis coupled with mass spectrometry showed a single peak centered on 575°C, with no peaks below 400°C, indicating that an insignificant quantity of amorphous carbon was present. Transmission electron microscopy verified that the products contained a large proportion of CNTs. © 2008 American Institute of Chemical Engineers AIChE J 2008