High yield synthesis of multi-walled carbon nanotubes by catalytic decomposition of ethane over iron supported on alumina catalyst

Ethane was successfully used as an active and efficient carbon source in a large scale synthesis of high quality carbon nanotubes by chemical vapour deposition (CVD) over Fe/Al2O3 catalyst with an iron loading of 20 wt.%. The multi-walled carbon nanotubes yield approaching 50 g per gram of catalyst per hour at 750 °C, which was among the highest yield reported today in the open literature. The active phase for growing carbon nanotubes is a mixture of a metastable iron carbide (Fe3C) and α-Fe which were formed in situ by the ethane dissociation followed by carbon diffusion through the starting α-Fe phase. The reaction products only contained multi-walled carbon nanotubes with very homogeneous diameters of around 30 nm and lengths up to several hundred nanometers without any trace of other impurities such as nanoparticles or amorphous soot. According to the observed results ethane is an active carbon source for growing multi-walled carbon nanotubes with high yield and selectivity. The reaction temperature should be keep ≤750 °C as synthesis carried out at 800 °C under similar reaction conditions led to the formation of amorphous soot and carbon nanoparticles mixed with nanotubes.