Preparation of carbon nanotubes from CO and in situ formed nano-sized Pd particles

Carbon nanotubes, typically of 0.5-mu m length and 20-nm diameter, were prepared with good selectivity by disproportionation of CO in He over a Pd/La2O3 catalyst. The catalyst was formed in situ by reduction of a La4PdO7 precursor. The obtained nanotubes had the so-called fishbone structure with the graphitic planes inclined at an angle to the long axis of the nanotube. The effect of CO concentration was studied at 673 degrees C, and it was found that, among the concentrations studied, 20 vol% CO in the gas was suitable for nanotube growth. The obtained nanotube/La2O3/Pd composite contained typically only 3 wt% nanotubes after 8 h of CO treatment. A process for selective dissolution of La2O3 and Pd was applied, and a product containing 85 wt% nanotubes was obtained. The nanotubes were characterized by high-resolution, transmission, and scanning electron microscope studies, combined with element analyses using energy dispersive spectrometers, x-ray powder diffraction studies, and thermogravimetric analysis.