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 pre pared with good selectivity by disproportionation of CO in He over a Pd/La2 O3 catalyst. The catalyst was formed in situ by reduction of a La4PdO7 prec ursor. The obtained nanotubes had the so-called fishbone structure with the graphitic planes inclined at an angle to the long axis of the nanotube. Th e 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 ty pically only 3 wt% nanotubes after 8 h of CO treatment. A process for selec tive dissolution of La2O3 and Pd was applied, and a product containing 85 w t% nanotubes was obtained. The nanotubes were characterized by high-resolut ion, transmission, and scanning electron microscope studies, combined with element analyses using energy dispersive spectrometers, x-ray powder diffra ction studies, and thermogravimetric analysis.