Carbon nanotubes and onions from methane decomposition using Ni/Al catalysts

Ni/Al catalysts with different Ni concentrations have been used successfully for the synthesis of carbon nanotubes and onions from methane by chemical vapor deposition. The catalyst nanoparticles were produced by a deposition–precipitation method, and the carbon products by the catalytic decomposition of methane at 600 °C. Carbon nanotubes (CNTs) were formed in the presence of a Ni/Al composite catalyst containing 20 wt.% nickel. The CNTs were multi-walled, 10–20 nm in diameter and up to 15 μm long. Hollow carbon onions were produced in the presence of a Ni/Al composite catalyst containing 80 wt.% nickel. The carbon onions were from 5 to 50 nm in diameter and consisted of several concentric carbon layers surrounding a hollow core. The mechanisms for the formation of both the CNTs and carbon onions were discussed on the basis of the experimental results.