Catalytic effect of metal cations on the formation of carbon nanotubes inside the channels of AlPO4-5 crystal

Single-walled 0.4 nm carbon nanotubes (SWNTs) were fabricated using various metal cation substituted AlPO4-5 (MeAPO-5) molecular sieves as the template. The catalytic behavior varies with different metal incorporation. The incorporation of metal cations (Mn, Mg, Co) and Si gives rise to the formation of negatively charged frameworks and Brønsted acid sites. These frameworks thus play an important catalytic role in the pyrolysis and conversion of the organic molecules to SWNTs within the crystal channels. It is shown that the MeAPO-5 single crystals have a higher density of SWNTs than those crystals without the metal cations. The experimental results agree with the predictions of first-principles calculations, which show the metal-incorporated frameworks to be favorable for the SWNTs formation.