We studied the carbonization mechanism of tetrapropylammonium-hydroxide (TPAOH) carbon precursors in the channels of AlPO-5 crystal, with the aim of producing higher-density and better-quality 4 A carbon nanotubes. The conversion process of TPAOH was investigated by using a combination of Fourier transform infrared (FTIR) spectra, mass spectrometry, and micro-Raman spectroscopy under various pyrolysis temperatures. During the pyrolysis process, the TPAOH molecules decomposed into lighter amines with the abstraction of propylene, with the stepwise formation of tripropylamine, dipropylamine, and n-propylamine. This leads to the formation of 0.4 nm single-walled carbon nanotubes (SWNTs) at about 723 K. The SWNTs density was found to be higher than that resulting from the carbon precursor of tripropylamine (TPA), because of the larger number of carbon atoms in the unit cell. Thermogravimetry (TG) measurements also indicated a higher loading density (in AlPO-5 crystals) for the TPAOH carbon precursors. © 2006 American Chemical Society.