This work investigates the synthesis of multilayered carbon nanotubes (CNTs) using the catalytic decomposition of acetylene at 700-850 degrees C over Fe- and Ni-supported Al2O3 catalysts in a fluidized bed reactor. Thermogravimetric analysis showed that the CNTs grown in a fluidized bed reactor have better thermal stability and higher production yield. compared to that in a fixed bed reactor. The CNT production yield increased with the growth temperature, and Fe-catalyst exhibited greater activity than Ni-catalyst in the formation of CNTs. According to Arrhenius plots, the apparent activation energies for the growth of CNTs were estimated to be 25.6 kJ/mol for Fe-catalyst and 65.6 kJ/mol for Ni-catalyst. The as-grown CNT products were characterized by high-resolution transmission electron spectroscopy, N-2 physisorption, Raman spectroscopy, and X-ray diffraction. After purification, the CNT products were of the multilayered type, which were composed of perfect graphene layers. The results of this study demonstrate that the fluidized bed technology favors the large-scale production of CNTs with uniformity and at low cost. (c) 2008 Elsevier B.V. All rights reserved.