Multi-layered carbon nanotubes (CNTs) have been successfully synthesized by using the catalytic chemical vapor deposition over Ni-and Co-supported CaCO3 catalysts at different reaction temperatures in a fluidized bed reactor. The as-grown CNTs were characterized by N-2 physisorption, high-resolution transmission electron microscopy, and X-ray diffraction. The CNT products are found to be mainly mesoporous, i.e., mesopore fraction: 84-92%. After chemical-wet purification, the CNTs appear as a multi-layered crystalline structure and their layer numbers show an increasing trend with growth temperature according to the calculation of Debye-Scherrer's equation. Through the calculation of Arrhenius plots, the apparent activation energies are found to be 104.6 kJ mol(-1) for Ni-catalyst and 61.6 kJ mol(-1) for Co-catalyst. Additionally, a linear relationship between the growth rate and the partial pressure of acetylene indicated that the reaction order of CNT growth is of first order in the fluidized bed reactor. (C) 2008 Elsevier B.V. All rights reserved.