Carbon nanotubes have been prepared by the catalytic decomposition of acetylene over Ni/Cr hydrotalcite-type anionic clay catalyst. Ni/Cr hydrotalcite-type anionic clay precursors have been prepared by co-precipitation technique. The role of stability of Ni nanoparticles obtained in situ from the decomposition of the catalyst oil the growth of MWNTs is discussed. The as-synthesized and purified carbon nanotubes are characterized by thermogravimetry, IR spectroscopy, X-ray diffraction, BET analysis, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy measurements. The hydrogen adsorption capacity of as-synthesized and purified multiwalled carbon nanotubes at 298 K has been obtained using a high-pressure hydrogen adsorption set-up and the results are discussed. (C) 2004 Elsevier B.V. All rights reserved.