In this study, a simple method for the addition of Cu to unsupported nickel nanoparticles is employed to investigate the promotion effect of copper during the nickel-catalyzed decomposition of methane into carbon nanotubes. Bulk nickel and copper acetates were mixed by grinding the parent salts in a mortar, to obtain samples with selected Ni/Cu atomic ratios (NiCu(0.03), NiCu(0.07) and NiCu(0.16)) that were decomposed in situ on methane streams using a thermogravimetric analyzer (TGA). Weight increase was related quantitatively to the production of carbon nanotubes by catalytic cracking of methane, and the materials were complementary characterized ex situ by electron microscopy. The results suggest that copper most likely induces the disaggregation of nickel particles during the course of the catalytic cracking, but copper by itself was not effective to improve quantitatively the production of carbon nanotubes. In spite of very low methane conversions, good quality multiwalled carbon nanotubes are obtained and characterized by HRTEM. (C) 2009 Elsevier B.V. All rights reserved.