Applied Catalysis A: General 229 (2002) 229–233 Heterogeneous catalytic production and mechanical resistance of nanotubes prepared on magnesium oxide supported Co-based catalysts I. Willems a,∗ , Z. Kónya b , A. Fonseca a , J. B.Nagy a a Laboratoire de Résonance MagnétiqueNucléaire, Facultés Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, Belgium b Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Bela ter 1, H-6720 Szeged, Hungary Received 19 June 2001; received in revised form 1 September 2001; accepted 10 September 2001 Abstract MgO-supported catalysts are used to produce high yield carbon nanotubes with few walls by the catalytic decomposition of acetylene. Low and high resolution transmission electron microscopy (TEM and HRTEM, respectively) reveals that the tubes possess many irregularities in their wall structure and that they appear as aggregates. The outer diameter of the multi-wall carbon nanotubes (MWNTs) obtained by this procedure is in the order of 5–10 nm while the inner diameter is less than 4 nm. Their resistance strongly depends on the post-synthetic treatments made upon them. Raw material obtained after synthesis is insensitive to ball-milling and tubes remain packed. The same feature appears after grinding the sample, treated with a concentrated acid in order to remove the support and the catalytic metal particles. The easy breaking of the tubes occurs after specific treatment of the sample. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Carbon nanotubes; CCVD technique; Heterogeneous catalysis 1. Introduction Since their discovery in 1991 [1], carbon nanotubes are generating a continuously growing interest. These hollow nanostructures have exceptional electrical [2] and mechanical [3] properties making them usable in many fields. Various production methods have been developed aiming at producing carbon nanotubes in large scale and at low costs, but also at controlling their characteristics and morphologies. Of the main synthetic processes, laser vaporization [4], electric arc discharge [5] and chemical deposition of hydro- carbons over metal catalysts (CCVD technique) [6], ∗ Corresponding author. E-mail address: isabelle.willems@fundp.ac.be (I. Willems). only the latter method supplies carbon nanotubes in high yield at a low cost of production. Being a cat- alytic process, the combinations of transition metals and supports can be changed depending on the char- acteristics required, for example the alignment [7] or the size of the tubes [8,9]. Nevertheless, it is im- portant to keep in mind that the separation of carbon nanotubes from the support should be made easily. In this work, we studied the influence on the syntheses of a variety of transition metal catalysts supported on magnesium oxide (MgO) because of its easy removal by acidic treatment. Well-dispersed metal particles supported on MgO were already used to synthesize single-wall nano-tubes in high yield [10,11]. We re- port the synthesis of multi-wall carbon nanotubes (MWNTs) having only a few walls. We also present 0926-860X/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0926-860X(02)00030-3