Carbon nanotubes (CNTs) were synthesized in a catalytic reaction over an iron catalyst using CaCO3 as a support. The purification of the carbon nanotubes (CNTs) and the oxidation of the CNTs surfaces were performed with HNO3. Iron-based catalysts supported on carbon nanotubes for use in the Fischer-Tropsch (FT) reaction were prepared either by incipient wetness or a deposition precipitation method using urea and then promoted with potassium and/or copper. The FT synthesis was carried out in a fixed-bed micro reactor (275 degrees C, 8 bar, CO/H-2 = 2). The effect of Cu and promoters on CO conversion, product selectivity and FT synthesis activity were investigated and compared with data reported on other carbon-based supports. The potassium promoted catalysts gave higher yields of CO2 and C-2 olefins and the lowest methane selectivity when compared to the unpromoted catalysts. Copper, while enhancing catalyst activity, did not have an effect on the FT product selectivity. (c) 2005 Elsevier B.V. All rights reserved.