Mono-(Co) and bimetallic (Fe-Co) catalysts supported by either 13X zeolite or CaCO3 were doped with potassium and tested in carbon nanotube (CNT) production using the chemical vapor deposition (CVD) method. In order to increase comparability, the evaluation of the performance of the catalysts a combinatorial arrangement was also used. Catalyst samples were characterized by carbon deposit and carbon yield values. For qualitative characterization, products were investigated by transmission electron microscopy. (C) 2008 Elsevier B.V. All rights reserved.