A series of silica supported Fe catalysts were prepared by different methods in order to obtain varying Fe particle sizes. The catalysts were characterized by XRD, TPR, BET, and TEM. The CNT growth from CO disproportionation was studied in order to establish a relationship between the CNT growth rate and the particle size. We found that there is an optimum catalyst particle size at around 13-15 nm which will lead to the maximum growth rate. The influence of the metal loading on the growth rate was also investigated. A CNT growth model has been formulated to explain the experimental results. (c) 2004 Elsevier B.V. All rights reserved.