The present work describes the development of a two-dimensional mathematical model of a pilot-scale fixed-bed reactor for Fe-based Fischer-Tropsch synthesis to evaluate the effect of tube diameter on temperature profile and catalyst performance. The entire chain lengths of the hydrocarbon products were lumped to form several representative components, and the apparent kinetic parameters for the reaction rates were estimated. The effectiveness of the developed model was corroborated by the comparison of temperature profiles, conversion, and selectivities between experimental and simulated results. The increase of tube diameter in the simulation showed that temperature increased in both the radial and the axial directions owing to the low radial heat transfer rate and the low heat transfer area, respectively. Finally, the specified diameter in the present study maintained the temperature below the threshold value and the methane selectivity below 10%. (C) 2014 Elsevier Ltd. All rights reserved.