Highly endothermic (or exothermic) heterogeneous catalytic reactions are performed commonly in Fixed bed reactors with small tube-to-particle-diameter ratios N both in industrial and lab scale applications. For these reactor configurations conventional plug How models and pseudo homogeneous kinetic models fail. An adequate modeling can be carried out with full computational Fluid dynamics (CFD) in combination with detailed reaction mechanisms. In this study, a full three-dimensional fixed bed reactor for the catalytic dry reforming of methane (DRM) over rhodium was simulated with a detailed reaction mechanism. The bed consists of 113 spherical solid particles in which thermal conductivity was considered. Two different Reynolds numbers were investigated, i.e., 35 and 700. The simulated DRM fixed bed reactor demonstrates the strong interaction between chemical kinetics and transport of momentum, heat and mass. The observed velocity, temperature and species fields are characterized by their three-dimensional behavior and interactions highlighting their complexity and discrepancy from lumped model predictions. In addition, the reaction mechanism determines regions with catalyst deactivation by carbon deposition. This study demonstrates the advantages of modeling heterogeneous catalytic fixed bed reactors with small N fully in three-dimensional in combination with detailed reaction mechanisms. Finally, this modeling approach reduces dependencies on empiricism for the calculation of multiscale reaction devices. (C) 2014 Elsevier Ltd. All rights reserved.