In terms of tons per day SO3 is one of the most important chemicals in the world. It is produced via the contact process in a gas phase catalytic oxidation reaction. The contact process consists of multiple catalyst beds, inter-stage cooling and an absorption step in the case of sulphuric acid production. Transferring this process to a microstructured reactor with its unique heat and mass transport properties should make it possible to develop a small scale one pass synthesis well suited for on-site SO3 production, e.g., for surfactant making. In a test reactor experiments were performed with different molar ratios of sulphur dioxide to oxygen, hydrodynamic residence time and reaction temperature. Numerical simulations with ANSYS FLUENT 12.0 were performed for a single channel configuration. For this purpose a detailed model of the flow, the heat distribution and the surface chemistry was used. For the surface chemistry a detailed kinetic model based on elementary steps occurring on the catalyst surface was used. The assumed multi-step mechanism involves coordination of SO2 on two surface sites. The simulations are compared to the experimental results. Good agreement between the model predictions and the experimental results is achieved. A sensitivity analysis was performed to get an idea of the rate determining steps. (C) 2011 Elsevier B.V. All rights reserved.