A multi-scale analysis of the diffusion and reaction in the catalyst coating of a reformer is done based on virtual reconstructions of the porous catalyst coating. Pore structure can have significant impact on reaction and transport processes in the catalyst coating and consequently on the reformer performance. In this work, tomography-based simulation of the methane steam reforming in the microstructure of a nickel-alumina spinet coating is presented. X-ray nano-and micro-computed tomography are done to reconstruct the catalyst pore structure at different length scales and to consider the effect of both intra-and inter-particle pores on the reacting flow in the coating. Results of the reacting flow simulation in the coating microstructure based on tomographic imaging are compared with the simulation using numerically reconstructed microstructure based on a random packing of spheres with similar morphological characteristics. The comparison shows that the rate of hydrogen production, in general, is higher in the particle packing due to better inter-particle pore connectivity. (C) 2015 Elsevier Ltd. All rights reserved.