This research presents a multi-scale analysis of the transport and reaction processes in the catalyst coating of a reformer to optimize the catalyst coating microstructure for methane steam reforming. A multi-scale methodology is developed to incorporate and analyze the effect of the catalyst coating morphology on the performance of a wall-coated reformer, based on hypothetical catalyst structures generated using an in-house particle packing code. The results show the significant effect of intra-particle and inter-particle porosity as well as particle size on the rate of hydrogen production in the coating. This study also shows that an optimal catalyst coating has decreasing porosity along the reformer length based on the difference in the degree of diffusion limitation. The results of the multi-scale analysis based on random particle packing are compared with the analysis based on the real catalyst coating pore structure obtained from nano- and micro-computed tomography. The comparison shows that despite similar morphological characteristics and transport properties, the rate of hydrogen production in the packing of overlapping spheres is higher than the rate in the real catalyst structure. This result also shows that by making a structured catalyst coating with a tailored pore network, the performance of the coating improves significantly. Based on the assumption that a structured catalyst coating can be represented by a random packing of spheres, a systematic parametric study is done using response surface methodology and Latin hypercube design of experiment to optimize the catalyst coating microstructure.