In a reactor with a porous catalyst on a channel wall, the local reaction rate and composition cannot be easily measured. This study built a model for evaluating the overall reaction rate by predicting the distribution of the concentration of chemical species in a porous catalyst as well as in a gas stream. Prior to taking into account the streamwise distribution, the validity of the function of the concentration profile in steam methane reforming, which is one-dimensional to the thickness direction of catalyst, was confirmed by comparison with the results of an experiment. Next, the model was coupled with the streamwise variation in the concentration. Consequently, we derived a model in which the local concentration can be specified at any position with the concentration at the inlet of the channel as the only input variable. Finally, a criterion for the condition in which the maximum yield of products can be obtained with the minimum volume was proposed with nondimensional groups. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.