A multi-scale, dynamic, two-dimensional, heterogeneous model for catalytic steam methane reforming (SMR) is developed. The model, derived from first principles, accounts for diffusional limitations for both mass and energy within large industrial-scale catalyst particles. The diffusional limitations have been incorporated, not by the conventional method of computing the effectiveness factor, but by accounting for the transfer of species as a function of the concentration and temperature gradients existing between the gas phase and catalyst surface along the reactor length. The model has been validated with available industrial steady-state data from literature. The model was then used to study the dynamic behaviour of key variables and the effects of feed disturbances on catalyst core and tube wall temperatures. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.