In the iodine-sulfur (I-S) thermochemical process for hydrogen production, the most endothermic high temperature step is the sulfuric acid decomposition which is catalytic process. Here, we introduce a model-based framework to address the effect of model uncertainty on catalyst identification, designing and optimization. To investigate the kinetic parameters, the experiments are performed in the packed bed reactor under the conditions of diffusion free regime. Further, the kinetic model is implemented in a two-dimensional heterogeneous model of the catalytic packed bed reactor developed in Multiphysics software in order to investigate the effects of catalyst composition, support material, catalyst pellet shapes, sizes (i.e., diffusional length), pellet intrinsic properties (i.e., porosity and thermal conductivity) and temperature on the catalyst effectiveness factor. The 7-hole cylindrical shapes with 0.75 and 1.5 mm principle dimension at 1073 K has been found to have negligible diffusional limitation and temperature gradients across their cross sections. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.