The dynamic performance of a reformer as a incorporating the catalyst deactivation at the reactor level is modelled by accounting a theoretical coking model. This model incorporates the effect of coke deposition on catalyst activity, diffusion resistance of reactants, and subsequently catalyst pore blockage. The influence of catalyst fouling on the conversion of the product of interest has been illustrated by coupling a rate equation for the formation of coke to the continuity equation for the main products. The transient coke uptake curves are shown to have two regions of kinetics controlled and diffusion controlled through internal effectiveness factor. The implications of varying pore size on the reactor performance through such curves are discussed. It is shown that small pore size (high surface to volume ratio) is not always efficient owing to rapid plugging. The energy intensive endothermic reaction system is coupled with an exothermic reaction to improve the thermal efficiency. The effect of this coupling on the coke formation and its implications on reactor performance is discussed incorporating the switching of species flow direction (co-flow and counter-flow) in combustion section. This modelling effort is unique is elucidating the spatial distribution of catalytic activity in a reformer, evolving owing to varying rates of local catalyst deactivation. Moreover, the simultaneous variation of catalyst activity and effective diffusivity have been modelled, which has never been investigated in the past. Conclusions from this work counter the often-maintained belief that enhanced heat transfer always enhance the reformer performance. We expect the broad conclusions of the modelling effort to direct future catalyst development. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.