This work is devoted to the investigation of a heat transfer inside a steam methane reformer filled with pre-heated Ni-based catalyst pellets of various shapes. A set of various pellets shapes were tested: spheres, cylinders and Raschig ring under various compositions of inlet steam-to-methane ratios. CFD-model was developed and realized via Ansys Fluent for heat transfer process investigation. The chemical kinetics model is based on experimentally derived reaction rate expressions taken from the literature. The distinguishing feature of the developed model is unsteady flow (transient) of reacting mixture over pre-heated Ni-based catalysts. This model allowed us to investigate the effect of endothermic chemical reactions on heat transfer between the catalysts and gas flow. Moreover, two cases were tested to understand the heat transfer in the reformer: the chemical reaction was switched on and switched off in the model. It was established that the heat transfer coefficient for a reacting flow (≈90W/(m²K)) is about twice higher than the heat transfer coefficient for a non-reacting flow.