A multidimensional heterogeneous and dynamic model of a fixed-bed heat exchanger reactor used for CO 2 methanation has been developed in this work that is based on mass, energy and momentum balances in the gas phase and mass and energy balances for the catalyst phase. The dynamic behavior of this reactor is simulated for transient variations in inlet gas temperature, cooling temperature, gas inlet flow rate, and outlet pressure. Simulation results showed that wrong-way behaviors can occur for any abrupt temperature changes. Conversely, temperature ramp changes enable to attenuate and even fade the wrong-way behavior. Traveling hot spots appear only when the change of an operating condition shifts the reactor from an ignited steady state to a non-ignited one. Inlet gas flow rate variations reveal overshoots and undershoots of the reactor maximum temperature.2) Wall thermal conductivity, k w (stainless steel) 17 W m 21 K 21 Catalyst thermal conductivity, k s 9 0.87 W m 21 K 21 Catalyst particle density, q s 58 1274 kg m 23 472

A simulation model of a fixed‐bed reactor‐exchanger dedicated to CO2 methanation on an industrial Ni/γ‐Al2O3 catalyst has been built on the basis of experimental characterization of heat transfer and kinetic parameters. An effective thermal conductivity of the bed and a wall heat transfer coefficient are determined from cooling experiments of different Ar‐H2 mixtures (thermal conductivity 0.02–0.25 W · m−1 · K−1) at different Reynolds numbers (particle Reynolds number 1–50). The flow dependent component of the Nusselt number correlates to the gas Prandtl number as Pr0.72. These heat transfer parameters and a kinetic model adapted to the Ni/γ‐Al2O3 catalyst are integrated in mass, heat, and momentum balance equations in the bed and at the particle scale to build a 2D heterogeneous model of the fixed‐bed reactor. CO2 methanation experiments in an annular fixed‐bed reactor‐exchanger filled with 400 g of Ni/γ‐Al2O3 catalyst at pressures from 0.4 to 0.8 MPa and coolant temperatures from 473 to 548 K (200 to 275 °C) are described in this paper and simulated by the model. CO2 conversion rate and CH4 selectivity at the reactor outlet and temperature elevations in the reactor are simulated by the model with a discrepancy lower than 10 %. For pressures above 0.4 MPa, a strong mass diffusion limitation inside the catalyst particles is shown and the efficiency decrease of the three reactions is explained.