Thermal management of CO2 methanation with axial staging of active metal concentration in Ni-YSZ tubular catalysts

CO2 methanation has attracted considerable interests as a promising approach to productively utilizing CO2 and reducing emissions to realize a low-carbon society. One major difficulty with packed bed reactors for catalyzed CO2 methanation is maintaining an optimal reactor temperature distribution. Although a high temperature increases the catalytic activity, it also leads to the formation of an inlet hotspot, which causes thermal runaway, unfavorable equilibrium products, and catalyst degradation. To address this, in this study, we proposed an approach to manage the temperature profile in CO2 methanation reactors by increasing catalytic activity along the reactor length using different Ni composition catalysts (gradient-distributed Ni-YSZ catalyst). Ni-based tubular catalysts with different Ni compositions were prepared and stacked in order of ascending Ni content from the inlet to the outlet. The effect of gradient Ni compositions on the temperature profile was investigated based on both numerical simulations and experimental observations. The gradient-distributed Ni catalyst could successfully prevent hotspot formation at the inlet of the reactor compared to the highly active uniform catalysts. The use of the catalyst caused a small difference in the reactor temperature (of ~70 °C) and afforded a high CH4 yield (~90%). The proposed approach using gradient-distributed catalysts could be a potential method to manage CO2 methanation reactor temperature and to achieve high CO2 conversion in compact reactors.