CO₂ activation by methane in a dual-bed configuration via methane cracking and iron oxide lattice oxygen transport - Concept and materials development

In this work we describe a novel process configuration for CO₂ activation into CO via methane cracking. This is achieved in a two-reactor configuration by circulating supported iron oxide/iron particles with deposited carbon between the two reactors. Thermodynamic equilibrium calculations indicate that reactor configurations with counter-current gas-solids flow enable a high CO yield and concentration in the product gas. With both reactors in counter-current flow at 850 °C the potentially achievable production of CO is estimated at 3.7 mol CO per mol of CH₄ with 84% purity in endothermal operation and 2.7 mol CO per mol of CH₄ with 88% purity in autothermal operation. Fe/support composite materials are developed for this application to fulfill the function of oxygen transport between the two reactors and serve as a substrate for solid carbon formation. Fe/BaZr_0.9Y_0.1O_3−δ (BZY) composites exhibit rapid reduction kinetics with H₂ that we ascribe to mixed-ionic-electronic conduction imparted by in-situ iron doping of the BZY support. In addition, the high proton conductivity of this support results in high CH₄ decomposition rates to form solid carbon and hydrogen, likely due to the acceleration of hydrogen abstraction from the methyl group on its surface. This mixed conductivity thus results in unique properties that can be exploited in such CH₄ decomposition process configurations.