Passive thermal regulation using a phase change material for chemical-loop reverse water–gas shift reaction

Abstract

The chemical-loop reverse water–gas shift reaction (CL-RWGS), a two-step CO₂ hydrogenation process where H₂ oxidation and CO₂ reduction occur, can overcome the equilibrium limitations of the RWGS reaction and achieve high CO₂ to CO conversion efficiencies. When this process is performed in a fixed-bed reactor, the oxide undergoes continuous in situ exothermic and endothermic reactions accompanied by severe temperature fluctuations that decrease the gas conversion efficiency. Therefore, the introduction of thermal regulation technology is of particular importance in the CL-RWGS. In this context, alloy-based microencapsulated phase-change material (MEPCM) are promising thermoregulating media owing to their high latent heat density and chemical stability, which enable thermal regulation through phase changes at a constant temperature. Herein, we propose a heat-storing functional oxygen-storage material based on the use of MEPCM supports. The prepared Fe₂O₃/Al-MEPCM achieved a high latent heat (137 J/g) and a good CO production rate (224 µmol/g min⁻¹). After 50 redox cycles, the oxygen storage capacity of the Fe₂O₃/Al-MEPCM remained above 75 %, and the Al-MEPCM served as a physical barrier to prevent sintering. Furthermore, temperature evaluations in the H₂ reduction mode using Fe₂O₃/Al-MEPCM showed that the temperature decreased by ∼ 80 °C in the absence of latent heat, whereas it remained constant at ∼ 640 °C in the presence of latent heat. Moreover, the latent heat (∼2940 J) was sufficiently large compared to the heat absorption (∼1809 J). The strategy of combining MEPCMs and oxygen storage materials for thermal regulation of the CL process therefore appears to have great potential for application in industrial processes.