Experimental study of Ce0.8Zr0.2O2-δ pellets as high-performance oxygen carriers for counter-current chemical looping reverse water-gas shift reaction

The reverse water-gas shift (RWGS) reaction is an attractive route for converting CO2 and renewable H2 into syngas, a key intermediate to produce sustainable chemicals and hydrocarbon fuels. However, conventional RWGS is limited by thermodynamic equilibrium, and generally requires high operating temperatures or excess H2 to achieve high CO2 conversion.,In this work, a counter-current chemical looping reverse water-gas shift (CL-RWGS) process was investigated in a lab-scale packed-bed reactor containing 60 g of 1-2 mm non-stoichiometric fluorite-type oxide (Ce0.8Zr0.2O2-δ, CZO82). Its reversible oxygen-exchange capacity, combined with counter-current operation, enabled CO2 conversions beyond the equilibrium limit of conventional RWGS. At a bed temperature of 820 °C and an H2/CO2 molar ratio of 1, the conversion of both H2 and CO2 exceeded 90%, compared with the equilibrium-limited conversion of approximately 50% for the conventional RWGS reaction. Near complete CO2 conversion with complete CO selectivity was also achieved at 620 °C by increasing the H2/CO2 molar ratio to 3. Unreacted H2 can be recovered following H2O condensation and blended with the CO product to obtain syngas with a composition tailored for downstream methanol or Fischer–Tropsch synthesis. After more than 100 redox cycles, characterisation of the recovered CZO82 pellets confirmed the retention of the fluorite crystal structure, with only minor crystallite growth and no measurable loss in oxygen exchange capacity. These results demonstrate the excellent stability of CZO82 and highlight the potential of the counter-current CL-RWGS process for future pilot-scale demonstration and integration with sustainable chemical and fuel production.