Heterojunction-redox catalysts of FexCoyMg10CaO for high-temperature CO2 capture and in situ conversion in the context of green manufacturing

The integration of carbon capture and CO2 utilization could be a promising solution to the crisis of global warming. By integrating calcium-looping (CaL) and the reverse-water-gas-shift (RWGS) reaction, a hightemperature CO2 capture and in situ conversion technology is successfully realized in one fixed-bed column at the same operating temperature of 650 degrees C. Inspired by the heterojunction photocatalytic mechanism, the heterojunction-redox catalysis strategy is proposed for the first time by doping the bimetallic Fe3+/Fe2+ and Co3+/Co2+ redox couples into a hierarchical porous CaO/MgO composite. The presence of different valence states of doped Fe and Co oxides not only provides extra oxygen vacancies to facilitate CO2 adsorption, and hence adsorption enhanced conversion (AEC), but also significantly lowers the electric potential difference of Fe3+/Fe2+ through the newly formed Fermi level in Fe5Co5Mg10CaO, which makes electron spillover easier to improve the catalytic activity in the RWGS reaction for CO2 conversion. More importantly, with the hightemperature refractory MgO and the highly disperse Fe and Co oxides in Fe5Co5Mg10CaO, the problem of CaO sintering is successfully solved. An excellent and stable high-temperature CO2 capture capacity of 9.0-9.2 mmol g(-1), an in situ CO2 conversion effeciency near 90% and a CO selectivity close to 100% are achieved in the integrated CaL/RWGS process. In addition, experimental and simulation scale-up studies further demonstrate its pratical scalability. Economic evaluation reveals that the integrated CaL/RWGS technology is much more cost-effective than the individual CaL and RWGS processes. Therefore, the heterojunction-redox strategy provides a unique way to design bifunctional adsorbent/catalyst materials. The integrated CaL/RWGS process could be a promising technology for CO2 capture and utilization.