Ni promoted Fe-CaO dual functional materials for calcium chemical dual looping

Reverse water-gas shift reaction using renewable H-2 is a promising route for CO2 upgrade, however, it is restricted by the equilibrium. The chemical looping reverse water-gas shift reaction using oxygen carriers (i.e. Fe) has proven a more effective CO2 utilization process to produce CO. However, CO2 with high purity is needed to obtain concentrated CO. Herein, we propose a calcium chemical dual looping using one-pot sol-gel synthesized Ca-Fe dual functional materials (DFMs). The CO2 in the exhaust gas (similar to 10% CO2) can be captured and transformed into carbonates and then in-situ converted into CO through continuous chemical looping in H-2 atmosphere. This process avoids CO2 enrichment, storage and transportation and simultaneously realizes efficient CO2 conversion. The Ca-Fe DFMs possessed significantly improved catalytic efficiency (enhanced real-time CO generation rate) compared to CaO. It is found that Ni1Fe9-CaO could optimally achieve 11.3 mmol g(DFM)(-1) CO yield, 82.5% CO2 conversion and 99.9% CO selectivity at 650 degrees C. Notably, Ni1Fe9-CaO displayed high CO2 conversion (>80%) and CO selectivity (>99.9%) during the cycle tests and possessed enhanced stability in relation to CO yield after 10 cycles (20.9% and 35.5% decrease for Ni1Fe9-CaO and CaO, respectively). Herein, Ca2Fe2O5 plays two roles: acting as an oxygen carrier for in-situ chemical looping to produce CO and a thermally stable physical barrier to retard the sintering of CaO. It is noted that Fe-related species could be reduced into the metallic state at the end of hydrogenation, resulting in CO formation in the following CO2 capture process.

Automated summary

Using Ca-Fe dual functional materials for chemical dual looping can convert CO2 in exhaust gas to CO, avoiding CO2 enrichment, storage, and transportation, achieving efficient CO2 conversion. This method has high catalytic efficiency and stability.