High-temperature CO2 capture and in-situ conversion over bifunctional Na2ZrO3 self-catalyst/sorbent for circular CO production
CO 2 capture and utilization to produce value-added fuels and chemicals offers a promising avenue to assist in the mitigation of the global warming crisis. However, there are economic challenges for the regeneration of some sorbents used in CO 2 capture, owing to sorbent sintering and high energy requirements, while direct conversion processes are hindered by the lack of cost-effective, efficient, selective, and stable catalysts. We demonstrate the use of sodium zirconate-looping (NaL) with the reverse-Boudouard (RB) reaction enabling high-temperature CO 2 capture and in-situ CO 2 conversion operating in a single isothermal reactor operating at 800 °C. While employing a mild combustion synthesis method, the dual-function material Na 2 ZrO 3 exhibited a high and stable CO 2 uptake capacity of 4.9 mmol CO 2 /g without the use of Ni catalysts. This is due to its fine particle size, macroporous structure, and well-dispersed ZrO 2 stabilizer within the Na 2 O matrix. The resulting Na 2 CO 3 -ZrO 2 and regenerated Na 2 ZrO 3 phases (as synergistic self-catalysts) mixed with renewable and cost-effective biochar (as a reductant) facilitated exceptional in-situ CO 2 conversion efficiency (~90 %), as well as high CO selectivity (approaching 100 %), and relative stability (~80 %) even after multiple cycles. Importantly, theoretical calculations aligned with mechanistic studies revealed that the activation energy barriers at two specific oxygen sites for the monatomic C-assisted CO 2 dissociation/gasification were lower than the desorption energy of CO 2 on the Na 2 ZrO 3 (101) surface, demonstrating the self-catalytic mechanism. Thus, this cost-effective and energy-efficient strategy provides a compelling prospect to make local emissions from large stationary sources CO 2 neutral without requiring carbon sequestration.
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