Material engineering of porous calcium oxide for boosting CO₂ capture

Isothermal calcium looping is a promising process to realize the integration of CO₂ capture and in-situ conversion — a next-generation carbon reduction technology. However, low isothermal carbonation-calcination activity and sintering-induced deactivation of the CaO-based CO₂ sorbents impede its further development. Herein, we adopt material engineering strategy to construct a MgO-incorporated CaO framework featuring hierarchically porous morphologies assembled by nano grains, where the high dispersion of Mg²⁺ species is critical to form and stabilize the porous structure. Combined advanced and in-situ characterizations reveal that small crystallite size, large specific surface area, and sufficient porosity are all indispensable to boost CO₂ capture capacity of the CaO-based material in isothermal carbonation-calcination cycles. The optimized material, possessing less than 25 nm of CaO crystallite, 69 m²/g of specific surface area and large volume of meso- and macro-pores, not only accomplishes a high CO₂ uptake (0.57 g/g) in the fast kinetics-controlled carbonation stage but also retains 95 % of the total capture capacity after more than 40 cycles at 650 °C — the lowest operating temperature for calcium looping process to date — superior to most reported MgO-stabilized CaO-based materials in terms of CO₂ capture activity and cyclic stability.