Elucidating the enhanced CO2 capture in core-shell Al-Zr modified CaO adsorbent: origins in microstructure and oxygen vacancy

A novel core–shell CaO based adsorbent with Al-Zr co-modification was synthesized via a facile one-pot calcination method. The CO 2 capture capacity and long-term stability of the adsorbents with different Ca/Al/Zr molar ratios were investigated. The co-doping strategy significantly enhanced the CO 2 capture capacity of the calcium-based adsorbents. Specifically, the optimized Ca24Al1Zr0.3 adsorbent exhibited excellent CO 2 adsorption performance in long-term adsorption–desorption cycles, with the CO 2 capacity of 0.53 g-CO 2 /g-ads after 40 cycles. The synergistic effects of Al-Zr co-doping were analyzed from a microstructural perspective. The core–shell Ca24Al1Zr0.3 adsorbent with a CaZrO 3 outer shell featured minimized particle size, abundant mesoporous and macroporous structures, and uniformly distributed doping components. Under the combined effects of structural modification and metal doping, it manifested enhanced CO 2 capture capacity. Based on the CO 2 adsorption mechanism of CaO, this study revealed that Al-Zr co-doping promotes oxygen vacancy generation and improves CO 2 adsorption performance. The Ca24Al1Zr0.3 adsorbent demonstrated the highest oxygen vacancy content and the most pronounced positive shift in Ca 2p binding energy. This shift enhanced electron-donating capability of calcium, effectively facilitating O 2− migration and CO 2 diffusion. Furthermore, the Ca24Al1Zr0.3 adsorbent exhibited superior carbonation reaction kinetics during long-term cyclic operation.