Improved CO2 capture performance of CeO2-doped CaO-based pellets: effects of particle size and steam treatment

Abstract

Rapid deactivation of CaO-based sorbents remains a major challenge for the calcium looping (CaL) process. Recently, CeO₂, known for its high Tammann temperature and abundant oxygen vacancies, has been extensively investigated for CaO-based sorbents to mitigate performance degradation. In this study, CeO₂-doped CaO-based pellets, prepared in a more industrially relevant form for the first time, were investigated. The incorporation of CeO₂ alleviated the negative impact of pelletization and particle size on performance. CeO₂-doped CaO-based pellets with different particle sizes (106–180, 180–250, 250–355, and 355–500 μm) exhibited nearly identical CO₂ capture performance, closely matching the reactivity of powdery CeO₂-doped CaO-based sorbents. Furthermore, the effects of two steam-based strategies—steam hydration and steam injection—on the reactivity of the CeO₂-doped pellets were explored. Hydration after the sixth calcination significantly enhanced the reactivity of CeO₂-doped CaO-based pellets. Hydration at 650 °C resulted in a conversion of 86.0% at the sixth cycle, surpassing the non-hydrated pellets by 55.4%. In contrast, steam hydration had minimal impact on the performance of undoped CaO-based pellets, indicating that CeO₂ greatly enhanced the improvement from steam hydration. The effect of steam injection was more complex and highly dependent on the steam concentration. Only a moderate steam concentration (10–15%) enhanced the reactivity, leading to higher carbonation conversions. With 10% steam during carbonation, the initial conversion surged to 93.8%, representing a 22.0% improvement over the counterpart without steam.

Keywords: CO₂ capture; Calcium looping (CaL); Stabilizer; Oxygen vacancy; Particle size; Steam.