Synergistic effects of CeO2 and Al2O3 on reactivity of CaO-based sorbents for CO2 capture

Abstract

The calcium looping (CaL) process, comprising reversible calcination and carbonation reactions with CO2 and CaO-based sorbents, stands out as a highly promising industrial approach for CO2 capture. A significant challenge, however, is the swift degradation of the reactivity of CaO-based sorbents. In this study, CeO2-stabilized and CeO2/Al2O3 co-stabilized CaO-based sorbents were produced via a Pechini technique. Results indicated that incorporating CeO2 enhanced the CO2 sorption performance of CaO-based sorbents. The most effective CeO2-stabilized CaO-based sorbents (a CeO2/CaO mass ratio of 15:85) demonstrated an initial sorption capacity of 0.479 gCO2/gmaterial, undergoing a 41% reduction in its initial reactivity by the 20th cycle. To enhance CO2 sorption stability and reduce the high cost linked with the expensive cerium precursor, Al2O3 was introduced as the second stabilizer into the CeO2-stabilized CaO-based sorbents. When the CeO2/Al2O3/CaO mass ratio was adjusted to 5:10:85, the CO2 sorption capacity of CeO2/Al2O3 co-stabilized CaO-based sorbents reached 0.354 gCO2/gmaterial in the 20th cycle. This represented only a 17.7% reduction in its initial performance, surpassing the CeO2-stabilized counterpart by 26.3%. Comprehensive characterizations, including scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), and electron paramagnetic resonance (EPR), revealed that incorporating Al2O3 into the CeO2-stabilized CaO-based sorbents served a dual purpose: acting as a stable framework to inhibit pore structure deterioration and increasing the concentration of oxygen vacancies. In consequence, the synergistic effect of CeO2 and Al2O3 improved both structural stability and oxygen vacancy concentration of the sorbents, ultimately leading to superior CO2 sorption performance.