New insights into stabilizing mechanism of Ca9Al6O18 stabilizing Ca-based sorbents for CO2 cyclic capture under mild conditions

Developing calcium-based sorbents to capture and separate CO2 from high-temperature flue gas is currently a potential route to alleviate a series of environmental problems caused by excessive CO2 emissions. However, to date, there is a lack of in-depth understanding of the anti-deactivation mechanism of stable materials for CaO during the cyclic adsorption-desorption process, leading to difficulties in the rational design of Ca-based materials. Herein, a novel slow-precipitation strategy that enables the in-situ synthesis of Ca9Al6O18-stabilized Cabased sorbents for cyclic carbon capture is exploited. The adsorption parameters are systematically optimized and the structural evolution and chemical property changes of Ca9Al6O18 are monitored. Interestingly, we find that the deactivation of pure CaO mainly comes from the grain growth towards the bulk phase during the cyclic desorption process under mild calcination conditions, rather than the specific Tammann temperature of the substances. The introduction of Ca9Al6O18 exhibits strong spatial confinement on the growth of CaO grains, as well as optimizing the internal pore structure of the particles, ensuring high stable CO2 capacity for long-term cycling under mild conditions, with a decay of 0.35% per cycle. This new understanding provides effective structural engineering strategies for designing applicable Ca-based carbon capture materials.