Of Glasses and Crystals: Mitigating the Deactivation of CaO-Based CO₂ Sorbents through Calcium Aluminosilicates

CaO-based sorbents are cost-efficient materials for high-temperature CO₂ capture, yet they rapidly deactivate over carbonation-regeneration cycles due to sintering, hindering their utilization at the industrial scale. Morphological stabilizers such as Al₂O₃ or SiO₂ (e.g., introduced via impregnation) can improve sintering resistance, but the sorbents still deactivate through the formation of mixed oxide phases and phase segregation, rendering the stabilization inefficient. Here, we introduce a strategy to mitigate these deactivation mechanisms by applying (Al,Si)O_x overcoats via atomic layer deposition onto CaCO₃ nanoparticles and benchmark the CO₂ uptake of the resulting sorbent after 10 carbonation-regeneration cycles against sorbents with optimized overcoats of only alumina/silica (+25%) and unstabilized CaCO₃ nanoparticles (+55%). ²⁷Al and ²⁹Si NMR studies reveal that the improved CO₂ uptake and structural stability of sorbents with (Al,Si)O_x overcoats is linked to the formation of glassy calcium aluminosilicate phases (Ca,Al,Si)O_x that prevent sintering and phase segregation, probably due to a slower self-diffusion of cations in the glassy phases, reducing in turn the formation of CO₂ capture-inactive Ca-containing mixed oxides. This strategy provides a roadmap for the design of more efficient CaO-based sorbents using glassy stabilizers.