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

Abstract

CaO-based sorbents are cost-efficient materials for high-temperature CO 2 capture, yet they rapidly deactivate over carbonation-regeneration cycles due to sintering, hindering their utilization at the industrial scale. Morphological stabilizers such as Al 2 O 3 or SiO 2 (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 CaCO 3 nanoparticles and benchmark the CO 2 uptake of the resulting sorbent after 10 carbonationregeneration cycles against sorbents with optimized overcoats of only alumina/silica (+25%) and unstabilized CaCO 3 nanoparticles (+55%). 27 Al and 29 Si NMR studies reveal that the improved CO 2 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 CO 2 capture-inactive Ca-containing mixed oxides. This strategy provides a roadmap for the design of more efficient CaO-based sorbents using glassy stabilizers.