Ball milling assisted Al/Si co-doping for enhanced performance of calcium-based CO2 adsorbents: Structural evolution and synergistic mechanisms

The rapid sintering and performance degradation of calcium-based adsorbents during cyclic CO 2 capture represent a major bottleneck limiting their large-scale application. While ball milling combined with inert oxide doping is an effective anti-sintering strategy, most studies focus on single-oxide doping systems using high-purity materials. In industrial applications, cost-effective Al 2 O 3 and SiO 2 -rich minerals or composite supports are commonly used as dopant sources. However, the synergistic mechanism between ball milling and such multi-component co-doping remains poorly understood, hindering the rational design of high-performance adsorbents. To address this, we investigate the synergistic modification mechanism of ball milling with Al 2 O 3 and SiO 2 co-doping. The results indicated that the synergistically modified sample (80Ca-10Al/10Si) exhibited excellent sintering-resistant stability, retaining a CO 2 capture capacity remaining at 0.36 g CO 2 /g adsorbent after 50 cycles. And ball milling achieved nanoscale homogeneous dispersion of Al and Si components within the CaO matrix. This subsequently facilitated the in-situ formation of an interwoven composite inert skeleton consisting of Ca 3 Al 2 O 6 and CaSiO 3 during cycling. This structure effectively pinned the CaO grain boundaries, suppressing high-temperature sintering. Concurrently, the modification increased the surface oxygen vacancy concentration, specific surface area and pore volume of the adsorbent. This change reduced the activation energy of the fast reaction stage by more than 40%, and consequently, a marked improvement in reaction kinetics. This work elucidates the synergistic mechanism of ball milling and multi-component doping in constructing a sintering-resistant nanocomposite structure, providing a new approach for designing calcium-based CO 2 adsorbents with high stability and reactivity.