CO2 sorbents derived from capsule-connected Ca-Al hydrotalcite-like via low-saturated coprecipitation

This work presents the synthesis of Ca-Al mixed oxides derived from Ca-Al-CO3 layered double hydroxides (LDHs), which were prepared using a low-saturated coprecipitation method at high constant pH. Compared to the high-saturated coprecipitation method, a better CO2 adsorption capacity and stability were obtained from the mixed oxides. This was attributed to the novel capsule-connected structure of LDHs nanoparticles, smaller crystal size of CaO, and uniform distribution of CaO and Al2O3. The effect of the coprecipitation temperature, Ca/Al ratio and methanol modification on the CO2 capture performance of Ca-Al mixed oxides was also investigated. The mixed oxides with 2:1 Ca/Al ratio modified by methanol showed a much greater stability with carbonation capacity of about 56.7 wt% after 30 carbonation/calcination cycles. A double exponential model was fitted to the CO2 adsorption curves, providing a good explanation for the disparity between CO2 uptakes with different Ca/Al ratios.