Elevated temperature CO2 capture on nano-structured MgO–Al2O3 aerogel: Effect of Mg/Al molar ratio

•Nano-structured MgO–Al2O3 aerogel adsorbents were prepared.•Prepared adsorbents showed better CO2 capacity than commercial adsorbents.•CO2 adsorptive performance increased with increasing basicity of adsorbent.•Medium basicity is the key factor in determining CO2 adsorptive performance.

Nano-structured MgO–Al2O3 aerogel adsorbents (denoted as MgAl-AE-X) with different Mg/Al molar ratio (X) were prepared by a single-step epoxide-driven sol–gel method and a subsequent CO2 supercritical drying method. The effect of Mg/Al molar ratio of nano-structured MgO–Al2O3 aerogel adsorbents on their physicochemical properties and CO2 adsorptive performance at elevated temperature (200 °C) was investigated. Successful formation of flower-like nano-structured MgAl-AE-X adsorbents was confirmed by N2 adsorption–desorption isotherms and SEM analyses. The crystalline structure of MgAl-AE-X adsorbents was transformed in the sequence of Al2O3 → MgAl2O4 → MgO-MgAl2O4 with increasing Mg/Al molar ratio from 0 to 3. All the MgAl-AE-X adsorbents were found to possess weak base site and medium base site except for strong base site. In the dynamic CO2 adsorption, both the total CO2 capacity and the 90% breakthrough CO2 capacity showed volcano-shaped curves with respect to Mg/Al molar ratio, and they were decreased in the order of MgAl-AE-0.5 > MgAl-AE-1.0 > MgAl-AE-2.0 > MgAl-AE-3.0 > MgAl-AE-0. It was found that the 90% breakthrough CO2 capacity increased with increasing medium basicity of the adsorbents. Among the adsorbents tested, MgAl-AE-0.5 (Mg/Al = 0.5) adsorbent with the highest medium basicity showed the best CO2 adsorptive performance. Thus, medium basicity of nano-structured MgO–Al2O3 aerogel adsorbents served as a crucial factor in determining CO2 adsorptive performance at elevated flue gas temperature (200 °C).