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

Abstract

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).