Direct Air Capture of CO2 over Amine-Modified Hierarchical Silica

Abstract

The current study reports the utilization of tetraethylenepentamine (TEPA)-modified hierarchical silica particles having bimodal meso/macroporosity for CO2 capture under simulated direct air capture (DAC) conditions (400 ppm CO2 in He). Results infer a typical relation between TEPA loading and CO2 capture, where TEPA-impregnated HS (HS-TEPA-70) exhibits exceptionally high CO2 uptake (5.20 mmol/g), shorter adsorption half time (110 min), and excellent amine efficiency (0.32 mmol of CO2/mmol of N) with moderate CO2/N2 selectivity at 30 °C under DAC conditions. HS-TEPA-70 also showed appreciable CO2 adsorption performance (5.88 mmol/g) under humid conditions (50 ± 3% RH) with 400 ppm CO2 in He at 30 °C. TEPA-impregnated HS even displays better thermal stability up to 10 consecutive adsorption–desorption cycles with minimal amine leaching and moderate CO2 regeneration energy. Moreover, the pelletized form of HS-TEPA-70 also demonstrates better CO2 adsorption performance (3.34 mmol/g), which makes it a promising candidate for CO2 capture from ambient air by temperature swing adsorption.