Alkyl-functionalization of (3-Aminopropyl)triethoxysilane-grafted zeolite beta for carbon dioxide capture in temperature swing adsorption

Amine-based solid sorbents are promising candidates for post-combustion CO₂ capture owing to their high sorption capacity at operating temperatures. Sorbents are required for stable CO₂ mixture sorption and regeneration. Herein, we report a novel alkyl-functionalization method for the stoichiometric conversion of primary amines to secondary amines in solid sorbents. (3-Aminopropyl)triethoxysilane (APTES) and alkyl-functionalized-APTES were grafted on zeolite beta through a reflux reaction; the alkyl-functionalization was confirmed by nuclear magnetic resonance and Fourier transform infrared analyses. Alkyl-functionalized-APTES zeolite exhibited a sorption capacity of 1.44 mmol/g (15% CO₂ balanced with N₂ at 90 °C), very high sorption rate of t_1/2 = 0.69 min (over 90% of the total sorption capacity within 5 min), and long-term stability after 20 cycles in a temperature swing adsorption (TSA) operation (above 0.9 mmol/g at pure CO₂ regeneration). Alkyl-functionalized-APTES zeolite beta showed higher sorption capacity and stability than APTES zeolite and PEI silica in TSA operation at CO₂ mixture sorption and CO₂ flow regeneration.