Engineering micropore walls of beta zeolites by post-functionalization for CO₂ adsorption performance screening under humid conditions

An aluminosilicate beta zeolite with a Si/Al ratio of 12.5 was post-functionalized with aryl diazonium derivatives to yield organic-functionalized zeolites. By grafting with different functional groups, we engineered zeolite micropore walls integrating various moieties, ranging from hydrophobic to hydrophilic and from basic to acidic units, with controllable loading contents. This approach enables the tailored development of various beta zeolites with systematically tuned porosities and functionalities while retaining the zeolite crystallinity. We show that this strategy can be used for the efficient screen for a suitable pore environment for CO₂ adsorption under humid conditions. The grafting of benzene onto the zeolite pore walls makes the pore environment hydrophobic, preventing losses of CO₂ adsorption capacity by the H₂O vapor (CO₂ adsorption capacity: 0.130 mmol g⁻¹ without humid vs 0.122 mmol CO₂ g⁻¹ with humid). The CO₂ uptake was enhanced by introducing various functional groups (e.g., –OH, –NH₂, –COOH) able to interact with CO₂. Among the modified zeolites, the benzylamine-functionalized beta framework exhibited the highest CO₂ uptake of 1.28 mmol g⁻¹ at 10.5 kPa and 20 ℃, which is 48.3% higher than that of the pristine zeolite (0.863 mmol g⁻¹). Furthermore, the benzylamine-functionalized beta zeolite exhibited higher CO₂ adsorption than its pristine counterpart under flue gas conditions (composition: 10.5% CO₂, 5% H₂O, 84.5% N₂), which might be attributed to the synergistic effect of the hydrophobic benzene and basic amine moieties in the benzylamine group. The engineering of zeolite micropore walls by post-synthetic functionalization is expected to extend the application of zeolites to challenging adsorption and separation processes.