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 benzylaminefunctionalized beta framework exhibited the highest CO2 uptake of 1.28 mmol g-1 at 10.5 kPa and 20 celcius, which is 48.3% higher than that of the pristine zeolite (0.863 mmol g-1). Furthermore, the benzylaminefunctionalized 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.