Electrostatic Potential Gradient Modulation by Organic Cations in Zeolite for Efficient C 2 H 2 /CO 2 Separation

The separation of acetylene (C2H2) and carbon dioxide (CO2) presents significant challenges due to the similar kinetic diameters and polarities. Traditional strategies to enhance C2H2 binding in zeolites via weak chemisorption are hindered by limitations such as low selectivity, high-temperature desorption, and inadequate stability. Herein, by leveraging the different priority affinity for complementary electrostatic environments (C2H2, negative potentials; CO2, positive potentials), we propose an innovative strategy for modulating the electrostatic potential gradient through introduction of low-charge density tetramethylammonium (TMeA+) cations within Y zeolite, systematically attenuating the positive electrostatic environment within the channel. This approach successfully achieves highly efficient C2H2/CO2 separation in TMeA-Y-5.8 (TMeA+ exchanged Y zeolite with a Si/Al ratio of 5.8) while circumventing the weak chemisorption, delivering an ideal adsorbed solution theory (IAST) selectivity of 16.1 for C2H2/CO2 (50/50, v/v) and a C2H2 adsorption capacity of 34.6 cm3/g at 10 kPa and 298 K. The dynamic C2H2/CO2 separation factor of TMeA-Y-5.8 (13.1) significantly outperforms that of NaY-5.8 (3.27) and NH4Y-5.8 (4.45) while maintaining a comparable C2H2 breakthrough time (C2H2/CO2/Ar = 10/5/85, v/v/v, 8 mL/min, 298 K). Periodic density functional theory (DFT) calculations and differential charge density conclusively revealed a selective and significant attenuation of the interactions between CO2 and TMeA-Y-5.8, coinciding with a diminished positive electrostatic potential within zeolite channels. Additionally, TMeA-Y-5.8 could achieve one-step purification of C2H2 from a ternary mixture of C2H2/C2H4/CO2. The exceptional regeneration capability (333 K), outstanding moisture resistance, and stable recyclability of TMeA-Y-5.8 collectively demonstrate the effectiveness and practical applicability of this electrostatic potential gradient modulation strategy.