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.