Cation Gating-Breathing Synergetic Mechanism in K-MER Zeolite Enables Unprecedented Selective CO₂ Separation from Hydrocarbon Gas Streams

Abstract

The ubiquitous presence of CO₂ impurity in industrial hydrocarbon streams underscores the critical need for developing efficient CO₂-selective adsorbents. Herein, we successfully synthesized a flexible K-MER-2.0 (a silica-alumina ratio of 2.0) zeolite without using organic template, which demonstrates exceptional selective adsorption performance in CO₂/hydrocarbon systems, particularly achieves unprecedented reverse separation of CO₂/C₂H₂. K-MER-2.0 exhibits CO₂ adsorption capacity of 70.9 cm³/g under ambident condition, accompanied by remarkable CO₂/C₂H₂ uptake ratio (13.4). Breakthrough experiments conducted with CO₂/C₂H₂ (50/50, v/v) mixture reveal that K-MER-2.0 delivers high dynamic CO₂ adsorption capcity (65.1 cm³/g) and separation factor (12.1), especially high C₂H₂ yield of 1872 mmol/kg, establishing a benchmark for CO₂/C₂H₂ reverse separation. The rapid adsorption kinetics, excellent regeneration capability and robust moisture resistance of K-MER-2.0 further validated its application potential under harsh practical conditions. Mechanistic analyses including CO₂/C₂H₂ adsorption isotherms and in-situ CO₂ powder X-ray diffraction (PXRD) pattern and periodic density functional theory (DFT) calculations reveal a unique CO₂-triggered cation gating-breathing synergetic mechanism in K-MER-2.0 zeolite. This stimulus-responsive mechanism facilitates selective framework expansion during CO₂ adsorption while preserving a constricted pore geometry that excludes C₂H₂ molecules. Such discriminative structural adaptability fundamentally drives the material's record-setting separation performance. In addition, the unique recognition ability for CO₂ endows K-MER-2.0 with good dynamic separation ability for binary mixtures of CO₂/hydrocarbon.