Directly synthesized high-silica CHA zeolite for efficient CO₂/N₂ separation

Carbon dioxide capture is an effective method to mitigate climate change. Highly CO₂-selective and highly moisture-resistant absorbent is essential for energy-efficient carbon capture by absorption. Herein, a highly CO₂-selective and high-silica CHA zeolite in a pure lithium form (Li-SSZ-13) was synthesized using a direct synthesis method for the first time. The effects of gel n(SiO₂)/n(Al₂O₃) ratio, gel n(SiO₂)/n(Li₂O) ratio and synthesis time on the crystallinity, yield, micropore volume and CO₂ loading of the crystals were systematically investigated. The adsorption isotherms of CO₂ and N₂ were measured for directly synthesized Li-SSZ-13, conventional Na-SSZ-13 and ion-exchanged Li-Na-SSZ-13 zeolites. The dynamic breakthrough adsorption properties were measured for Li-SSZ-13 in comparison with Na-SSZ-13 and Li-Na-SSZ-13. The obtained Li-SSZ-13 exhibited a high CO₂ adsorption capacity of 4.48 mmol/g and a high CO₂/N₂ IAST selectivity of 310 at 100 kPa and 273 K, which were 45.0 % and 441 % higher than Na-SSZ-13 zeolite, 24.8 % and 179 % higher than Li-Na-SSZ-13 zeolite, respectively. It suggests that directly synthesized Li-SSZ-13 zeolite has great potential for efficient CO₂ capture from flue gas.