High-Temperature and Low-Concentration Deep Flue Gas Desulfurization with Low-Si/Al (∼5)-Ratio Zeolite Na-SSZ-13

The development of exceptionally stable porous solid physisorbents is vital for deep flue gas desulfurization (FGD) and SO₂ recovery, as the corrosive and reactive nature of SO₂ restricts the applicability of most porous materials in this demanding scenario. Herein, we report the synthesis of microporous SSZ-13 zeolite to obtain the exceedingly stable Na-SSZ-13 with low-Si/Al-ratio (5:1), and systematically evaluate its dynamic SO₂ adsorption performance. Na-SSZ-13 exhibits excellent water, thermal, and chemical stability, high SO₂ affinity and adsorption kinetics with extraordinary SO₂/CO₂ separation selectivity (2673 at zero coverage, 298 K), and exceptional low-concentration SO₂ adsorption capacity (4.6/2.7 mmol g^-1 at 0.1/0.002 bar) with the highest surface-specific SO₂ uptake among reported zeolites. Column breakthrough experiments demonstrate efficient SO₂ capture capability from a quaternary flue-gas mixture at high temperature (323 - 423 K). Moreover, it achieves 96.5% purity of the recovered SO₂ during the regeneration process, and shows fully reversible SO₂ uptake and excellent cycling stability. GCMC simulations, DFT calculations, and in situ DRIFT analyses reveal a selective SO₂ adsorption mechanism with the counter-cations (Na⁺) serving as primary SO₂ adsorption sites, elucidating the role of cation···SO₂ interactions that underpin the application of zeolite-based materials for deep FGD under high-temperature and low-concentration working conditions.