Synthesis of Core–Shell ETS-4@LSX zeolite composite to enhance CO2/N2 selectivity in flue gas separation

Abstract

The selective removal of CO₂ from the flue gas remains a quite challenging due to the weak selectivity of CO₂/N₂ in adsorbents. Therefore, it is necessary to design an effective sorbent to improve its selectivity. This work attempts to synthesis of novel core-shell ETS-4@LSX composite via a seed-assisted hydrothermal method. In this composite structure, a small pore titanosilcate ETS-4 as a core, while a large pore aluminosilicate LSX forms the outer shell. The effects of ETS-4 seed loading (1–5 wt.%) and crystallization time on the formation and structural integrity of the core–shell architecture was systematically investigated. The structural and physicochemical properties of samples were characterized by XRD, FE-SEM, HR-TEM, EDS, FT-IR, TGA, N₂ adsorption-desorption, and pore size distribution. From XRD pattern and FE-SEM results confirmed that the composite synthesized with 2 wt% ETS-4 seed and 3 h crystallization time has pure phase of ETS-4@LSX structure. HR-TEM imaging revealed uniform growth of LSX over the ETS-4 surface, resulting in the formation of a continuous shell. The 2 wt% ETS-4@LSX composite demonstrated an outstanding CO₂/N₂ equilibrium selectivity of 81.4 at 1 bar and 303 K with five and seven times higher than that of pure LSX and ETS-4, respectively. At 20 bar, the composite achieved a CO₂ uptake of 5.25 mmol g⁻¹ and an N₂ uptake of 0.50 mmol g⁻¹. Dynamic adsorption study exhibited the 2 wt% ETS-4@LSX has 3.52 mmol g⁻¹ CO₂ sorption capacity and N₂ uptake capacity of 0.26 mmol g⁻¹. The enhanced adsorption capacity and selectivity of ETS-4@LSX are attributed to its dual-pore structure, highlighting its potential as an effective adsorbent for CO₂ capture from flue gas.