Size effects of extraframework monovalent cations on the thermal stability and nitrogen adsorption of LSX zeolite

• In situ HTXRD characterization of (Na or Li)-LSX at various temperature was obtained.
• Thermal stability of Li-LSX was decreased as a compared with that of Na-LSX.
• Effect of water-absorbed amount of Li-LSX on structural stability was remarkable.

The Li-LSX zeolite was synthesized via ion exchange method with Na-LSX zeolite as a starting material, and its structural properties were characterized using FT-IR, SEM and TG-DSC techniques. The results showed that the water adsorption capacity of Li-LSX was enhanced but its thermal stability was decreased compared with that of Na-LSX. Meanwhile, combined with in situ HTXRD patterns, the parallel exothermal DSC profiles demonstrated that cationic radius and adsorbed water in FAU framework had remarkable influence on the thermal stability of Li-LSX and Na-LSX. In addition, the amount of N2 adsorbed on Li-LSX at room temperature (298 K) was around 19.76 g/cm3, which was higher than that of Na-LSX (5.42 g/cm3). Whereas, N2 adsorption–desorption isotherm of Li-LSX at 77 K showed the BET surface area (778.0 m2/g) and relevant pore volume (0.40 cm3/g) were higher than those of Na-LSX (622.5 m2/g and 0.33 cm3/g), respectively. These results suggested that the N2 adsorption capacities of LSX zeolites at 77 K could be determined mainly according to their porosity; while, at 298 K, the adsorption capacities depended on both the N2–cation interaction and their porosity. Therefore, it was concluded that the charge density and cationic radius (Na+ and Li+) had a remarkable influence on their adsorption performance, structural parameters (textural parameters) and their stability.

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