Thermal stability of P-loaded Li-LSX zeolites for air separation

To investigate the effects of phosphorus doping on the thermal stability and air separation of the low-silica X (LSX) zeolite, different amounts of phosphorus were loaded into the channels of a commercial Li⁺-exchanged LSX (Li-LSX) zeolite via wet impregnation. The pristine Li-LSX zeolite exhibited an exothermic peak above 500 °C, attributed to framework collapse, and its characteristic peaks of the FAU structure almost disappeared and transformed to the nepheline phase upon calcination at 600 °C. Meanwhile, due to the weaker electric field of Li⁺ by phosphorus, the weight loss of chemisorbed water in the phosphorus-modified zeolites exhibited a significant decrease with phosphorus addition, and the FAU structures were well preserved even after calcination at 600 °C. Notably, the Li-LSX zeolite modified with a low phosphorus loading (0.12 wt%) not only well preserved most elemental compositions and framework structure but also weakened the interactions of Li⁺ cations with water molecules, greatly improved thermal stability and exhibited a relatively higher N₂ adsorption capacity and no significant differences in the O₂ adsorption capacity with an N₂/O₂ selectivity coefficient of 8.39, which can fully meet the industrial requirements.