Pure Silica with Ordered Silanols for Propylene/Propane Adsorptive Separation Unraveled by Three-Dimensional Electron...

Adsorptive separation of propylene (C₃H₆) from propane (C₃H₈), which could deal with energy-intensive cryogenic distillation technologies, remains challenging due to their similar physiochemical properties. Herein, we present a pure silica zeolite with ordered silanols (OSs), whose crystallographic structure was unraveled by the advanced three-dimensional electron diffraction (3D ED), displaying the highly efficient separation of propylene from propane under ambient conditions. The 3D ED technique enables us to investigate its 8-ring pore opening transformation from the round one to the elliptical one during the removal of organic structure-directing agents. Such unique elliptical 8-ring pore openings can exclude larger-size propane and only adsorb propylene. Its C₃H₆/C₃H₈ separation performance is also confirmed by column breakthrough experiments, showing a high dynamic adsorption capacity of 53.36 cm³ g^-1 for C₃H₆ but negligible C₃H₈ under ambient conditions. The dynamic capacity for C₃H₆ is superior to that of the well-known pure silica DDR-type zeolite (31.07 cm³ g^-1). The density functional theory calculation demonstrates that the adsorbed propylene is distributed in the heart-shaped cavity and has a weak interaction with the OSs.