Direct imaging and mechanism study of C₆ α-olefin adsorption on faujasite and Linde Type A zeolites

Linear α-olefins are important chemical raw materials. To purify α-olefins from a high-temperature Fischer–Tropsch synthetic oil, it is necessary to separate the α-olefins from the paraffins, which is challenging. Adsorption separation by zeolites is a promising alternative to energy-intensive distillation for α-olefin/paraffin separation. An integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM) technique is used in combination with density functional theory (DFT) simulations and batch adsorption experiments to study the adsorption behavior of C₆ α-olefins and the mechanism of selective adsorption of C₆ α-olefin/paraffin. Direct electron microscopy real-space imaging of the atomic frameworks of the faujasite (FAU) and Linde Type A (LTA) zeolites and the C₆ α-olefin-adsorption positions on their lattices is achieved through iDPC-STEM. The images provide direct evidence that C₆ α-olefins preferentially adsorb at the edges of the FAU and LTA zeolite cavities. DFT calculations further reveal the relationship between host–guest interactions and different molecular orientations. Calculated and experimental results also show that the presence of calcium cations can enhance the selectivity of zeolites for α-olefin/paraffin adsorption. This work provides a means to investigate the behavior of guest molecules and the host–guest interactions in the adsorption or catalytic process of nanoporous materials.