Highly Selective Adsorption of Para‐Xylene, Ethylbenzene, and Explicit Exclusion of Ortho‐Xylene from Xylene Isomers Using a Pillar‐Layered MOF with Tuned Pore Channels

Abstract Xylene isomer separation is a long‐standing challenge due to the nearly identical properties of para‐xylene (PX), meta‐xylene (MX), ortho‐xylene (OX), and ethylbenzene (EB). Here, we report a rationally designed pillar‐layered metal–organic framework (MOF), Ni‐HDB, incorporating a cylindrical 1,4‐diazabicyclo[2.2.2]octane (DABCO) pillar that blocks lateral channels and directs molecular transport through elliptical windows (3.2 × 6.7 Å 2 ). These apertures closely match the dimensions of PX and EB, enabling kinetic sieving. As a result, Ni‐HDB exhibits high selectivity for PX and EB, moderate selectivity for MX, and exclusion of OX under ambient conditions. It achieves record liquid‐phase selectivities for EB/OX (1943), PX/OX (951), and MX/OX (158), along with high PX and MX adsorption capacities. Comparative studies with isoreticular analogues confirm that DABCO‐driven confinement is key to enhancing size‐based selectivity. Density functional theory calculations indicate kinetic preference for PX and EB, thermodynamic favorability for MX, and exclusion of OX. Ni‐HDB also shows excellent thermal and structural stability, with no performance loss over ten cycles. These results highlight the importance of channel geometry in MOFs and provide a framework for developing next‐generation adsorbents for energy‐efficient hydrocarbon separations.