Energetic origins of light-alkane diffusion barriers under anisotropic confinement in MFI zeolites

Intracrystalline diffusion in MFI zeolites plays a critical role in shape-selective catalysis, yet the microscopic origins of diffusion anisotropy remain incompletely understood. In this work, periodic density functional theory and climbing-image nudged elastic band simulations were used to investigate the diffusion of methane, ethane, propane, and n -butane in MFI straight and sinusoidal channels. Deformation-interaction energy analysis quantified the contributions of host–guest interactions, guest molecular deformation, and framework deformation to the static potential energy barrier. The results show that methane and ethane exhibit relatively low static potential energy barriers in both channel systems, whereas the influence of channel topology becomes increasingly significant with increasing carbon-chain length. Propane shows comparable barriers in the two channels, with a slightly higher value in the straight channel, whereas n -butane exhibits a substantially higher barrier in the sinusoidal channel. Host–guest interactions dominate the barrier in the straight channel, while framework and molecular deformation become increasingly important in the sinusoidal channel. The lower n -butane barrier in the straight channel is associated with asynchronous deformation response of the guest molecule and zeolite framework, in which molecular structural adjustment and local pore deformation occur sequentially along the diffusion pathway. Independent Gradient Model based on Hirshfeld partition analysis confirms that van der Waals interactions govern host–guest interactions throughout transport. Within the relaxed IZA-DLS76-derived MFI model, the calculated static CI-NEB pathways indicate that host–guest structural coupling can contribute substantially to diffusion resistance beyond simple geometric confinement.