A Molecular Lubrication Strategy Enabled by Propane Impurity for Self-Enhancing Its Kinetic Separation in MOFs with Diffusion-Restricted Channels

The removal of trace alkane impurities remains challenging due to their similar molecular properties. Here we propose a self-boosting kinetic separation process enabled by a "molecular lubrication" strategy, in which trace propane acts as a dynamic lubricant within a tailored Fe-based MOF featuring a bottleneck pore structure. Using in situ synchrotron XRD, DFT, and molecular simulations, we show that propane preferentially occupies the wide cavities rather than the narrow pore necks, smoothing the diffusion pathway and lowering the energy barrier. This leads to a volcano-shaped pressure dependence of diffusivity with an optimum at ∼5 kPa. Breakthrough experiments with a natural-gas mixture (CH₄/C₂H₆/C₃H₈ = 85/10/5, v/v/v) yield methane purity ≥99.99%. Six-bed vacuum pressure-swing adsorption simulations further demonstrate a high CH₄ recovery (80.4%), purity (≥99.95%), and productivity (4.04 mol kg⁻¹ h⁻¹). This work illustrates how trace-impurity-induced lubrication can be harnessed to design MOFs with enhanced diffusion kinetics for gas separation.