Inflection in the loading dependence of the Maxwell-Stefan diffusivity of iso-butane in MFI zeolite

Up to loading Θ = 4 molecules per unit cell, iso-butane (iC4) locates preferentially at the intersections of MFI zeolite. At higher loadings Θ > 4, ic4 molecules occupy channel interior positions. Infra-red microscopy measurements of the diffusivity of iC4 in MFI shows a strong inflection at Θ = 4. This inflection can be rationlized by Kinetic Monte Carlo simulations.