Disorder-Induced Time-Dependent Diffusion in Zeolites

TL;DR

This paper investigates how disorder in zeolites causes time-dependent diffusion discrepancies between microscopic and macroscopic measurements, especially for ionic and large polarizable molecules.

Contribution

It introduces a model linking framework disorder to electrostatic potential variations, explaining diffusion measurement discrepancies in zeolites.

Findings

Discrepancies are almost inevitable for ionic species.

Significant discrepancies for polarizable species occur with long alkanes or benzene.

Characteristic time scales depend on species and zeolite disorder.

Abstract

We suggest that disordered framework aluminums and non-framework cations can create a disordered electrostatic potential in zeolites that can lead to a discrepancy between diffusivities measured by microscopic and macroscopic experimental techniques. We calculate the value of the discrepancy and the characteristic time scale at which it occurs for several ionic and polarizable species diffusing in zeolites. For ionic species, a discrepancy is almost inevitable. For polarizable species, a significant discrepancy may occur in some zeolites only for long alkanes or large species such as benzene.