Time‐resolved powder diffraction as an analytical tool for diffusion studies in microporous topologies

Investigations on an MFI/ p ‐xylene system by time‐resolved X‐ray powder diffraction in two selected angular domains show that it is possible to derive kinetic and diffusion parameters describing a spontaneous desorption process. The corresponding value of the overall diffusion coefficient, calculated for the MFI,8 p ‐xylene (S) → MFI,4 p ‐xylene (S) + 4 p ‐xylene (g) reaction, is in the 0.4–0.6 × 10 −10 cm 2 s −1 range. The desorption proceeds via a two‐phased system. Accordingly, the only solid species involved in this desorption are the high‐ and low‐coverage XYLII and XYLI phases, containing respectively eight and four p ‐xylene molecules per unit cell. Similar results are also observed for the MFI/benzene, toluene and pyridine systems, which all present high‐coverage phases, with eight molecules per unit cell, desorbing via a two‐phased system.