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Time‐resolved powder diffraction as an analytical tool for diffusion studies in microporous topologies
Author(s) -
Mentzen B. F.
Publication year - 1988
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889888002134
Subject(s) - desorption , diffusion , microporous material , p xylene , benzene , o xylene , toluene , molecule , powder diffraction , xylene , chemistry , diffraction , analytical chemistry (journal) , materials science , crystallography , thermodynamics , organic chemistry , adsorption , physics , optics
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.