In SituPFG NMR Study of Intracrystalline Diffusion during Ethene Conversion in ZSM-5

Diffusion Measurements by NMR Techniques

“…21 Time dependence of the relative amount of isopropanol and propene during the conversion of isopropanol in Na-X and their self-diffusivities at 473 K. From [174] with permission diffusivity after low-temperature treatment (D∼10 -10 m 2 s -1 ). This finding is in agreement with the results of self-diffusion measurements of CF 4 with co-adsorbed benzene and n-hexane, where the diffusivity of the probe molecules is much more significantly reduced by benzene than by n-hexane [236]. This large effect may be explained by the differences in the preferred adsorption siting: Both experimental evidence and MD simulations suggest that the n-alkanes prefer the channel segments [179], while aromatics adsorb preferentially in the channel intersections [181,182].…”

“…By monitoring the diffusivity of an inert molecule it is also possible directly to trace any changes in the transport properties of the catalyst during the reaction. As an example of this procedure, in [236] tetrafluoromethane is used to follow the transport inhibition within ZSM-5 during ethene conversion. In these studies, an H-ZSM-5 zeolite was loaded with 4 CF 4 and 12 ethene molecules per unit cell and kept at a temperature of 343 K. The representation of the results in Fig.…”

High‐Resolution Single‐Turnover Mapping Reveals Intraparticle Diffusion Limitation in Ti‐MCM‐41‐Catalyzed Epoxidation

“…[9] Despite the relatively large pore size, maximal utilization of the Ti sites in diffusion unlimited conditions remains a major challenge. [14,15] Recent technological evolutions in optical microscopy now offer the opportunity to confront these insights with in situ observations for single catalyst particles.The high spatiotemporal resolution (submicrometer and milliseconds) of (single-molecule) fluorescence microscopy has proven to be extremely useful to study catalysis at the level of individual particles or even at the level of individual reaction events, [16][17][18][19][20][21][22][23][24] as well as to investigate diffusion processes in mesoporous materials. It was recently demonstrated that a decrease in particle size to about 100 nm was accompanied with a relevant increase in selectivity and reaction rate for the epoxidation of cyclohexene and cholesterol.…”

Morphological Synthesis of Zeolites

“…Therefore, the synthesis of large, single zeolite crystals is highly desirable from the point of view of structural determination or discovering the crystallization mechanism. Although recent advances in X-ray powder diffractometry combined with sensitive spectroscopic methods such as multinuclear NMR methods have made structural determination from polycrystalline powders amenable (indeed most zeolites are structurally characterized by powder data) [20], diffraction data from a single crystal often remain the most accurate means of unambiguous structure elucidation, including the location of both the framework and extraframework atoms in a zeolite [21][22][23][24][25][26][27][28].…”