Optical Investigation of the Intergrowth Structure and Accessibility of Brønsted Acid Sites in Etched SSZ-13 Zeolite Crystals by Confocal Fluorescence Microscopy

Abstract

Template decomposition followed by confocal fluorescence microscopy reveals a tetragonal-pyramidal intergrowth of subunits in micrometer-sized nearly cubic SSZ-13 zeolite crystals. In order to accentuate intergrowth boundaries and defect-rich areas within the individual large zeolite crystals, a treatment with an etching NaOH solution is applied. The defective areas are visualized by monitoring the spatial distribution of fluorescent tracer molecules within the individual SSZ-13 crystals by confocal fluorescence microscopy. These fluorescent tracer molecules are formed at the inner and outer crystal surfaces by utilizing the catalytic activity of the zeolite in the oligomerization reaction of styrene derivatives. This approach reveals various types of etching patterns that are an indication for the defectiveness of the studied crystals. We can show that specially one type of crystals, denoted as core-shell type, is highly accessible to the styrene molecules after etching. Despite the large crystal dimensions, the whole core-shell type SSZ-13 crystal is utilized for catalytic reaction. Furthermore, the confocal fluorescence microscopy measurements indicate a nonuniform distribution of the catalytically important Brønsted acid sites underlining the importance of space-resolved measurements.

Noninvasive Nanoscopy Uncovers the Impact of the Hierarchical Porous Structure on the Catalytic Activity of Single Dealuminated Mordenite Crystals

“…Whereas the overall effect of meso‐ and macropore introduction on catalytic performance has thoroughly been investigated at the ensemble‐averaged scale level, the direct impact of extraframework porosity on the local, nanoscale reactivity remains relatively unexplored . Nonetheless, small‐scale, microscopy‐based investigations seem especially essential in view of several recent studies, which revealed the major impact of structural and compositional heterogeneities on the catalytic performance within and between individual catalyst particles …”

Umwandlung von Methanol in Kohlenwasserstoffe: Wie Zeolith‐Hohlräume und Porengröße die Produktselektivität bestimmen

“…Obwohl H-ZSM-5 der zurzeit bevorzugte MTG-Katalysator ist, wird die Suche nach anderen Topologien, die eine klare obere Grenze bei C 9 -Arenen ergeben (Abschnitt 2.1) oder die Bildung von aromatischen Bestandteilen (z. B. zur Bildung von nanoskaligen [207] oder defektreichen Kristallen, die empfänglich für die Bildung von Mesoporen sind, [217] um Diffusionsbehinderungen zu minimieren. 1D-10-Ring Topologien, Abschnitt 3.2) verhindern, fortgesetzt werden.…”

Review. Fluorescence Microscopy Studies of Porous Silica Materials

“…In their study, they used a combination of confocal fluorescence microscopy, electron backscatter diffraction from samples prepared by focused ion beam sectioning, transmission electron microscopy imaging and diffraction, atomic force microscopy, and X-ray photo-electron spectroscopy to study a wide range of coffinshaped MFI-type zeolite crystals, and presented an overview of the morphology-dependent MFI-type intergrowth structures. Sommer et al used a Brønsted acid-catalyzed oligomerization of styrene derivatives to study the intergrowth structure and the active site accessibility in etched SSZ-13 zeolites by confocal fluorescence microscopy [77]. The authors found a high degree of heterogeneity in the density of defects and the catalytic activity among different crystals within one SSZ-13 batch.…”