Morphology of large ZSM-5 crystals unraveled by fluorescence microscopy

Understanding the internal structure of ZSM-5 crystallites is essential for improving catalyst performance. In this work, a combination of fluorescence microscopy, AFM, SEM, and optical observations is employed to study intergrowth phenomena and pore accessibility in a set of five ZSM-5 samples with...

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Published in:Journal of the American Chemical Society Vol. 130; no. 17; pp. 5763 - 5772
Main Authors: Roeffaers, Maarten B. J., Ameloot, Rob, Baruah, Mukulesh, Uji-i, Hiroshi, Bulut, Metin, De Cremer, Gert, Mueller, Ulrich, Jacobs, Pierre A., Hofkens, Johan, Sels, Bert F., De Vos, Dirk E.
Format: Journal Article
Language:English
Published: WASHINGTON Amer Chemical Soc 30.04.2008
Subjects:
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
SILICALITE
CATALYSIS
H-ZSM-5
KINETICS
GROWTH
SORPTION
MOLECULAR-SIEVES
SINGLE MOLECULES
ZEOLITE CRYSTALS
INTERGROWTH
ISSN:0002-7863, 1520-5126, 1520-5126
Online Access:Get more information
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Summary:Understanding the internal structure of ZSM-5 crystallites is essential for improving catalyst performance. In this work, a combination of fluorescence microscopy, AFM, SEM, and optical observations is employed to study intergrowth phenomena and pore accessibility in a set of five ZSM-5 samples with different crystal morphologies. An amine-functionalized perylene dye is used to probe acid sites on the external crystal surface, while DAMPI (4-(4-diethylaminostyryl)-N-methylpyridinium iodide) is used to map access to the straight channels in MFI from the outer surface. The use of these dyes is validated by studying the well-understood rounded-boat type ZSM-5 crystals. Next coffin-shaped ZSM-5 crystals are considered; we critically evaluate the seemingly conflicting 2-component and 3-component models that have been proposed to account for the hourglass structure in these crystals. The data prove that observation of an hourglass structure is essentially unrelated to a 901 rotation of the pyramidal crystal components under the (010) face. Hence, in perfectly formed coffin-shaped crystals, the straight channels can be accessed from (010). However, in other crystal batches, sections with a 90 degrees rotation can be found; they are indeed located inside the crystal sections under (010) but often only partially occupy these pyramidal components. In such a case, both straight and sinusoidal pores surface at the hexagonal face. The results largely support the 3-component model, but with the added notion that 900 rotated sections (as proposed in the 2-component model) are most likely to be formed inside the defect-rich, pyramidal crystal sections under the (010) faces.
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ISSN:0002-7863
1520-5126
1520-5126
DOI:10.1021/ja7113147