title: Morphology of large ZSM-5 crystals unraveled by fluorescence microscopy.
abstract: 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 90 degree 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 90 degree 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.
authors.affiliation: Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium.
authors.forename: Maarten B J
authors.initials: MB
authors.lastname: Roeffaers
authors.forename: Rob
authors.initials: R
authors.lastname: Ameloot
authors.forename: Mukulesh
authors.initials: M
authors.lastname: Baruah
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Uji-I
authors.forename: Metin
authors.initials: M
authors.lastname: Bulut
authors.forename: Gert
authors.initials: G
authors.lastname: De Cremer
authors.forename: Ulrich
authors.initials: U
authors.lastname: Müller
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Jacobs
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.forename: Bert F
authors.initials: BF
authors.lastname: Sels
authors.forename: Dirk E
authors.initials: DE
authors.lastname: De Vos