Regular Intergrowth in the AFI-Type Crystals:  Influence on the Intracrystalline Adsorbate Distribution As Observed by Interference and FTIR-Microscopy

Lehmann, E.; Chmelik, Christian; Scheidt, Holger A.; Vasenkov, Sergey; Staudte, B.; Kärger, Jörg; Kremer, Friedrich; Zadrozna, G.; Kornatowski, J.

doi:10.1021/ja026400z

Cited by 81 publications

(88 citation statements)

References 10 publications

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“…On heating, the template decomposes accompanied by the formation of light-absorbing and -emitting species. As the accessibility of the porous network in the subunits varies, [29,30] following the template removal process in time enables visualization and reconstruction of the individual building blocks. Recently, the intergrowth structure of similar, though larger, ZSM-5 crystals was revealed in this manner.…”

Section: Resultsmentioning

confidence: 99%

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

Kox

Stavitski

Groen

et al. 2008

Chemistry A European J

116

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A combination of optical and fluorescence microscopy was used to study the morphology of micro‐ and mesoporous H‐ZSM‐5 zeolite crystals (17×4×4 μm) and to evaluate, in a spatially resolved manner, the effect of mesoporosity, introduced via desilication, on catalytic performance. For this purpose, the oligomerization of various styrene molecules was used as a model reaction, in which the carbocation intermediates formed in the zeolite pores act as reporter molecules. In situ confocal fluorescence measurements after the template removal process showed that the crystals generally consist of three different subunits that have pyramidal boundaries with each other. Examination of these crystals during styrene oligomerization revealed differences in the catalytic activity between the purely microporous and the combined micro‐ and mesoporous crystals. The introduction of intracrystalline mesoporosity limits the formation to dimeric carbocation intermediates and facilitates the transport of styrene molecules inside the zeolite volume. This leads to a more uniform coloration and fluorescence pattern of the crystals. Moreover, the oligomerization of various styrene compounds, which differ in their reactivity, provides a good way of estimating the Brønsted acid strength in a spatially resolved manner, showing a nonhomogeneously distributed Brønsted acidity over the volume of the crystals. More detailed information on the structure of the ZSM‐5 crystals was revealed for mesoporous crystals during the oligomerization of 4‐methoxystyrene. This reaction induced an “explosion” of the crystal leading to the formation of a complex system with at least eight different subunits. Finally, polarized‐light microscopy was used to unravel the pore geometry in these individual building blocks. The observed differences in catalytic behavior between micro‐ and mesoporous ZSM‐5 crystals are strengthened by the microspectroscopic techniques employed, which show that upon desilication the crystal morphology is affected, the product distribution is changed towards less conjugated carbocation intermediates, and that a gradient in Brønsted acid strength appears to be present.

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Section: Resultsmentioning

confidence: 99%

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

Kox

Stavitski

Groen

et al. 2008

Chemistry A European J

116

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“…Nonetheless, it should be mentioned that, only recently, Thompho et al 22 have introduced a potential for such silanol groups on a silicalite-1 surface and that future studies should take into account the surface saturation. Another important point with respect to studying a realistic crystal are lattice defects 23 and crystal intergrowth, 24 all of which are not considered in this study but which are very likely be found in real zeolite crystals. From another point of view, this underlines the complementary relationship between experiments and simulations.…”

Section: Methodsmentioning

confidence: 99%

On the Effects of the External Surface on the Equilibrium Transport in Zeolite Crystals

2009

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With the aid of molecular simulation techniques (molecular dynamics, grand-canonical Monte Carlo, and reactive flux correlation function RFCF), the influence of the external surface on the equilibrium permeation of methane and ethane into and out of an AFI-type zeolite crystal has been studied. In particular, "extended dynamically corrected transition state theory", which has been proven to describe the transport of tracers in periodic crystals correctly, has been applied to surface problems. The results suggest that the molecules follow paths that are close to the pore wall in the interior and also at the crystal surface. Moreover, the recrossing rate at the surface turns out to be non-negligible, yet, in contrast to the intracrystalline recrossing rate, remains almost constant over loading which gives indication to diffusive barrier crossing at the crystal surface. As a consequence of very different adsorption and desorption barriers, the corresponding permeabilities are shown to be not equal for one and the same condition (T and p). The critical crystal length, beyond which surface effects can be certainly neglected, is computed on basis of flux densities. Entrance/exit effects, in the present cases, are practically important solely for ethane at low pressures. The influence of the type of external surface on the surface flux is, hereby, rather small, because the transport at the surface is controlled by the slow supply from the gas phase. This has been evidenced by a simplified thermodynamic model that has been derived within this work and which is based on rapidly assessable simulation data. Finally, we propose a procedure for estimating the importance of different factors that have an impact on surface effects.

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“…The IFM method has been successfully used to study micropore diffusion in a variety of zeolites such as ferrierite [6], CrAPO-5 and SAPO-5 [7][8][9][10] and MFI [11,12]. The measured concentration profiles in these systems have been used to determine whether the diffusion is one-dimensional, two-dimensional or three-dimensional.…”

Section: Introductionmentioning

confidence: 99%

Analysis of thermal effects in infrared and interference microscopy: n-Butane-5A and methanol–ferrierite systems

Heinke¹,

Chmelik²,

Kortunov³

et al. 2007

Microporous and Mesoporous Materials

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…rger, J. (2007). Analysis of thermal effects in infrared and interference microscopy: n-Butane-5A and methanol-ferrierite systems. Microporous and Mesoporous Materials, This p(lpcr is dedicated \0 lhe memory of Professor LOVUI Rees. a pionccr of zeolite research who made muny seminal contributions. most n:ccn tly wi th respect to the accurate measurement of intracrystalline diffusion by thc frcqucncy rcsponse mc thod. Hc was a good fricnd and a valued collc3guc. His percep tivc comme nts and unfailing good humour will be sorely missed.

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Regular Intergrowth in the AFI-Type Crystals: Influence on the Intracrystalline Adsorbate Distribution As Observed by Interference and FTIR-Microscopy

Cited by 81 publications

References 10 publications

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

On the Effects of the External Surface on the Equilibrium Transport in Zeolite Crystals

Analysis of thermal effects in infrared and interference microscopy: n-Butane-5A and methanol–ferrierite systems

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