The Role of Mesopores in Intracrystalline Transport in USY Zeolite:  PFG NMR Diffusion Study on Various Length Scales

Kortunov, Pavel; Vasenkov, Sergey; Kärger, Jörg; Valiullin, Rustem; Gottschalk, Pia; Elía, M. Fé; Pérez, María Olga Guerrero; Stöcker, Michael; Drescher, B.; McElhiney, G.; Berger, C.; Gläser, Roger; Weitkamp, Jens

doi:10.1021/ja053134r

Cited by 219 publications

(203 citation statements)

References 23 publications

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“…On the other hand, it has been recognized that the extent to which mass transport is improved is highly dependent on the "quality" of meso-(or macro-) pores, as mesopores can enhance mass transport only if they are connected with the exterior surface of zeolite crystals 12b, 14a, 15 . Weitkamp et al 16 have observed that the presence of intracrystal mesopores in USY has virtually no impact on mass transport, a phenomenon that . It is therefore desirable to find ways that can produce HPZs with small primary particle size that can shorten the diffusion pathway, and at the same time keep the mesopores connected to the external surfaces.…”

Section: Introductionmentioning

confidence: 99%

A solvent evaporation route towards fabrication of hierarchically porous ZSM-11 with highly accessible mesopores

Song

Liu

et al. 2015

RSC Adv.

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Abstract:A route to generate hierarchically porous zeolite ZSM-11 (MEL) has been paved via solvent evaporation induced self-assembly to produce a dry gel and its subsequent transformation into zeolite by steam-assisted-crystallization. The structure evolution has been monitored to shed light on the structure evolution during crystallization process.Measurements such as XRD, SEM, TEM, N 2 -physisorption, and TEM for inverse replica of

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Section: Introductionmentioning

confidence: 99%

A solvent evaporation route towards fabrication of hierarchically porous ZSM-11 with highly accessible mesopores

Song

Liu

et al. 2015

RSC Adv.

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“…However, M41S materials generally exhibit weak acidity and low hydrothermal stability due to their amorphous frameworks. As a consequence, new synthesis strategies have been developed to obtain materials which com-bine the advantages of mesoporous materials and those of zeolites [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. For example, Corma et al [21] reported a post-synthesis dealumination process via steaming or acid leaching on full-grown zeolites.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and characterization of Pd/ZSM-5/MCM-48 biporous catalysts with superior activity for benzene oxidation

Cheng

et al. 2010

Applied Catalysis A: General

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a b s t r a c t ZSM-5/MCM-48 composite materials with different acidities and enhanced thermal stability have been synthesized via a simple and reliable in situ overgrowth method. The as-prepared biporous materials and the Pd-impregnated catalysts were systematically investigated by various techniques, including XRD, ICP-OES, N 2 adsorption/desorption, H 2 chemisorption, SEM, TEM/HRTEM, FT-IR, 27 Al MAS NMR, NH 3 -TPD, H 2 -TPR and XPS. The characterization results reveal that all composite catalysts exhibit high surface area, large pore volume and long pore diameter. The quantity of acid sites increases as the ZSM-5 additive amount increases, and Al atoms are in the tetrahedral coordination positions in composite materials. The activity tests demonstrate that all the Pd-loaded catalysts are active in the total elimination of benzene, while the catalytic activity values of Pd-loaded ZSM-5/MCM-48 composite catalysts are much higher than those of Pd/ZSM-5 or Pd/MCM-48 alone. Both Pd 0 and Pd 2+ are responsible for the oxidation reaction, and the catalytic activities are primarily related to the support acidity and the Pd dispersion. In addition, the stability of the composite catalysts also improves with an appropriate amount of ZSM-5 additives in MCM-48. This research shows that the novel Pd-loaded composite catalysts are promising materials in the elimination of VOCs.

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“…One of the main drawbacks of this method is that the Brønsted acidity of the zeolite material is severely affected, and the materials may thus become less suitable for acid-catalyzed reactions. Moreover, it has been demonstrated that this postsynthesis modification treatment most often leads to encapsulated porosity, [12,13] which is not readily accessible and, therefore, only contributes to the improved diffusion in a limited way.…”

Section: Introductionmentioning

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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The Role of Mesopores in Intracrystalline Transport in USY Zeolite: PFG NMR Diffusion Study on Various Length Scales

Cited by 219 publications

References 23 publications

A solvent evaporation route towards fabrication of hierarchically porous ZSM-11 with highly accessible mesopores

A solvent evaporation route towards fabrication of hierarchically porous ZSM-11 with highly accessible mesopores

Synthesis and characterization of Pd/ZSM-5/MCM-48 biporous catalysts with superior activity for benzene oxidation

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

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