The Preparation and Characterization of Aluminum-Deficient Zeolites

Scherzer, Julius

doi:10.1021/bk-1984-0248.ch010

Cited by 166 publications

(85 citation statements)

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“…In order to retain the crystal structure of dealuminated zeolite crystal, the post dealumination can also be carried out in aqueous solutions containing ammonium hexafluorosilicate [20,21] and SiCl 4 [22][23][24]. This can heal the dealuminated framework sites with silicate species during the dealumination treatment.…”

Section: Post-synthetic Demetallation Of Zeolite Crystalsmentioning

confidence: 99%

Hierarchically Nanoporous Zeolites and Their Heterogeneous Catalysis: Current Status and Future Perspectives

Somorjai

2014

Catal Lett

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The research field of hierarchically nanoporous zeolites has been growing at an enormous pace over the past decades. Hierarchically nanoporous zeolites have versatile structural properties such as high surface area and large pore volume that can alleviate diffusional limitations of conventional zeolites with solely microporous framework. In this review, various synthesis strategies to hierarchically nanoporous zeolites and their structural advantages in catalytic reactions will be reviewed. In the first part, many novel synthetic approaches for hierarchically nanoporous zeolites such as post-demetallation, softtemplating, hard-templating, and dual-pore-generating surfactant-directed methods will be introduced. In the second part, catalytic applications of hierarchically nanoporous zeolites on various chemical reactions involving isomerization, cracking, alkylation and oxidation will be discussed. The present comprehensive review will provide future opportunities and perspectives on the research of hierarchically nanoporous zeolites including their applications to catalytic reactions.

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Section: Post-synthetic Demetallation Of Zeolite Crystalsmentioning

confidence: 99%

Hierarchically Nanoporous Zeolites and Their Heterogeneous Catalysis: Current Status and Future Perspectives

Somorjai

2014

Catal Lett

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“…Therefore, the data presented in Tables 2 and 3 The steaming treatment, as pointed above, may cause dealumination by a process similar to the one that occurs in zeolites. This process is expected to bring about a reduction of the number of Brönsted acid sites creating extra-framework aluminum [37] or at least the hydrolysis of some bonds changing the coordination of aluminum sites, as suggested by the changes in the 27 Al NMR spectra. Along with this process, also the partial degradation of the structure has influence on the measured acidity and catalytic activity since it can block the accessibility of molecules to a part of potential active sites.…”

Section: Catalytic Testsmentioning

confidence: 99%

Al-containing MCM-41 type materials prepared by different synthesis methods: Hydrothermal stability and catalytic properties

Lourenço¹,

Fernandes²,

Henriques³

et al. 2006

Microporous and Mesoporous Materials

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Al-containing MCM-41 type materials were prepared by three different synthesis methods (aluminum grafting on the calcined MCM-41, pH adjustment during the crystallization period and crystallization in the presence of zeolite seeds). The samples were characterized by powder XRD, nitrogen adsorption, 27 Al MAS NMR and FTIR with pyridine as probe molecule. All the samples exhibit a high hydrothermal stability at high temperature just with a minor structural degradation. N 2 adsorption data obtained for the sample prepared from a gel containing zeolite seeds suggest a higher structural resistance to the hydrothermal treatment in comparison with the samples prepared by other methods. A different type of pyridine adsorbed, probably interacting simultaneously with a Brönsted and a Lewis acid site, is observed upon pyridine adsorption. This type of adsorption is stronger for the sample prepared in the presence of zeolite seeds and is not observed on Al-grafted MCM-41. 2The catalytic activity towards the isomerization of α-pinene depends mainly on the number of Brönsted acid sites. The data obtained in this study strongly indicate that for this type of materials, the Lewis acid sites do not influence the selectivity for the isomerization products.

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“…Commonly used methods include the preparation of composite materials in which zeolite domains are embedded in mesoporous supports, the synthesis of micro-and mesoporous zeolitic material through carbon templating, soft templating using multifunctional surfactants, and dealumination by hydrothermal treatment or acid leaching. [6][7][8][9][10][11] The latter method, in which aluminum is selectively removed from the zeolite framework, has been successfully applied to create mesoporosity in zeolite Y and mordenite. 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.…”

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 Preparation and Characterization of Aluminum-Deficient Zeolites

Cited by 166 publications

References 0 publications

Hierarchically Nanoporous Zeolites and Their Heterogeneous Catalysis: Current Status and Future Perspectives

Hierarchically Nanoporous Zeolites and Their Heterogeneous Catalysis: Current Status and Future Perspectives

Al-containing MCM-41 type materials prepared by different synthesis methods: Hydrothermal stability and catalytic properties

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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