Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication

Mitchell, Sharon; Milina, Maria; Verel, René; Hernández-Rodríguez, M.J.; Pinar, Ana B.; McCusker, Lynne B.; Pérez‐Ramírez, Javier

doi:10.1002/chem.201500992

Cited by 45 publications

(38 citation statements)

References 44 publications

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“…This effect could be interpreted as the result of removal of those debris of zeolite which blocked the pore mouth of the zeolite which accompanied by a considerable decrease of BET and micropore area. In addition, The B/L ratio also further increased with a long time of acid wash. As reported in the literature the desilication with NaOH led to significantly realuminum in the surface of zeolite and produced tetrahedrally coordinated Al species . This effect is more pronounced for zeolites with Al‐rich composition.…”

Section: Resultssupporting

confidence: 61%

Influence of Acid Wash on the Structural and Catalytic Properties of the Hierarchical Zeolite Y

Zheng

et al. 2016

ChemistrySelect

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Although the hierarchical architectures of zeolites are important, the precise control of their acidities also has a great influence on their catalytic properties. The hierarchical zeolite Y with high mesoporosity and well crystal structure was prepared. Then this hierarchical zeolite Y was washed with acid solution for different time. It was found that very limited mesopores formed during this acid wash procedure. However, their acidities characteristics changed dramatically. It has been found that the Brønsted acidities increased with acid wash procedure for a short time. If acid wash was performed on the resultant sample for a long time, the Lewis acidities begin decreased and the B/L ratio increased, which was most likely the result of removal of tetrahedrally coordinated EFAl species formed during desilication. This study showed that the improved accessibility of the active sites and the persevered crystallinity of the hierarchical zeolite Y were both responsible for the increased catalytic activities and an appropriate acid wash treatment comprised a powerful approach to tune the functions and catalytic properties of hierarchical zeolites Y.

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Section: Resultssupporting

confidence: 61%

Influence of Acid Wash on the Structural and Catalytic Properties of the Hierarchical Zeolite Y

Zheng

et al. 2016

ChemistrySelect

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“…During base leaching, desilication plays a major role in forming new pores and as such the Si/Al ratio of zeolite decreases from 58 to 32. Previous studies demonstrate that aluminium atoms that concern zeolite acidity were usually affected during base leaching and the redistribution of aluminium atoms lead to a decreased percentage of Brønsted over Lewis acid sites . In this study, we employed infrared spectroscopy after adsorption of alkylpyridines of different size (pyridine: 0.57 nm, 2,6‐lutidine: 0.67 nm, and 2,4,6‐collidine: 0.74 nm) to probe the accessibility of the acid sites .…”

Section: Resultsmentioning

confidence: 99%

“…With the introduction of a hollow structure, a more uniform chemical environment for aluminium was observed, as the small cross‐peaks inherent in the parent zeolite were eliminated (Figure b). The signals were narrow in the F2 projection, indicating a small quadrupolar interaction of aluminium . Table summarizes the results of isotropic chemical shift ( δ i so ) and the quadrupolar interaction product ( P Q ).…”

Section: Resultsmentioning

confidence: 99%

“…Previous studies demonstrate that aluminium atoms that concern zeolite acidity were usually affectedd uring base leachinga nd the redistribution of aluminiuma toms lead to a decreased percentage of Brønsted over Lewis acid sites. [29] In this study,w ee mployed infrared spectroscopy after adsorption of alkylpyridines of different size (pyridine:0 .57 nm, 2,6-lutidine:0 .67 nm, and 2,4,6-collidine:0 .74 nm) to probe the accessibility of the acid sites. [30] Figure 6s hows that pyridine adsorption on acid sites distinguishes Brønsted sites (1545 cm À1 )w ith Lewis sites (1455 cm À1 ).…”

Section: Resultsmentioning

confidence: 99%

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Variation of Aluminium Distribution in Small‐Sized ZSM‐5 Crystals during Desilication

Roy

Krumeich

et al. 2019

Chemistry A European J

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Hollow ZSM‐5 zeolites of size below one micrometer can be produced by desilication of crystals with aluminium zoning. The parent crystals have a core–shell structure: the core part has nearly no aluminium, whereas the aluminium content in the shell increases when extending to exterior surface. Transmission electron microscopy confirmed the preservation of the crystalline shell after base leaching, but could not identify its subtle change. An increase of the Si/Al ratio of the surface was detected upon leaching the parent material to form the hollow zeolite by using ambient pressure X‐ray photoelectron spectroscopy and infrared spectroscopy of substituted alkylpyridines. 27Al MAS NMR showed that base leaching results in a reduced percentage of distorted tetrahedrally coordinated aluminium. The reprecipitation of dissolved species occurs and tetrahedrally coordinated tin atoms can thus be introduced to the shell framework. Overall, the formation of hollow ZSM‐5 zeolites by desilication involves not only the removal of silicon‐rich core, but also a reduced percentage of exterior aluminium‐related acid sites, which should be considered while using hollow zeolites in acid‐catalyzed reactions.

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“…It is well known that partitioning of ions at the interface of zeolites and aqueous solutions is a very complex phenomenon involving the interplay of chemical, electrostatic (physical forces) and crystallographic factors, the investigation of which can only be performed through a multidisciplinary study. Scope of this work is the investigation of the adsorption/desorption behavior of two trivalent rare‐earth cations, neodymium (Nd 3+ ) and yttrium (Y 3+ ), at the interface of sodium form of zeolite FAU X (usually denoted NaX).…”

Section: Introductionmentioning

confidence: 99%

Formation of Supramolecular Clusters at the Interface of Zeolite X Following the Adsorption of Rare‐Earth Cations and Their Impact on the Macroscopic Properties of the Zeolite

et al. 2018

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The adsorption behavior of neodymium (Nd ) and yttrium (Y ) cations on synthetic FAU zeolite X in its sodium form (NaX) has been investigated by means of macroscopic (adsorption isotherm determination and thermal analysis) and microscopic measurements (including solid-state NMR spectroscopy and X-ray powder diffraction). The multidisciplinary study reveals some unexpected features. Firstly, adsorption constants of cations are not correlated to their ionic radii or hydration enthalpy. The adsorption constant of Y on NaX was indeed about twice that of Nd , which is the opposite of what could be expected based on the size of the cations. In addition, adsorption was accompanied by partial dealumination of the zeolite framework. The extent of dealumination changed depending on the exchanged cations, with the extent being more significant on the Nd-exchanged zeolite than on the Y-exchanged one. The most interesting finding of this study, however, is the presence of supramolecular clusters composed of water, Nd , residual sodium ions, and extra-framework aluminum at the interface of Nd-exchanged zeolite. The hypothesis that these host-guest complexes are responsible of the significantly different behavior exhibited by NaX towards the adsorption/desorption of Nd and Y has been formulated.

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Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication

Cited by 45 publications

References 44 publications

Influence of Acid Wash on the Structural and Catalytic Properties of the Hierarchical Zeolite Y

Influence of Acid Wash on the Structural and Catalytic Properties of the Hierarchical Zeolite Y

Variation of Aluminium Distribution in Small‐Sized ZSM‐5 Crystals during Desilication

Formation of Supramolecular Clusters at the Interface of Zeolite X Following the Adsorption of Rare‐Earth Cations and Their Impact on the Macroscopic Properties of the Zeolite

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