Spatial distribution, strength, and dealumination behavior of acid sites in nanocrystalline MFI zeolites and their catalytic consequences

Kim, Kyoung-Soo; Ryoo, Ryong; Jang, Hee-Jin; Choi, Minkee

doi:10.1016/j.jcat.2012.01.009

Cited by 134 publications

(62 citation statements)

References 48 publications

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“…However,asimilar effect of the thermal treatment was seen in all cases. In this case, different sensitivity to the atmosphere during calcination could stem from the large organic content that needs to be removed in hierarchical zeolites prepared by seed silanization, which may exacerbate hot spot formation.T he observed reductioni nt he thermal stability is also in contrastt oarecent study by Kim et al, [20] who reported that the external acid sites associated with nanocrystalline zeolites showedi mproved hydrothermal stabilityw ith respect to the internal acid sites based on the IR spectroscopy study of adsorbed pyridine and 2,6-di-tert-butylpyridine. However,t he different affinity of these probe molecules for the acid sites wasn ot taken into account and no quantification of the concentration of Lewis acid sites was provided.…”

Section: Preserving the Aluminum Distributioncontrasting

confidence: 56%

Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication

Mitchell

Milina

Verel

et al. 2015

Chemistry A European J

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A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends.

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Section: Preserving the Aluminum Distributioncontrasting

confidence: 56%

Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication

Mitchell

Milina

Verel

et al. 2015

Chemistry A European J

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“…The acid site strength in 2D MFI has been measured by FTIR spectra of pyridine adsorption after desorption at different temperatures [247,249,253]. In comparison to 3D MFI zeolites, the unilamellar 2D MFI nanosheets have weaker acid strength.…”

Section: Acidity Characterization For 2d Mfi Zeolitesmentioning

confidence: 99%

Two-Dimensional Zeolite Materials: Structural and Acidity Properties

Schulman

Liu

2020

Materials

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Zeolites are generally defined as three-dimensional (3D) crystalline microporous aluminosilicates in which silicon (Si4+) and aluminum (Al3+) are coordinated tetrahedrally with oxygen to form large negative lattices and consequent Brønsted acidity. Two-dimensional (2D) zeolite nanosheets with single-unit-cell or near single-unit-cell thickness (~2–3 nm) represent an emerging type of zeolite material. The extremely thin slices of crystals in 2D zeolites produce high external surface areas (up to 50% of total surface area compared to ~2% in micron-sized 3D zeolite) and expose most of their active sites on external surfaces, enabling beneficial effects for the adsorption and reaction performance for processing bulky molecules. This review summarizes the structural properties of 2D layered precursors and 2D zeolite derivatives, as well as the acidity properties of 2D zeolite derivative structures, especially in connection to their 3D conventional zeolite analogues’ structural and compositional properties. The timeline of the synthesis and recognition of 2D zeolites, as well as the structure and composition properties of each 2D zeolite, are discussed initially. The qualitative and quantitative measurements on the acid site type, strength, and accessibility of 2D zeolites are then presented. Future research and development directions to advance understanding of 2D zeolite materials are also discussed.

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“…These MFI materials have been shown to increase the rate of catalytic conversion in several reactions as compared to conventional MFI (especially those involving large reactant molecules), and the pivotal role played by the external acid sites in catalyzing these reactions has been elucidated. [18][19][20][21] The concentration of acid sites in zeolites is typically dictated by their silicon-to-aluminum (Si/Al) ratio. The Si/Al ratio is an important property that can also affect the product selectivity [22] in some reactions, and understanding the effects of varying this parameter is a key aspect of uncovering the structure-catalytic property relations.…”

Section: Introductionmentioning

confidence: 99%

Effect of Si/Al Ratio on the Catalytic Activity of Two‐Dimensional MFI Nanosheets in Aromatic Alkylation and Alcohol Etherification

et al. 2019

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Zeolite catalysts with pronounced two‐dimensional (2D) morphologies, specifically 2D MFI nanosheets composed of multilamellar stacks of MFI nanosheets, are hypothesized to offer accessibility advantages in catalytic reactions involving large, bulky molecules. The Si/Al ratio of zeolite catalysts is an important parameter determining their performance. However, the effect of Si/Al ratio on catalytic reactivity is not well understood in 2D zeolite catalysts. To provide further insight into this issue, the catalytic performance of 2D MFI nanosheet materials with different Si/Al ratios is compared using the liquid phase Friedel‐Crafts alkylation of mesitylene with benzyl alcohol & the self‐etherification of benzyl alcohol that occurs in parallel, both of which are catalyzed by Brønsted acid sites. The turnover frequency (TOF) of the catalysts is found to decrease with decreasing Si/Al ratio, with the etherification reaction being the main contributor to this trend. When the same reaction is carried out in the presence of a bulky poison, 2,6 di‐tert‐butylpyridine (DTBP), to selectively deactivate the external acid sites, only the etherification reaction of benzyl alcohol takes place in the micropores of the 2D MFI catalyst and the effectiveness factor is found to decrease with decreasing Si/Al ratio. The single component adsorption isotherms of benzyl alcohol show that the uptake normalized per acid site decreases with decreasing Si/Al ratio. Thus, increasing the density of acid sites in the micropores by decreasing the Si/Al ratio makes it more difficult for the reactant molecules to access them, as demonstrated by the decrease in TOF and the effectiveness factor. While the micropore reactions (benzene alkylation, alcohol etherification) showed a clear trend with Si/Al ratio, the reaction catalyzed on the external surface (mesitylene alkylation) did not, showing distinct differences in reactivity.

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Spatial distribution, strength, and dealumination behavior of acid sites in nanocrystalline MFI zeolites and their catalytic consequences

Cited by 134 publications

References 48 publications

Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication

Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication

Two-Dimensional Zeolite Materials: Structural and Acidity Properties

Effect of Si/Al Ratio on the Catalytic Activity of Two‐Dimensional MFI Nanosheets in Aromatic Alkylation and Alcohol Etherification

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