Synthesis strategies to control the Al distribution in zeolites: thermodynamic and kinetic aspects

Bae, Juna; Dusselier, Michiel

doi:10.1039/d2cc05370e

Cited by 35 publications

(20 citation statements)

References 131 publications

(246 reference statements)

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“…Given that positive charges on these OSDAs compensate for the negatively charged aluminosilicate framework, it is natural to assume that the OSDAs can control the location of Al. [15][16][17] Although kinetics 14 and the presence of alkali metal cations 18 play major roles, a general agreement for experimental and computational studies is that the positive charge introduced by OSDAs is in proximity to Al in zeolites. 10,13,17,[19][20][21] However, a general understanding of factors contributing to the strength of this Al site-directing ability for different OSDAs is still lacking.…”

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confidence: 91%

“…7 Indeed, several studies have demonstrated that zeolite catalysts with varying Al distributions can exhibit different catalytic behaviors. [8][9][10][11][12][13][14] An intuitive strategy to control the location of Al employs organic structure-directing agents (OSDAs). [15][16][17] OSDAs are generally organics that fit into the internal space of zeolite structures through van der Waals interactions.…”

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confidence: 99%

“…7 Indeed, several studies have demonstrated that zeolite catalysts with varying Al distributions can exhibit different catalytic behaviors. 8–14…”

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confidence: 99%

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Analysis of Al site-directing ability of organic structure-directing agents in FER and CHA zeolites: a computational exploration of energetic preferences

Oishi¹,

Muraoka²,

Nakayama³

2023

Chem. Commun.

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confidence: 91%

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Analysis of Al site-directing ability of organic structure-directing agents in FER and CHA zeolites: a computational exploration of energetic preferences

Oishi¹,

Muraoka²,

Nakayama³

2023

Chem. Commun.

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“…While the topic of Si, Al ordering in a zeolite is a topic widely studied, as well as the role of OSDAs in the synthesis of zeolites, ,,− the reasons why (or if) the aluminum contributes to stabilize such a zeolite phase is a less explored aspect, and this is the aim of the present study. Following the idea of our previous work regarding the roles of fluoride and aluminum as SDAs in the synthesis of zeolites, we now try to compare the role of aluminum and fluoride on the synthesis of recently synthesized aluminosilicate zeolites PST-21 (PWO), PST-22 (PWW), and ERS-7 (ESV) by selecting certain specific cases in which different zeolites are obtained using the same OSDA when the synthesis gel has a silicate or aluminosilicate chemical composition.…”

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confidence: 99%

The Directing Role of Aluminum in the Synthesis of PST-21 (PWO), PST-22 (PWW), and ERS-7 (ESV) Zeolites

Altundal,

Sastre

2023

J. Phys. Chem. C

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Zeolites are a diverse class of crystalline microporous materials of, mainly, aluminosilicate chemical composition. Organic structure-directing agents (OSDAs) are generally utilized in zeolite synthesis to drive the outcome to a specific zeolite phase. In addition to OSDA, the presence and content of aluminum in the gel play a role in driving the synthesis under specific conditions. The structure-directing role of aluminum as well as fluoride in zeolite synthesis was explored through the analysis of three recently synthesized aluminosilicate zeolites, PST-21 (PWO), PST-22 (PWW), and ERS-7 (ESV), using a force field simulation approach. An updated and recently proposed method based on the calculation of “synthesis energy” is used to predict the stability of zeolites at pure-silica and aluminosilicate gel compositions, also able to include fluoride anions as well as OSDAs, and hence largely general. The results are not only demonstrating that the calculated structures with lowest “synthesis energy” correspond to those experimentally obtained under “standard” (meaning HF/SDA = 1) synthesis conditions but also that new structures obtained under the recently introduced “excess fluoride approach” are those which follow with energy slightly larger than the lowest, as calculated from the list of competing zeolites. With this method, we were able to rationalize the structure-directing effect of aluminum, in the presence of fluoride and OSDAs, in the synthesis of zeolites.

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“…65 As a result, significant effort has been dedicated to understanding the means by which to intentionally synthesize paired Al zeolites. The influence of kinetic factors, [66][67] Si source, 68 Al Source, 68 structure directing agents (SDA) [69][70] have all been investigated. The cations present in the SDAs that balance the charge of the Al 3+ , plays a role in Al siting within the zeolite.…”

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Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Abdelrahman

Lawal

2023

Preprint

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The spatial distribution of tetrahedrally coordinated aluminum incorporated into a mordenite framework inverse framework zeolite was investigated through the proton site-selective probe chemistry of alkylamine Hofmann elimination. Protons associated with paired Al sites were exclusively exchanged with divalent cobalt, while isolated protons remained intact and readily quantified through Hofmann elimination of adsorbed alkylammonium species. Through a combination of temperature-programmed methods and spectroscopic characterization, the stability of the adsorbed alkylammonium was found to be crucial to the accurate estimation of isolated protons. Only alkylammonium species undergoing Hofmann elimination through a primary carbocation were found to exclusively probe isolated protons on the surface of cobalt-exchanged ZSM-5. More stable secondary and tertiary carbocations typically used in the characterization of acid sites, resulted in significant overestimates of protonic site densities. The result is contrary to purely protonic zeolites, where alkylammonium stability is inconsequential to the quantification of the acid sites they are coordinated with. Consequently, n-propylamine was found to be a suitable reactive probe molecule for the quantification of isolated protonic sites on divalent metal-cation zeolite surfaces, forming n-propylammonium upon adsorption. Ensuring accurate probing of isolated protons on the surface of metal cation exchanged zeolites was also demonstrated to require control of ion-exchange conditions and sufficient extent of zeolite exposure to the adsorbing n-propylamine. The fraction of paired Al sites in ZSM-5 was measured to systematically increase with Al content, ranging between 6 and 63 % across a Si/Al of 140 and 11.5, respectively. Experimentally measured Al pairing was in excellent quantitative agreement with a binomial distribution, suggesting a random incorporation of Al into the tetrahedral sites of ZSM-5 at next-nearest-neighboring positions.

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Synthesis strategies to control the Al distribution in zeolites: thermodynamic and kinetic aspects

Abstract: The activity and selectivity of acid-catalyzed chemistry is highly dependent on the Brønsted and Lewis acid sites generated by Al substitutions in a zeolite framework with the desired pore architecture....

Cited by 35 publications

References 131 publications

Analysis of Al site-directing ability of organic structure-directing agents in FER and CHA zeolites: a computational exploration of energetic preferences

Analysis of Al site-directing ability of organic structure-directing agents in FER and CHA zeolites: a computational exploration of energetic preferences

The Directing Role of Aluminum in the Synthesis of PST-21 (PWO), PST-22 (PWW), and ERS-7 (ESV) Zeolites

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

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