Impact of acid site speciation and spatial gradients on zeolite catalysis

Le, Thuy T.; Chawla, Aseem; Rimer, Jeffrey D.

doi:10.1016/j.jcat.2020.08.008

Cited by 80 publications

(68 citation statements)

References 101 publications

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“…32,34,[39][40][41][42] In comparison to this mechanism, the proposal of Lewis acidity that is inherent to the zeolite framework is less rigorously examined, but has received greater attention of late. 26,35,43,44 NMR experiments performed at high fields have enabled the characterization of a second framework Al(IV) site, 45 and the elucidation of the acidic nature of tri-coordinated framework aluminum in dehydrated ZSM-5. 43 The precursor to Lewis acid sites in this mechanism -unlike for the Lewis acid sites generated from EFAl -is tetrahedral framework aluminum.…”

Section: Introductionmentioning

confidence: 99%

On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

2021

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Section: Introductionmentioning

confidence: 99%

On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

2021

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Section: Introductionmentioning

confidence: 99%

“…Such framework provides zeolites with sorption, catalysis, ion-exchange or molecular sieving properties. Due to their practical features, zeolites are widely applied in environmental engineering [9], civil engineering [10,11], catalysis [12][13][14], and medicine [15][16][17]. Over 100 natural zeolites can be distinguished, among which only several types, like clinoptilolite or phillipsite, are accessible for mining and further use.…”

Section: Introductionmentioning

confidence: 99%

Recycling of Waste Solution after Hydrothermal Conversion of Fly Ash on a Semi-Technical Scale for Zeolite Synthesis

et al. 2021

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Nowadays, using fly ash for zeolites production has become a well-known strategy aimed on sustainable development. During zeolite synthesis in a hydrothermal conversion large amount of post-reaction solution is generated. In this work, the solution was used as a substrate for Na-A and Na-X zeolites synthesis at laboratory and technical scale. Obtained materials were characterized using particle size analysis, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR), and nitrogen adsorption/desorption isotherm. Produced zeolites revealed high purity (>98%) and monomineral zeolitic phase composition. The SiO2 content was in the range 39–42% and 40–38%, whereas Al2O3 content was 23–22% and 25–26% for Na-X and Na-A, respectively. TEM and BET analyses revealed Na-X zeolite pores were almost identical to commercial 13X with SBET in the range 671–734 m2/g. FTIR indicated slight differences between materials obtained at laboratory and technical scale in Si-O-(Si/Al) bridges of the zeolitic skeleton. The results showed good replicability of the laboratory process in the larger scale. The proposed method allows for waste solution reusability with a view to highly pure zeolites production in line with circular economy assumptions.

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“…These peaks can be assigned to BAS with enhanced acidity. 46,52 The low amount of extraframework Al V and Al VI species resulting from the dealumination process prefer to locate in proximity with surface BASs, the synergetic effects thereby contributing to the formation of BASs with stronger acidity 56,57 (Figure 5d).…”

Section: Resultsmentioning

confidence: 99%

Synergy of Extraframework Al³⁺ Cations and Brønsted Acid Sites on Hierarchical ZSM-5 Zeolites for Butanol-to-Olefin Conversion

et al. 2021

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ZSM-5 zeolite catalyzed dehydration of biobutanol has been widely used for the sustainable production of butene. Brønsted acid sites (BASs) in zeolites usually act as catalytically active sites. Lewis acid sites (LASs) are also active for alcohol dehydration. Therefore, extraframework aluminum species have been introduced to zeolites as LASs. Tricoordinated Al species are the strongest LASs, which can enhance the acidity of adjacent surface BASs. Here, we combined solid-state nuclear magnetic resonance (NMR) spectroscopy and in situ diffuse reflectance infrared spectroscopy (DRIFTS) to investigate the local structures and acidity of hierarchical ZSM-5 zeolites with/without the introduction of Al3+ cations as well as their correlations with the catalytic performance in biobutanol dehydration. 27Al magic angle spinning (MAS) NMR, 27Al multiple-quantum (MQ) MAS NMR, and 31P MAS NMR after loading trimethylphosphine oxide (TMPO) probe molecules showed that the tricoordinated Al species are dominant acid sites after introducing Al3+ cations into pure silica hierarchical ZSM-5 zeolites. For BASs-rich hierarchical ZSM-5 zeolites (SiO2/Al2O3 = 50), the Al3+ cations tend to stay in proximity to the bridging Si–OH–Al and thereby strongly enhance the acidic strength of BASs via the synergy of LASs and BASs. Contributing from the synergy effect, the ultrastrong BAS has been formed, which gives an obvious improvement in the biobutanol conversion and butene selectivity. In situ DRIFTS showed that tricoordinated Al3+ cations cooperating with BASs can promote the formation of butoxy intermediates at a low reaction temperature, which further improves the butanol dehydration.

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Impact of acid site speciation and spatial gradients on zeolite catalysis

Cited by 80 publications

References 101 publications

On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

Recycling of Waste Solution after Hydrothermal Conversion of Fly Ash on a Semi-Technical Scale for Zeolite Synthesis

Synergy of Extraframework Al³⁺ Cations and Brønsted Acid Sites on Hierarchical ZSM-5 Zeolites for Butanol-to-Olefin Conversion

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Impact of acid site speciation and spatial gradients on zeolite catalysis

Cited by 80 publications

References 101 publications

On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

Recycling of Waste Solution after Hydrothermal Conversion of Fly Ash on a Semi-Technical Scale for Zeolite Synthesis

Synergy of Extraframework Al3+ Cations and Brønsted Acid Sites on Hierarchical ZSM-5 Zeolites for Butanol-to-Olefin Conversion

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Synergy of Extraframework Al³⁺ Cations and Brønsted Acid Sites on Hierarchical ZSM-5 Zeolites for Butanol-to-Olefin Conversion