Hydrogen Bond Formation of Brønsted Acid Sites in Zeolites

Schroeder, Christian; Siozios, Vassilios; Mück‐Lichtenfeld, Christian; Hunger, Michael; Koller, Hubert

doi:10.1021/acs.chemmater.9b04714

Cited by 53 publications

(159 citation statements)

References 67 publications

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“…[46][47][48][49] H4 corresponds to acid sites with enhanced acidity tentatively associated with isolated Brønsted sites (AlOHSi). [50] In our case,H4isnot related to any ammonium residue as the { 1 H}-15 NCPNMR spectrum does not show any ammonium cations,i na greement with the zeolite IR spectrum where the characteristic deformation vibration band of ammonium at 1455 cm À1 is absent, Figure S7. [16] Ther emaining signal at 2.6 ppm corresponds to extra-framework aluminum species H EFAL .…”

Section: Hm As Nmr Spectroscopysupporting

confidence: 46%

“…TheNMR study clearly showed that in contrast to Y, USY displays extremely high acidic sites (H4 sites) that might correspond to isolated Brønsted sites (AlOHSi). [50] These acid sites are absent in Y. Theshortening of the diffusion pathlengths,i.e., the additional mesoporosity introduced during stabilization, is also present, but it is not the major factor for this high performance.T oe xclude this possibility,ahomemade nanosized zeolite,n ano-Y (70 nm particle size,referred to as Y-70 in the original report), [53] with as imilar framework (Si/Al = 1.7) composition is tested in…”

Section: Discussionmentioning

confidence: 99%

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Unlocking the Potential of Hidden Sites in Faujasite: New Insights in a Proton Transfer Mechanism

et al. 2021

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Zeolite Yand its ultra-stabilized hierarchicald erivative (USY) are the most widely used zeolite-based heterogeneous catalysts in oil refining,p etrochemisty,a nd other chemicals manufacturing.A fter almost 60 years of academic and industrial research, their resilience is unique as no other catalyst displaced them from key processes such as FCC and hydrocracking.The present study highlights the key difference leading to the exceptional catalytic performance of USY versus the parent zeolite Yi namulti-technique study combining advanced spectroscopies (IR and solid-state NMR) and molecular modeling.The results highlight ahitherto unreported proton transfer involving inaccessible active sites in sodalite cages that contributes to the exceptional catalytic performance of USY.

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Section: Hm As Nmr Spectroscopysupporting

confidence: 46%

Section: Discussionmentioning

confidence: 99%

Unlocking the Potential of Hidden Sites in Faujasite: New Insights in a Proton Transfer Mechanism

et al. 2021

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“…The NMR parameters extracted from this data are listed in Table 2. Although we used two lines for 1 H, it must be understood as a continuous distribution of 1 H environments arising from a broad range of Si(OH)Al hydrogenbonded Brønsted acid sites [48][49][50] and possibly Al(OH)Al sites. 51 This asymmetric distribution, ranging from 0 ppm to 10 ppm with a maximum at 2.6 ppm, is similar for all three coordination states of aluminum.…”

Section: Sitementioning

confidence: 99%

Atomic-Scale Structure and its Impact on Chemical Properties of Aluminum Oxide Layers Prepared by Atomic Layer Deposition on Silica

Kaushik¹,

Leroy²,

Chen³

et al. 2021

Preprint

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We report the atomic-scale structure of alumina layers obtained by atomic layer deposition (ALD) of trimethylaluminium onto partially dehydroxylated silica. Such a detailed insight into the atomic structure of the species formed with increasing Al content was gained using a variety of one- and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments involving 27Al, 1H and 29Si nuclei. 15N dynamic nuclear polarization surface-enhanced NMR spectroscopy (15N DNP SENS) and infrared spectroscopy using 15N-labelled pyridine as a probe molecule reveal that aluminium oxide layers on amorphous silica contain both strong Bronsted and strong Lewis acid sites, whereby the relative abundance and nature of these sites, and therefore the acidity of the surface, evolve with increasing thickness of the alumina film.

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“…[3f, 4] BAS can also form hydrogen bonds when suitable OÀ O distances and mutual alignments of O atoms exist. [5] A hydrogen bond is defined [6] by a 1 H chemical shift that is deshielded from the unperturbed BAS at typically 4 ppm. Here, we employ a combination of solid-state NMR methods and DFT calculations of zeolite cluster models for zeolite SSZ-42.…”

mentioning

confidence: 99%

Hydrogen Bonds Dominate Brønsted Acid Sites in Zeolite SSZ‐42: A Classification of Their Diversity

2021

Self Cite

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The zeolite catalyst SSZ-42 shows a remarkable high abundance ( � 80 %) of hydrogen-bonded Brønsted acid sites (BAS), which are deshielded from the 1 H chemical shift of unperturbed BAS at typically 4 ppm. This is due to their interaction with neighboring oxygen atoms in the zeolite framework when oxygen alignments are suitable. The classification and diversity of hydrogen bonding is assessed by DFT calculations, showing that oval-shaped 6-rings and 5rings allow for a stronger hydrogen bond to oxygen atoms on the opposite ring side, yielding higher experimental chemical shifts (δ ( 1 H) = 6.4 ppm), than circular 6-rings (δ( 1 H) = ppm). Cage-like structures and intra-tetrahedral interactions can also form hydrogen bonds. The alignment of oxygen atoms is expected to impact their role in the stabilization of intermediates in catalytic reactions, such as surface alkoxy groups and possibly transition states.Zeolites belong to the most successful inorganic materials in large-scale applications, including ion-exchange, adsorption/separation processes, and heterogeneous catalysis. [1] Their hydrothermal syntheses often rely on organic structure-directing agents (OSDAs), typically quaternary ammonium cations, filling the pore system in the as-made material. [2] The charge of the OSDAs can be balanced by AlO 4/2

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Hydrogen Bond Formation of Brønsted Acid Sites in Zeolites

Cited by 53 publications

References 67 publications

Unlocking the Potential of Hidden Sites in Faujasite: New Insights in a Proton Transfer Mechanism

Unlocking the Potential of Hidden Sites in Faujasite: New Insights in a Proton Transfer Mechanism

Atomic-Scale Structure and its Impact on Chemical Properties of Aluminum Oxide Layers Prepared by Atomic Layer Deposition on Silica

Hydrogen Bonds Dominate Brønsted Acid Sites in Zeolite SSZ‐42: A Classification of Their Diversity

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