Origin of Water-Induced Brønsted Acid Sites in Sn-BEA Zeolites

Sushkevich, Vitaly L.; Kots, Pavel A.; Kolyagin, Yu. G.; Yakimov, Alexander V.; Marikutsa, Artem; Ivanova, I. I.

doi:10.1021/acs.jpcc.8b12462

Cited by 45 publications

(47 citation statements)

References 64 publications

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“…Thus, it can be concluded that Sn‐Beta possesses relatively strong Lewis acid sites alongside Brønsted acidic active sites, whereas Hf‐BEA only contains Lewis acid active sites, which are of a lower strength to those found in Sn‐BEA. We note that the observation of Brønsted acidity in Sn‐BEA is supported by recent NMR studies, [24a] whilst the weaker Lewis acid strength of Hf‐BEA relative to Sn‐BEA is supported by 15 N MAS NMR studies of various Lewis and Brønsted acidic silicates [26] …”

Section: Resultssupporting

confidence: 72%

Solvent‐Activated Hafnium‐Containing Zeolites Enable Selective and Continuous Glucose–Fructose Isomerisation

et al. 2020

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The isomerisation of glucose to fructose is a critical step towards manufacturing petroleum-free chemicals from lignocellulosic biomass. Herein we show that Hf-containing zeolites are unique catalysts for this reaction, enabling true thermodynamic equilibrium to be achieved in a single step during intensified continuous operation, which no chemical or biological catalyst has yet been able to achieve. Unprecedented single-pass yields of 58 % are observed at a fructose selectivity of 94 %, and continuous operation for over 100 hours is demonstrated. The unexpected performance of the catalyst is realised following a period of activation within the reactor, during which time interaction with the solvent generates a state of activity that is absent in the synthesised catalyst. Mechanistic studies by X-ray absorption spectroscopy, chemisorption FTIR, operando UV/Vis and 1 H-13 C HSQC NMR spectroscopy indicate that activity arises from isolated Hf IV atoms with monofunctional acidic properties.

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Section: Resultssupporting

confidence: 72%

Solvent‐Activated Hafnium‐Containing Zeolites Enable Selective and Continuous Glucose–Fructose Isomerisation

et al. 2020

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“…Exposure of Sn-Beta to Na + -containing solutions, thought to exchange Si–OH groups proximal to open Sn sites, decreased glucose–fructose isomerization reactivity (353 K), consistent with DFT-predicted stabilization of the kinetically relevant 1,2-hydride shift transition state by a proximal Si–OH group . Others have since affirmed that proximal Si–OH groups at open sites participate cooperatively in fructose etherification, also suggesting that they behave as weak Brønsted acid sites to catalyze dehydration of oxanobornene to p -xylene and isobutene oligomerization . This role of a proximal binding site is reminiscent of that proposed for paired Mg 2+ cations during DNA hydrolysis over DNA Polymerase I and in glucose isomerization at Mn 2+ pairs in glucose isomerase …”

Section: Kinetic and Thermodynamic Factors That Underpin Descriptions...supporting

confidence: 64%

“…69 Others have since affirmed that proximal Si−OH groups at open sites participate cooperatively in fructose etherification, 70 also suggesting that they behave as weak Brønsted acid sites 38 to catalyze dehydration of oxanobornene to p-xylene 71 and isobutene oligomerization. 72 This role of a proximal binding site is reminiscent of that proposed for paired Mg 2+ cations during DNA hydrolysis over DNA Polymerase I 73 and in glucose isomerization at Mn 2+ pairs in glucose isomerase. 74 Harris et al 65 used pyridine to titrate Sn-Beta in vacuo, prior to measuring first-order glucose isomerization rate constants (373 K, per Sn), quantifying the number of active sites to be equal to the number of Sn 2316 sites.…”

Section: Influence Of Local Site Configuration On Catalysismentioning

confidence: 87%

Opportunities in Catalysis over Metal-Zeotypes Enabled by Descriptions of Active Centers Beyond Their Binding Site

et al. 2020

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Active centers in porous solid catalysts are multifaceted in structure, comprised of primary sites that bind intermediates, secondary environments that confine intermediates and transition states, and coadsorbed intraporous molecules, clusters, and networks of reactants and solvents that interact with species along reaction coordinates. Zeotypes are a class of microporous oxides whose lattices are substituted with metal heteroatoms, which serve as primary binding sites to catalyze a variety of chemical transformations including reductions, oxidations, and condensations. Research efforts continue to develop more complete mechanistic descriptions of catalytic behavior, requiring increasingly accurate descriptions of all moieties that comprise active centers. Framework metal heteroatoms adopt various local configurations that are difficult to control synthetically and are susceptible to restructuring during reaction. These binding sites contain structural and catalytic diversity even when they are located in the nominally simplest zeotype frameworks, as is typically the case for "model" heterogeneous catalyst materials of purportedly well-defined structure. Secondary environments are well-documented to influence catalysis via shape selectivity and confinement effects, yet their polarity, as defined by the oxide framework and any polar binding sites it contains (e.g., heteroatoms, hydroxyl groups), also influences the structures and Gibbs free energies of intermediates and transition states, as well as coadsorbed intraporous molecules, leading to further catalytic diversity. These three aspects that describe active centers at and beyond their binding sites must be accounted for in quantitative descriptions of the kinetic and thermodynamic factors that dictate catalysis over metal-containing zeotypes. Advances in describing the structural and catalytic diversity of these materials have required harnessing state of the art computational, spectroscopic, material synthesis, and chemical characterization methods. Herein, we outline opportunities to leverage experiment and theory to interrogate these aspects of active centers with increasing fidelity, to further advance molecular descriptions of catalysis over metal-containing zeotypes and broaden their range of catalytic behavior.

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“…At the first step, the reactivity of different sites toward hydrolysis was addressed by a detailed in situ 119 Sn MAS NMR study of 119 Sn-BEA-vac400 interaction with adsorbed D 2 O. In contrast to our previous studies, , here, the spectra recorded by the direct-polarization Hahn-echo (DP-HE) sequence were analyzed. Compared with CPMG-based techniques, DP-HE has much lower sensitivity, but using this classical technique allows us to get quantitative spectral data with the highest possible resolution.…”

Section: Resultsmentioning

confidence: 99%

Tuning of Sn-BEA Reactivity by Controlling Tin Location in the BEA Framework

et al. 2021

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The combined application of 119Sn MAS NMR spectroscopy, adsorption of probe molecules, and catalytic testing in the MPVO conversion of cyclohexanone into cyclohexanol have been used to uncover T-positions in the zeolite Sn-BEA structure, providing for Sn-sites responsible for its high catalytic activity. The results reveal that tin atoms located in T3, T4, and T9 positions (group I) and in T1, T2, and T8 positions (group II) of the zeolite BEA structure generate Sn-sites with the highest Lewis acidity and the highest ability to hydrolyze, respectively, and therefore provide for the highest catalytic activity. In contrast, the sites in T5–T7 positions (group III) occupy more energetically favorable T-positions, leading to less reactive Sn-sites. Besides that, it has been shown that the content of different Sn-sites can be altered by the variation of the duration of hydrothermal synthesis of Sn-BEA and that the highest content of the most reactive sites can be achieved at the end of crystallization and the onset of the postcrystallization period.

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Origin of Water-Induced Brønsted Acid Sites in Sn-BEA Zeolites

Cited by 45 publications

References 64 publications

Solvent‐Activated Hafnium‐Containing Zeolites Enable Selective and Continuous Glucose–Fructose Isomerisation

Solvent‐Activated Hafnium‐Containing Zeolites Enable Selective and Continuous Glucose–Fructose Isomerisation

Opportunities in Catalysis over Metal-Zeotypes Enabled by Descriptions of Active Centers Beyond Their Binding Site

Tuning of Sn-BEA Reactivity by Controlling Tin Location in the BEA Framework

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