Genesis and Stability of Hydronium Ions in Zeolite Channels

Wang, Meng; Jaegers, Nicholas R.; Lee, Mal‐Soon; Wan, Chuan; Hu, Jian Zhi; Shi, Hui; Mei, Donghai; Burton, Sarah D.; Camaioni, Donald M.; Gutiérrez, Oliver Y.; Glezakou, Vassiliki Alexandra; Rousseau, Roger; Wang, Yong; Lercher, Johannes A.

doi:10.1021/jacs.8b07969

Cited by 151 publications

(221 citation statements)

References 91 publications

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“…As a point of reference, the proton affinity of a water trimer is similar to that of ammonia 44 , ca. 9 eV, and the facile formation of hydrated H 3 O + in zeolites has been extensively discussed in the literature [44][45][46][47][48] . A single acetonitrile molecule does not become spontaneously protonated by the Al-O-Si bridge BAS, while the dimeric [(CH 3 CN) 2 H] + cluster is basic enough to spontaneously abstract the proton.…”

Section: Resultsmentioning

confidence: 99%

Understanding solvent effects on adsorption and protonation in porous catalysts

Gould

Cho

et al. 2020

Nat Commun

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Solvent selection is a pressing challenge in developing efficient and selective liquid phase catalytic processes, as predictive understanding of the solvent effect remains lacking. In this work, an attenuated total reflection infrared spectroscopy technique is developed to quantitatively measure adsorption isotherms on porous materials in solvent and decouple the thermodynamic contributions of van der Waals interactions within zeolite pore walls from those of pore-phase proton transfer. While both the pore diameter and the solvent identity dramatically impact the confinement (adsorption) step, the solvent identity plays a dominant role in proton-transfer. Combined computational and experimental investigations show increasingly favorable pore-phase proton transfer to pyridine in the order: water < acetonitrile < 1,4dioxane. Equilibrium methods unaffected by mass transfer limitations are outlined for quantitatively estimating fundamental thermodynamic values using statistical thermodynamics.

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Section: Resultsmentioning

confidence: 99%

Understanding solvent effects on adsorption and protonation in porous catalysts

Gould

Cho

et al. 2020

Nat Commun

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“…Water adsorbed at Na + cations, such as existing in aluminosilicates for the compensation of negative framework charges, is observed at 3.5 ppm (Kasai and Jones 1984). In zeolites containing Brønsted acid sites [Si-(OH)-Al], adsorbed water can be protonated and forms hydroxonium ions, which leads to 1 H MAS NMR signals at 9 ppm in a hydrated state (Wang et al 2019). For comparison, the signal of hydroxonium protons in H 3 OClO 4 was observed at 10.7 ppm, while the signal of hydroxonium protons at the K + position in alunite mineral occurs at 11.4 ppm (Ratcliffe et al 1985).…”

Section: Introductionmentioning

confidence: 99%

Effect of aluminum and sodium on the sorption of water and methanol in microporous MFI-type zeolites and mesoporous SBA-15 materials

Rieg

Beurer

et al. 2020

Adsorption

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The interaction and nature of surface sites for water and methanol sorption on MFI-type zeolites and mesoporous SBA-15 were investigated by solid-state NMR spectroscopy and correlated with the desorption enthalpies determined via TGA/DSC. For siliceous Silicalite-1, 29Si CPMAS NMR studies support stronger methanol than water interactions with SiOH groups of Q3-type. On siliceous SBA-15, SiOH groups of Q2-type are accompanied by an enhanced hydrophilicity. In aluminum-containing Na-ZSM-5, Na+ cations are strong adsorption sites for water and methanol as evidenced by 23Na MAS NMR in agreement with high desorption enthalpies of ΔH = 66–74 kJ/mol. Solid-state NMR of aluminum-containing Na-[Al]SBA-15, in contrast, has shown negligible water and methanol interactions with sodium and aluminum. Desorption enthalpies of ΔH = 44–60 kJ/mol hint at adsorption sites consisting of SiOH groups influenced by distant framework aluminum. On H-ZSM-5, Brønsted acidic OH groups are strong adsorption sites as indicated by partial protonation of water and methanol causing low-field shifts of their 1H MAS NMR signals and enhanced desorption enthalpies. Due to the small number of Brønsted acid sites in aluminum-containing H-[Al]SBA-15, water and methanol adsorption on this material is suggested to mainly occur at SiOH groups with distant framework aluminum species, as in the case of Na-[Al]SBA-15.

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“…4.2 and 8.5 ppm. The former is assigned to the Brønsted acid center (also named as bridging hydroxyl group), while the latter resonance has been assigned to H 3 O + ions stabilized inside ZSM‐5 channels …”

Section: Resultsmentioning

confidence: 99%

Quantification of Brønsted Acid Sites in Zeolites by Water Desorption Thermogravimetry

et al. 2020

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The many studies that have been conducted on water adsorption on zeolites were carried out in "adsorption" mode, from adsorption isotherms or single-point measurements, with the samples being first degassed at high temperature, and then exposed to water vapor at variable partial pressure. Here, we report Thermogravimetric Analysis (TGA) studies of HZSM-5 saturated with water at room temperature, thus studying water adsorption in "desorption" mode. TGA was used to ascertain the amount of water remaining as a function of the pretreatment temperature, and to identify the temperature at which one water molecule per framework Al atom persists. 1860 Ison and Gorte studied water adsorption on a HZSM-5 with SAR = 70 via temperature programmed desorption (TPD), thermogravimetric analysis (TGA), and transmission infrared spectroscopy (IR), [8] and found clusters of up to 5.3 waters per Al at 306 K. An adsorption energy of 12.1 kcal/mol and 8.2 kcal/mol was calculated for 0.7 and 2.0 waters per Al, respectively, leading to the conclusion that the first water forming a hydronium ion, H 3 O + , at the acid sites is more strongly held than subsequent waters that form clusters. Eckstein et al., also reported that water adsorption on HZSM-5 is proportional to the Al content showing a maximum of 7 waters per Brønsted acid site. [9] All these previous works studied water in "adsorption" mode, from adsorption isotherms or single-point measurements whereby the samples were first degassed at high temperature and then exposed to water vapor at variable partial pressure. Herein, we report TGA studies of HZSM-5 samples of varying SAR saturated with water at room temperature using tempera-Carlos Bornes is a PhD student at CICECO -Aveiro Institute of Materials, University of Aveiro. He obtained his M. Sc. in 2017 from the Department of Chemistry, University of Aveiro, working on the characterization of zeolites by solid-state NMR spectroscopic methods. His current line of research is the characterization of the acid properties of zeolites using solid-state NMR and computational methods. Jeffrey Amelse received a B.Mark Peacock works at BP since 1998 in a range of catalysis development roles & focuses on advanced catalyst characterisation since 2008, primarily focusing on powder X-ray diffraction, In-situ pXRD as well as thermal analysis (TGA) and combustion elemental analysis. His experience covers a range of zeolite catalysts, binders as well and many heterogeneous metal/ metal oxide based systems. Christopher L. Marshall is a senior research chemist in the Catalysis Science Group of the Chemical Sciences and Engineering Division at Argonne. His research concentrates on the synthesis, testing and in situ characterization of refining, chemical and biomass conversion catalysts. Synthesis work has recently concentrated on the use of atomic layer deposition for stabilization and improved performance of supported catalysts. Michael M. Schwartz, now retired, obtained his Ph.D. (1970) at Florida State University. . His current research inter...

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Genesis and Stability of Hydronium Ions in Zeolite Channels

Cited by 151 publications

References 91 publications

Understanding solvent effects on adsorption and protonation in porous catalysts

Understanding solvent effects on adsorption and protonation in porous catalysts

Effect of aluminum and sodium on the sorption of water and methanol in microporous MFI-type zeolites and mesoporous SBA-15 materials

Quantification of Brønsted Acid Sites in Zeolites by Water Desorption Thermogravimetry

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