Trace water amounts can increase benzene H/D exchange rates in an acidic zeolite

Chen, Kuizhi; Gumidyala, Abhishek; Abdolrhamani, Maryam; Villines, Cameron; Crossley, Steven; White, Jeffery L.

doi:10.1016/j.jcat.2017.04.026

Cited by 26 publications

(36 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Haw and coworkers reported that co-solvating nitromethane enhanced the extent of gas-phase proton-transfer from H-Al-MFI to 13 C-labeled acetone detected by 13 C NMR, which enabled acetone dimerization only when nitromethane was cofed in a ow reactor (513 K). 49 These concepts can be extended to co-adsorbed H 2 O, which enhances gas-phase rates of alkane C-H bond activation, 50 H-D exchange, 51 and steam dealumination 52 in H-zeolites, and enables distinct H 3 O + -mediated pathways in aqueous-phase hydrogenation of furanics 53 and aldol condensation of ketones. 54 In gas-phase alcohol dehydration reactions, H 2 O inhibits the rates of forming both alkenes and ethers in unimolecular and bimolecular pathways, respectively.…”

Section: Introductionmentioning

confidence: 99%

Structure and solvation of confined water and water–ethanol clusters within microporous Brønsted acids and their effects on ethanol dehydration catalysis

et al. 2020

View full text Add to dashboard Cite

show abstract

Section: Introductionmentioning

confidence: 99%

Structure and solvation of confined water and water–ethanol clusters within microporous Brønsted acids and their effects on ethanol dehydration catalysis

et al. 2020

View full text Add to dashboard Cite

show abstract

“…2D spin-exchange spectroscopy (2D EXSY) provides information about the proximity of chemically different protons. , For a sufficiently long mixing time, the protons that are close in space will show cross-peaks in the 2D NMR spectrum. As can be seen in the 2D EXSY spectrum of USY measured at a mixing time of 1 s (Figure ), the sodalite, supercage, and EF proton spins show such cross-peaks.…”

Section: Resultsmentioning

confidence: 99%

Nature of Enhanced Brønsted Acidity Induced by Extraframework Aluminum in an Ultrastabilized Faujasite Zeolite: An In Situ NMR Study

et al. 2021

View full text Add to dashboard Cite

The enhancing effect of extraframework Al (EFAl) species on the acidity of bridging hydroxyl groups in a steam-calcined faujasite zeolite (ultrastabilized Y, USY) was investigated by in situ monitoring the H/D exchange reaction between benzene and deuterated zeolites by 1 H MAS NMR spectroscopy. This exchange reaction involves Brønsted acid sites (BAS) located in sodalite cages and supercages. In a reference faujasite zeolite free from EFAl, both populations of BAS are equally and relatively slowly reactive toward C 6 H 6 . In USY, in stark contrast, the H/D exchange of sodalite hydroxyl groups is significantly faster than that of hydroxyl groups located in the faujasite supercages, even though benzene has only access to the supercages. This evidences selective enhancement of BAS near Lewis acidic EFAl species, which according to the NMR findings are located in the faujasite sodalite cages.

show abstract

“…In situ solid state 1 H MAS NMR methods were used to follow hydrogen/deuterium exchange reactions . Typically, 1 equiv (1 benzene per Al atom in the zeolite) of C 6 D 6 molecules was adsorbed on activated HZSM-5 using an evacuated and dry vacuum line.…”

Section: Methodsmentioning

confidence: 99%

“…In situ solid state 1 H MAS NMR methods were used to follow hydrogen/deuterium exchange reactions. 24 Typically, 1 equiv (1 benzene per Al atom in the zeolite) of C 6 D 6 molecules was adsorbed on activated HZSM-5 using an evacuated and dry vacuum line. H/D isotopic exchange took place immediately after adsorptions, while the adsorption processes usually took 3−5 min for completion.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Assessment, Control, and Impact of Brønsted Acid Site Heterogeneity in Zeolite HZSM-5

2018

Self Cite

View full text Add to dashboard Cite

Acidic zeolites are solid aluminosilicate catalysts whose utility arises from Brønsted sites that predominately reside in their crystalline framework structure. Data described herein indicate that extra-framework aluminum (EFAl) moieties, often proposed as important species in overall catalyst activity via Brønsted−Lewis synergies, can themselves contribute protons that are also reactive Brønsted acid centers. While the MFI family of zeolites is a relatively simple channel-structure type, the quantitative spectroscopic detection of all protons shows that the distribution of reactive Brønsted acid site protons arising from framework and extraframework moieties can be complex. Experiments show that postsynthetic treatments can be used to modify this distribution, in theory enabling routes to HZSM-5 catalysts with only one type of reactive Brønsted site. Quantitative spin-counting NMR experiments combined with chemical washing using ammonium hexafluorosilicate (AHFS) show that the number of framework bridging acid sites (BAS) in typical commercial MFI catalysts (Si/Al equal 15 and 40) is between 50 and 60% of that expected based on the total Al content. Acidic protons from EFAl constitute the major fraction of remaining Brønsted sites. Probe-molecule reactions demonstrate that catalysts with only framework BAS are significantly less reactive than those with both extraframework and framework Brønsted acid sites. Various postsynthetic methods are compared to optimize the desired Brønsted acid site distribution in MFI catalysts, including both removal and re-introduction of acidic protons from EFAl sites.

show abstract

Trace water amounts can increase benzene H/D exchange rates in an acidic zeolite

Cited by 26 publications

References 42 publications

Structure and solvation of confined water and water–ethanol clusters within microporous Brønsted acids and their effects on ethanol dehydration catalysis

Structure and solvation of confined water and water–ethanol clusters within microporous Brønsted acids and their effects on ethanol dehydration catalysis

Nature of Enhanced Brønsted Acidity Induced by Extraframework Aluminum in an Ultrastabilized Faujasite Zeolite: An In Situ NMR Study

Assessment, Control, and Impact of Brønsted Acid Site Heterogeneity in Zeolite HZSM-5

Contact Info

Product

Resources

About