Quantification of Acid Sites in H-ZSM-5, H-β, and H-Y Zeolites

Kotrel, S.; Rosynek, Michael P.; Lunsford, Jack H.

doi:10.1006/jcat.1998.2339

Cited by 42 publications

(20 citation statements)

References 10 publications

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“…30,31,39 The band centred near 3610 cm~1 is typical for the SiÈOHÈ Al groups of any protonic zeolite, in agreement with its strongly acidic behaviour. In accordance with the recent data of Koterl et al 44 we observe a splitting of this band. In fact, the negative band observed in the subtraction spectrum after PN adsorption (near 3612 cm~1) does not perfectly correspond with the positive very weak, but still evident, band in the unsubtracted spectrum (3608 cm~1).…”

Section: Discussionsupporting

confidence: 93%

Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FTIR, XRD and MAS-NMR study

Trombetta

Busca

Storaro

et al. 2000

Phys. Chem. Chem. Phys.

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Samples of beta-zeolite thermally treated at different temperatures and acid leached with diluted hydrochloric acid solution have been investigated by XRD, Al-27 MAS-NMR spectroscopy and FTIR spectroscopy. The results have been used to interpret the behaviour of the samples as catalysts for the acylation of 2-methoxy-naphthalene. It has been shown that the as prepared sample presents two types of extraframework species. These are identified as Al hydroxo-ions highly dispersed in the internal zeolite channels and Al oxide nanoparticles. Calcination causes dealumination of the framework and progressive conversion of the Al hydroxo-ions into Al oxide nanoparticles that reduce the zeolite channels practicability, modifying the shape selectivity effect. The Bronsted acid sites present in the sinusoidal channels (nu(OH)=3608 cm(-1)) can be distinguished from those located in the larger ones (nu(OH)=3620-3612 cm(-1)), due to the inability of the bulky probe molecule pivalonitrile to enter the former. However, internal terminal silanols (nu(OH)=3735 cm(-1)) also apparently display a significant Bronsted acidity, definitely higher than the acidity of those absorbing at 3747 cm(-1), thought to be located at the external crystal surface. The strongest Lewis acidity is displayed by the aluminum hydroxo-ions, while that of alumina nanoparticles is a little weaker. Acid-leached beta-zeolite also displays a medium strength Lewis acidity, likely due to framework Al cations. Thus a partial reinterpretation of the real structure of beta-zeolite and a partial reassignment of the bands due to the surface hydroxy groups are proposed

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Section: Discussionsupporting

confidence: 93%

Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FTIR, XRD and MAS-NMR study

Trombetta

Busca

Storaro

et al. 2000

Phys. Chem. Chem. Phys.

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“…These bands were assigned to acidic (Si-OH-Al) hydroxy groups and (Si-OH) silanol groups, respectively. 10 After BP sorption was complete, the 3611 cm 21 band decreased in intensity and a new broad band appeared at 3300 cm 21 . The dehydrated M m/n ZSM-5 ( M = Li + , Na + , K + , Rb + , Cs + , Zn 2+ , Cd 2+ ) exchanged zeolites (24 h, 773 K, O 2 ) did not exhibit any intense OH stretching band at 3611 cm 21 .…”

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confidence: 97%

Electron transfer mechanisms of biphenyl sorption in M-ZSM-5 (M=H+, Cu2+) zeolites

2000

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“…Most data agree suggesting that, when the Al content is relatively low, the amount of Brønsted sites in zeolites actually strictly depends on Al concentration, according to the theory. The ratio between catalytically active sites and Al ions ranges apparently from 80 to 100 % for highly siliceous extraframework-species-free zeolites [9,10,11].…”

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confidence: 99%

On the Lewis acidity of protonic zeolites

Phung

Busca

2015

Applied Catalysis A: General

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IR spectra of hydroxyl groups, adsorbed CO, pivalonitrile and pyridine on three H-MFI zeolite samples and on two H-Y faujasites are reported and discussed. Samples richer in Al (H-MFI (Si/Al2 = 30) and H-Y (Si/Al2 = 5.1)) show the presence of extraframework species and the presence of Lewis acidity together with Brønsted acidity. H-MFI with lowest Al content (Si/Al2 = 280) does not show any extraframework species (EF) and only presents Brønsted acidity. H-MFI with intermediate Al content (Si/Al2 = 50) possess very small amount of EF species and of Lewis acidity. H-Y with low Al content (Si/Al2 = 30) does not show extraframework species but shows the presence of Lewis acidity together with Brønsted acidity. The role of extraframework material as carrier of Lewis acidity is confirmed. It is proposed that Lewis acidity of low Al-content H-Y can arise from framework tetrahedral Al ions, which can enlarge their coordination to five without any previous dehydroxylation. A support for this hypothesis is given by the reversible shift of the LF OH stretching band, whose extent depends on the strength of the basic molecules: this is certainly not due to a direct interaction of the OH groups responsible for the LF band, which are located in cavities (sodalite cavity and hexagonal prisms) where the molecular probes cannot access

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Quantification of Acid Sites in H-ZSM-5, H-β, and H-Y Zeolites

Cited by 42 publications

References 10 publications

Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FTIR, XRD and MAS-NMR study

Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FTIR, XRD and MAS-NMR study

Electron transfer mechanisms of biphenyl sorption in M-ZSM-5 (M=H+, Cu2+) zeolites

On the Lewis acidity of protonic zeolites

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