Characterization of Brønsted and Lewis acidity in zeolites by solid-state NMR and the recent progress in the REDOR technique

Blumenfeld, A.L.; Fripiat, J. J.

doi:10.1002/(sici)1097-458x(199912)37:13<s118::aid-mrc574>3.0.co;2-k

Cited by 11 publications

(8 citation statements)

References 83 publications

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“…A decrease in the framework Al content causes a decrease in the number of exchangeable cations [22], protons in this case, although it increases the strength of the Brønsted sites [40]. Moreover, the lower micropore and total pore volumes found for the dealuminated Faujasite also affected negatively the proton mobility through the zeolite channels.…”

Section: Dealumination Of Faujasite Zeolitementioning

confidence: 87%

On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

Zhang

Désilets

Felice

et al. 2011

Journal of Power Sources

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a b s t r a c tAlthough zeolites are introduced to decrease methanol crossover of Nafion membranes for direct methanol fuel cells (DMFCs), little is known about the effect of their intrinsic properties and the interaction with the ionomer. In this work, Nafion-Faujasite composite membranes prepared by solution casting were characterized by extensive physicochemical and electrochemical techniques. Faujasite was found to undergo severe dealumination during the membrane activation, but its structure remained intact. The zeolite interacts with Nafion probably through hydrogen bonding between Si-OH and SO 3 H groups, which combined with the increase of the water uptake and the water mobility, and the addition of a less conductive phase (the zeolite) leads to an optimum proton conductivity between 0.98 and 2 wt% of zeolite. Hot pressing the membranes before their assembling with the electrodes enhanced the DMFC performance by reducing the methanol crossover and the serial resistance.

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Section: Dealumination Of Faujasite Zeolitementioning

confidence: 87%

On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

Zhang

Désilets

Felice

et al. 2011

Journal of Power Sources

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“…There are two kinds of coordinated Al atoms in the product. The small signal with a chemical shift of about 50 ppm corresponds to the four-coordinated Al atoms in the framework, while the peaks around 15 ppm correspond to the nonframework five-coordinated Al atoms [25,26]. The 27 Al MAS NMR result shows only a limited amount of the tetrahedrally coordinated Al atoms are introduced into the ITQ-37 framework.…”

Section: Characterization Of Itq-37mentioning

confidence: 99%

Synthesis and characterization of chiral zeolite ITQ-37 by using achiral organic structure-directing agent

Qian

Jiang

et al. 2012

Microporous and Mesoporous Materials

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“…NMR spectroscopy is an element-selective, site-specific, and inherently quantitative tool for detailed structural characterization . With a 100% natural abundance, a moderately high gyromagnetic ratio of γ = 6.976 × 10 7 rad·T –1 ·s –1 , and a medium-sized nuclear electric quadrupole moment, eQ = 0.15 × 10 –28 m 2 , the 27 Al nucleus ( I = 5/2) is an excellent candidate for NMR spectroscopic experiments. , Indeed, 27 Al NMR has found widespread use for the structural characterization of aluminum-based melts and glasses, polyoxoanions, zeolites, − catalysts, and metal–organic frameworks . Overall, very few review articles focusing on NMR studies of intermetallic compounds have appeared, and these few tend to be limited to studies of individual nuclei ( 69,71 Ga, 45 Sc, 25 Mg) in specific groups of intermetallic compounds.…”

Section: Introductionmentioning

confidence: 99%

Structural Characterization of Intermetallic Compounds by ²⁷Al Solid State NMR Spectroscopy

2017

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Intermetallic compounds are of broad interest for solid state chemists, condensed matter physicists, and material scientists due to their intriguing crystal chemistry, their physical properties, and their potential applications, ranging from lab curiosities to everyday objects. To characterize and understand the properties of new compounds and novel materials, the availability of structural information, particularly single-crystal X-ray diffraction data, is a mandatory prerequisite. Especially when it comes to the formation of compounds with deficient or mixed site occupancies, superstructures, or representatives crystallizing in other, thus far unknown structure types, a complementary method for structural analysis is of great value. Solid state nuclear magnetic resonance spectroscopy has been a valuable tool in many areas of chemistry, being an element-selective, site-specific, and inherently quantitative tool for detailed structural characterization. Magic-angle spinning conditions eliminate or reduce the effect of anisotropic interactions in the solid state, producing high-resolution spectra. Until recently, Al NMR studies of intermetallic aluminum compounds have been relatively sparse and mostly limited to binary systems. In this Account, we will summarize the current state of the art of high-resolutionAl NMR in intermetallic compounds focusing on recent research efforts in our laboratories and the interpretation of NMR parameters in terms of the structural details of the compounds investigated. Besides theoretical aspects of Al NMR spectroscopy, short paragraphs on experimental details and the crystal chemistry of the discussed compounds are given. In the main part of this Account, we focus on three key aspects: (i) crystal structure validation, (ii) structural disorder and mixed site occupancies, and (iii) the electronic structure, all of which can be investigated by spectroscopic means. For the first part, we have chosen the ternary equiatomic compounds CaAuAl (TiNiSi type), BaAuAl (LaIrSi type), and BaPtAl (own type). Structural disorder and mixed site occupancies have been probed in the ScTAl series (T = Cr, Ru, Ag, Re) crystallizing in the TiNiSi, HfRhSn, and MgZn-type structures. Also NaAuAl and the Heusler compounds, Sc(TT')Al (T = T' = Ni, Pd, Pt, Cu, Ag, Au), have been used for structure validation purposes, based on the number and signal area ratios of the resonances observed and on the comparison between experimental and theoretically calculated nuclear electric quadrupolar interaction parameters. Electronic structure information available from Al magnetic shielding will be discussed based on experimental data obtained for the RETAl series (RE = Y, Lu; T = Pd, Pt), the extended RETAl series (RE = Y, Lu; T = Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt), and the ordered Heusler compounds ScTAl (T = Ni, Pd, Pt, Cu, Ag, Au).

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Characterization of Brønsted and Lewis acidity in zeolites by solid-state NMR and the recent progress in the REDOR technique

Cited by 11 publications

References 83 publications

On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

Synthesis and characterization of chiral zeolite ITQ-37 by using achiral organic structure-directing agent

Structural Characterization of Intermetallic Compounds by ²⁷Al Solid State NMR Spectroscopy

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Characterization of Brønsted and Lewis acidity in zeolites by solid-state NMR and the recent progress in the REDOR technique

Cited by 11 publications

References 83 publications

On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

Synthesis and characterization of chiral zeolite ITQ-37 by using achiral organic structure-directing agent

Structural Characterization of Intermetallic Compounds by 27Al Solid State NMR Spectroscopy

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Structural Characterization of Intermetallic Compounds by ²⁷Al Solid State NMR Spectroscopy