Proton mobility in H-ZSM5 studied by impedance spectroscopy

Franke, Marion E.

doi:10.1016/s0167-2738(98)00436-6

Cited by 75 publications

(67 citation statements)

References 19 publications

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“…This is seen most clearly for the data at 773 and 873 K. The semicircle is caused by at least one ionic relaxation mode [30], and a decreasing diameter of the semicircle with increasing temperature indicates a thermally activated process. In accordance with reports on the ionic conductivity of zeolites [8][9][10], the data obtained were further analyzed by means of the spectral plot of the imaginary part of the modulus M 00 (=2pmC 0 Z 00 , m: measuring frequency, C 0 : capacitance of the empty capacitor) to overemphasize the high frequency (HF) part of the spectra by a factor of 2pmC 0 [8]. Consequently, the modulus spectra allow ready visualization of relaxation processes, especially at high frequencies, which might be hidden in the Argand plot.…”

Section: Ac Impedance Spectroscopy (Is)supporting

confidence: 92%

“…This is based on the presence of partially occupied edge-sharing [LiO 4 ]-tetrahedra within densely packed Li 2 O-layers where Li cations can find shorter pathways for charge transportation (about 2.5 Å ) [6]. This feature is unusual in known Libearing zeolites [8][9][10]. Most Li-exchanged microporous materials contain only extra-framework Li cations far apart from each other in porous cages and channels.…”

Section: Introductionmentioning

confidence: 99%

“…Discussion of the cationic conductivity in zeolite-like materials is greatly simplified when they are studied in their dehydrated forms, since water molecules in microporous structures significantly influence the mobility as well as characteristic energies of the metal cations [8][9][10]. Hydrated cations have a weaker interaction with the negatively charged framework.…”

Section: Introductionmentioning

confidence: 99%

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Lithium dynamics in the zeolite-like lithosilicate RUB-29 and its high-temperature structure after dehydration (Cs14Li42Si72O172)

Park

Parise

Franke

et al. 2008

Microporous and Mesoporous Materials

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The thermally induced modifications of the zeolite-like lithosilicate In particular, extra-framework Li cations located within porous 8-and 10-membered ring-channels, where these Li cations were partially coordinated with zeolitic water in the original structure, migrate into densely packed Li 2 O-layers after dehydration. As a result of the migration, the number of empty sites relevant for Li hopping in Li 2 O-layers decreases, which give a negative effect on the long-range charge transfer in dehydrated RUB-29. Its DC conductivity values estimated from AC impedance spectra lie between 2 · 10 À5 and 6 · 10 À5 S cm À1 at 873 K, and a low activation energy of 51 kJ/mol (ffi 0.53 eV) could be determined for the bulk charge transfer process in dehydrated RUB-29.Li

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Section: Ac Impedance Spectroscopy (Is)supporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Lithium dynamics in the zeolite-like lithosilicate RUB-29 and its high-temperature structure after dehydration (Cs14Li42Si72O172)

Park

Parise

Franke

et al. 2008

Microporous and Mesoporous Materials

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“…The powders were kindly provided by Clariant International Ltd. For zeolites in their H-form, the charge compensating cations are simply protons and no active metal ions are present (Franke and Simon, 1999). The number of acidic sites of the zeolite is directly dependent to the Al content.…”

Section: Methodsmentioning

confidence: 99%

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

Dietrich

Rauch

Simon

et al. 2015

J. Sens. Sens. Syst.

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Abstract.To meet today's emission standards, the ammonia-based selective catalytic reduction (SCR) has become the major NO x control strategy for light and heavy diesel engines. Before NO x reduction can proceed, adsorption of ammonia on the acidic sites of the catalyst is necessary. For improvements in efficiency and control of the exhaust gas aftertreatment, a better understanding of the ammonia storage on the acidic sites of zeolite-based SCR catalysts is needed. Thereby, the correlation of dielectric properties of the catalyst material itself with the ammonia storage is a promising approach. Recently, a laboratory setup using microwave cavity perturbation to measure the dielectric properties of catalyst material has been described. This study shows the first experimental data on zeolite-based SCR materials in their H-form. The SCR powder samples are monitored by microwave cavity perturbation while storing and depleting ammonia, both with and without admixed NO x at different temperatures. Its complex dielectric permittivity is found to correlate closely with the stored mass of ammonia. The influence of the temperature and the Si / Al ratio of the zeolite to the ammonia storage behavior are also examined. These measurements disclose different temperature dependencies and differing sensitivities to ammonia storage for both real and imaginary parts of the complex permittivity. The apparent constant sensitivity of the real part can be related to the polarity of the adsorbed ammonia molecules, whereas the imaginary part depends on the Si / Al ratio and is related to the conductivity mechanisms of the zeolite material by proton hopping. It provides information about the zeolite structure and the number of (and the distance between) acidic storage sites, in addition to the stored ammonia mass.

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“…In a series of papers on ionic motion in zeolites [3][4][5][6] , it was suggested the presentation of data in the modulus representation, equation 1, and in particular the imaginary part of the modulus, M" as a function of frequency, rather than traditional impedance (Z) data, allowed for more straight forward visualization of ionic conduction and local relaxations. In equation S1, i is the square root of -1, ω is the frequency in radians per second, C 0 is the empty cell capacitance, M* is the complex modulus, and Z* is the complex impedance.…”

mentioning

confidence: 99%

Conductivity of Mono- and Divalent Cations in the Microporous Zincosilicate VPI-9

McKeen

Davis

2009

J. Phys. Chem. C

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Impedance spectroscopy is used to investigate the long-range ionic conductivity of the microporous, zincosilicate VPI-9 (Si/Zn ) 4.0) (International Zeolite Association framework type VNI) containing the alkali cations Li + , Na + , K + , Rb + , and Cs + , and the alkaline earth cations Mg 2+ , Ca 2+ , and Sr 2+ . Monovalent cation-exchanged samples Li-and Na-VPI-9 lose X-ray crystallinity upon vacuum dehydration at 450 °C, whereas K-, Rb-, and Cs-VPI-9 remain crystalline and exhibit conductivities of 1.7 × 10 -4 , 3.5 × 10 -4 , and 4.9 × 10 -4 S/cm, respectively, at 450 °C and activation energies of 0.72, 0.64, and 0.69 eV, respectively, in the temperature range 150-450 °C. Divalent cation-exchanged sample Mg-VPI-9 also loses X-ray crystallinity, but Ca-and Sr-VPI-9 remain crystalline and exhibit conductivities of 2.3 × 10 -6 S/cm and 7.7 × 10 -7 S/cm, respectively, at 450 °C, and activation energies of 0.88 and 0.91 eV, respectively, over the temperature range 150-450 °C. When compared to aluminosilicate zeolite X (Si/Al ) 1.25) exchanged with the same cations, all crystalline M-VPI-9 materials have greater conductivities than M-X, with the exception of K-X (1.6 × 10 -3 S/cm at 450 °C), with the greatest differences arising between the divalent exchanged materials. Dense, crystalline zincosilicate samples with the compositions K 2 ZnSi x O 2(x+1) (x ) 2-5), Rb 2 ZnSi 5 O 12 , and Cs 2 ZnSi 5 O 12 are also prepared and characterized for comparison with the microporous materials and exhibit much lower conductivities than their microporous counterparts at the same composition.

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Proton mobility in H-ZSM5 studied by impedance spectroscopy

Cited by 75 publications

References 19 publications

Lithium dynamics in the zeolite-like lithosilicate RUB-29 and its high-temperature structure after dehydration (Cs14Li42Si72O172)

Lithium dynamics in the zeolite-like lithosilicate RUB-29 and its high-temperature structure after dehydration (Cs14Li42Si72O172)

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

Conductivity of Mono- and Divalent Cations in the Microporous Zincosilicate VPI-9

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