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Titolo:
Diffusion of ammonia in silicalite studied by QENS and PFG NMR
Autore:
Jobic, H; Ernst, H; Heink, W; Karger, J; Tuel, A; Bee, M;
Indirizzi:
Inst Rech Catalyse, CNRS, F-69626 Villeurbanne, France Inst Rech CatalyseVilleurbanne France F-69626 9626 Villeurbanne, France Univ Leipzig, Fak Phys & Geowissensch, D-04103 Leipzig, Germany Univ Leipzig Leipzig Germany D-04103 wissensch, D-04103 Leipzig, Germany Univ Grenoble 1, Spectrometrie Phys Lab, F-38402 St Martin Dheres, France Univ Grenoble 1 St Martin Dheres France F-38402 St Martin Dheres, France
Titolo Testata:
MICROPOROUS AND MESOPOROUS MATERIALS
fascicolo: 1-3, volume: 26, anno: 1998,
pagine: 67 - 75
SICI:
1387-1811(199812)26:1-3<67:DOAISS>2.0.ZU;2-Z
Fonte:
ISI
Lingua:
ENG
Soggetto:
ELASTIC NEUTRON-SCATTERING; TEMPERATURE-PROGRAMMED DESORPTION; SELF-DIFFUSION; ZEOLITE ZSM-5; MOLECULES; DYNAMICS; METHANE; SITES;
Keywords:
ammonia; diffusion; QENS; PFG NMR; silicalite;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
18
Recensione:
Indirizzi per estratti:
Indirizzo: Jobic, H Instceech Catalyse, CNRS, 2 Ave Albert Einstein, F-69626 Villeurbanne, Fran Inst Rech Catalyse 2 Ave Albert Einstein Villeurbanne France F-69626
Citazione:
H. Jobic et al., "Diffusion of ammonia in silicalite studied by QENS and PFG NMR", MICROP M M, 26(1-3), 1998, pp. 67-75

Abstract

Ammonia diffusivities in silicalite have been studied by quasi-elastic neutron scattering (QENS) and pulsed-field gradient (PFG) NMR for temperaturesbetween 200 and 500 K and loadings from 1.5 up to 4.3 molecules per unit cell. The diffusion coefficients obtained by both techniques increase with increasing ammonia concentration. The QENS diffusivities refer to only a certain fraction of molecules, because during the time scale of the measurement the other part of molecules is essentially immobile, in interaction with silanol groups. During the much larger time scale of the PFG NMR experiment, ammonia molecules assume both states of mobility, leading to an average diffusivity which is smaller than the diffusivity of the mobile molecules recorded by QENS. The difference between the diffusivities derived from both techniques decreases when the proportion of immobile molecules is taken into account. The residence time of ammonia in interaction with silanol groupsis about two orders of magnitude longer than with oxygen atoms. (C) 1998 Elsevier Science B.V. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 07/07/20 alle ore 12:49:30