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Titolo:
Double resonance NMR and molecular simulations of hydrofluorocarbon binding on faujasite zeolites NaX and NaY: the importance of hydrogen bonding in controlling adsorption geometries
Autore:
Lim, KH; Jousse, F; Auerbach, SM; Grey, CP;
Indirizzi:
SUNY Stony Brook, Dept Chem, Stony Brook, NY 11794 USA SUNY Stony Brook Stony Brook NY USA 11794 Chem, Stony Brook, NY 11794 USA Univ Massachusetts, Dept Chem, Amherst, MA 01003 USA Univ Massachusetts Amherst MA USA 01003 Dept Chem, Amherst, MA 01003 USA Univ Massachusetts, Dept Chem Engn, Amherst, MA 01003 USA Univ Massachusetts Amherst MA USA 01003 Chem Engn, Amherst, MA 01003 USA
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 41, volume: 105, anno: 2001,
pagine: 9918 - 9929
SICI:
1520-6106(20011018)105:41<9918:DRNAMS>2.0.ZU;2-H
Fonte:
ISI
Lingua:
ENG
Soggetto:
MAS NMR; NEUTRON-DIFFRACTION; CROSS-POLARIZATION; QUADRUPOLAR NUCLEI; MAGNETIC-RESONANCE; MONTE-CARLO; Y-ZEOLITE; X-ZEOLITE; SPECTROSCOPY; BENZENE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
36
Recensione:
Indirizzi per estratti:
Indirizzo: Grey, CP SUNY Stony Brook, Dept Chem, Stony Brook, NY 11794 USA SUNY StonyBrook Stony Brook NY USA 11794 ny Brook, NY 11794 USA
Citazione:
K.H. Lim et al., "Double resonance NMR and molecular simulations of hydrofluorocarbon binding on faujasite zeolites NaX and NaY: the importance of hydrogen bonding in controlling adsorption geometries", J PHYS CH B, 105(41), 2001, pp. 9918-9929

Abstract

Double resonance NMR experiments have been used to study the binding of the asymmetric hydrofluorocarbons (HFCs) CF3CFH2 (HFC-134a), CF3CF2H (HFC-125) and CF2HCFH2 (HFC-143) on zeolites NaX and NaY. By exploiting the very large differences in F-19 chemical shifts for the -CF3-xHx end groups of eachmolecule, individual F-19 --> Na-23 cross-polarization (CP) build-up curves involving polarization transfer from different parts of the molecule havebeen obtained. CP efficiencies in the order CF(3)much less than CF2H < CFH2 were found, indicating that the hydrogen-containing groups are bound morestrongly to the zeolite framework. This effect is most pronounced for the lowest-sodium content zeolite studied (NaY: Si/Al = 7.6), and increases with HFC loading. Both the H-1 NMR resonances and H-1 - Al-27 and H-1 - O-17 CP MAS NMR experiments are consistent with H-bonding interactions with the zeolite framework. Molecular dynamics and docking calculations for HFC-134 and 134a on model NaY and NaX zeolites revealed the importance of both H-bonding and Na-F interactions in determining the low-energy sorption sites. Stable binding sites for HFC-134a in NaY were found by docking to involve only CFH2-Na(SII) contacts, in qualitative agreement with the CP results. The simulations indicate that Na-binding to the groups with more H atoms is favored by the possibility of achieving shorter Na-F distances and maximizing the number of H-bonds with the framework. The higher sodium content zeolitecontaining both SII and SIII cations gives minimum energy binding sites involving multiple Na-F and H-bonding contacts. For HFC-134 (gauche conformer), the global energy minimum actually involves several H-bonds but no shortNa-F contacts.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 31/03/20 alle ore 16:31:56