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Titolo:
New insight into cation relocations within the pores of zeolite Rho: In situ synchrotron X-ray and neutron powder diffraction studies of Pb- and Cd-exchanged Rho
Autore:
Lee, Y; Reisner, BA; Hanson, JC; Jones, GA; Parise, JB; Corbin, DR; Toby, BH; Freitag, A; Larese, JZ;
Indirizzi:
SUNY Stony Brook, Dept Geosci, Stony Brook, NY 11794 USA SUNY Stony BrookStony Brook NY USA 11794 osci, Stony Brook, NY 11794 USA SUNY Stony Brook, Dept Chem, Stony Brook, NY 11794 USA SUNY Stony Brook Stony Brook NY USA 11794 Chem, Stony Brook, NY 11794 USA Natl Inst Stand & Technol, Ctr Neutron Res, Gaithersburg, MD 20899 USA Natl Inst Stand & Technol Gaithersburg MD USA 20899 ersburg, MD 20899 USA Brookhaven Natl Lab, Dept Chem, Upton, NY 11973 USA Brookhaven Natl Lab Upton NY USA 11973 ab, Dept Chem, Upton, NY 11973 USA Dupont Co, Expt Stn, Chem Res & Dev, Wilmington, DE 19880 USA Dupont Co Wilmington DE USA 19880 hem Res & Dev, Wilmington, DE 19880 USA
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 30, volume: 105, anno: 2001,
pagine: 7188 - 7199
SICI:
1520-6106(20010802)105:30<7188:NIICRW>2.0.ZU;2-H
Fonte:
ISI
Lingua:
ENG
Soggetto:
STRUCTURAL CHARACTERIZATION; RIETVELD REFINEMENT; PHASE-TRANSITION; FLEXIBILITY; DEHYDRATION; FRAMEWORK; NMR;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
24
Recensione:
Indirizzi per estratti:
Indirizzo: Lee, Y SUNY Stony Brook, Dept Geosci, Stony Brook, NY 11794 USA SUNY StonyBrook Stony Brook NY USA 11794 tony Brook, NY 11794 USA
Citazione:
Y. Lee et al., "New insight into cation relocations within the pores of zeolite Rho: In situ synchrotron X-ray and neutron powder diffraction studies of Pb- and Cd-exchanged Rho", J PHYS CH B, 105(30), 2001, pp. 7188-7199

Abstract

Upon heating, certain cations exchanged into zeolite RHO undergo large shifts in their positions within the pores. In several of these materials, negative thermal expansion is observed in conjunction with these cation relocations. Rather than being the purely temperature-driven effects presumed in previous reports, a combination of in situ time-resolved synchrotron X-ray and neutron powder diffraction studies indicates that the cation relocations and framework distortions observed in Pb- and Cd-exchanged zeolite rho are mediated by the presence of water in specific sites in the pores of RHO. Rietveld refinements using these data reveal that the initial unit cell contraction (50 degreesC less than or equal to T less than or equal to 100 degreesC) is due to the loss of unbound water in the -cages of rho. Water molecules in the double eight-ring (D8R) building units persist after this step, bound to the extraframework cations. The framework then contracts as water molecules are gradually removed (200 degreesC :less than or equal to T less than or equal to 400 degreesC). During this period, the extraframework cations migrate from the single eight-ring (S8R) site to the double eight-ring (D8R) sites in a concerted manner with the dehydration at the D8R. Upon complete removal of bound waters (400 degreesC less than or equal to T lessthan or equal to 500 degreesC), lead and cadmium cations experience different rearrangements. Cd2+ ions relocate from the D8R and S8R sites to the single six-ring (S6R) site, while all Pb2+ ions migrate from the S8R site to the D8R site. Neither transition is reversible upon cooling to room temperature in vacuo although both are reversible in the presence of water vapor. The role of water in these samples appears to determine the coordination environment of the extraframework cations uniquely since other sorbates. suchas Kr, methanol, and CO. do not cause significant changes in either extraframework cation or framework atomic positions.

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Documento generato il 09/07/20 alle ore 17:01:02