Tetrahedral atom ordering in a zeolite framework

A key factor affecting its physicochemical properties

Jiho Shin, Deu S. Bhange, Miguel A. Camblor, Yongjae Lee, Wha Jung Kim, In Sik Nam, Suk Bong Hong

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

Three gallosilicate natrolites with closely similar chemical composition but differing in the distribution of Si and Ga over crystallographically different tetrahedral sites (T-sites) show striking differences in their cation exchange performance. The ability to exchange Na+ by the larger alkali metal cations decreases upon increasing the size of the cation, as expected, but also with the degree of T-atom ordering. To seek an insight into this phenomenon, the crystal structures of 11 different zeolites, which show variations in degree of T-atom ordering, nature of countercation, and hydration state, have been refined using synchrotron diffraction data. While the three as-made sodium materials were characterized to have a low, medium, and high degree of ordering, respectively, their pore sizes are close to the size of the bare Na+ cation and much smaller than that of the larger alkali cations, which are nonetheless exchanged into the materials, each one at a different level. Interestingly, large differences are also manifested when the Na+ back-exchange is performed on the dehydrated K+ forms, with crystallographic pore sizes too small even to allow the passage of Na +. Although the thermodynamic data point to small differences in the enthalpy of the Na+/K+ exchange in the three materials, comparison of the static crystallographic pore sizes and the diameter of the exchanged cations lead us to conclude that during the exchange process these zeolites undergo significant deformations that dynamically open the pores, allowing cation traffic even for Cs+ in the case of the most disordered material. In addition to the very large topological flexibility typical of the natrolite framework, we propose as a hypothesis that there is an additional flexibility mechanism that decreases the rigidity of the natrolite chain itself and is dependent on preferential siting of Si or Ga on crystallographically different T-sites.

Original languageEnglish
Pages (from-to)10587-10598
Number of pages12
JournalJournal of the American Chemical Society
Volume133
Issue number27
DOIs
Publication statusPublished - 2011 Jul 13

Fingerprint

Zeolites
Cations
Positive ions
Atoms
Pore size
Ion exchange
Alkali Metals
Synchrotrons
Alkalies
Alkali metals
Thermodynamics
Rigidity
Hydration
Enthalpy
Diffraction
Crystal structure
Sodium
Chemical analysis

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Shin, Jiho ; Bhange, Deu S. ; Camblor, Miguel A. ; Lee, Yongjae ; Kim, Wha Jung ; Nam, In Sik ; Hong, Suk Bong. / Tetrahedral atom ordering in a zeolite framework : A key factor affecting its physicochemical properties. In: Journal of the American Chemical Society. 2011 ; Vol. 133, No. 27. pp. 10587-10598.
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abstract = "Three gallosilicate natrolites with closely similar chemical composition but differing in the distribution of Si and Ga over crystallographically different tetrahedral sites (T-sites) show striking differences in their cation exchange performance. The ability to exchange Na+ by the larger alkali metal cations decreases upon increasing the size of the cation, as expected, but also with the degree of T-atom ordering. To seek an insight into this phenomenon, the crystal structures of 11 different zeolites, which show variations in degree of T-atom ordering, nature of countercation, and hydration state, have been refined using synchrotron diffraction data. While the three as-made sodium materials were characterized to have a low, medium, and high degree of ordering, respectively, their pore sizes are close to the size of the bare Na+ cation and much smaller than that of the larger alkali cations, which are nonetheless exchanged into the materials, each one at a different level. Interestingly, large differences are also manifested when the Na+ back-exchange is performed on the dehydrated K+ forms, with crystallographic pore sizes too small even to allow the passage of Na +. Although the thermodynamic data point to small differences in the enthalpy of the Na+/K+ exchange in the three materials, comparison of the static crystallographic pore sizes and the diameter of the exchanged cations lead us to conclude that during the exchange process these zeolites undergo significant deformations that dynamically open the pores, allowing cation traffic even for Cs+ in the case of the most disordered material. In addition to the very large topological flexibility typical of the natrolite framework, we propose as a hypothesis that there is an additional flexibility mechanism that decreases the rigidity of the natrolite chain itself and is dependent on preferential siting of Si or Ga on crystallographically different T-sites.",
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Tetrahedral atom ordering in a zeolite framework : A key factor affecting its physicochemical properties. / Shin, Jiho; Bhange, Deu S.; Camblor, Miguel A.; Lee, Yongjae; Kim, Wha Jung; Nam, In Sik; Hong, Suk Bong.

In: Journal of the American Chemical Society, Vol. 133, No. 27, 13.07.2011, p. 10587-10598.

Research output: Contribution to journalArticle

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