Theoretical studies on acidity and site selectivity of cations in faujasite zeolite

Kyoung Tai No, Hakze Chon, Taikyue Ree, Mu Shik Jhon

Research output: Contribution to journalArticle

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Abstract

The influence of the silicon to aluminum ratio (1, 1.4, and 2) on the acidity and site selectivity of cations in faujasite-type zeolite is explained by using calculated atomic net charges and cation-binding energies. The chemical formulae of model compounds are K96+Al96Si96O384 (1:1), K80+Al80Si112O384 (1.4:1), and K64+Al64Si128O384 (2:1). Many experimental results (X-ray data, infrared spectra, and dealumination experiments) suggest that a covalent character is dominant in the zeolite framework. The net charges of framework atoms are derived by using the assumption of equalization of electronegativity in all the atoms. The atomic net charges of hydrogen atoms in fully decationated faujasite-type zeolite (HxAlxSi1-xO2) increase with a decrease of the aluminum content. The net charges of aluminum atoms in Kx+AlxSi1-xO2 also increase with a decrease of aluminum content. It is easily explained from the calculated atomic net charges that both Brønsted acidity and Lewis acidity of the X-type zeolites are less than those of Y-type zeolite. The distribition of cations in model compounds is determined by calculating the binding energies for several possible cases of cation arrangements. Generally, the binding energies of cations decrease with a decrease of the aluminum content. The calculated binding energies indicate that sites I and I′ which belong to the same hexagonal prism normally cannot be occupied simultaneously. When the binding energies of cations in sites I and I′ are larger than those in sites II and III, the sum of the occupancy factors of sites I and I′ is nearly equal to one. The site preference series are obtained as follows: for 1:1 model, I > III′ > II > III > I′; for the 1.4:1 model, I > I′ > II > III′ > III; and for the 2:1 model, I′ > I > II > III′ > III.

Original languageEnglish
Pages (from-to)2065-2070
Number of pages6
JournalJournal of Physical Chemistry
Volume85
Issue number14
DOIs
Publication statusPublished - 1981 Jan 1

Fingerprint

Zeolites
Acidity
acidity
Cations
Binding energy
Aluminum
selectivity
Positive ions
cations
binding energy
aluminum
Atoms
atoms
Electronegativity
Silicon
Prisms
zeolites
prisms
faujasite
Hydrogen

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Physical and Theoretical Chemistry

Cite this

No, Kyoung Tai ; Chon, Hakze ; Ree, Taikyue ; Jhon, Mu Shik. / Theoretical studies on acidity and site selectivity of cations in faujasite zeolite. In: Journal of Physical Chemistry. 1981 ; Vol. 85, No. 14. pp. 2065-2070.
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abstract = "The influence of the silicon to aluminum ratio (1, 1.4, and 2) on the acidity and site selectivity of cations in faujasite-type zeolite is explained by using calculated atomic net charges and cation-binding energies. The chemical formulae of model compounds are K96+Al96Si96O384 (1:1), K80+Al80Si112O384 (1.4:1), and K64+Al64Si128O384 (2:1). Many experimental results (X-ray data, infrared spectra, and dealumination experiments) suggest that a covalent character is dominant in the zeolite framework. The net charges of framework atoms are derived by using the assumption of equalization of electronegativity in all the atoms. The atomic net charges of hydrogen atoms in fully decationated faujasite-type zeolite (HxAlxSi1-xO2) increase with a decrease of the aluminum content. The net charges of aluminum atoms in Kx+AlxSi1-xO2 also increase with a decrease of aluminum content. It is easily explained from the calculated atomic net charges that both Br{\o}nsted acidity and Lewis acidity of the X-type zeolites are less than those of Y-type zeolite. The distribition of cations in model compounds is determined by calculating the binding energies for several possible cases of cation arrangements. Generally, the binding energies of cations decrease with a decrease of the aluminum content. The calculated binding energies indicate that sites I and I′ which belong to the same hexagonal prism normally cannot be occupied simultaneously. When the binding energies of cations in sites I and I′ are larger than those in sites II and III, the sum of the occupancy factors of sites I and I′ is nearly equal to one. The site preference series are obtained as follows: for 1:1 model, I > III′ > II > III > I′; for the 1.4:1 model, I > I′ > II > III′ > III; and for the 2:1 model, I′ > I > II > III′ > III.",
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Theoretical studies on acidity and site selectivity of cations in faujasite zeolite. / No, Kyoung Tai; Chon, Hakze; Ree, Taikyue; Jhon, Mu Shik.

In: Journal of Physical Chemistry, Vol. 85, No. 14, 01.01.1981, p. 2065-2070.

Research output: Contribution to journalArticle

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