The Ion-Exchange Properties of Zeolites. I. Univalent Ion Exchange in Synthetic Faujasite

Large single crystals of zeolite, |Na75|[Si117Al75O384]-FAU (Na-Y, Si/Al = 1.56), were synthesized from gels with composition of 3.58SiO2 : 2.08NaAlO2 : 7.59NaOH : 455H2O : 5.06TEA : 2.23TCl. One of these, a colorless single-crystal was ion exchanged by allowing aqueous 0.02 M CsOH to flow past the crystal at 293 K for 3 days, followed by dehydration at 673 K and 1 × 10 -6 Torr for 2 days. The crystal structure of fully dehydrated partially Cs

Section: å)mentioning

confidence: 99%

Synthesis of Fully Dehydrated Partially Cs⁺-exchanged Zeolite Y (FAU, Si/Al = 1.56), |Cs₄₅Na₃₀|[Si₁₁₇Al₇₅O₃₈₄]-FAU and Its Single-crystal Structure

Seo¹,

Kim²,

Lee³

et al. 2009

“…It is this cation crowding that is responsible for the reluctance of Cs + to exchange completely for Na + into FAU from aqueous solution, not the inability of Cs + to enter sodalite cavities and D6Rs. 12 Compared with other structure refinement, 14 and Na + ions were found at site I. Furthermore, Na + ions at site I are replaced by Cs + ions at high cesium exchange levels.…”

Section: Discussionmentioning

confidence: 73%

“…22,23 In spite of a number of attempts, fully Cs + -exchanged zeolite for Na + in zeolite X has not been achieved by conventional aqueous methods of ion exchange. 12,16,24,25 This work was done to confirm the special cation site selectivity that Cs + ions can occupy double six-rings. In addition, it was hoped that fully Cs + -exchanged zeolite X could be prepared from the conventional ion exchange method using different solution.…”

Section: Introductionmentioning

confidence: 98%

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Crystal Structure of Fully Dehydrated Partially Cs⁺-Exchanged Zeolite X, Cs₅₂Na₄₀-X (The Highest Cs⁺-Exchanged Level Achieved by Conventional Method and Confirmation of Special Site Selectivity)

Bae

2007

The crystal structure of fully dehydrated partially Cs + -exchanged zeolite X, [Cs 52 Na 40 Si 100 Al 92 O 384 ], a = 24.9765(10) Å, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd at 21 °C. The crystal was prepared by flow method for 5 days using exchange solution in which mole ratio of CsOH and CsNO 3 was 1 : 1 with total concentration of 0.05 M. The crystal was then dehydrated at 400 °C and 2 × 10 −6 Torr for 2 days. The structure was refined to the final error indices, R 1 = 0.051 and wR 2 (based on F 2 ) = 0.094 with 247 reflections for which F o > 4σ (F o ). In this structure, about fifty-two Cs + ions per unit cell are located at six different crystallographic sites with special selectivity; about one Cs + ion is located at site I, at the centers of double oxygen-rings (D6Rs), two Cs + ions are located at site I', and six Cs + ions are found at site II'. This is contrary to common view that Cs + ions cannot pass sodalite cavities nor D6Rs because six-ring entrances are too small. Ring-opening by the formation of -OH groups and ring-flexing make Cs + ions at sites I, I', and II' enter six-oxygen rings. The defects of zeolite frameworks also give enough mobility to Cs + ions to enter sodalite cavities and D6Rs. Another six Cs + ions are found at site II, thirty-six are located at site III, and one is located at site III' in the supercage, respectively. Forty Na + ions per unit cell are located at two different crystallographic sites; about fourteen are located at site I, the centers of D6Rs and twenty-six are also located at site II in the supercage. Cs + ions and Na + ions at site II are recessed ca. 0.34(1) Å and 1.91(1) Å into the supercage, respectively. In this work, the highest exchange level of Cs + ions per unit cell was achieved in zeolite X by conventional aqueous solution methods and it was also shown that Cs + ion could pass through the sixoxygen rings.

“…6,7,12 Compared with the other available cations for selective nitrogen adsorption like Ca, Li source is expensive and it was reported that the Li ions are hard to be exchanged to X zeolite. 14 To reduce the usage of Li ions, many researches, such as introduction of second and/or third cations and Li recovery from waste solution of ion-exchange treatment, were conducted. [15][16][17][18] It was reported that some second cations like Ca and Sr were effective in reducing the Li ratio without decrease in adsorption performance.…”

Section: Introductionmentioning

confidence: 99%

Li⁺- and H⁺-Exchanged Low-Silica X Zeolite as Selective Nitrogen Adsorbent for Air Separation

Kim¹

2003

Li+ and H + co-exchanged LSXs (Li-H-LSX) with various ratios of Li + and H + were prepared, and those adsorption characteristics of nitrogen and oxygen were compared with Li-Na-LSX and Li-Ca-LSX. Li-H-LSX showed higher nitrogen capacity and selectivity than that of Li-Na-LSX in the wide range of Li-exchanged ratio. The nitrogen capacity of Li-Ca-LSX was slightly higher than that of fully Li-or Ca-exchanged LSX (Li-LSX or Ca-LSX). However, Li-Ca-LSX showed low nitrogen/oxygen adsorption selectivity until the Li content reached about 80%, which was a tendency near that of Ca-LSX.