Crystallographic study on the selectivity, occupancy, and distribution of Sr2+ ions within zeolite Y in the presence of competing Na+ ions in aqueous exchange solution

Three single-crystals of fully dehydrated and partially Sr 2+ -exchanged zeolites Y (Si/Al = 1.56) were prepared by the flow method using mixed ion-exchange solutions. The Sr(NO 3 ) 2 :NaNO 3 molar ratios of the ion exchange solution were 1:100 (crystal 1), 1:250 (crystal 2), and 1:500 (crystal 3) with a total concentration of 0.05 M. The single-crystals were then vacuum dehydrated at 723 K and 1 × 10 −4 Pa for 2 days. The structures of the crystals were determined by single-crystal synchrotron X-ray diffraction technique in the cubic space group F d 3 ¯ m , at 100(1) K, and were then refined to the final error indices of R 1 / wR 2 = 0.044/0.167, 0.051/0.175, and 0.069/0.219 for crystals 1, 2, and 3, respectively. The unit-cell formulas of crystals 1, 2, and 3 were |Sr 17 Na 41 |[Si 117 Al 75 O 384 ]-FAU, |Sr 13 Na 49 |[Si 117 Al 75 O 384 ]-FAU, and |Sr 9 Na 57 |[Si 117 Al 75 O 384 ]-FAU, respectively. In all three crystals, the Sr 2+ ions preferred to occupy site I in the D6Rs, with the remainder occupying site II. The Sr 2+ ions are also located at site I′ in crystal 1. On the other hand, the Na + ions are located at sites I′, II, and III′ in all crystals. With increasing the molar concentration of Na + in the given exchange solution, the occupancies of the Sr 2+ ions at sites I, I′, and II decreased, whereas the occupancies of the Na + ions at sites I′, II, and III′ increased.