Crystal Structures of Vacuum-Dehydrated Ni2+-Exchanged Zeolite Y (FAU, Si/Al = 1.69) Containing Three-Coordinate Ni2+, Ni8O4·xH2O8+, x ≤ 4, Clusters with Near Cubic Ni4O4 Cores, and H+

Abstract

Five single crystals of vacuum-dehydrated Ni2+-exchanged zeolite Y (Ni−Y) were variously prepared by the exchange of Na−Y or K−Y (Na71− or K71−Si121Al71O384, Si/Al = 1.69) with Ni2+ using flowing aqueous 0.05 M Ni(NO3)2 at 294 or 353 K, followed by vacuum dehydration at 2.0 × 10−6 Torr and 623 or 723 K. Their crystal structures and chemical compositions were determined using synchrotron X-radiation and energy dispersive X-ray (EDX) analyses to give Nin−Y, where 25.3 ≤ n ≤ 34.1 per unit cell: |NiuMvHw[Ni8O4·xH2O]y[Al(OH)4]z|[Si121+zAl71−zO384]−FAU, where 21.4 ≤ u ≤ 24.2, M = Na and/or Ca, 3.3 ≤ v ≤ 13.1, 9.5 ≤ w ≤ 21.6, 2 ≤ x ≤ 4, 0.3 ≤ y ≤ 3.2, and 0 ≤ z ≤ 2.5. In each of the five crystal structures (space group Fd3m; mean a = 24.47 A), Ni2+ is found at sites I, I′, a second I′, II′, and sometimes II; unexpectedly, Na+ and Ca2+ are found at another site II. Two extra-framework oxygen positions (Oe), one in the sodalite cavity and the other nearby in the supercage, are seen on 3-fold axes in all crystals....