Single-crystal structures of fully and partially dehydrated zeolite Y (FAU, Si/Al = 1.56) largely Co2+ exchanged at pH 5.1

The structures of fully and partially dehydrated zeolite Y Co2+ exchanged at pH 5.1, were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd3¯m and were refined to the final error indices R1/wR2 = 0.046/0.120 and 0.062/0.191, respectively. Two crystals were used; their unit-cell formulas are approximately |Co31Na8H5|[Si117Al75O384]-FAU and |Co30.5Na6(H3O)4(H2O)4H4|[Si117Al75O384]-FAU, respectively. In the fully dehydrated structure, Co2+ ions occupy sites I, I′ and II; the Na+ ions are also at site II. In the partially dehydrated structure, Co2+ occupies sites I′, II′, II, and III′; the Na+ ions are at site I′. Some H3O+ ions are seen in the partially dehydrated structure, and H+ ions must be present in both crystals for charge balance. Upon dehydration Co2+ ions move into the hexagonal prisms and Na+ ions move from sodalite cavities to supercages.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two crystal structures of zeolite Y Co2+-exchanged at a low pH, 5.1, were determined. ► The extent of Co2+ exchange was about 70%, of H3O+ exchange about 15%. ► Upon dehydration Co2+ ions concentrate in double 6-rings, Na+ ions in supercages. ► Some H3O+ decomposed upon partial dehydration, all upon full dehydration. ► One structure is compared to that of zeolite X Co2+-exchanged at pH 6-7.