Synthesis of fully dehydrated fully Zn{sup 2+}-exchanged zeolite Y and its crystal structure determined by pulsed-neutron diffraction
- Univ. of Hawaii, Honolulu, HI (United States)
Fully dehydrated, fully Zn{sup 2+}-exchanged zeolite Y has been synthesized by the reduction of all H{sup +} ions in H-Y by zinc vapor. This solvent-free ion-exchange reaction goes to completion at 420 {degrees}C with about 0.2 Torr of Zn{sup 0} to give Zn{sub 27.5}Si{sub 137}Al{sub 55}O{sub 384} (a{sub 0} = 24.4688 (3) {Angstrom}). The crystal structure was determined in the cubic space group Fd3m by pulsed-neutron powder-diffraction methods at 10 K and was refined to R{sub p} = 0.0268 and R{sub wp} = 0.0368. Two different Zn{sup 2+} positions were found in the structure. The Zn(1) position is located on a threefold axis in the sodalite unit adjacent to a single 6-ring (site II{sup {prime}}), 2.183 (12) {Angstrom} from three nearest framework oxygens. The Zn(2) position is also on a threefold axis in the sodalite unit, but is adjacent to a double 6-ring (site I{sup {prime}}), 2.228 (15) {Angstrom} from three nearest framework oxygens. It must be true, on the basis of refined fractional occupancy parameters and to avoid 3.1-{Angstrom} Zn(1)-Zn(2) distances, that about half of the sodalite cavities contain about four Zn(1) ions in the four tetrahedrally arranged single 6-rings and that the other half contain about three Zn(2) ions in three of the four tetrahedrally arranged double 6-rings. Based on this crystal structure, it is proposed that Zn(2) is initially preferred (Zn{sup 2+} can bond to O(3), the most electronegative oxygen) but that at higher loadings the increased number of short 3.90 {Angstrom} intrasodalite Zn(2)-Zn(2) distances causes Zn(1) to be the preferred site. 26 refs., 3 figs., 3 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 273692
- Journal Information:
- Journal of Physical Chemistry, Vol. 96, Issue 14; Other Information: PBD: 9 Jul 1992
- Country of Publication:
- United States
- Language:
- English
Similar Records
Hydronium ions in zeolites. 1. Structures of partially and fully dehydrated Na, H{sub 3}O-X by X-ray and neutron diffraction
Crystal structure of partially Pd{sup 2+}-exchanged zeolite X dehydrated in oxygen at 400 C. Formation of linear Pd{sub 2}O{sub 3} clusters proposed to be HO-Pd{sup IV}-O-Pd{sup IV}-OH in (Pd{sup 2+}){sub 14}(HOPdOPdOH{sup 4+}){sub 8}(Na{sup +}){sub 32}-Si{sub 100}Al{sub 92}O{sub 384}