Time-of-flight powder neutron diffraction studies of dehydrated synthetic gallosilicate zeolites X, XY, and Y
The structures of dehydrated synthetic gallosilicate zeolites with the faujasite (FAU) framework, Na/sub x/Ga/sub x/Si/sub 192-x/O/sub 384/ with x = 85 (type X), x = 72 (XY), and x = 57 (Y), have been determined by full-profile analyses of time-of-flight powder neutron diffraction data. The structures are each described satisfactorily in space group Fd3m, indicating no long-range order of silicon and gallium. The cubic unit cell constants of the three zeolites are not collinear with x. In contrast, both the mean T-O bond length (T identical with tetrahedral species Si, Ga, or Al) and the mean T-O-T angle vary nearly linearly with x. Literature data for analogous aluminosilicate zeolites reveal similar trends which are related to variations with x in the /sup 29/Si chemical shifts. The observed sodium cation configurations are consistent for both the dehydrated aluminosilicate and gallosilicate zeolites. Each of the four sodium ion sites has an upper population limit, and the nonframework cation configuration thus evolves with composition in discontinuous stages. It is suggested that such changes in the cation arrangements are implicated in observed discontinuities in the variation with composition of certain macroscopic properties of FAU framework zeolites.
- Research Organization:
- Exxon Research and Engineering Co., Annandale, NJ
- OSTI ID:
- 6946841
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 90:26
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
GALLIUM COMPOUNDS
CRYSTAL STRUCTURE
SILICATES
SODIUM COMPOUNDS
EXPERIMENTAL DATA
NEUTRON DIFFRACTION
POWDERS
SPACE GROUPS
TIME-OF-FLIGHT METHOD
ZEOLITES
ALKALI METAL COMPOUNDS
COHERENT SCATTERING
DATA
DIFFRACTION
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
MINERALS
NUMERICAL DATA
OXYGEN COMPOUNDS
SCATTERING
SILICON COMPOUNDS
400201* - Chemical & Physicochemical Properties
020400 - Petroleum- Processing