High-resolution silicon-29 nuclear magnetic resonance and neutron powder diffraction study of Na-A zeolite. Loewenstein's rule vindicated

Journal Article · Thu Sep 15 04:00:00 EDT 1983 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100242a041· OSTI ID:5641592

Bennett, J M ^[1]; Blackwell, C S; Cox, D E

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1. Union Carbide Corp., Tarrytown, NY

The structure of a sample of sodium (Na)-A zeolite dehydrated by heating at 300/sup 0/C was examined by magic angle spinning (MAS) silicon 29 (/sup 29/Si) NMR and neutron powder diffraction techniques. The /sup 29/Si NMR chemical shifts for Na-A zeolite and a series of nitrogenous A zeolites with various Si aluminum (Al) ratios demonstrate conclusively that in the former each Si is surrounded by four Al and no Si near neighbors. This 4:0 ordering scheme is consistent with previous x-ray structure determinations and does not violate Loewenstein's rule. Neutron powder diffraction data taken at 4.5 and 296 K reveal that this sample of Na-A zeolite has rhombohedral symmetry at these temperatures, in agreement with the results of a recent neutron study by Bursill et al., but different from the cubic Fm3c symmetry reported in an independent neutron investigation by Adams et al., and a recent x-ray single-crystal study by Pluth and Smith. However, there is a transition to the cubic structure at about 335 K. Structural analysis at selected temperatures between 4.5 and 603 K was carried out by Rietveld refinement of the neutron data. Above the transition, the results are consistent with the x-ray single-crystal refinement by Pluth and Smith. Below the transition, constrained refinement strongly indicates that ordering of Na atoms in partially occupied sites takes place, with a consequent lowering of the symmetry to at least R3c. Since the present sample contains about 3 wt % of water which can only be driven off by heating between 400 and 700/sup 0/C, it seems likely that the presence or absence of a transition depends upon the nature and extent of the residual hydration. 9 figures, 5 tables.

• DOE Contract Number: AC02-76CH00016
• OSTI ID: 5641592
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 87:19; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BOND LENGTHS
CHALCOGENIDES
COHERENT SCATTERING
COMPARATIVE EVALUATIONS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CUBIC LATTICES
DATA
DEHYDRATION
DIFFRACTION
DIMENSIONS
EXPERIMENTAL DATA
HIGH TEMPERATURE
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
LENGTH
MATERIALS
MEDIUM TEMPERATURE
MINERALS
NEUTRON DIFFRACTION
NMR SPECTRA
NUMERICAL DATA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
POWDERS
SCATTERING
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SODIUM COMPOUNDS
SODIUM OXIDES
SPACE GROUPS
SPECTRA
SPECTRAL SHIFT
STRUCTURAL CHEMICAL ANALYSIS
TEMPERATURE DEPENDENCE
TRIGONAL LATTICES
ULTRALOW TEMPERATURE
ZEOLITES