Zeolite sodium sodalite

Cancrinites are one of the rarest members of the feldspathoid group, classified as such due to its low silicon content. However, cancrinite is also classified as a zeolite, due to its open pore structure, which confers molecular sieve properties [1], Likewise, variable sodium carbonate and NaOH concentrations in the hydrothermal synthesis of cancrinite could direct the synthesis of the intermediate phase or the disordered cancrinite formation [2], The intermediate phase is described as a phase between cancrinite and sodalite [3], The disordered cancrinite is an intermediate phase which is much closer to the cancrinite structure than sodalite structure [2],... 

Extraframework cations are needed in anionic zeolites for charge balance, and for several zeolite topologies their locations are well investigated [281, 282]. Different cations have been investigated by solid state NMR in the past with different NMR properties and different project targets. We restrict this section to a tutorial example on sodium cation motion in sodalite and cancrinite structures [283-285], 23Na has a nuclear electric quadrupole moment, and quadrupolar interaction is useful to investigate jump processes, especially when they are well defined. 

Sodium is the sixth most abundant element on earth. It comprises about 2.6% weight of the earth s crust. Its salt, sodium chloride, is the major component of seawater. The concentration of sodium in seawater is 1.08%. As a very reactive element, sodium is never found in free elemental form. It occurs in nature in many minerals such as cryolite, amphibole, zeolite, sodalite, and soda niter. Sodium chloride (NaCl) is the most common salt of sodium. Some other important salts are caustic soda (NaOH), soda ash (Na2C03), baking soda (NaHCOs), Chile saltpeter (NaNOs), borax (Na2B407 IOH2O), sodium thiosulfate (Na2S203), sodium sulfate (Na2S04), and sodium phosphates. 

Research in zeolites has also branched out to try to prepare new materials by incorporating various molecules and ions in the cages of these microporous and mesoporous structures. An early example of this was the preparation of the pigment ultramarine used in many paints and colourants. It is based on the zeolite sodalite (SOD) structure and contains 83 ions trapped in the cages this is the same anion found in the mineral lapis lazuli, to which it imparts the beautiful deep blue colour. Treatment of zeolites such as Na-zeolite Y with sodium vapour traps Na4 ions in the cavities, which impart a deep red colour. 

Zeolite A. The structure of zeolite A contains two types of voids (1) the a cage, 11.4 A in diameter, and (2) the P cage (or sodalite unit), 6.6 A in diameter (7). Table I compares experimentally determined pore volumes of zeolite A with the void volume as calculated from the structure (no influence of cations considered). Since the sodium zeolite A does not adsorb normal paraffins, data are included for the calcium-exchanged form. Also shown in column 5 is the void fraction, Vi, as calculated by... 

The observations made here are not sufficient to prove any particular synthesis mechanism. However we may speculate as to mechanisms that are consistent with the observations. The synthesis of LTA probably proceeds by formation of sodalite units from D4R. This mechanism has been postulated before(14,15). D4R are present in silicate solutions containing sodium(16), potassium(17), and TMA(18) and in aluminosilicate solutions containing TMA(19). In TMA silicate solutions the fraction of Si in D4R decreases with dilution(20) and in TMA aluminosilicate solutions D4R s decrease with decreasing Si/Al(21). D4R with strict alternation of Si and Al, as required for zeolite A, can join in only one way and this is apparently facile as no template... 

It should be noted that zeolites will form from reactant gels with very low water contents ) although reaction rates are low. Also, the conversion of the zeolite chabazite in the absence of added water to give a range of other more compact framework structures has been reported. Particularly relevant was the conversion of a silicaceous sodium-form of chabazite to nosean (sodalite) at ca. 300°C. 1 )... 

Sodium-23 MASNMR measurements have been used to examine the extent to which this method can be used to determine the cation distribution in hydrated and dehydrated Y-zeolites. Results have been obtained on Na-Y and series of partially exchanged (NH, Na)-Y, (Ca,Na)-Y and (La,Na)-Y zeolites which demonstrate that the sodium cations in the supercages can be distinguished from those in the smaller sodalite cages and hexagonal prisms. For the hydrated Y zeolites, spectral simulation with symmetric lines allows the cation distribution to be determined quantitatively. 

For calcium zeolites, x-ray diffraction and infrared studies together have shown that the first 16 or 18 calcium ions introduced into the unit cell of the sodium form are located in the hexagonal prisms and sodalite portions of the structure 1, 2, 23). Addition of further calcium ions results in the occupation of sites in the supercages. The changes in intensity of the hydroxyl infrared bands and the onset of the cation-pyridine interactions indicate that the same preferential location of calcium ions in calcium hydrogen Y zeolite occurs (23). 

Long ago it was observed that the sorption of sodium by anhydrous Na-Y led to a bright red zeolite Y which was shown by ESR to contain clusters of (Na4)3 .21 Not until recently was the structure and location of (Na4)3 within the zeolite fully confirmed.22 One atom of sodium had reacted with three Na" " ions to give four equivalent Na" ions, arranged tetrahedrally within the sodalite unit, with one electron uniformly delocalized about them. 

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