Sodalite lattice

Figure 30 Proton-exchange reaction between methanol molecule and the Bronsted proton of sodalite lattice. Solid and dotted lines show distances between the methanol oxygen and the methanol and zeolite protons and respectively.

The product from the Duolite columns will be evaporated to form 2M Na2C03-0.002M CS2CO3. Barrer (2) has found that alkaline solutions of sodium carbonate react with kaolinite to form sodalite containing tightly bound sodium carbonate. We have experiments in progress to determine whether cesium is also bound in the sodalite lattice. 

Linear correlations were also found between 8jso and the sodalite lattice parameter a (Figure 10.5B) given by... 

The nitrite sodalite system was modelled by one cell (lattice parameter 8.923 A), so that the chemical formula Nas[Al6Si6024](N02)2 corresponds to the atoms in the simulation cell. This choice was adopted also for nitrate sodalite (constrained and unconstrained). The unconstrained nitrite sodalite + O2 system was simulated by using the cell parameter of nitrate sodalite (lattice parameter 8.996 A) [3], locating in the starting configuration the O2 molecule midway between two NO2 in the simulation cell. 

Both Br and C1 MAS NMR have been used in the investigation of sodium, silver and halo-sodalite semiconductor supralattices. Useful information is available on the environments of the encapsulated clusters within the sodalite lattice. The Na4X (X = Cl, Br) tetrahedra provide a symmetric environment around the halide and give rise to narrow resonances for specific locations. The spectra are sensitive to the distribution of anion empty cavities or to T containing cavities. 

Using data from rotation and Laue photographs, it is shown that the unit of structure of sodalite, containing < NaiAlzSiiOi2Gl, has a0 = 8.87 A. The lattice is the simple cubic one, Fc the structure closely approximates one based on a body centered lattice, however. The atomic arrangement has... 

The question of methanol protonation was revisited by Shah et al. (237, 238), who used first-principles calculations to study the adsorption of methanol in chabazite and sodalite. The computational demands of this technique are such that only the most symmetrical zeolite lattices are accessible at present, but this limitation is sure to change in the future. Pseudopotentials were used to model the core electrons, verified by reproduction of the lattice parameter of a-quartz and the gas-phase geometry of methanol. In chabazite, methanol was found to be adsorbed in the 8-ring channel of the structure. The optimized structure corresponds to the ion-paired complex, previously designated as a saddle point on the basis of cluster calculations. No stable minimum was found corresponding to the neutral complex. Shah et al. (237) concluded that any barrier to protonation is more than compensated for by the electrostatic potential within the 8-ring. 

Ultramarine is essentially a three-dimensional aluminosilicate lattice with entrapped sodium ions and ionic sulfur groups (Fig. 32). The lattice has the sodalite structure, with a cubic unit cell dimension of ca. 0.9 nm. In synthetic ultramarine derived from china clay by calcination (see Section 3.5.3), the lattice distribution of silicon and aluminum ions is disordered. This contrasts with the ordered array in natural ultramarines. 

The ground mixture is heated to about 750 °C under reducing conditions, normally in a batch process. This can be done in directly fired kilns with the blend in lidded crucibles of controlled porosity, or muffle kilns. The heating medium can be solid fuel, oil, or gas. The sodium carbonate reacts with the sulfur and reducing agent at 300 °C to form sodium polysulfide. At higher temperatures the clay lattice reforms into a three-dimensional framework, which at 700 °C is transformed to the sodalite structure, with entrapped sodium and polysulfide ions. 

Trapping or encapsulation represents a second situation wherein guests are introduced at high temperature and at high pressure of the guest. Crystals are chilled, and then the pressure is released. The host lattice is permanent, and the windows are small. Examples are sodalite hydrate, cancrinite hydrate, and analcite. 

Cation Siting in Linde A. At the time this work was completed, x-ray studies on hydrated NaA (3, 4) and hydrated KA (5) had shown that 8 of the 12 exchangeable cations per unit cell are firmly bound to the zeolite framework and would therefore be expected to have the major influence on the lattice vibrations. These cations are sited in front of the sodalite... 

Recent work by Rabo et al. (57) opens new possibilities for controlling the activity and selectivity of zeolite catalysts. Occlusion of various guest molecules into the sodalite cavities of Y zeolites can significantly change the catalytic properties of the zeolites for carbonium-type reactions. Anions of occluded salts are located close to the center of the sodalite cavity and strongly influence the arrangement of cations in the faujasite lattice and hence the catalytic activity. 

This is a very significant conclusion because it is widely believed (9) that, in order to synthesize systems with 5-rings, such as ZSM-5, the only requirement is to synthesize systems low in alumina. Both our quantum-chemical and our electrostatic lattice calculations contradict this theory. The calculations show, for example, that sodalite, which contains only 4- and 6-rings and no alumina, is more stable than ZSM-5, in which 5-rings predominate. This agrees with recent experimental work relating to the synthesis of high-silica sodalite (10). 

Results of Lattice Energy Minimization Calculations. Relative lattice energies of faujasite, mordenite, silicalite and sodalite were compared. For the framework and cation positions of faujasite and sodalite the same data were used as before, from Hseu (18) and Olson (19), and Baerlocher (20) and Chao (21), respectively. For mordenite and sodalite the data of Meier (22) and Mortier (23 ) (on mordenite) and Baerlocher and Meier (24) (on sodalite) were used. 

Figure 2.29 The Sodalite/Ultramarine framework, which results by sharing of the square faces of the 024h orbit truncated octahedron over the extended lattice again, shown as a decoration of vertices of the cube. 

The ultramarine and sodalite framework lattice is shown in Figure 2.29. This framework results when the square faces of the truncated octahedron are shared. Again, the perspective in the figure emphasizes the possibility of constructing the extended lattice of P4-3m symmetry. 

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