Silicate zeolite structure types

Zeolites are covered in ICSD. The Atlas of Zeolite Structure Types contains in addition critical discussions by experts and registration of the essential silicate frameworks. 

The zeolites are another structure type of alumino silicate minerals. The eighteenth century identification of this mineral group was made on a few... 

The samples used were a standard Na-A zeolite and five nitrogeneous types of zeolite A, or N-A.(18) The N-A zeolites are siliceous analogues of zeolite A, synthesized with tetramethyl-ammonium cation. The Si Al ratio varied from 0.94 (NaA) to 3.54 for the most siliceous N-A sample.t The ratios were determined by wet chemical analysis, and the structure type and absence of impurity phases were confirmed by X-ray powder diffraction techniques. Adsorption measurements (oxygen, -183°C) showed a zeolite A content of greater than 90%. 

The new large-aperture MCM-41 family of zeolites mentioned earlier have FD s far below those expected from this analysis. This is due to the novel structural type of these frameworks. They consist of a silica bilayer wrapped onto hyperbolic surfaces (or cylinders), rather than the hyperbolic silica monolayers characteristic of conventional zeolites. The structures of MCM-41 zeolites are closer to those of the double-layer sheet silicates [20] than zeolites. In these cases, the connectivity within each layer is three (the fourth link fuses the two layers), and pores of infinite radius are apparently realisable, e.g. CaAl2Si208, which is a flat bilayer ... 

Studying the polymerization state of the silicate in the solution during the formation of zeolites is a very important and complex issue. After years of study, it has been found that some correlations exist between the polymerization state of the silicate in the solution and the structure type of zeolites, while the polymerization state and its distribution could be affected by many factors such as alkalinity, nature of the cation, organic templates, temperature, and pressure. These parameters could partially determine the condensation rate between polymerized silicate and aluminate, which will finally affect the formation of zeolite structure. 

The continuous effort of numerous academic and industrial laboratories around the world has resulted in recent years in successful synthesis of a number of new porous materials including new structural types of zeolites and zeolypes, siliceous and non-siliceous mesoporous molecular sieves, mesoporous zeolite single crystals, and micro/mesoporous or micro/macroporous composite materials of different chemical compositions. As a consequence of the success of basic research in this area, zeolites have found new industrial applications. 

Zeolites containing phosphorus in the tetrahedral site in the framework have been synthesized. Phosphorus incorporation in a variety of structural types of zeolite frameworks has been achieved analcime, phillipsite, chabazite, Type A zeolite, Type L zeolite, and Type B ( ) zeolite. The syntheses and properties of some of the new aluminosilicophos-phate zeolites are described. The synthesis technique involves gel crystallization where incorporation of phosphorus is accomplished by controlled copolymerization and coprecipitation of all the framework component oxides, aluminate, silicate, and phosphate, into a relatively homogeneous gel phase. Subsequent crystallization of the gel is carried out at temperatures in the region of 80° to 210°C. Proof and mechanism of framework substitution of phosphorus is based on electron microprobe analysis, infrared spectroscopy, and other characterization. 

Gravimetric, microcalorimetric, in-situ XRD and in-situ FTIR spectroscopic studies of the interaction of trichloroethene and tetrachloroethene on high siliceous zeolites were carried out to look further into knowledge of adsorption processes of large admolecules in the microporous network of MFI adsorbents. Trichloroethene gives classical type I isotherms whereas tetrachloroethene gives stepped isotherms at 298 K. Furthermore, structural changes of the adsorbent were observed for the adsorption of either trichloroethene or tetrachloroethene. A comparative analysis of macroscopic and microscopic data is proposed and correlations are established between thermodynamic and structural data. 

Zeolites [64] are crystalline aluminosilicates with a three dimensional micro-porous framework formed by corner sharing SiO and AIO4. (i.e. TO4) tetra-hedra. A framework with Si02 composition is stoichiometrically neutral. The substitution of Si by Al in such a silicate framework, results in an excess negative charge, which is compensated by cations or protons. Zeolites have unique adsorption and catalytic properties. Their diversity in framework composition and structure type leads to almost unlimited design opportunities. 

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