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Synthesis of chabazite nanoparticles
Hydrogen-exchanged zeolites, whose framework-bound protons give rise to very high acidity are exploited in many organic reactions, including crude oil cracking, isomerisation and fuel synthesis. Because of high selectivity of zeolites, they are often the most efficient and cost-effective method for a number of refinery conversions .
The naturally occurring zeolites are an important group of minerals for industrial and other purposes . The discovery in 1957 of largedeposits of relatively high purity zeolite minerals in volcanic tuffs in the western United States and in a number of other countries represents the beginning of the commercial natural zeolite era. Prior to that time there was no recognized indication that zeolite minerals with properties useful as molecular sieve materials occurred in large deposits. Commercialization of the natural zeolites chabazite, erionite, and mordenite as molecular sieve zeolites commenced in 1962 with their introduction as new adsorbent materials with improved stability characteristics. The applications of clinoptiolite in radioactive waste recovery and in waste water treatment during the same period of the 60's were based not only on superior stability characteristics but also high cation exchange selectivity for cesium, strontium, and for ammonium ion.
Synthesis of Titanium Chabazite: A New Shape …
Zeolite-like materials have structures similar to zeolites but elements other than Si, Al and O can be present in them. For example, the isoelectronic substitution of 2Si → Al + P has led to the discovery of a wide range of AlPO structures and related phosphate materials . Considerable success have been done recently on making tetrahedral frameworks with the congeners of Al and Si in the next row of the periodic table, namely, Ga and Ge , and only recently the first chiral germanosilicate ITQ-37 has the been discovered with a zeolite-like framework consisting entirely of tetrahedrally coordinated positions occupied by germanium and silicon . Although hundreds of laboratories are trying to synthesize new materials with novel zeolite framework structures, only 191 zeolite framework types have been approved by the .
Dealumination of the small-pore zeolite chabazite (CHA) was performed with ammonium hexafluorosilicate under solid and liquid-state conditions to increase the Si-to-Al ratio from 2.0 to 6.0. In the solid state, the mesopore fraction increased with repeating hydrothermal synthesis at 423 K, which was confirmed by nitrogen adsorption–desorption. In the liquid state, the formation of mesopores decreased substantially and the resulting CHA had an Si-to-Al ratio of ca. 5. The result of desorption of NO–NO2 from the Cu ion-exchanged dealuminated CHA in the solid state indicated that the presence of mesopores reduced NO–NO2 adsorption and desorption of NO2 occurred at 383 and 683 K whereas for the high-silica analog SSZ-13 desorption of NO2 occurred mostly at 473 and at 673 K.
Microwave synthesis of zeolite CHA (chabazite) …
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