Silicon-aluminum zeolite

Aluminum siting in the framework of silicon rich zeolites. A ZSM-5 study... 

Molecular sieving, 18 269-272 effect of temperature, 18 271, 272 sorbate structure, 18 270, 271 molecular dimensions, 18 270, 271 polarity, 18 271 zeolitic, 39 352 structure, 18 269, 270 effect of cation, 18 269, 270 of solvation, 18 270 ring shape, 18 269 ring size, 18 269 silicon aluminum ratio, 18 270... 

When 1,2-dichlorobenzene in hydrogen-saturated deionized water was exposed to a slurry of palladium catalyst (1%) at room temperature, benzene formed via the intermediate chlorobenzene. The reaction rate decreased in the order of MCM-41 (mesoporous oxide having a silicon aluminum ratio of 35) > alumina > Y (dealuminated zeolite having a silicon aluminum ratio of 15). It appeared the reaction rate was directly proportional to the surface area of the support catalyst used (Schiith and Reinhard, 1997). 

Tn the past four years there has been great interest in how the variation A of the silicon aluminum ratio of zeolites affects their catalytic and sorptive properties. Ward (1) and Tsutsumi et al. (2) found that catalytic activity increased with increase in the silicon aluminum ratio of X and Y zeolites. As the Al content decreases, the interaluminum distance increases, and the cations or protons present experience weaker electrostatic shielding and form strong Bronsted acids (3). 

We report here a novel method of increasing the silicon-aluminum ratio of HY zeolite by reaction with the organosilicon compound, tetra-... 

In this section, a hydrothermal treatment that produces phase transformations in clinoptilolite and allows us to synthesize zeolites X and Y is described. Zeolites X and Y have the FAU-type framework however, the zeolite X has a silicon/aluminum ratio in the range 1 < Si/Al < 1.5 and zeolite Y has a silicon/aluminum ratio in the range 1.5 < Si/Al < =7.0. 

Breck has reviewed the early literature where Ga3+, P5+, and Ge4 were potentially incorporated into a few zeolite structures via a primary synthesis route (2). Evidence has also been presented to show that the small amounts of Fe3+, typically present in both natural and synthetic zeolites, are located in framework tetrahedral positions (3). A more recent review of "isomorphic substitution" in zeolites, via primary synthesis methods, speculates on the potential Impact of such substitutions on catalysis (4). The vast majority of work has been related to the high silica zeolites, particularly of the ZSM-5 type. Another approach to substitution of metal atoms into the open frameworks of zeolite structures has been to replace the typical silica alumina gel with gels containing other metal atoms. This concept has resulted in numerous unique molecular sieve compositions containing aluminum and phosphorus 5 silicon, aluminum and phosphorus (6) and with... 

Silicoaluminophosphates (SAPO s) (1) are molecular sieves which contain tetrahedra of oxygen surrounded silicon, aluminum, and phosphorus. These microporous solids not only exhibit properties characteristic of zeolites but also show unusual physiochemical traits ascribable to their unique chemical compositions (1,2). 

Zeolites with a silicon/aluminum ratio of 1, because of their low water content, have the highest possible ion-exchange capacity, when computed on this basis. Linde 4A and Linde 13-X exhibit selectivity patterns characteristic of high-field-strength exchangers despite their open structure and higher water content. 

Molecular sieve zeolites have become established as an area of scientific research and as commercial materials for use as sorbents and catalysts. Continuing studies on their synthesis, structure, and sorption properties will, undoubtedly, lead to broader application. In addition, crystalline zeolites offer one of the best vehicles for studying the fundamentals of heterogeneous catalysis. Several discoveries reported at this conference point toward new fields of investigation and potential commercial utility. These include phosphorus substitution into the silicon-aluminum framework, the structural modifications leading to ultrastable faujasite, and the catalytic properties of sodium mordenite. 

Dealumination and silicon-enrichment reaction of (NH SiF6 (AHFS) with zeolites Besides the hydrothermal method for preparation of ultra-stable Y zeolite (USY), Breck and Skeels[23] in 1983 invented a new secondary synthesis method for silicon-enriched zeolites. This method uses an ammonium hexafluorosilicate solution to remove the aluminum atoms from the framework structure of Y zeolite to the solution, and to insert silicon atoms back into the Al-removal vacancies in the framework so as to form a more or less perfect Y zeolite with a high Si/Al ratio. In comparison with the USY prepared by the hydrothermal method, the framework silicon-enriched Y zeolite obtained through the current technique possesses fewer framework hydroxyl vacancies, and the resulting zeolite has an ideal crystal lattice, and hence higher structural stability. Meanwhile, there... 

The NZ was supplied by Nemetali , Vranjska Banja, Serbia Montenegro. The mineralogical composition of the natural zeolite is 90% clinoptiolite and the rest is mordenite and haylandrite. The chemical analysis of the natural zeolite shows that the oxides of silicon, aluminum, calcium and iron are the main constituents while other oxides are present in trace amounts (Table 1). Prior to the experiments, the NZ was dried at 300°C for 48 h in order to remove any traces of moisture or other constituents. The properties of the adsorbents used are listed in Table 2. 

J. Turkevich (Princeton University, Princeton, N. J. 08540) In connection with Figure 3, I would like to know how the silicon-aluminum ratio is determined. The synthetic zeolites and maybe natural ones are obtained from silica-rich gels which increase in silica-alumina ratio in the mother liquid as the silicon-aluminum ratio increases in the crystals. Silica may be occluded and adsorbed as a colloidal gel on the zeolite and difficult to wash off. The silica ratio as measured will be higher and the lines asymetrically lower. 

X-ray crystallography a diffraction technique employed to study the distances between atoms or ions in crystalline materials zeolite a mineral typically composed of silicon, aluminum, oxygen, and metals that is characterized by the presence of uniform pores of molecular scale... 

In material science applications solid state NMR often employs a 200—750 MHz NMR spectrometer (Table 7.1) with a wide-bore magnet and high-power RF amplifiers and matching NMR probes [10—12]. This equipment is especially useful for analysis of polymer structures with and NMR and for analysis of zeolites with and Si NMR. In polymers, local dynamics can be studied with time scales ranging from seconds to picoseconds phase separations can be studied with domain sizes from nanometers to micrometers. For zeolites, the structures are characterized in terms of silicon/aluminum ratios, aluminum—hydrogen distances, and the chemistry of catalytic sites. 

Klinowski, J., Thomas, J. M., Fyfe, C. A. and Parzaile, V. E. (1981) Application of Magic Angle Spinning Silicon-29 Nuclear Magnetic Resonance. Evidence for Two Different Kinds of Silicon-Aluminum Ordering in Zeolite Structures, J. Phys. Chem., 85, 2590-2594. 

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