Zeolite silicon aluminum ordering

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. 

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). 

Silicon and Aluminum Ordering of Zeolites Interpretation of Silicon-29 NMR Data for Faujasite and ZK4... 

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. 

In order to further extend our understanding of the origin of chemical shift variations in zeolites, we have examined the effects of gallium substitution for aluminum in the framework on the silicon NMR spectra of sodalite and faujasite. Gallium substitution in zeolites is well known though most preparations... 

A new zeolite cannot be deMed solely by the symmetry difference from order or disorder of the aluminum and silicon in the framework. 

Alumipophosphate molecular sieve membranes. In addition to zeolites, Haag Tsikoyiannis [1991] have also briefly described another type of molecular sieve membranes consisting of AIPO4 units whose aluminum or phosphorous constituent may be substituted by other elements such as silicon or metals. These membranes are made from aluminophosphates, silico-aluminophosphates, metalo-aluminophosphates or metalo-aluminophosphosilicates. Like zeolites, these materials have ordered pore structures that can discriminate molecules based on their molecular dimensions. Their separation and catalytic properties can also be tailored with similar techniques employed for zeolites. The procedures for calcining the membranes or separating them from non-porous subsuates are essentially the same as those described earlier for zeolites. 

Kleitz gave a detailed description of material synthesis in Chapter 9. Nevertheless, a few comments regarding silicate chemistry are in order. Silicon, analogous to carbon, is typically found in zeolites and OMS phases in a tetrahedral coordination environment. While silicon can also be found in an octahedral coordination environment this is not significant to the materials described here. The main elements comprising these materials are silicon, oxygen, and to a much smaller extent aluminum or other... 

Aluminum ( Al) (/=5/2). From Al 3Q MAS NMR spectroscopy and DFT computations of Al isotropic chemical Shifts, the locations of isolated A1 atoms in the complete A1 distribution in silicon-rich zeolites, independent of the presence of Al-0-(Si-0)n-Al (n = 1, 2) sequences in their frameworks.The chemical shift of Al and Si MAS NMR spectra were used to investigate the structural transformation from well crystal to short-range-ordered (SRO) particles for Zeolite A, which was attributed to the loss of external linkage of double four rings units in the... 

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