Silicate zeolite

Many catalysts have been used but the standard catalysts are generally mixtures of silica and alumina or natural or synthetic aluminium silicate zeolites. 

Several different possible zeolite structures may result, and if the sodium content is too high, calcium and magnesium are excluded and a hard zeolite scale of sodium-aluminum silicate preferentially forms. If only calcium is present, calcium-aluminum silicate zeolite forms, also as a hard scale. If only magnesium is present in solution, it forms the flocculant magnesium aluminate, MgAl204. 

The Zeolite Group. Amethyst Galleries, Inc., http //galleries.com/minerals/silicate/zeolites.htm... 

The development and application of multidimensional solid state homo- and heteronuclear correlation (HETCOR) NMR techniques have lead to an increasingly important role in structure solution of zeolitic materials and have had many practical applications in the detailed structural characterization of completely siliceous zeolites[6,7] and AlPOs.[8-ll] However, HETCOR NMR is not readily applicable to aluminosilicates... 

Hydroxylation of benzene with hydrogen peroxide in the presence of solid zeolite catalyst (titan-silicate-zeolite) was chosen by Radoiu et al. [57] as a model heterogeneous liquid-phase reaction for study of microwave effects, Scheme 10.12. 

Marquez, F., Marti, V., Palomares, E., Garcia, H. and Adam, W. (2002). Observation of azo chromophore fluorescence and phosphorescence emissions from DBH by applying exclusively the orbital confinement effect in siliceous zeolites devoid of charge-balancing cations. J. Am. Chem. Soc. 124, 7264-7265... 

Siliceous fibers, silylation of, 22 703 Siliceous minerals, 22 365-366 structure of, 22 366 Siliceous zeolites, 16 818 SILIC F-Silicalite... 

Anderson, M.W., Klinowski,)., and Xinsheng, L. (1984) Alumination of Highly Siliceous Zeolites. J. Chem. Soc. Chem. Commun., 1596-1597. 

Guo, G. and Long, Y. (2001) Process for separating p-xylene with hydrophobic silicic zeolite by selective adsorption. C.N. Patent 1,280,977. 

Woodcock, D.A. and Lightfoot, P. (1999) Negative thermal expansion in the siliceous zeolites chabazite and ITQ-4 a neutron power diffraction smdy. Chem. Mater., 11, 2508-2514. 

Clearly, changing the Si/Al ratio of a zeolite also changes its cation content the fewer aluminium atoms, the fewer cations will be present to balance the charges. The highly siliceous zeolites are inherently hydrophobic in character, and their affinity is for hydrocarbons. 

The infrared stretching frequency of the hydroxyl associated with the Bronsted sites in decationized zeolites, fails in the range 3600 to 3660 cm. As the Si/Al ratio in the framework increases, this frequency tends to decrease. What does this suggest about the acidity of the highly siliceous zeolites ... 

The ZSM series (for Zeolite Socony Mobil) of highly siliceous zeolites is prepared from solutions containing alkylammonium bases. 

Equation (13) works well for materials with framework Si/Al ratios below ca. 10. For more siliceous zeolites, the 29Si MAS NMR spectrum is dominated by the Si (4 Al) signal and the estimation of composition becomes inaccurate. In these cases, the relative amounts of framework and nonframework aluminum can be estimated from 27A1 NMR spectra (Section HI,I). 

In the light of what has been said in Sections III,B-III,D about the appearance and interpretation of 29Si MAS NMR spectra of zeolites, one might expect the spectrum of a highly siliceous zeolite to be uncomplicated displaying a single Si(4Si) signal, sometimes with a smaller Si(3Si) resonance,... 

The intensities of the two signals in the spectrum of the siliceous zeolite omega are in the 2 1 ratio. While zeolite omega is more appropriately called synthetic mazzite (94), both the previously suggested structure (95) and the structure of mazzite (96) call for two nonequivalent tetrahedral sites in a 2 1 population ratio. Accordingly, Thomas et al. (91) were able to assign the... 

This was a liquid-phase process which used what was described as siliceous zeolitic catalysts. Hydrogen was not required in the process. Reactor pressure was 4.5 MPa and WHSV of 0.68 kg oil/h kg catalyst. The initial reactor temperature was 127°C and was raised as the catalyst deactivated to maintain toluene conversion. The catalyst was regenerated after the temperature reached about 315°C. Regeneration consisted of conventional controlled burning of the coke deposit. The catalyst life was reported to be at least 1.5 yr. 

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