Zeolites composition

Zeolite Composition Pore diameter Si02/Al203... 

Preparation of chitosan-zeolite composites by in-situ zeolite synthesis... 

The composite contains 8% of mineral fraction according to thermogravimetric data. The X-ray powder pattern of the chitosan-zeolite composite is reported in figure 3 and shows the formation of zeolite A. It can be observed that, at difference with the composites with high mineral content prepared by encapsulation, the XRD pattern of chitosan is observable. 

The N2 adsorption-desorption isotherms of dried chitosan gel and chitosan-zeolite composites are reported in Figure 4 (a). Dried chitosan gels present a surface area lower than 5 m2 g"1 and virtually no porosity, the evaporation of water having brought about the coalescence of the polymer fibrils. The composites with a small amount of zeolites (less than 8 % for the zeolite X composite) present a type 4 isotherm leaning towards... 

Zeolite compositions, 16 813t Zeolite crystallization, 16 830-831 Zeolite HZSM5... 

Grose, R.W. and Flanigen, E.M. (1981) Novel zeolite compositions and processes for preparing and using same US Patent 4,257,885. 

Ward, J.W. (1975) Ammonia-stable Y zeolite compositions. US Patent 3,929,572. 

Vassilakis, J.G. and Best, D.F. (1991) Novel zeolite compositions derived from zeolite Y. US Patent 5,013,599. 

Breck, D.W. and Skeels, G.W. (1985) Silicon substimted zeolite compositions and process for preparing same US Patent 4,503,023. 

Vaughan, D.E.W. and Strohmeier, K.G. (1994) Process for preparing LTL nano-crystalline zeolite compositions. US Patent 5,318,766. 

Tavalaro, A. and Tavolaro, P. (2007) LTA zeolite composite membrane preparation, characterization and application in a zeohtic membrane reactor. Catal. Commun., 8, 789-794. 

K. (2008) Catalytic activities and structures of silicalite-l/H-ZSM-5 zeolite composites. Micropor. Mesopor. Mater., 115,106. 

The dye-zeolite composites reported so far show fascinating photonic antenna properties which are perhaps comparable to some extent to those of natural systems. Tuning their chemical and photochemical behavior, organizing information exchange between their inside and the external world, but also organizing individual crystals on a surface in order to realize, for example, monodirectional functionalities remain a challenge which we address in this section. 

As we reported in Section IV.A, refraction and total internal reflection can occur in dye-loaded zeolite L microcrystals. Therefore, a bundle of light rays in, for example, a POPOP-loaded zeolite composite can circulate inside the hexagon. If the emission can circulate often enough in the same volume and the loss of the zeolite L ring cavity is small enough, lasing should be possible. 

The cation plays a prominent structure-directing role in zeolite crystallization. The unique structural characteristics of zeolite frameworks containing polyhedral cages (62, 63) have led to the postulate that the cation stabilizes the formation of structural subunits which are the precursors or nucleating species in crystallization. The many zeolite compositions and complex cation base systems studied allow a test of the structuredirecting role of the cation and the cation templating concept. Table I summarizes the cation base systems from which zeolites have been synthesized. The systems used before 1969 are indicated to illustrate the number and complexities of new cation systems investigated since that time. Table II presents a summary of zeolite framework structure types, the cation systems in which they have been formed, and a proposal for a cation specificity for the formation of each framework type. A similar... 

To commence measurements, 1 ml of labeled solution was added to one arm (donor), and at the same time an equal volume of unlabeled solution was dispensed to the remaining arm (receptor). Aliquots of 0.1 ml were withdrawn from both arms at suitable time intervals over 4r-5 days. The activity of samples from the receptor side was determined by liquid scintillation counting, and Wt/Wm vs. y/t plots were constructed. The temperature range studied was 20-50°C. (Note salicylic acid was shown not to penetrate disks composed of polystyrene alone, and self-diffusion kinetics were reproducible between different disks of the same polystyrene/zeolite composition). 

The paper deals with some new data concerning the state of the metal after reduction and the catalytic functions of zeolite catalysts containing nickel and platinum. By using the molecular sieve selectivity in the hydrogenation of mesitylene it has been proved that metal (platinum) is contained in the volume of the zeolite crystal. The temperature dependence of the formation of nickel crystals was investigated. The aluminosilicate structure and the zeolite composition influence mainly the formation of the metal surface which determines the catalytic activity. In the hydrocracking of cumene and disproportionation of toluene a bifunctional action of catalysts has been established. Hydrogen retarded the reaction. 

The two-step method described before was applied in the preparation of N-containing carbons. In the first step, FA was polymerized in the nanochannels of zeolite Y. The resulting PFA/zeolite composite was heated up to 800°C and then subjected to CVD of acetonitrile over the composite... 

Green KJ, Rudham R. Photocatalytic oxidation of propan-2-ol by semiconductor-zeolite composites. J Chem Soc Faraday Trans 1993 89 1867-70. 

Different ways have been proposed to prepare zeolite membranes. A layer of a zeolite structure can be synthesized on a porous alumina or Vycor glass support [27, 28]. Another way is to allow zeolite crystals to grow on a support and then to plug the intercrystalline pores with a dense matrix [29], However, these two ways often lead to defects which strongly decrease the performance of the resulting membrane. A different approach consists in the direct synthesis of a thin (but fragile) unsupported monolithic zeolite membrane [30]. Recent papers have reported on the preparation of zeolite composite membranes by hydrothermal synthesis of a zeolite structure in (or on) a porous substrate [31-34]. These membranes can act as molecular sieve separators (Fig. 2), suggesting that dcfcct-frcc materials can be prepared in this way. The control of the thickness of the separative layer seems to be the key for the future of zeolite membranes. 

The reaction of zeolites with an aqueous fluorosilicate solution under relatively mild conditions has been shown to yield zeolites with silicon enriched frameworks which are essentially free of structural defects (1). As a result of the treatment, the framework topologies of the respective zeolites are relatively unchanged, but the zeolite compositions which are produced either do not occur naturally or are not synthesized directly. The fluorosi1icate treatment process has been termed "Secondary Synthesis". 

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