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Zeolite definition

Although the title of this book, Perspectives in Molecular Sieve Science, avoids the zeolite definition controversy, a large majority of the research reported here centers on traditional zeolites. Only three of the 39 chapters comprising the book deal with materials that are clearly nonzeolitic Two cover clay-type derivatives, and one deals with carbon molecular sieves. Not surprisingly, interest in these materials lies in their possible use as catalysts. Only four chapters present work on mineral zeolites and three on aluminum phosphate-type molecular sieves. Two of those chapters are by workers from Union Carbide, the laboratory that did the pioneering work in this field. It is surprising that other workers have not submitted papers on the aluminum phosphates, but perhaps this situation indicates that although much activity may be underway, laboratories hesitate to publish until patent positions are established in this potentially lucrative area. Union Carbide s synthetic faujasites (zeolites X and Y) and zeolite A receive the most attention, while ZSM-5-class materials are accorded more attention than zeolite A alone. This reflects the important roles that zeolites X and Y and ZSM-5 materials have already played as catalysts. [Pg.639]

Synonyms Aluminosilicic acid, sodium salt Aluminum sodium silicate Silicic acid, aluminum sodium salt Sodium aluminosilicate Sodium aluminum silicate Sodium feldspar Zeolite Zeolites Definition Series of hydrated sodium aluminum silicates produced by reaction of sodium silicate and kaolinite clay Formula NajO AI2O3 SiOa with mole ratio = 1 1 13.2 Properties Wh. fine amorphous powd. or beads, odorless and tasteless insol. in water, alcohol, org. soivs. partly sol. in strong acids and alkali hydroxides 80-100 C pH 6.5-10.5 (20% slurry)... [Pg.1355]

CAS 1318-02-1 EINECS/ELINCS 215-283-8 Synonyms Aluminosilicates, zeolites Definition Hydrated alkali aluminum silicate Formuia NajO AI2O3 xSiOj yHjO Properties Dens. 0.58-0.75 pH 5-12 Toxicoiogy Irritant mutagen TSCA listed Storage Hygroscopic... [Pg.1422]

Synonyms Aluminosilicic acid, sodium salt Aluminum sodium silicate Silicic acid, aluminum sodium salt Sodium aluminosilicate Sodium aluminum silicate Sodium feldspar Zeolite Zeolites Definition Series of hydrated sodium aluminum silicates produced by reaction of sodium silicate and kaolinite clay... [Pg.4110]

Adsorbents such as some silica gels and types of carbons and zeolites have pores of the order of molecular dimensions, that is, from several up to 10-15 A in diameter. Adsorption in such pores is not readily treated as a capillary condensation phenomenon—in fact, there is typically no hysteresis loop. What happens physically is that as multilayer adsorption develops, the pore becomes filled by a meeting of the adsorbed films from opposing walls. Pores showing this type of adsorption behavior have come to be called micropores—a conventional definition is that micropore diameters are of width not exceeding 20 A (larger pores are called mesopores), see Ref. 221a. [Pg.669]

The traditional definition of a zeolite refers to microporous, crystalline, hydrated aluminosilicates with a tliree-dimensional framework consisting of comer-linked SiO or AlO tetrahedra, although today the definition is used in a much broader sense, comprising microporous crystalline solids containing a variety of elements as tetrahedral building units. The aluminosilicate-based zeolites are represented by the empirical fonmila... [Pg.2777]

As surface area and pore structure are properties of key importance for any catalyst or support material, we will first describe how these properties can be measured. First, it is useful to draw a clear borderline between roughness and porosity. If most features on a surface are deeper than they are wide, then we call the surface porous (Fig. 5.16). Although it is convenient to think about pores in terms of hollow cylinders, one should realize that pores may have all kinds of shapes. The pore system of zeolites consists of microporous channels and cages, whereas the pores of a silica gel support are formed by the interstices between spheres. Alumina and carbon black, on the other hand, have platelet structures, resulting in slit-shaped pores. All support materials may contain micro, meso and macropores (see text box for definitions). [Pg.182]

The carbeniiun ion so formed then reacts in the ICC 1 manner except perhaps for not abstracting a hydride ion from another alkane. Although initial views that zeolites in general were super acids have come into question, definite super acids have been found such as calcined H2S04 Zr(0H)4 which catalyze the isomerization of alkanes at low T. [Pg.65]

The presence of methylenic bands shifted at higher frequency in the very early stages of the polymerization reaction has also been reported by Nishimura and Thomas [114]. A few years later, Spoto et al. [30,77] reported an ethylene polymerization study on a Cr/silicalite, the aluminum-free ZSM-5 molecular sieve. This system is characterized by localized nests of hydroxyls [26,27,115], which can act as grafting centers for chromium ions, thus showing a definite propensity for the formation of mononuclear chromium species. In these samples two types of chromium are present those located in the internal nests and those located on the external surface. Besides the doublet at 2920-2850 cm two additional broad bands at 2931 and 2860 cm are observed. Even in this favorable case no evidence of CH3 groups was obtained [30,77]. The first doublet is assigned to the CH2 stretching mode of the chains formed on the external surface of the zeolite. The bands at 2931 and... [Pg.23]

Gopa et al. [23] reported about open Zeolite/water systems for the storage of solar heat. In their work they were presenting stability tests, methods for the definition of the adsorption enthalpy in dependence on the adsorbed amount of water and the possible heating power during the discharging process. [Pg.380]

Figure 258 shows this definition schematically. AHdehum is the enthalpy difference of the air stream caused by the adsorption within the zeolite tank only. AHcooi includes the cooling effect caused by the cold recovery. [Pg.425]

Fischer-Tropsch synthesis could be "tailored by the use of iron, cobalt and ruthenium carbonyl complexes deposited on faujasite Y-type zeolite as starting materials for the preparation of catalysts. Short chain hydrocarbons, i.e. in the C-j-Cq range are obtained. It appears that the formation and the stabilization of small metallic aggregates into the zeolite supercage are the prerequisite to induce a chain length limitation in the hydrocondensation of carbon monoxide. However, the control of this selectivity through either a definite particle size of the metal or a shape selectivity of the zeolite is still a matter of speculation. Further work is needed to solve this dilemna. [Pg.201]

In discussing gas phase separations, a few definitions will help in understanding the subject matter. Adsorbents, sometimes referred to here as sorbents, are solid chemical substances that possess micro-porous surfaces that can admit molecules to the interior surface of the structure. Zeolites in particular are solid, micro-porous, alumino-silicates with adsorption and or ion exchange capability. They affect separations by adsorbing molecules into their micro-structures. [Pg.274]

Introductory Chapter 1 provides a historical overview of molecular sieve materials. Chapter 2 covers the definition of a zeolite and describes their basic and composite building units and how they are linked in zeolite frameworks. It defines pores, channels, cages and cavities and it gives references for finding detailed... [Pg.625]

Within a discussion of nanostructured catalysts, mention must be made of zeolitic systems. Zeolites are a broad family of natural and synthetic aluminosiU-cates that exhibit two important properties that makes them ideal for consideration as heterogeneous catalysts they are crystalline and porous. Crystallinity brings with it precise definition at the atomic scale that is absent with amorphous or polycrystaUine metal oxides. The combination of a well-defined structure and... [Pg.143]

Measurement of the thermokinetic parameter can be used to provide a more detailed characterization of the acid properties of solid acid catalysts, for example, differentiate reversible and irreversible adsorption processes. For example, Auroux et al. [162] used volumetric, calorimetric, and thermokinetic data of ammonia adsorption to obtain a better definition of the acidity of decationated and boron-modified ZSM5 zeolites (Figure 13.7). [Pg.221]

Zeolitic materials have been prominent amongst those so far studied by high resolution powder diffraction using synchrotron X-rays [36]. High definition synchrotron PXD data has been helpful in a number of framework structure determinations and has facilitated studies of planar faulting (see below). Successful Rietveld refinements of the framework structures of zeolite ZSM-11 [37, 38] and silica-ZSM-12 [39], and of the complete structures of zeolite Y containing cadmium sulfide [40] and cadmium selenide [41] clusters have been described. [Pg.135]

The efiect is thus not related to geometrical constraints induced on complexes anchored in mesoporous charmels (sometimes also called as confinement efiect, even if this definition is not properly correct), neither to shape-selectivity effects as possible in zeolites, since the size of mesoporous charmels is much larger than those of micro-porous materials. Instead, an effective modification on the characteristics of the fluids is observed due to the electrostatic field generated by the charmel walls. This is an enthalpic effect versus an entropic effect as observed when the modification is instead related to limitations in the translation modes of molecules. Recently, it was also demonstrated that wall curvature influence the molecular orientation of the... [Pg.90]

The g tensors and hyperfine constants of the paramagnetic centers observed in irradiated NH4Y zeolites after various activation treatments are given in Table VIII. Despite the abundance of experimental results, many of the structures proposed for these centers should be regarded as suggestive rather than definitive, as previously noted by Kasai and Bishop (264). Neither the axially symmetric g tensor of the V center associated with two aluminum atoms nor the isotropic g tensor of the V center associated with one aluminum atom reported by Vedrine et al. (266) is consistent with the symmetry of the respective models proposed above. [Pg.68]


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See also in sourсe #XX -- [ Pg.258 ]




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