Zeolite Types A, X, and

Type A zeolites are synthesized in the sodium form, with 12 sodium cations occupying all eight sites in 1 and three sites in II, plus one site in III. This is 

A detailed discussion on the sites of important cations in zeolites A, X, Y, chabazite (cage-type with 8-oxygen ring window) and heulandite (channel-type) is given in 7.4.1. 

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An early report from Shukla et al.129 showed efficient hydrolysis and isomerization reactions of disaccharides, including cellobiose, maltose, and lactose, over zeolites type A, X, and Y. Abbadi et al.130 studied the hydrolysis of maltose, amylose, and starch over the zeolitic materials H-mordenite, H-beta, and mesoporous MCM-41. The effect of temperature and pressure, as well as that of the Si/Al ratio of H-mordenite and H-beta zeolites, on their catalytic activity was investigated for the... 

The manufacture of the industrially important zeolite types A, X and Y is generally carried out by mixing sodium aluminate and sodium silicate solutions, whereupon a sodium aluminosilicate get is formed. In this gel Si02- and Al203-containing compounds pass into the liquid phase, from which the zeolites are formed by cry.stallization. As the zeolite growth components are removed from the solution more gel dissolves. The reaction mechanism for zeolite formation is presently not yet fully understood. There is experimental evidence that, depending upon the reaction conditions, different mechanisms are possible. 

The microporous alumino-silicate zeolites (Types A, X, and mordenite are frequently used) provide a variety of pore openings (3-10 A), cavity and channel sizes, and framework Si/Al ratios. They are also available in various cationic exchanged forms (Na, K, Li, Ag, Ca, Ba, Mg), which govern their pore openings and cationic adsorption site polarities. They are highly hydrophilic materials and must be dehydrated before use. The amorphous adsorbents contain an intricate network of micropores and mesopores of various shapes and sizes. The pore size distribution may vary over a wide range. The activated carbons and the polymeric sorbents are relatively hydrophobic in nature. The silica and alumina gels are more hydrophilic (less than zeolites) and they must also be dehydrated before use. 

K. Watanabe, N. Austin, and M. R. Stapleton, Mol. SimuL, 15, 197 (1995). A Force Field Specifically Parametrized for Oxygen, Nitrogen and Argon Adsorption in Zeolite Types A, X, and Y. 

Figure 7.5. Compositional synthesis windows for the Na20-Al203-Si02-H20 system at 100°C and 90-98 mol% H2O. Source of Si02 is (a) sodium silicate and (b) colloidal silica. The area enclosing a letter represents the composition that yields the corresponding phase, while the + marks the typical composition of the product. A, X, and Y = zeolites types A, X, and Y B = zeolite P R = chabazite S = gmelinite and HS = hydroxysodalite (from Breck and Flanigen, 1968, with permission).

Even in more conventional PSA dehydration zeolites including types A, X and Y have aU been employed in pressure swing drying. Compound beds of alumina and zeoUtes X or Y have been employed for PSA dehydration and CO2 removal for pre-purification of feed to air separation units. 

The influence of the reduction temperature was studied for nickel-zeolite catalysts. Molecular sieves of type A, X, and Y which contained about 7-8 wt % nickel were used. Figure 1 shows the results of the study on the formation of metal surface in reduction temperatures from 250 to 600° C. Reduction of nickel with hydrogen begins at 250-300° C for all... 

This paper presents some results of the studies of the influence of ion exchange cations on adsorption, kinetics, and chromatographic characteristics of zeolites of types A, X, and Y. 

The detailed structures of zeolites are varied and complex, but the common pseudo-cubic basket-like frameworks of linked tetrahedra are depicted in Figure 1.7. These typify the unit cage structures found for the mineral faujasite and the synthetic zeolites whose structures are generically described as types A, X, and Y. The constitution, channel diameters, and ion exchange capacities for various natural and synthetic zeolites are shown in Table 1.4. 

Beattie (6, 7) investigated the electrical conductivity of dehydrated analcites and chabazite. Freeman and Stamires (19) confirmed the conclusions of Barrer and Rees (4) and Beattie (6, 7) by electrical conductivity measurements at 200 Hz on various ion-exchanged forms of dehydrated synthetic zeolites of type A, X, and Y. They found a purely ionic conduction with a strong dependence of the activation energies on the nature of the zeolite and the kind of cation. The decrease of the activation energy in X and Y zeolites with increasing monovalent cationic... 

Si/Al molar ratio in the activated fly ash, zeolites can be classified/graded as low silica zeolites , intermediate silica zeolites and high silica zeolites , as listed in Table 2.2. In general, for zeolites, an increase in this parameter (i.e., Si/Al from 0.5 to infinity) [5] can significantly result in the increase in various other parameters (viz., acid resistivity, thermal stability and hydrophobicity) except few parameters (viz., hydrophilicity, acid site density and cation concentration) which get decreased [5, 8, 10,40, 41]. In general, synthetic zeolites hold some key advantages over their counterparts i.e. natural zeolites. Zeolites type A, X, Y, P and Na-Pl are well known synthetic zeolites synthesized from fly ash which have a wider range of industrial applications than the natural zeolites [1, 8, 20, 22, 36, 42, 43]. 

Commercially significant zeolites include the synthetic zeolites type A (LTA), X (FAU), Y (FAU), L (LTL), mordenite (MOR), ZSM-5 (MFI), beta ( BEA/BEC), MCM-22 (MTW), zeolites E (EDI) andW (MER) and the natural zeolites mordenite (MOR), chabazite (CHA), erionite (ERl) and clinoptiloUte (HEU). Details of the structures of some of these are given in this section. Tables in each section lists the type material (the common name for the material for which the three letter code was established), the chemical formula representative of the unit cell contents for the type material, the space group and lattice parameters, the pore structure and known mineral and synthetic forms. 

Tphe study of the properties of zeolites, either synthetic or natural, has A received a great deal of attention in recent years. Among the synthetic zeolites, the faujasites X and Y types have been most frequently and thoroughly studied. A summary of the advances in this area is found in a recent review by Sherry (1). 

Figure 1. Relationship between the measured adsorption volumes, Fp (measd) and calculated void volume Vp of several zeolites. The dashed line corresponds to Vp (measd) = Vp (calcd). The symbols represent the zeolites as described in Tables I-VI A, X, L, Z (mordenite Zeolon), omega (to), and offretite-type 0. Vertical shaded areas containing plotted values of Vp (measd) correspond to calculated values of Vp for the main pore systems. The narrow area, 0, corresponds to the main c-axis void of zeolite 0. The value of Vp for Zt = Vp for zeolite 0. Symbols with the subscript t (At Xt) etc.) represent values of Vp for the total void volume shown by narrow shaded areas. The neopentane (NP) volumes lie consistently below the dashed line thus showing a paeking effect. In all of these zeolites of varying structure, the H20 and N2 volumes correspond with complete filling of the total voids even though this is not possible in the case of N2 in zeolites A, X, and L.

Figure 2. Dependence of catalytic activity of zeolites type A and X on size of nickel crystals in benzene hydrogenation = type A O = type X...

Cation-exchanged KX and CaY zeolites are also known to be used for the separation of glucose and fructose on the basis of the selective adsorption properties of that kind of material.122-251 Some experiments have then been performed in the presence of Ca- and Ba-exchanged A, X and Y zeolites. Unfortunately, the CaY zeolite claimed for the separation of glucose and fructose was not as efficient as expected for a two-stage process involving isomerization followed by separation on the same type of material. 

The framework charge-compensating cations in a zeolite, which for synthetic zeolites are normally sodium ions, can be exchanged for other cations of different type and/or valency. However, care must be taken during ion exchange to avoid strongly acidic solutions which can lead to proton exchange with the zeolite metal cations or even structure collapse. For example, zeolites A, X, and Y decompose in 0.1 N HCI. The more silica-rich zeolites such as mordenite are, however, stable under such conditions. Acidity can be introduced into a zeolite in a number of different ways ... 

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