Zeolites Linde Type

The ion pump needs no forepump, but it is necessary to reduce the pressure initially to 10 or 10 ° Torr before turning on the pump. With care, this may be accomplished with a rotaiy oil pump, but it is often done instead with a sorption pump such as the Varian Vac-Sorb pump, in which the air in the system is adsorbed on a molecular sieve (synthetic zeolite, Linde type 5A) chilled with liquid nitrogen. This type of pump has the advantage of presenting no danger of contaminating the system with oil. 

Three examples will suffice to demonstrate this information Figure 3 shows the polyhedral units in the synthetic zeolite Linde Type A, which link to provide a three-dimensional interconnecting array of channels, Figure 4 illustrates the essentially two-dimensional system of channels in the mordenite framework, and Figure 5 shows the major channels in synthetic zeolite Linde Type L arranged as parallel one-dimensional channels and shown as a stereo pair. Table 6 lists the Atlas notations for these structures with explanations, including the symbols used in Tables 2-5. 

The aluminophosphate analog of zeolite Linde-type L (LTL) consists of 1-D 12-membered ring channels with cylindrical pore openings of 0.71 nm (35). 

The structural unit in Type A zeolite (Linde Type A or LTA), as well as in Types X and Y (faujasite or FAU), is the truncated octahedron shown in Figure 7.1(a). This unit is also called sodalite cage or beta cage, as sodalite is formed by directly... 

The nomenclature of zeolites is rather arbitrary and follows no obvious rules because every producer of synthetic zeolites uses his/her own acronyms for the materials. However, as mentioned before, at least the structure types of the different zeolites have a unique code. For example, FAU represents Faujasite-type zeolites, LTA Linde Type A zeolites, MFI Mobile Five, and BEA Zeolite Beta. The structure commission of the International Zeolite Association (IZA) is the committee granting the respective three-letter codes [4], Some typical zeolites, which are of importance as catalysts in petrochemistry, will be described in the following sections. 

Garcia-Sanchez, A., Garcia-Perez, E., Dubbeldam, D., Krishna, R., and Calero, S. (2007) A simulation study of alkanes in Linde type A zeolites. Adsorp. Sci. Technol, 25, 417-427. 

Synthesis and Crystal Structure of Zeolite Rho—A New Zeolite Related to Linde Type A... 

Pure component loadings for CO2, N2 and O2 on commercial pelleted forms of Linde type 4A, 5A and 13X molecular sieve zeolites were derived from various gravimetric and volumetric measurements. The range of pressures and temperatures over which these measurements were made were at least as broad as those encountered in the breakthrough experiments described here, to permit accurate estimations of heats of adsorption in the manner described by equation (6) above. As mentioned above, the pure component data were correlated to the LRC model, and the CO2 loadings predicted by the multicomponent LRC model compared to actual loadings in the breakthrough runs at bed saturation. 

Figure 9.6 Topologies of zeolite structure types, (a) Sodalite (b) Linde type A (c) faujasite (zeolite X and Y) (d) AlP04-5 and (e) ZSM-5. The vertices represent the positions of AI04 or Si()4 letrahedra while straight lines represent Si-O-Si or Si-O-Al linkages. (Reproduced with permission from [5]).

It was observed in synthetic Linde Type Na-Y, Ba-Y and Zn-Y zeolites (a crystalline aluminosilicate with the formula Nax(A102)x(Si02)y, etc.) that after the NO adsorption, only NO radicals could be detected at 77 K [99]. The use of 15NO gas confirmed the results with uNO. After UV irradiation at 77 K of the NO-treated Ba-Y, only N02 radical spectrum was observed. This photoinduced signal was stable at 77 K, decayed gradually at room temperature (Tj/2 = several hours) and disappeared completely when the sample was annealed at 50° for 30 min [99]. The role of NO, N02 and N2O3 species, photoelectron transfer between them and their reversible transformations have anready been discussed. 

The lanthanum exchanged Y zeolite (LaY) was made by contacting an ammonium Y (Linde type 31-200 powder) with an aqueous solution of lanthanum chloride. Approximately 60-70 percent of the ammonium ions were exchanged in the procedure. The resulting LaY powder was pressed into tablets, crushed and sieved to -60+80 mesh. 

Nowadays many large pore zeolites are known (Table 1). However, only zeolite Beta seems to have the right overall characteristic for organic reactions. Beta is commercially available in various Si A1 ratios. The commercially available Faujasite, Mordenite and Linde type L all have low Si Al ratios, while the high-silica zeolite ZSM-12 has a parallel channel system giving rise to diffusional problems. The recently discovered zeolites DAF-1, CIT-1 and ITQ-7 require expensive templates and the synthesis is often quite delicate. 

Three well known zeolite structure types - Linde L(18), mazzite(19) and the hypothetical omega-structure(20) - have essentially identical hexagonal lattice constants with =18A and .=7.5A, but only mazzite has a 7.5A x 18A layer that contains an n-glide plane operator the thickness of this layer is -15.5A. If the hexagonal overgrowth is mazzite, the electron micrograph interpretation implies that ECR-1 comprises mazzite sheets interconnected with some other subunit to form the observed 26A repeat distance. The... 

FIGURE 25.18 Main zeolite structures. SOD sodalite LTA Linde type A zeolite FAU faujasite, zeolites X or Y MOR mordenite LTL Linde type L zeolite MFI ZSM-5. (From Ozin, G.A., Kuperman, A., and Stein, A., Angew. Chem. Int. Ed. Engl., 28, 359, 1989.)... 

More than one hundred different zeotype structures, based on different topologies of the linkage of corner-sharing [TO4/2] tetrahedra (T = Al, Si, P. . . ), have been discovered so far. The various topologies are compiled in the "Zeolite Atlas" [21] under their respective three-letter code (e.g., LTA for "Linde Type A" or zeolite A, MFI for "ZSM-5" or "Mobil Five"). Apart from the framework composition, the high variability of framework structures is related to the fact that all of these compounds are metastable [14] and are formed by kinetic control under the influence of various SDAs. 

Linde type X and Y zeolites are two typical microporous materials with the FAU framework. So far, both low-silica type X and high-silica type Y molecular sieves are... 

Linde type L zeolite is characterized by a 1-dimensional system of channels parallel to... 

The dehydration of these materials makes void volume available to molecules whose shape and size have to be compatible with the size of the cavities and pores. The diameter of these cavities or pores depends on the type of zeolite and varies from 0.4 nm (Linde type A) to 0.75 nm (Linde-Y) which corresponds typically to the size of molecules and is expressed in the word molecular sieve given to such materials. It follows that diffusivities of reagents or products often play a determining role in catalysis. This holds true particularly in shape selectivity features. 

GIS). A three letter code (e.g. GIS) is assigned to confirmed framework types by the Structure Commission of the International Zeolite Association according to rules set up by an 1UPAC Commission on Zeolite Nomenclature [3,4]. The codes are normally derived from the name of the zeolite or type material , e.g. FAU from the mineral faujasite, LTA from Linde Type A, and MFI from ZSM-5 (Zeolite Socony Mobil - five). Information pertinent to these framework types is published in the Atlas of Zeolite Framework Types [5] and on the internet at http //www.iza-strncture.org/databases/. As new codes are approved, they arc announced on the IZA Structure Commission s WWW pages (http //www.iza-structure.org/) and included in the internet version of the Atlas. As of January 2005, 161 zeolite framework types had been confirmed by the Structure Commission. In this chapter, all references to materials whose framework types are known will be accompanied by the appropriate three letter code in boldface type. 

FT—Far IR Spectroscopic Studies of Alkali and Alkaline Earth Linde Type A Zeolites... 

Pinpointing the siting of cations in Linde Type A zeolites is crucial in the design and understanding of experiments aimed at fine tuning the dimensions of the entrance windows of the supercages. 

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