Faujasite-Type Zeolites FAU

Since the pioneering work by Flanigen et al. [ 112], many other studies of zeolite frameworks have appeared which used the IR/KBr technique, and frequently the interpretation of the obtained spectra was in line with or analogous to that given byFlanigenetal. [112] and Flanigen [ 114]. In many cases, the IR or Raman spectroscopic experiments were imdertaken in order to complement a general characterization of the molecular sieves imder study by, e.g., NIR, UV-Visible, XRD, MAS NMR spectroscopies or adsorption measurements. 

The experimental results of IR and Raman studies on framework vibrations offaujasite-type Na-X by Miecznikowski and Hanuza [246] and Geidel [240,248] and Geidel et al. [113], respectively, were compared by Geidel et al. [113]. The band positions and assignments proposed by Geidel et al. [ 113] are summarized and compared in Table 5. 

the IR and Raman spectra of Al-free faujasite structures were compared. The spectra show bands in the asynunetric (1200-1000 cm ) and symmetric (850-700 cm ) stretching regions of the framework vibrations however, they contain a lower number of bands than predicted as IR- and Raman-active. Strong Raman bands around 500 cm were ascribed by Geidel 

Falabella et al. [250] included IR framework spectra in their report on structural and acidity properties of RE-Y (where RE=La, Nd, Sm, Gd, Dy). Ballivet et al. [251] obtained IR spectra of La, Na-Y zeolites in the region of framework vibrations as well as in the OH stretching region (cf. Sect. 5.4.1.1) and used the spectral features in the range 1300-400 cm in dependence on the activation temperature for structural and stability determinations. 

Yu et al. [252] successfully employed UV Raman laser spectroscopy for the characterization of the framework vibration range of zeolites A,X, Y, MOR, L, and Beta. UV Raman laser spectroscopy proved to be advantageous in that it was much less disturbed by fluorescence than the conventional Raman laser technique. The authors claimed that x-membered rings (xMR) in the structures were manifested by absorptions in the wavenumber ranges (in cm 0 470-530 (4MR), 370-430 (5MR), 290-410 (6MR) and 220-280 (8MR). The method was also used for the characterization of TS-1, [Fe]ZSM-5, [V]MCM-41 and in synthesis studies (vide infra). 

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P-21 - Comparative study of the acidity of the structurally related faujasite type zeolites FAU, EMT and ZSM-20... 

Figure 1. Pseudo-unit cell of faujasite type zeolite (FAU).

The connectivity (topology) of the zeolite framework is characteristic for a given zeolite type, whereas the composition of the framework and the type of extra-framework species can vary. Each zeolite structure type is denoted by a three-letter code [4], As an example, Faujasite-type zeolites have the structure type FAU. The pores and cages of the different zeolites are thus formed by modifications of the TO4 connectivity of the zeolite framework. 

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. 

Among the many possible candidates for catalyst support, some zeolite topologies constitute a particular group of carriers. It seems that Romanovski et al. [4] were the very first to report an in situ synthesis of transition metal Pc (MePc) complexes in the supercages of faujasite type zeolites. The synthesis was later successfully repeated by Schulz-Ekloff et al. [5] and Herron [6]. It is assumed that formation of MePc out of four 1,2-dicyanobenzene (DCB) molecules in the supercages of Me-exchanged faujasite (FAU)-type zeolites is accompanied by a two-electron oxidation of (residual) water molecules ... 

Fig. 45. IR bands of pyridine (nigt, mode, [679]) adsorbed on Bronsted acid sites (B-sites), true Lewis sites (L-sites) and cations (C-sites) in hydrogen faujasite-type zeolite H-Y (H-FAU), hydrogen mordenite (H-MOR) and sodium mordenite (Na-MOR) see text...

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.)... 

An inspection of the industrial use of zeolites as catalysts shows, however, that only a rather limited number of zeolite topologies are currently used in major industrial processes. Among the more important ones are ultrastable Y (USY) (FAU), rare-earth-exchanged faujasite-type (X, Y) (FAU) andZSM-5-type (MFI) zeolites in fluid catalytic cracking (FCC) of oil fractions [4] noble-metal-loaded U SY for hydroisomerization and hydrocracking of naphtha feedstocks [5] mordenite (MOR) and zeolite Omega (MAZ) -based catalysts for C4-C6 alkane isomerization [6] zeolites ZSM-23 (MTT), ZSM-35 (FER), ZSM-5 for selective oil dewaxing [7] ZSM-5, silicalite (MFI), MCM-22 (MWW), Beta-type (BEA) zeolites for aromatics alkylation to yield ethylbenzene, p-xylene. 

The application of zeolite encapsulated metal chelate complexes in catalysis is a promising area of research. In particular shape selective oxidations catalyzed by metallophthalocyanines (MPc), shown in Figure 1, included in synthetic faujasite (FAU) type zeolites (2-10) appear to be competitive with other molecular sieve based catalysts that may have commercial potential. The restricted apertures ( 7.4 A) to the supercages (12A) in FAU type zeolites precludes removal of the large MPc complex unless the zeolite lattice is destroyed. Such physically trapped complexes have been termed ship-in-a-bottle complexes as well as zeozymes (to reflect the biomimetic reactivity that is often associated with these catalysts). 

Zeolite structures are designated by a three capital-letter code, for example, FAU stands for the faujasite structure, to which the well-known X and Y zeolites belong. A very useful short notation is used for the description of the pore system(s) each pore network is characterized by the channel directions, the number of atoms (in bold type) in the apertures, the crystallographic free diameter of the apermre (in A), asterisks (1, 2, or 3) indicating whether the systems is one-, two-, or three-dimensional. To completely specify the pore system, the eventual presence of cages (or channel intersections) should be indicated, along with their... 

In Figure 2.20, the FAU-type framework, which is congruent with the structure of the natural zeolite, faujasite, and the synthetic zeolites, X, Y, LZ-210, and SAPO-37, is shown [108],... 

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. 

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