Zeolites framework topologies

Table 9.1 Characteristics of some common zeolite framework topologies.

In this model, where no preference of Si-Al over Al-Al pairing is assumed, the NMR spectrum is determined by the simple probabilities of uncorrelated occupancies of the four nearest neighbors. Therefore, the peak intensities for the completely random model are independent of the details of the zeolite framework topology. They are... 

Gasoline composition from hexadecane cracking over calcined and steamed AFS and USY zeolites can be represented by general correlations as shown in Figure 5. As these correlations are unique to zeolite Y, they indicate that the Y zeolite framework topology plays an important role in the mechanism of product formation. The method of dealumination and subsequent steam treatment lead to various PONA compositions however, these compositions result from a... 

It is clear that in the case of MFI, the zeolite pore entrances should not be considered as rigid apertures. Instead, zeolite framework topologies can show flexibility. While the O-Si-0 angle in the tetrahedral unit is rigid (109 + 1 °), the Si-O-Si angle between the units can vary between 145 and 180°. Based on isomorphous substitution of Si by other T-atoms in the framework [18], framework defects [19], cation positions, changes in the water content [16], external forces on the crystalline material [20] and upon adsorption of guest molecules [21] phase transitions can occur that have a dramatic influence in particular cases on the framework atom positions. 

There is a large variety of zeolite framework topologies, and new framework topologies are still discovered regularly. These topologies are identified by... 

Shao L, Li Y, Yu J, Xu R. Divalent-metal-stabilized aluminophosphates exhibiting a new zeolite framework topology. Inorg Chem 2012 51 225-9. 

Leonowicz ME, Vaughan DEW. Proposed synthetic zeolite ECR-1 structure gives a new zeolite framework topology. Nature 1987 329 819-21. 

Without any doubt, the zeolite framework porous characteristics (micropores sizes and topology) largely govern the zeolite properties and their industrial applications. Nevertheless for some zeolite uses, as for instance, host materials for confined phases, the zeolite inner surface characteristics should be precised to understand their influence on such low dimensionality sorbed systems. In that paper, we present illustrative examples of zeolite inner surface influence on confined methane phases. Our investigation extends from relatively complex zeolite inner surface types (as for MOR structural types) to the model inner surface ones (well illustrated by the AFI zeolite type). Sorption isotherm measurements associated with neutron diffraction experiments are used in the present study. 

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 >24 structures of AlP04-based molecular sieves reported to date include zeolite topological analogs and a large number of novel structures. The major structures are shown in Table 1.3. They include 15 novel structures as well as seven structures with framework topologies related to those found in the zeolites... 

In the metal aluminophosphate (MeAPO) family the framework composition contains metal, aluminum and phosphorus [27]. The metal (Me) species include the divalent forms of Co, Fe, Mg, Mn and Zn and trivalent Fe. As in the case of SAPO, the MeAPOs exhibit both structural diversity and even more extensive composihonal variation. Seventeen microporous structures have been reported, 11 of these never before observed in zeoUtes. Structure types crystallized in the MeAPO family include framework topologies related to the zeolites, for example, -34 (CHA) and -35 (LEV), and to the AIPO4S, e.g., -5 and -11, as well as novel structures, e.g., -36 (O.Snm pore) and -39 (0.4nm pore). The MeAPOs represent the first demonstrated incorporation of divalent elements into microporous frameworks. 

Tschortnerite (TSC) surely is the most remarkable novel zeohte mineral discovered [67]. Its unique framework topology contains five different cages D-6Rs, D-8Rs, sodahte cages, truncated cubo-octahedra and a unique 96-membered cage. Cu-containmg clusters are encapsulated within the truncated cubo-octahedra. The pore structure is three-dimensional with 8R charmels, and the framework density of 12.2 is among the lowest known for zeolites. The framework is alumina-rich with Si/Al = 1, unusual for zeohte minerals. 

Bu, X., Gier, T.E., Feng, P., and Stucky, G.D. (1998) Cobalt phosphate based zeolite structures with the edingtonite framework topology. Chem. Mater., 10, 2546-2551. 

One of the most signiflcant variables affecting zeolite adsorption properties is the framework structure. Each framework type (e.g., FAU, LTA, MOR) has its own unique topology, cage type (alpha, beta), channel system (one-, two-, three-dimensional), free apertures, preferred cation locations, preferred water adsorption sites and kinetic pore diameter. Some zeolite characteristics are shown in Table 6.4. More detailed information on zeolite framework structures can be found in Breck s book entitled Zeolite Molecular Sieves [21] and in Chapter 2. 

Table I. Maximum Topological Symmetry of Some Zeolite Frameworks ...

Of the zeolites reported since 1969, most represent compositional variants of previously known framework structure types with respect to cation, framework, and intercalated salt compositions. Zeolite species that may represent new types of framework topologies include Losod (18) ZSM-5, 8, and 11 (8, 10, 11) ZSM-10 (12) Ba-N and Ba-T (20) and Li,Na-0 (24). Zeolites Z-21 (82) and Na-V (29) are not included because of their apparent structural relationship to zeolite N. Except for Losod, no structural studies have been reported. 

This fifth edition of the Zeolite Powder Pattern Collection contains calculated patterns of 226 zeolite materials representing 176 framework topologies - an increase of 43 new topologies since the fourth edition in 2001. 

Each species is also denoted by a three-letter structure code that describes the framework topology (connectivity, channel dimensionality etc). Examples are given in Table 9.1 common structures of some representative zeolites are shown in Figure 9.6. 

Table II gives the unit cell composition of the 10 of our as synthesized samples for which an accurate analysis was possible. Also are included and adapted 3 other Nu-10 samples for which an analysis was available in the literature (samples 14, 15, 18). We also included the composition of silica-ZSM-22, another zeolite possessing the same framework topology as Nu-10 (12), that was synthesized in presence of diethylamine (DA) under veiy particular conditions (12).

Zeolite Nu-10 was demonstrated to possess the identical framework topology than zeolites ZSM-22 (55), Theta-1 (57), KZ-2 (38) and ISI-1 (59). The complete crystal structure of Theta-1, ZSM-22 and of its Si end-member was elucidated (Table m). 

---