Sodalite faujasite structure

Figure 12. The structure of zeolite-A formed by linking truncated octahedra through double four-membered rings (a), the sodalite structure formed by direct face-sharing of four-membered rings in the neighboring truncated octahedra (b), and the faujasite structure formed by linking the truncated octahedra through double six-membered rings (c).

The naming of zeolites and related structures has been somewhat unsystematic. Some structures were named after the parent minerals (e.g., sodalite, faujasite), while others were named by researchers, or after the projects which synthesized them (e.g., ZSM [Zeolite Socony Mobil]). Unfortunately, this led to the same zeolites synthesized by different routes and bearing different names—in some cases, up to 20 different trade names ... 

The crystal structures of 4 ammonium exchanged, heat-treated faujasites were determined from x-ray powder data. Structure I, often called decationated Y, has lost 15 framework aluminum atoms and 21 framework 0(1) atoms (bridging oxygen atoms) per unit cell, and 15 Al(OH)2+ ions are present in the sodalite cages. Structure 11, called ammonium-aluminum Y hydrate, shows a complete rehydroxyla-tion of the vacant 0(1) positions. Structure III, called ultrastable Y, shows the same 15 framework aluminum atoms absent, and the removal of 25 0(3) and 13 0(h) framework oxygen atoms. Structure TV, which is a repetitive exchanged and heat-treated version of Structure 111, has a mean Si-O bond length of 1.610 A, which indicates that little framework aluminum is present. 

Ab-initio quantum chemical calculations at the HF/3-21G level of theory were applied to consider the nature of the active sites of sodalite P-cage of the LTA type zeolite and faujasite structures. Especially, the nature of sodium, potassium and silicon atoms encapsulated within the sodalitic P-cage, and their structural and molecular parameters have been described. We have shown that up to four sodium and four potassium atoms as well as five silicon atoms could be encapsulated within the sodalite P-cage. The unique properties of these nano-size materials relate directly to the encapsulated guest atom containing fragments stabilized within the sodalite P-cage of the LTA type zeolite or faujasite structures. 

Similarly, IR investigation of CO adsorption on molecular sieves was used to characterize Lewis acidity of cations (C-sites) and true Lewis acidity (L-sites) [ 740]. The interaction of CO with cations (acid C-sites) was dealt with already in Sect. 5.5.2.2. In particular, Angell and Schaffer [595] have carried out a detailed study of CO adsorption on a series of X- and Y-type zeoHtes containing monovalent and divalent cations of alkali, alkaline earth and transition metals. A linear relationship was found between the position of the IR stretching band of adsorbed CO and the Coulomb field, q/r, of the respective cationic adsorption center. This is similar to the observation made by Ward in the case of pyridine attached to cations (vide supra). It should be noted, however, that CO, like pyridine, is not capable of entering the sodalite cages and the hexagonal prisms of the faujasite structure, so that the cations located there are not detected by these probes. 

Figure 5.5 Faujasite structure (left) and sodalite cage with double 6 connectors (right)...

The cations, M, are distributed over cation sites located in the supercages, the sodalite cages and the hexagonal prisms of the faujasite structure (ref.9). The SiCl4 molecule has access to the supercages only. When the number of supercage cations is compared to the number of A1 atoms that were actually... 

The crystal structure of the faujasite is built up by linking the sodalite cages tetrahedrally through their hexagonal faces forming connecting hexagonal prisms. 

Other framework structures based on zeolites have also been synthesized which contain atoms other than aluminium and silicon, such as boron, gallium, germanium, and phosphorus, which are tetrahedrally coordinated by oxygen. Such compounds are known as zeotypes. Pure aluminium phosphate, commonly called ALPO, and its derivatives, can take the same structural forms as some of the zeolites such as sodalite (SOD), faujasite (FAU), and chabazite (CHA) (e.g., ALPO-20 is isostructural... 

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