Zeolite cage

Figure B3.3.14. Template molecule in a zeolite cage. The CFIA stmcture (periodic in the calculation but only a fragment shown here) is drawn by omitting the oxygens which are positioned approximately halfway along the lines shown coimecting the tetrahedral silicon atoms. The molecule shown is 4-piperidinopiperidine, which was generated from the dicyclohexane motif suggested by computer. Thanks are due to D W Lewis and C R A Catlow for this figure. For fiirther details see [225].

The more permeable component is called the. st ga.s, so it is the one enriched in the permeate stream. Permeability through polymers is the product of solubihty and diffusivity. The diffusivity of a gas in a membrane is inversely proportional to its kinetic diameter, a value determined from zeolite cage exclusion data (see Table 22-23 after Breck, Zeolite Molecular Sieves, Wiley, NY, 1974, p. 636). 

Table 1 19F chemical shifts and fluoride location in high-silica zeolites cages are indicated by the... 

A) Thermal or hydrothermal treatment of zeolites. This results in partial framework dealumination, but the aluminum remains in the zeolite cages or channels. 

When the two-step process is repeated on the same material, the thermal treatment following the chemical dealumina t ion results in further expulsion of aluminum from the framework into zeolite cages or channels. The solubilization of non-framework aluminum during the first chemical treatment appears to facilitate further framework dealumination during the subsequent thermal treatment due to the altered steric and electrostatic parameters in the zeolite channels. The newly formed non-framework aluminum species can be readily solubilized by acid treatment. This cyclic method has allowed the almost total removal of aluminum from mordenite (5). 

It has already been mentioned that the formation of ultrastable Y zeolites has been related to the expulsion of A1 from the framework into the zeolite cages in the presence of steam (8,9), and the filling of framework vacancies by silicon atoms (11,12). This results in a smaller unit cell size and lower ion- exchange capacity (6). It also results in a shift of X-ray diffraction peaks to higher 20 values. Ultrastable Y zeolites prepared with two calcination steps (USY-B) have a more silicious framework than those prepared with a single calcination step (USY-A). Furthermore, since fewer aluminum atoms are left in the USY-B framework, its unit cell size and ion-exchange capacity are also lower and most of the nonframework aluminum is in neutral form (18). 

Figure 4.2 Zeolite cages as found in Sodalite (SOD), Zeolite A (LTA), and Faujasites (FAU). (Reprinted from D.

Professor M. R. Maurya is currently heading the Department of Chemistry, IIT Roorkee. He has more than 26 years of teaching and research experience. He had worked in Loyola University of Chicago, USA, Iowa State University, Ames, Iowa, USA, National Chemical Laboratory, Pune, and Pune University Pune, before joining department of Chemistry at IIT Roorkee in 1996 and became full professor in 2008. His current area of research interests include structural and functional models of vanadate-dependent haloperoxidases, coordination polymers and their catalytic study, metal complexes encapsulated in zeolite cages and their catalytic study, polymer-anchored metal complexes and their catalytic study, and medicinal aspects of coordination compounds. So far, he has guided 21 doctoral and 7 Master s theses, co-authored more than 140 research papers in the international refereed journals. 

FIGURE 9.3. FTIR spectrum of Pd carbonyl cluster in zeolite cages. 

O2, H2, and CO adsorbed and condensed on (H,Na)-Y zeolite cages as studied by variable temperature IR spectroscopy. Phys. Chem. Chem. Phys., 8,1186-1196. 

Newsam, J. M. (1986). The zeolitic cage structure. Science 231 1093-1099. Novak, F., and L. Zak (1970). Dravite Asbestos from Chvaletia. Acta Universitatis Carolinae, Geologica 1 27—44. 

Fe(CO)s], [Fe2(CO)g], [Co2(CO)8] and [Os3(CO)i2]) have been reacted with dicyanobenzene to form intrazeolite [M(Pc)] complexes [140]. Another class of materials prepared by the intrazeolite template synthesis method has been mixed ligand metal carbonyls and metal carbonyl clusters, frequently by reductive car-bonylation of metal ions in zeolite cages [175]. However, because these are frequently decomposed in situ to form, for example, nanoparticles, they are outside the scope of this chapter, and will be considered here only when they are used as precursors for metal complexes. 

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