Zeolites natural types

Zeolite, or more properly, faujasite, is the key ingredient of the FCC catalyst. It provides product selectivity and much of the catalytic activity. The catalyst s performance largely depends on the nature and quality of the zeolite. Understanding the zeolite structure, types, cracking mechanism, and properties is essential in choosing the right catalyst to produce the desired yields. 

The IZA has several established Commissions. The Structure Commission formed in 1977 has published four editions of the Atlas of Zeolite Structure Types (1978, 1987, 1992, 1996) and two subsequent editions in the Atlas of Zeolite Framework Types (2001, 2007). An up-to-date version is maintained on the World Wide Web at the IZA Structure Commission web site (http //www.iza-structure.org). Subsequently commissions were established in catalysis (1998), synthesis (1992), ordered mesoporous materials (2001) and natural zeolites (2001). The synthesis commission published a volume, Verified Syntheses of Zeolitic Materials , in 1998, with a second revised edition in 2001 (http //www.iza-structure.org). 

The section on crystallization comprises zeolite synthesis, kinetics and mechanism of formation, stability relationships, recrystallization processes as well as the genesis of natural zeolites. Recent advances in this field have been surveyed, and some new perspectives have been outlined in the review by E. M. Flanigen. Most of the studies in this field are still empirical because of the complexity of the systems involved. Considerable progress has been made, however, towards a better understanding of the processes and mechanisms governing zeolite crystallization. It is not unreasonable to expect that conditions for synthesizing new zeolite structure types can eventually be predicted. 

There are about a hundred zeolite framework types. Some of these are found in nature, and are classified as minerals. However, most zeolite framework types are not found in nature but are synthetic, with the first having been reported in 1956. More are reported every year due to active research efforts in zeolite synthesis. 

J.V. Smith, J.M. Bennett, and E.M. Flanigen, Dehydrated Lanthanum-exchanged Type Y Zeolite. Nature (London), 1967, 215, 241-244. 

Beattie (6, 7) investigated the electrical conductivity of dehydrated analcites and chabazite. Freeman and Stamires (19) confirmed the conclusions of Barrer and Rees (4) and Beattie (6, 7) by electrical conductivity measurements at 200 Hz on various ion-exchanged forms of dehydrated synthetic zeolites of type A, X, and Y. They found a purely ionic conduction with a strong dependence of the activation energies on the nature of the zeolite and the kind of cation. The decrease of the activation energy in X and Y zeolites with increasing monovalent cationic... 

W. M. Meier and D. H. Olson, Atlas of Zeolite Structure Types, Structure Commission of the International Zeolite Association, 1978 It has recently been demonstrated that the use of synchrotron x-ray sources permits single crystal studies to be carried out on much smaller samples. P. Eisenberger, J. B. Newsam, M. E. Leonowicz, and D. E. W. Vaughan, Nature 309 45 (1984) The use of Rietveld refinement techniques allows better. structural information to be obtained from powder diffraction data. W. I. F. David, W. T. A. Harrison, and M. W. Johnson, in High Resolution Powder Diffraction, Materials Science Forum, vol. 9 (C. R. A. 

W.M. Meier and D.H. Olson, Atlas of Zeolite Structure Types, Butterworth-Heinemann, 1992. M.E. Davis, C. Saldarriaga, C. Montes, J. Garces, and C. Crowder, Nature, 1988, 331, 698. 

MCM-41 type is that in the nanocrystalline and delaminated zeolites there is short-range order and consequently the active sites are of zeolitic nature. 

These zeohtes are synthesized by chemical processes, which result in a more uniform and purer state as compared to the natural types in terms of their lattice stmctures, sizes of pores and cages in their frameworks. The principal raw materials useM for synthesis of synthetic zeolites can be pure chemicals rich in silica and alumina, minerals available on the earth or hy-products of industries. Fly ash being an abundantly and cheaply available industrial by-product, rich in minerals containing sihca and alumina can be an alternative material for synthesis of synthetic zeolites [20, 34—39]. The type of zeolites formed is a function of the temperature, pressure, concentration of the reagent solutions, pH, process of activation and ageing period, Si02 and AI2O3 contents of the raw materials [1, 8]. Based on the... 

Zeolites are tire product of a hydrotliennal conversion process [28]. As such tliey can be found in sedimentary deposits especially in areas tliat show signs of fonner volcanic activity. There are about 40 naturally occurring zeolite types. Types such as chabazite, clinoptilolite, mordenite and phillipsite occur witli up to 80% phase purity in quite large... 

Adsorbents Table 16-3 classifies common adsorbents by structure type and water adsorption characteristics. Structured adsorbents take advantage of their crystalline structure (zeolites and sllicalite) and/or their molecular sieving properties. The hydrophobic (nonpolar surface) or hydrophihc (polar surface) character may vary depending on the competing adsorbate. A large number of zeolites have been identified, and these include both synthetic and naturally occurring (e.g., mordenite and chabazite) varieties. 

I have carried out widespread studies on the application of a sensitive and selective preconcentration method for the determination of trace a mounts of nickel by atomic absorption spectrometry. The method is based on soi ption of Cu(II) ions on natural Analcime Zeolit column modified with a new Schiff base 5-((4-hexaoxyphenylazo)-N-(n-hexyl-aminophenyl)) Salicylaldimine and then eluted with O.IM EDTA and determination by EAAS. Various parameters such as the effect of pH, flow rate, type and minimum amount of stripping and the effects of various cationic interferences on the recovery of ions were studied in the present work. 

Over the years, thousands of compounds have been tried as cracking catalysts. These compounds fall into two general categories natural and synthetic. Natural catalyst, as the name denotes, is a naturally occurring clay that is given relatively mild treating and screening before use. The synthetic catalysts are of more importance because of their widespread use. Of the synthetic catalysts, two main types are amorphous and zeolitic. 

Zeolites are naturally occurring hydrous aluminum-sodium silicates in porous granule form. They are capable of exchanging their sodium base for calcium or magnesium and of expelling these alkaline earth metals for sodium by treatment with salt. Thus, they are a type of ion-exchange media. (Some zeolites act as molecular sieves by adsorption of water and polar compounds.)... 

Under the mineralogical name zeolite such sieves occur naturally. For technical purposes due to their higher uniformity only synthetic zeolites are used [10], In the empirical formula Me is an exchangeable cation of the valence n (zeolites are cation exchangers). Molecular sieves have a very regular and orderly crystal structure, which is characterized by a three-dimensional system of cavities with a diameter of 11 A. These cavities are interconnected by pores with a constant diameter. The value of this diameter depends on the type of the exchangeable cation Me. It is 5 A, if in the above formula Me stands for 75% Na+ and 25% Ca2+. 

Spectroscopy. In the methods discussed so far, the information obtained is essentially limited to the analysis of mass balances. In that re.spect they are blind methods, since they only yield macroscopic averaged information. It is also possible to study the spectrum of a suitable probe molecule adsorbed on a catalyst surface and to derive information on the type and nature of the surface sites from it. A good illustration is that of pyridine adsorbed on a zeolite containing both Lewis (L) and Brbnsted (B) acid sites. Figure 3.53 shows a typical IR ab.sorption spectrum of adsorbed pyridine. The spectrum exhibits four bands that can be assigned to adsorbed pyridine and pyridinium ions. Pyridine adsorbed on a Bronsted site forms a (protonated) pyridium ion whereas adsorption on a Lewis site only leads to the formation of a co-ordination complex. 

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