Natural zeolites

Voids The space between the resinous particles in an ion-exchange bed. Zeolite Naturally occurring hydrous silicates exhibiting limited base exchange. 

M.J., and Valenda, S. (2004) Supramo-lecular self-assembled molecules as organic directing agent for synthesis of zeolites. Nature, 431, 287-290. 

The study of zeolites as adsorbent materials began in 1938 when Professor Barrer published a series of papers on the adsorptive properties of zeolites [28], In the last 50 years, zeolites, natural and synthetic, have turned out to be one of the most significant materials in modem technology [27-37], Zeolites have been shown to be good adsorbents for H20, NH3, H2S, NO, N02, S02, C02, linear and branched hydrocarbons, aromatic hydrocarbons, alcohols, ketones, and other molecules [2,31,34], Adsorption is not only an industrial application of zeolites but also a powerful means of characterizing these materials [1-11], since the adsorption of a specific molecule gives information about the microporous volume, the mesoporous area and volume, the size of the pores, the energetics of adsorption, and molecular transport. 

Separation of molecules with different sizes can be achieved by a proper choice of zeolites (nature of the zeolite and adjustment of the pore architecture, especially the pore size). The simplest forms of shape selectivity come from the impossibility of certain molecules in a reactant mixture entering the zeolite pores (reactant shape selectivity) or of certain product molecules (formed inside the pore network) exiting from these pores (product shape selectivity). In practice, reactant and product shape selectivities are observed not only when the size of molecules is larger than the size of the pore apertures (size exclusion) but also when their diffusion rate is significantly lower than that of the other molecules. Differences of diffiisivities by 2 orders of magnitude are required to produce significant selectivities between reactant species (35). 

Zeolites natural and synthetic hydrated aluminosilicates with open framework structures enclosing cavities and channels in which reside mobile cations and water molecules... 

G. Manos, A. A. Garforth, and J. Dwyer, Catalytic Degradation of High-Density Polyethylene on an Ultrastable-Y Zeolite. Nature of Initial Polymer Reactions, Pattern of Formation of Gas and Liquid Products, and Temperature Effects, Ind. Eng. Chem. Res., 39, 1203 (2000). 

However, in the post-treatment approach, the sur ce area decreases quickly with the formation of zeolite phase. The mesoporous material eventually becomes an aggregate of zeolite nanocrystals. The zeolite seed hydrothermal amroach, on the other han produces materials with only indirect hints of zeolitic nature. Neither the FTIR nor Ae XRD spectrum showed strong evidence for the formation of zeolite structure. 

A. Corma, F. Rey, J. Rius, M.J. Sabater, and S. Valencia, Supramolecular Self-assembled Molecules as Organic Directing Agent for Synthesis of Zeolites. Nature (London), 2004,431, 287-290. 

L.R.M. Martens, PJ. Grobert, and P.A. Jacobs, Preparation and Catalytic Properties of Ionic Sodium Clusters in Zeolites. Nature London), 1985, 315, 568-570. 

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

The unit cell thus contains a total of 16 molecules of water, corresponding to the composition M3[M (CN)6]a 12 HgO. The analytical data and the densities indicate a water content of 11 to 14 molecules per formula unit. The degree of hydration is very sensitive to changes in humidity and temperature. This rather broad range of hydration follows quite naturally from the zeolitic nature of part of the water. The structure factor calculations have been carried out on the basis of 12 water molecules per formula unit. Attempts to locate additional water have not been fruitful. 

Smit B 1993 Computer Simulation m the Gibbs Ensemble. In Allen M P and D J Tildesley (Editors) Computer Simulation in Chemical Physics Dordrecht, Kluwer. NATO ASI Series 397, pp. 173-210 Smit B and T L M Maesen 1995. Commensurate Freezing of Alkanes in the Channels of a Zeolite. Nature 374.42-44. 

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. 

ITQ-2 zeolite prepared by delamination of MCM-22 precursor, is formed by disordered individual sheets of crystalline zeolitic layers in where the Bronsted acid sites are of zeolitic nature and the vast majority of them aecessible to large molecules. The delaminated zeolite combines the acid characteristic of microporous zeolites with accessibility of the sites of mesoporous Al/MCM-41 and amorphous silica-alumina. The superior catalytic performance of delaminated zeolites compared to conventional zeolites and Al/MCM- 1 is examplified for reactions involving large reactant molecules, namely the preparation of dimethyl acetals, the Beckmann rearrangement of bulky cycloalkanone oximes and hydroxylation of aromatics. 

P-15 - Model hydrocracking catalysts combining NiMo sulfide and large-pore zeolite effect of the zeolite nature on the location of NiMo sulfide in relation with catalytic properties... 

The zeolite nature and the substitution pattern in the starting materials proved critical 2-substituted arylvinylketones reacted more readily in H-ZSM5, giving high yield (>90%)... 

Observation of the ion-exchange properties of soils 1858 Zeolites natural ion-exchangers in the soils 1917 Determination of ammonia in urine using a synthetic zeolite... 

Armbruster T., Gunter M.E. Crystal structure of natural zeolites. Natural zeolites Occurrence, properties, applications. In Reviews in Mineralogy and Geochemistry 45, D.L. Bish and D.W. Ming (Eds.), Mineralogical Society of America, Washington, D.C., 2001, pp. 1-67. 

Aluminate sodalites belong to a structural family which, in principle, has been known for quite a long time and which is closely related to various zeolites. Naturally occurring sodalites belong to the class of aluminosilicates (e.g., sodalite in the proper sense has the idealized formula Nag [A1 pSig02i ] CI2) 5 whereas aluminate sodalites have a composition Mg [a1 2 24 2 (pseudo-)cubic cell... 

Sun J, Bonneau C, Cantfn A, Corma A, Dfaz-Cabanas Ml, Moliner M, et al. The lTQ-37 mesoporous chiral zeolite. Nature 2009 458 1154-7. 

Researchers [36, 38] have characterized NaOH activated fly ash residues (zeolites) and have ascertained their highly zeolitic nature [7]. It has also been opined [37,39] that the purity of these residues is mainly decided by their cation exchange capacity, mineralogy and morphology. However, study of pore characteristics (viz., size and volume) of such residues has not been explored in detail. 

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