Aluminosilicates application

T. (2004) Noncovalent anchoring of asymmetric hydrogenation catalysts on a new mesoporous aluminosilicate application and solvent effects. Chem. Eur. ]., 10, 5829. 

Guth J-L and Kessler H 1999 Synthesis of aluminosilicate zeolites and related silica-based materials Catalysis and Zeolites, Fundamentals and Applications ed J Weitkamp and L Puppe (Berlin Springer) pp 1-52... 

The structural complexity of the 3D framework aluminosilicates precludes a detailed treatment here, but many of the minerals are of paramount importance. The group includes the feldspars (which are the most abundant of all minerals, and comprise 60% of the earth s crust), the zeolites (which find major applications as molecular sieves, desiccants, ion exchangers and water softeners), and the ultramarines which, as their name implies, often have an intense blue colour. All are constructed from Si04 units in which each O atom is shared by 2 tetrahedra (as in the various forms of Si02 itself), but up to one-half of the Si... 

Microporous catalysts are heterogeneous catalysts used in catalytic converters and for many other specialized applications, because of their very large surface areas and reaction specificity. Zeolites, for example, are microporous aluminosilicates (see Section 14.19) with three-dimensional structures riddled with hexagonal channels connected by tunnels (Fig. 13.38). The enclosed nature of the active sites in zeolites gives them a special advantage over other heterogeneous catalysts, because an intermediate can be held in place inside the channels until the products form. Moreover, the channels allow products to grow only to a particular size. 

Aluminosilicate glasses are used in certain AB cement formulations, and the acid-base balance in them is important. The Bronsted-Lowry theory cannot be applied to these aluminosilicate glasses it does not recognize silica as an acid, because silica is an aprotic acid. However, for most purposes the Bronsted-Lowry theory is a suitable conceptual framework although not of universal application in AB cement theory. 

Thus an acid-base reaction involves the transfer of an oxide ion (compared with the transfer of a proton in the Bronsted theory) and the theory is particularly applicable in considering acid-base relationships in oxide, silicate and aluminosilicate glasses. However, we shall find that it is subsumed within the Lewis definition. 

Schmidt, W., Purrmann, R., Jochum, P. Glasser, O. (1981a). Calcium aluminosilicate glass powder and its use. European Patent Application 23,013. 

The development and application of multidimensional solid state homo- and heteronuclear correlation (HETCOR) NMR techniques have lead to an increasingly important role in structure solution of zeolitic materials and have had many practical applications in the detailed structural characterization of completely siliceous zeolites[6,7] and AlPOs.[8-ll] However, HETCOR NMR is not readily applicable to aluminosilicates... 

This application of sensitivity enhanced RAPT-CP-CPMG HETCOR, to microporous aluminosilicates illustrates the potential of... 

Many different zeolite structures are already known, but there is permanent need for new or improved ones to satisfy novel and specific industrial and technological applications. To successfully accomplish this task, a deeper understanding of the zeolite crystallization process is certainly needed. One of the important parts in that study is the structural investigations of their amorphous aluminosilicate precursors (gels). 

The FPI principle can also be used to develop thin-film-coating-based chemical sensors. For example, a thin layer of zeolite film has been coated to a cleaved endface of a single-mode fiber to form a low-finesse FPI sensor for chemical detection. Zeolite presents a group of crystalline aluminosilicate materials with uniform subnanometer or nanometer scale pores. Traditionally, porous zeolite materials have been used as adsorbents, catalysts, and molecular sieves for molecular or ionic separation, electrode modification, and selectivity enhancement for chemical sensors. Recently, it has been revealed that zeolites possess a unique combination of chemical and optical properties. When properly integrated with a photonic device, these unique properties may be fully utilized to develop miniaturized optical chemical sensors with high sensitivity and potentially high selectivity for various in situ monitoring applications. 

In general, zeolites are crystalline aluminosilicates with microporous channels and/or cages in their structures. The first zeolitic minerals were discovered in 1756 by the Swedish mineralogist Cronstedt [3], Upon heating of the minerals, he observed the release of steam from the crystals and called this new class of minerals zeolites (Greek zeos = to boil, lithos = stone). Currently, about 160 different zeolite structure topologies are known [4] and many of them are found in natural zeolites. However, for catalytic applications only a small number of synthetic zeolites are used. Natural zeolites typically have many impurities and are therefore of limited use for catalytic applications. Synthetic zeolites can be obtained with exactly defined compositions, and desired particle sizes and shapes can be obtained by controlling the crystallization process. 

Sorption processes are influenced not just by the natures of the absorbate ion(s) and the mineral surface, but also by the solution pH and the concentrations of the various components in the solution. Even apparently simple absorption reactions may involve a series of chemical equilibria, especially in natural systems. Thus in only a comparatively small number of cases has an understanding been achieved of either the precise chemical form(s) of the adsorbed species or of the exact nature of the adsorption sites. The difficulties of such characterization arise from (i) the number of sites for adsorption on the mineral surface that are present because of the isomorphous substitutions and structural defects that commonly occur in aluminosilicate minerals, and (ii) the difference in the chemistry of solutions in contact with a solid surface as compound to bulk solution. Much of our present understanding is derived from experiments using spectroscopic techniques which are able to produce information at the molecular level. Although individual methods may often be applicable to only special situations, significant advances in our knowledge have been made... 

The name of zeolites, which originates from the Greek words zeo (to boil) and lithos (stone), was given some 250 years ago to a family of minerals (hydrated aluminosilicates) that exhibited intumescence when heated in a flame. However, the history of zeolites really began 60 years ago with the development of synthesis methods. Commercial applications in three main fields—ion exchange, adsorption, and catalysis—were rapidly developed, the corresponding processes being more environmentally friendly than their predecessors. 

Since this initial work there has been a plethora of literature on mesoporous molecular sieves. In addition to the silica and aluminosilicate frameworks similar mesoporous structures of metal oxides now include the oxides of Fe, Ti, V, Sb, Zr, Mn, W and others. Templates have been expanded to include nonionic, neutral surfactants and block copolymers. Pore sizes have broadened to the macroscopic size, in excess of 40 nm in diameter. A recent detailed review of the mesoporous molecular sieves is given in ref [73]. Vartuli and Degnan have reported a Mobil M41S mesoporous-based catalyst in commercial use, but to date the application has not been publicly identified.[74]. 

The model of Richet and Bottinga (1985) considers the heat capacity of the melt to be variable with T and allows better reproducibility of experimental evidence in composi-tionally simple systems. The Stebbins-Carmichael model seems to reproduce the experimental observations on aluminosilicate melts better (Berman and Brown, 1987). Application of both models to natural melts gives substantially identical results (i.e., differences of about 1%, within the range of data uncertainty cf Berman and Brown, 1987). 

Chakraborty S. and Ganguly J. (1992). Cation diffusion in aluminosilicate garnets Experimental determination in spessartine-almandine diffusion couples, evaluation of effective binary diffusion coefficients, and applications. Contrib. Mineral Petrol, 111 74-86. 

Ganguly J. and Saxena S. K. (1984). Mixing properties of aluminosilicate garnets Constraints from natural and experimental data and applications to geothermo-barometry. Amer. Mineral, 69 79-87. 

Zeolites are crystalline aluminosilicates with a regular pore structure. These materials have been used in major catalytic processes for a number of years. The application using the largest quantities of zeolites is FCC [102]. The zeolites with significant cracking activity are dealuminated Y zeolites that exhibit greatly increased hydrothermal stability, and are accordingly called ultrastable Y zeolites (USY), ZSM-5 (alternatively known as MFI), mordenite, offretite, and erionite [103]. 

The present study deals with the application of RDF to the sodium aluminosilicate hydrogels, which were formed by mixing, aging and heating of sodium silicate solution with sodium aluminate solution under stirring, in order to produce NaA-zeolite crystal. 

Molecular sieves are used in a variety of fuel processing applications. Uses include drying and water removal from fuel, product purification, hydrocarbon separation and catalysis. Molecular sieves are composed of sodium and calcium aluminosilicate crystals which have been produced from natural or synthetic zeolite compounds. The crystals are dehydrated through heating and are processed to ensure that pore sizes are tightly controlled. 

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