Silicates, crystalline alumino

Zeolites are crystalline alumino-silicate materials with Mj [Alj Si, 62] X n H2O, where M is a cation of valence m. Their frameworks are built from comer-shared TO -tetrahedra (T stands for Si, Al, P, Ga, Ge, etc.) to produce channels or cavities (spaces) of molecular dimensions. Based on the characteristic stmctures, zeolites have attracted much attention not only for catalytic applications but also as containers in which materials are confined. It is becoming more and more important to understand the fine stmctures of zeolites in order to synthesize high quality or novel zeolites not only for producing better catalysts but also for better containers of confined materials. 

Shively, J.H. and Archer, E.D. (1972) Selected adsorption with a silanized crystalline alumino-silicate. US Patent 3,558,595. 

Wilson, W.B. (1972) Fluoride-containing crystalline alumino-silicates. US Patent 3,702,312. 

Venuto, P. B., Landis, P. S. Organic reactions catalyzed by crystalline alumino-silicates. III. Condensation reactions of carbonyl compounds, J. Catal., 1966, 6, 237-244. 

III. The dissolution rate is controlled by diffusion through a continuously growing precipitate layer that forms on the silicate surface. Such a protective barrier has been postulated to consist of an amorphous alumino-silica phase (14) or a mono- or multi-phase crystalline alumino-silicate assemblage (15). 

The molecular sieve adsorbent material is a hard, granular substance that is beadlike in appearance. Molecular sieves are crystalline alumino-silicates. 

Systematic studies carried out at C.F.R.I. pertainining to catalytic vapour phase synthesis of pyridine bases, namely 2 4-picolines through cyclodehydrogenation reaction of acetaldehyde and anunonia have been described. Metal oxide modified amorphous silica-aliunina and crystalline alumino-silicate namely ZSM-5 zeolites were found to be active and selective catalysts towards the formation of the lower pyridines bases. The method of preparation, pretreatment vis-a-vis the acidity have been found to affect the catalytic activity and selectivity. It is interesting to observe that metal modified crystalline alumino-silicate ZSM-5 is more selective than amorphous silica-alumina for the formation of 2 4-picoline. A plausible reaction mechanism based on the findings of this study has been proposed. 

Clay minerals are a complex group of finely crystalline to amorphous hydrated silicates, mainly alumino-silicates, which were largely formed by alteration, or weathering of silicate minerals. 

Zeolites are crystalline alumino silicates with internal voids, channels or cavities, denoted, according to lUPAC, as micropores below 2mn and mesopores between 2 and 50 nm. These pores give zeolites a place of choice for nanometric technology and chemistry. They can contain (and protect) metallic nanoparticles or nanometric molecular complexes. Zeolites can protect metals from sintering. Up to a certain... 

Zeolites are crystalline alumino-silicates, which contain a three-dimensional network of Si04- and A104-tetrahedral voids of a specific size. These voids have different diameters, depending on the structure. Figure 3.50 shows zeolite structures with voids of varying diameters. 

Zeolites are crystalline alumino-silicates of formulas Mx/n(Alx+Sii.x)02 yH20 (M" = H+, NH4+, Na+, Fe +, La +...). They are among the most common minerals in nature, and have been extensively used in heterogeneous catalysis since 1970. They present many holes, channels and cavities. Since oxides and zeolites are used extensively in heterogeneous catalysis, it is essential to consider their acid-base properties as defined by their Lewis acid or base and Brpnsted acid or base properties. Indeed, these oxides not only play a role as support, but they also take a very active part in the activation processes. 

Zeolites are alumino-silicate materials containing extensive channels which connect cavities throughout giant three-dimensional crystalline structures. 

Both humic acids and fulvic acids have a strong affinity for particulate and crystalline substances possessing oxygen atoms at their surfaces and they have been reported to bring about the dissolution of iron phosphate, calcium phosphate (61), uranium dioxide (65), hydrated magnesium alumino-silicates (66) and limonite, a complex mixture of hydrated ferric oxides (67). 

The zeolite component belongs to a broad class of minerals composed of crystalline hydrous alumino silicates containing one or more alkali or alkaline earth metals. Some of the naturally occuring zeolites are analcite, chabasite, mordenite, natrolite and faujasite, all of which are generally found in small deposits. 

Molecular sieves are synthetic crystalline metal alumino-silicates that have very fine holes in their structure. The size of the holes is in the order of 4 to 5 angstroms (10 10 m) in diameter. The water molecules enter the holes and are trapped in them. Commercially, they are supplied in the form of a castor oil paste. 

Highly crystalline microporous titano-alumino-silicate ETAS-10 materials with different framework aluminium contents (Al/Ti molar ratio 0.1-0.48) have been studied by Si MAS NMR. ... 

Zeolites are crystalUne alumino silicates with a highly ordered crystalline structure. Cavities of a definitive size are formed in three-dimensional network composed of Si04 and AIO4 tetrahedra. The lattice contains cavities of varying diameters, depending on the type of zeohtes. A distinction is made between large-, medium- and small-pore zeolites. 

Zeolum. [Tosdi] Crystalline hydrous alumino-silicate adsorbent for natural gas, pettx)cheinical, refrigotidon, paint, insulated gas, gas chromatography. 

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