Silicate porous silicates

Nickel is the most used catalyst, 20 to 25 percent Ni on a porous siliceous support in the form of flakes that are readily fQterable. The pores allow access of the reacdants to the extended pore surface, which is in the range of 200 to 600 mVg (977 X 10 to 2,931 X 10 ftMbm) of... 

A porous siliceous rock resulting from the decomposition of chert or siliceous limestone. Used as a base in soap and scouring powders, in metal polishing, as a filtering agent, and in wood and paint fillers. A cryptocrystalline form of free silica. 

In the same spirit DFT studies on peroxo-complexes in titanosilicalite-1 catalyst were performed [3]. This topic was selected since Ti-containing porous silicates exhibited excellent catalytic activities in the oxidation of various organic compounds in the presence of hydrogen peroxide under mild conditions. Catalytic reactions include epoxidation of alkenes, oxidation of alkanes, alcohols, amines, hydroxylation of aromatics, and ammoximation of ketones. The studies comprised detailed analysis of the activated adsorption of hydrogen peroxide with... 

Encapsulation of proteins in transparent porous silicate-glasses prepared by the sol-gel method. Science, 255, 1113-1115. 

Subsequently, Goncalves cl al.97 reported the acetylation of glycerol with acetic acid performed over different solid acids, including montmorillonite K-10 and such acid zeolites as HZSM-5 and HUSY. Among the siliceous porous materials examined, montmorillonite K-10 gave the best performance, with 96% conversion into the mono-, di- and tri-acetylated derivatives. When zeolites were used, the conversion was lower than with the other catalysts, giving a 30% conversion for HZSM-5 and only 14% for HUSY. However, selectivity for the primary monoacetylated product,... 

L.M. Ellerby, C.R. Nishida, F. Nishida, S.A. Yamanaka, B. Dunn, J.S. Valentine, and J.I. Zink, Encapsulation of proteins in transparent porous silicate glasses prepared by the sol-gel method. Science 255, 1113-1115 (1992). 

Hammel, J. J., W. P. Marshall, W. J. Robertson and H. W. Barch. 1987. Porous siliceous-containing gas enriching material and process of manufacture and use. European Patent Appl. 0,248,931. 

Fio. 1. Schemdic illustration of the structure of (A) octadecyl and (B) octyl silica. The ciots-hatcbed and the open areas represent the solid iuid open areas of the porous siliceous support. I... 

Bi-phasic porous silicates containing amorphous and crystalline components can be prepared as stable pellets even if different crystallization routes known from the conventional crystallization processes are employed. Thus the inorganic template-free crystallization route and the crystallization in presence of propylamine could be applied and optimized for the crystallization on and into porous glasses, the so-called supported crystallization. 

Organically modified porous silicates have been prepared under acidic conditions, by direct reaction of a mixture of phenyltriethoxysilane (PTES) and tetraethoxysilane (TEOS), and an aqueous solution of cetyltrimethylammonium bromide (CTAB). For a 1 4 molar ratio between PTES and TEOS, the hexagonal (2d, p6m) phase, but also a cubic phase analogous to the already reported SBA-1 phase (Pm3n), can be prepared. The surfactant can then be efficiently removed by calcination at 350°C, leading to phenyl-functionalized microporous silicates with two types of architecture. The influence of several parameters (PTES/TEOS ratio ethanol content) that affect the organization of the samples, will be discussed. 

By preparing polycyclic aromatic hydrocarbon nanocrystals grown in porous silicate films, Botzung-Appert et al. [57] have prepared potential fluorescent sensors based on electronic energy transfer quenching to an acceptor... 

The sol-gel procedure enables encapsulation of enzymes in optically transparent, porous silicate matrices, under mild room-temperature conditions. The small pores prevent microbial degradation and, due to the biomolecule size, they will not diffuse out of the polymer network. The physical encapsulation avoids self-aggregation effects as well as protein unfolding and denaturalization. At the same time, the catalytic activity is maintained as the enzymes are able to react with small substrates that can transfer across or within the support, assuring continuous transformations [75]. 

A. Stein, B. J. Melde, and R. C. Schroden, Hybrid inorganic-organic meso-porous silicates-nanoscopic reactors coming of age, Advanced Materials 12, 1403-1419 (2000). 

Figure 4.11 Experimental SAW frequency transients during exposure to methanol iplpo = 0.05) for 360 nm-thick polysiloxane film deposited on bare quartz ( ) and on a 150 nm-thick porous silicate film on the quartz substrate ( ). The larger initial fiequency drop with the porous film is due to permeation of methanol through the polysiloxane film and adsorption onto the surfaces of the underlying porous film. Data points are overlapping at early times. (Reprinted with permission. See Ref. (86).)...

Inorganic monolithics like calcium aluminate, calcium silicate, sodium silicate and potassium silicate gunites are able to withstand the dry flue gases at high temperatures. Because they are porous and tend to crack, however, they allow acid vapors to reach the substrate and condense. 

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