Silica source

The higher intensities /3 measured for ion exchanged gels (gels prepared by procedure b) comparing to /3 of gels prepared by procedure a, are probably the result of the different silica source used. It was found that gels prepared from sodium silicate contain... 

Mesoporous silica was prepared using sodium silicate as silica source and cetyltrimethylammoniumbromide (CTMABr) as template as elsewhere [7]. The aluminosilicates were prepared with a similar procedure by using sodium aluminate as aluminum source, which was dissolved in the surfactant solution as described before [3]. Si/Al molar ratios were of 6, 10, 30 and 80, the impregnated iron amount was 6 wt. 

The synthesis of ECS-2 was carried out following the procedure reported by Carati et al. [5], ECS-2 was obtained using l,4-bis-(triethoxysilyl)-benzene (BTEB) as silica source while sodium aluminate (NaAlC ) and NaOH were used as aluminum and alkaline sources, respectively. The resulting gel was charged into a stainless steel autoclave and heated at a temperature of 100°C for 28 days under autogeneous pressure. Once cooled... 

Later, Thangaraj et al. (275,281) developed a novel, improved route (prehydrolysis method) for the preparation of good quality TS-1 samples. In this method the silica source (tetraethyl orthosilicate TEOS) in Ao-propanol was first hydrolyzed with 20% aqueous TPAOH solution prior to the (dropwise) addition of titanium butoxide in dry iso-propanol under vigorous stirring. Crystallization was done statically at 443 K for 1-5 days and the solid was calcined at 823 K for 10 h. The TS-1 samples thus obtained exhibited high catalytic activity in hydroxylation reactions. 

Similarly, reactive oxide mixtures are also used to synthesize aluminophosphate molecular sieves, usually starting from phosphoric acid along with the addition of alumina and silica sources analogous to those used in zeolite synthesis with a notable exception alkylammonium salts and amines were ultilized in structure-direchng and space filling to the exclusion of alkali hydroxide solutions and alkali metal salts. 

Supported Ziegler-type neodymium surface species (54, see below) have been prepared by mixing molecular components composed of [Nd(naph)3] (derived from naphthenonic acids) and alkyl aluminium reagents such as Al2Et3Cl3, Al( Bu)3 and/or Al( Bu)2H at 50-60°C with silica (source QiLu Petrochemicals Co., China) [158-160]. Although the immobihzed neodymium species are iU-defined, the materials display interesting properties in butadiene polymerization (Section 12.4.1.2). 

The starting material, especially the silica source, and the stirring condition during crystallization were found to affect not only the rate of crystallization but also the crystallization area of high silica zeolites, while water content in a reactant mixture was found not to be critical. 

Blended hydraulic cements are used to conserve energy. They are intimate and uniform blends of fine materials such as Pordand cement, ground blast furnace slag, fly ash, and other pozzolans, ie, fine, reactive silica sources. ASTM C595 lists five classes or types. 

Figure 1. Infrared spectra of silicate solutions with different silica sources and bases (see Table I)...

X-ray and sorption analyses of the solid phase revealed that in the case of metasilicate only small amounts of zeolites were formed from the hydrogel after 1 hr of aging with heating after a longer period—e.g., 24 hr, almost quantitative transformations into zeolite X, with a small amount of zeolite A, were observed. In one experiment (V) no zeolite A was found. If sol was used as the silica source, the crystallization was almost complete after 1 hr of aging, but about half of the product was zeolite A. Some samples (KG, Gk, Gz) contained small amounts (up to 20%) of zeolite X in the solid phase after prolonged aging. 

A novel synthesis has been introduced to control the morphology and the porosity of micron size silica particles. Homo-polymers were used as templates, tetraethoxysilane as a silica source, alcohol/water mixtures as solvents and ammonia as a catalyst. The particle size could be adjusted in a range of 100 - 250 nm and the pore diameter between 2-50 nm. 

The synthetic procedure for preparing the MCM-41 mesoporous materials is based on the delayed-neutralization process reported in our previous paper.[l 1] The silica source is sodium... 

The synthesis of MCM-41 structure in fluoride medium has been reported by Silva and Pastore [10], who used sodium silicate as silica source and carried out crystallization at 150 °C. They suggested the behaviour of Si02-CTMA+-F system was significantly different from that reported previously on the mesophase system. It is known that fluoride ions do influence the nature, activity and polymerizing capacity of silica precursors, and a fluorinated silica surface is much more hydrophobic and more resistant to the attack of water molecules than a silanol silica surface [11]. 

The pH value will control the condensation of silica, so the pH value should be adjusted to form monomer then oligomer of silica in order to obtain its condensation and polymerization around the micelles of surfactant Under acidic conditions, silica source such as... 

To study the influence of the silica source on the mesoporous materials formation, we have performed synthesis by adding different source of silica neutral TMOS and ionic sodium silicate to the micellar solution. Syntheses were made either under acidic (pH = 2) or basic (pH = 10) conditions for TMOS. Table 1 contains essential information of the obtained products. 

Silica source PH Heating time (days) Heating temperature Sbet (m2/g) V (cm3/g) 0 (nm)... 

Figurel. Nitrogen adsorption isotherms (A) and pore size distributions (B) of samples synthesized with different silica source, a TMOS, pH = 10, b TMOS, pH =2 and c sodium silicate, pH = 10...

Polyoxyethylene alkyl ether and in particular decaoxyethylene oleyl ether CigHj5 (CH2CH20)io can be used as templating agent for silica mesoporous materials formation. The synthesis can be performed under both acidic or basic conditions with tetramethoxysilane (TMOS) as silica source while no mesoporous compound was obtained with sodium silicate. 

Synthesis of MCM-41 with Additives. The hydrothermal crystallization procedure as described earlier [10] was modified by adding additional salts like tetraalkylammonium (TAA+) bromide or alkali bromides to the synthesis gel [11]. Sodium silicate solution ( 14% NaOH, 27% Si02) was used as the silicon source. Cetyltrimethylammonium (CTA) bromide was used as the surfactant (Cl6). Other surfactants like octadecylltrimethylammonium (ODA) bromide (C,8), myristyltrimethylammonium (MTA) bromide (C,4) were also used to get MCM-41 structures with different pore diameter. Different tetralkylammonium or alkali halide salts were dissolved in little water and added to the gel before addition of the silica source. The final gel mixture was stirred for 2 h at room temperature and then transferred into polypropylene bottles and statically heated at 100°C for 4 days under autogeneous pressure. The final solid material obtained was washed with plenty of water, dried and calcined (heating rate l°C/min) at 560°C for 6 h. 

The main experiments performed with the two different silica sources are reported in Table 1 and the Si liquid state NMR spectra of experiments 3, 4, and 11 (Table 1) are given in Figure 1. 

In the presence of D4R species as silica source (second set of experiments Table 1), the aggregation numbers, with and without silica (experiments 11 and 10, respectively), are characteristic of spherical micelles. Moreover, the addition of D4R units has no effect on the pyrene fluorescence lifetime (x), which means that there is no Br /silicate exchange in this micelles-containing system. As it is well known [21], the presence of methanol leads to a decrease of the aggregation number (compare experiments 9 and 10). 

Si02 0.0015 Ti(OEt)4 0.12 CTABr 0.26 TMAOH 24.3 H20 were CTABr is cetyltrimethylammonium bromide (from Aldrich), TMAOH is tetramethylammonium hydroxide (from Aldrich). The silica source was Aerosil-200 from Degussa and Ti(OEt)4 was supplied by Alpha Products. The crystallization was performed at 100°C for 48 hours in Teflon lined stainsteel autoclaves. The solid was recovered by filtration and exhaustive washing with distilled water until neutral pH in the filtrate was obtained. Then, the Ti-MCM-41 was dried at 60°C for 24 hours. The occluded surfactant was removed by calcination at 540°C in nitrogen for 1 hour and subsequently, for 5 hours in air. 

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