Aqueous Route

An additional effect of the use of an organic medium in the catalyst preparation is creation of mote defects in the crystalline lattice when compared to a catalyst made by the aqueous route (123). These defects persist in the active phase and are thought to result in creation of strong Lewis acid sites on the surface of the catalysts (123,127). These sites ate viewed as being responsible for the activation of butane on the catalyst surface by means of abstraction of a hydrogen atom. 

Niederberger, M., Gamweitner, G., Pinna, N. and Neri, G. (2005) Non-aqueous routes to crystalline metal oxide nanopartides formation mechanisms and applications. Progress in Solid State Chemistry, 33 (2—4), 59—70. 

Preparation of (1,2-B9C2H,, )2Co has also been accomplished by the aqueous route. The neutral complex, C5H5Co(l,2-B9C2H,) was obtained in low yield by reaction of an equimolar mixture of C5H5 and 1,2-B9C2Hn2 with cobalt(II) chloride. The proton NMR spectrum of this compound is consistent with a sandwich-bonded structure similar to the iron analog (see Fig. 5). 

Salts of the tetrafluoroaluminate (TFA) anion have been known for many years. Yet aqueous routes to pure materials have not been established despite the substantial amount of literature available on the subject. The present review will discuss the various synthetic methods that have been employed and will demonstrate a revised method for preparing pure TFA salts. These materials are important because TFA is able to stimulate various guanosine nucleotide-binding proteins (G-proteins) and inhibit P-type ATPases by serving as a nonhydrolyzing phosphate mimic. Additionally, various TFA salts serve as precursors to aluminum trifluoride, which is used as a catalyst for chlorofluorocarbon isomerizations and fluorinations. 

Among the many non-aqueous routes to M( t3-S)(S)4+ compounds one (originally discovered by Federov) begins with Mo3(/x.3-S)(S2)3X4, a solid state compound with intermolecular (jl-X bridges (X = Cl, Br).49 A representative reaction50 is... 

This phenomenon has also been observed for catalysts prepared using an aqueous route (182). Both the iron and cobalt promoters led to an increase in selectivity. The iron-promoted catalyst was characterized by an increase in activity, but the cobalt-promoted catalyst was characterized by a decrease in activity. The decrease in activity of the cobalt-doped catalyst was attributed to the formation of VOPO4 in the final catalyst. The VOPO4 is formed by the oxidation of V0HP04 1 H20 during the introduction of the promoters in the incipient wetness technique. A similar effect was reported for catalysts doped with indium and tetraethy-lorthosilicate (TEOS) (181). The improved performance was observed only with both promoters in the catalyst. It was proposed that the... 

In contrast to the dry methods, there are other conventional methods related to post heat treatment from precipitates from the aqueous solutions. The ambient aqueous routes and the hydrothermal methods at elevated temperature usually lead to rare earth precipitates like hydroxides, carbonates, instead of oxides. In fact, the hydrothermal treatment of rare earth oxide powders results in a hydration process to form hydroxides. Subsequently, the precursor could be used to produce rare earth oxide nanocrystals with post annealing at varied temperatures and in appropriate atmosphere. 

Ambient aqueous routes and hydrothermal routes The synthesis of rare earth orthophosphate NCs could be carried out in aqueous solutions by the precipitation of rare earth cations by phosphate anions, due to the low aqueous solubility of RPO4. A typical synthesis begins with soluble rare earth salts in aqueous solution, such as nitrates or chlorides, and a phosphate source like phosphate M H3 P04, triphosphate M5P3O10 (M = Na, K, or NH4), or PI3PO4. The two solutions are mixed at room temperature or elevated temperature to form gel-like precipitation as precursor. Then the mixture of precipitation and mother liquor is... 

Closely related to the above method is the formation of X = 2-5 species by the acidification of K2S with formic acid nnder anhydrous conditions. This nonaqueous method has the advantage of avoiding some of the side reactions associated with the aqueous route. 

Alternative aqueous routes have been used by a number of groups to prepare V0HP04 ViH20. Oxalic acid [88, 92], lactic acid [93], phosphorous acid [93] and NH2OH.HCI [75] have all been investigated as reducing agents in place of hydrochloric acid. 

BioHioCNH2R, and BioHioCH has been reported. The syntheses are based on two general reactions very closely related to the preparative methods recently described for the [3]-l,2-dicarbaundecahydroundecaboranyl [ (3)-l,2-dicarbollyl ] sandwich complexes (1) the reaction of NasBioHioCH and an anhydrous metal chloride, and (2) the reaction of CsBioHisCH, aqueous sodium hydroxide, and a metal chloride. Complexes of Fe(III), Co(III), and Ni(IV) with the three types of monocarbon carborane anions indicated above can be conveniently prepared by the aqueous route. The preparations of CssNi-(BioHioCH)2 and (BioHioCNH3)2Ni by this route are described here. 

F.Q. Zhang, Y. Meng, D. Gu, Y. Yan, C.Z. Yu, B. Tu, and D.Y. Zhao, A Facile Aqueous Route to Synthesize Highly Ordered Mesoporous Polymers and Carbon Frameworks with Ia3d Bicontinuous Cubic Structure. J. Am. Chem. Soc., 2005, 127, 13508-13509. 

Small hydrophilic drugs are restricted to the paracellular route, or to aqueous routes that normally absorb nutrients, vitamins or cofactors. 

As many carbonate complexes are synthesized usually in aqueous solution under fairly alkaline conditions, the possibility of contamination by hydroxy species is often a problem. To circumvent this, the use of bicarbonate ion (via saturation of sodium carbonate solution with COj) rather than the carbonate ion can often avoid the precipitation of these contaminants. Many other synthetic methods use carbon dioxide as their starting point. Transition metal hydroxo complexes are, in general, capable of reacting with CO2 to produce the corresponding carbonate complex. The rate of CO2 uptake, which depends upon the nucleophilicity of the OH entity, proceeds by a mechanism that can be regarded as hydroxide addition across the unsaturated C02. There are few non-aqueous routes to carbonate complexes but one reaction (3), illustrative of a synthetic pathway of great potential, is that used to prepare platinum and copper complexes. Ruthenium and osmium carbonate complexes result from the oxidation of coordinated carbon monoxide by dioxygen insertion (4). ... 

NANO SOLS FOR MIXED AQUEOUS/NON-AQUEOUS ROUTES... 

Table 15.2 Poly(imide)s Produced by the Aqueous Route ...

In contrast to the conventional route, the aqueous route runs via carboxylic salt and amine salt precursors. In the first step of the synthesis, the dianhydride is refluxed in water in order to completely hydrolyze it. After cooling down to room temperature, the aqueous solution of the dicarbox-ylic acid is neutralized with the respective diamine and a salt is formed. The salt precipitates out from the aqueous solution. The precipitate is dried and heated up to 180-220°C for dehydration to form the final PI product. " ... 

Products that have been produced by the aqueous route are shown in Table 15.2. The infrared (IR) speetra of eonunereially available Ultem 1000 and the type synthesized by the aqueous route are virtually indistinguishable. ... 

Zhang F, Meng Y, Gu D, Yan Y, Yu C, Tu B, Zhao D (2(X)5) A facile aqueous route to synthesize highly ordered mesoporous polymers and carbon frameworks with Ia3d bicontinuous cubic structure. J Am Chem Soc 127 13508-13509... 

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