Incorporation during hydrothermal

Zeolite-hosted dyes can be prepared by ion-exchange of cationic dye molecules or by incorporation during hydrothermal crystallization [100]. Optical absorption bands of molecular sieve-accomodated dyes can be... 

Present data do not justify the attribution of this V species to a real substitutional V site in the zeolite framework, because the amount of these V sites is very low and at present the degree of incorporation of these sites in the zeolite cannot be extended. It is therefore reasonable to assume that these V sites form at defect sites, possibly hydroxyl nests, the formation of which may be enhanced by the presence of V during hydrothermal synthesis, in agreement with Rigutto and van Bekkum (5). 

Rockwell Hanford Operations has supported a research effort to develop sensors that can be incorporated into autoclaves to continuously monitor the Eh and pH conditions existing during hydrothermal interaction tests. These sensors must be mechanically stable at temperatures up to 300°C and pressures up to 300 bars and must be chemically stable in the presence of complex hydrothermal solutions. The sensors must also be easily incorporated into the standard autoclaves currently in use, and must be operable in a radiation environment. 

The above procedure of incorporating sodium to fresh catalyst has an inherent shortcoming. Sodium from FCC feedstock accumulate on catalysts which have been hydrothermally aged. During hydrothermal aging, the zeolite unit cell size decreases from above 24.50 A to typically lower than 24.30 A, the surf ace area of both zeolite and matrix decreases and transformation of kaolin clay to metakaolin occurs. 

Incorporation of Phthalocyanines into the Molecular Sieve Si-MCM-41 during Hydrothermal Synthesis (Section 8.2.2) [56]... 

Synthetic layered hydroxides with hydrotalcite-like structures are used as heterogeneous catalysts for base-catalyzed reactions. One of their major drawbacks for technological application is their low stability during hydrothermal and/or thermal treatments. Recent attempts to incorporate large, preferably multicharged anions into their interlayer spaces introduced new routes for preparation of more stable materials. The effect of intercalated polymetalates or transition metal complex anions in the fi amework of layered hydroxides is twofold They increase the gallery heights and thermal stability on one hand and introduce additional Lewis or Bronsted acidic sites in a basic framework on the other hand. 

The two most obvious and common ways to incorporate matter into zeolite pores are (i) by adsorption and diffusion from gas or liquid phase, and (ii) by ion exchange. A third, usually more difficult approach involves incorporation of species during hydrothermal synthesis. The zeolite pores can be viewed as nanometer size reaction chambers that accommodate numerous organic and inorganic molecules with enough space for chemical conversions. It follows that there is a vast potential for ingenious chemistry in these hosts. 

Pt(NH3) ions since the molecular dimensions of these metal complexes exceed the pore apertures. Platinum was incorporated during the synthesis of the zeo-hte by mixing solutions of K2PtCl4 with solutions of sodium metasiUcate and sodium aluminate in the required amounts. More recently, Davis et al. [129,130] prepared intrazeoHtic 2-5 nm ruthenium particles in NaA and CaA zeoHtes by addition of [Ru(NH3)5Cl] CI2 to the hydrothermal synthesis mix of zeolite A. This technique of metal loading has never been widely used to prepare metal clusters in zeolites but is frequently employed to substitute lattice aluminum in zeoHtes or aluminophosphates by metal ions. 

Zeolite synthesis around a metal complex was introduced by Balkus [40]. The metal complex is added to the zeolite synthesis mixture and is incorporated into the zeolite structure during the zeolite synthesis. Of course, this procedure is only applicable when the metal complex is soluble in the synthesis mixture and can withstand the hydrothermal synthesis conditions. Another requirement is that the zeolite structure-directing agent added must be removable by a milder... 

All of the experimental evidence shows extraction of Li from hasalt, altered hasalt and sediments even at temperatures <100°C. Lithium was incorporated into clays at temperatures up to 150°C during hasalt alteration (Seyfried et al. 1984 James et al. 2003), with affinity proportional to the fluid/rock ratio, such that Li was simultaneously added to and removed from fluids. Under high temperature, solid-dominated hydrothermal conditions (c. 350°C), Li was universally removed from materials and kept in solution, rather than in alteration minerals. The limited isotopic fractionation at these conditions has been estimated as a 0.994 (= (fl.i/ Li,ecomiMynm imk)/( LiALis tai )) Chan et al. 1993 Seyfried et al. 1998). 

Other chemicals behave conservatively during the low-temperature mixing process and, thus, can also be used as geothermometers. As shown in Figure 19.14b, the hydrothermal system is a sink for magnesium because of incorporation into silicate rocks (Eq. 19.1). Extrapolation of this trend to zero magnesiiun ion concentration also yields... 

Organically modified mesoporous titanium-substituted MCM-41 materials (Ti-MCM-41-R, R= C6H5, CH3) have been synthesized. These materials show higher hydrophobicity than unmodified Ti-MCM-41. This high hydrophobicity has a strong influence on the activity improvement in the oxidation of alkenes with H202. Furthermore, hydrothermal treatment during synthesis has increased titanium incorporation. 

The amount of titanium incorporation has been increased from the Si/Ti ratio of 490 to that of 56 for Ti-MCM-41-Ph and from 570 to 52 for Ti-MCM-41-Me when the hydrothermal treatment at87°C was applied during the synthesis. Ti-incorporation into the framework was favored in the hydrothermal treatment. 

Niobium and titanium incorporation in a molecular sieve can be achieved either by hydrothermal synthesis (direct synthesis) or by post-synthesis modification (secondary synthesis). The grafting method has shown promise for developing active oxidation catalyst in a simple and convenient way. Recently, the grafting of metallocene complexes onto mesoporous silica has been reported as alternate route to the synthesis of an active epoxidation catalyst [21]. Further the control of active sites, the specific removal of organic material (template or surfactant) occluded within mesoporous molecular sieves during synthesis can also be important and useful to develop an active epoxidation catalyst. Thermal method is quite often used to eliminate organic species from porous materials. However, several techniques such as supercritical fluid extraction (SFE) and plasma [22], ozone treatment [23], ion exchange [24-26] are also reported. 

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