Amorphous components aluminosilicates

Our synthetic routes to ZK4 were modifications of those described by Kerr (21). An amorphous, basic aluminosilicate gel containing tetramethylammonlum (TMA) Ion was heated at 100°C to promote formation of ZK4 crystals. Preparation of the gel Involved the vigorous mixing at room temperature of one component acting as a source of sodium and alumina, with another component acting as a source of TMA and silica. The alumina used was sodium... 

Aluminosilicates are the active components of amorphous silica—alumina catalysts and of crystalline, well-defined compounds, called zeolites. Amorphous silica—alumina catalysts and similar mixed oxide preparations have been developed for cracking (see Sect. 2.5) and quite early [36,37] their high acid strength, comparable with that of sulphuric acid, was connected with their catalytic activity. Methods for the determination of the distribution of the acid sites according to their strength have been found, e.g. by titration with f-butylamine in a non-aqueous medium using adsorbed Hammett indicators for the H0 scale [38],... 

Two main components were used in the model catalysts described in this paper. One component was a europium exchanged ammonium Y zeolite (EuNH-Y). The other component was an amorphous aluminosilicate containing about 75% Si 0 and 25% Al203 (AAA-alumina). All materials were artificially V-contaminated by impregnation with vanadyl naphthenate solutions in benzene. Tetraphenyl tin (in hot toluene) was the passivating agent used. It was added either before or after loading vanadium on the zeolite (EuNH-Y), on the gel or on a gel-zeolite mixture. 

In the study of soil science, most attention has historically been paid to the aluminosilicate clays, which dominate the properties of temperate soils, the first to be scientifically studied. More recently, the importance of the amorphous aluminosilicates has been shown in young soils, in soils derived from volcanic ash and in leached, acidic soil (e.g. podzols or spodosols). The hydrous oxides are especially important components of old, highly weathered soils, such as those found in the tropics (e.g. oxisols). This is an important distinction as the charge on the aluminosilicate clays is predominantly a permanent negative charge, while the amorphous aluminosilicates and hydrous oxides have a variable,... 

The proposition of different views on the formation mechanism of zeolites is due to the complexity of the formation of zeolites. The crystallization system of zeolites has solid and liquid components. The solid phase contains amorphous gel and zeolite crystals, while the liquid phase contains silicate ions with various polymeric states, aluminate, and aluminosilicate ions with various structures and polymeric states. The procedure for the synthesis of zeolites is not complicated, but the crystallization mechanism involved is... 

All of the organic matter and part of the aluminosilicates, hydroxyoxides, and silica in soil exist in structures too small or too poorly crystalline to be detectable by x-ray diffraction, These amorphous materials are not well understood, but they should logically be among the most reactive of soil components, because their structure is so open and their surface area so great, They represent a transition state between unweathered parent materials and well-crystallized secondary soil minerals. 

Metal silicates may crystallize in the amorphous mass after aging, especially if components are present in suitable stoichiometric proportions. Also in some instances, microcrystalline metal silicates may be formed immediately if the solutions of metal salt and silicate are brought together at high temperature or in very dilute solution. It is unlikely, in any case, that macrocrystalline metal silicates similar to those found in minerals will be formed, except at high temperature under pressure. However, when aluminum is present for form aluminosilicate ions, fairly rapid crystallization of certain aluminosilicates such as the zeolites can occur at 100 C. 

In preparation series b the addition of 20 wL% AI(P03)3 constitutes an amount of 3/4 of the binder mass in fact. There is a surplus of added AI(P03)3. Corresponding to the above three steps of reaction, the amount of crystalline by-products NatP207 and Na2HP04 increases also with an increase in added AI(P03)3 in this preparation series b of note is the observation of the crystalline aluminosilicate, sodalite. This fact can be valued as a hint for introduction of aluminate in the formed network. Evaluations of the balance of components show a distinct dominance of the silicate for the amorphous phase (Reference ). 

As expected in the P spectra of Figure 3 the resonances of the crystalline by-products Na4P207 (+2 ppm) and Na HP04 (+6 ppm) appear. Nevertheless, the elevated background in the from +10 to -25 ppm can be valued as a hint for amorphous phosphate arrangements in the case of preparation with 20 wt.% A1(P03)3. The type and the degree of binding of these phosphate components in the aluminosilicate network remains uncertain. 

Dupain et al. (2006). The 3%-crystalline H-ZSM-5 sample, not diluted with amorphous silica-alumina (ASA), showed high conversion activity (79 wt%), very close to that of the diluted catalyst of the crystalline H-ZSM-5. It can thus be suggested that the acid sites present in this sample are much more active for the conversion of wax compared to those of Al-MCM-41 and ASA, although the very-low crystallinity H-ZSM-5 sample consists mainly of XRD amorphous aluminosilicate phase. Fig. 18.13 shows the yields (wt% on feed) of various gasoUne components. The data in Fig. 18.13 can also be used for a qualitalive comparison of catalyst performance with regard to their selectivity toward specific gasoline components, especially in the case of H-Y- and H-ZSM-5-based catalysts, which showed similar percent conversion of wax (Fig. 18.12). The H-Y-st. catalyst presented a significant selectivity... 

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