Aluminosilicates, precursors

Many different zeolite structures are already known, but there is permanent need for new or improved ones to satisfy novel and specific industrial and technological applications. To successfully accomplish this task, a deeper understanding of the zeolite crystallization process is certainly needed. One of the important parts in that study is the structural investigations of their amorphous aluminosilicate precursors (gels). 

In such complex system as aluminosilicate precursor gels, various lifetime components can appear reflecting material structure. The gel structure is a result of direct interaction of cations with silicate, aluminate and aluminosilicate anions, redistribution of charges and electron density over the system of aluminosiloxane bonds with effect on the formation of different structural units [24],... 

The presence of even traces of ethanol in the synthesis batch, stemming from an incomplete hydrolysis of Si(OEt)4 during the ageing period results in a drastical reduction of the ZSM-20 crystallization rate zeolite Beta is then readily formed and achieves a fast growth at the expense of the ZSM-20 "Figure 3".This goes in line with the higher yields of Si-richer Beta observed when this zeolite is intentionally prepared in presence of ethanol (311.This was attributed to the lower solubility of silica in EtOH (311. but it is also probable that the whole system (nature and solubility of ZSM-20 aluminosilicate precursors and intermediates) is perturbed (321. 

It is also remarkable that the total amount of Na+is very low in samples synthesized from Si(OEt)4, irrespective of the synthesis temperature (TableVII). Presumably the Si(OH)4 species progressively released by hydrolysis have time to form the adequate TEA aluminosilicate precursors and few Si-O-Na defects are created, as indicated by 29si NMR (61). Conversely, a large amount of reactive silica species stemming from Aerosil are immediately available and are randomly neutralized either by TEA+ or Na+. A highly defected structure is therefore more easily generated. 

Temuujin J., Jadambaa T.S., Okada K., Mackenzie K.J.D. Mechanochemical preparation of aluminosilicate precursors from gibbcite - siUca acid mixtures. Mat. Letters 1998 36 48-51. 

Temuujin J., Okada K., Mackenzie K.J.D. Characterization of aluminosilicate (mullite) precursors prepared by mechanochemical process. J. Mat. Res. 1998 13 2184-88. Temuujin J., Jadambaa T.S., Okada K., Mackenzie K.J.D. Preparation of aluminosilicate precursor by silica mixtures. Bull. Mat. Sci. 1998 21 185-87. Karagedov G.R.,Liubuschko G.l. Mechanochemically stimulated synthesis of monophase mullite. Chem. Sustainable Development 1998 6 161-63. 

L. Schreyeck, P. Caullet, J.C. Mougenel, J.L. Guth, and B. Marler, A Layered Microporous Aluminosilicate Precursor of Ler-Type Zeolite. J. Chem. Soc., Chem. Commun., 1995, 2187-2188. 

Xiao[207] reported the preparation of ordered hexagonal mesoporous aluminosilicates (MAS-5) with uniform pore sizes from self-assembly of preformed aluminosilicate precursors with CTAB surfactant. The XRD pattern for a typical as-made MAS-5 sample shows four well resolved peaks that can be indexed as (100), (110), (200), and (210) reflections associated with the hexagonal symmetry. No diffraction peak was observed in the region of higher angles 10-40°, which indicates the absence of large... 

Strong acidic and high temperature hydrothermally stable mesoporous aluminosilicates with well-ordered hexagonal structure (MAS-5) have been successfully synthesized from assembly of pre-formed aluminosilicate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The MAS-5 shows extraordinary stability both in boiling water (over 300 h) and in steam (800°C for 2 h). Temperature programmed desorption of NH3 shows that acidic strength of MAS-5 is much higher than that of MCM-41. 

Han, Y. Wu, S. Sun, Y. Li. D. Xiao. F.S. Liu. J. Zhang. X. Hydrothermally stable ordered hexagonal mesoporous aluminosilicates assembled from a triblock copolymer and preformed aluminosilicate precursors in strongly acidic media. Chem. Mater. 2002, 14 (3). 1144-1148. 

Aluminosilicate gels are prepared by the mixing of reactive sources of alumina and silica. These include fumed silica, silica sols and alkoxides of silica, and aluminium, aluminates, aluminium salts and alkoxides of aluminium. Other synthetic routes have been explored that use structured aluminosilicate precursors, such as zeolites themselves, to supply aluminate and silicate species to... 

Leivo J, Linden M, Teixeira CV, Puputti J, Rosenholm J, Levanen E et al (2006) Sol-gel s5mthesis of a nanoparticulate aluminosilicate precursor fm homogeneous mullite ceramics. J Mater Res 21 1279-1285... 

The formation of the sodium aluminosilicate precursor is regarded to be critical. Its formation conditions and properties are considered responsible for the crystalline zeolites quality parameters. Two major targets of process optimization are to ensure the specified particle size, that is, to obtain a low-grit product, while keeping the time required for the process as short as possible. 

Most recently, Roesky and coworkers described several elegant molecules of the type shown in equations 59 that offer potential as aluminosilicate precursors. ... 

The precursor method of ceramic processing is promising as it offers significant advantages such as control over chemical and phase purity of the resultant ceramic material, low processing temperatures, and processable precursors (P). Precursor syntheses are often easy and efficient. However, the processable precursors described in the literature are typically limited by the availability of salts of different metals and their solubilities in common solvents 10). To our knowledge, simple, inexpensive, general synthetic routes to processable multimetallic aluminosilicate precursors were unknown, until recently. 

Herein we describe the extension of this process to the synthesis of a trimetallic potassium aluminosilicate precursor and the delineation of the proposed precursor structure. 

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