Zeolite synthesis variables

So, how does one prepare a new zeolite The de novo design of a zeolite synthesis must take into account a multitude of variables that may or may not operate... 

Two synthesis variables seemed to have received most attention in the work reviewed here, the cation composition and the nature and source of the aluminosilicate reactant. Extensive use of mixed bases of the alkali, alkaline earth, and organic cations have been reported as well as a wide variety of reactant aluminosilicates including solutions, hydrogels, glasses, kaolin (raw and calcined), and naturally occurring zeolites. 

A study is presented of the synthesis and properties of the novel synthetic zeolite omega. The synthesis variables and kinetics of formation are discussed, as well as the ion exchange, sorption, and thermal properties. By decomposition of imbibed tetra-methylammonium ions and exhaustive treatments of the zeolite with ammonium ions, a pure hydrogen form can be obtained which is a suitable substrate for the preparation of hydrocarbon conversion catalysts. Several catalysts were prepared and utilized to isomerize n-hexane, and to hydrocrack a heavy gas oil. 

We describe a systematic investigation of various synthesis variables that usually affect the crystallization of faujasite-type structures from Si, Al, Na, tetraethylammonium (TEA) hydrogels.A careful control of parameters such as the composition of the precursor hydrogel, temperature and crystallization time is needed to selectively prepare and stabilize pure zeolite ZSM-20 in high yield. 

Just like IR spectroscopy, Raman can detect small. X-ray amorphous zeolite particles. Therefore RWan has been used to examine both the liquid and the solid phase of zeolite synthesis mixtures [28], Ex situ methods (with separation of solid and liquid) and in situ methods have been applied. In studying the liquid phase [10-11], one should remember that (i) minimum concentrations for detection of spontaneous Raman from liquids are typic ly 0.05 - 0.1 M, [15-27, 29] (ii) that the cross-section of the Al(OH)4 species is much stronger than e.g. for silicate or aluminosilicate anions [30]. Thus species which are present in low concentration or with variable structures may easily be overlooked in Raman spectra of the synthesis liquors. 

X type zeolites have been synthesized in the presence of metallophthalocyanines (MPc, where M = Fe, Co, Ni, Cu) resulting in partial inclusion of these complexes. Synthesis variables such as metal loading, order of mixing, and aging will be discussed. 

Synthesis, two-stage Synthesis, ultrasound Synthesis, vanadosilicates Synthesis, variable-temperature Synthesis, zeolites from bentonite Synthesis, zeolites from fly ash Synthesis, zeolites from MCM-41 Synthesis, zeolites, modelling Synthesis, zeolites, substituted Synthesis, ZSM-34... 

It is often said that the property of acidity is manifest only in the presence of a base, and NMR studies of probe molecules became common following studies of amines by Ellis [4] and Maciel [5, 6] and phosphines by Lunsford [7] in the early to mid 80s. More recently, the maturation of variable temperature MAS NMR has permitted the study of reactive probe molecules which are revealing not only in themselves but also in the intermediates and products that they form on the solid acid. We carried out detailed studies of aldol reactions in zeolites beginning with the early 1993 report of the synthesis of crotonaldehyde from acetaldehyde in HZSM-5 [8] and continuing through investigations of acetone, cyclopentanone [9] and propanal [10], The formation of mesityl oxide 1, from dimerization and dehydration of... 

Figure 2 clearly indicates a large variability in both the sites occupied by Al atoms and the concentration of the Al atoms in these sites for the ZSM-5 samples studied. Even samples with similar framework aluminum concentration exhibit very different Al sitings as well as Al concentrations in the individual occupied T sites. This fact clearly rules out that the Al siting in the zeolite framework is random or is controlled by thermodynamic stability. It rather shows that the conditions of the synthesis are responsible for the Al siting in the framework. 

Cancrinites are one of the rarest members of the feldspathoid group, classified as such due to its low silicon content. However, cancrinite is also classified as a zeolite, due to its open pore structure, which confers molecular sieve properties [1], Likewise, variable sodium carbonate and NaOH concentrations in the hydrothermal synthesis of cancrinite could direct the synthesis of the intermediate phase or the disordered cancrinite formation [2], The intermediate phase is described as a phase between cancrinite and sodalite [3], The disordered cancrinite is an intermediate phase which is much closer to the cancrinite structure than sodalite structure [2],... 

Zeolites are normally prepared by crystallization (precipitation) in hydrothermal conditions (T = 350-525 K) of (Si,Al)-containing hydrogels [3]. Above 373 K, crystallization is normally performed under autogeneous pressure. Both batch and continuous synthesis methods can be envisaged. Variables which affect the synthesis of zeolites fall into 3 categories ... 

The synthesis of zeolite A, mixtures of A and X, and zeolite X using batch compositions not previously reported are described. The synthesis regions defined by triangular coordinates demonstrate that any of these materials may be made in the same area. The results are described in terms of the time required to initiate crystallization at a given reaction temperature. Control of the factors which can influence the crystallization time are discussed in terms of "time table selectors" and "species selectors . Once a metastable species has preferentially crystallized, it can transform to a more stable phase. For example, when synthesis conditions are chosen to produce zeolite A, the rate of hydroxysodalite formation is dependent on five variables. These variables and their effect on the conversion of zeolite A to hydroxysodalite are described mathematically. 

Four additional factors can also contribute to a limited shift in the time required for crystallization. These are the rate at which the sodium aluminate solution is added to the sodium silicate solution (13), anion activation (14, 15, 16), the source of Si02 (17), and the reaction temperature (10). It has been found that the effect of these variables is most pronounced when synthesizing higher Si02/Al203 ratio zeolites, such as X and Y. Their effect on the synthesis of zeolite A is considerably less and sometimes negligible. 

Starting with any given set of zeolite A synthesis conditions, one may control the amount of hydroxysodalite formed by properly manipulating these variables. It should be noted that more than one factor can vary at the same time. If their variation produces compensating effects, i.e. lower Na20/Si02 ratio and lower H2O/... 

Given a set of synthesis conditions and sufficient reaction time to produce hydroxysodalite, pure zeolite A can be obtained by decreasing the reaction time until the % HS approaches 0. If the reaction time is fixed, any of the other variables can be varied and achieve the same result. An example of how reaction time affects the conversion of zeolite A to hydroxysodalite, when all other variables are held constant, appears on Figure 9. 

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