Zeolite syntheses

This is the first monograph that was devoted to structure, chemistry and use of zeolites. It reviews zeolite synthesis to 1973, gives a detailed structural description of synthetic and mineral zeolites, illustrates their physical properties and describes applications. 

A complete survey to 1981 of low or medium Si/AI zeolite synthesis and transformations. 

Structure-based Design of Templates for Zeolite Synthesis... 

Volume 24 Zeolites Synthesis, Structure, Technology and Application. Proceedings of an... 

J. A. Martens, Synthesis of High-Silica Aluminosilicate Zeolites, Elsevier, Amsterdam, 1987, 390 pp. M. L. Occelli and H. E. Robson (eds.). Zeolite Synthesis, ACS Symposium Series No. 398, 1989, 664 pp. J. Klinowski and P. J. Barrie (eds.) Recent Advances in Zeolite Science, Elsevier, Amsterdam, 1990, 310 pp. G. V. Tsitsishvili, T. G. Andronikashvili, G. M. Kirov and L. D. Filizova, Natural Zeolites, Ellis Horwood, Chichester, 1990, 274 pp. 

BROMIDES IN ZEOLITE SYNTHESIS / ZEOLITES IN BROMIDE SYNTHESIS AND CONVERSION... 

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

Quaternary ammonium compounds as structure directing agents in zeolite synthesis... 

In zeolite synthesis (ref. 2) an aqueous mixture containing a silicon source, an aluminum source, an alkali source (usually NaOH) is autoclaved and subjected to hydrothermal treatment. Hydrated Na-ions are then filling the pore system in the as-synthesized zeolite. In the case of relatively high Si/Al zeolites an organic template is required which is usually a tetraalkylammonium compound, applied as the bromide or the hydroxide. 

The importance of quats as structure-directing agents in zeolite synthesis was recently underlined (ref. 5) by the synthesis of the new zeolites SSZ-26 and -33, which combine 10- and 12-ring pores. The templates applied are shown in Figure 3. 

Since then, organic amines, quaternary-ammonium bases, metal complexes, and other compounds have been extensively used in zeolite synthesis, acting as space fillers with low specificity, structure-directing agent, or true templates ... 

The pore size of most zeolites is <1.5nm. This microporosity limits their utility in most areas of chemistry, where the molecules used are much larger, and for which mesoporous materials would be necessary. Unfortunately, attempts to use larger template molecules in the zeolite synthesis, an approach which should in theory lead to larger pore size zeolites, have met with very little success. Indeed, some zeolitic materials have been prepared which have mesopores - none of these has ever displayed any real stability and most collapse on attempts to use them. A new methodology was thus required. 

Commercial porous ceramic tubes (SCT /US Filter Membralox Tl-70 [7]) were used in this study as support for the zeolite material. They are made (Figure 1) of three consecutive layers of tnacroporous a-Al203 with average pore sizes decreasing from the external to the internal layer. A thin toplayer made of mesoporous y-Al203 was also present in some samples. For gas permeability, gas separation and catalytic measurements the tubes were first sealed at both ends with an enamel layer before zeolite synthesis. Tubes with porous lengths up to 20 cm were used in this study. 

Ail these data confirm that a well-defined zeolite silicalite-type crystalline phase has been formed in the presence of the alumina porous tube (which seems indispensable for the zeolite synthesis, as no material is formed in its absence). 

At present, the major applications of zeolites in catalysis are in the oil refinery. They find increasing application in petrochemical processes. When considering the enormous success of the application of zeolites in bulk chemistry, it is to be expected that the same trend will be seen in fine chemicals production. For this sector, it is fortunate that in bulk chemistry so much development work is being done in catalysis and in particular in zeolite synthesis and application. 

A1 3Q MAS NMR spectroscopy and DFT/MM calculations were employed to study the A1 siting in eleven differently synthesized samples of the ZSM-5 zeolite. The results of our study reveal that the occupation of the distinguishable framework T sites by A1 and the concentration of A1 in these T sites are neither random nor controlled by a simple rule. They both depend on the conditions of the zeolite synthesis. We further found that at least 10 out of the 24 distinguishable framework T sites are occupied by A1 in our ZSM-5 samples. 

We have demonstrated that a combined experimental (27A1 3Q MAS NMR) and theoretical (QM-Pot employing the bare framework model) approach represents a powerful tool for the determination of the local geometry of framework A104 tetrahedra, the prediction of27A1 isotropic chemical shifts in hydrated silicon rich zeolites, and the identification of A1 siting in the framework of silicon-rich zeolites. Experimental evidence is provided for the occupation of at least 10 out of 24 distinguishable framework T sites by A1 atoms in silicon-rich ZSM-5. The conclusion is reached that the A1 distribution over the framework T sites is neither random nor controlled by a simple rule, but depends on the conditions of the zeolite synthesis. 

IR and Raman spectroscopy can fulfill these requirements and they are also robust enough for in situ silicate analysis in plant reactors [7]. Both of these techniques have been used for identifying the symmetric (s) and asymmetric (as), stretching (va, vas) and bending (5a, 5as) O-Si-O vibrations in aqueous alkaline silicate solutions which are the cheapest hence most frequently used ingredients for zeolite synthesis [8, 9 and references herein]. However, this information has to be "translated" into siloxane ring... 

Microporous nanoparticles with ordered zeolitic structure such as Ti-Beta are used for incorporation into walls or deposition into pores of mesoporous materials to form the micro/mesoporous composite materials [1-3], Microporous particles need to be small enough to be successfully incorporated in the composite structure. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit ordered zeolitic structure. To study the growth of Ti-Beta particles we used 29Si solid-state and liquid-state NMR spectroscopy combined with x-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM). With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. 

During the last decade large progresses have been performed in the so much difficult art of zeolites synthesis. As a consequence, the amounts of structural defects and chemical impurities have been reduced in zeolite samples (crystallites of larger sizes and well-defined morphology have been synthesized ). At the same time, the zeolite sorption capacities increase. Such an observation is well illustrated by the sorption... 

Preparation of chitosan-zeolite composites by in-situ zeolite synthesis... 

A preformed chitosan-silica composite with 60% weight inorganic part [7] is used as the source of silica for the zeolite synthesis. An alkaline solution of sodium aluminate (Na 2.1 M, Al 1 M) was used in three methods of preparation (A) beads of the chitosan-silica composite were stirred overnight in the aluminate solution, extracted and submitted to a hydrothermal treatment at 80 °C during 48h (B) beads of the chitosan-silica composite were immersed in the aluminate solution and the system underwent a hydrothermal treatment at 80 °C for 48h (C) beads of the chitosan-silica composite were stirred overnight in the aluminate solution, extracted, dried at 80 °C and exposed to water vapour at 80°C during 48h. 

Figure 4. (a) Adsorption-desorption isotherms of N2 at -196°C of 80°C-outgassed (empty squares) chitosan, (filled trangles) zeolite X-chitosan composite from in-situ zeolite synthesis and (empty triangles) zeolite Y-chitosan composite from encapsulation of the zeolite in the gelling chitosan. (b) Scanning electron micrographs of a calcined zeolite-chitosan bead prepared by zeolitisation of a silica-chitosan composite. 

MFI and MTW zeolites with Fe species introduced during zeolite synthesis were investigated. Fe-silicalite and Fe-MTW catalysts were synthesized accordingly to... 

Three methods can be followed for the synthesis of a SIB catalyst (i) zeolite synthesis around the metal complex (ii) template synthesis and (iii) the flexible ligand method. 

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... 

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... 

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