Zeolite synthesis strategies

Wilson ST. Overview of zeolite synthesis strategies. In Xu R, Gao Z, Chen J, Yan W, editors. From zeolites to porous MOF materials—the 40th anniversary of international zeolite conference Stndies in surface science and catalysis, 170A. Amsterdam Elsevier 2007. p. 3-18. 

A third possibility for the synthesis of nanomaterials in constrained volumes is the use of molds (Figure 3.1c). Advantages of this method include its simplicity, versatility, and precise control over the shape of the solid, even with intricate forms. An elegant example of this strategy is the preparation of zeolites which precisely replicate the complex microstructure of wood. To do this, Dong et al. [43] infiltrated a zeolite synthesis solution into a wood sample. After the necessary hydrothermal treatment, and subsequent calcination to remove the template as well as the wood, a zeolitic structure was obtained that reproduced with full detail and fidelity the wooden sample used as a mold. 

Zeolite materials are used commercially as shape/ size selective catalysts in the petrochemical and petroleum refining industry, and as molecular sieving separation media for gases and hydrocarbons. For both applications, zeolites are used in powder composite form such as pellets and granules. In this entry, we focus on zeolite membranes. We define zeolite membranes as a continuous phase of zeolite-based materials (pure zeolite or composite) that separate two spaces. Zeolite membranes are generally uniform thin films attached to a porous or a nonporous substrate. They can also be self-standing without a substrate. Note that we have included zeolite films and layers on nonporous substrate in this entry because we believe many of the synthesis strategies and applications reported for those nonporous substrates are easily transferred to a porous substrate to prepare a zeolite membrane. 

A series of original synthesis strategies has been also reported recently such as flow-through reactors for the homogeneous synthesis of zeolite membranes [77], centrifugal force field [114] or electrophoresis [115] for the preparation of A-type membranes, and pulse laser deposition (PLD) for the secondary growth of oriented MCM-22 membranes [116]. 

Here we report a synthesis strategy which has allowed us to produce Ti-Beta samples with a much higher Si/Al ratio than any one reported up to now, together with predesigned zeolite crystals containing very low A1 content all of it located in the... 

Considering the history of zeolite synthesis and the evolution of synthetic strategies as a whole we propose that it was, and still is, geomi-metic, in the very same sense that Vincent proposed for biomimetic materials synthetic zeolites realise the abstraction of good design from... 

There are several examples in which two organic entities are used in zeolite synthesis, following two distinct types of strategy. In the first strategy the idea is simply that each OSDA could fit a different type of void, as exemplified by the synthesis of MWW zeolites by Camblor et and Zones et Zeolite MWW has two kinds of void... 

However, there are at least two additional important structure-direction factors interplaying with that of fluoride in the synthesis of pure-silica zeolites by the fluoride route the OSDA and the degree of dilution of the synthesis gel. Villaescusa and Camblor have shown that the general concepts outlined above regarding structure-direction by OSD As can be successfully used in the search for new pure-silica materials, as shown for instance by the synthesis strategies that finally lead to the three-dimensional large pore zeolite ITQ-7. Nonetheless, we would like to point out at least one peculiarity, in this respect, of the fluoride route small cations may show by this route a rather specific structure-direction effect (like 1,3,5-trimethylimidazolium, which has a (C- -N)/N ratio of 8 but shows a rather large specificity towards zeolite ITQ-12 in fluoride aqueous medium). 

Less favorable experimental conditions were met for Cu(I)-NO complexes formed over Cu-ZSM-5 that prevented a determination of the Al hf coupling data because of short electron spin relaxation times and larger distributions of Al nuclear quadrupole couplings, probably due to an inhomogeneous distribution of Al framework atoms. Detailed local structures of the complexes in Cu-ZSM-5 zeolites, 02-Al-02-Cu(l)-N0, were recently proposed on the basis of quantum chemical calculations [59]. To experimentally verify the theoretically proposed structural properties of the Cu(l)-NO species formed in ZSM-5, it is highly desirable to develop improved synthesis strategies for high siliceous zeolites that lead to a better statistical Al distribution in the crystallites. 

These structures are unique for several reasons. First, they represent three new multidimensional 12-MR systems, which are rare even among zeolites. Second, the amount of framework substitution by metals such as Mn2+ and Mg2+ was unknown prior to this series. Also, the ease of forming both gallium and aluminum phosphates appear to be comparable. Finally, it would appear the charge-matching approach has proven to be a successful strategy for the synthesis of new molecular sieves. It is not clear whether these materials are thermally or hydrothermally stable but they do represent novel pore structures that should impart some unusual properties. 

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