Zeolites templated growth

Schmidt, I., Boisen, A., Gustavsson, E., Stahl, K., Pehrson, S., Dahl, S., Carlsson, A. and Jacobsen, C. J. H. Carbon nanotube templated growth of mesoporous zeolite single crystals, Chem. Mater., 2001, 13, 4416-4418. 

Syntheses of KZ-2 and ZSM-22 zeolites isomorphously substituted with iron or aluminium were carried out for a wide range of the Si/T ratio (T=Al, Fe). Effect of the gel composition on size and morphology of the crystals formed was studied. It has been shown that using diethylamine as a template it is possible to synthesize iron containing KZ-2 zeolites with the similar crystals (in size and morphology) independently of Si/Fe ratio in gel. No such effect was observed when the syntheses were carried out in the presence of aluminium in the gel. The results point to an important role of the nature of T cations in the process of the zeolite crystal growth. 

Lonally, the templates were chosen by trial and error or exhaustive enumeration. A itafional method named ZEBEDDE (ZEolites By Evolutionary De novo DEsign) en developed to try to introduce some rationale into the selection of templates et al. 1996 Willock et al. 1997]. The templates are grown within the zeolite by an iterative inside-out approach, starting from a seed molecule. At each jn an action is randomly selected from a list that includes the addition of new (from a library of fragments), random translation or rotation, random bond rota-ing formation or energy minimisation of the template. A cost function based on erlap of van der Waals spheres is used to control the growth of the template ale ... 

Quaternary ammonium bromides and hydroxides (quats) are applied as templates in the synthesis of zeolites with relatively high Si/Al ratio. Examples will be given of the use of mon-, di-, poly- and associated quats as templates in zeolite growth. Templated zeolites of the MFI-type can be grown in a lateral or in an axial way onto metal supports, providing promising composite systems, for separation and catalysis, respectively. 

PolycrystalHne membrane growth proceeds by initial formation of a gel layer on the surface of the support crystallization takes place at the interface between the bulk Hquid phase and the gel layer, resulting in deposition of zeolite nuclei and crystals formed [8]. Concurrently, the crystals deposited onto the support surface continue to grow, eventually resulting in a continuous membrane layer. Postsynthesis treatment is necessary when a template is used in synthesis to activate the zeolite and open the pores. Usually this is accomplished through calcination or burn out of the organic molecule. 

In this study, we have shown that both alcohol and D20 have an Important effect on the nucleation and crystal growth of zeolites with Si/Al ratios between 1-2. In the case of alcohol, the formation of large pore zeolites such as zeolites X or Y is markedly accelerated at low alcohol levels. We attribute this to a stabilization of the cation-water complex and structured H20 which act as templates. However, at high alcohol levels, the structure of water disintegrates and leads to the formation of more condensed zeolites such as sodalite or cancrinite. Synthesis of zeolite A in D20 is slower than that in water, which primarily arises from the primary and secondary isotope effect during the condensation polymerization reactions necessary for zeolite growth. 

Zeolite ZSM-23 can be readily synthesized with pyrrolidine as organic template and fumed silica as silica source. Pyrrolidine seems to intervene in the nucleation and crystal growth process, in the latter case most probably as pore-filling agent. By proper optimization of the gel composition and the synthesis conditions, ZSM-23 can be synthesized in less than one day. The synthesis of ZSM-23 has some... 

In the search for zeolites with new pore dimensions and channel structure, researchers employed the use of templating molecules to direct the growth of the aluminosilicates. Tetramethylammonium was the first of these templates used to prepare sodalite and others soon followed [61]. Recently, spectroscopic studies have... 

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