Synthesis of zeolite

Gradual heating of this mixture up to ca. 200°C results in dissolution of the gel and forms clusters of SiOyAlO - tmits which are the basic building blocks for the zeolite. In the presence of the amine or surfactant, these building blocks polymerize to form the zeolite which crystallizes slowly from the reaction mixture. At this point, the zeolite still contains the occluded organic template. The resultant template can easily be removed by heating to 200-400°C. This process is also called as calcination. 

a heterogeneous solid acid catalyst with MFI cages connected by 10-ring micropores, has been widely used in the fields of oil refining and petrochemical industries [32]. 

Many surfactants have been used as templates for creating inter/intrac-rystalline mesoporosity in zeolites. For example, Schuth et al. synthesized mesoporous silicalite-1 zeolite by using an organic aerogel as a soft template [33]. Similarly, Xiao et al. prepared structured zeolites templated by 

2 Synthesis of Zeolites. A better molecular level understanding of the zeolite synthesis steps occurring in solution should assist in the development of new zeolitic materials. Raman spectroscopy offers the advantage that it can provide fundamental information about the aqueous phase as well as the solid amorphous and crystalline phases present during the zeolite synthesis. Several Raman studies on the synthesis of aluminosilicate zeolitic materials have recently been reported.  

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Schunk S A and Schuth F 1998 Synthesis of zeolite-like inorganic compounds Molecular Sieves Science and Technology vo 1, ed H G Karge and J Weitkamp (Berlin Springer) pp 229-63... 

Jansen J C 1991 Synthesis of zeolites Stud. Surf. Sol. Catal. 58 77-136... 

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. 

Li, Y. and Yang, W. (2008) Microwave synthesis of zeolite membranes a review. Journal ofMemhrance Science, 316, 3-17. 

The initial transition of dissolved silicate molecules into solid nanoparticles is perhaps the least explored step in the synthesis of zeolites. One impediment to understanding this mysterious step is the poorly elucidated molecular composition of dissolved particles. The major mechanistic ideas for the formation of zeolites approach these structures differently i) many researchers believe that secondary building units (SBU) must be present to form initial nanoslabs [1,2] ii) some others prioritize the role of monomers to feed artificially introduced crystal nuclei or assume that even these nuclei form via appropriate aggregation of monomers [3] iii) silicate solutions are also frequently viewed as random mixtures of various siloxane polymers which condense first into an irregular gel configuration which can rearrange subsequently into a desired crystal nucleus at appropriate conditions [4,5],... 

Microwave processing of zeolites and their application in the catalysis of synthetic organic reactions has recently been excellently reviewed by Cundy [23] and other authors [24], The microwave synthesis of zeolites and mesoporous materials was surveyed, with emphasis on those aspects which differ from conventional thermal methods. The observed rate enhancement of microwave-mediated organic synthesis... 

Fig. 5 (a) Structure directing agent (SDA) in the synthesis of zeolite ITQ-3 N quaternary nitrogen A-I carbon atoms of SDA, l,3,3,6,6-pentamethyl-6-azonium-bicyclo[3.2.1]octane some 13C line assignments were not unequivocally possible, so these are left open the orientation of the dipole moment was calculated with a semiempirical AM-1 simulation with the origin at the center of gravity of the molecular cation (b) 13C H 27A1 REAPDOR experiment on synthetic zeolite ITQ-3. Adapted from [204]... 

Cundy, C.S. and Cox, P.A. (2003). The hydrothermal synthesis of zeolites history and development from the earliest days to the present time. Chem, Rev. 103, 663-701... 

As was shown here in some examples, the field of catalysis over zeolites, although marnre, is still very much alive. The chemists who work with the synthesis zeolites continue to be very creative, the focus now being placed on the synthesis of materials that can catalyze reactions other than the acidic ones and/or reactions of bulkier molecules, that is, synthesis of zeolites with larger micropores or with a very large external surface, such as nanosize and delaminated zeolites. New concepts related to the mode of action of zeolite catalysts continue to emerge, as shown here with the shape selectivity of the external surface. These concepts are particularly useful to scientifically design selective and stable catalysts. 

Recently the synthesis of zeolitic membranes was reported by Suzuki... 

M.J., and Valenda, S. (2004) Supramo-lecular self-assembled molecules as organic directing agent for synthesis of zeolites. Nature, 431, 287-290. 

Synthesis of Zeolites and Manufacture of Zeolitic Catalysts and Adsorbents... 

Microwave Synthesis of Zeolites and Molecular Sieves The use of microwaves holds promise for efficiency improvements in zeolite synthesis due to the rapid heating possible when using microwave radiation [166], The first report of microwave synthesis of zeolites was by Mobil Oil in 1988, which broadly claimed the synthesis of zeolite materials in the presence of a microwave-sympathetic material, such as water or other pro tic component [167]. A number of reports have appeared since, including synthesis of zeolites Y, ZSM-5 [168] and metaUoaluminophosphate-type materials, such as MAPO-5 [169], There have also been extensive investigations in using microwaves for zeoHte membrane synthesis. Recent reviews discuss the progress in microwave zeoHte synthesis [170, 171]. 

Continuous and Semi-Continuous Zeolite Synthesis The first report of continuous synthesis, rather than the usual batch-wise synthesis of zeolites, was from Mobil Oil in 1963 [172]. Another similar patent was from Alcoa Aluminum in 1969 [173]. 

Yu, J. (2007) Synthesis of zeolites, in Introduction to Zeolite Zeolite Molecular Sieves, Studies in Surface Science and Catalysis, vol. 168, Elsevier Science Publishers B V, Amsterdam, p. 52. 

Z., and Chen, J. (2005) Effect of agitation on the synthesis of zeolite beta and its synthesis mechanism in absence... 

Many of the characterization techniques described in this chapter require ambient or vacuum conditions, which may or may not be translatable to operational conditions. In situ or in opemndo characterization avoids such issues and can provide insight and information under more realistic conditions. Such approaches are becoming more common in X-ray adsorption spectroscopy (XAS) methods ofXANES and EXAFS, in NMR and in transmission electron microscopy where environmental instruments and cells are becoming common. In situ MAS NMR has been used to characterize reaction intermediates, organic deposits, surface complexes and the nature of transition state and reaction pathways. The formation of alkoxy species on zeolites upon adsorption of olefins or alcohols have been observed by C in situ and ex situ NMR [253]. Sensitivity enhancement techniques play an important role in the progress of this area. In operando infrared and RAMAN is becoming more widely used. In situ RAMAN spectroscopy has been used to online monitor synthesis of zeolites in pressurized reactors [254]. Such techniques will become commonplace. 

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