Zeolite Synthesis and Crystallization

A scope of profitable apphcations of Raman spectroscopy is seen in studies of zeoHte syntheses. 

IR spectra of suspensions of amorphous and crystalline colloidal silica aggregates were obtained by Mintova et al. [868]. These spectra revealed the presence of small (nano-sized) siHcate units possibly containing D5R subunits. A complete transformation to crystalline particles of MEL-type zeoHte was observed after an additional hydrothermal treatment of the aged precursor suspensions at 363 K for 68 h. 

Decomposition of organic cations in offretite and ZSM-34 crystals was followed via FTIR spectroscopy by Occelli et al. [873] in that the decrease of the bands of the organic species and the concomitant appearance of the new bands in the OH stretching region was monitored. The protonic nature of the newly formed hydroxy groups was confirmed by their interaction with the probe pyridine and generation of the bands of pyridinium ions (cf. Sect. 5.5.2.6.2). 

More recently, Schoeman and Regev [874] studied the crystallization of sih-cahte-1 inter alia by DRIFT spectroscopy. A band at 550 cm was found to be typical of the presence of MFI-structured material. 

The growth of silicalite-1 films on gold supports was monitored via scanning electron microscopy. X-ray diffraction and reflection/absorption infi ared spectroscopy in the work by Engstroem et al. [875]. The development of peaks at 1229, 

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The major effect of new advanced techniques on catalyst structure is found in zeolite catalysis. NMR techniques, especially MASNMR, have helped to explain aluminum distribution in zeolites and to increase our understanding of critical parameters in zeolite synthesis and crystallization. MASNMR, combined with TEM, STEM, XPS, and diagnostic catalytic reaction probes, has advanced our knowledge of the critical relationship between the structure and reactivity patterns of zeolites in the chemical fuels industry. Throughout the symposium upon which this book is based, many correlations were evident between theoretical quantum mechanical calculations and the structures elucidated by these techniques. 

F. Fajula, Zeolite synthesis and crystal tailoring, in Guidelines for mastering the Properties of Molecular Sieves, Nato ASI Series, Series B Physics Vol. 221, Eds. D. Barthomeuf et al.. Plenum Press, New York and London (1989)53. 

However, a detailed discussion of the progress in Raman studies of adsorbed molecules is beyond the scope of this chapter, and we therefore refer to previous extended reviews [194, 195]. In subsequent sections we will focus on some selected studies dealing with Raman spectroscopy. Fimdamentals of Raman spectroscopy especially in surface research including zeolites are treated, e.g., in Refs. [ 183,185]. Examples of application of Raman spectroscopy in zeoUte research are provided, for instance, in Sects. 5.2 (frameworks), 5.3 (extra-framework cations), 5.S.2.7 (adsorption of complex molecules) and 5.6.2 (zeolite synthesis and crystallization). 

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. 

Synthesis and Crystal Structure of Zeolite Rho—A New Zeolite Related to Linde Type A... 

The NMR and X-ray diffraction data are only consistent with substitution of boron into the framework structure of the mordenite. Although we prepared boron substituted mordenite directly from modified gels, direct synthesis has severe limitations. The solution chemistry of the substituting element can interfere with zeolite nucleation and crystallization, as... 

In the early days of XPS the first applications of the technique to zeolites were dealing with the determination of Si/Al ratios calculated using equation (23) and their comparison with bulk values [14-16]. This of course allowed to detect important compositional gradients in the surface region, a piece of information which is related to the mechanism of zeolite synthesis and which is technically important in order to monitor the concentration of Brdnsted acid sites on the external surface of the zeolite crystals. The measurement of... 

Xu Quinhua and Yan Aizhen, Hydrothermal synthesis and crystallization of zeolites Prog.Cryst Growth and Charact. Vol 21 (1990)... 

Copper(n) Phosphonates - p-Cu (CH3P03), an Original 3-Dimensional Structure with a Channel-Type Arrangement/norg. Chem. 1994, 55, 4885 Drumel, S. Janvier, P Demand, D. Bujoli, B., Synthesis and Crystal-Structure of Zn(03PC2H4NH2), the First Functionalized Zeolite-Like Phosphonate / Chem. Soc. Chem. Commun. 1995, 1051 Drumel, S. Janvier, P Barboux, P Bujoli-Doeuff, M. Bujoli, B., Synthesis, Structure, and Reactivity of Some Functionalized Zinc and Copper(ll) Phosphonates Inorg. Chem. 1995,34, 148. 

Wang YX, Gies H, Marler B, Muller U. Synthesis and crystal structure of zeolite RUB-41 obtained as calcination product of a layered precursor a systematic approach to a new synthesis route. Chem Mater 2005 17 43-9. 

Ikeda T, Kayamori S, Mizukami E. Synthesis and crystal structure of layered silicate PLS-3 and PLS-4 as a topotactic zeolite precursor. J Mater Chem 2009 19 5518-25. 

Reprinted with permission from Huber, G.W., Iborra, S., Cotma, A., 2006. Synthesis of transportation fuels from biomass chemistry, catalysts, and engineering. Chemical Reviews 106 (9), 4044—4098. Copyright (2006) American Chemical Society Reprinted from Martinez, A., L6pez, C., 2005. The influence of ZSM-5 zeolite composition and crystal size on the in situ conversion of Fischer—Tropsch products over hybrid catalysts. Applied Catalysis A General 294 (2), 251—259 with permission from Elsevier. 

In recent years, there has been a growing interest in the synthesis and application of nano-scale zeolites. Zeolites with a crystal size smaller than 100 nm are the potential replacement for existing zeolite catalysts and can be used in novel environmentally benign catalytic processes. It is well known that the crystal size of zeolites has a great effect on their catalytic properties. The improved catalytic activity and selectivity as well as lower coke formation and better durability can be obtained over nano-sized zeolite crystals [2]. 

Alkali ions (salts) influence the formation of the precursor gel for most of the synthetic zeolites (3,34,39,40). Na+ ions were shown to enhance in various ways the nucleation process (structure-directing role) (40-42), the subsequent precipitation and crystallization of the zeolite (salting-out effect) (JO and the final size and morphology of the crystallites (34,43). Informations on the various roles played by the inorganic (alkali) cations in synthesis of ZSM-5, such as reported in some recent publications (7,8,10,14,17,29,30,44,45) remain fragmentary, sometines contradictory and essentially qualitative. 

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