In-Situ Crystallization Method

Conventional hydrothermal synthesis is the most common method for zeolite membrane preparation. In the in-situ crystallization method, a porous support is immersed in a zeolite synthesis solution. A membrane 

The in-situ crystallization synthesis is easy to operate, but the separation properties of the resultant membranes cannot be controlled with ease, because the formation of zeolite film and microstructure depends significantly not only on the chemical and structural nature of the support surface but also on the synthesis conditions - such as synthesis solution composition, pH, temperature, presence of impurities, and even nutrient sources. Furthermore, this synthesis method also needs a relatively long crystallization time - from a few hours to a few days -leading to the formation of impure zeolites. Moreover, the zeolite crystals 

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For the deposition of active phase(s), impregnation, adsorption and ion exchange, (co)precipitation, deposition precipitation, and in situ crystallization methods can be used. Moreover, it is possible to mix the active phase in the mixture for extrusion or to deposit the active phase by using a mixed sol containing both the precursors of the oxidic species and the active phase or a slurry with the precursor powder of the active phase. Other coating techniques, e.g., CVD or CVI techniques, can also be used. The dispersion of the active phase depends strongly on the method and conditions used, its precursors form as well as on the history of the active phase. 

Madhusoodana CD, Das RN, Kameshima Y, Yasumori A, and Okada K. Characterization and adsorption behavior of ZSM-5 zeolite film on cordierite honeycombs prepared by a novel in situ crystallization method. J For Mater 2001 8(4) 265-271. 

In situ-crystallization method a hydrothermal crystallization method is used to make nanozeolites grow directly in the channel and on the extra surface of carriers. However, the large zeolite particles tend to form on the extra surface of carriers in this method, which destroys the continuity of carriers, and prevents the contact of reactant molecules and reactive centers. 

Figure 3.1 Flow chart of the in-situ crystallization method for the synthesis of zeolite membranes.

Zeolite membranes are generally synthesized as a thin, continuous film about 2-20 xm thick on either metallic or ceramic porous supports (e.g., alumina, zirco-nia, quartz, siHcon, stainless steel) to enhance their mechanical strength. Typical supported membrane synthesis follows one of two common growth methods (i) in situ crystallization or (ii) secondary growth. Figure 10.2 shows the general experimental procedure for both approaches. 

Figure 10.2 Schematic of the experimental procedures involved for two common zeolite synthesis methods including in situ crystallization and secondary (seeded) grow.

Figures 3.24(a) and (b) show morphodroms of silicate crystals growing from silicate solutions Fig. 3.24(a) shows the results of observations on quenched products, and Fig. 3.24(b) summarizes the results obtained by a high-temperature in situ observation method of growth [23]. In these cases also, as apart from the liquidus of solid-solution component, it is seen that the morphology of crystals changes from polyhedral, through hopper, to dendritic, then spherulitic. The predictions described in Section 3.12 are thus confirmed by experiment.

In addition to simplifying the workup procedures, use of catalytic amounts of the titanium-tartrate complex in the epoxidation of low molecular weight alcohols makes in situ derivatization of the crude epoxy alcohol feasible (Table 5)42, Catalytic epoxidation and in situ derivatization allowed the preparation of glycidol, an epoxy alcohol accessible only in very low yield by the stoichiometric method. The in situ derivatization method also makes possible the enhancement of enantiomeric excess through crystallization. Derivatives of low molecular weight alcohols, such as the 4-nitrobenzoates, undergo significant enantiomeric enrichment upon crystallization (Table 5). 

As mentioned in the previous section, hollow zeolite spheres of LTA, FAU, BEA, MFI can be prepared in the presence of polystyrene beads as templates by using an LBL self-assembly technique. Recently, several research groups have tried to adopt similar methods to synthesize zeolite-template composites on the surfaces of templates with various shapes and sizes, properties, and structures through self-assembly or in situ-crystallization approaches. Subsequent removal of the templates forms zeolite materials with analogical skeletons of the templates. Up to now, the reported templates include microspheres, carbon fibers, polyurethane foams, and microbe structures,[144,145] as well... 

Polycrystalline zeolite membranes consist of inter-grown zeolite crystals with no apparent cracks or pinholes (Fig. lA). These films are composed of only zeolite (i.e., there are no non-zeolite components such as amorphous silica or polymer). They are normally supported on a substrate although free-standing films have also been synthesized. Membranes can be prepared on different substrates such as silicon wafer, quartz, porous alumina, carbon, glass, stainless steel (SS), gold, etc. Polycrystalline films are primarily prepared by hydrothermal synthesis methods including in situ crystallization, seeded growth,and vapor transport, " and have potential use in all of the applications discussed in this entry. 

The composites included in Table 6.3 were prepared by different methods, indicated in the first column by impregnation (I), recast (R), sol-gel reaction (SG), in-situ crystallization (ISC), melt and extrusion (ME), and in-situ polymerization (ISP). A half of the membranes in Table 6.3 were prepared by the recast procedure, and the selectivity and maximum power density was calculated with reference to the Nafion recast membrane. For the rest of the membranes the Nafion matrix (112, 115 or 117) is indicated. 

The materials of interest for earth sciences are generally very complex from the chemical viewpoint, and may sometimes contain most of the elements of the periodic table, with concentrations varying from the trace- to the major-element level and with variable spatial distribution (zoning). As a consequence, their complete structural and chemical characterization is possible only by means of in situ analytical methods that are able to solve specific measurement problems. The starting material is often available in very small amounts (e.g., some crystals) thus, the requirement of minimum (or even null) sample consumption is also important. 

Dacquin et al. [51] used a method called in situ crystallization in a confined space to prepare a LaNiOs/SBAlO catalyst. As evidenced by TEM analysis, very small nanoparticles of perovskite were generated within the silica porosity with a size between 2 and 5 nm and an average closed to 3 nm. The reduction step performed at 700 °C gives Ni° particles well dispersed within the matrix porosity and their size remained close to the support pore size. The catalytic activity for syngas production was doubled compared to bulk LaNiOs precursor, it remains... 

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