Microporous phases

All preparations were structurally characterized by means of XRD (Siemens 5005). TEM imaging was performed with a Philips CM200 instrument. 27A1 and 29Si MAS NMR (Broker 500 MFlz and 360 MFlz respectively) was used to study the microporous phase and the kinetic of its formation. The relaxation delays were 0.2s and 200s respectively. Acidity was determined by the adsorption of carbon monoxide after activating the samples in vacuum (10 6 mbar) at 450°C for 1 h. The spectra were recorded on a Equinox 55 Broker spectrometer with a resolution of 2 cm 1 and normalized to 10 mg of sample. 

The formation of the microporous phase dispersed in porous, amorphous matrices was followed by XRD and TEM. The XRD patterns of the BEA-composite prepared using the Al-poor aluminosilicate (6A187Si) are shown in Figure 1. BEA was the sole... 

Irrespectively of the iron content, the applied synthesis procedure yielded highly crystalline microporous products i.e. the Fe-ZSM-22 zeolite. No contamination with other microporous phases or unreacted amorphous material was detected. The SEM analysis revealed that size and morphology of the crystals depended on the Si/Fe ratio. The ZSM-22 samples poor in Fe (Si/Fe=150) consisted of rice-like isolated crystals up to 5 p. On the other hand the preparation with a high iron content (Fe=27, 36) consisted of agglomerates of very small (<0.5 p) poorly defined crystals. The incorporation of Fe3+ into the framework positions was confirmed by XRD - an increase of the unit cell parameters with the increase in the number of the Fe atoms introduced into the framework was observed, and by IR - the Si-OH-Fe band at 3620 cm 1 appeared in the spectra of activated Fe-TON samples. 

Figures 4-b and 4-d depict the pore size distribution curves of the SBA samples after these different treatments. For the sample SBA-A treated in acidic medium, the BET surface area (869 m2g" ), the mean pore diameter (6.4 nm) and the pore size distribution curve are similar to those from the pure parent silica SBA. For neutral treatment, the surface area (667 m2 g 1) decreases slightly. This can be related to the reduction of the microporous phase of the sample as shown in the pore size distribution curve. However, the mean pore diameter remains unchanged. Conversely, the structural properties of SBA-B are modified after treatment in basic solution. In this case, we observe a strong decreasing of the specific surface (454 m2 g 1) accompanied by a total loss of the microporous phase and an increasing of the mean mesoporous diameter (7.2 nm). It seems that in basic medium, a leaching phenomenon inside the mesoporous channels does occur, leading to a partial dissolution of the wall and resulting in smaller wall thickness (4.3 nm). Compared with the results on MCM-41, which show that the mesoporous structure collapses in basic solution [9,10], we can say that the stability of SBA materials in this medium is much higher.

Hydrothermal synthesis at 180°C using borax, V205, and en, as starting reagents can result in phase-pure formation of the water soluble cluster compound 2 Na10[Vj2BlgO60Hg]. The Na ions can then be exchanged with M2 at lower temperatures to form insoluble materials. Some of these have since been shown to be microporous phases. 

The selective reduction of steroid ketones by means of LiAlH4-activated template polymers can be carried out following the principle of an ion exchanger. Although the application of polymers in template syntheses is currently limited, and the reactions do not always run satisfactorily, this method appears to be a landmark for future rational syntheses. Microporous phases with three-dimensional lattice networks and defined pore structures and sizes can be obtained by the use of molecules or hydrated ions of alkali metals or alkaline earth metals as templates [73]. A concept developed by the Mobil Oil Company for the synthesis of porous materials employs a regular arrangement of molecules formed... 

The symmetric, microporous polymer membranes made by phase inversion are widely used for separations on a laboratory and industrial scale.22 Typical applications range from the clarification of turbid solutions to the removal of bacteria or enzymes, the detection of pathological components, and the detoxification of blood in an artificial kidney. The separation mechanism is that of a typical depth filter which traps the particles somewhere within the structure. In addition to the simple "sieving" effect, microporous phase inversion membranes often show a high tendency of adsorption because of their extremely large internal surface. They are, therefore, particularly well suited when a complete re-... 

S mthesize and characterize of thin films and bulk novel microporous phases including of Al/Si zeolite thin films doped and/or ion exchanged with other elements, unsupported aluminosilicate zeolite membranes, and silicotitanate phases. 

The approach for this program is the development of defect-free thin film zeolite membranes and new bulk microporous phases for the selective separation of light gases. The development of these membranes includes synthesis, modeling/ simulation, permeation studies and validation for separation and isolation of H2. The permeation of pure and mixed gases through membranes is studied at room temperature and 80°C. The modeling and... 

We are interested in vanadoborate cluster materials both as precursors to porous solids and as a new class of molecular magnets. We have synthesized a variety of vanadoborate cluster compounds 1-7, primarily by use of two different synthetic routes. The first involves hydrothermal synthesis, using sodium tetraborate ( borax ) as the boron source and the second uses molten boric acid as the reaction medium. In general anionic clusters are found. Herein we report that these have novel electronic and bonding arangements which affect their magnetic behaviour and also that they may be cross-linked together by metal centers such as Cd to form stable microporous phases. 

The luminescent lifetime of the anhydrous compound has also been studied but no definitive result was obtained. The authors concluded this paper saying that the anhydrous microporous phase presenting ID channels can be potentially considered as luminescent probe for detecting small molecules. That is the reason why two years later another group published another paper on this family. In this paper (Pan et al., 2001) the synthesis, via hydrothermal method, and the crystal stracture (see fig. 12) of a compound with chemical formula Er4(bdc)6-6H20 are described. 

Porous materials are classified into several kinds depending on the pore size. According to the International Union of Pure and Applied Chemistry (lUPAC) notation, microporous materials have pore diameters of less than 2 mn and mesoporous materials have pore diameters between 2 and 50 nm. Macroporous materials have pore diameters of greater than 50 nm. Hydrothermal synthesis has been the technique of choice to prepare microporous phases. Ordered porous materials, including ordered mesoporous materials and the metal organic frameworks (MOFs), have also been synthesized generally under hydrothermal conditions [1-5]. In this section, we briefly present the synthesis of mesoporous silica materials and MOFs. 

The aluminophosphate and related analogues of zeolites can often be grown to sizes exceeding those attainable with the aluminosilicate zeolites. This reflects the fundamentally different nature of the solutions used for the syntheses. Non-aluminosihcate molecular sieves often crystalhze from solutions which are less alkahne than zeohte synthesis mixtures. The problems associated with instabihty of the microporous phases under hydrothermal conditions may be smaller with non-aluminosihcate materials. 

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