Framework mordenite

Structure of mordenite framework as viewed along c-axis (66). 

Figure 1. Mordenite framework structure viewed in the crdirection...

After that, it is seen one step at llOkJ/mol, that is, a high value of adsorption heat this fact indicates that the NH3 molecules strongly interact through their dipole moments with the mordenite framework [31,49], Thereafter, a decrease of the adsorption heat up to a value of the adsorption heat, equivalent to the liquefaction heat of NH3 at 42kJ/mol, is seen [49],... 

Mordenite. It has been reported that partial substitution of boron in mordenite occurs when boric acid is added to the synthesis gel (6.7). Evidence for boron substitution for aluminum in mordenite samples prepared in borosilicate glass reactors has also appeared (8). We sought to determine the extent of boron substitution into the mordenite framework which can be affected by direct synthesis. 

Three examples will suffice to demonstrate this information Figure 3 shows the polyhedral units in the synthetic zeolite Linde Type A, which link to provide a three-dimensional interconnecting array of channels, Figure 4 illustrates the essentially two-dimensional system of channels in the mordenite framework, and Figure 5 shows the major channels in synthetic zeolite Linde Type L arranged as parallel one-dimensional channels and shown as a stereo pair. Table 6 lists the Atlas notations for these structures with explanations, including the symbols used in Tables 2-5. 

Mordenite is a naturally-occurring silica-rich zeolite (Si/Al 5) which also can be synthesized readily (34). Meier determined the structure of its fully hydrated sodium form (28). The mordenite framework is characterized by a micropore system composed essentially of parallel elliptical cylinders of maximum and minimum crystallographic free diameters of 7.0 and 5.7A, respectively, these main channels being interconnected by smaller side channels. 

Interrupted mordenite framework. 03 and 09 are terminal oxygens, where the framework is not fully connected. 

Figure 1. The variation of interaction energy between the p-IBEB and mordenite framework as the molecule diffuses through the 12-m channel. The configuration of the molecule at the minimum energy location is also shown.

The mordenite framework structure (see Plate VII and Fig. 9.3) has a complex topology, containing unidirectional 12-ring channels together with... 

Figure 2.47 Projection of the mordenite framework along the [001] direction. The different positions of the T- and 0-atoms are labeled. Reproduced from Ref. (597).

For example, a mordenite framework inverted (MFI)-type membrane is capable of producing a hydrogen flux that is around 1—2 m (STP)/m h bar (Caro, Noack,... 

Amorphous metallic particles, containing some boron, have been generated in a mordenite matrix by reducing the ion-exchanged M -mordenite (M = Fe, Co, Ni) at ambient temperature with sodium borohydride [96Z1]. The Ni-B particles have a smaller size (20...40 nm) compared to the Co-B (70... 120 nm) and Fe-B (140.. .200 nm) ones. The Ni-B particles are deposited in defect pores within the mordenite framework, while the Co-B and Fe-B particles are deposited on the external surfaces. The differences seem to arise owing to an easier reducibility of Ni compared to Co or Fe and a reduction of Ni in solid, but Co and Fe in solution [96Z1]. 

A complete description of the peculiarities of TS-1 material and catalysts based upon it is not the objective of this chapter. An abundance of high-quality papers concerning TS-1 are available, as are papers on related materials, syntheses, characterizations and applications. " However, a few words are needed. Incorporation of titanium, in a tetrahedral coordination, into high-silica molecular sieve frameworks is the basis of the exceptional catal3hic properties of the material. By using a mental model, if an all-silica MFl framework (mordenite framework inverted, eg. silicalite-1, S-1) is the host of atomically dispersed titanium, we are in the presence of a TS-1 material. 

Schlenker, J. L., Pluth, J. J., Smith, J. V. (1979). Positions of cations and molecules in zeolites with the mordenite framework. 9. Dehydrated H-mordenite via acid exchange. Materials Research Bulletin, 14, 849. 

Figure 8 NH4+Z surface complex eight-ring cluster embedded into the mordenite framework...

Besides the classical Si and Al-containing zeolites, there is an ongoing search toward other Lewis acidic zeolites and other microporous materials suitable for this reaction. Taaming et al. made a comparison between beta zeolites substituted with Al, Sn, Zr, and Tl. As with the homogeneous catalysts, this comparison pointed to Sn-based catalysts as extremely selective for this reaction. The authors obtained lactic acid and lactate yields of 90% and >99% at 125 and 80°C, respectively, with an Si Sn ratio of 125 [67]. Since then, numerous reports were published including Sn-montmorillonite [68], mesoporous Sn-MCM-41 (Mobil Composition of Matter) [69,70], Sn-MFI (Mordenite Framework Inverted) [70,71], Sn-deAl-beta [72], Sn-SBA-15 (Santa Barbara Amorphous type material) [70], Sn-MWW (Zeolite Framework Type M-22)... 

Mordenite Framework Inverted (MFI) zeolite membranes were synthesized on the inner surface of a-alumina tubes (Pall Corp.) from an aluminum-free precursor solution containing Si02, NaOH, H2O, and template tetrapropylammonium hydroxide (TPAOH) by in situ hydrothermal crystallization at 453 K for 20 h (Tang et al. 2009). The resultant zeolite membrane had a thickness of 2-3 xm. The membrane surface was modified by the in situ catalytic cracking deposition of methyl-diethoxysilane (MDBS) molecules at the sites of [(tSi-0")H ] whereas MDBS vapor was carried by an equimolar H2/CO2 mixture flowing over the membrane surface at a pressure of 1.5 bar and a temperature of 723 K. 

The morphological quality of zeolite membranes can be evaluated using different techniques. The thickness and morphology of the zeolite films are evaluated using scanning electron microscopy (SEM). In particular, a cross-sectional view shows the thickness of the zeolite layer on the support and the top view shows the size and also the shape of the crystals. Figure 6.1 shows the top view of a supported mordenite framework inverted (MFI) zeolite membrane. 

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