Zeolites microstructure

Q. Probing the Nature of Zeolitic Microstructure by High-Resolution... 

Resulting zeolitised solid has appreciable microporosity and zeolitic microstructure, and shows enhanced cracking of large molecules. ... 

Mallouk and coworkers explored the electrochemistry and photochemical evolution of hydrogen from water using a zeolite modified electrode. Methylviologen (MV ) was encapsulated in platinized zeolite L powder onto which ZifiTMPyP" ) was externally adsorbed (Figure 106). Taking advantage of the zeolite microstructure in an attempt... 

Volume 12 Metal Microstructures in Zeolites. Preparation - Properties -Applications. Proceedings of a Workshop, Bremen, September 22-24,1982 edited by P.A. Jacobs, N.l. Jaeger, P. Jitu and G. Schulz-Ekloff... 

Examples of the unique insights obtained by solid state NMR applications to materials science include the Si/Al distribution in zeolites, the hydrogen microstructure in amorphous films of hydrogenated silicon, and the mechanism for the zeolite-catalyzed oligomerization of olefins. ... 

The application of zeolite membranes in microreactors is still in an early stage of development, and suffers sometimes from unexpected problems arising from template removal [70]. However, several application examples of zeolite membranes in microstructured devices have been demonstrated yielding similar advantages as were to be expected from experiences on the macroscale. Because of the high surface to volume ratio of microreactors, the application of zeolite membranes in these systems has great potential. 

Volume 12 Metal Microstructures in Zeolites. Preparation - Properties - Applications. 

There are many different zeolite structures but only a few have been studied extensively for membrane applications. Table 10.1 lists some of these structures and their basic properties. One of the most critical selection criterion when choosing a zeolite for a particular application is the pore size exhibited by the material. Figure 10.1 compares the effective pore size of the different zeolitic materials with various molecule kinetic diameters. Because the pores of zeolites are not perfectly circular each zeolite type is represented by a shaded area that indicates the range of molecules that may stiU enter the pore network, even if they diffuse with difficulty. By far the most common membrane material studied is MFI-type zeolite (ZSM-5, Al-free siUcahte-l) due to ease of preparation, control of microstructure and versatility of applications [7]. 

For multi-component systems it seems intuitive that single-component diffusion and adsorption data would enable one to predict which component would be selectively passed through a membrane. This is only the case where molecular sieving is observed for all other separations where the molecules interact with one another and with the zeolite framework their behavior is determined by these interactions. Differences in membrane properties such as quahty, microstructure, composition and modification can also play a large role in the observed separation characteristics. In many cases, these properties can be manipulated in order to tailor a membrane for a specific apphcation or separation. 

Dong, J., lin, Y.S., Hu, M.Z.C., Peascoe, R.A., and Payzant, E.A. (2000) Template-removal-associated microstructural development of porous-ceramic-sup-ported MFI zeolite membranes. 

Lower dilution levels did not allow sufficient depolymerlzatlon and higher dilution caused excessive depolymerlzatlon In the aged solutions. Pillared clays prepared from aged dilute solutions had an enhanced microstructure which showed an Increased activity for selectively cracking large molecules to the light cycle oil range. This microstructure Is lost In the presence of steam which also reduces the formation of catalytic coke. Addition of rare earth zeolite to pillared clay can partially overcome the effects of this loss of microstructure. 

Silica is of particular importance because of its use as a stable catalyst support with low acidity and its relationship to zeolite catalysts, which will be discussed in chapter 4. Silicon is an abundant material in the earth s crust and occurs in various forms including silica. Silica is also polymorphous with the main forms being quartz, cristobalite and trydimite. The stable room temperature form is quartz (Si02). Recently, a new family of stable silica-based ceramics from chemically stabilized cristobalites has been described using electron microscopy (Gai et al 1993). We describe the synthesis and microstructures of these ceramic supports in chapters 3 and 5. 

R 22] This microstructured reactor will in the future be supplemented by a hydrocarbon adsorber in order to reach future zero emission regulations. A hydrocarbon adsorber equipped with a ceramic layer of zeolite will adsorb unburnt hydrocarbons during the engine start-up and desorb the gases when the pipe temperature rises above 150 °C which is obtained by the heated converter right behind the adsorber. 

A third possibility for the synthesis of nanomaterials in constrained volumes is the use of molds (Figure 3.1c). Advantages of this method include its simplicity, versatility, and precise control over the shape of the solid, even with intricate forms. An elegant example of this strategy is the preparation of zeolites which precisely replicate the complex microstructure of wood. To do this, Dong et al. [43] infiltrated a zeolite synthesis solution into a wood sample. After the necessary hydrothermal treatment, and subsequent calcination to remove the template as well as the wood, a zeolitic structure was obtained that reproduced with full detail and fidelity the wooden sample used as a mold. 

Lunsford, J. H. In Metal Microstructures in Zeolites Jacobs, P. A. Jaeger, P. Jiru, P. Schulz-Ekloff, G., Eds. Studies in Surface Science and Catalysis 12 Elsevier Scientific Publishing Company Amsterdam, The Netherlands, 1982, 1-13. 

James Wei Perhaps I don t quite understand your terms. Would you consider a zeolite a microstructure catalyst ... 

Many new adsorbents have been developed over the past 20 years including carbon molecular sieves, new zeolites and aluminophosphates, pillared clays and model mesoporous solids. In addition, various spectroscopic, microscopic and scattering techniques can now be employed for studying the state of the adsorbate and microstructure of the adsorbent. Major advances have been made in the experimental measurement of isotherms and heats of adsorption and in the computer simulation of physisorption. 

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