Zeolites future applications

Future applications will also be considered, in particular with respect to the use of these techniques combined with the NMR of other nuclei (Na, Al, Si) for the investigation of zeolite synthesis mechanisms (12-14). 

Zeolitic membranes is still a young research area with a lot of promise for future applications. A long road, however, has to be traveled before they will become a commod-... 

This contribution briefly highlights current trends in the synthesis of new types of zeolite-based molecular sieves showing recent development in this very topical area. We have tried to cover the most important examples of the development of these molecular sieves, in which a high potential for future applications of molecular sieves is expected. At the end of... 

Future applications of adsorption are limited by the availability of new and better sorbents. Ideally, the sorbent shonld be tailored with specific attributes to meet the needs of each specific application. Development of better sorbents can also improve the performance of the cnrrent commercial processes. A good example is the invention of the LiX (Si/Al = 1) zeolite (Chao, 1989). Air separation has been performed by pressnre swing adsorption, and the generic sorbents 13X (i.e., NaX) and 5A (i.e., CaA) zeolites were nsed prior to this invention. By switching from NaX to LiX (Si/Al = 1), the prodnctivity of oxygen increased instantly by 1.4-2.7 times and the power consnmption reduced by 21-27% depending on the operating conditions nsed (Leavitt, 1995). 

Sol-gel method (Zhang, 2002), replica process (Imai, 1999), and template approach (Kobayashi, 2000) have been reported as the procedures for the preparation of Ti02 nanotubes, and hollow tubes in the diameter of over 100 nm have been prepared. In practice, these materials have not been successfully commercialized as photocatalyst probably due to difficulties of its durability, costs, etc, however morphological approach may be effective in future application to air and water purification in light of its large surface area and unique structure like zeolite. 

A next-future application of MOFs is predicted for MOF-oiganic polymer-based mixed matrix membranes in hollow fiber or spiral wound geometry. Established membrane production technologies such as hollow fiber spinning or foil casting can be used for the preparation of mixed matrix membranes. Further, MOFs match much better with organic polymers than zeolites, for example, even if the latter have been hydrophobized, such as by silylation. 

Numerous applications of organic zeolites have been proposed. In the future they could serve as catalytic sites and miniature reaction chambers as well as storage compartments and stationary chromatographic phases to be used for the... 

Volume 24 Zeolites Synthesis, Structure, Technology and Application. Proceedings of an International Symposium, Portoroz-Portorose, September 3-8, 1984 edited by B. Drzaj, S. Hocevar and S. Pejovnik Volume 25 Catalytic Polymerization of Olefins. Proceedings of the International Symposium on Future Aspects of Olefin Polymerization, Tokyo, July 4-6, 1985 edited by T. Keii and K. Soga... 

All these aspects were thoroughly discussed by lecturers and participants during the round table organized during the Poitiers School on The Future Trends in Zeolite Applications . Special emphasis was placed on the role played by the sites at the external surface (pockets, etc.) or at the pore mouth, by mesopores, extraframework aluminum species, as well as by the polarity of reactant and product molecules. Other important topics dealt with the remarkable catalytic properties of BEA zeolites for fine chemical synthesis, the potential of mesoporous molecular sieves, zeolitic membranes and the role of combinatorial catalysis in the development of zeolite catalysts. It is our hope that the fruits of these discussions will appear in the literature or even better as new and environmentally friendly products or processes. 

Within the vast group of zeolite catalysts, the focus herein is on one subgroup materials that contain reduced particles of a transition metal or several transition metals dispersed inside zeolite cavities. Present applications and the future potential of these materials in the petroleum and petrochemical industries have been reviewed by Minachev and Isakov (14), Kouwen-hoven (15), Uytterhoeven (16), Maxwell (17,18), Delafosse (79), and... 

The specific properties of zeolites, coupled with the separation properties of membranes, open the field to many areas of research for the future. This explains why the preparation and application of zeolite membranes is the subject of intensive research. By combining their adsorption and molecular sieving properties, zeolite membranes have been used for the separation of mixtures containing nonadsorbing molecules, different organic compounds, permanent gas-vapor mixtures, or water-organic mixtures. 

S.T. Sie, Past, Present and Future Role of Microporous Catalysts in the Petroleum Industry. In Advanced Zeolite Science and Applications (J. Jansen, M. Stocker, H. Kaige, and J. Weit-kamp, eds.). Studies in Surface Science and Catalysis no. 85. Elsevier, Amsterdam, 1994, pp. 587-631. 

The preliminary studies of the solid-state interaction between niobium oxide and Y-type zeolites do not provide information about the location of the niobium cations in the zeolite structure or whether niobium is partially introduced into the zeolite lattice as well. Future studies with the application of NMR spectroscopy should answer this question. 

Strength (FLS) empirical approach are discussed in Section 3 as methods for determining the molecular structures of metal-oxide species from their Raman spectra. The state-of-the-art in Raman instrumentation as well as new instrumental developments are discussed in Section 4. Sampling techniques typically employed in Raman spectroscopy experiments, ambient as well as in situ, are reviewed in Section S. The application of Raman spectroscopy to problems in heterogeneous catalysis (bulk mixed-oxide catalysts, supported metal-oxide catalysts, zeolites, and chemisorption studies) is discussed in depth in Section 6 by selecting a few recent examples from the literature. The future potential of Raman spectroscopy in heterogeneous catalysis is discussed in the fmal section. 

To conclude this review, I highlight three topics within heterogeneous catalysis for which DFT-based calculations appear poised to allow rapid progress in the near future, the development of catalysts for use in reversible hydrogen storage, electrocatalysis for fuel cell applications, and catalysis in zeolites. 

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