Reactions in Zeolites

Zeolites are naturally occurring minerals found in volcanic rocks where they have been formed by hydrothermal processes. The term zeolite has been introduced by the Swedish mineralogist Cronstedt who gave the name according to the observation of the large amount of water they release upon heating. ZeoUte is indeed derived from the Greek zein (to boil) and Uthos (stone). 

The number of known zeoUtic structures is currently 174 but, according to theoretical work based on these existing stable structures, there might be several million structures available which would be more or less stable. Hence designing a zeolitic material for a 

Molecular Encapsulation Organic Reactions in Constrained Systems Edited by Udo H. Drinker and Jean-Luc Mieusset 2010 John Wiley Sons, Ltd 

In 1999, Tanabe and Hoelderich have reviewed 74 industrial processes ranging from cracking to fine chemical synthesis in which zeolites are used as a catalyst. 

Numerous books and reviews have already been published concerning organic reactions catalysed by zeolites. Due to their pore sizes, their internal shapes and their compositions, zeolites are weU known for their selectivity properties, discriminating reactants, intermediates, transition states or products.  

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Xu T, Munson E J and Flaw J F 1994 Toward a systematic chemistry of organic reactions in zeolites in situ NMR studies of ketones J. Am. Chem. Soc. 116 1962-72... 

Sorption, Diffusion, and Catalytic Reaction in Zeolites L. Riekert... 

It is often said that the property of acidity is manifest only in the presence of a base, and NMR studies of probe molecules became common following studies of amines by Ellis [4] and Maciel [5, 6] and phosphines by Lunsford [7] in the early to mid 80s. More recently, the maturation of variable temperature MAS NMR has permitted the study of reactive probe molecules which are revealing not only in themselves but also in the intermediates and products that they form on the solid acid. We carried out detailed studies of aldol reactions in zeolites beginning with the early 1993 report of the synthesis of crotonaldehyde from acetaldehyde in HZSM-5 [8] and continuing through investigations of acetone, cyclopentanone [9] and propanal [10], The formation of mesityl oxide 1, from dimerization and dehydration of... 

N. Y. Chen, T. F. Degnan, C. M. Smith 1994, Molecular Transport and Reaction in Zeolites, VCH Publishers, New York. 

Clennan, E.L. and Sram, J.P. (1999). Photooxidation in zeolites. Part 2 a new mechanistic model for reaction selectivity in singlet oxygen ene reactions in zeolitic medsia. 

Zhou, W. and Clennan, E.L. (1999). Organic reactions in zeolites. 1. Photooxidations of sulfides in methylene blue doped zeolite Y. J. Am. Chem. Soc. 121, 2915-2916... 

Na - K - Co exchange in Y zeolite. Heterovalent exchange reactions in zeolites generally show an even more pronounced dependency on loading (116-118). Rees (116) observed variations of the selectivity coefficient by a factor 1000 for the Na-Ca and Na-llg exchange in zeolite A at 25 °C. An+exajnple of e treipe variations is shown in fig. 9 for the K -Co and Na -Co selectivities in zeolite Y at 45 °C (117). The exchange... 

In the first chapter, Bates and van Santen summarize the theoretical foundations of catalysis in acidic zeolites. Being the most important crystalline materials used as catalysts, zeolites have been the obvious starting point for applications of theory to catalysis by solids and surfaces. Impressive progress has been made in the application of theory to account for transport, sorption, and reaction in zeolites, and the comparisons with experimental results indicate some marked successes as well as opportunities for improving both the theoretical and experimental foundations. 

Charge and Electron Transfer Reactions in Zeolites Kyung Byung Yoon... 

Lombardo and Bell (1991) reviewed stochastic models of the description of rate processes on the catalyst surface, such as adsorption, diffusion, desorption, and surface reaction, which make it possible to account for surface structure of crystallites, spatial inhomogeneities, and local fluctuations of concentrations. Comparison of dynamic MC and mean-field (effective) description of the problem of diffusion and reaction in zeolites has been made by Coppens et al. (1999). Gracia and Wolf (2004) present results of recent MC simulations of CO oxidation on Pt-supported catalysts. 

Holderich W.F., Organic Reactions in Zeolites, in Comprehensive Supramolecular Chemistry, Ed. Alberti G. and Bein T. (Pergamon, 1996), 671-692. 

The kinetics of reactions in zeolites is conventionally related to the reactant concentrations in the gas phase. Reaction within the pores of zeolites, however, involves adsorption, diffusion of reactants into the pores, reactions of adsorbed species inside the pores, desorption of products, and diffusion of products out of the pores (92). Therefore, intrinsic kinetics based on the concentration of species adsorbed inside the pores is expected to be very useful for catalyst development. TEOM is an excellent technique for measurement of adsorption of reactants under reaction conditions as well as measurement of this adsorption as a function of the coke content (3,88). This technique makes it possible to obtain intrinsic activity of each acidic active site directly and to understand deactivation mechanisms in detail. 

Catalytic oxidation-reduction (redox) reactions in zeolites are generally limited to reactions of molecules for which total oxidation products are desired. One important class of such reactions falls under the category of emission control catalysis. This encompasses a broad range of potential reactions and applications for zeolite catalysts. As potential catalysts one may consider the entire spectrum of zeolitic structural types combined with the broad range of base exchange cations which are known to carry out redox reactions. 

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