Heterogeneous catalysis synthetic zeolites

This encouraging preliminary synthetic work needs to be followed by a detailed structural analysis of the Pc network materials. In particular, the potential nanoporosity of the 3-D system is to be explored using nitrogen adsorption measurements. Should a high surface area be obtained, these materials would offer an interesting alternative to zeolite encapsulated Pcs for efficient heterogeneous catalysis. 

Heterogeneous catalysis in heterocyclic chemistry 84MI6. Transformations of heterocycles over synthetic zeolites 81H(16)1755. 

New types of mesoporous molecular sieves (their first synthesis opened a new subfield of molecular sieve chemistry) have been prepared over the last ten years by new synthetic approaches, different from those known for zeolites. The variety of the synthetic procedures described and the differences in the textural properties due to different synthetic procedures, as well as to the high temperature treatment, give evidence that mesoporous molecular sieves of different chemical compositions are very interesting materials not only in materials science. They could be important also for the application as heterogeneous catalysis, support for immobilization of homogeneous catalysts, adsorbents or materials for synthesis of new types of inclusion compounds. 

Heterogeneous catalysis offers an opportunity to achieve selectivity based on molecular size and shape. Excellently suited for this purpose are zeolites with their crystal structure of regularly repeating unit cells with voids large enough to accommodate reactants. For catalysis, natural zeolites have been large replaced by synthetic products. Table 9.3 lists structural information on some of the most common natural and synthetic materials. 

Heterogeneous catalysis The best known catalyst is titanium silicate - (TS-1) a synthetic zeolite of ZSM family which does not contain any aluminium and in which titanium atoms replace some silicium atoms within the crystal lattice (Ti/Si 5 %) (ref. 3). A process based on this catalysis is used in Italy (ref. 4). Although its performance levels are good, and the HQ/PC ratio can be modified (ref. 5) the high cost of the catalyst and its uncertain lifetime are the major handicaps preventing its extension. 

Owing to the great interest in the argument, minireviews have been published on the use of solid catalysts in Friedel-Crafts acylation. Kouwen-hoven and van Bekkum, in a chapter of the Handbook of Heterogeneous Catalysis, faced the basic problem of the use of zeolites in the reaction. A further essential overview of the same argument was reported by Metivier in Fine Chemicals through Heterogeneous Catalysis Furthermore, Bezouhanova described the synthetic aspects of the zeolite-catalyzed preparation of aromatic ketones. ... 

It is well known that zeolites containing a high proportion of five-membered rings of tetrahedra in their framework are widely used in heterogeneous catalysis these include synthetic ZSM-5, ZSM-11, beta, theta-1, NU-87, the synthetic analogues of natural mordenite and ferrierite and the natural zeolite heulandite. 

Although the homogeneous catalyst systems have been successfully applied in commercial practice, some intrinsic problems associated with catalyst separation remain. This has led to considerable interest in the development of a suitable heterogeneous analog. Rhodium compounds have been heterogenenized on substrates such as carbon (197), alumina (198, 199), and synthetic polymers (200). More recently, zeolites have also attracted quite some attention as a support material for carbonylation catalysis, as is discussed later. 

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