Pentasil zeolites using organics

Table VIII. Characteristics of some pentasil zeolites obtained from synthesis B using various organic bases or cations (adapted from ref (25), by permission).

Table II. The different types of organic compounds, which can be used for the syntheses of pentasil zeolites...

Amorphous silica-alumina was prepared by both co-precipitation as well as stepwise precipitation techniques(9). Zeolite of pentasil variety was synthesised under hydro-thermal conditions using organic bases like TPAOH as templates following the procedure as described in (10). Zn modified ZSM-5 was prepared as follows ... 

In the last 20 years, the use of zeolites in the organic synthesis of intermediate products and fine chemicals has made rapid developments [4]. Especially pentasil zeolites have been used with great success. The syntheses can involve a whole series of steps, some of which are quite complicated. An overview is given in Table 7-10. 

Over the past ten years, remarkable and rapid progress has been made in the use of zeolites, particularly pentasil zeolites in the organic synthesis of intermediates and fine chemicals [14 - 24]. This new area represents a second promising development in zeolite catalysis in addition to refinery technology and petrochemistry, which continues to be of great economic importance. 

Zeolite ZSM-5, as a member of the family of pentasil zeolites, has aroused tremendous interest after its first discovery by the research group of Mobile Company in the year 1972 [1]. With its adjustable framework A1 content (from 0 to about 8A1 per unit cell), two dimensional micropore channels (0.55 nm x 0.54 nm Fig. la), sinusoidal pore geometry along c axis (Fig.lb) and easy insertion of hetero-T atoms, this material plays an important role in many of crucial catalytic processes such as hydro-cracking, de-waxing, alkylation, etc., [2-5] as well as in separation of organic compounds with different sizes and shapes [6]. In the case when zeolite ZSM-5 was used as catalyst, most of reactions are diffusion-controlled [7]. This means that the product distribution largely depend on the nature and location of active sites in the crystalline framework of catalyst. Thus, the increase of the... 

Specific structure-directing effects of some organic bases or cations When in the procedure BT Pr N is replaced by other organics, various pentasil-type zeolitic precursors are formed. It appears that specific zeolites are formed only when quaternary ammonium salts are used, their nature (structure) being essentially dependent on the length of the alkyl chains pure ZSM-8, ZSM-5 and ZSM-11 are obtained respectively with Et N+, Pr N+ and Bu N cations. TG data indicate that the latter fill nearly completely the zeolitic channel system (Table VIII). 

Table I. Organic compounds, which were mostly used in syntheses of zeolites of pentasil-type. Abbreviations are TPA for te-trapropylammonium cation, TEPA for triethylmonopropylam monium cation, TEA for tetrabutylanmonium cation, TBP for tetrabutylphosphonium cation, TPA for tripropylamine and CgDN for hexamethyldiamine...

The silicon-rich pentasils are mainly synthesized in the presence of organic cations. Their open structures seem to be formed around hydrated cations or other cations such as NRJ. In particular, templates such as tetrapropylammonium hydroxide are used, and are of decisive importance for the crystallization of the zeolite structures. The C, H, and N of the tertiary ammonium cation is removed in the subsequent calcination of the microcrystalhne product. 

The search for new selectivity promoters will be improved, and more and more unusual elements such as Sc, Y, Ga, Hf, and Ta will be used. The zeolites have major potential, and it is expected that especially the pentasils and the metal-doped zeolites will achieve wider application in organic syntheses. The industrial application of aluminosilicates and sheet sihcates is also imminent. 

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