Pentasil zeolite

FIGURE 1.9. Schematic diagram of one layer of a pentasil zeolite structure showing how the framework is built up from the D5R units. (From ref. 27, reprinted with permission.) 

FIGURE 1.11. Comparison of adsorption equilibrium isotherms for water, oxygen, and n-hexane on NaX zeolite and silicalite. (From ref. 26, reprinted by permission from Nature, 271, 512. Copyright 1978 Macmillan Journals Limited.) 

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Sticking with nylon production, high-silica pentasil zeolites are used by Sumitomo to overcome environmental issues associated with the conversion of cyclohexanone oxime to caprolactam (Chapter 1, Scheme 1.4). 

The majority of intrazeolite photooxygenations have been conducted in NaY,84 85 however, one study in the pentasil zeolite ZSM-5 demonstrates that steric confinement effects can play important roles.84 A comparison of the reactions of a series of tri-substituted alkenes in isooctane, NaY, and in ZSM-5 is given in Fig. 21. The reactions... 

One of the earliest direct bonuses of imaging zeolitic catalysts by HRTEM was the discovery (10) that the nominally phase-pure ZSM-5 (structure code MFI) contained sub-unit-cell coherent intergrowths of ZSM-11 (MEL). It soon became apparent (46) that, depending on the mode of synthesis of these and other pentasil (zeolitic) catalysts, some specimens of ZSM-5 contained recurrent (regular) intergrowths of ZSM-11. It also emerged that intergrowths of offretite and erionite are features of both nominally phase-pure erionite and of pure offretite and of many members of the so-called ABC-6 family of zeolites (47). 

The discovery of the new class of high-silica zeolites "pentasil" during the last decade has attracted considerable interest due to the important applications of these zeolites in catalysis. The best known member of this family of zeolites is ZSM-5, developed in the Mobil laboratories. The unusual properties of pentasil zeolites have rekindled the interest in other high-silica zeolites, prepared by dea-lumination of low-silica zeolites. In this paper we shall review the preparation methods of aluminum-deficient zeolites, and shall discuss the properties of these materials, with emphasis on recent advances in their characterization. 

Since the actual role of the various organics in directing specific zeolitic structures remains confusing or at least obscure, we have tried to explain the nature and the structure of the different pentasil zeolites synthesized under identical experimental... 

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

Titanium in the framework of pentasil zeolites induces oxygenation activity with diluted hydrogen peroxide as oxidant, thus constituting a new catalytic system. 

The first in situ MAS NMR investigation of the synthesis of MTBE on acidic zeolites was performed by Mildner et al. (228) under batch reaction conditions. In this investigation, the temperature-jump MAS NMR technique (stop-and-go experiment, see Section III.A) was applied to characterize the reaction dynamics under non-equilibrium conditions on a boron-modified pentasil zeolite ( si/... 

Ipatieff and coworkers observed first that A1C13 catalyzes the destructive alkylation of aromatics with branched alkanes.179 For example, rm-butylbenzene (35%), p-di-rm-butylbenzene (25%), and considerable isobutane are the main products when benzene is reacted at 20-50°C with 2,2,4-trimethylpentane. Toluene and biphenyl are alkylated at 100°C in a similar way.180 Straight-chain alkanes required more severe reaction conditions. n-Pentane reacted at 175°C to yield 8% propylbenzene, 25% ethylbenzene, and 20% toluene.181 Phosphoric acid afforded similar products at higher temperature (450°C).182 Pentasil zeolites and dealumi-nated pentasils have been found to promote alkylation of benzene with C2—C4 alkanes to form toluene and xylenes.183,184... 

A uniquely high degree of terminal (methyl) selectivities in photochlorination of n-alkanes adsorbed on pentasil zeolites was reported.125 Monochlorination at the terminal methyl group was found to be a function of conversion, water content, Si/Al ratio of the zeolite, and loading of the alkane. 

Since isobutylene is a very reactive olefin, its oligomerization can be promoted by almost any electrophilic catalyst. More recently fluorinated alumina,6 cation-exchange resins,7 benzylsulfonic acid siloxane,8 pentasil zeolites,9 and perfluori-nated resinosulfonic acids10 were studied. Some of these catalysts may bring about improved oligomerization. 

As it was shown in the case of pentasil zeolites (MOR, FER, MFI), UV-VIS-NIR DR spectroscopy and UV-VIS emission spectroscopy appear to be extremely powerfiill tools for the characterization of transition metal ions in molecular sieve matrices [1,5]. The aim of this study is to employ this promissing and powerfull technique for the characterization of siting of metal cations exchanged into the (A1)MCM-41 matrix. 

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