Zeolite as catalysts

J. A. Johnson and A. R. Oroskar, "Sorbex Technology for Industrial Scale Separation," iu H. G. Karge and J. Weitkamp, eds.. Zeolites as Catalysts,... 

Zeolites as catalysts and promoters in organic bromide synthesis and conversion In the second part of this contribution the use of zeolites in the synthesis and conversion of organic bromides will be discussed (ref. 16). 

Volume 46 Zeolites as Catalysts, Sorbents and Detergent Builders. Applications and... 

In fact, the selective catalytic removal of NO in presence of excess oxygen remains a challenge. Most of the cunent studies involve C1-C4 hydrocarbons as reductants and zeolites as catalysts, among which Cu-exchanged MFI zeolites are considered as one of the most active [2]. The reductant shows a complex influence in this reaction it has been thus reported that a Cu/Zr02 catalysts are active with pro-pene but show low activity with propane as reductant [3]. For a practical use reduction by higher alkanes would be attractive, siiKe it would be easier to handle in a vehicle. 

Only one publication describes the use of a zeolite as catalyst in the hydroamina-tion ofalkynes. MeNH2 reacts with 1-propyne over a Zn(ll) ion-exchanged Y zeolite (ZnY) at room temperature and atmospheric pressure to give a mixture of N-iso-propylidenemethylamine and N-n-propylidenemethylamine (Eq. 4.58) [238]. 

A. Corma, S. Iborra, S. Miquel, and J. Primo, Preparation of environmentally friendly alkylglucoside surfactants using zeolites as catalysts, J. Catal., 161 (1996) 713-719. 

This side reaction leads to undesirable losses of xylenes. With REHY zeolite as catalyst, disproportionation occurs at a rate comparable to that of isomerization of m-xylene (8), e.g., 14% disproportionation at 16% isomerization. In fact, the product, trimethylbenzene, is postulated as an important intermediate in isomerization (8). 

Figure 4.20 MTG/MTO reaction path and aromatics distribution with different zeolites as catalysts. (Reprinted from C.D. Chang, W.H. Lang, W.K. Bell, Catalysis in Organic Reactions, Molecular Shape-Selective Catalysis in Zeolites, pp. 93-94. Copyright 1981. With permission from Marcel Dekker.)...

There are several means to maximize the yield in the desired monoalkylation product high aromatic/alkylation agent ratio, association of a transalkylation unit to the alkylation unit, and use of a shape selective zeolite as catalyst. 

Palm oil has been cracked at atmospheric pressure and a reaction temperature of 723 K to produce biofuel in a fixed-bed microreactor. The reaction was carried out over microporous HZSM-5 zeolite, mesoporous MCM-41, and composite micromesoporous zeolite as catalysts. The products obtained were gas, organic liquid product, water, and coke. The organic liquid product was composed of hydrocarbons corresponding to gasoline, kerosene, and diesel boiling point range. The maximiun conversion of palm oil, 99 wt.%, and gasoUne yield of 48 wt.% was... 

Several publications have been dedicated to the study of In-based zeolites as catalysts in different catalytic processes (e.g., SCR of NO, alkylaromatic transformation, etc.) and the role played by the acidic character in their good performances was followed mostly by IR technique [256-259] or NH3-TPD [260], It was observed... 

A. Endoh, K. Nishiyama, K. Tsutsumi, T. Takaishi, Zeolites as Catalysts, Sorbents and Detergent Builders(Stud. Surf. Sci. Catal., 46), Elsevier, Amsterdam, 1989, p.779. 

M. Bulow, J. Caro, B. Rohl-Kiihn and B. Zibrowius, in Zeolites as Catalysts, Sorbents and Detergent Builders - Applications and Innovations Proc. Int. Symp. Zeolites, Wurzburg, F.R.G., September 4-8, 1988 (H.G. Karge and J. Weitkamp, Eds.) Elsevier, Amsterdam, 1989 Studies in Surf. Sci. and Catalysis, 46 (1989) pp. 505-507. 

A third way of using zeolites as catalysts is to replace the Na ions with other metal ions such as Ni, Pd, or Pt and then reduce them in situ so that metal atoms are deposited within the framework. The resultant material displays the properties associated... 

Cince the catalytic activity of synthetic zeolites was first revealed (1, 2), catalytic properties of zeolites have received increasing attention. The role of zeolites as catalysts, together with their catalytic polyfunctionality, results from specific properties of the individual catalytic reaction and of the individual zeolite. These circumstances as well as the different experimental conditions under which they have been studied make it difficult to generalize on the experimental data from zeolite catalysis. As new data have accumulated, new theories about the nature of the catalytic activity of zeolites have evolved (8-9). The most common theories correlate zeolite catalytic activity with their proton-donating and electron-deficient functions. As proton-donating sites or Bronsted acid sites one considers hydroxyl groups of decationized zeolites these are formed by direct substitution of part of the cations for protons on decomposition of NH4+ cations or as a result of hydrolysis after substitution of alkali cations for rare earth cations. As electron-deficient sites or Lewis acid sites one considers usually three-coordinated aluminum atoms, formed as a result of dehydroxylation of H-zeolites by calcination (8,10-13). 

Feolite catalysts modified by transition metals are interesting and difficult subjects to study. In one of the first studies of zeolites as catalysts, Rabo and co-workers (1) used a zeolite catalyst containing 0.5% platinum for isomerization of n-paraffins. In this reaction the metal-zeolite system acted as a typical representative of the bifunctional catalysts. Studies of zeolites modified by transition metals ( 2, 3, Jf) showed that their polyfunctional properties are determined by the structural and chemical properties of the zeolite and by the state of the metal in it. In this paper we discuss new data on the metal state after reduction as well as the catalytic functions of zeolite catalysts containing nickel and platinum. 

As reported in the literature, the acylation of aromatic hydrocarbons can be carried out by using zeolites as catalysts and carboxylic acids or acyl chlorides as acylating agents. Thus toluene can be acylated by carboxylic acids in the liquid phase in the presence of cation exchanged Y-zeolites (ref. 1). The acylation of phenol or phenol derivatives is also reported. The acylation of anisole by carboxylic acids and acyl chlorides was obtained in the presence of various zeolites in the liquid phase (ref. 2). The acylation of phenol by acetic acid was also carried out with silicalite (ref. 3) or HZSM5 (ref. 4). The para isomer has been generally favoured except in the latter case in which ortho-hydroxyacetophenone was obtained preferentially. One possible explanation for the high ortho-selectivity in the case of the acylation of phenol by acetic acid is that phenylacetate could be an intermediate from which ortho-hydroxyacetophenone would be formed intramolecularly. 

TRIPLE BOND HYDRATION USING ZEOLITES AS CATALYSTS... 

Our current interest in the development of heterogeneous catalysis led us to consider the use of such zeolites as catalysts in the hydration reaction of C =C and C = N triple bonds in liquid phase. 

In recent years, a large body of work emphasized the use of zeolites for production of fine chemicals (refs.1-4). The interests stand in replacement of liquid acids to lower corrosion of equipment and pollution, and to reach specific selectivities. However, the hopes raised up in a rapid development of processes seems restrained nowadays. Many patents claimed zeolites as catalysts but very few have received industrial applications. Actually, basic research on the stability, the origin of deactivation, the regenerability of the catalysts have to be developed. Moreover, fundamental aspects of the mechanism of this new kind of reactions are lacking, in particular, the possibility of radical mechanisms, which are rather scarce with hydrocarbons, but can likely occur when heteroatoms are involved in the reactant. Those were our objectives in the study of the isomerisation of substituted halobenzenes on zeolites (refs.5-7). Indeed this reaction was claimed to occur readily on zeolites (refs.8-9), but it is supposed that no industrial development has followed. 

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