Catalytic Properties of the Zeolites

In the case of a catalytic membrane reactor (CMR), the membrane is (made) intrinsically catalytically active. This can be done by using the intrinsic catalytic properties of the zeolite or by making the membrane catalytically active. When an active phase is deposited on top of a membrane layer, this is also called a CMR because this becomes part of the composite membrane. In addition to the catalytic activity of the membrane, a catalyst bed can be present (PBCMR). The advantages of a CMR are as follows ... 

CoSalen Y carries oxygen as a cargo.72 The catalytic properties of the zeolite-encapsulated metal complexes depend mainly on the complexed metal atoms, which are used usually as oxidation catalysts but other applications are also beginning to emerge. The zeolite-encapsulated catalysts can be regarded as biomimetic oxidation catalysts.73 In liquid-phase oxidation reactions catalyzed... 

Recent work by Rabo et al. (57) opens new possibilities for controlling the activity and selectivity of zeolite catalysts. Occlusion of various guest molecules into the sodalite cavities of Y zeolites can significantly change the catalytic properties of the zeolites for carbonium-type reactions. Anions of occluded salts are located close to the center of the sodalite cavity and strongly influence the arrangement of cations in the faujasite lattice and hence the catalytic activity. 

In the present work, the reaction selected to examine the effect of altering the cation on the catalytic properties of the zeolite was n-butene isomerization. This reaction has a highly selective character and does not require extreme conditions. The rate of 1-butene disappearance gives a convenient measure of activity, and the initial product ratio (cis-2-hutene/trans-2-hutene) can provide a guide to the nature of the reaction mechanism (7). 

These shape-selective zeolites can be converted into a catalytically active form by ion exchange since K has a deleterious effect on the catalytic properties of the zeolite. Peterson, Helferich and Blytas (9a) and Sherry (9b) found that with ion exchange below 300°C the K content of erionite could not be reduced below 1.95 weight % or 2 K ions per unit cell without impairing their crystal structures. 

However, the channel-modification method has its own disadvantages. Because the modifier interacts with the whole channel system, then, besides the pore diameter, the properties of the zeolite internal surface can also be varied. This may affect the adsorption and catalytic properties of the zeolite involved. In addition, because a large amount of modifier enters the zeolite channels, the void volume of the zeolite becomes smaller and consequently the adsorption capacity and the space available for reaction are reduced accordingly. 

In this paper, the activity and selectivity of pure FAU zeolite samples NaX, NaY, HFAU and NaHFAU(Y) for transformation of traces (1000 ppm) of dichloromethane in presence of air with 4% steam were determined. With all zeolites, dichloromethane can be transformed into formaldehyde plus chlorhydric acid then into CO and CO2. The catalytic properties of the zeolites will be discussed in the light of their physicochemical properties. 

B. W. Burbridge, I. M. Keen, and M. K. Eyles, Physical and Catalytic Properties of the Zeolite Mordenite, preprints of the 2nd International Conference on Molecular Sieves and Zeolites, pp. 400-409 (1970). 

Since then chemists worldwide have prepared numerous tailor-made modified zeolites, and the synthetic potential for the production of organic intermediates and high-value fine chemicals is enormous. How can the success of this new class of catalysts in industry and academe be explained It is due to the outstanding catalytic properties of the zeolites. No other class of catalysts offers so much potential for variation and so many advantages in application. Their advantages over conventional catalysts can be summarized as follows ... 

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