X and Y zeolites

Bronsted acid sites in HY-zeolites mainly originate from protons that neutralize the alumina tetrahedra. When HY-zeolite (X- and Y-zeolites... 

The zeolites with applications to FCC are Type X, Type Y, and ZSM-5. Both X and Y zeolites have essentially the same crystalline structure. The X zeolite has a lower silica-alumina ratio than the Y zeolite. The X zeolite also has a lower thermal and hydrothermal... 

The breakthrough in FCC catalyst was the use of X and Y zeolites during the early 1960s. The addition of these zeolites substantially increased catalyst activity and selectivity. Product distribution with a zeolite-containing catalyst is different from the distribution with an amorphous silica-alumina catalyst (Table 4-3). In addition, zeolites are 1,000 times more active than the amorphous silica alumina catalysts. 

Catalytic cracking with faujasite zeolites X and y zeolites... 

Zeolite structures are designated by a three capital-letter code, for example, FAU stands for the faujasite structure, to which the well-known X and Y zeolites belong. A very useful short notation is used for the description of the pore system(s) each pore network is characterized by the channel directions, the number of atoms (in bold type) in the apertures, the crystallographic free diameter of the apermre (in A), asterisks (1, 2, or 3) indicating whether the systems is one-, two-, or three-dimensional. To completely specify the pore system, the eventual presence of cages (or channel intersections) should be indicated, along with their... 

Martra and coworkers studied low-temperature CO and room-temperature CO2 adsorphon on Na- and Ba-exchanged X and Y zeolites [138]. They were able to determine from the CO adsorphon IR data that Ba ions located in the Sn sites in both X and Y zeolites exhibit higher Lewis acid strength compared to Na ions in the same sites. Furthermore, the Lewis acid shength of both Ba and Na ions was dependent on the framework aluminum content of the zeolite. Using CO2 as a probe, they found that subshtuhng Na with Ba caused a reduchon in the basicity of the framework oxygens in proximity to the cahons. 

Table 6.7 Correlation of exchanged X- and Y-zeolite Si , values to PX/MX, PX/OX selectivity.

Suntornpun, R. (2002) Acid-base interaction between Cs aromatics and X and Y zeolites. M.S. Thesis in Petrochemical Technology. The Petroleum and Petrochemical College, Chulalong-kom University, Bangkok, Thailand. 

As mentioned above, the main types of zeoHtes in industrial catalytic application today are Zeolite Y (FAU) and its variants, ZSM-5 and SUicahte (MFI), Mordenite (MOR) and Beta (BEA). After the first commercial synthesis of X and Y zeolites in the mid- to late 1940s by workers at the Union Carbide Corporation [21, 22],... 

Because BaO/NaX zeolite catalysts exhibited the best performance, further investigations have been carried out recently to characterize the oxidative methylation of toluene catalyzed by BaO-modified X- and Y-zeolites, mordenite, ZSM-5, sil-icalite, and ALPO4-5 (230). The authors found that activity and basicity of BaO-modified zeolites and zeolite-like catalysts depend on both the structural type and composition. Thus, for samples of the same structural type (BaO/NaX zeolite. 

Co and Cu exchanged X and Y zeolites catalyze the decomposition of t-butyl hydroperoxide with generation of t-butoxy and t-butylperoxy radicals. When this decomposition is performed in the presence of olefins, such as cyclohexene or 1-octene, the corresponding epoxides are formed with selectivities ranging from 10 to 50% based on decomposed t-butyl hydroperoxide... 

A comparative study with various types of zeolite showed that Cs-exchanged X and Y zeolites were active for toluene alkylation but primarily catalyzed the decomposition of methanol to CO.431 L and Beta zeolites, in turn, were less active and required higher reaction temperature but were much more selective, providing only very little CO. Adding boron to Cs-exchanged zeolites promotes the alkylation reaction 432 It appears that boron reduces the decomposition of methanol to CO without inhibiting active sites for side-chain alkylation. 

This paper presents some data relating to these aspects which have been obtained in the course of an extensive experimental study of the ion-exchange behavior of transition-metal ions in X and Y zeolites. 

Tn the past four years there has been great interest in how the variation A of the silicon aluminum ratio of zeolites affects their catalytic and sorptive properties. Ward (1) and Tsutsumi et al. (2) found that catalytic activity increased with increase in the silicon aluminum ratio of X and Y zeolites. As the Al content decreases, the interaluminum distance increases, and the cations or protons present experience weaker electrostatic shielding and form strong Bronsted acids (3). 

Information published during thepast few years about the faujasite class of zeolites indicated that they present a possibly unique system in which the necessary conditions might be met. Sherry (4, 5) reported that rare earths, as compared with alkali or alkaline earth metals, are readily exchanged into Linde X from dilute aqueous solutions, and that they strongly favor the zeolite phase. When such an exchanged zeolite is dehydrated by heating to 350-700° C, the lanthanide ions move into the small pore system (6>, 7) after which they are not readily exchanged back out of the crystal. Smith (8) has reviewed the structure of lanthanide X and Y zeolites. 

The ability of water molecules to promote a reaction depends on many factors. In most cases, zeolites with monovalent cations have low activity. However, the addition of water molecules to X and Y zeolites with monovalent ions increased the isomerization of cyclopropane (63). De-cationized zeolites can be promoted readily with water, and the process is reversible (2, 60, 64). It was shown (2) that the promoting ability of water molecules in faujasites is less when the Si02/Al203 increases. Dealu-minated faujasites are even more difficult to promote. For erionite and mordenite the maximum effect of water was observed only after treatment with liquid water and subsequent heating (2). The effect of water on zeolites saturated with polyvalent cations is less pronounced (65, 66, 67). However, the presence of multivalent cations stabilizes the catalytic activity. Water and alcohols were reported to promote ion exchanged zeolites for n-pentane isomerization (68) and n-hexadecane hydrocracking (69). 

Ward (, 6) determined the acidity of several transition metal X and Y zeolites by infrared spectroscopy but could find no simple relationship between the proton acid concentration and physical parameters of metal ions or catalytic activity for o-xylene isomerization. 

It is necessary to mention that observed VIS spectra of the Co those reported for pentasil containing zeolites (with deformed six-member rings present in the framework) and different from the spectra of the Co2+ ions located in A, X and Y zeolites [1,5,8,9], It indicates that deformed six-member rings are present in the structure of MCM-41, but the confirmation of this suggestion requires further detailed study. 

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