X, ZEOLITE

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... 

Deuterium NMR has recently been used to study molecular motion of organic adsorbates on alumina (1.) and in framework aluminosilicates (2). The advantage of NMR is that the quadrupole interaction dominates the spectrum. This intramolecular interaction depends on the average ordering and dynamics of the individual molecules. In the present work we describe NMR measurements of deuterated benzene in (Na)X and (Cs,Na)X zeolite. 

A similar effect was observed earlier in [5] for ethene adsorption by X zeolite modified with bivalent cations of Cd and Ca. The C-H stretching bands, which are intense for free ethene, are not detectable at low pressure, while the normally forbidden C-H deformation and C=C stretching bands are the strongest in the spectrum. Further, ethene is weakly adsorbed by monovalent cations such as K, Na or Li and the relative intensities of C-H stretching bands are very strong. 

Reactions with salts. This procedure is more limited and is illustrated by the use of chromium chloride solutions under reflux for partial dealumination of Y and X zeolites (19), as well as of erionite (20). It is assumed that in this case a partial substitution of chromium for aluminum takes place, leading to the formation of Si-O-Cr bonds in the framework (19). Up to 40 percent of aluminum was removed by this method. Zeolites can also be dealuminated with solutions of ammonium fluorosilicate (107). 

Many types of zeolites are known but only a rather small number of zeolites are used in catalysis. In this section, the most important zeolites will be introduced. We will focus on the most commonly used types which are Zeolite X, Zeolite Y, ZSM-5, and Zeolite Beta. Apart from these, a couple of other zeolites, e.g., Mordenite or Zeolite L, are also used for specific reactions but they are produced on a smaller scale. Most of these zeolites have a remarkable thermal stability and can be heated to a temperature of 600°C without structural damage some of them resist even temperatures of 800 to 1000°C. 

A Na-X zeolite (cubic symmetry) has an XRD pattern as shown below. Calculate the lattice constant a of this zeolite from the 20 positions of the reflections. The wavelength of the x-rays is X = 0.154056 nm (Cu Ka radiation). 

ESR and ESEM studies of Cu(II) in a series of alkali metal ion-exchanged Tl-X zeolites were able to demonstrate the influence of mixed co-cations on the coordination and location of Cu(II) (60). The presence of Tl(l) forces of Cu(II) into the -cage to form a hexaaqua species, whereas Na and K result in the formation of triaqua or monoaqua species. In NaTl-X zeolite, both species are present with the same intensity, indicating that both cations can influence the location and coordination geometry of Cu(II). The Cu(II) species observed after dehydration of Tl-rich NaTl-X and KT1-X zeolites was able to interact with ethanol and DMSO adsorbates but no such interaction was observed with CsTl-X zeolites. This interaction with polar adsorbates was interpreted in terms of migrations of the copper from the -cages. 

M. Che, M. Richard, and D. OUvier ferromagnetic resonance study of dispersed nickel particles prepared by reduction of nickel ion-exchanged X-zeolites by hydrogen molecules or hydrogen atom beams, J. Chem. Soc. Faraday Trans. 176,1526-1534 (1980). 

Synthetic forms Beryllophosphate X, Li-LSX, LZ-210, SAPO-37, siliceous Na-Y, zeolite X (Linde X), zeolite Y (Linde Y), zincophospate X... 

Flanigen monitored the changes in the IR spectra that occur during the synthesis of NaX zeolite from a sodium aluminosilicate gel. The appearance of absorption bands due to the formation of structural units in the zeoUte as the crystallization of NaX proceeded were observed [93]. In particular, the growth of a band around 575 cm indicated the formation of double six-rings which is one of the structural sub-units of X zeolite. 

McCulloch, B. and Gatter, M.G. (1991) Process for extracting meta-dichlorobenzene from isomer mixtures with mixed alkali metal exchanged X zeolite adsorbents. U.S. Patent 4,995,380. 

Barthomeuf, D.M. (1985) Process for separating ethylbenzene from xylenes by selective adsorption on a cesium substituted X zeolite. U.S. Patent 4,593,149. 

Furlan, LT., Chaves, B.C., and Santana, C.C. (1992) Separation of liquid mixtures of p-xylenes and o-xylenes in X zeolites the role of water content on the adsorbent selectivity. Ind. Eng. 

Table 6.6 Durene/isodurene selectivity as a function of X-zeolite exchanged cation.

J.A. (1998) Influence of the activation temperature on the physical properties and catalytic activity of La-X zeolites for isobutane/n-butene alkylation. Micropor. Mesopor. Mater., 22, 379-388. 

Blower, C. J., Smith, T. D. The gas-phase decomposition of nitromethane over metal ion-exchanged sodium Y zeolite and sodium X zeolite. Zeolites, 1993, Volume 13, Issue 5, 394-398. 

Vedrine et al. (102a) have reported a different type of motion for 02 in a Ce-X zeolite which is characterized by unusual parameters gt = 2.0242, g2 = 2.0208, g3 = 2.0112, and At = 24, A2 = 66, A3 = 12 G. However, inspection of the published spectra indicates that A, and A3 are difficult to estimate. The two oxygens are apparently equivalent and the spectrum is tentatively interpreted in terms of a rotation of 02 about an axis perpendicular to the internuclear axis at 77 K, i.e., the y axis in Fig. 4. This is difficult to reconcile with the observed orthorhombic g and A tensors, which are not averaged. A rotation of 02 around the internuclear axis has also been reported by Breysse et al. (62) for 02 with equivalent nuclei adsorbed on Th02. The gxx and gyy components, which are distinct at 77 K, are averaged to gL = (gxx + gyy)/ 2 at 298 K and this is explained in terms of a rotation around the internuclear z axis. The l70 hyperfine tensor, however, is not completely averaged, ff one assumes that Ayy is zero at 77 K, as for most oxides (Appendix B), then Ayy and Axx should average to A = (Axx + Ayy)f2 = 37.5 G at 298 K. This value is substantially different from the experimental one of 65 G reported by the authors (62). 

Rb+- and Cs+-impregnated X zeolites were found to exhibit the highest activity and selectivity in these transformations. A CsX zeolite treated with boric acid, for example, gave better than 50% overall selectivity in the formation of styrene and ethylbenzene (410°C, 60% conversion).275 Treatment of these catalysts with copper or silver nitrate resulted in further improvements in catalyst performance.276 The promoting role of these metals was suggested to be their involvement in dehydrogenation of methyl alcohol. 

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