Zeolite faujasite

Faujasite is a naturally occurring mineral, having a specific crystalline, alumina-silicate structure, used in the manufacturing of the FCC catalyst. Zeolite faujasite is a synthetic form of the mineral. 

The frameworks of zeolites are formed by fully connected Si04 and A104 tetrahedra linked by shared oxygen atoms as shown in Figure 4.1 (top) for a Faujasite-type zeolite. Faujasite is a zeolitic mineral, which can be found in nature. Synthetic Faujasite-type zeolites are of particular importance in zeolite catalysis as we will see below. 

Figure 2.34 illustrates the MAS NMR spectrum of the zeolite faujasite. Use this figure to determine which Si environments are most likely to be present. 

The influence of the nonuniform character of the interior of zeolites on the photophysics of adsorbed guest molecules has been observed. Pyrene molecules included in zeolite faujasites show both monomer and excimer emission [232,233]. As in the case of silica surfaces, the excitation spectra of the emission corresponding to the monomer and the excimer differ (Figure 36), suggesting that there are at least two independent sites, each responsible for monomer emission and excimer emission. Time-resolved emission studies of pyrene included in Na + -X and Na + -Y (<0.1 molecule per cage) indicate... 

Ramamurthy and coworkers studied the photo-Fries rearrangement of phenyl acetate and phenyl benzoate and photo-Claisen rearrangement of allyl phenyl ether (Fig. 34) included in two types of zeolite (faujasites X and Y and pen-tasils ZSM-5 andZSM-11) [192], The photolysis was performed with the zeolite slurry in either hexane or iso-octane. One of the most remarkable observations is that the product distribution is altered within zeolites from that in isotropic solvent. Furthermore, while in solution, nearly a 1 1 mixture of ortho and para isomers 40 and 41 (Fig. 34) was obtained, within zeolites one is able to direct the photoreaction selectively toward either the ortho or the para products by conducting the reaction either within faujasites or pentasils, respectively (Fig. 34). 

In Figure 2.20, the FAU-type framework, which is congruent with the structure of the natural zeolite, faujasite, and the synthetic zeolites, X, Y, LZ-210, and SAPO-37, is shown [108],... 

The structure of the zeolite faujasite is shown in following figure. In this convention representation the framework structure is shown without depicting, atoms directly. Each line represents an SiOSi or Si O Al connection. Four lines meet at tetrahedral vertices representing the positions of the four-coordinate Si or A1 atoms. Spacefilling models of this zeolite show that the pores can accommodate molecules up to about 750 pm in diameter. 

This way ofitnagining polyhedral linkages can be extended zeohtes X and Y and the natural zeolite faujasite. Here... 

The application of Equations (13)-(20) is illustrated for binary mixtures of ethylene (1) and ethane (2) adsorbed on NaX zeolite (faujasite). The constants for the singlegas adsorption equations of state are given in Tables 1 and 2. The selectivity of NaX for ethylene relative to ethane is a function of temperature, pressure, and the composition of the gas. The selectivity at constant temperature (20 °C) is shown in Figure 3. The selectivity at the limit of zero pressure is the ratio of Henry s constants (Xi/X2=33.7). At constant mole fraction of ethylene in the gas, the selectivity decreases rapidly with increasing pressure. At constant pressure, the selectivity decreases with increasing mole fraction of ethylene in the gas. The selectivity at constant pressure and gas composition decreases with temperature, as shown in Figure 4. Decrease of the selectivity with temperature, pressure, and the mole fraction of the preferentially adsorbed species is typical behavior for binary adsorption. 

It might be desirable to load cesium onto chabazite before mineralization. Chabazite reacts hydrothermally with aqueous cesium chloride to form pollucite, a naturally occurring mineral with cesium trapped in aluminosilicate cages. Reaction of cesium-loaded chabazite with pure water might produce pollucite or the sodium zeolite, faujasite. 

Fig. 18.1. The zeolite faujasite. Si04 tetrahedra are represented in gray, and water molecules and extra-framework cations have been omitted for clarity.

Localization of stationary points along the reaction path for reactions taking place inside the zeolite pores is one of the greatest challenges in zeolite modeling. The reactions of hydrocarbons are particularly difficult to model since the hydrocarbon...zeolite interaction can be dominated by the dispersion interaction that is not properly accounted at the DFT level. Only one example is presented here. Clark et al. investigated the role of benzenium-lype carbenium ion in the bimolecular w-xylene disproportionation reaction in zeolite faujasite.163] The benzenium-type carbenium ion 1 was identified in zeolite catalyst for the... 

A zeolite, faujasite. Note the large channel in the centre of the structure, and the smaller ones surrounding it. Some or all of these channels can be occupied by balancing cations and by molecules. Occupation of these channels by molecules leads to the use of zeolites as catalysts. S... 

The effective diifusivity measurement of gases by tracer-pulse chromatography in porous solids has been extended to include zeolites [faujasites, mordenites, 3A and 5A molecular sieves (35)]. The measured diffusions in this case were a strong function of molecular size. 

TVdTcDaniel and Maher (9) have reported a new form of the zeolite faujasite that is thermally stable at temperatures in excess of 1000°C. This stability is in contrast with other reported hydrogen or decationated faujasites, which are less stable than the cation forms. According to these authors, the conversion of faujasite to the hydrogen form leads to a partial destruction of the cation exchange sites which has been explained only by an alteration in the silica-alumina anionic framework. 

Since the initial work of Lippmaa et al. [18], there have been many studies of the Si MAS NMR spectra of low Si/Al ratio zeolites. The general features of these spectra are now well understood, and results from the early studies have been reviewed [1]. In general, the Si MAS NMR spectra of simple zeolites contain a maximum of five reasonably well-resolved peaks, as illustrated in Fig. 5 for the zeolite analcite. It was demonstrated by Lippmaa et al. [18] that these five peaks correspond to the five possible distributions of Si and Al around a silicon nucleus at the center of an Si04 tetrahedron namely, Si[4Al], Si[3Al, lSi], Si[2Al, 2Si], Si[Al, 3Si], and Si[4Si]. In addition, as shown in Fig. 6, the ranges of chemical shift over which the resonances occur are reasonably characteristic of the composition of the first coordination sphere, and the spectra may thus be used to probe the local Si/Al distributions in simple zeolite lattices. A particularly useful feature of these spectra is that the Si/Al ratio of the lattice can be calculated directly. This possibility has been investigated in detail for the previously described zeolite faujasite, which can be obtained by direct synthesis with the same basic structure but over a wide range of compositions (Si/Al = 1 -... 

Note that adsorption of water water and ammonia on cations located in the channels of the zeolite faujasite, depicted in Fig.(5.3), shows the logaritmic dependence predicted by Eq,(5.27). 7 — 70 is the surface or lattice stabilization energy. The corresponding changes in enthalpy or entropy are ... 

Rh was also attached to sodium Y-zeolite (faujasite type) via equilibration with [Rh(NH3)g] CI3. This system was activated by treatment with H2/ CO at 8 MPa and 130 °C and it showed some activity in the hydroformylation of hex-l-ene and hexa-1,5-dienes. Re-use of the catalyst resulted in a decrease in activity. 

Bifunctional Catalysts. One reason invoked (there are others) for why metal particles with high dispersion are desirable for catalysis is that the ratio of surface metal atoms to total number of atoms is quite high. Consider the potential cluster size for two zeolites faujasite and ZSM-12. Faujasite has supercages, which for the purposes of this question can be described as spherical with a diameter of 12 A, and ZSM-12 has a one-dimensional elliptical pore structure of dimensions 5.6 x 6.0 A. Assuming the metal atoms of inteiest have a diameter of 1.0 A and the cluster has a packing fraction corresponding to an FCC structure (0.74), estimate the number of atoms in a metal cluster in each of the two zeolites mentioned above. 

The stick model of the zeolite faujasite which is very familiar to most of us gives the impression that the zeolite is all open space. Figure 4 shows a Courtauld model of the same structure made at Mobil which gives an entirely different impression. The holes are still there but the structure is shown to be very solid indeed. The 12-member ring of faujasite is shown at the center. 

Various metal complexes such as metal phthalocyanines, metal salenes or Ru pyridyl complexes have been incorporated in molecular sieves such as cavity-structured zeolites (faujasites, supercages with 1.3-nm diameter), channel-structured aluminium phosphates (AIPO4-5, channel diameter 0.73 nm) and channel-structured silicates MCM-41 (channel diameter 3.2 nm) [51-53]. Different strategies were applied for the inclusion of the phthalocyanines. For example, whereas the zeolite-encaged phthalocyanines (1 R = -FI M = Co(II), Ru(II), etc.) are synthesized by the reaction of a transition metal ion-exchanged zeolite with phthalonitrile in a closed-bomb vessel [54], in the cases of AIPO4-5 and MCM-41 substituted derivatives of phthalocyanines were added to the mixture during the hydrothermal synthesis of the molecular sieve [55,56]. 

Figure 8-3. Molecular sieve zeolite faujasite. Left Structure of the zeolite with supercages of 1.3-tun diameter. Right Model for the incorporated metal phthalocyanine 1 (R = -H) with diameter 1.2 nm.

Kassab, E., Seiti, K. and Allavena, M. (1991) Theoretical Determination of Relative Acidity in Zeolite (Faujasite). ]. Phys. Chem., 95, 9425-9431. 

One gram of TMS-capped silica was treated with 15 mL of 0.25 M TMSI in dry acetonitrile at 70° C for a period of at least 12 h. Temperatures of less than40°C (which were sufficient to deprotect systems based on one benzyl carbamate per imprint molecule) did not show appreciable deprotection of material 1. Given the treatment necessary to achieve carbamate deprotection, it is important to emphasize that the TMSI procedure does not change the connectivity of the silica framework, as ascertained by studies on model crystalline materials such as a high-silica zeolite faujasite [42]. Following TMSI treatment, the silica was filtered and washed with acetonitrile, methanol, saturated aqueous sodium bicarbonate, methanol, and acetonitrile. The purpose of the aqueous treatment was hydrolysis of the silyl carbamate intermediate as shown in Fig. 6b-c. 

FIGURE 44 Line drawing of the structure of the zeolite faujasite. 

Tables 8-11 list results for some commonly studied zeolites. Faujasite and silicalite are industrially important catalysts when they contain aluminum. The structural features of sodalite are predicted best by both Jackson and Catlow s potentiaPS and Schroder s empirical force field. a pgr faujasite, all force fields are similar in their ability to predict the observed unit cell dimensions, whereas the best for mordenite and silicalite is Sierka and Sauer s potential, which consistently reproduces unit cells both for dense and microporous silica. In general, shell model potentials provide slightly better structural agreement with experiment for zeolites than do ion pair potentials and molecular mechanics force fields.

Zeolites. Zeolites are crystalline inorganic polymers made of aluminosilicates and have open framework structures. Natural zeolites (faujasites) have pores of sufficient size to be useful in petroleum refining. Synthetic faujasite-type zeolites are now available in large commercial quantities and have become an important catalyst in the petroleum industry. Comprehensive reviews on the application of zeolite catalysis are available (ll lS). 

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