Of dealuminated faujasite

In Fig. 2.1.6.6, the FTIR spectra of the Jacobsen ligand (a), the Jacobsen catalyst (bj, and the immobilized manganese salen complex in the cages of dealuminated faujasite zeolite (c) are compared. While spectra a and b have been measured using the standard KBr technique, the spectrum c of the ship in a bottle catalyst has been recorded using a self-supported wafer. The bands at wavenumbers 1466 cm, 1434 cm" , 1399 cm" and 1365 cm" in spectrum c can be assigned to the... 

Chemical and thermal stability of dealuminated faujasite-type zeolites in gaseous and aqueous phases". Applied Catal., 2S. 71-87. 

Fig. 9a, b. MAS NMR spectra of dealuminated faujasites prepared by treatment with SiCl4 from a Na-Y and b Lio.62Na-Y [165]... 

STUDY OF THE PORE NETWORK OF DEALUMINATED FAUJASITES BY WATER VAPOR ADSORPTION... 

In all cases, the high activity and selectivity of this zeolite as compared to other three-dimensional zeolites, such as beta or dealuminated Faujasite zeolite, is related to the easier and/or faster diffusion of the products and to minimization of undesired consecutive reactions. 

Besides di- and poly-saccharides, zeolites have been applied for hydrolysis of simple glycosides as described by Le Strat and Morreau.132 Methyl a- and /i-D-glucopyrano-sides were treated with water in the presence of dealuminated HY faujasite with an Si/Al ratio of 15, at temperatures ranging between 100 and 150 °C. It was observed that the reaction rate for the (i glycoside was about 5-6 times higher than that for the oc anomer, a result that might arise from the shape-selective properties of the zeolite and stereoelectronic effects on the surface of the solid. 

J.-F. Chapat, A. Finiels, J. Joffre, and C. Moreau, Synthesis of butyl-a and / -d-glucopyranosides in the presence of dealuminated H-Y faujasites Kinetic study, mechanism, stereoelectronic effects, and microreversibility principle, /. Catal., 185 (1999) 445—453. 

A modification of the above cyclic method has proved more effective in the dealumination of Y zeolites. An almost aluminum-free, Y-type structure was obtained by using a process involving the following steps a) calcination, under steam, of a low-soda (about 3 wt.% Na O), ammonium exchanged Y zeolite b) further ammonium exchange of the calcined zeolite c) high-temperature calcination of the zeolite, under steam d) acid treatment of the zeolite. Steps a) and c) lead to the formation of ultrastable zeolites USY-A and USY-B, respectively. Acid treatment of the USY-B zeolite can yield a series of aluminum-deficient Y zeolites with different degrees of dealumination, whose composition depends upon the conditions of the acid treatment. Under severe reaction conditions (5N HC1, 90°C) an almost aluminum-free Y-type structure can be obtained ("silica-faujasite") (28,29). 

The increase in octane observed using dealuminated faujasite compared to high cell size rare earth exchanged faujasite has been correlated with the Si/AI ratio of the sieve and with the sodium content (3). While the relationship between Si/Al ratio as measured by unit cell is confirmed by pilot unit studies in our laboratory. Figure 1, the relationship with sodium content is more complicated. Figure 2. Sodium added to the catalyst after hydrothermal dealumination reduces activity but does not affect octane, while sodium present before hydrothermal dealumination increases activity but does reduce octane. This result implies that selectivity for octane is related to structures formed during... 

Zeolite catalysts in many forms are used for important commercial processes. The studies were extended to L zeolites, mordenite, erionite, and dealuminated faujasites and mordenites. More attention is paid now to zeolites with univalent and multivalent cations and to multicomponent catalysts. Among these some important examples are the tellurium-containing catalyst for hydrocarbon dehydrocyclization (42), the difunctional Ni- and Pd-zeolite catalysts for benzene hydrodimerization to phenylcyclohexane (42), the catalyst for the hydrogenation of phenol cyclohexanol (44), the 4% Ni/NaY which forms butanol, 2-ethylhexanol, 2-ethylhexanal, and 2-ethylhexanol from a mixture of n-butyraldehyde and hydrogen. 

The use of traditional and new techniques to elucidate the structure of synthetic faujasites with different silica alumina ratios, dealuminated by steaming and chemical treatment, and with and without faulting will be described. The migration and fixation of cations and the role of aluminum in the dealumination of the zeolite will be discussed. 

Cotterman et al. (34) showed that hexadecane-cracking activity of AFS and USY zeolites appeared to be a function of total Al content, independent of method of dealumination, implying that hexadecane cracking occurs over both framework- and extra-framework-acid sites. Hence, extra-framework material in mildly steamed synthetic faujasite, USY, makes a significant contribution to catalyst activity, as previously reported (32). Gasoline selectivity is influenced by both the method of dealumination and steam treatment, and depends on both framework-acid sites and the presence of extra-framework material. 

In hydrothermally dealuminated faujasites additional 27A1 lines in the 50-30 ppm range appear, in addition to the tetrahedral and octahedral lines at 60 and 0 ppm. Gilson found a line at 34 ppm in zeolite Y with framework Si/Al = 20 by steaming at 760°C in 100% steam. Freude and coworkers (39,40) have described the use of 1H-and 27A1-MAS-NMR techniques to determine the dealumination mechanism in the hydrothermal and acid treatment of zeolite Y. They determined the framework aluminum from the equivalence of A102 anions in the framework and NH4 + cations using the Kjeldahl method to determine the amount of NH3 in the zeolite. 

The effect of dealumination can be observed in a series of commercial Y-faujasites with Si Al ratios of 2.6, 5.8, 12.8 and 24. The modification of the acidity resulting from the dealumination is illustrated by the curves of differential heats of ammonia adsorphon (Figure 9.16). 

Reports on the thermal stabilities of faujasites and mordenites are largely confined to their resistance to collapse at elevated temperatures. There is, however, a need to extend these works to the investigations of reactions which occur during the thermal treatment of hydrogen zeolites. These include aluminum migration, dehydroxylation and formation of new active sites. The present study is concerned with the effect of calcination temperature on the crystallinity, the extent of thermal dealumination, concentration of hydroxyl groups and catalytic activity of hydrogen faujasites and mordenites with different Si/Al framework ratios. 

Hydrothermal treatment of zeohtes is an essential step in the preparation of US-Y based catalysts. It results in signiflcant modification of the faujasite structure (dealumination and partial destruction of the zeohte fi-amework) and of the acidic properties. Increased hydrothermal stabflity of the framework, lower concentration and higher strength of the add sites compared with the initial zeohte are the most important properties of the steamed catalysts [1,2,12]. 

The catalytic activity and stability of aluminosilicate zeolites is strongly influenced by removal of Al from the framework sites into extraframework positions. This can be accomplished by dehydroxylation or calcination followed by steam treatment, the latter process producing ultrastable zeolites. Early Al NMR studies indicated the appearance of the 30 ppm resonance attributed to Al when faujasite and other zeolites are steamed (Gilson et al. 1987). Double rotation Al NMR studies at two magnetic fields (Ray and Samoson 1993) indicated that the nature of the Al species depends on the method of dealumination the 30 ppm resonance in zeolite-Y samples treated... 

For the autoxiation of long chain thiols in organic medium CoPc in dealuminated Y is the preferred catalyst. As the weak ionization of thiol into thiolatc in such conditions is difficult and the oxygen solubility at higher reaction temperatures is low, the combination of a hydrophobic support consisting of a dealuminated faujasite or a VPI-5 AIPO4 with a substituted Pc such as tetra-nitro-Pc, perfluoro- or perchloro-Pc, should yield an optimally designed catalyst. 

Figure 17. 27A1-NMR spectrum of hydrothermally dealuminated faujasite. (Reproduced with permission from ref. 62. Copyright 1987 The Royal Society of Chemistry.)...

For the conversion of m-xylene, the activity of H-faujasite depends strongly on its degree of dealumination. Maximum catalytic activity is obtained for aluminum T-atom fractions equal to 0.10. Surprisingly, in contrast to both theoretical predictions and to the behaviour of H-ZSM-5, for dealuminated H-faujasites the turnover frequency per protonic aluminum site exhibits a pronounced maximum when the aluminum T-atom fraction is 0.09. The present results can be rationalized if, besides the classical predictions on zeolite acidity, a new concept of "hidden acid sites" is handled. Changes of the m-xylene isomerisation and disproportionation selectivities with the degree of dealumination of faujasite are in agreement with this concept. 

The degree of crystallinity of the samples was determined using the intensity of the [5,3,3] reflection with XRD and considering the parent NaY to be 100% crystalline. The Alp content was derived from the unit cell size, aQ, applying the relation of Fitchner-Schmittler et al. (16). Lattice constants, Alp/Alp+Sip ratio s and degrees of crystallinity of the dealuminated faujasites are listed in Table I. 

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