DEALUMINATED FAUJASITE

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. 

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... 

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... 

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. 

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. 

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.)...

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. 

The behaviours of the acidified montmorillonite (K 10) and of the silica-alumina (SA) are similar to the one of the dealuminated faujasite, except for the presence of induction. With SA, the best yield is in accordance with the best diffusion of the primary product through the amorphous structure of the catalyst. 

Attempts have been made to correlate this behavior with the ring sizes and average T-O-T angles present in zeolites of different topologies [300]. However, the observed frequency dependencies were not fairly uniform. In particular, for A-type zeolites a trend reversed to that for faujasites has been observed by changing the nsi/n i ratio systematically [290]. Hence, the frequency shifts obviously arise from different effects of structural changes, altered nature of normal modes, and electron density distribution and from combinations of these effects. Instead of the band shift observed for aliunimun-rich samples, for highly dealuminated faujasites the band width of the most prominent peak was discovered to reflect the aliuninum content at low levels [295]. 

The CO-induced shift of v(OH) of the bridging hydroxyls is typically around —300 cm (Table 2.6), corresponding to a PA of 1160 kj moP. A similar shift was found by DFT calculations (285). The highest acidity of zeolite hydroxyls was reported for dealuminated faujasites (17J-J73) in this case, the PA reaches a value of about 10801 moP. ... 

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

Dealuminated faujasites with Si/Al ratios ranging from 2.3 to 67 were obtained by Shibuichi et al. [153], and the molar differential heats of adsorption of ammonia were measured at relatively high temperature (473-623 K) after... 

Catalytic Selectivity of FCC Catalysts Containing Dealuminated Faujasite... 

Rakiewicz EF, Mueller KT, Jarvie TP, Sutovich KJ, Roberie TG, Peters AW. Sohd-state NMR studies of silanol groups in mildly and highly dealuminated faujasites. Microporous Mater 1996 7 81-8. 

Biaglow AI, Gorte RJ, White D. NMR studies of acetone in dealuminated faujasites - a probe for nonframework alumina. J Catal 1994 150 221-4. 

H. Stach, J. Janchen, U. Lohse et al.. Relationship between acid strength and framework aluminium content in dealuminated faujasites. Cattil. Lett. 13,389-393 (1992)... 

Furthermore, it proved to be a typically hydrophobic adsorbent. The adsorption isotherms of organic compounds showed the rectangular shape with saturation at very low pressures (see Fig. 8) typical of the adsorption on high-alumi-na zeolites. In contrast, ammonia and especially water are much less or practically not adsorbed (isotherms (d) and (e) in Fig. 8). [See the striking difference in the adsorption of water on Na-Y (dotted isotherm e) and dealiuninated Y (continuously traced isotherm e Fig. 8).] This distinctly hydrophobic adsorption behavior of highly dealuminated faujasite indicates that the framework must be virtually free of lattice vacancies necessarily associated with hydrophilic internal silanol groups. 

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... 

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