Dealuminated faujasite catalysts

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. 

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. 

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. 

Catalytic Selectivity of FCC Catalysts Containing Dealuminated Faujasite... 

Partially proton-exchanged Na faujasite X, in turn, is the best catalyst for selective monochlorination with tert-butyl hypochlorite.258 NaX, NaY, and NaKL zeolites used in the chlorination of toluene with sulfuryl chloride undergo rapid deactivation because of the accumulation of polychlorinated toluenes in the pores of the catalysts and dealumination.259, 260 Direct electrophilic fluorination of aromatics can be effected by using Selectfluor in the presence of triflic acid.261 Electrophilic fluorination may also be carried out by R2NF and R3N+FA reagents.262 Elemental fluorine may also act as a powerful electrophile in acidic media (sulfuric acid, trifluoroacetic acid, or formic acid), but monosubstituted aromatics give isomeric mixtures.263-265... 

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. 

With increasing temperatures the NO conversion over most catalysts of this group passes throu a maximum (33). Cu/ZSM-5 has the highest maximum at the lowest temperature, namely, 500°C. The activity of Cu in other zeolites, e.g., mordenite, ferrierite, faujasite, /3 and L, is distinctly lower (33,35). A rough correlation seems to exist between activity and Si/Al ratio of these zeolites (33) Li and Hall state, however, that the Si/Al cannot be the sole controlling factor, because Cu/Y and dealuminated Cu/Y have very similar activities (i5). 

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]. 

These dealumination procedures result in Al deficient zeolites of the high thermal stability. In the case of faujasite Y, the so called ultra-stable Y zeolite (US-Y) is used as a catalyst for cracking catalysis (47). It was reported that the total acidity of (48) Al-deficient zeoITtes was less than that of the parent zeolite buT with stronger acidic sites (49). For mordenite, this acidity decreases linearly with Al content (50, 51). However calorimetric measurement of the NH- heat of adsorption has shown that when the total number of acidic sites decreases regularly with dealumination, as could be reasonably expected, the strength of the strongest acid sites is enhanced (52). 

The Diels-Alder cycloaddition reaction of dihydropyran with acrolein was performed in the presence of various H-form zeolites such as H-Faujasites, H-p, H-Mordenites which differ both in their shape selective as well as their acidic properties. The activity of the different catalysts was determined and the reaction products were identified. High 3delds in cycloadduct were obtained over dealuminated HY (Si/Al=15) and Hp (Si/Al=25) compared to HM (Si/Al=10). These results were accounted for in terms of acidity, shape selectivity and microporosity vs mesoporosity properties. The activity and the regioselectivity were then discussed in terms of frontier orbital interactions on the basis of MNDO calculations for thermal and catalyzed reactions by complexing the diene and the dienophile with Bronsted and Lewis acidic sites. From these calculations, Bronsted acidic sites appeared to be more efficient than Lewis acidic sites to achieve Diels-Alder reactions. 

Special mention merits the work carried out on the hexagonal faujasite (HEMT) as alkylation catalyst (129-131). It was found that the as-made (Si/Al = 3.9) as well as the dealuminated (Si/Al = 6.1) HEMT were more selective toward the formation of trimethylpentanes than was the corresponding cubic faujasite (Y zeolite). HEMT zeolite also deactivates much slower than Y, giving mainly paraffinic coke. Differences in behavior of the two zeolites were explained on the basis of a larger ratio of strong to weak acid sites in the case of HEMT. 

As already mentioned, the zeolitic component is the most important component in the FCC catalyst, being able to provide the catalyst with both the convenient activity and selectivity. In FCC catalysts, the zeolite employed is faujasite, or rather, the faujasite zeolite (FAU) structure. The Si/Al ratio of the prepared Y-zeolite is an important feature of such material, in that the higher the Si/Al ratio, the more stable against acid and hydrothermal dealumination the zeolite is. 

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