Faujasite hydrogen forms

Materials. The NaY faujasite was supplied by Linde Co (SK UO Sieves). A conventional exchange with NH Cl provides a NH Y sample (unit cell composition (NH J gNa-jQAl5531-135033 ). Heating this sample for 15h in oxygen and 3h in vacuo (l0 5torr) at 350°C leads to the hydrogen form HY. 

The revolutionary zeolite cracking catalyst (synthetic Linde X and Y) was introduced commercially over 28 years ago, but considerable effort is still being expended on the improvement of its stability and catalytic properties. Decreasing the aluminum content of the zeolite framework and the replacing the rare-earth with the hydrogen form have greatly increased activity at the expense of stability. The thermal stability of the faujasites is fairly well understood, while the reasons for the increased catalytic activitity are still not fully known. 

The reaction between alcohols and hydrogen sulphide can proceed not only via one reaction pathway. The reaction pathway depends on the type of zeolites. It was stated that over hydrogen forms of faujasite type zeolites the Brflnsted acid sites play the role of active centres and the reaction proceeds between chemisorbed alcohol and physisorbed H2S (ref.2). However, in the absence of Brttnsted acid sites the cations seem to play the role of active centres (ref.7). It was suggested that on cationic forms of zeolites the reaction takes place between dissociatively adsorbed hydrogen sulphide and alcohol. The results obtained in this work confirm this sugge-... 

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 thermal stability of hydrogen forms of faujasite-type zeolites turned out to be crucial in their important industrial application as cracking catalysts [401, 402], techniques were developed for stability improvement, as for instance the treatment via steaming of the catalysts [403-406]. This procedure of treatment of NH4- or H-forms of faujasite-type catalysts requires the presence of water vapor at elevated temperatures [404-407]. It proved to reduce the density of strong Bronsted sites (indicated by the bands at ca. 3640 and 3550 cm ), to increase the concentration of non-acid silanol groups (i.e., the intensity of the 3740 cm -band) and to generate additional OH groups different from those... 

In various zeolites in the hydrogen form (mordenite, faujasite, offretite, erionite, ZSM-5) ultraviolet spectroscopy showed the presence of two types of A1 species. A band at 240 nm is related to framework Al-0 units and the band at 320 nm may be connected to oxoaluminum stmctures inside the zeolite matrix (34). 

In a study by Brueva et al. [ 147], the calorimetric values obtained by ammonia adsorption at 573 K over hydrogen forms of H-Y zeohtes suggested that in parent H-Y the strong sites were mainly in the range 105-110 kJ mol , whereas dealumination of faujasites resulted in the appearance of stronger acid sites with q > 120 kJ mol [ 147). Relationships between addity and catalytic activity were also discussed. 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Fatty acid, MRNi hydrogenation, 32 243-245 Faujasites, 34 160-183 acidic sites, 27 151-154 alkaline and rare earth forms, 27 160-165 amine titration, 27 163 infrared smdies, 27 160-163 surface acidity and catalytic activity, 27 163-165... 

Selective hydroxylation of phenol with hydrogen peroxide was reported on acid zeolite catalysts [91-92]. Peroxonium ions, formed by H2O2 protonation, are the oxidizing species. When the reaction is carried out on a faujasite catalyst, a mixture of hydroxybenzenes and tars is obtained [91]. In the presence of H-ZSM-5 on the other hand, no tar formation was mentioned (which does not necessarily mean that it was absent) and p-selectivities close to 100% were reported for the hydroxylation [92]. These superior selectivities reflect the shape selective properties of ZSM type zeolites. 

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. 

Copper(II)-exchanged faujasite was tested in the Ruff degradation of calcium gluconate and compared, under the same reaction conditions, with homogeneous catalysis by copper(II) sulphate. The amount of copper was the same in both cases and the reactions were stopped when hydrogen peroxide was totally consumed. D-arabinose and D-erythrose were the main products, glyceraldehyde was formed in small amount 2% yield). Blank experiment was carried out with the starting Na-faujasite, for the same reaction time as the one required for the oxidation in presence of copper zeolite. 

At the same time, specific properties (primarily the Si/Al ratio) of a zeolite should be taken into account when discussing the mechanism of its dehy-droxylation. It is quite possible that the mechanism typical of H forms of faujasites would be completely improper for high-silica-containing zeolites. Thus, in their studies of dehydroxylated forms of ZSM-5 zeolite by means of IR spectroscopy of molecular hydrogen adsorbed at low temperatures, Kazansky et al. (72, 76) have demonstrated that the Uytterhoeven-Cristner-Hall scheme seems valid in this case. 

As indicated above (Table I), 2- and 3-valent cation forms of mordenite are considerably less active in cyclohexane isomerization than that of hydrogen. It is this property of mordenite-supported catalysts that distinguishes them sharply from zeolites of the faujasite type. Thus, in the case of faujasites, the activity of H-form (decationized form) and 2-valent modifications (such as Ca and Mg ) in acid-base reactions (cracking, isomerization, alkylation) is the same, while H-mordenite is many times as active as any cation form under study. 

Sodium forms of Y zeolites with Si/Al ratios between 2.1 and 2.9 were used as parent materials to produce hydrogen faujasites by thermal decomposition of the... 

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