Synthesis of isoamyl acetate usin NaX and NaY zeolites as catalysts

A liquid phase esterification reaction between glacial acetic acid and isoamyl alcohol has been studied using NaX and NaY zeolites as catalysts. The influence of calcination temperature, the amount of catalysts, reaction temperature, time of esterification and the molar ratio of the reactants has been investigated. Water insoluble products have been isolated from the reaction mixture and analyzed for the ester. Both NaX and NaY are found to be active as catalysts in the reaction. However, their catalytic activity varies with the reaction conditions and their calcination temperature. The reaction has been found to be 100% selective to ester formation. Catalytic activity of the zeolites has been correlated with their surface acidity.     

苯并噻吩在酸改性NaY分子筛上的吸附

以NaY分子筛为母体,通过柠檬酸、磷酸改性分别得到吸附剂NaY-C和NaY-P.采用SEM、XRD、XRF、N₂物理吸附及NH₃-TPD表征可知,柠檬酸改性后得到的NaY-C吸附剂介孔表面积增加,分子筛骨架结构保持不变.同时,磷酸改性使得NaY分子筛表面弱酸量减少强酸量增加,改性后所得吸附剂NaY-P的强酸量大于NaY-C.吸附实验表明,NaY-C和NaY-P均可完全脱除模拟油品中的苯并噻吩,同时NaY-C吸附剂对0^#柴油的脱硫能力优于NaY-P吸附剂.再生实验中NaY-C和NaY-P吸附剂对模拟油品的脱硫率由第一次的100%分别下降至第6次的91.97%和85.96%.由此可知,柠檬酸改性NaY分子筛所得NaY-C吸附剂的脱硫能力优于NaY-P,原因是吸附剂上的介孔更易于发生吸附脱硫.     

Thermal behaviour of fibrous zeolites of the natrolite group

The western region of the Deccan Volcanic Province (DVP) is constituted of tholeiitic lava flows. They host numerous cavities, varying in size and shape, largely occupied by zeolites and a variety of secondary minerals, amongst which the fibrous zeolites (natrolite group), are particularly gorgeous and attractive. Scolecite and mesolite are the only two members commonly occurring in this region. Our data on their thermal behaviour significantly differs from that reported in previous literature. Scolecite, Ca₈(Al₁₆Si₂₄O₈₀)·24H₂O shows three distinct steps instead of two and water loss is observed even beyond 550°C. It is held that the first step corresponds to the expulsion of water from the site farthest away from Ca and the next two steps in succession correspond to the two sites nearer to Ca. Mesolite, Na₁₆Ca₁₆(Al₄₈Si₇₂O₂₄₀)· 64H₂O has much more complex behaviour with four or five steps of water expulsion and a major loss around 248–270°C in a double reaction attributed here to the expulsion of water from scolecite type channels. It is further held that the natrolite type channels are emptied in further steps. Loss of water in steps even beyond 400°C is particularly noted and such reactions are well reflected in the TG and the DTG. Peak temperature dependence on sample amounts is also evident. Successive phase transformations above 700°C, up to 1000°C are reflected in the DTA curves.     

Stabilized zeolites of Y-type. Their adsorption and catalytic properties

The stabilized decationized form of a Y-type zeolite has been prepared by the self-steaming calcination method. The temperature of the stabilization process influenced the nature of the interaction with ethylene.

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Y . .

     

Thermal stability of products prepared by the combination of cyclodextrins and zeolites

Derivatographic and calorimetric measurements were used to study the thermal properties of combined inclusion compounds of zeolite-cyclodextrin type and of zeolite-cyclodextrin-pharmaceutical type. There were differences in the characteristic decomposition temperature intervals and in the modes of cyclodextrin and pharmaceutical liberation from the products. Calorimetric measurements revealed that the process in the newly-formed complex host is connected with a glass transition. The products are intended for use in veterinary medicine.     

Thermal analysis of fluorine containing gels and precursors of high silica zeolites

By means of simultaneous DTA-, TG- and DTG-technique, the silicate gels and the MFI crystals obtained from these gels have been investigated. The gels have been prepared in presence and in absence of tetrapropylammonium cation (TPA⁺) and with Li⁺, Na⁺, NH ₄ ⁺ and K⁺ fluorides. In absence of TPA⁺ no thermal effects have been observed in Li⁺- and Na⁺-gels. The effects observed in the NH ₄ ⁺ -gel stem from a decomposition and release of inorganic phases: SiF₄, NH₄F, NH₃. The DTA/DTG effects in the TPA⁺ containing gels and in the MFI crystals of monodisperse size are attributed to the decomposition of TPA⁺ cation. It can be concluded from these effects that the interaction between the gels and the TPA⁺ cation is rather weak. The interaction between TPA⁺ and MFI crystals obtained in fluoride medium is stronger than the interaction with crystals obtained from alkaline media. Similar thermal effects are obtained after grinding the long crystals to those having a large distribution of crystal sizes.

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Zusammenfassung Mittels simultaner DTA-, TG- und DTG-Techniken wurden Kieselgele und die MFI-Kristalle dieser Gele untersucht. Die Gele wurden in und ohne Gegenwart von Tetrapropylammoniumkationen (TPA⁺) und mit Li⁺-, Na⁺-, NH ₄ ^– und Kaliumfluoriden hergestellt. Bei Abwesenheit von TPA⁺ werden für Li⁺- und Na⁺-Gele keine thermischen Effekte beobachtet. Der bei NH ^4– -Gelen beobachtete Effekt ergibt sich aus der Zersetzung und Abspaltung von anorganischen Phasen: SiF₄, NH₄F, NH₃. Die DTA/DTG-Effekte in TPA⁺-haltigen Gelen und in den MFI-Kristallen monodispersen Ausmaes werden der Zersetzung des TPA⁺-Kations zugeschrieben. Daraus kann man schlieen, da die Wechselwirkung zwischen den Gelen und dem TPA⁺-Kation eher schwach ist. Die Wechselwirkung zwischen TPA⁺ und MFI-Kristallen aus fluoridischen Medien ist strker als die Wechselwirkung mit Kristallen aus alkalischen Medien. Ähnliche thermische Effekts erhlt man, nachdem man die langen Kristalle zerkleinert und eine breite Kristallgrenverteilung erhlt.

     

Physicochemical properties of alkali-metal exchanged type X zeolites

The changes in the physicochemical properties of a series of faujasite type X zeolites cation exchanged with K⁺, Rb⁺ and Cs⁺ have been studied by XRD, IR, thermoanalytical methods and sorption measurements. As a consequence of the enhanced scattering of X-rays by larger alkali metal cations, the percent relative intensity of the XRD peaks of cation exchanged zeolites was found to have decreased considerably. The framework IR spectra also showed analogous changes. The alkali metal exchange was found to enhance the thermal stability of the parent zeolite. The available void volume and specific surface area (obtained by low temperature nitrogen sorption) also decreased with the increase in the degree of exchange and cationic size. Equilibrium sorption capacities (298 K andP/P ₀=0.5) for water,n-hexane, cyclohexane and 1,3,5-trimethylbenzene also exhibited the same trend.NCL communication no. 6056.     

Carbonates in zeolites: Formation,properties, reactivity

Two possible schemes of carbonate formation (with and without water participation) in cationic form zeolites are considered. Activation energy for the formation of hydrogen carbonate in NaX zeolite from water and carbon dioxide is calculated at the DFT level with periodic boundary conditions, while the problems of modeling the formation of symmetric carbonate in the same zeolite are discussed. The formation of copper carbonate is studied using binuclear CuOCu clusters from CO₂ where the influence of water on the barrier is discussed. The questions related to DFT application to binuclear copper clusters are also considered by comparison with the data obtained at the MP2 level. The reactivity of copper carbonate is tested in the reaction with methanol. © 2015 Wiley Periodicals, Inc.     

The state of water in Y-type zeolites

Conclusions By titration with Fischer's solution and thermodesorption the authors show that the firmly combined water conteat of Y-type zeolites depends on the nature of the ion-exchange cation and the heat-treatment conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 276–279, February, 1976.     

Isomerization of dimethylnaphthalenes over zeolites

A dimethylnaphthalene (DMN) isomer mixture from a reforming unit was reacted at 350°C and atmospheric pressure over H-mordenites (Si/Al ranging from 5 to 100), a partially decationated NaY (Si/Al=2.4) and a slightly dealuminated HY (Si/Al=5), with the aim of increasing the 2,6- and 2,7-DMN content by isomerization. The best results were obtained on H-mordenite with Si/Al=10, where shape selective effects made possible to double the amount of the valuable isomers while limiting to a negligible extent the side reactions of disproportionation and dealkylation.     

Methanol-based synthesis of hydrocarbons on bifunctional Y-type zeolites

The directions of methanol conversion on Pt, Pd, Zn, Ni metals and Y zeolites and on bifunctional metal-Y-zeolite catalysts have been studied. The increase of the hydrogenation activity of bifunctional catalysts enhances the rate of methanol conversion and decreases the selectivity of hydrocarbon formation.

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- Y, - Y.

     

Characterization of the acidic properties of zeolites by means of temperature-programmed desorption (TPD) of ammonia

Desorption energy distributions were calculated for temperature-programmed desorption (TPD) of ammonia from H zeolites of different type by means of regularization. This method does not require any limiting assumptions about the distribution function. It could be shown that the desorption energy distributions obtained are nearly independent of the experimental conditions and therefore they should represent a suitable measure for the distribution of the strength of acidic sites. The calculated desorption energy distributions for the ammonia desorption from the isolated bridging SiOHAl groups of H zeolites of different type significantly differ from each other in shape. The increase of the desorption energy of the main range of the distribution functions correlates well with the increase of the average acid strength of the SiOHAl groups with decreasing Al content of the zeolites.     

Differential Thermal Analysis as an Acidity Probe in Zeolite Catalysts

Abstract

Differential thermal analysis is used as an acidity strength probe for a series of mordenite (zeolite) catalysts via determining the temperature at which presorbed pyridine completely desorbs from the catalyst. The findings obtained for metal(s) containing mordenite catalysts have been correlated with the Pearson's assumption concerning Lewis acids and bases and the Pauling's electronegativity of the metals contained and found compatible.

The investigated catalysts can be arranged in their observed order of acidity strength as follows: HTI > Th-HM > Re-HM > Pt-HM > Pt-Th-HM > Pt-Re-HM.     

State of alkali azides in zeolites studied by thermal analysis

Thermal behaviour of pure LiN₃, NaN₃, CsN₃ and their mixture with the respective LiY-FAU, NaY-FAU, CsY-FAU zeolite was investigated by means of thermogravimetry and IR spectroscopy. Thermodesorption of CO₂ was applied to compare the basicity of the alkali ionexchanged Y zeolites. Two of the investigated systems, the NaN₃/NaY-FAU and the CsN₃/CsY-FAU gave single, well defined and reproducible azide decomposition features rendering these samples to apply as catalyst precursors for preparation of zeolite with basic character.     

Thermal and structural properties of rare earth exchanged zeolites

A series of rare earth zeolites of types X and Y were prepared by cation exchange. Thermal analysis curves (TG/DTA) were employed to estimate the structural changes in the zeolite framework. Analogous investigations were carried out by independent methods such as XRD and IR spectroscopy. The results indicate increased thermal stability on the replacement of sodium by rare earth. Partial replacement of rare earth by ammonium/hydrogen enhances the thermal stability. The type Y zeolites are more stable than those of X type.

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Zusammenfassung Eine Reihe von Ionen der Seltenen Erdmetalle enthaltenden Zeolithen des Typs X und Y wurden durch Ionenaustausch hergestellt. Thermoanalytische Kurven (TG/DTA) wurden zur Beurteilung der strukturellen Veränderungen des Zeolithgitters herangezogen. Analoge Untersuchungen wurden mit unabhängigen Methoden (XRD und IR-Spektroskopie) ausgeführt. Es wurde festgestellt, daß ein Ersatz der Natriumionen durch Ionen der Seltenen Erdmetalle zu einer Erhöhung der thermischen Stabilität führt. Ein teilweiser Ersatz der Seltenen Erdmetallionen durch Ammonium-/Wasserstoffionen erhöht die thermische Stabilität. Zeolithe des Typs Y sind stabiler als die des X-Typs.

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X . (/) . - . . . X .

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NCL Communication No: 2186     

The influence of adamantane on the reaction of n -heptane over H-Y, H-β and H-mordenite zeolites

The effect of adamantane (Ad) on the activity and selectivity of acidic zeolites Y, β and mordenite (M) in the isomerization and cracking ofn-heptane (C₇) in He at 443 K was studied.Ad was found to promote the isomerization of C₇. TheAd uptake of the zeolites, and the IR spectra obtained from the zeolite-boundAd were determined. It was found thatAd did not remain completely unconverted under the conditions of the C₇ reaction. The activity of the catalysts in the conversion ofAd increased in the sequence of H-Y<H-β<H-M. Existing data suggest that a fraction of theAd, responsible for the cocatalytic effect, can participate in hydride transfer processes and remain unconverted, while another fraction, depending on catalyst acidity, is converted to dimer and oligomers.     

Factors affecting drug adsorption on beta zeolites

The adsorption behaviour of three commonly used drugs, namely ketoprofen, hydrochlorothiazide and atenolol, from diluted aqueous solutions on beta zeolites with different SiO₂/Al₂O₃ ratio (i.e. 25, 38 and 360) was investigated by changing the ionic strength and the pH, before and after thermal treatment of the adsorbents. The selective adsorption of drugs was confirmed by thermogravimetry and X‐ray diffraction. The adsorption capacity of beta zeolites was strongly dependent on both the solution pH and the alumina content of the adsorbent. Such a remarkable difference was interpreted as a function of the interactions between drug molecules and zeolite surface functional groups. Atenolol was readily adsorbed on the less hydrophobic zeolite, under pH conditions in which electrostatic interactions were predominant. On the other hand, ketoprofen adsorption was mainly driven by hydrophobic interactions. For undissociated molecules the adsorption capability increased with the increase of hydrophobicity.     

Theoretical study on reactions catalyzed by gallium-substituted zeolites

The dehydrogenation and cracking reactions of light alkanes in gallium-containing zeolites were studied using density functional theory. Gallium isomorphically substituted, generating Brønsted acid sites, was used in the computations. The following reactions were examined: dehydrogenation of methane, ethane, propane, isobutane and cracking of ethane, propane and isobutene, all catalyzed by the framework gallium species. The cracking reaction seems to be favored relative to the dehydrogenation when framework gallium species are used. This behavior is also observed in aluminum-containing zeolites (H-ZSM5). The geometries and energetics of the transition states found for the gallium zeolites were compared with theoretical data for the same transition states in aluminum zeolites. There seems to be no significant difference between framework gallium and framework aluminum species. Therefore the framework gallium should not be the species responsible for the catalytic enhancement observed in gallium-containing zeolites.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

FTIR characterization of metal-loaded zeolites

FTIR transmission spectra of self-supporting zeolite wafers of Na₁₂A (Linde 4A), Na_3.6Ca_4.2A (Linde 5A) and Ag_11.8Na_0.2A in the range of 20 to 13 500 cm^–1 are reported. Reduction of Ag⁺ by H₂ is probed directly in the FAR IR and indirectly by adsorption of CO and CO₂.