Conversion of dimethyl disulfide in the presence of zeolites

Dimethyl disulfide conversion in the presence of zeolites was studied at atmospheric pressure and T = 190–350°C. For all catalysts, the products of the reaction at T = 190°C—methanethiol, dimethyl sulfide, and hydrogen sulfide—result directly from dimethyl disulfide. The relative reaction rate and the dimethyl sulfide selectivity decreases in the order HZSM-5 ≥ CoHZSM-5 > HNaY > NaX, NaY. The methanethiol formation selectivity changes in the reverse order. The highest methanethiol selectivity at T = 190°C is shown by the sodium zeolites; the highest dimethyl sulfide selectivity, by the high-silicz zeolite HZSM-5. Raising the reaction temperature increases the reaction rate and changes the process route: at high temperatures, dimethyl disulfide decomposes to methanethiol, which then condenses to yield dimethyl sulfide and hydrogen sulfide. The observed regularities are explained in terms of the different acidic properties of the zeolite surfaces.     

Untersuchungen an oxidischen Katalysatoren. XL. Beeinflussung des katalytischen Verhaltens Bifunktioneller Ni/HNaY-Zeolith-Katalysatoren durch Übergangsmetallionen der VI. Nebengruppe

Studies on Oxide Catalysts. XL. Modification of the Catalytic Behaviour of Bifunctional Zeolites Ni/HNaY by Group VIB Transition Metal Ions The catalytic properties of zeolites Ni/HNaY modified by addition of transition metalions of group VIB are investigated in the conversion of n-hexane and cyclohexane. Nature and amount of the component additional introduced into the Ni/HNaY zeolites exhibit strong influence on the catalytic activity, the selectivity, and the sulphur resistance of these catalysts. The action of the added component is discussed considering electronic effects on the nickel metal.     

Features of the Distribution of Aluminum in Mordeniteclinoptilolite Catalysts for the Hydroisomerization of n-Hexane

The content of tetrahedral, extraskeletal, and ion-exchanged aluminum in zeolites consisting of natural and decationized forms of mordeniteclinoptilolite rocks after acidic activation were studied. The results were compared with acidity and catalytic activity properties of modified samples of rocks and synthetic mordenite in the hydroisomerization of n-hexane.     

Hydroxidgruppen an Zeolithen. II. Zahl und Eigenschaften von Hydroxidgruppen an CeNaY- und HNaY-Zeolithen unterschiedlichen Austauschgrades

Hydroxide Groups on Zeolites. II. Number and Properties of Hydroxide Groups on CeNaY and HNaY Zeolites of Different Exchange Degree The number of hydroxide groups on CeNaY and HNaY zeolites was examined by D₂ exchange, and their properties in dependence of the cation exchange degrees were studied by IR spectroscopy. On CeNaY zeolites there exist six kinds and on HNaY zeolites at least seven kinds of hydroxide groups. On the CeNaY zeolites, the hydroxide groups are produced by dissociative chemisorption of water on Ce³⁺ ions. Their total number increases continuously with increasing exchange degree. Some of the hydroxide groups are acid BRÖNSTED centers whose number increases with increasing exchange degree and decreases with the temperature of preheating increasing to about 600°C. On the HNaY zeolites, the hydroxide groups are produced by thermal decomposition of the NH⁺₄ ions, by dealumination and interaction of the Al³⁺ ions produced in this way in the place of cations with water. Above the threshold value of 35% the total number of the hydroxide groups increases very rapidly with increasing exchange degree. One part of the hydroxide groups decreasing with increasing exchange degree acts as acid BRÖNSTED centers. The number of these centers does not decrease until at preheating temperatures above 450°C.     

Untersuchungen an oxidischen Katalysatoren. XXXVIII. Zum bifunktionellen Zusammenwirken metallischer und acider Zentren in Metall/HNaY-Zeolith-Katalysatoren

Studies on Oxide Catalysts. XXXVIII. On the Bifunctional Action of Metal Sites and Acid Sites in Metal/HNaY Zeolite Catalysts The catalytic activity and selectivity of HNaY zeolites containing nickel were investigated in the isomerization of n-hexane. In order to characterize independently the catalytic properties of the supported metal, the catalytic behaviour of these samples was determined in the dehydrogenation reaction of cyclohexane and in the hydrogenolysis of ethane. The catalytic properties of the metal in metal/HNaY zeolite catalysts are strongly modified by acid sites of the zeolite. This modification of the catalytic properties is attributed to electronic interactions between metal and zeolite.     

Adsorption of methanol on sodium faujasites and mordenites

Calorimetry and IR spectroscopy were used to study the adsorption of methanol on faujasites and mordenites with different Si/Al ratios. It was shown that the disturbance of the OH bonds in CH₃OH weakens and the heat of adsorption decreases as the cation content in the zeolites decreases. The protic acid sites in decationized mordenite form strong hydrogen bonds with the adsorbed molecules.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 476–479, March, 1993.     

IR spectroscopic study of the adsorption of MeOH and H2O on decationized zeolites

The IR spectra of decationized zeolites with adsorbed bases have been analyzed. A correlation between the shift (OH) of the center of gravity of the set of bandsA,B, andC (components of the (OH) vibration) and the strength of the H-bond between the bridging hydroxyl groups and the molecule of a base has been found. This is evidence in support of the Fermi-resonance nature of the perturbations of the (OH) vibration. Spectral data on the adsorption of H₂O and MeOH on decationized zcolitcs that cannot be interpreted in terms of the formation of complexes with strong H-bonds have been obtained. Arguments in favor of the formation of H₃O⁺ and MeOH₂ ⁺ ions linked to the neighboring oxygen atoms in the zeolitc latticevia two identical hydrogen bridges have been presented.Na—Y zeolites were synthesized by N. N. FeoktistovaTranslated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1377–1381, June, 1996.     

Density Functional Investigation of Methanethiol and Dimethyl Sulfide Adsorption on Zeolite

The density functional theory and cluster model methods have been employed to investigate the interactions between methanethiol, dimethyl sulfide and zeolites. The molecular complexes formed by adsorption of methanethiol or dimethyl sulfide on silanol H3SiOSi(OH)2OSiH3 with five coordination forms or four coordination forms, and complexes formed by interactions of Bronsted acid sites of bridging hydroxyl H3Si(OH)Al(OH)2OSiH3 with methanethiol or dimethyl sulfide have been investigated. Full optimization and frequency analysis of all cluster models have been carried out using the B3LYP hybrid method at 6-31 G (d,p) basis set level for hydrogen, silicon, aluminum, oxygen, carbon, and sulfur atoms. The structures and energy changes of different coordination forms between methanethiol and H3Si(OH)Al(OH)2OSiH3, dimethyl sulfide and H3Si(OH)Al(OH)2OSiH3, methanethiol and H3SiOSi(OH)2OSiH3, dimethyl sulfide and H3SiOSi(OH)2OSiH3 complexes have been comparatively studied. The calculated results showed the nature of interactions that led to the formation of all complexes was van der Waals force confirmed by an insignificant change of geometric structures and properties. The conclusions that methanethiol and dimethyl sulfide molecules were adsorbed on bridging hydroxyl group prior to silanol group were obtained on the basis of adsorption heat, the most stable adsorption models of a 6 ring structure for interaction between bridging hydroxyl and methanethiol, and a 7 ring structure for interaction between bridging hydroxyl and dimethyl sulfide.     

N<Subscript>2</Subscript> and CO as probe molecules for determining the properties of acid sites on the surface of zeolites

The applicability of molecular nitrogen as a probe for the Brønsted and Lewis acid sites of HNaY and HZSM-5 zeolites was studied by Fourier transform IR spectroscopy. The integrated absorption coefficients of bands due to N—N vibrations in complexes with Brønsted and Lewis acid sites were determined. The correlation between the integrated absorption coefficients and the positions of bands due to N—N vibrations in nitrogen interacting with the acid sites of test samples is discussed. We propose using the low-temperature adsorption of nitrogen for express determination of the concentrations of strong Lewis and Brønsted acid sites in zeolites.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 108–114.Original Russian Text Copyright © 2005 by Malyshev, Paukshtis, Malysheva, Toktarev, Vostrikova.     

含镍Y沸石的硫化及加氢脱硫性能

本文制备了不同形态的含镍Y沸石, 研究了温度, 时间和H~2S浓度对含镍Y沸石硫化的影响, 发现负载型含镍Y沸石最易硫化, 离子交换型次之, 骨架型最难硫化。考察了沸石表面硫化物物种的热稳定性和水热稳定性。指出高温下沸石脱附的水蒸汽能使硫化物发生水解, 导致催化剂失硫。用XRD, IR和化学分析等方法对硫化的含镍沸石催化剂进行表征, 硫化后沸石表面形成的NiS~x有可能是属正交晶系的Ni~7S~6化合物。对噻吩加氢脱硫反应, 硫化的含骨架镍Y沸石无催化活性, 硫化的离子交换型含镍Y沸石活性比负载型含镍Y沸石高5-6倍左右, 因其酸性较强。催化剂表面酸性位和硫化镍活性位共存, 对噻吩加氢脱硫反应是有利的。     

Activity of catalysts in the synthesis of dimethyl sulfide from dimethyl disulfide

Dimethyl disulfide conversion at T = 190–350°C over catalysts containing acid and basic sites is reported. The products of this reaction are dimethyl sulfide, methanethiol, hydrogen sulfide, carbon disulfide, methane, and ethylene. At 190°C, these products form via parallel reactions. At higher temperature of up to 350°C, dimethyl sulfide can form by the condensation of the resulting methanethiol. The strong basic sites of the catalysts are uninvolved in dimethyl sulfide formation. Over catalysts whose surface has only strong protonic or strong Lewis acid sites, dimethyl sulfide formation does take place, but slowly and nonselectively. The highest dimethyl sulfide formation activity and selectivity are shown by catalysts having medium-strength basic sites along with strong protonic and strong Lewis acid sites.     

Thermal properties of Y-type zeolites

The thermal and structural properties of two parent NaY zeolites and of those modified by ion exchange (ReNaY, HNaY, FeNaY) were investigated by simultaneous thermal analysis (TG-DTA-DTG) and by X-ray diffraction spectroscopy. Both the intracrystalline water and the zeolite framework were in our attention. The impurities (Fe) located in the lattice as well as the ions which entered by ion exchange (Re, H, Fe) influence the properties of the zeolites. The values of the activation energy of the dehydration process prove that the water molecules are more strongly bonded in all modified samples than in the parent ones. As compared to the NaY zeolites, an increased thermal stability, of about 100°C was revealed for ReNaY or of about 180°C for HNaY, and a decreased stability, of about 50°C, for FeNaY samples. The temperature at which the lattice break-down beginsT _amf, estimated by following the X-ray diffraction patterns for samples heated in air at temperatures from 300 to 1100°C, is the temperature which may be related to the structural characteristics of the zeolites, i.e., to the lattice constant of the uncalcined materials. The XRD studies reveal the heterogeneity of the crystallites constituting the zeolite material from both the point of view of the lattice constant values and the thermal stability. As the temperatureT _amf, generally, does not coincide with the temperature of the first exothermic peak,T ₁, of the DTA curve, we suggest the temperatureT _amf to be taken as an unambiguous measure of the thermal stability.     

Exploring Alkylated Ferrocene Sulfonates as Electrocatalysts for Sulfide Detection

Alkylated ferrocene sulfonate compounds, 1,1′‐dimethyl ferrocene sulfonate, t‐butyl ferrocene sulfonate, ethyl ferrocene sulfonate, and n‐butyl ferrocene sulfonate are explored for the electrocatalytic detection of sulfide at a boron‐doped diamond electrode. Voltammetric interrogation of the ferrocene sulfonate compounds is investigated to determine oxidizing potentials, diffusion coefficients and responses towards sulfide. In the latter case, measurement of the electrocatalytic rate constants by means of chronoamperometry indicates a high electrocatalytic activity (ca. 10³ M^?1 s^?1) towards sulfide.     

Mechanism of Aniline Methylation on Zeolite Catalysts Investigated by In Situ 13C NMR Spectroscopy

The alkylation reaction of aniline with methanol on zeolites HY and CsOH/CsNaY was studied by in situ ¹³C NMR spectroscopy under flow and batch conditions. Attention was focused on the identification of intermediates and on the determination of the formation mechanisms of N-methylaniline, N,N-dimethylaniline, and toluidines. To refine the main steps of the reaction, the transformations of the following individual compounds and intermediates, which were detected in the course of alkylation, were studied: dimethyl ether, surface methoxy groups, methylanilinium ions, formaldehyde, and N-methyleneaniline. It was found that N-methylaniline and N,N-dimethylaniline were formed as a result of aniline methylation by methanol dehydration products (methoxy groups or dimethyl ether) on acidic zeolites or as a result of alkylation by formaldehyde or methoxy groups on basic zeolites. Toluidines were formed by the isomerization ofN-methylanilinium ions, which were produced only on acidic zeolites, rather than by the direct alkylation of aniline.     

Activity of palladium sulfide catalysts in the reaction of gas-phase hydrogenation of 2-methylthiophene

In the interaction of hydrogen with 2-methylthiophene in the gas phase over palladium sulfide catalysts at 180–260?C and 0.1–0.8 MPa, the saturation of the thiophene ring resulting in 2-methylthiolane and the hydrogenolysis of 2-methylthiophene occurs. When the conversion is lower than 60%, these reactions occur independently; at higher conversions, methylthiolane also undergoes hydrogenolysis. The specific catalytic activity of PdS supported on γ-Al₂O₃, TiO₂, and carbon and without support is much lower in the hydrogenation of 2-methylthiophene than the activity of PdS supported on SiO₂, aluminosilicate, and zeolite HNaY having strong Brönsted acid surface sites.     

Investigation of the effect of carbon monoxide on the oxidative carbonylation of methanol to dimethyl carbonate over CuX and CuZSM-5 zeolites

Direct synthesis of dimethyl carbonate offers prospects for a “green chemistry” replacement to eliminate use of phosgene for polymer production and other processes. The carbonylation of methanol to produce dimethyl carbonate over Cu⁺X and Cu⁺ZSM-5 zeolites prepared by solid-state ion exchange has been investigated, focusing on the interaction of carbon monoxide with the Cu⁺ zeolites. The methanol carbonylation mechanism reported previously has been extended to account for carbon monoxide adsorption at high pressure. The comparison of the results obtained from Cu⁺X and Cu⁺ZSM-5 show that strong CO adsorption on the catalyst is not related to increased rate of dimethyl carbonate production. The rate limiting step for DMC production is best described as the Eley-Rideal reaction of gas-phase CO with surface methoxide.     

多级孔ZSM-5分子筛的合成及其在甲醇脱水制二甲醚反应中的应用

以四丙基氨为微孔模版剂,阳离子高分子聚合物为介孔模版剂,合成了具有多级介孔的ZSM-5分子筛,并用于甲醇气相脱水合成二甲醚.结果表明,加入阳离子高分子聚合物后,合成的HZSM-5分子筛样品既保持了其MFI典型结构,又呈现了多级介孔特征;随着阳离子高分子聚合物模板剂加入量的增加,其多级介孔特征更为明显.具有多级介孔的HZSM-5分子筛表现出比常规微孔HZSM-5分子筛高的反应稳定性和二甲醚选择性,这主要是由于其织构和酸性的双重作用.     

Interaction of aromatics with Br?nsted sites in zeolites: Demarcation line between regions of stable existence of H-complexes and ion pairs for various types of bases

Interaction of naphthalene, α-methylnaphthalene, and hexamethylbenzene with OH groups of SiO₂, HNaY and H-ZSM-5 zeolites was studied by IR spectroscopy. The results are compared with data obtained for other types of organic bases. Specificity in the generation of H-complexes of olefins, arenes, naphthalenes, N- and O-bases with Br?nsted surface sites was elucidated. Each type of base appears to have its particular correlation of (PA^a-PA^b) and the shift of Δυ_OH band in H-complexes. It has been found that if (PA^a-PA^b) is less than 85±5 kcal/mol, the formation of ion pairs is thermodynamically more favorable than that of H-complexes for all types of organic compounds.     

Activity of cobalt sulfide catalysts in the hydrogenolysis of dimethyl disulfide to methanethiol: Effects of the nature of a support and the procedure of supporting a cobalt precursor

The conversion of dimethyl disulfide to methanethiol on various catalysts containing supported cobalt sulfide in an atmosphere of hydrogen was studied at atmospheric pressure and T = 190°C. On CoS introduced into the channels of zeolite HSZM-5, the process occurred at a high rate but with a low selectivity for methanethiol because the proton centers of the support participated in a side reaction with the formation of dimethyl sulfide and hydrogen sulfide. Under the action of sulfide catalysts supported onto a carbon support, aluminum oxide, silicon dioxide, and an amorphous aluminosilicate, the decomposition of dimethyl disulfide to methanethiol occurred with 95–100% selectivity. The CoS/Al₂O₃ catalysts were found to be most efficient. The specific activity of alumina-cobalt sulfide catalysts only slightly depended on the phase composition and specific surface area of Al₂O₃. The conditions of the thermal treatment and sulfurization of catalysts and, particularly, the procedure of supporting a cobalt precursor onto the support were of key importance. Catalysts prepared through the stage of supporting nanodispersed cobalt hydroxide were much more active than the catalysts based on supported cobalt salts.