51V NMR Study of VOCl3Immobilized on the SiO2and MgCl2Surface

The magnetic shielding tensor and quadrupole interaction parameters, as well as the mutual orientation of tensors for the (SiO)VOCl₂complex obtained by the immobilization of VOCl₃on the SiO₂surface are determined. The state of VOCl₃on the surfaces of MgCl₂and modified SiO₂with all surface OH groups replaced by Cl atoms is studied. To prepare the modified SiO₂, CCl₄and SiCl₄are used as chlorinating agents. The formation of structurally similar pentavalent vanadium complexes on the surface of these supports is shown. A model for the coordination environment of vanadium on the chlorine-containing supports is proposed. The vanadium atom exists in the distorted pentahedral environment and is bound to the support through either two chlorine atoms or chlorine and oxygen atoms. A correlation between the coordination of VOCl₃and catalytic properties of VOCl₃/MgCl₂is assumed.     

Stoichiometry of Oxidation Reactions Involving α-Oxygen on FeZSM-5 Zeolite

The stoichiometry of the low-temperature reaction between surface -oxygen formed by decomposing N₂O over Fe-containing ZSM-5 zeolite and methane, hydrogen (deuterium), and carbon monoxide is studied. Methane and hydrogen react with -oxygen in stoichiometric ratios of 1 : 1.8 and 1 : 1.6, respectively. The observed stoichiometry is due to the mechanisms of the corresponding reactions. According to a mechanism proposed for the interaction of -oxygen with methane and hydrogen, this reaction is accompanied by the dissociation of CH₄and H₂molecules. For hydrogen, such a mechanism is supported by IR spectroscopic studies of resulting surface compounds, namely, of new hydroxyl groups that were formed on the zeolite surface in the course of the reaction. -Oxygen reacts with CO in the ratio of 1 : 1 to form CO₂in amounts equal to those of -oxygen on the surface.     

Promotion of Catalytic Properties of Sulfated Zirconium and Aluminum Oxides with Carbon Tetrachloride

The promoting effect of minor amounts of carbon tetrachloride on the catalytic activity and working life of sulfated zirconium and aluminum oxides is considered for the example of isobutane alkylation with butenes.     

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.     

Interaction of butylamines with protonic centers of HNaY zeolite

IR-spectroscopic studies of the interaction of tert-, sec- and n-butylamine with HNaY protonic centers at 373–725 K and P_amine=0.13–13.3 kPa indicate that the deamination proceeds through intermediate butylammonium ions whose decomposition is the rate-determining step and can provide directly ammonium ions. The temperature of incipient reaction increases in the series: tert-

- -, - - 373 723 0,13 13,3 . , . . : -<-<-.

     

IR spectroscopic studies of H2S adsorption on acid and base catalysts

IR spectra of H₂S adsorbed on various types of catalysts have been studied by monitoring changes in the properties of their surfaces from the spectra of probe molecules. It is shown that H₂S is adsorbed only dissociatively on basic centers (BC); on proton centers (PC) it forms H-complexes, while with the participation of strong Lewis acid centers (LAC), it is adsorbed both associatively and dissociatively.

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- H₂S , -. , H₂S (), () -, ()- , .

     

Reaction of tetrahydrofuran with H2S in the presence of Na+/γ-Al2O3

Modification of -Al₂O₃ by sodium hydroxide promotes the increase of surface basicity but does not exert a strong effect on catalytic activity in the reaction of thiolane production from tetrahydrofuran and H₂S. Introduction of NaOH to -Al₂O₃ in small concentration increases the number of Lewis acid centers but decreases their strength. The activity of Na/-Al₂O₃ referred to one Lewis acid center drops.     

Reaction of nitrogen oxides with salts of metal-substituted heteropolyanions

We have used IR spectroscopy to study the reaction with NO and NO₂ of solid tetramethylammonium and cesium salts of heteropolyanions (HPA) PW₁₁M(L) _0.39 ^n– [M=V(V), Cr(III), Mn(II), Fe(II, III), Co(II), Ni(II), Cu(II); L=H₂O, OH^– or O^2–], preevacuated at 110°C or 300°C. Only in the case of Fe(II)-substituted heteropolyanions are nitrosyl complexes formed: PW₁₁Fe(NO)O ₃₉ ^5– (vNO=1730 cm^–1), which leads to stabilization of the NO molecules with respect to oxidation by oxygen. We observed reversible reaction with NO₂ by the listed heteropoly complexes. The vibrational frequencies of adsorbed NO₂ are virtually independent of the metal M and its coordination environment in the heteropolyanion (v₁=1335–1360) and v₃=1620–1640 cm^–1). This provides a basis for assuming that the NO₂ groups are bonded to the oxygen atoms in the heteropoly anion with formation of the fragments O_HPA...NO₂.Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1966–1971, September, 1992.     

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.     

Synthesis of methylmercaptane in the presence of base catalysts

Interaction of methanol with H₂S has been studied at 360–500°C in the presence of Al₂O₃ promoted by alkaline metal compounds. As found, catalysts, obtained via promoting Al₂O₃ by carbonate, and potassium or sodium hydroxide, are more basic in relation to tung-state samples. The total catalytic activity increased, while the selectivity toward methylmercaptane decreased with increasing surface basicity.

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360–500°C Al₂O₃, . , , Al₂O₃ , . - .