Kinetics of autocatalytic hydrolysis of tetraethyl orthosilicate in the presence of aluminium nitrate

Kinetics of autocatalytic hydrolysis of tetraethyl orthosilicate in the presence of aluminium nitrate has been studied experimentally. According to the suggested reaction mechanism and the proposed mathematical model, kinetic constants have been determined.

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. , .

     

Interaction of PM12?nVnO40?(3+n) (M=Mo, W) heteropoly complexes with nitrogen oxide

In aqueous solution, PM_12–nV_nO₄₀ ^–(3+n) (M=Mo,W) hetero-polyanions provide a much faster oxidation of NO than mononuclear VO ₂ ⁺ ions, yielding HNO₂, NO ₃ ^– and reduced HPA.

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, PM_12–nV_nO₄₀ ^–(3+n) (M=Mo,W) , VO ₂ ⁺ , NO HNO₂ NO ₃ ^– .

     

Comparative analysis of catalytic properties of 3d metal acetylacetonates in liquid-phase oxidation of dibenzyl ether

Studies of the liquid-phase oxidation of dibenzyl ether in the presence of 12 acetylacetonates of 3d metals and a comparative analysis of the dependence of the catalytic activity and selectivity of chelates on the atomic number and valence state have been carried out.

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12 3d . .

     

Thermal and other studies on bivalent metal selenltes

BaSeO₃·2·5H₂O(I), PbSeO₃· 2H₂O(II) and CdSeO₃·3.5H₂O(III) were prepared and analysed. Their hygroscopicity and solubility was investigated. These compounds have high thermal Stability, as shown by their TG and DTA data. IR spectra show multi-dentate coordination of selenite to cations, due to considerable splitting of the asymmetric v₃ and v₄ bands of SeO ₃ ^{2 –} in the 780-730 cm^–1 and 420-325 cm^–1 region.Tentative structures have been proposed involving bridging oxygen atoms.

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Zusammenfassung BaSeO₃-2.5H₂O(I), PbSeO₃ · 2H₂O(II) und CdSeO₃· 3.5H₂O(III) wurden hergestellt, analysiert sowie deren Hygroskopizität und Löslichkeit untersucht. TG- und DTA-Untersuchungen erweisen die hohe thermische Stabilität dieser Verbindungen. Die IR-Spektren zeigen mehrzählige Koordination von Selenit zu Kationen, was aus einer beträchtlichen Aufspaltung der antisymmetrischenv ₃ undv ₄ Banden von SeO ₃ ^{2 –} im Bereich 780-730cm^–1 bzw. 420-325 cm^–1 hervorgeht. Es wurden versuchsweise Strukturen mit überbrückenden Sauerstoffatomen vorgeschlagen.

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BaSeO₃· 2,5H₂O, PbSeO₃ · 2H₂O CdSeO₃ · 3,5H₂O . . - , v ₃ v ₄ SeO ₃ ² }- 780-730 420-325 ^–1. , .

     

The thermal decomposition reactions of bis-(pyridine-2-aldoxime)-copper(II) complexes

The thermal properties of some complexes of copper(II) with pyridine-2-aldoxime (HPAO), where the ligand appears either as the ion (PAO^–) or as a neutral molecule, were determined in vacuo and in dynamic nitrogen and oxygen gas atmospheres. The study was carried out by thermoanalytical (TG, DTG. DTA), spectroscopic and spectrometric (UV-visible, IR, diffuse reflectance, mass) techniques.The initial decomposition temperature is influenced by the number of acid hydrogens in the complex; the thermal stability sequence in vacuo is: [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]The thermal decomposition reactions occur in several separate steps, the first of which gives rise to partial ligand decomposition, the reduction of copper(II) to copper(I), and the conversion of the residual pyridine-2-aldoxime into acid amide.

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Zusammenfassung Die thermischen Eigenschaften einiger Komplexe von Kupfer(II) mit Pyridin-2-aldoxim (HPAO), in denen der Ligand entweder als Ion (PAO^–) oder als neutrales Molekül vorliegt, wurden im Vakuum und in dynamischer N₂- und O₂-Atmosphäre ermittelt. Zur Untersuchung wurden thermoanalytische (TG, DTG, DTA) und spektrometrische (UV-sichtbar, IR, diffuse Reflektionsspektrophotometrie, Massenspektrometrie) Techniken herangezogen. Die Temperatur, bei der die Zersetzung beginnt, wird durch die Zahl der sauren Wasserstoffatome im Komplex beeinflußt; für die thermische Stabilität im Vakuum gilt die Reihenfolge [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]. Die thermischen Zersetzurigsreaktionen verlaufen in mehreren diskreten Schritten, wobei der erste von diesen eine partielle Zersetzung des Liganden, die Reduktion von Kupfer(II) zu Kupfer(I) und die Konversion des verbleibenden Pyridin-2-aldoxims in das Säureamid in sich einschließt.

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-2- ( ), (-), . (, , ) , - , , - . , [Cu(PAO)₂H]CI > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂] , , -2- .

     

Thermal and infrared spectral analyses of sabugalite

The thermal decomposition and infrared spectrum of sabugalite were studied. The infrared spectrum was interpreted on the basis of site and factor symmetry analysis and correlated with the X-ray powder diffraction data. The dehydration of sabugalite is characterized by three endotherms. The anhydrous phase decomposes at 440–680 °C. On the basis of the infrared spectrum in Nujol, oxonium ions are postulated in the structure of sabugalite. The infrared spectrum in a KBr disk is probably influenced by the sample preparation mode. Sabugalite does not form a meta I hydrate. Its first new partly dehydrated phase is isostructural with metaautunite II.

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Zusammenfassung Die thermische Zersetzung und das IR-Spektrum von Sabugalit wurden untersucht. Das IR-Sektrum wird auf der Grundlage von Site- und Faktor-Symmetrie-Analysen interpretiert und mit Pulver-Röntgenbeugungsdaten korreliert. Die Entwässerung von Sabugalit ergibt 3 endotherme Effekte. Die wasserfreie Phase zersetzt sich bei 440 bis 680 °C. Auf Grund des IR-Spektrums in Nujol werden Oxonium-Ionen in der Struktur des Sabugalit vermutet. Das IR-Spektrum in KBr-Tabletten wird wahrscheinlich durch die Probenpräparation beeinflusst. Sabugalit bildet kein Metal-Hydrat. Seine erste teilweise entwässerte Phase ist isostrukturell mit Metaautunit II.

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. ** - . . 40–80°. , . . I . II.

     

Catalytic conversion of dimethylsulfide to methylmercaptan

The effect of reaction conditions on the methylmercaptan formation from dimethylsulfide in H₂S catalyzed by -Al₂O₃ has been studied. The reaction is first order with respect to dimethylsulfide. It has been revealed that the maximum activity in this reaction is observed for the catalysts whose surface contains a large number of aprotonic acid centers and moderate-strength basic sites.

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-Al₂O₃. , . . , , .

     

Mössbauer study of the thermal decompositions of alkaline earth tris(oxalato)ferrates(III)

The thermal decompositions of alkaline earth tris(oxalato)ferrates(III) (Mg, Ca, Sr and Ba) have been studied by Mössbauer spectroscopy and other techniques. During the thermal decomposition, dehydration occurs first, followed by reduction to iron(II) species, and oxides and ferrites (MFe^IIIO₄) are then formed at higher temperature. In the case of strontium tris(oxalato)ferrate(III), strontium ferrite (SrFe^IVO₄) is formed at 700°.

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Zusammenfassung Die thermische Zersetzung von Tris(oxalato)ferraten(III) der Erdalkalimetalle (Mg, Ca, Sr, Ba) wurde durch Mössbauer-Spektroskopie und andere Techniken untersucht. Im Verlaufe der thermischen Zersetzung verläuft zunächst die Dehydratisierung, gefolgt von der Reduktion zu Eisen(II)-Species. Oxide und Ferrite (MFe^IIIO₄) werden danach bei höheren Temperaturen gebildet. Strontium-tris(oxalato)-ferrat(III) geht bei 700 °C in Strontiumferrit (SrFe^IVO₄) über.

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() () , , ë . , , MFe^IIIO₄. 700° SrFe^IVO₄.

     

Dispersity of oxidized and reduced palladium on Al2O3

The amount of PdO not dissolving in dilute HCl as a function of its content in palladium catalysts calcined in air has been determined. Mean size of Pd particles in the same samples has been evaluated from oxygen chemisorption. A comparison of these data indicates their correlation, which permits to determine Pd dispersity variations according to the solubility of supported PdO before reduction.

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. . , .

     

Composition and properties of the cobalt-molybdenum oxide system

The physico-chemical and catalytic properties of the Co–Mo oxide system have been studied in a wide range of various molybdenum to cobalt ratios. The activity increase at 1.21Mo:Co?11 is assumed to be due to the formation of solid solutions.

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- Co–Mo- . , - 1,21Mo:Co>11 .

     

Radical addition of methyldichlorosilane to vinyl acetate

The GC-MS method was used to identify the addition products of methyldichlorosilane to vinyl acetate. Radiation-induced addition of methyldichlorosilane to vinyl acetate produces 2-methyldichlorosilylethyl ethyl ether. The reaction follows a radical-chain mechanism. The ratio of the rate constants of methyldichlorosilyl radical addition to C=C and C=O to vinyl acetate amounts to 0.4±0.1 (303 K).

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- . , - 2- . , C=C C=O 0,4±0,1.

     

Mössbauer studies of thermal decomposition of metal(III) hexacyanoferrates(II)

The thermal decomposition of metal(III) hexacyanoferrates(II) (Al, As, Sb, Bi) was studied up to 700° in air by employing Mössbauer, infrared spectroscopy and thermal analysis techniques. With the exception of the bismuth compound, the isomer shift of these hexacyanoferrates(II) increases on dehydration at 200°. Dehydration is complete at 200°, decomposition into the ferrite at 300°, and formation of-Fe₂O₃ from aluminium and bismuth hexacyanoferrates(II) and Fe₃O₄ from antimony and arsenic hexacyanoferrates(II) at 700°.

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Zusammenfassung Die thermische Zersetzung von Metall(III)ferrocyaniden (Al, As, Sb, Bi) wurde bis zu 700° in Luft unter Anwendung der Mössbauer und Infrarotspektroskopie, sowie thermoanalytischer Techniken untersucht. Die Isomerverschiebung dieser Ferrocyanide nimmt mit der Dehydratisierung bei 200° zu, mit Ausnahme des Wismuts. Die Dehydratisierung ist bei 200° abgeschlossen, die Zersetzung zum Ferrit bei 300° und die Bildung von-Fe₂O₃ aus Aluminium- und Wismutferrocyanid, von Fe₃O₄ aus Antimon- und Arsenferrocyanid bei 700°.

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Résumé On a étudié dans l'air jusqu'à 700°, la décomposition thermique des ferrocyanures de métaux trivalents (Al, As, Sb, Bi), par spectroscopies Mössbauer et infrarouge, ainsi que par les techniques d'analyse thermique. Le déplacement des isomères de ces ferrocyanures augmente lors de la déshydratation à 200°, à l'exception du bismuth. La déshydratation est complète à 200°, la décomposition en ferrite à 300°, la formation d'-Fe₂O₃ à partir des ferrocyanures d'aluminium et de bismuth ainsi que du Fe₃O₄ à partir des ferrocyanures de l'antimoine et de l'arsenic à 700°

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-, , — Al, As, Sb, Bi- 700° . , , 200°. 200°, 300° -Fe₂O₃. 700° Fe₃O₄.

     

Determination of hydroxyl groups and/or water on the surface of oxide catalysts by a pulse chromatographic method

A pulse chromatographic method based on the reaction of gaseous dimethylzinc tetrahydrofura nate was developed for the determination of surface hydroxyl groups and/or adsorbed water in solid porous materials. The procedure is rapid and gives results comparable to other methods. Some heterogeneous catalysts and supports have been analyzed.

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, , / , . , . .

     

Potassium addition to Fe/MgO, Ni/MgO and Ni/SiO2: Reducibility, dispersity and stabilization of the promoter by the support

The influence of potassium addition on the morphological properties of Fe/MgO and Ni/MgO has been investigated: KNO₃ addition to precursors results in a decrease of the reducibility and in a smaller dispersity of the metallic phase. A loss of potassium is observed at reduction temperatures in excess of 773 K. Silica-supported Ni behaves differently: silica inhibits the potassium volatilization and nickel reducibility is enhanced. This illustrates how promoter effects can be influenced by the nature of support.

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Fe/MgO Ni/MgO: KNO₃ . , 773 K. , : . .

     

Effect of the roughness factor on the surface oxidation of ruthenium catalysts

The surface oxidation of ruthenium catalysts with different roughness factor values has been analyzed. It is shown that electro formation of oxidized species on the exposed surface of ruthenium is strongly affected by the rougher characteristics of the surface. This effect has been explained through the addition and removal of protons to and from the oxidized species.

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. , . .

     

Kinetic analysis of thermogravimetric data. XI thermal decomposition of some metal dithionates

A thermal analytical study of Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba and Zn dithionates is reported. The decomposition of the dithionate ion is endothermic in the case of the Na, K, Rb, Cs and NH₄ salts, but exothermic with Li, Mg, Sr, Ba and Zn. Kinetic parameters have been derived from the TG curves by means of the Coats-Redfern method. The validity of a linear kinetic compensation law is reported for the loss of crystal water and separately for the decomposition of the dithionate ion.

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Zusammenfassung Es wird über eine thermoanalytische Untersuchung der Dithionate von Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba und Zn berichtet. Die Zersetzung des DithionatIons ist im Falle von Na, K, Rb, Cs und NH₄-Salzen endotherm, im Falle von Li, Mg, Sr, Ba und Zn hingegen exotherm. Die kinetischen Parameter wurden aus den TG-Kurven mittels der Coats-Redfern-Methode abgeleitet. Es wird über die Gültigkeit eines linearen kinetischen Kompensationsgesetzes für den Verlust von Kristallwasser berichtet und gesondert für die Zersetzung des Dithionat-Ions.

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Résumé On présente les résultats d'une étude par analyse thermique des dithionates de Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba et Zn. La décomposition est endothermique dans le cas des sels de Na, K, Rb, Cs et ammonium tandis qu'elle est exothermique dans le cas des sels de Li, Mg, Sr, Ba et Zn. Les paramètres cinétiques sont déduits des courbes TG par la méthode de Coats-Redfern. La validité d'une loi de compensation cinétique linéaire est étudiée pour la perte de l'eau d'hydratation ainsi que pour la décomposition de l'ion dithionate.

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Li, Na, K, Rb, Cs,. NH₄, Mg, Ca, Sr, Ba Zn. [ Na, K, Rb, Cs NH₄ , Li, Mg, Sr, Ba Zn . - . .

     

Oxidative dehydrogenation (OXD) of n-butane I. Activity of natural quartz II. Kinetic and catalytic activity of nickel oxides

The oxidative dehydrogenation of n-butane on nickel oxide catalysts and on natural quartz, used as catalysts diluent, were studied. It is assumed that oxygen ions from the oxide lattice participate in the initial step of the reaction.

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- , . , .

     

IR study of 1-hexene isomerization on HZSM-5 zeolites

In the IR spectra of 1-hexene adsorbed on HZSM-5 zeolites with different Si/Al ratios, a new band at 1510 cm^–1 has been observed. The cis/trans-2-hexene and trans-2-hexene/1-hexene ratios were determined.

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1-, HZSM-5 Si/Al, 1510 cm^–1. /-2- -2-/1-.

     

Intermediate oxygen-containing compounds in oxidative condensation of methane over sodium-manganese catalysts

CH₂O conversion over sodium-manganese oxide and oxychloride catalysts in methane dehydrodimerization have been studied under unsteady-state conditions at high temperatures (600–750 °C). It has been established that formaldehyde conversions produce deep oxidation (CO, CO₂), condensation (C₂H₄, C₂H₆) and methanation products through CH₃O^– formation and decomposition.

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(600–750°C) CH₂O - . , (CO, CO₂) (C₂H₄, C₂H₆), , CH₃O^–.

     

Relaxation of the rate of o-xylene oxidation to phthalic anhydride on vanadium catalysts

Based on numerical analysis of experimental data, the main ideas of the reaction mechanism have been confirmed and kinetic principles of the non-steady=state reaction have been determined.

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