Kinetics of oxidation of acrolein on a vanadium-molybdenum oxide catalyst

A kinetic study has shown that, in the range of low conversions, the reaction rate depends only on the partial pressure of oxygen. Comparison of the oxidation of acrolein and I-deuteroacrolein suggests that the splitting of the H–CO bond is not rate-limiting.

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, , , . 1- , H–CO .

     

Catalytic preparation of diacetone alcohol in controlled flow conditions

Catalytic preparation of diacetone alcohol from acetone was studied using strong basic ion exchangers as catalysts. A continuous process was carried out in an enlarged laboratory set-up with controlled flow rate. Experiments were performed with respect to experiment duration, temperature, flow rate, catalyst porosity and catalyst-acetone ratio. The quantity of DAA was determined by gas chromatography. The effects of temperature, catalyst porosity and catalyst-acetone ratio on the reaction course were significant in comparison with other parameters examined. An exponential dependence of C/A ratio on DAA yield was found.

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() , . . , , , /. . , / (/) . - /.

     

Beitrag zur aufeinanderfolgenden thermochemischen Bestimmung von SiO2 und Al2O3 Aus flusssaurer lösung

Zusammenfassung Die vorliegende Arbeit gibt eingangs einen Überblick von Publikationen, die sich mit der thermochemischen Bestimmung von SiO₂ und Al₂O₃ aus flußsaurer Lösung befassen. Davon ausgehend werden Versuche beschrieben und Ergebnisse diskutiert, die mit konstanten Einwaagen von 700 mg SiO₂ und etwa 100 mg Al₂O₃ aus flußsaurer Lösung und verschiedenen Kombinationen von Injektionsreagenzien erhalten wurden und die auf die Belange der Analyse von gefällten Natriumaluminiumsilicaten abgestimmt waren. Die vorgenommenen Untersuchungen führen zu den Schluß, daß Al₂O₃ und SiO₂ in Natriumaluminiumsilicaten aus flußsaurer Lösung mit der Injektionsreagenskombination SrCl₂KCl bestimmt werden sollten.

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The first part of the paper gives a review of the literature dealing with thermochemical determinations of SiO₂ and Al₂O₃ in hydrofluoric acid solution. The results of experiments with constant samples weights of 700 mg SiO₂ and about 100 mg Al₂O₃ in hydrofluoric acid solution with differently combined injection reagents are discussed. The determinations were based on the analysis of precipitated sodium aluminium silicates.The investigations revealed that combined SrCl₂/KCl solution should be used as injection reagent for determination of the Al₂O₃ and SiO₂ contents of sodium aluminium silicates in hydrofluoric acid.

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, . , (700 ) ( 100 ) , . . , SrCl₂-KCl .

     

Simple catalytic mechanism permitting a multiplicity of catalyst steady states

The conditions of the existence of several steady states for a three-step mechanism, viz. a catalytic trigger (consecutive), are discussed.

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- ().

     

Investigation of kinetics and mechanism of maleic anhydride interaction with pentachlorinated phosphorus

Kinetics and mechanism of the interaction of maleic anhydride with pentachlorinated phosphorus have been studied. Kinetic parameters of a model making it possible to control this reaction have been calculated.

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, , .

     

IR-spectroscopic studies of the interaction of pyridine bases with vanadium and molybdenum oxides supported on magnesia

As shown by IR-spectroscopic studies, pyridine bases interacting with V₂O₅ and MoO₃ supported on MgO form hydrogen bonds with surface hydroxyls and coordinate bonds with V and Mo ions. The interaction of 2,6-dimethylpyridine adsorbed on the surface with oxygen leads to the formation of 6-methylpyridine-2-carboxaldehyde, whose formyl group interacts with surface hydroxyls.

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, V₂O₅ MoO₃, MgO, V Mo. 2,6- 6--2-, OH-.

     

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

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CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

Studies of the dynamic properties of heterogeneous catalytic reactions in a closed adiabatic gradientless system over biographically inhomogeneous catalyst surface

The dynamic of a closed adiabatic system of constant volume consisting of an ideal gas mixture and particles adsorbed over the biographically inhomogeneous catalyst surface, has been studied. The asymptotic stability of a point of detailed equilibrium in each reaction simplex has been proved.

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, , . , .

     

On the nature of active centers in catalysts for propylene oxidation to acetone

Acid-base properties of binary tin-oxide catalysts for the oxidation of propylene to acetone have been studied. It has been revealed that active catalysts should have both Brönsted acid- and base centers.

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- . , .

     

Study of reversible proton transfer from 2,2,2-trifluoronitroethane to amines by dynamic1H and19F NMR

The interaction between the weak CH-acid CF₃CH₂NO₂ and aliphatic amines has been studied by NMR in CDCl₃ and CFCl₃ solutions. It is shown that no measurable amounts of H-bonded complexes are formed. However, reversible proton transfer with the formation of ion pairs takes place. The kinetic parameters of this process have been determined.

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CH- CF₃CH₂NO₂ CDCl₃ CFCl₃. , , . .

     

Effect of heating rate on activation energies derived by a dynamic kinetic method

Alkaline fading of bromophenol blue was chosen for the investigation of the effect of heating rate on the activation energies derived from the dynamic kinetic method. Freeman and Carroll's treatment was adopted to compute the activation energies from experimental data taken with three heating rates: namely 1°, 0.5° and 0.25°/min. It was found that the activation energy increases as the heating rate decreases. This is attributed to the non-equilibrium conditions. By extrapolating to zero heating rate, the activation energy obtained is comparable to that obtained via classical isothermal kinetics.

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Zusammenfassung Die in alkalischem Medium erfolgende Entfärbung von Bromphenolblau wurde zum Studium des Einflusses der Aufheizgeschwindigkeit auf die nach der dynamischen kinetischen Methode erhaltenen Aktivierungsenergien herangezogen. Das Verfahren von Freeman und Carroll wurde zur Berechnung der Aktivierungsenergien aus Versuchsdaten, welche bei drei Aufheizgeschwindigkeiten, nämlich 1°, 0.5° und 0.25°/min erhalten worden waren, verwendet. Es wurde festgestellt, daß die Aktivierungsenergie mit abnehmender Aufheizgeschwindigkeit zunimmt. Der Grund hierfür wird den Nicht-Gleichgewichtsbedingungen zugeschrieben. Wird auf Aufheizgeschwindigkeit=0 extrapoliert, so ist die erhaltene Aktivierungsenergie mit der nach klassischer isothermer Kinetik erhaltenen vergleichbar.

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Résumé On a choisi la décoloration du bleu de bromophénol en milieu alcalin pour étudier l'influence de la vitesse de chauffage sur l'énergie d'activation calculée à partir des données fournies par une méthode d'étude cinétique dynamique. On a adopté la méthode de Freeman et Carroll pour calculer les énergies d'activation à partir des données expérimentales obtenues avec trois vitesses de chauffage, à savoir 1°, 0.5° et 0.25°/min. On montre que l'énergie d'activation augmente quand la vitesse de chauffage diminue. On attribue ce phénomène aux conditions de non-équilibre. En extrapolant pour une vitesse de chauffage nulle, on obtient une énergie d'activation comparable à celle calculée par la méthode classique en cinétique isotherme.

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, . , (1°, 0,5°, 0,25°/) . , .

     

Reaction mechanism and principles of choosing catalysts for selective oxidation at C?H bonds

Reaction mechanism for selective oxidation of organic compounds at C–H bonds is discussed. The criteria of selecting catalysts for these reactions have been formulated; 1) fast heterolytic activation of C–H bonds; 2) relatively slow primary activation of oxygen; 3) fast diffusion of oxygen vacancies; 4) fast electron transfer from the adsorbed substrate to catalyst.

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C–H . : 1) C–H ; 2) ; 3) ; 4) .

     

TPD studies of hydrogen sorption on platinum powder catalysts modified with adsorbed gold

It has been shown that hydrogen determined from the TPD curves of platinum saturated with hydrogen sorbed above room temperature is chiefly absorbed and not adsorbed hydrogen; this absorbed hydrogen has no effect on the charging curve.

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, , , , ; .

     

Temperature dependence of the initial quantum yield of oxygen photoadsorption on zinc oxide

The initial quantum yield of photoadsorption at =365–577 nm is shown to decrease with the temperature increase. Experimental data are partly accounted for by the temperature shift of the long wavelength edge of the fundamental absorption band that is of low activity in oxygen photoadsorption.

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, 365–577 . , .

     

Structural and thermal studies on sisal fibre

Mechanical characteristics of sisal fibre, such as UTS and Young's modulus, have been determined. The thermal degradation of sisal fibre has been observed by running its DSC and TG/DTG.

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Zusammenfassung Die mechanischen Kennwerte (UTS, Young's Modul) von Sisalfasern wurden bestimmt. Der thermische Abbau von Sisalfasern wurde mittels DSC und TG/DTG untersucht.

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, . / .

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The authors wish to thank Dr. R. K. Tiwari, Dr. S. V. Prasad and Dr. M. Patel for their useful suggestions.     

Applications of thermal analysis

This review paper outlines some current developments in thermal analysis. The current status of standard methods, in particular those issued by the American Society for Testing and Materials (ASTM), using thermal analysis techniques are discussed. In the second place a simple method for the determination of the oxidative stability of polyethylene by DTA is reviewed. Finally the paper surveys some of the more recent work being carried out in fossil fuels and fuel oils.

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Zusammenfassung Dieses Referat umreisst einige zeitgemässe Entwicklungen der Thermoanalyse. Es wird der derzeitige Stand der Standardmethoden besprochen, besonders derjenigen, die durch die American Society for Testing + Materials (ASTM) veröffentlicht wurden, und die ein thermoanalytisches Verfahren verwenden. In zweiter Reihe wird eine einfache Methode zur Bestimmung der oxydation Stabilität des Polyäthylens mittels DTA bekanntgemacht. Zum Schluss übersieht die Arbeit einige neuere Arbeiten, die an festen Heizmaterialien und Heizölen durchgeführt wurden.

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. , , , ASTM. ' . , .

     

Thermal decomposition of Y,La and light lanthanide ferulates

The conditions of thermal decomposition of Y, La and light lanthanide ferulates have been studied. On heating, these complexes decomposed in various ways; lanthanum ferulate in four stages, Ce(III) ferulate in three stages, and the ferulates of Y, Pr(III), Nd, Sm, Eu(III) and Gd in two stages, the oxides finally being formed. The complexes lose crystallization water to form anhydrous or hydrated salts, and are then decomposed directly to oxides. Only lanthanum ferulate decomposes to the oxide with intermediate formation of La₂O₂CO₃. The temperatures of oxide formation change periodically with the decrease in the ionic potential in the lanthanide series.

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Zusammenfassung Es wurden die Bedingungen der Zersetzung der Y-, La- und leichten Lanthanidferulate untersucht. Die erhaltenen Komplexe werden beim Erhitzen auf verschiedene Weise zersetzt. Lanthanferulat wird über vier, Ce(III)-Ferulat über drei und die Ferulate von Y, Pr(III), Nd, Sm, Eu(III) und Gd über zwei Zwischenstufen in das entsprechende Oxid überführt. Aus den Komplexen entstehen zunächst unter Verlust von Kristallwasser wasserfreie oder hydratisierte Salze, die dann direkt zu den Oxiden abgebaut werden. Nur Lanthanferulat wird über eine intermediäre Verbindung des Typs M₂O₂CO₃ zum Oxid abgebaut. Die Bildungstemperaturen der Oxide ändern sich periodisch mit abnehmenden Ionenpotential in der Lanthanidenreihe.

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Y, La . . , — , Y, (III) Nd, Sm,Eu(III) Gd — . , , . L₂₂₃. .

     

Methanol conversion to hydrocarbons and dimethyl ether on decationized zeolite T

Methanol transformations over the hydrogen forms of zeolite T (32%–76% decationization and 13%–32% dealumination) during contact with methanol vapor was studied at 200°–400°C. The catalysts used show a high activity in methanol conversion into light hydrocarbons and dimethyl ether but over a short period.

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T (32–16% 13–32% ) 200–400°C. , .