Catalytic activity of transition metal silicides in hydrogen oxidation

The catalytic activity of transition metal silicides in H₂ oxidation is much higher compared to metal-like carbides, which can be due to the lower electronegativity of silicon compared to carbon.

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, , .

     

Oscillation chemiluminescence in liquid phase oxidation of organic compounds

It is for the first time that distinct chemiluminescence oscillations have been observed in the liquid phase oxidation for the system: oxidative substrate — thermal initiator — photosensitizer — O₂. Oscillations and their parameters are dependent on the experimental conditions.

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: — — —O₂. .

     

Evaluation of triplet repulsion energies

The equation is suggested for predicting triplet repulsion energies. X=R–R^o, while R^o and¹V^o are the equilibrium bond length and the spectroscopic dissociation energy, respectively. Parameters and may be estimated from known bond properties.

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( X=R–R^o, a R^{o 1}V^o , . , .

     

Reaction between the OH group of hydroxyproline and diisocyanate catalyzed by an organotin compound

We have studied the kinetics of the reaction of L-hydroxyproline with OCH(CH₂)₆NCO, catalyzed by organotin, avoiding side reactions by protecting the other active hydrogens of the aminoacid, and comparing it with the MeOH/n-BuNCO system.

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L-- -OCN(CH₂)₆NCO, , . . - .

     

A new Ba(OH)2 catalyst for synthesis of diacetone alcohol

The application of new Ba(OH)₂ catalysts for the preparation of diacetone alcohol is described. No loss of activity is observed when they are stored in a dessiccator over NaOH. The same yield as that described in the literature is obtained, but in a much shorter reaction time (9.5 h against 72–120 h)

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Ba(OH)₂ . NaOH . , , (9,5 72–120 ).

     

Chemiluminescent method to measure generation rates of active centers in reaction of hydrogen peroxide with hemin and pyridinehemichrome

A chemiluminescent method was used to measure generation rates of active intermediates in the interaction of hemin with hydrogen peroxide with and without pyridine at pH=8–9. The effect of various inhibitors in these two cases has been examined.

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pH=8+9. .

     

Influence of HCl on butene isomerization catalyzed by ethanolic rhodium trichloride II. Calculation and interpretation of the rate constants of the triangle scheme

The values of the rate constants of the triangle scheme, calculated by means of a non-linear least-squares method, depend systematically on the HCl concentration. The alteration of the cis-trans selectivity expressed by the ratio k_1c/k_1t might indicate a change in the mechanism of isomerization with the HCl concentration.

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, , . - , k_1c/k_1t, .

     

Determination of CO adsorption heats from kinetic data for CO hydrogenation over metals

Studies of catalytic CO hydrogenation following the Langmuir-Hinshelwood mechanism indicate that the observed decrease in the activation energy with increasing temperature is due to the decreased surface coverage with reactants. The relationships obtained permit to carry out approximate estimates for the adsorption heat of CO.

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CO, -, , . CO.

     

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-.

     

A study of thermal preparation OF c-Mn2P4O12

With the application of thermogravimetry under quasi-isothermal-isobaric conditions, the reaction course of the calcination of Mn(H₂PO₄ · H₂O to give dimanganese cyclotetraphosphate has been studied. Isothermal calcination was also carried out in an electric furnace at various temperatures (200 min). The reaction products were analyzed by chromatography, IR and NMR spectrocopy, and X-ray diffraction analysis. The compositions of the calcinates were determined through extraction with various inorganic and organic solvents.

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Zusammenfassung Der Verlauf der Dimangan-cyclotetraphosphat ergebenden Kalzinierung von Mn(H₂PO₄)₂ · H₂O wurde thermogravimetrisch unter quasi-isothermen-isobaren Bedingungen untersucht. Isotherme Kalzinierung wurde auch im elektrischen Ofen (200 min) bei verschiedenen Temperaturen ausgeführt. Die Reaktionsprodukte wurden chromatographisch, IR- und NMR-spektroskopisch sowie röntgendiffraktometrisch analysiert. Die Zusammensetzung der kalzinierten Produkte wurde via Extraktion mit verschiedenen anorganischen und organischen Lösungsmitteln bestimmt.

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Mn(H₂PO₄ · H₂O. . . - , - - . .

     

Studies of immobilized V?P/SiO2 catalysts

It has been revealed by the ESR method that complexes of O ₂ ^– with palladium compounds are formed during the interaction of H₂O₂ with palladium acetate in various solutions.

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H₂O₂ O ₂ ^– .

     

Assay of nitro and nitroso compounds by solution thermochemistry

Some nitro and nitroso compounds have been determined by direct reduction with Ti(III) chloride without the necessity for degassing the analyte solutions. Methods have been developed for the determination of some binary mixtures by both enthalpimetry and catalytic thermometric titrimetry. The accuracy at the 0.1 mMole level is±1%, and the time taken for a single titration is less than 2 minutes.

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Zusammenfassung Einige Nitro- und Nitrosoverbindungen wurden durch direkte Reduktion mit Ti(III)-chlorid bestimmt, ohne dass die Notwendigkeit der Verdampfung der Analysenlösung besteht. Es wurden Methoden zur Bestimmung einiger binärer Gemische durch Enthalpimetrie und katalytische thermometrische entwickelt. Die Genauigkeit beträgt im Bereich von 0.1 mMol±1%, und eine Titration erfordert weniger als 2 Minuten.

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- . . 0,1 ± 1%, , 2 .

     

Effect of the activation conditions on the catalytic properties of Pt/Al2O3 catalysts

The effect of the activation conditions of Pt/Al₂O₃ catalysts has been investigated in the hydrogenation of benzene and in the hydrogenolysis of ethane. Whatever the conditions of calcination or reduction, specific activities of all catalysts for benzene hydrogenation remain constant. On the other hand, for identical dispersities, the cacination in a wet argon flow increases the specific activity of platinum for hydrogenolysis of ethane, pointing out the role of wet pretreatment on defect building or on the faceting of supported metallic catalysts.

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Pt/Al₂O₃ . , . , , . .

     

Hydrogen pressure dependence of the reaction of neopentane with hydrogen over Pd/SiO2 and Pt/SiO2 catalysts

H₂ pressure influences in different ways the reaction rates of neopentane conversion over Pd/SiO₂ and Pt/SiO₂ catalysts. It seems that on Pt/SiO₂ both isomerization and hydrogenolysis involve a common surface intermediate (probably an adalkyl), whereas on Pd/SiO₂ the hydrogenolysis goes via more dehydrogenated species than those involved in isomerization.

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H₂ Pt/SiO₂ Pd/SiO₂. , Pt/SiO₂ (, ), Pd/SiO₂ , .

     

The transitions in phases II–III–IV in high purity ammonium nitrate

The phase changes in high-purity ammonium nitrate were studied by a differential thermal analysis (DTA) apparatus designed for constant heating and cooling rates and continuous cycling for 3-gram samples. On the basis of DTA and X-ray diffraction data very consistent behavior is observed. Phase IV III transformation on heating in the range 43 to 51 and Phase II IV transformation on cooling in the range 49 to 53 are demonstrated. The III II transition at about 86 is seen with repeated temperature cycling. This repeatable behavior not consistently seen by investigators using other techniques is believed to be due to the high purity material and constant heating and cooling rates.

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Zusammenfassung Die PhasenübergÄnge von hochreinem Ammoniumnitrat wurden mit Hilfe einer differentialthermoanalytischen Apparatur mit konstanten Aufheiz- und Abkühlungsgeschwindigkeiten und mit kontinuierlichen Temperaturzyklen für ungefÄhr 3 g betragende Proben geprüft. Diese Untersuchung, weiterhin röntgendiffraktometrische Aufnahmen zeigten ein sehr übereinstimmendes Verhalten. Die Phasenumwandlung IV III erfolgte beim Erhitzen zwischen 43–51, die Phasenumwandlung II IV beim Abkühlen zwischen 49–53. Die Umwandlung III II bei ungefÄhr 86 wurde im wiederholenden Temperaturzyklus beobachtet. Dieses reproduzierbare Verhalten, welches nicht mit Untersuchungen durch andere Methoden übereinstimmt, wird der hohen Reinheit der Substanzen und den konstanten Aufheiz- und Abkühlungsgeschwindigkeiten zugeschrieben.

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Résumé On a étudié les changements de phase du nitrate d'ammonium de haute pureté à l'aide d'un analyseur thermique différentiel conÇu pour réaliser des vitesses d'échauffement et de refroidissement constantes ainsi que des cycles thermiques avec environ 3 g d'échantillon. Les résultats d'ATD et de diffraction X indiquent un comportement tout à fait constant. La tranformation de la phase IV en phase III se produit entre 43 et 51 à l'échauffement et celle de la phase II en phase IV entre 49 et 53 au refroidissement. On observe la transition III II à 86 environ, avec des cycles thermiques répétés. On explique ce comportement bien défini, qui n'a pas été toujours remarqué par les chercheurs utilisant d'autres techniques, par l'emploi d'un échantillon de haute pureté et de vitesses d'échauffement et de refroidissement constantes.

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(). , , — 3 . . IVIII 43–51 C II–IV 49–53 C. IIIII 86 C . , , .

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This work was supported by the United States Atomic Energy Commission.     

Effect of bond energies of a catalyst with reacting atoms on the selectivity of CO hydrogenation over metals

In hydrogenation over metals (M)_j carbon monoxide is adsorbed as a molecule. C–O bond rupture in partially hydrogenated complex, MCHOH, leads to MO and MCH₂ and then to hydrocarbons, while transformation of MCHOH into MCH₂OH gives alcohols and other oxygen-containing compounds. Selectivity towards hydrocarbons increases with increasing energy of M–O bonds.

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(M) . C–O MCHOH MO MCH₂ — ; MCHOH MCH₂OH . M–O.

     

Reactivity of coordinated O2? ion-radicals in the oxidation of organic compounds

By the flow ESR method, the rates of the reaction of the radical complex Ti(IV)(O ₂ ^– ) with some aromatic compounds in aqueous solution have been measured. An elementary step of these reactions seems to be one-electron oxidation with the formation of a substrate cation-radical.

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- Ti(IV)(O ₂ ^– ) . - -.

     

PMR study of the lifetime of complexes with a strong hydrogen bond at low temperatures

The kinetics of formation and cleavage of hydrogen bonds in complexes of carboxylic acids with proton acceptors have been studied by PMR spectroscopy over the range –100 to 150°C. The activation parameters of the processes have been measured.

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¹H –100° ÷–155°C . .

     

Topological aspects of differential thermal analysis

The most important calorimetric methods have been reviewed: the differential thermal analysis (DTA) as basic disposition and the scanning calorimetry (DSC) as well as the adiabatic rate calorimetry (ARC). The thermal circuits of these are expressed by bond diagrams as conceived by topological thermodynamics. It has been stated that the heat flux associated with the process of transformation is virtually (uncompensated) transferred in the DTA system, really transferred (compensated) in the DSC and ARC systems, between the two containers through a transfer medium assumed to be purely dissipative.

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Zusammenfassung Eine Übersicht über die wichtigsten kalorimetrischen Methoden, sowie die Differentialthermoanalyse (DTA) als Grundverfahren, die Abtastkalorimetrie (DSC) und die adiabatische Geschwindigkeitskalorimetrie (ARC) wird gegeben. Die thermischen Kreise derselben werden durch Bindungsdiagramme, wie sie an Hand der topologischen Thermodynamik erhalten werden, ausgedrückt. Es wurde festgestellt, dass die Wärmeströmung mit dem Umwandlungsprozess assoziiert scheinbar (unkompensiert) in das DTA-System, wahrhaftig (kompensiert) in die Systeme DSC und ARC übertragen wird, undzwar zwischen den zwei Behältern durch ein als rein zerstreuend angenommenes Transfermedium.

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Résumé Mise au point sur les méthodes calorimétriques les plus importantes: l'analyse thermique différentielle (ATD) comme technique de base, l'analyse calorimétrique différentielle à compensation de puissance (DSC) et la calorimétrie à vitesse adiabatique (ARC). Les circuits thermiques de ces techniques s'expriment par des diagrammes de liaisons comme ceux conçus par la thermodynamique topologique. On établit que le flux de chaleur associé au processus de la transformation est virtuellement transferré (sans compensation) en ATD et réellement transferré (avec compensation) en DSC et ARC, entre les deux conteneurs par un milieu de transfert supposé être purement dissipatif.

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