Steady state catalytic properties and oxygen binding energy of cadmium-molybdenum catalysts in methanol oxidation

On normal cadmium molybdate the products of methanol oxidation are primarily CO₂ and H₂. After the introduction of excess MoO₃ to reach Mo/Cd=1.2, methanol is oxidized to formaldehyde and carbon monoxide via a consecutive scheme. The oxygen binding energy in the steady state for the first sample is by 30 kcal/mol higher than that for the second catalyst. The activation energies of methanol conversion are 11.5 and 20 kcal/mol, respectively.

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CO₂ H₂. MoO₃ Mo/Cd=1, 2 . 1- 30 / , , , , 11,5 20 /.

     

Kinetics and mechanism of phenylacetylene hydrogenation under hydrogen pressure

Kinetic and potentiometric curves of phenylacetylene hydrogenation on a 5% Pt/C catalyst in ethanol under hydrogen pressure have been studied. On the basis of chromatographic data a possible scheme of the process is suggested.

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. 5% Pt/C . .

     

Kinetics and mechanism of homogeneous catalytic oxidation of pyrocatechol in aqueous solutions containing Cu(II) and histidine

Kinetic studies of pyrocatechol oxidation by oxygen in weakly acidic aqueous solutions containing pyrocatechol, Cu(II) ions and histidine, indicate that the reaction involves mixed copper-pyrocatechol histidine complexes. The proposed mechanism of the process agrees with the kinetic relationships obtained.

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, , Cu(II) . , . , -.

     

Effect of α-methylstyrene of the curing behaviour of vinyl ester resins

The curing behaviour of bismethacryloxy derivative of diglycidyl ether of bisphenol A (vinyl ester resin) containing styrene as the reactive diluent (40% w/w) was studied using gel point determination method and DSC. Seven samples of styrene/-methylstyrene in the ratio 400, 355, 3010, 2515, 2020, 1525 and 040 were studied. Delayed curing was observed in samples containing increasing proportions of -methylstyrene. The energy of activation decreased from 869 kJ mol^–1 to 333 kJ mol^–1 as the concentration of -methylstyrene increased in the formulations. However, no difference in thermal stability was observed by replacement of styrene by -methylstyrene. It was concluded that in vinyl ester resin samples 10–15% -methylstyrene and 30-25% styrene can be used as reactive diluent.

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Zusammenfassung Mittels DSC und Bestimmung der Gelierungstemperatur wurde das Aushärteverhalften des Bismethakryloxyderivaten des Diglycidyläthers von Bisphenol A (Vinylesterharz) mit 40 Gewichtsprozenten Styrol als reaktives Streckmittel untersucht. Es würden sieben Proben mit einem Styrol/-Methylstyrol Verhältnis von 400, 355, 3010, 2515, 2020, 1525 und 040 untersucht. Mit steigendem Anteil an -Methylstyrol konnte eine Verzögerung der Aushärtung sowie ein Absinken der Aktivierungsenergie von 869 kJ · mol^–1 auf 333 kJ · mol^–1 beobachtet werden. Der Ersatz von Styrol durch -Methylstyrol veränderte jedoch die thermische Stabilität in keiner Weise. Vinylesterharzproben mit 10–15% -Methylstyrol und 30–25% Styrol können als reaktive Streckmittel in Vinylesterharzen verwendet werden.

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- - , 40 .% . /-, 400, 355, 3010, 2515, 2020, 1525 040. - . - 869 333 · ^–1. , .. , , 10–15% - 30–25% .

     

Interaction of oxygen with preadsorbed hydrogen on magnesium oxide studied by temperature-Programmed desorption method

The interaction of oxygen with preadsorbed hydrogen on thermally activated magnesium oxide has been studied by temperature-programmed desorption (TPD) method. It was found that oxygen at 450 K reacts with preadsorbed hydrogen and the resulting hydroxylation suppresses the adsorptive capacity of magnesia with respect to oxygen.

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. , 450 K , .

     

Use of EGD for the characterization of fining processes of glass melt

The control and optimization of the glass-making process is a serious problem in glass production. An EGD procedure involving high-temperature vacuum extraction and total pressure measurement allows determination of the fining state (Läuterzustand) and fining behaviour (Läuterverhalten). The fining state is characterized by the contents of CO₂, N₂ and other gases from the batch reactions, and gas inclusions. Oxygen evolved in a second step is characteristic for the fining behaviour.

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Zusammenfassung Die Kontrolle und Optimierung des Gasgehaltes von Glasschmelzen ist eine wichtige Voraussetzung für eine gleichbleibende Qualität der Glasprouktion. Eine EGD-Technik mit Hilfe der Hochvakuumheißextraktion und Gasdruckmessung erlaubt, den Läuterzustand und das Läuterverhalten einer Glasprobe zu bestimmen. Der Läuterzustand wird durch die Gase aus den Gemengereaktionen und Gemengeeinschlüssen (CO₂, N₂ u. a.) bestimmt. Das Läuterverhalten ergibt sich aus der Menge des in einer zweiten Stufe extrahierbaren Sauerstoffs.

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. , , . , , , . , , .

     

Diffusion-controlled recombination of peroxide radicals in polyatomic esters

Pulse photolysis measurements of rate constants for the decay of peroxide radicals of seven polyatomic esters show that the reaction is diffusion-controlled for esters with 2 cP. The Smoluchowsky equation is suggested to calculate 2k_t for esters with short alkyl radicals.

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. , - , 2 . 2k_t .

     

Mechanism of homogeneous catalysis of isotope exchange during interaction of dihydrogen with alkaline solutions

The mechanism of hydrogen isotope exchange in aqueous alkaline solutions (AAS) of D₂ has been studied using Interacting Bonds Method (IBM) data obtained for hydrogen interaction with the molecular ion H₃O ₂ ^– . Models for the activated and metastable intermediate complexes are described.

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- D₂ (). () H₃O ₂ ^– . .

     

Dynamic purity determinations. I. Location of the solidus by nuclear magnetic resonance

The error in purity determinations by differential scanning calorimetry has been studied on two different kinds of systems, metallic and organic, the latter with different types of impurities added. The organic systems have been corrected for solid-solubility error by a nuclear magnetic resonance technique.The impurities chosen for the organic systems were either quite dissimilar to the matrix or similar enough to render solid solution probable. This solid solution leads to deviations from the equation used for dynamic purity determinations. The nuclear magnetic resonance determination of the solidus establishes the proper starting temperature for area summation on a DSC curve.

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Zusammenfassung Der Fehler in Reinheitsbestimmungen mittels Differential-Scanning-kalorimetrie wurde an zwei verschiedenartigen Systemen untersucht, metallisch und organisch, wobei zu letzteren verschiedentliche Verunreinigungen zugefügt wurden. Der durch Feststoff-Feststofflöslichkeit verursachte Fehler in den organischen Systemen wurde mittels einer kernmagnetischen Resonanzmethode korrigiert.Die für die organischen Systeme gewählten Verunreinigungen waren entweder sehr verschieden von der Matrix, oder aber genügend ähnlich, um feste Lösungen wahrscheinlich zu machen. Diese festen Lösungen führen zu Abweichungen von der für dynamische Reinheitsbestimmungen angewendeten Gleichung. Die Bestimmung der kernmagnetischen Resonanz des Feststoffs ermöglicht die Bestimmung der richtigen Anfangstemperatur für die Flächen-summierung auf der DSC-Kurve.

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: . . . , , , , . , . -.

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On leave from The Institute for Physical Chemistry, Polish Academy of Science, Warsaw, Poland.

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The authors are grateful to the National Science Foundation for its support through Research Grant CHE 76-08765, and to S. E. Walter for assistance with some calculations.     

Reaction kinetics by thermal analysis

The application of thermal analysis in the study of reaction kinetics and reaction mechanisms in combination with presently available powerful analytical tools, in the sphere of materials with particular reference to high energy materials is presented and discussed. Also an attempt has been made to correlate the kinetic data obtained by TA with the performance characteristics, for some important materials.

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Zusammenfassung Es wird die Anwendung der Thermoanalyse bei der Untersuchung der Reaktionskinetik und des Reaktionsmechanismus in Zusammenwirkung mit den gegenwärtig zur Verfügung stehenden leistungsfähigen analytischen Werkzeugen auf dem Gebiet von Materialien mit speziellem Bezug auf energiereiche Stoffe dargestellt Und besprochen. Es wurde auch versucht, die durch TA erhaltenen kinetischen Daten einiger wichtiger Stoffe mit deren Leistungskenndaten in Beziehung zu stellen.

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. , , .

     

Kinetic data on the interaction between triplet anthraquinone and 2-naphthol in oxygen

During the photooxidation of ethylbenzene in the presence of 2-naphthol a new interaction has been found between the sensitizer anthraquinone and the inhibitor. The quantum yield and the kinetics of this interaction have been investigated in the temperature interval of 28–98°C.

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-, , 28–98°C , .

     

Reaction kinetics of electron transfer between tungstovanadophosphoric heteropolyanions and Fe(II) ions

The reduction of PW_12–nV_nO₄₀ ^(3+n)– (n=1–4) heteropolyanions with Fe(II) ions occurs via intermediate complex formation. The rate constants of electron transfer in this complex tend to decrease in accord with the change of the oxidation potential of the heteropolyanions.

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PW_12–nV_nO ₄₀ ^–(3+n) (n=1–4) Fe(II) . .

     

Kinetics and mechanism of the permanganate oxidation of trans-crotonic acid

The kinetics and intermediates of the permanganate oxidation of trans-crotonic acid have been investigated in the pH range of 0.5–5.0 using the stoppedflow technique. The formation of manganese(III) as a short-lived intermediate has been established. The reaction is first order with respect to both MnO ₄ ^– and crotonic acid (crotonate). The resolved rate constants at 25°C are 730 and 410 M^–1 sec^–1 for the acid and the anion, respectively. The reaction mechanism is discussed.

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pH=0,5–5,0, . (III) . MnO ₄ ^– , (). 25°C 730 410 M^{–1 –1} , . .

     

Kinetic studies of methanethiol disproportionation

Kinetic regularities in catalytic disproportionation of methanethiol to dimethyl sulfide and hydrogen sulfide have been studied in a flow circulation reactor. A kinetic equation is suggested to describe the reaction on inhomogeneous surfaces.

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- - . , .

     

SEM-EDAX investigations of use-related microstructural changes in an ammonia synthesis catalyst

Changes in the topography and distribution of the chemical constituents in the microspaces of oxide type catalysts and prereduced catalysts have been investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDAX) before and after six years of use in industrial ammonia synthesis reactors.

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6- .

     

Kinetics of ammonia decomposition of polycrystalline rhodium at pressures between 0.013 and 103 kPa

The rates of ammonia decomposition on polycrystalline Rh wires between 600 and 1800 K and at pressures between 13.3 Pa and 103 kPa were measured and fitted with a Langmuir-Hinshelwood unimolecular reaction rate expression. At high temperatures and pressures the reaction seems to be mass transfer controlled.

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Rh 600–1800 K 13,3 –103 . , -. .

     

Sensitization of the photoadsorption of O2 and NO on SnO2

Photoadsorption activity of SnO₂ with respect to O₂ and NO after CO chemisorption has been revealed to be drastically increased. Photoadsorption is suggested to be sensitized by surface carbonates formed due to CO chemisorption.

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. , .

     

Interaction of styrene with triphenylphosphinecobalt complexes

The interaction of the cobalt phosphine complexes Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ and H₃Co(PPh₃)₃ with styrene yields mono and dinuclear complexes identified by the ESR method. A paramagnetic complex, Co(PPh₃) (styrene)₂, is one of the intermediates in the catalytic hydrogenation of styrene.

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Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ H₃Co(PPh₃)₃ . , Co(PPh₃) ()₂.