Specificity of hydrogen adsorption on chromia-supported platinum group metal catalysts

Hydrogen adsorption on chromia supported Pd, Rh and Pt was studied under various pretreatment conditions. The reduction temperature influences strongly the hydrogen uptake for all these metals. Platinum supported on chromia shows an unusually high hydrogen adsorption stoichiometry.

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Pd, Rh Pt, Cr₂O₃, . , . Cr₂O₃ .

     

Catalytic epoxidation of propylene with tert-butyl peroxide in presence of molybdenum complexes on polymer carriers

A polymer catalyst has been synthesized on the basis of Amberlite IRA-45 anion-exchange resin modified with molybdenum hexacarbonyl. Its catalytic activity in the epoxidation of propylene with tert-butyl hydroperoxide is similar to the activity of Mo(CO)₆ used under homogeneous conditions.

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, - Amberlite IRA-45, . - Mo(CO)₆, .

     

Influence of external electric field on the rate of hydrogen isotope exchange between hydroxyl-containing molecules in CCl4

Rates of the fast proton-deuteron exchange between CH₃OD and C₆H₅OH (1), and CH₃OD and CH₃COOH (2) in dilute CCl₄ solutions have been measured by a kinetic IR spectroscopy technique. Under an imposed external electric field (10 V/m), the exchange rate in system (2) increases, which is not observed in (1). The effect is interpreted assuming that, in the second case, a cyclic ion pair with a high dipole moment is formed as a reaction intermediate.

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- CH₃OD C₆H₅OH (1), CH₃OD CH₃COOH (2) CCl₄. (IO⁷ B/) (2) , (1). (2) , .

     

Propylene oxidation over tin-molybdenum oxide catalysts

The influence of preparation of tin-molybdenum catalysts on their phase composition and activity has been elucidated. The mutual dissolution of Sn and Mo oxides leads to a considerable increase in their activities and selectivities in the partial oxidation of propylene to acetone.

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. , .

     

Steady conduction of heat in prolate spheroidal systems

The steady local temperature distribution has been determined for arbitrary prolate spheroidal systems with various boundary conditions. The temperature was derived for all possible systems, such as when the temperature was kept constant on the hyperbolic surfaces and variable on the prolate spheroidal surfaces, and vice versa. In'the latter case, roots with respect to the degree of the associated Legendre function for arguments larger than unity had to be determined. Some of the presented solutions have been evaluated numerically, and the isothermal surfaces have been presented.

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Zusammenfassung Für beliebig ausgedehnte sphäroide Systeme wurde mit verschiedenen Randbedingungen eine stationäre lokale Temperaturverteilung ermittelt. Die Temperatur wurde für alle möglichen Fälle ermittelt, so auch für den Fall, in dem die Temperatur an der Hyperbeloberfläche konstant gehalten und an den ausgedehnten sphäroiden Flächen veränderlich ist bzw. umgekehrt. Für letzteren Fall mußten für Argumente größer als eins Wurzeln betreffs des Grades der zugehörigen Legendre Funktion ermittelt werden. Einige der dargestellten Lösungen wurden numerisch ermittelt und die isothermen Flächen dargestellt.

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. , . , . .

     

Effect of ligands on the hydrogenation selectivity in the presence of rhenium catalysts

It has been established that the catalytic activity of rhenium oxohalide complexes with phosphorus- or sulfur-containing ligands in hydroganation of C₆–C₁₀ olefins, nitrobenzene and p-nitrotoluene is primarily determined by the original ligand to rhenium ion bond. Chain length of olefins does not affect their hydrogenation rate.

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- C₆–C₁₀, - - . .

     

Testing of nickel phosphate (NiP) catalyst for ethylbenzene oxydehydrogenation by means of isopropanol dehydration

It has been shown that NiP catalyst, if fresh, contains a high concentration of the same type acid-base surface centers as those participating in i-PrOH dehydration on -Al₂O₃. The concentration of these centers diminishes rapidly after a modification of NiP surface in a stream of ethylbenzene (EtPh) oxydehydrogenation products.

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, NiP - , , i-PrOH -Al₂O₃. NiP .

     

Nature of Lewis acidity in H-zeolites

It has been revealed that in crystalline aluminosilicates the three-coordinated aluminium ion belonging to the lattice is not the Lewis acid center. The latter is the off-lattice aluminium ion compensating the excess of the negative charge in the lattice or acting as cation valence-bonded to the oxygen anion of the SiO₄ tetrahedron.

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, , , . , , , SiO₄-, .

     

Thermogravimetric study of magnetite reduction at low temperature

Results on hydrogen reduction of pure magnetite to iron at low temperature are reported as part of research on ammonia synthesis catalyst. Experimental work was carried out by thermogravimetry and by electron microscopy.The reduction has a typical S-shaped kinetic curve, with a poorly reproducible induction period. The slope of the reduction curve at 50% conversion (k _0.5) was found to depend on sample mass (2–50 mg), particle size, temperature (220–280C) and presence of moisture in the hydrogen .The results suggest both interparticle and intraparticle (through iron ash) diffusion to be slow. Morphological examinations of the sample at various reduction degrees support this interpretation.

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Zusammenfassung Die Ergebnisse der Reduktion von reinem Magnetit zu Eisen durch Wasserstoff bei niedrigen Temperaturen werden als Teil einer Forschungsarbeit über Katalysatoren zur Ammoniak-Synthese mitgeteilt. Die Versuche wurden mittels Thermogravimetrie und Elektronenmikroskopie durchgeführt.Die Reduktion verläuft nach einer typisch S-förmigen kinetischen Kurve, mit einer schlecht reproduzierbaren Induktionsperiode. Es wurde festgestellt, daß die Steile der Kurve bei 50% Konversion (k _0.5) von der Probenmenge (2–50 mg), der Teilchengröße, der Temperatur (220 bis 280) und der Feuchtigkeit des Wasserstoffes abhängt.Diese Ergebnisse lassen darauf schliessen, daß sowohl die interpartikuläre als auch die intrapartikuläre Diffusion (durch die Eisen-Asche) langsam ist. Diese Deutung wird durch morphologische Prüfung des Musters bei verschiedenen Reduktionsstufen unterstützt.

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Résumé On communique les résultats obtenus en réduisant par l'hydrogène à basse température la magnétite pure en fer, travail faisant partie de recherches sur les catalyseurs pour la synthèse de l'ammoniac. Les expériences ont été effectuées par thermogravimétrie et par microscopic électronique.La courbe cinétique de la réduction présente la forme en S type, avec une période d'induction peu reproductible. Il est apparu que la pente de la courbe de réduction, pour un taux de conversion de 50% (k _0.5) dépendait de la prise d'essai (2–50 mg), de la dimension des particules, de la température (220 à 280) et de la présence d'humidité dans l'hydrogène .Ces résultats permettent de conclure que les processus de diffusion sont lents, qu'ils soient de type interparticule ou intraparticule. L'examen morphologique des échantillons pour divers degrés de réduction a confirmé cette interprétation.

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, , . . S- , . , 50% (_0.5) (2–50 ), , (220–280) (₂)=1,2 ). , , , , . .

     

Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

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, . : > > > . .

     

Influence of excess MoO3 in a non-stoichiometric cadmium-molybdenum catalyst on the catalytic properties in methanol oxidation

By IR and Raman spectroscopy it has been shown that excess MoO₃ is bound molecularly on the surface of CdMoO₄, presumably on sites of C₂ and C_i symmetry. This increases the activity and selectivity of the catalyst in methanol oxidation to formaldehyde.

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, , MoO₃ CdMoO₄, C₂ C_i. .

     

Catalytic deactivation dynamics of zeolites in multicycle processes

Catalytic deactivation dynamics of zeolites in multicycle processes has been calculated. It has been revealed that in naphthalene sorption on NaX zeolites surface deactivation is predominant with its similarity criterion close to unity and a high fraction of deactivation. Calculated data for several multicycle processes are given.

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. , NaX . .

     

Relation between the catalytic and acidic properties of zeolite catalysts

Influence of the strength and concentration of non protic centers on the catalytic activity of metal-zeolite catalysts in isomerization of n-butane has been studied. A relationship between the specific activity and the center strength is suggested.

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-. , .

     

Activity of γ-Al2O3 modified by NaOH in disproportionation of methanethiol

Na⁺/Al₂O₃ catalysts in disproportionation of methanethiol are highly selective towards dimethyl sulfide but less active compared to -Al₂O₃. Their activity falls with increasing Na⁺ in the sample. This decrease is due to the neutralization of Brönsted acid centers on the catalyst.

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Na⁺/Al₂O₃ , , -Al₂O₃. Na⁺ . .

     

Influence of anchored cerium ions on the dispersity and activity of Pd/SiO2 catalysts

(Pd+Ce)/SiO₂ catalysts prepared by decomposition of organometallic complexes of Ce and Pd have higher activity, dispersity and selectivity in methanol synthesis than Pd/SiO₂ catalysts.

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, (Pd+Ce)/SiO₂ , Ce Pd, Pd/SiO₂.

     

Ausbrennen von Kohlenstoffhaltigen,in den Ziegelrohstoff Eingepressten Stoffen

Zusammenfassung Die Kinetik der Ausbrennung organischer Stoffe im Ziegelscherben wird verfolgt und erläutert. Die Möglichkeiten der Beeinflussung des energetischen Aufwandes unter Nutzung moderner analytischer Methoden sind festzustellen. Bei einem diffusen Ausbrennen ist die Dichte und Durchlässigkeit des Scherbens massgebend. Praktische Anwendungsmöglichkeiten verschiedener auszubrennender Stoffe in unterschiedlichen Rohstoffen der Ziegelindustrie.

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The kinetics of burn-out of organic materials in bricks has been followed and explained. It is to establish that using new analytical methods the energy consumption can be influenced. The diffuse burn-out is determined by the density and permeability of bricks. There is a possibility for practical use of the results in the brick-industry with the different compounds to be burnt out from various raw materials.

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$ . , . . .

     

Kinetic conversion of complex hydrocarbon mixtures in reforming on platinum/alumina catalysts

General forms of the kinetic equations for the conversion of various hydrocarbons in reforming of multicomponent gasoline fractions on platinum/alumina catalysts have been confirmed experimentally by using a gradientless method.

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.

     

Differential scanning calorimetry of spin-oriented polyester yarn

Polyester yarn spun over a range of wind-up speeds has been characterized using differential scanning calorimetry. Samples prohibited from shrinking during the thermal analysis show slightly smaller heats of fusion and crystallization and reduced cold crystallization temperatures than samples that are free-to-shrink, particularly in the intermediate wind-up speed region. One critical observation made is that the cold crystallization temperature reaches a minimum at some relatively low overall molecular orientation (n 0.020) and fails to decrease further. A likely explanation is that crystallization continuously removes polymer from the melt in the spinline in regions where the local orientation reaches some critically high value.

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Zusammenfassung Mit verschiedenen Aufspulgeschwindigkeiten gesponnenes Polyestergarn wurde durch DSC charackterisiert. Die während der tyermischen Analyse am Schrumpfen gehinderten Proben zeigen, besonders bei mittleren Aufspulgeschwindigkeiten, eine etwas geringere Schmelz- und Kristallisationswärme und niedrigere kalte Kristallisationstemperaturen als Proben, die ungehindert schrumpfen konnten. Die kalte Kristallisationstemperatur erreicht bei enier relativ niedrigen Gesamtmolekularorientierung (n 0.020) ein Minimum und nimmt nicht weiter ab. Wahrscheinlich ist, dass durch die Kristallisation das Polymer in den Bereichen, in denen die lokale Orientierung einen kritischen Wert erreicht, kontinuierlich aus der Schmelze entfernt wird.

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, , . , - , , , , , , . , (n0.020) . , , .

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The author appreciates the input provided by Dr. R. M. Mininni and the help of Dr. W. E. Bessey in fiber spinning and Ms. E. Fernekess in thermal analysis. The author is grateful to Celanese Corporation for allowing publication of this work.     

Dielectric differential thermal analysis

Thermodielectric analysis has been used to test some very well-characterized kaolins from Cuban deposits. The samples were analysed by thermal analysis, X-ray diffraction, infrared spectrometry, electron microscopy and chemical analysis.The dielectrical thermograms show that the most evident effect for the hydrated versions is the water peak. The second dielectric effect, at high temperatures, is related to the cationic conductions. A relation involving the K content of the sample was observed.

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Zusammenfassung Mittels thermodielektrischer Analyse wurden einige gut charakterisierte Kaoline aus kubanischen Lagerstätten untersucht. Die Proben wurden mittels Thermoanalyse (TA), Röntgendiffraktion (XRD), Infrarotspektroskopie (IR), Elektronenmikroskopie (EM) und Elementaranalyse untersucht. Die Dielektrothermogramme zeigen, daß bei den hydratierten Versionen der augenscheinlichste Effekt der Wasserpeak ist. Der zweite dielektrische Effekt bei höheren Temperaturen wird mit der Kationenleitung in Zusammenhang gebracht, wodurch es möglich wird, Informationen über den K-Gehalt der Proben zu erlangen.

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. (), , , . , . , , , .

     

Usefulness of kinetic parameters in investigations of thermal decompositions of solids

The theoretical curves in the coordinates a vs. time for isothermal, and avs. temperature for non-isothermal experiments are calculated as functions of three kinetic parameters: activation energyE, pre-exponentical factorA and theg() function describing the mechanism of thermal decomposition of solids. The results show that conclusions not taking into consideration all three parameters can lead to information of little value concerning the mechanism of the decomposition and kinetic calculations. A correlation between non-isothermal and isothermal experiments, important for determination of the thermal stabilities of the compounds, is impossible without a knowledge of theg() function.

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Zusammenfassung Theoretische Umsatzkurven gegent für isotherme bzw gegen Temperatur für nichtisotherme Versuchsführung wurden berechnet in Abhängigkeit von den drei kinetischen Parametern AktivierungsenergieE, PräexponentialfaktorA und derg()-Funktion, die den Mechanismus der Zersetzung von Festkörpern beschreibt. Die Ergebnisse zeigen, dass Schlussfolgerungen, die nicht alle drei Parameter berücksichtigen, zu, Ergebnissen von geringer Aussagekraft bezüglich des Zersetzungsmechanismus und der kinetischen Interpretation führen. Eine Korrelation nicht-isothermer und isothermer Experimente, die für die Bestimmung der thermischen Stabilität der Verbindungen wichtig ist, ist ohne Kenntnis der Funktiong() unmöglich.

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- - : , - g(), . , , , . , g().