Oxidation of ethylene to ethylene oxide: A tpr study on fresh and aged catalysts

The deactivation of a silver catalyst was investigated after six years of industrial production of ethylene oxide. Temperature-programmed reduction was used to characterize the chemical nature of the silver and its reactivity towards oxygen. The fresh and some aged catalysts were examined, also after different thermal treatments.During the industrial run, the surface species were modified and some oxygen diffused into the bulk of the metal. Aging caused permanent changes in the characteristics of the silver, resulting in a different interaction with oxygen. The TPR spectra exhibited a trend along the reactor axis, suggesting a correlation with the degree of deactivation of the catalyst.

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Zusammenfassung Die Desaktivierung eines Silberkatalysators wurde nach 6-jährigem Einsatz zur industriellen Produktion untersucht. Temperaturprogrammierte Reduktion wurde angewandt, um die chemische Natur des Silbers und dessen Reaktivität gegenüber Sauerstoff zu charakterisieren. Frische und einige gealterte Katalysatoren wurden nach verschiedenen thermischen Vorbehandlungen untersucht. Die Alterung verursachte bleibende Veränderungen in charakteristischen Eigenschaften des Silbers, was in der unterschiedlichen Wechselwirkung mit Sauerstoff zum Ausdruck kommt. Die TPR-Resultate zeigen einen Trend entlang der Reaktorachse, was auf eine Korrelation mit dem Grad der Desaktivierung des Katalysators hindeutet.

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

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The experimental contributions by F. Genoni and G. Valassina are gratefully acknowledged.     

Kinetics and mechanism of oxidation of quinol by alkaline hexacyanoferrate(III)

The reaction between quinol and alkaline hexacyanoferrate(III) at constant ionic strength gives p-benzoquinone. The rate of the reaction was first order in the concentrations of substrate, oxidant and alkali. The slow step of the reaction involves the formation of the p-benzosemiquinone radical, which was detected by esr spectroscopy as a five-line spectrum with peak intensity ratios of 14641.

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(III) -. , . - , , 14641.

     

Interaction of nitric oxide with NiCr2O4

Interaction of NO with NiCr₂O₄ has been studied at 473–1173 K. It has been established that on nickel-chromium spinels NO decomposition practically does not take place. Nitric oxide can interact only with prereduced samples to reoxidize them.

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473–1173 NO NiCr₂O₄. , NO . (II) ; .

     

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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. , .

     

Study of crystal transformations by an evolved gas analysis technique

Small organic molecules can be entrapped within inorganic crystalline materials during precipitation. The material has no apparent influence on solid-solid transition temperatures, but some of it is released during the transition.Detection of the escape is reproducible within 1°C and may be used for temperature calibration. More generally, the escape of the organic during chemical reactions could be used for many of the applications of emanation thermal analysis.In coupled systems such as DTA or TG with mass spectrometry, or other systems involving gas transport, the time delay of the system can be measured accurately.

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Zusammenfassung Kleine organische Moleküle können während der Fällung in anorganische kristalline Substanzen eingeschlossen werden. Die Substanz hat keine scheinbare Wirkung auf Fest-Fest-Übergangstemperaturen, doch wird ein Teil derselben während des Überganges freigesetzt. Der Nachweis der freigesetzten Substanz ist innerhalb von 1°C reproduzierbar und kann zur Temperatureichung eingesetzt werden. Verallgemeinert könnte das Entfliehen organischer Substanzen im Laufe chemischer Reaktionen bei vielen Anwendungen der Emanations-Thermalanalyse eingesetzt werden. In gekoppelten Systemen, wie z.B. DTA oder TG mit Massenspektrometrie, oder andere Systeme mit Gastransport, kann die Verzögerung des Systems genau gemessen werden.

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Résumé De petites molécules organiques peuvent se trouver incluses dans des substances inorganiques cristallines, au moment de la précipitation. Les températures de transition solidesolide ne s'en trouvent apparemment pas affectées mais une partie de ces molécules incluses peut être éliminée pendant la transition. La détection du matériau qui s'échappe est reproductible à 1°C près et se prête à l'étalonnage de la température. En termes plus généraux, le départ de la substance organique au cours des réactions chimiques peut être utilisé pour de nombreuses applications de l'analyse thermique d'émanation. Dans le cas de techniques associées, comme l'ATD ou la TG avec la spectrométrie de masse, ou encore d'autres techniques avec transport de gaz, on peut mesurer exactement le temps de réponse du système.

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. —, . 1°, . . , , - , , , .

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The authors are grateful to the National Science Foundation for support of parts of this work through institutional and research grants and to the Goodyear Tire and Rubber Company for use of the Chromatograph and other facilities.     

Adsorption and hydrogenation of unsaturated aldehydes over rhodium black

Hydrogenation selectivity of conjugated ethylenic bonds of unsaturated aldehydes over rhodium black is shown to be determined by intramolecular interactions in surface complexes due to the electronic structure of the initial unsaturated aldehydes.

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- , .

     

ESR studies of Mo?Mg oxide catalysts

For 0.1–0.5 wt.% Mo–Mg oxide samples with high concentration of⁹⁵Mo isotopes two types of Mo⁵⁺ have been identified. Their role in the formation of O ₂ ^– anion-radicals in low-temperature oxygen adsorption on reduced samples has been established.

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, ⁹⁵Mo, Mo⁵⁺ Mo–Mg (0,1–0,5 .% Mo) - O ₂ ^– .

     

Effect of the partial pressure of reactants on the selectivity of methylcyclopentane hydrogenolysis over a platinum catalyst

The kinetics of methylcyclopentane hydrogenolysis on a Pt/Al₂O₃ catalyst (10% Pt) has been studied at 230°C. The selectivity to 2-methyl- and methylpentane formation depends on the partial pressures of the starting reactants (methylcyclopentane and hydrogen); the surface coverage by these reactants must be taken into account in selectivity studies.

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Pt/Al₂O₃ (10% Pt) 230°C. 2-- 3- ( ). .

     

Effect of reductant adsorption on the ESR parameters of O

The change in the ESR parameters of O ₂ ^– ion-radicals under the effect of adsorption of reducing molecules on zinc oxide consists in the increase of the Z-component of the g-tensor. This change is assumed to be due to the transition of O ₂ ^– coordination from -to the -type.

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- O ₂ ^– , Z- g-. , O ₂ ^– - -.

     

Generation of model reactions leading to limit cycle behavior

The system of differential equations by Feistel and Ebeling has been generalized. Some new formal kinetic reactions with two internal components, which may exhibit limit cycle behavior have been studied. Based upon the numerical integration of the deterministic models of these reactions the oscillatory character of the systems has been confirmed.

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. , . .

     

Formation of oxalates and carbonates in the thermal decompositions of alkali metal formates

The influences of gaseous and solid reactants on the yields of oxalates and carbonates in the thermal decompositions of alkali metal formates have been studied. A mechanism of formation of these products is proposed, which explains the influences of basic and acidic species formed in the medium on the thermal decompositions of the alkali metal formates.

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Zusammenfassung Der einfluß von gasförmigen und festen Reaktanten auf die Ausbeute von oxalaten und Karbonaten bei der thermischen Zersetzung von Alkalimetallformiaten wurde untersucht. Es wurde ein Mechanismus für die Bildung dieser Produkte vorgeschlagen, der den Einfluß der während der thermischen Zersetzung von Alkalimetallformiaten entstehenden Basen und Säuren erklärt.

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, . , , .

     

High-temperature X-ray diffraction studies of the formation of V?Mo?O catalyst

High-temperature X-ray diffraction analysis in the temperature range of 553–823 K was used to study the formation and the region of thermal stability of VMo₃O₁₁ being an active component of the V–Mo–O catalyst for acrolein oxidation to acrylic acid.

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553–823 K VMo₃O₁₁, V-Mo-O .

     

Calorimetric studies of adsorptive properties of metallic carbides and nitrides of transition elements. Adsorption of H2, CO and O2 on titanium nitrides

Adsorption heats of hydrogen, oxygen and carbon monoxide on titanium nitrides have been measured calorimetrically in the temperature range from 473 to 673 K. With increasing Me/N ratio, the adsorption heat of oxygen grows.

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, 473–673 . Me/N.

     

Kinetics of isotopic exchange due to one elementary reaction

Kinetic equations of the isotopic exchange in a system with one elementary reaction have been derived. A principle of quasistationarity in the isotopic kinetics has been formulated.

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. .

     

An IR study of the Ziegler system Co(acad)3/Mg(n-butyl)2 in THF

Applying IR spectroscopy for studying the Ziegler system Co(acac)₃/Mg(Bu)₂ (Bu=n-butyl) in tetrahydrofuran, it could be shown that the following reactions take place: reduction of cobalt (III), exchange of the acetylacetonate groups and their interaction with Mg(Bu)₂.

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Co(acac)₃/Mg(Bu)₂ (Bu=-) - , (III), Mg(Bu)₂.

     

Electronic spectrum and thermal decomposition of nickel(II) complex with bis(N-γ-pyridyl-4-phenylbenzamide-hydrazone)

The unit cell parameters and the space group of the investigated compound were determined by means of X-ray diffraction.Analysis of the diffusion-reflection spectra of the crystalline powder and the absorption spectra of its alcoholic solutions permitted identification and quantitative characterization of the absorption bands of the crystalline complex of NiL₂(ClO₄)₂·3H₂O.Application of differential-thermal analysis allowed determination of the mechanism of thermal decomposition of the compound. From these measurements, the expected configuration of the basic molecule was verified, involving determination of the number of non-coordinated water molecules.

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Zusammenfassung Mittels Röntgendiffraktionsmethoden wurden Gitterzellenkonstanten sowie die Raumgruppe der untersuchten Verbindung bestimmt. Durch Analyse der erhaltenen Diffusions-Reflexionsspektren von kristallinem Pulver und des Absorptionsspektrums einer alkoholischen Lösung der Verbindung war es möglich, die Absorptionsbanden des Kristallkomplexes NiL₂(ClO₄)₂·3H₂O zu identifizieren und quantitativ zu charakterisieren. Anwendung von Differentialthermoanalyse ermöglicht die Bestimmung des Mechanismus der Zersetzungsreaktion der Verbindung. Durch diese Messungen, einschliesslich der Bestimmung der Anzahl nichtkoordinierter Wassermoleküle, wurde die erwartete Konfiguration des Grundmoleküles überprüft.

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NiL₂(ClO₄)₂·₂, L-N-- -4- . L-N---4- . , , . . , .

     

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 . .

     

Use of DSC robotic systems in pharmaceutical analysis

DSC is extremely valuable for analysis of pharmaceuticals. The introduction of robotic systems with data acquisition and processing makes it very competitive to other methods in the field of purity determination or solid state characterization of raw materials. Some applications are also possible to dosage forms. Applications of DSC robotics with statistical results are given.

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Zusammenfassung Zur Analyse von Arzneimitteln ist DSC außerst wertvoll. Die Einführung von Robotersystemen mit Datenaquisition und -aufarbeitung macht dieses Verfahren auf dem Gebiet der Reinheitsuntersuchung und Feststoffcharakterisierung der Rohmaterialien konkurrenzfähig im. Vergleich zu anderen Methoden. Einige Varianten lassen sich auch auf fertige Präparate anwenden. Es wird die Anwendung von computerisierten DSC-Systemen einschließlich statistischen Ergebnissen gegeben.

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Many thanks to Mrs C. Goldbronn and Mr P. Piechon for their technical assistance.     

Formation of hexagonal MoO3 upon the decomposition of silica-supported ammonium paramolybdate

Upon the decomposition of silica-supported ammonium paramolybdate, hexagonal MoO₃ is formed at 300–350 °C. Irreversible transformation of hexagonal to rhombic MoO₃ is observed with increasing calcination temperature. The hexagonal MoO₃ structure is probably stabilized by the insertion of ammonium and silicon ions into the lattice of molybdenum trioxide.

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, , 300–359 °C . MoO₃ . MoO₃, , MoO₃.