Adsorption of carbon monoxide and oxygen on Pt(110)

Adsorption of CO and O₂ on Pt(110) was studied by XPS, LEED and TDS methods to elucidate the role of O_ads states and structural rearrangements of the surface under the action of CO_ads in the appearance of self-oscillations in the rate of CO oxidation on Pt(110).

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, CO O₂ Pt(110) O CO CO Pt(110).

     

Hreels studies of Hads effect on NO adsorption on Pt(111)

HREELS studies of NO molecular adsorption on clean and hydrogen covered Pt(111) have revealed that a reversible transition between bridge (₁) and on-top (₂) states of NO_ads is realized in the (NO+H₂)/Pt(111) system. In the presence of H_ads the adsorption of NO in the ₁ state is inhibited and the main state of NO_ads is ₂. Upon heating the layer (₂-NO_ads+H_ads) hydrogen desorption is accompanied by on-top to bridge state conversion.

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NO Pt(III). , (NO+H₂)/Pt(III) (₁) (₂) NO. H NO ₁ , , ₂ NO. (₂-NO+H) NO .

     

Catalytic properties and phase composition of multicomponent catalysts for oxidative ammonolysis of propane

Studies of the phase composition and catalytic properties of several complex oxide catalysts for oxidative ammonolysis of propane indicate that the active phases of these catalysts are antimonates of the respective metals. Phosphorus and tungsten additives to the catalysts promote the formation of such phase compositions, i.e. the formation of antimonates and the binding of excess antimony oxide.

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. , ; , .

     

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.     

Studies of the chemical exchange kinetics of glycinate ions in mixed ligand complexes of copper (II) and glycylglycine

Nuclear magnetic resonance studies of the chemical exchange kinetics of glycinate ions in binary and ternary complexes of copper(II) and glycylglycine indicate the increase in the exchange rate of glycinate ions in the ternary complex. This phenomenon is assumed to be due to the glycinate ion coordination in the axial—equatorial position.

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(II) . . , - - .

     

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 .

     

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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, . , , .

     

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) ; .

     

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 ^– - -.

     

Kinetic and mechanistic studies on the oxidation of arginine and histidine by chloramine-T in hydrochloric acid medium

The oxidation of amino acids by chloramine-T (CAT) in HCl medium at 30°C indicates simultaneous catalysis by H⁺ and Cl^– ions in the HCl concentration range of 0.04–0.12 M. The reaction is first order with respect to concentrations [CAT], [H⁺] and [arginine], but zero order with respect to [histidine]. The rate depends also on Cl^– concentration following 0.7th order. At HCl concentrations >0.12 M, the rate equation is:w=k[CAT] [amino acid]^0.6 and is independent of the [Cl^–]. A suitable mechanism has been suggested.

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-T (CAT) HCl (30°C) H⁺, Cl^– [HCl]=0,04–0,12M. [CAT], [H⁺] [] []. [Cl^–]^0,7. [HCl]>0,12M =k · [CAT][]^0,6 [Cl^–]. .

     

Structural studies of nickel-based Raney catalysts

Electron microscopy and Mössbauer spectroscopy studies of nickel-based Raney catalysts have revealed that the catalysts are formed through the successive aggregation of their structural elements. Catalyst particles are covered by a thin layer of nickel oxide.

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. , . .

     

Kinetics and mechanism of the oxidation of benzyl alcohol by potassium chlorochromate

The kinetics of the oxidation of benzyl alcohol by potassium chlorochromate, KCrClO₃, has been studied in dimethyl sulfoxide-dichloromethane medium. The reaction is catalyzed by acid. The effects of temperature and solvent composition were studied and activation parameters evaluated. Probable mechanisms are discussed.

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, KCrClO₃, . . . .

     

The evaporation of potassium from phlogopite

The evaporation of potassium from phlogopite was investigated by roasting phlogopite with different chemical reagents. The possible reactions between reactants and the sample at different temperatures were investigated by thermogravimetry. Gypsum, calcite, sodium chloride, activated carbon, calcium chloride and fluoride were used as chemical reactants. Similar tests were carried out by batch experiments using muffle furnace and tube oven and finally the sample mixtures were heated in a vacuum. The use of a vacuum enabled an almost complete extraction of potassium in solid state at the lowest temperature so far investigated. The structure of phlogopite was shown to be destroyed by raising the temperature. The extraction of potassium from feldspar, a sample from Lohja, Finland was also investigated.

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Zusammenfassung Beim Abrösten von Phlogopit mit verschiedenen chemischen Stoffen wurde das Verdampfen von Kalium aus Phlogopit untersucht. Die möglichen Reaktionen zwischen der Probe und der Reaktionspartnern bei verschiedenen Temperaturen wurden mittels Thermogravimetrie untersucht. Als Reaktant wurden Gips, Kalzit, Natriumchlorid, Aktivkohle, Kalziumchlorid und -fluorid verwendet. Ähnliche Untersuchungen wurden in Reihenexperimenten mittels Muffel- und Röhrenofen und letztlich durch Erhitzen der Proben im Vakuum durchgeführt. Die Anwendung von Vakuum ermöglicht bei den niedrigsten der angewendeten Temperaturen einen fast vollständigen Auszug des Kaliums aus dem Feststoff, Durch Erhöhen der Temperatur wurde die Struktur von Phlogopit nachweislich zerstört. Die Extraktion von Kalium aus einer Feldspatprobe aus Lohja, Finnland, wurde ebenfalls untersucht.

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. . , , , , . , , . , , . , . //.

     

The thermal behaviour of solvates in the LiCI(MgCl2, AlCl3) water-1,4-dioxane systems

The thermal behaviour of the solvates and mixed solvates in the LiCl(MgCl₂, AlCl₃)-water-1,4-dioxane systems was investigated by means of DTA measurements of the melting behaviour and by quasi-isothermal and quasi-isobaric investigations of the thermal decomposition processes.The compounds melt incongruently. The positions of the melting points and the processes of thermal decomposition confirm the assumption that 1,4-dioxane is bonded in the first coordination sphere in the mixed solvate of lithium, but in the cases of magnesium and aluminium chloride it is bonded via hydrogen-bonds and not directly to the cations. Only for the lithium and magnesium compounds does the decomposition of the anhydrous solvates result in anhydrous chlorides.

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Zusammenfassung Das thermische Verhalten der Solvate und Mischsolvate der Systeme LiCl, (MgCl₂, AlCl₃)-Wasser-1,4 Dioxan wurde mit Hilfe von DTA-Messungen zum Schmelzverhalten, und quasi-isothermen und quasi-isobaren Untersuchungen zum Ablauf der thermischen Zersetzung Untersucht. Die Verbindungen schmelzen inkongruent. Die Lage der Schmelzpunkte und der Verlauf der thermischen Zersetzung bekräftigen die Vorstellungen, daß 1,4 Dioxan im Mischsolvat des Lithiums in der ersten Koordinationsphäre direkt am Kation, hingegen bei Magnesium und Aluminium über Wasserstoffbrücken gebunden ist. Die Zersetzung der wasserfreien Solvate führt nur im Fall der Lithium- und Magnesiumverbindungen zu den wasserfreien Chloriden.

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( , )--1,4- , - - — . . , 1,4- . , , . .

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The valuable assistance of Dr. Frahghänel in the separation of the solid phase by means of the hightemperature centrifuge is gratefully acknowledged.     

Investigation of surface phenomena on solid catalysts by simultaneous thermogravimetry and DTA

Thermogravimetry and simultaneous DTA were used to investigate the phenomena of adsorption, desorption and surface reactions on solid catalysts. The measurements were carried out with NaX and X-type ion-exchanged zeolites and silica-alumina gels (Ketjen) treated with sodium hydroxide in the presence of carbon dioxide. On the basis of the quantitative results it is possible to give an interpretation of the surface phenomena and to establish the existence of various active centres on the surfaces of the catalysts. In the case of the adsorption of carbon dioxide on X-type zeolites, the quantity of carbon dioxide adsorbed is much smaller on ion-exchanged zeolites than on NaX.

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Zusammenfassung Thermogravimetrie und simultane DTA wurden zur Untersuchung der Adsorptions-, Desorptions-Erscheinungen und Oberflächenreaktionen an festen Katalysatoren eingesetzt. Die Messungen wurden and NaX und Zeolithen des Typs X sowie an Silika-Aluminiumoxidgelen Ketjen durchgeführt, welche mit Natriumhydroxid in Gegenwart von Kohlendioxid behandelt worden waren. Aufgrund der quantitativen Ergebnisse ist es möglich eine Deutung der Oberfiächenerscheinungen zu geben und die Existenz verschiedener aktiver Zentren an der Katalysatorenoberfläche nachzuweisen. Im Falle der Adsorption von Kohlendioxid an Zeolithen des Typs X ist die Menge des adsorbierten Kohlendioxids am Ionenaustauscher viel niedriger als am NaX.

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Résumé Application de la TG et de l'ATD simultanées à l'étude des phénomènes d'adsorption, de désorption et de réactions de surface sur des catalyseurs solides. Les mesures ont été effectuées avec des zéolites échangeuses d'ions de type NaX et X ainsi qu'avec des gels Ketjen silice-alumine traités par NaOH en présence de CO₂. Les résultats quantitatifs permettent de donner une interprétation des phénomènes de surface et d'établir l'existence de divers centres actifs à la surface des catalyseurs. Dans le cas de l'adsorption de CO₂ sur les zéolites de type X, la quantité de CO₂ adsorbé est beaucoup plus faible que sur les zéolites de type NaX.

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DTA , . - NaX X - « », . . X, - , NaX.

     

IR spectra of CO and NO adsorbed on CuO

The original heterogeneity of CuO surface is suggested to account for the presence of two states of surface copper cations with different effective charges.

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CuO, . , .

     

Coadsorption of ethylene and oxygen on an iridium surface

It is established that the hydrocarbon coverage (0<1) formed at T<400 K on the Ir surface is oxidized upon oxygen exposures to CO and H₂O by an adsorption mechanism. Complete oxidation to CO₂ and H₂O is achieved at T350 K after C₂H₄ exposures of the oxygen coverage.

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, (<1), T<400 K Ir, CO H₂O . CO₂ H₂O T350 K C₂H₄ .

     

Ethylene oxidation by lithium nitrate in the presence of palladium acetate in acetic acid

Data are reported on variations of the gas phase volume and product accumulation in ethylene oxidation by lithium nitrate in acetic acid solutions, catalyzed by palladium acetate. An assumption is made on the routes of nitrate ion reduction.

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, , . -.