Steady state kinetic equation for SO2 oxidation on vanadium catalysts

From the analysis of the detailed reaction mechanism and taking into account vanadium complex formation processes, a steady state kinetic equation has been derived to describe experimental data in a wide range of reaction conditions.

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, .

     

Modifying action of carbon dioxide in catalytic oxidation of ethylene on silver

Carbon dioxide exerts a strong inhibitory effect on oxygen adsorption and complete oxidation of ethylene on silver but has little effect on the rate of ethylene oxidation to ethylene oxide.

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.

     

Methanation of CO2 over Ru?SiO2 catalyst

Using Ru–SiO₂ catalyst, the kinetics of methanation of carbon dioxide has been studied. In the temperature range of 320–460°C a simple power law model is found to predict experimental results with a good agreement over the range of variables studied.

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Ru/SiO₂. , 320–460°C.

     

An evolved gas analysis study of the reduction of nickel oxide by hydrogen

The reduction of NiO by H₂ was followed by conventional thermogravimetry and a new evolved gas analysis approach which follows the course of the reaction by measuring the H₂O content of the gas stream. Excellent correspondence is observed between the two techniques for simultaneous measurements. Heating rates between 0.5 and 10° min^–1 shift the temperature of the reaction as does changing the surface area of the NiO. These shifts are discussed in terms of the Neel temperature (T _N) of NiO and the thermal history of the sample. No correlation between reaction rate andT _N is observed under dynamic conditions. Preheating the sample in vacuum at 130° has a marked effect on shape of the DTG and EGA curves.

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Zusammenfassung Die Reduktion von NiO durch H₂ wurde durch konventionelle Thermogravimetrie und eine neue Analyse des entwickelten Gases untersucht, welche den Reaktions-ablauf durch Messung des H₂O-Gehalts des Gasstromes verfolgt. Eine ausgezeichnete Übereinstimmung beider Techniken wird bei simultanen Messungen beobachtet. Aufheizgeschwindig keiten zwischen 0.5 und 10° min^–1 verschieben die Temperatur der Reaktion und verändern die Oberfläche des NiO. Diese Verschiebungen werden auf Grund der Neel-Temperatur (T _N) des NiO und der thermischen Vergangenheit der Probe erörtert. Unter dynamischen Bedingungen wird keine Korrelation zwischen der Reaktionsgeschwindigkeit undT _N beobachtet. Das Vorwärmen der Probe im Vakuum bei 130° zeigt einen deutlichen Einfluß auf die Form der DTG und EGA Kurven.

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() ( ), H₂O . . 0.5 10° , . (T _N) . T _N. 130° - -.

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Presented at the 11th Annual NATAS Meeting, New Orleans, LA, Oct. 19–21, 1981.

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The authors are grateful to Mr. F. Schrey for measurements of the surface area.     

TPD studies of hydrogen adsorption on group VIII metals

Hydrogen desorption proceeds in several temperature regions and differs by its order of magnitude and activation energy. Differential curves of adsorbed hydrogen distribution with respect to the desorption activation energy, dN/dE (E), show a considerable inhomogeneity of adsorbed atomic species and the energetic homogeneity of molecular species.

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. dN/dE (E) .

     

The kinetic equation in the DTA study of the silica gel to cristobalite transformation

The importance of the choice of a suitable kinetic equation in the DTA study of the silica gel to cristobalite transformation is pointed out. It is shown that isothermal and non-isothermal data reported in the literature are better fitted by a Johnson-Mehl-Avrami equation withn=3, rather than a first-order one.

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Zusammenfassung Die Bedeutung der Wahl einer entsprechenden kinetischen Gleichung bei der DTA-Untersuchung von Kieselgel zur Cristobalittransformation wurde aufgezeigt. Es wurde bewiesen, daß isotherme und nichtisotherme Angaben der Literatur durch eine Johnson-Mehl-Avrami-Gleichung mit n=3 besser interpoliert werden können als durch eine Gleichung »erster Ordnung«.

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Résumé On souligne l'importance du choix d'une équation cinétique convenable lors de l'étude par ATD de la transformation du gel de silice en cristobalite. On montre que les résultats cités dans la littérature obtenus en régimes isothermes et non-isothermes sont mieux interpolés par l'équation de Johnson-Mehl-Avrami avecn=3 que par une équation du «premier ordre».

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. , , , -- =3, « ».

     

A stochastic analysis of catalyst deactivation in presence of external transfer limitations

The paper analyzes the simplest case of concentration independent deactivation of a catalyst surface in the presence of external transport limitations and accounts for the variations around the mean value of the activity of the catalysts leading to a stochastic formulation. The results reveal interesting features which would not be evident from the conventional deterministic analysis.

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- , , . , .

     

Non-equilibrium ion-(polar) molecule reaction rate coefficients

Using the Fokker-Planck version of an approximate Boltzmann equation for the ion (translational) energy distribution function f_I we have calculated the deviation, k, of the non-equilibrium ion-(polar)molecule reaction rate coefficient k (based) on f_I from its equilibrium value k⁽⁰⁾. The _D (dipole moment)-dependence of the reaction cross section applied leads to a corresponding dependence of k on _D.

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- , k - ( f_I) k⁽⁰⁾. k _D.

     

Catalytic activity of rhodium-indigo sulfonates in hydrogen-water isotope exchange

Rhodium indigo sulfonate complexes are effective catalysts of isotope exchange between hydrogen and water. A study has been made of the transformation of initial complexes into catalytically active forms. Kinetic regularities of isotope exchange and an equation for the reaction rate have been obtained.

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. . .

     

A thermal synthesis of a new tin(IV) dithiocarbamate

A new tin dithiocarbamate containing sulphur bridges, di--sulphidobis [bis(N,N-diethyldithiocarbamato)tin(IV)], has been isolated from the thermal decomposition of tetrakis(N,N-diethyldithiocarbamato)tin(IV). A dimeric structure is proposed on the basis of results from mass spectrometry, infrared spectroscopy, thermal analysis and vapour pressure osmometry.

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Zusammenfassung Ein neues, Schwefelbrücken enthaltendes Zinn-Dithiocarbamat, Di--sulfidobis[bis(N,N-diäthyldithiocarbamato)Zinn(IV)], wurde bei der Zersetzung von Tetrakis(N,N-diäthyl-dithiocarbamato)Zinn(IV) isoliert. Aufgrund der Ergebnisse der Massenspektrometrie, der Infrarotspektroskopie, der Thermoanalyse und der Dampfdruck-Osmometrie wird eine Dimerstruktur vorgeschlagen.

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Résumé Un nouveau dithiocarbamate d'étain contenant des ponts de soufre, le di--sulfidobis[bis(N,N-diéthyl-dithiocarbamato)é tain(IV)], a été isolé lors de la décomposition thermique du tétrakis(N,N-diethyl-dithiocarbamato) étain(IV). Une structure dimère est proposéeà partir des résultats obtenus par spectrométrie de masse, spectroscopie infrarouge, analyse thermique et osmométrie sous pression de vapeur.

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—-- [/N,N- (/IV)], [/N,N- (/IV)], , (N,N- ) (IV). - , , .

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The authors gratefully acknowledge the assistance given by Dr. A. G. Wedd with the vacuum sublimation technique. One of us, G. K. B., is grateful for a research scholarship provided by La Trobe University.     

Cyclohexane conversion on nickel mordenite

Two series of nickel mordenite catalysts have been prepared on the basis of Na-mordenite and H-mordenite. Their catalytic activity in cyclohexane conversion has been studied. It has been found that the properties of the catalysts are strongly dependent on the acidity of mordenite.

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NaM HM. .

     

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.

     

Computation in kinetics, III. A new method for kinetic model search based on simultaneous regression estimation of rate constants, stoichiometry and/or reaction order

Modified samples of natural mordenites have been found to catalyze the oxidative condensation of methane to yield ethane and ethylene. The selectivity towards C₂ hydrocarbons increases, whereas the acidity of zeolites falls.

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, . C₂ .

     

A device for pulse investigation of heterogeneous catalytic reactions

In the present work a simple device is described for the pulse investigation of heterogeneous catalytic reactions and catalysts. Owing to the possibility for separate adjustment of the gas flow rate in the catalytic reactor and in the chromatographic column, it can be used for kinetic measurements too.

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- . , .

     

Thermal behaviour or thallium(I) fatty acid salts,I

We have studied the thermal behaviours of the fatty acid (C₁-C₉, C₁₂, C₁₄, C₁₆ and C₁₈) thallium(I) salts.Investigating the dependence of the thermal decomposition reactions on the experimental conditions, we established that they decompose differently depending on the atmosphere, and on the shape and material of the sample holders.We also determined the heat-stable temperature ranges of the compounds in which they can be investigated without any thermal decomposition.The temperatures and enthalpy changes of the polymorphic and phase changes were measured and the corresponding entropy changes were calculated.

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Zusammenfassung Das thermische Verhalten der Thallium(I)-Salze der Fettsäuren mit C₁ bis C₉, C₁₂, C₁₄ und C₁₈ wurden untersucht. Die Temperaturen und Enthalpien der einzelnen polymorphen und Phasenänderungen, sowie die thermische Stabilität der Verbindungen wurden bestimmt. Es wurde festgestellt, daß die zu Ketonen und Gemischt-Ketonen führende thermische Zersetzung in der Schmelzphase von Destillationsprozessen begleitet wird, welche von der Molekülstruktur und von zahlreichen Versuchsbedingungen abhängig sind.

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Résumé Etude du comportement thermique des sels de thallium(I) d'acides gras (de C₁ à C₉, C₁₂, C₁₄ et C₁₈). L'étude de la décomposition thermique en fonction des conditions expérimentales a permis d'établir que les sels étudiés se décomposent différemment suivant l'atmosphère utilisée, ainsi que suivant la forme et la nature des supports échantillons. Détermination des domaines de température où ces composés restent thermiquement stables. Mesure des températures et des variations d'enthalpie des transitions de phase et des transitions polymorphiques et calcul des variations d'entropie correspondantes.

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(I) C₁-C₉, C₁₂, C₁₄, C₁₆, C₁₈. , . , , , .

     

AES studies on a Pd-modified silver catalyst

Silver crystals electrodeposited from AgNO₃ (8%) and Pd²⁺ (250 mg/dm³) electrolyte before and after exposing to the conditions of the methanol to formaldehyde oxidation process were investigated by AES. Carbon, sulfur, oxygen and palladium on the surface were observed. Higher Pd concentration on the silver surface than in the bulk was found. Its amount on the surface decreased with the temperature increase.

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, - , AgNO₃ (8%) Pd⁺² (250 /), AES. , , - . , - Pd , , .

     

Comparative thermal analysis (CTA) of thermally-stable polymers and model compounds. Polyimides and model compounds

The method of comparative thermal analysis has been used to determine the thermal stability of polyimides and their model compounds. The extent of defects in the investigated polyimides was determined by gas chromatography. The dependence of the extent of the defects on the chemical structure of the initial components and the supermolecular structure of the polyimides was established.

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Zusammenfassung Die Methode der vergleichenden Thermoanalyse wurde zur Bestimmung der Hitzestabilität von Polyimiden und ihren Modellverbindungen eingesetzt. Das Ausmass der Defekte in den untersuchten Polyimiden wurde gaschromatographisch bestimmt. Die Abhängigkeit des Umfangs der Defekte von der chemischen Struktur der Ausgangskomponenten und der supermolekularen Struktur der Polyimide wurde festgestellt.

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Résumé La méthode d'analyse thermique comparée (CTA) a été utilisée pour étudier la stabilité thermique des polyimides et de leurs composés modèles. On a déterminé par chromatographie en phase gazeuse l'étendue des défauts dans les polyimides étudiés. On a établie de même les rapports qui existent entre l'étendue des défauts dans la structure chimique des composants initiaux et la structure supermoléculaire des polyimides.

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, . . .

     

A metal reactor for the diaphragm method with chambers providing complete mixing

A new metal reactor with two chambers in which complete mixing of gases is achieved has been developed for use in the diaphragm method. This apparatus is suitable for the determination of the effective diffusion coefficient and its temperature dependence. It can also be used to determine the type of transport, the gas permeability coefficient and to investigate the macrokinetics of catalytic processes.

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. : ; ; .

     

Study of hydroisomerization of n-hexane on natural mordenite catalyst

A mordenite-containing rock sample from the Tokaj Mountains (Hungary) and its various forms modified by chemical treatment have been tested for catalytic properties during isomerization of n-hexane. Addition of Pt to the catalyst leads to a sharp decrease in the rate of cracking and in the rate of deactivation and this results in a catalyst of high selectivity for hexane isomers.

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(), , , , -. Pt , .

     

Thermal studies on copper(II)-5,5′-thiodisalicylic acid complexes

Aquo, ammonia and pyridine complexes of copper(II) with 5,5-thiodisalicylic acid have been investigated by TG and DTG. All these complexes decompose in three distinct steps, viz. dehydration, loss of axial bases and decarboxylation of the aromatic ligand. The thermal curves of the aquo and pyridine complexes show water loss in two distinct steps. The decreasing order of thermal stability of the complexes is py > NH₃ > H₂O.

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Zusammenfassung Aquo-, Ammoniak- und Pyridinkomplexe von Kupfer(II) mit 5,5-Thiodisalicylsäure wurden durch TG und DTG untersucht. Diese Komplexe werden in den drei Stufen, Dehydratisierung, Verlust axialer Basen und Decarboxylierung des aromatischen Liganden zersetzt. Die Abbaukurven der Aquo- und Pyridinkomplexe zeigen einen Wasserverlust in zwei Stufen. Die abnehmende Reihenfolge der Thermostabilität der Komplexe ist py > NH₃ > H₂O.

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, (II) 5,5- . , : , . - , . : > NH₃ > ₂.