A surface potential study of adsorbed oxygen species on a Bi2Mo3O12 catalyst

Bi₂Mo₃O₁₂ is a selective oxidation catalyst of propylene into acrolein. Surface potential measurements proved the presence of an equilibrium between gaseous oxygen and the O^2– species adsorbed on the surface of the catalyst, under oxygen atmosphere, in the range 538K–673K. This is in accordance with the fact that O^2– is a selective oxidation species. An oxygen adsorption mechanism is also discussed.

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Bi₂Mo₃O₁₂ . O^–2, , 538–613 . , O^–2 . .

     

Kinetic studies of ozonation of polyhydric alcohols

Kinetic studies of the oxidation of polyhydric alcohols by ozone-oxygen mixtures in aqueous solutions at 284–302 K indicate that the second-order effective rate constantk decreases with increasing substrate concentration.

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- 284–302 . , .

     

Heterogeneous decay of fluorine atoms

The probability of decay of fluorine atoms on the surface of molybdenum glass, quartz, Teflon, copper, nickel, gold and on aluminium alloy at 20–300 °C has been determined.

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, , , , , 20–300 °C.

     

Water-gas shift reaction over chromia-promoted magnetite. Use of temperature-programmed desorption and chemical trapping in the study of the reaction mechanism

The mechanism of WGSR has been studied on an Fe–Cr catalyst. Although after reaction (from 250 to 400°C) formate species have been characterized on the Fe–Cr catalyst, by chemical trapping, TPD studies after reaction and after HCOOH adsorption have shown that formates are not the main intermediates. The disproportionation of CO or the regenerative mechanism seems to be more probable.

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CO+H₂OCO₂+H₂ Fe–Cr. ( 250 400°C) Fe–Cr , , , . CO .

     

Application of simultaneous thermomicroscopy/DSC to the study of phase diagrams

The correlation between morphological changes and DSC recordings gives valuable information on the mechanism of phase transformations. The present paper describes a new instrument for simultaneous DSC and thermomicroscopy in transmitted light, where a DSC device is placed in a commercially available hot-stage. The application of this DSC/thermomicroscopy is exemplified by study of the phase diagrams for KNO₃-NaNO₃, diphenylamine-benzophenone and a liquid crystal system.

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Zusammenfassung Die Korrelation zwischen morphologischen Veränderungen und DSC-Kurven ergibt wertvolle Informationen über den Mechanismus von Phasenumwandlungen. Es wird ein neues Gerät zur simultanen DSC und Thermomikroskopie im durchfallenden Licht beschrieben, in dem die DSC-Einheit in einem im Handel erhältlichen hot-stage untergebracht ist. Die Anwendbarkeit dieses DSC/Thermomikroskops wird durch Untersuchung der Phasendiagramme KNO₃-NaNO₃, Dyphenylamin-Benzophenon und eines Flüssigkeitskristallsystems demonstriert.

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. , . KNO₃-NaNO₃, - .

     

Thermal properties of some metal chelates of di-isobutyldithiocarbamic acid

The thermal properties of some metal chelates of di-isobutyldithiocarbamic acid have been investigated in an inert atmosphere, with a view to applying them to gas chromatographic separation. In spite of the slight decomposition occurring during volatilization, most of the metal chelates may be successfully separated by gaschromatography on short nonpolar glass capillary or fused silica columns. There is no clear correlation between the gaschromatographic behaviour and the thermal stability of the metal chelates studied here.

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Zusammenfassung Die thermischen Eigenschaften einiger Metallchelate der Di-isobutyl-dithiocarbaminsäure wurden in einer inerten Atmosphäre hinsichtlich der Möglichkeiten ihrer gaschromatographischen Trennung untersucht. Trotz der während der Verflüchtigung eintretenden geringfügigen Zersetzung kann der grösste Teil der Metallchelate durch Gaschromatographie erfolgreich in kurzen nichtpolaren Glaskapillarkolonnen oder in mit geschmolzenem SiO₂ bedeckten Kolonnen getrennt werden. Es besteht keine eindeutige Korrelation zwischen dem gaschromatographischen Verhalten und der thermischen Stabilität der untersuchten Metallchelate.

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. , . .

     

Effect of the experimental conditions on the thermooxidative behaviour of vegetable oils

The thermooxidative behaviour of sunflower and rapeseed oils has been investigated by means of a derivatograph, using both dynamic and static (isothermal) temperature programs. The aim was to find the optimum experimental conditions for studying the oxidative stability of edible oils, in order to determine their storability. A novel method has been developed for the rapid indication of stability by modelling the oxidative changes under isothermal conditions.

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Zusammenfassung Das thermooxidative Verhalten von Sonnenblumen- und Rapsöl wurde mittels eines Derivatographen unter Einsatz dynamischer und statischer (isothermer) Temperaturprogramme untersucht. Der Zweck der Arbeit war die optimalen Versuchsbedingungen zur Bestimmung der Oxidationsstabilität von Speiseölen zu finden um ihre Lagerfähigkeit zu bestimmen. Eine neue Methode zur schnellen Ermittlung der Stabilität wurde mittels Modellierung der oxidativen Änderungen unter isothermen Bedingungen erarbeitet.

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Résumé On a étudié l'oxydabilité thermique des huiles de tournesol et de colza, à l'aide d'unDerivatigraph et en utilisant des programmes de température dynamiques et statiques (isothermes). Le but du travail était de trouver les conditions d'expérience les mieux adaptées à l'étude de la résistance à l'oxydation des huiles alimentaires afin de déterminer les conditions de leur stockage. On a mis au point une nouvelle méthode qui indique rapidement la stabilité de l'huile en reproduisant les changements d'oxydation en conditions isothermes.

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, ( ) . , , . .

     

Epoxidation of propylene over silver sponge catalysts

The oxidation of propylene with air on silver catalysts of macropore structure has been studied both in a flow and an open recirculation reactor. Under strictly isothermal conditions, avoiding the local overheating of the catalyst, propylene oxide was produced with a selectivity as high as about 50%.

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, . , , , 50%-.

     

Consecutive hydrogenation of pseudoionon. Application of diffusion kinetic model to predict experimental reactor operation

A method for the calculation of fixed catalyst bed reactors by using a diffusion kinetic model is suggested. Correlation between calculated curves for the time distribution of the reaction mixture composition and experimental data is given.

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=qo . .

     

Surface acidity of cerium exchanged Y-zeolite

Surface acidities of Ce^III, Ce^IV and [Ce^III, Ce^IV] containing Na-Y zeolites were determined by means of n-butylamine titration in benzene using Hammett indicators in the range H_o: +6.8 to H_o: –8.2. Total acidites of Ce^IVNaY zeolites until 51% Ce^IV exchange were found to be small (0.80 mequ/g at H_o: +6.8) but formed preferably strong acidic centers (H_o: –5.6) even at low degrees of exchange. Ce^IIINaY displayed an acidity pattern similar to that which is known from lanthanum exchanged NaY faujasites under the same pretreatment conditions.

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NaY, Ce^III, Ce^IV [Ce^III, Ce^IV], -, H_o: +6,8 H_o:–8,2. Ce^IVNaY 51%- Ce^IV (=0,80 / H_o: +6,8), (H_o: –5,6) . Ce^IIINaY NaY .

     

Catalytic effect of hydroxy groups on reaction of polyamine with tert-butyl acrylate

The reaction of N-cyclohexyl-1,3-propanediamine with tert-butyl acrylate and the catalytic effect of hydroxy groups on the reaction course was investigated by Near Infrared spectroscopy. The reaction was found to be bimolecular and of second order. The dependence of rate constant on catalyst concentration (diols) is linear and the structure of diol used has no effect.

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N--1,3- -. . . () , .

     

Effect of CO on CO2 methanation over a supported Ni?La2O3-Ru catalyst

Complete methanation of CO₂ and CO on a composite catalyst by onepass operation with a high space-time yield and 100% selectivity at a low temperature such as 270 °C was achieved. In simultaneous methanation, CO methanation accelerates CO₂ methanation.

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CO₂ CO -, co 100%- , 270 °C. , CO CO₂.

     

Uncatalyzed and catalyzed bromate driven oscillations in salicylic and 5-sulfosalicylic acid

Kinetics of the reactions of WCl₆ with Ph₄Sn, Ph₃SnCl and Ph₂SnCl₂ have been studied by UV-VIS spectroscopy. Approximate values of the corresponding rate constants in benzene have been obtained.

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WCl₆ Ph₄Sn, Ph₃SnCl Ph₂SnCl₂, , - . .

     

Kinetics of the thermal degradation of polyimides

A number of temperature and kinetic parameters of thermal degradation of polyimides over the temperature range from 20 to 1000° have been determined on the basis of thermogravimetric investigations of a polyimide sample obtained from pyromellitic dianhydride and diaminodiphenyl ether. It was shown that such kinetic parameters as the reaction order and the activation energy of thermal degradation are directly dependent on the conditions under which the thermal analysis is carried out. It was found that when the static and dynamic conditions of the environment of a polymer sample are varied, the thermochemical processes occurring in a polyimide over the temperature range investigated are drastically changed.A critical analysis of the possibility of comparing the kinetic data on thermal degradation with the criteria generally used for the evaluation of the thermal stability of polyimides was carried out. The dynamic kinetic characteristics of the degradation of polyimide were correlated to prolonged thermal stability.

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Zusammenfassung Eine Anzahl von Temperatur- und kinetischen Parametern des thermischen Abbaus von Polyimiden wurde im Temperaturbereich von 20 bis 1000° aufgrund von an aus Pyromellitdianhydrid und Diaminodiphenyläther erhaltenen Polyimidproben durchgeführten Untersuchungen bestimmt. Es wurde gezeigt, daß kinetische Parameter wie die Reaktionsordnung und die Aktivierungsenergie der thermischen Zersetzung unmittelbar von den Bedingungen abhängig sind, unter welchen die Thermoanalyse durchgeführt wurde. Es wurde gefunden, daß im Falle der Änderung der statischen und dynamischen Bedingungen der Umgebung einer Polymerprobe, die in einem Polyimid in dem untersuchten Temperaturbereich stattfindenden thermochemischen Vorgänge drastisch geändert werden.Eine kritische Analyse der Möglichkeit des Vergleichs kinetischer Angaben bezüglich des thermischen Abbaus mit den zur Bewertung der Thermostabilität von Polyimiden allgemein gebräuchlichen Kriterien wurde durchgeführt. Die dynamischen kinetischen Charakteristika des Abbaus von Polyimiden wurden mit der verlängerten Thermostabilität korreliert.

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, , 20–1000°. , , . , , . , . .

     

Catalytic and acidic properties of different metal-zeolite catalysts

Catalytic and acidic properties of bifunctional catalysts containing faujasite, superhigh-silica zeolite and mordenite have been studied in isomerization of C₈-alkylaromatic hydrocarbons.

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C₈ , , - .

     

Fe2O3 transformation to iron chlorides in radical chain gas-phase chlorination of methane

It has been established that the formation of iron chlorides in chain gas-phase reaction of methane chlorination is observed starting with T650 K. At Cl₂:CH₄=4:1, Fe₂O₃ is transformed to FeCl₃. With increasing methane concentration (Cl₂:CH₄=1:1), besides FeCl₃, FeCl₂ is also formed. Kinetic regularities of the reaction have been studied at 600–1200 for both gaseous mixtures.

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, 650 . : 41, Fe₂O₃ FeCl₃. (Cl₂CH₄=11) , FeCl₃ FeCl₂. 600–1200 -.

     

Hydrocarbon conversion over Pt?Re/Al2O3-ZSM-5 bifunctional catalysts. II. Sulfur resistance of Pt?Re/Al2O3 modified with ZSM-5

The sulfur resistance of Pt–Re/Al₂O₃-ZSM-5 catalyst has been investigated for normal heptane reforming. It was found that while sulfur acts as a poison for Pt–Re/Al₂O₃, it can play an important role in activity maintenance and aromatics production when ZSM-5 zeolite is present.

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Pt–Re/Al₂O₃-ZSM-5 -. , , Pt–Re/Al₂O₃, ZSM-5.

     

Kinetic consequences of displacement adsorption in heterogeneous catalysis

Kinetic analysis of the simple reaction scheme of the heterogeneously catalyzed reaction AB has been made for the classical Langmuir adsorption and the Ipateev displacement adsorption. It has been shown that the only kinetic consequence of displacement adsorption is the different physical meaning of the parameters of the rate equation. Its form remains the same for both adsorption modes. This conclusion seems to be general also for other reaction schemes.

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AB . , . . .

     

Mass spectrometric method to determine the mode of carbon-metal bonding during catalytic hydrogenolysis of hydrocarbons

A new method based on high-resolution mass-spectrometry has been developed to distinguish between the modes of adsorption of ethane (i.e. 1,2- or 1,1-diadsorbed form) on the catalyst surface. It has been established that under the conditions of H-D exchange, the 1,2-diadsorbed mode is operative, whereas at higher temperatures this interaction can be converted into 1,1-attachment.

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, - , (.. 1,2- 1,1- ) . , H-D 1,2- , 1,1-.