V2O5/TiO2 oxidation catalysts, III. Oxidation of CO on pure and sodium-doped systems

The activity of vanadia/titania catalysts in CO oxidation has been tested and found to be of the same order as that observed for unsupported vanadia; the simultaneous presence of vanadium-sodium compounds cancels the activity, probably because of the elimination of labile V=0 species at surface defects.

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V₂O₅/TiO₂ CO, V₂O₅; - , , V=0 .

     

Reduction behavior of Cu?SiO2 catalyst prepared by ion exchange for selective dehydrogenation to produce methyl formate from methanol

Reducibility of Cu–SiO₂ catalyst prepared by ion exchange method, being effective for selective dehydrogenation to produce methyl formate from methanol at lower temperatures, has been studied by a TPR technique. The results suggest that easier reduction leads to an increase of dispersity of Cu particles.

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, - , , . , , Cu.

     

Experimental setup to study catalysts by combined pulse microcatalytic and ESR spectroscopic methods

A setup consisting of an ESR spectrometer and a pulse microcatalytic installation is suggested for simultaneous kinetic and spectral measurements directly in catalytic processes.

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- , , .

     

Influence of substituents on hydrogenation of nitro groups in aromatic hydrocarbons catalyzed by rhenium thiocomplexes

Homogeneous hydrogenation studies of (NO₂)_1–2–C₆H_3–4–L nitro compounds (where L=–H,–NH₂,–COOH,–CHO,–OH,–CH₃ and –CH=CH–COOH) catalyzed by Re₂S₆TThio₃Cl₂ in dimethylformamide solutions at and T=343 K, have revealed that the reaction is enhanced by electron-acceptor substitutents and hindered by electron-donor ones.

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(NO₂)_1–2–C₆H_3–4–L, L=–H,–NH₂,–COOH,–CHO,–OH,–CH₃,–CH=CH–COOH, Re₂S₆Thio₃Cl₂ 343 . , .

     

Studies on the characteristics of the isomers of hexachlorocyclohexane (HCCH) by thermogravimetry

A new method of determination of HCCH isomers by thermogravimetry is described. The thermal changes of the isomers, the decomposition characteristics and the parameters for identification are discussed.

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Zusammenfassung Eine neue Methode der Bestimmung von HCCH-Isomeren durch Thermogravimetrie wird beschrieben. Die thermischen Änderungen der Isomere, die Zersetzungscharakteristika und die Identifizierungsparameter werden erörtert.

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Résumé On décrit une nouvelle méthode de détermination des isomères HCCH par thermogravimétrie. On discute les modifications thermiques des isomères, les caractéristiques de décomposition et les paramètres d'identification.

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. , .

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We are grateful to Dr. B. L. Amla, Director of this Institute, for his encoragement, and to Shri Hanumantha Rao Judav for his assistance.     

Kinetic equation of heterogeneous catalytic isotope exchange

A kinetic equation is derived for the bimolecular isotope exchange reaction between AX _n ^* and BX _m ^o , all atoms of element X in each molecule being equivalent. The equation can be generalized for homogeneous and heterogeneous catalytic isotope exchange.

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, AX _n ^* BX _m ^o , X . , - .

     

Thermal and photochemical stability of polystyrene and its blends with polyvinyl chloride

The influence of some irregularities in polystyrene (PS) and polyvinyl chloride (PVC) chains on their thermal stability was investigated. UV irradiation caused an increase in the content of these irregularities in the polymers. It was found that the presence of carbonyl groups and crosslinking of the polymer chains hamper the thermal dehydrochlorination of PVC and the total decomposition of both polymers. On the other hand, weak peroxy linkages (which facilitate degradation processes) and conjugated double bonds decrease the temperature of total decomposition of PS and PVC blends.

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Zusammenfassung Es wurde der Einfluß von Unregmlmäßigkeiten in Polystyrol (PS)- und Polyvinylchlorid (PVC)-Ketten auf deren thermische Stabilität untersucht. UV-Bestrahlung verursacht ein Ansteigen des Gehaltes an Unregelmäßigkeiten in den Polymeren. Es wurde festgestellt, daß die Gegenwart von Carbonylgruppen und Querverbindungen der Polymerketten die thermische Dehydrochlorierung von PVC und eine vollständige Zersetzung beider Polymere verhindern. Andererseits senken Peroxidverknüpfungen (die die Degradierungsvorgänge erleichtern) und konjugierte Doppelbindungen die Temperatur für eine vollständige Zersetzung von PS und PVC Gemischen.

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. - . , . , , , .

     

Gradient systems are cross-catalytic

If the kinetic differential equation of a chemical mechanism is a gradient system, the mechanism is essentially cross-catalytic. Consequently, rather few conservative (in the Horn-Jackson sense) mechanisms have a kinetic differential equation of the gradient type. Relations with thermodynamics are only briefly mentioned.

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, , , . ( -) . .

     

Parent and mixed ligand complexes in the copper(II)-ethylene glycol-sulphate system

Eleven copper(II)-ethylene glycol-sulphate complexes of different compositions were prepared, one of them-CuGl₂(H₂O)₂SO₄-in single-crystal form. A thermoanalytical study of these complexes revealed three types of thermal decomposition pattern. The X-ray structure of the single-crystal demonstrated the presence of ethylene glycol bridges resulting in endless chains in the crystal.

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Zusammenfassung Elf Kupfer(II)-äthylenglykol-sulfat-Komplexe unterschiedlicher Zusammensetzung wurden dargestellt, einer davon — CuGl₂(H₂O)₂SO₄ — in Form von Einkristallen. Die thermoanalytische Untersuchung dieser Komplexe ergab drei Typen der thermischen Zersetzung. Die röntgendiffraktometrische Bestimmung der Struktur des in Form von Einkristallen erhaltenen Komplexes zeigte, daß den Kristall endlose Ketten von Äthylenglykolbrücken durchziehen.

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() — , — CuGl₂(H₂O)₂SO₄ — . . , , .

     

Catalytic properties of rare earth manganites and related compounds

Perovskite-type oxides REMnO₃ (RE=La-Dy) and PrMn_1–xNi_xO₃ (x=0–0.8) have been prepared. The catalytic activity and the reducibility of these oxides were investigated. The effect of RE, Ni ions on catalytic property, and the relation between catalytic activity and reducibility are discussed.

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, , REMnO₃ (RE=La, Pr, Nd, Sm, Eu, Gd, Dy) PrMn_1–xNi_xO₃ (x=00,8). . RE Ni , .

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Project Supported by the Science Fund of the Chinese Academy of Sciences     

Cluster model for the surface OH groups of beryllium oxide

Cluster models calculated by a semiempirical CNDO method are used to describe properties of the surface hydroxy groups of beryllium oxide. The results are compared with those obtained from IR studeies and with data on BeO energy bands.

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- , . , BeO.

     

Kinetic laws for dehydrogenation of cyclohexane over Pd/C catalysts

A kinetic equation for cyclohexane dehydrogenation at P_O=1.0 MPa has been obtained.

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1,0 .

     

Oxidative dehydrogenation of ethylbenzene over a charcoal catalyst

The oxidative dehydrogenation of ethylbenzene over a charcoal catalyst has been studied by the pulse technique. The styrene yields for the oxidation of ethylbenzene by gaseous oxygen and upon the interaction of ethylbenzene with oxygen adsorbed on charcoal are shown to be the same.

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. , , , .

     

Behavior of CSTR upon fast external effects: Possibility of increasing average conversion

The objective of the work was to study the influence of external factors (changes in composition, load and temperature) on the regimes of heterogeneous catalytic reactors. As shown, a rather fast change in external parameters causes an internal reorganization of the CSTR thus leading to an increase in average conversion.

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( , , ). , , , .

     

Thermal analysis of spurrite from a rotary cement kiln

A number of samples from the pre-burning zone of a wet-process cement rotary kiln were examined by combined DTA/TG and XRD for estimation of spurrite (2Ca₂SiO₄·CaCO₃). It was found that decarbonation temperatures of spurrite range from 1130 to 1190 K and they are 45 to 75 K higher than that of calcite occurring in the same sample. In the TG curves calcite and spurrite can be easily distinguished and accordingly both can be estimated from the same TG scan. Combined DTA/TG, supplemented by XRD, is a very effective method for qualitative and quantitative estimation of spurrite in cement rotary kiln materials.

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Zusammenfassung Unter kombinierter Anwendung von DTA/TG und Röntgendiffraktionsverfahren wurde eine Anzahl Proben aus einem Vorkalzinator eines Drehrohrofens zur Zementherstellung nach dem Naßverfahren auf Spurrit (2Ca₂SiO₄·CaCO₃) untersucht. Es wurde festgestellt, daß die Temperatur für das Austreiben von CO₂ bei Spurrit zwischen 1130 und 1190 K und somit um 45–75 °C höher als bei in derselben Probe vorliegenden Kalzit liegt. Aufgrund der TG-Kurven können Kalzit und Spurrit leicht voneinander unterschieden und demzufolge mit einem einzigen TG-Scan bestimmt werden. Kombinierte DTA/TG, ergänzt durch Röntgendiffraktionsverfahren ist eine sehr leistungsstarke Methode zur qualitativen und quantitativen Bestimmung von Spurrit in Stoffen aus Zementdrehrohröfen.

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(2Ca₂SiO₄ · CaCO₃), / , , . , 1130– 1190 , 46–75 , . . /, , .

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The authors are very grateful to Mr. A. H. Dalmia, president, M/s. Orissa Cement Limited, Rajgangpur for allowing to collect the samples during the stoppage of the kiln and also for his permission to publish the paper.     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .

     

Oxidative dehydrogenation of n-butane, III. Kinetic and catalytic activity of ferric oxide

Catalytic activity of ferric oxide was evaluated in the oxidative dehydrogenation of n-butane. The apparent activation energy determined in the kinetic region was 37.7 kcal/mol. The activity of this oxide was undetectable up to 430°C. Reaction product distributions are shown as functions of temperature in the range of 430–650°C.

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(III) -. 37,7 /. 430°C. 430–650°C.

     

The effect of the network structure of the thermal properties ofcis-1,4-polyisoprene vulcanizates

The thermal properties ofcis-1,4-polyisoprene and its vulcanizates were investigated by means of thermal analysis and complementary methods. It was found that cross-linking generally increases the thermal stability of this elastomer, though distinct differences between peroxide and sulphur vulcanizates were observed. Polysulphide cross-links cleave readily at elevated temperature, and transform to cross-links of lower sulphidity, mainly disulphide. However, some of them are probably oxidized first to sulphoxides, and further to sulphenic or thiosulphoxylic acids. The products formed involve the ionic decomposition of the peroxides and thereby prevent the autocatalytic thermooxidative destruction ofcis-1,4-polyisoprene.

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Zusammenfassung Es wurden die thermischen Eigenschaften voncis-1,4-Polyisopren und dessen Vulkanisaten untersucht. Dabei wurden die Derivatographie und komplementäre analytische Methoden benutzt. Es wurde festgestellt, dass die Vernetzung im allgemeinen die thermische Stabilität von diesen Elastomeren erhöht, obwohl ein ausgeprägter Unterschied zwischen Peroxid- und Schwefelvulkanisaten beobachtet wurde. Die polysulfidischen Brücken wurden bei erhöhter Temperatur leicht gespalten und verwandeln sich in Brücken, die eine niedrigere Schwefelatomzahl besitzen und zwar hauptsächlich disulfidisch sind. Ein Teil der Schwefelatome wurde jedoch wahrscheínlich unter Bildung von Sulfin- und Thio-Sulfoxysäuren oxydiert. Diese Produkte verursachen ionische Zersetzung von Peroxiden und verhindern auf diese Weise die autokatalytische thermooxidative Zersetzung voncis-1,4-Polyisopren.

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-1,4- . , , , , . , , , . , , , . , -1,4 .

     

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.     

A thermogravimetric study of the solid-state reaction between alumina and strontium carbonate

The kinetics of the solid-state reaction between alumina and strontium carbonate were studied by thermogravimetry. The effects of the structure ( or) and/or doping (with Li⁺ or Cd²⁺) of the alumina on the kinetics of the reaction were examined. The results obtained were correlated with the phase composition and structural changes, followed by a number of physicochemical analyses (DTA, XRA and IRA) throughout the course of the reaction.

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Zusammenfassung Die Kinetik der Festkörperreaktion zwischen Aluminiumoxid und Strontium-carbonat wurde thermogravimetrisch untersucht. Die Effekte der Struktur ( und) und/oder des Dopens des Aluminiumoxids (mit Li⁺ oder Cd²⁺) auf die Kinetik der Reaktion wurde untersucht. Die erhaltenen Ergebnisse wurden mit der Phasenzusammensetzung und mit durch physikalisch-chemische Analysenverfahren (DTA, XRA und IRA) während des Reaktionsverlaufs verfolgten strukturellen Veränderungen in Beziehung gebracht.

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. ( ) Li⁺ Cd²⁺ . , , - .