Kinetics of thermal decomposition of MCO3 to MO (M=Ca,Sr and Ba)

The kinetics of the thermal decompositions of CaCO₃, SrCO₃ and BaCO₃ into their oxides were studied by thermogravimetry at constant and linearly increasing temperatures. The kinetics of the isothermal decompositions of calcium and strontium carbonates were described by the lawR _n =1–(1–)^1/n , wheren=1.8 and 1.2, respectively. The kinetics of the non-isothermal decompositions of the two carbonates, analysed by the Ozawa and Coats-Redfern methods, were in keeping with the isothermal kinetics. True kinetic compensation laws were established for each decomposition of the two carbonates, including the data under both isothermal and non-isothermal conditions.As concerns the decompositions of BaCO₃, however, there was some difference between the kinetic features relating the isothermal and non-isothermal conditions. A true kinetic compensation law was not established in this case.

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Zusammenfassung Die Kinetik der thermischen Zersetzung von CaCO₃, SrCO₃ und BaCO₃ zu den Oxiden wurden durch Thermogravimetrie bei konstanter und linear ansteigender Temperatur untersucht. Die Kinetik der isothermen Zersetzung von Calcium- und Strontium-carbonat folgt dem GesetzR _n =1–(1 –)^1/n, won=1,8 bzw. 1,2. Die Kinetik der nichtisothermen nach den Methoden von Ozawa und Coats-Redfern analysierten Zersetzung der zwei Carbonate ist in Übereinstimmung mit der isothermen Zersetzung. Wahre kinetische Kompensationsgesetze wurden für die Zersetzung der beiden Carbonate erhalten, einschließlich der sich sowohl auf isotherme als auch auf nichtisotherme Bedingungen beziehenden Daten. Was die Zersetzung von Bariumcarbonat betrifft, so wurden einige Unterschiede im kinetischen Verhalten bei der Zersetzung unter isothermen und nichtisothermen Bedingungen festgestellt. Ein wahres kinetisches Kompensationsgesetz konnte in diesem Falle nicht ermittelt werden.

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, . R _n =1–(1–)^1/n , , , 1,8 1,2. , -, . « » , . , , . - «» .

     

X-ray study of Re/Al2O3 and Re+Pt/Al2O3 catalysts using synchrotron radiation

Uning synchrotron radiation, L_III rhenium absorption spectra have been studied for Re/Al₂O₃ and Re+Pt/Al₂O₃ catalysts obtained by impregnation. For individual rhenium compounds a linear dependence between the shift of absorption edge and the state of rhenium oxidation has been found. The absorption spectra of reduced catalysts are significantly broadened as compared with those of individual compounds of the same valency. This points to the presence of rhenium compounds in different oxidation states.

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L_III- , Re/Al₂O₃ Re+Pt/Al₂O₃, . . . .

     

Shape selectivity and maximum molecular size in methanol to hydrocarbons transformation

The maximum product size obtained during methanol to hydrocarbons transformation on medium and large pore zeolites and amorphous silica-aluminas is not governed by shape selectivity but it is a consequence of operational conditions and other process characteristics such as the occurrence of cracking reactions.

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, , , .

     

Effect of free phosphine on the reactivity of phosphine-containing rhodium(I) complexes

The photolysis products of SO₂-pentane-NO mixtures are N₂O, H₂O and a compound designated as RNO. Kinetic data obtained by OC method confirm the previously proposed scheme of photolysis. Also studied was the photolysis of SO₂, NO and cyclohexane mixtures. From comparison of spectral characteristics of RNO and its analog 2-methyl-2-nitrosopropane, the probable structure of RNO is suggested.

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SO₂--NO N₂O, H₂O , RNO. , , . SO₂ NO . RNO 2--2- RNO.

     

Thermal degradation of some polymers based on ethylene glycol dimethacrylate

Thermogravimetric analysis and pyrolysis in combination with gas chromatography were used to study the thermal behaviour of some cross-linked polymers of ethylene glycol dimethacrylate. The investigated polymers show a complex thermal degradation mechanism. The complexity of the reaction increases together with increase of the ethylene glycol chain in the macromolecule and with increase of the pyrolysis temperature. At low temperature, the thermal decomposition products of the analyzed polymers are mainly the constituent monomers. At high temperatures, besides the monomer, other decomposition products are formed as a result of thermal cracking reactions, i.e. secondary reactions of decomposition and recombination.

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Zusammenfassung Zur Untersuchung des thermischen Verhaltens einiger quervernetzter Polymere auf Äthylenglykoldimetacrylatbasis wurden thermogravimetrische Analyse und Pyrolyse in Zusammenhang mit der Gaschromatographie angewendet. Die untersuchten Polymere zeigten einen komplexen thermischen Zersetzungsmechanismus. Die Komplexizität der Reaktion nimmt mit Zunahme der Anzahl der Äthylenglykolketten im Makromolekül und mit Zunahme der Pyrolysentemperatur gleichermaßen zu. Bei niedrigeren Temperaturen stellen die Hauptzerfallsprodukte der analysierten Polymere hauptsächlich deren Monomere dar. Bei höheren Temperaturen werden als Ergebnis thermischer Krackreaktionen, z. B. sekundäre Zersetzungs- und Rekombinationsreaktionen, neben den Monomeren auch andere Zersetzungsprodukte gebildet.

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. . . . , , , .

     

Improved deactivation profile observed for Pt/H-chabazites and Pt/H-Y zeolite

The presence of small platinum crystallites in the framework of protonic offretite, erionite and Y-zeolite causes an improved deactivation profile during n-butane conversion and reflects a stronger shape-selectivity compared to the analogous behavior of the monofuctional (protonic) zeolites.

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, - - () .

     

Mechanism of catalysis and factors responsible for oxide catalyst activity in deep oxidation reactions

A general scheme for the deep oxidation mechanism on oxide catalysts including stepwise and concerted mechanisms as well as their mutual transformations is suggested. The principal factor responsible for the activity in the concerted mechanism region is the rate of oxygen binding. For the stepwise mechanism the main factor is the rate of catalyst interaction with oxidizable reactant.

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, . , . .

     

Reaction routes for hydrogenation of acetylene-ethylene mixtures using a double labelling method

Hydrogenation of C₂H₂:C₂H₄ mixtures using a double labelling method has been studied. Both in the presence and absence of ethylene the rate of acetylene hydrogenation on its partial pressure proceeds through a maximum and the rate is higher when ethylene is added. Using¹⁴C–C₂H₂ it was demonstrated that at low acetylene partial pressures the main route of acetylene hydrogenation was the formation of ethane and C₄ hydrocarbons. Using¹⁴C–C₂H₄ it was also shown that at certain acetylene partial pressures the formation of ethane from ethylene completely ceased. Different surface species are suggested and a reaction mechanism is proposed.

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C₂H₂:C₂H₄, . , , . C¹⁴–C₂H₂, , C₄. C¹⁴–C₂H₄, , . .

     

Methanol oxidation on copper-oxide catalysts

Complete oxidation of methanol on CuO and CuO/Al₂O₃ catalysts has been studied. The main kinetic parameters have been determined. A possible mechanism and the nature of the rate-determining step are discussed.

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CuO CuO/Al₂O₃. . .

     

M?ssbauer spectroscopic studies of the state of Pt?Sn/Al2O3 catalyst for hydrocarbon conversion

Mössbauer spectroscopic studies of the state of Pt–Sn catalyst for hydrocarbon conversion supported on prechlorinated -Al₂O₃ indicate that, unlike nonchlorinated Al₂O₃, this system is much more reduced and besides Pt₃Sn–PtSn₂, its surface contains sigfificant amounts of Sn(II) and Sn(IV) chlorides bonded to the surface.

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Pt–Sn , -Al₂O₃. , Al₂O₃, Pt–Sn Pt₃Sn–PtSn₂ Sn(II) (IV), .

     

Active state of molybdenum in molybdenum-alumina catalysts for propylene oxidation

Catalytic properties of molybdenum-alumina catalysts for propylene oxidation are shown to be determined by water-soluble molybdenum compounds, being apparently aluminomolybdenum heteropoly acids bonded to the catalyst surface.

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, , , , , .

     

Reduction of an amorphous NiO?Al2O3/SiO2 catalyst by different olefins and hydrogen

By static magnetic measurements it was found that the ability to reduction of an amorphous NiO–Al₂O₃/SiO₂ catalyst decreases in the order: but-2-eneshydrogen isobutene>but-1-ene>propeneethene. The reduction temperatures are significantly higher than the dimerization reaction temperatures.

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, NiO–Al₂O₃/SiO₂ : -2>-1> . .

     

Thermal analysis of ethylenediamine complexes of Ni(II) chloride

Thermal analysis of mono-, bis- and trisethylenediamine (en) complexes of Ni(II) chloride was carried out using TG, DTG and DTA techniques. The kinetic parameters were estimated from dynamic TG studies using the Coats and Redfern equation. The thermal stability of the metal-ligand (Ni-N) bond in, the complex was found to decrease with increasing Nien ratio. The DTA studies showed that the loss of en was initially endothermic but became increasingly exothermic with the progress of the decomposition. The final step in the case of all the three complexes was always composite in nature causing the loss of both Cl atoms with simultaneous oxidation of Ni to NiO. The dissociation of the Ni-en bonds appears to be regulated by the nucleation and growth mechanism. Kinetic parameters corresponding to various steps of decomposition of all the three complexes were evaluated.

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Zusammenfassung Mittels TG-, DTG- und DTA-Verfahren wurde eine Thermountersuchung des mono-, bis- und tris-Äthylendiammin (en) komplexes von Ni(II)-chlorid durchgeführt. Unter Zuhilfenahme der Gleichung von Coats und Redfern wurden die kinetischen Parameter anhand der Daten aus dynamischen TG-Untersuchungen abgeschätzt. Es wurde gefunden, daß die thermische Stabilität der Metall-Ligand Bindung (Ni-N) der Komplexe mit anwachsendem Ni:en Verhältnis absinkt. Aufgrund der DTA Untersuchungen erwies sich die Abgabe von en anfänglich als endotherm, mit fortschreitender Zersetzung jedoch als zunehmend exotherm. Bei allen drei Komplexen war der letzte Schritt immer komplexer Natur und beinhaltete die Abgabe beider Chloratome verbunden mit einer gleichzeitigen Oxidation von Ni zu NiO. Die Dissoziation der Ni-en Bindung scheint durch einen Keimbildungs- und Wachstums-mechanismus bestimmt zu werden. Die kinetischen Parameter für die einzelnen Zersetzungsschritte aller drei Komplexe wurden ermittelt.

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, -, - . -, . , - : . , , . , . - « ». .

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A research grant to LSP from the C.S.I.R. (India) and a JRF to SRN are thankfully acknowledged.     

Sur le Polymorphisme du barbital et le systeme eau-barbital

The crystal structures of three forms (I, II and IV) of barbital are well known.The DTA curve of barbital I is marked by only one endotherm, at 186°, which is the melting point of this crystalline form. For barbital II, the DTA curve shows a first endotherm at 160°, which indicates the transition point II I, and then an endotherm at 186° for the melting of form I. By fast cooling of a boiling saturated aqueous solution, another crystalline form of barbital (form X) can be obtained. The DTA curve of this new sample shows another endotherm, at 119°, preceding the endotherms at 160 and 186°. Though the TG curve does not indicate any weight loss at this temperature, this endotherm does not indicate a new phase transition, but a monotectic equilibrium.This monotectic equilibrium (x _L1=78 mol % H₂O,x _L2=98 mol % H₂O) is observed at 119° in the phase diagrams (isochöric sections atV/m=7 cm³·g^–1) of the water-barbital systems established for form I, form II and form X.

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Zusammenfassung Die Kristallstrukturen von 3 Barbitalformen (I, II und IV) sind gut bekannt. Die DTA-Kurve von Barbital I weist nur einen endothermen Peak bei 186° auf, der dem Schmelzpunkt dieser kristallinen Form entspricht. Die DTA-Kurve von Barbital II zeigt einen ersten endothermen, dem Umwandlungspunkt II I kennzeichnenden Peak bei 160° und dann einen zweiten endothermen Peak bei 186° für das Schmelzen der Form I. Durch schnelles Abkühlen einer kochenden gesättigten wässrigen Lösung kann eine andere kristalline Form des Barbitais (Form X) erhalten werden. Die DTA-Kurve dieser neuen Probe zeigt einen weiteren endothermen Peak bei 119°. Obwohl aus der TG-Kurve bei dieser Temperatur kein Gewichtsverlust ersichtlich ist, zeigt dieser endotherme Peak doch keinen neuen Phasenübergang, sondern ein monotektisches Gleichgewicht an. Dieses monotektische Gleichgewicht (x _L1=78 mol% H₂O,x _L2=98 mol% H₂O) wird in den Phasendiagrammen (isochore Schnittpunkte beiV/m=7 cm³·g^–1) der für die Formen I, II and X aufgestellten Wasser/Barbital-Systeme bei 119° beobachtet.

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: I, II IV. I 186°, . II 160°, II I, 186°, I. ( X), . 119°, 160 186°. - , , . (x _Li=78 % ,x _Li=98 % ) 119° ( V/m=7 cm³ · ^–1) - , I, II X.

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A la suite de ce travail, nous envisageons également de rechercher les phases qui seraient susceptibles d'abaisser la température de l'équilibre monotectique.     

Further investigations on the temperature-dependence of magnetic susceptibility and thermogravimetry of stoichiometric antimony triselenide and antimony tritelluride semiconductors

Stoichiometrically adjusted antimony triselenide and antimony tritelluride semiconductors were carefully prepared for the first time. Numerous measurements were carried out, involving X-ray diffraction analysis, true density, thermogravimetric analysis and the temperature-dependence of the magnetic susceptibility. The results obtained indicated that antimony triselenide and antimony tritelluride polycrystals possess mass susceptibilities of –0.361×10^–6 and –0.386×10^–6 C.G.S., respectively. The results are discussed on the basis of electronegativity difference, partial ionicity of the bond, and bond strength.

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Zusammenfassung Stöchiometrische Antimontriselenid- und Antimontritellurid-Halbleiter wurden erstmals hergestellt. Zahlreiche Messungen wurden daran ausgeführt, und zwar Röntgendiffraktometrie, wahre Dichte, Thermogravimetrie und Temperaturabhängigkeit der magnetischen Susceptibilität. Die erhaltenen Ergebnisse zeigen, daß Polykristalle von Antimontriselenid und Antimontritellurid Massensusceptibilitäten von –0.361 · 10^–6 bzw. –0.386 ·10^–6 c.g.s. besitzen. Die erhaltenen Ergebnisse werden auf der Basis der Elektronegativitätsdifferenz, der partiellen Ionisierung und der Bindungsstärken diskutiert.

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- . , , . , - , , –0,361 · 10^–6 -0,386 · 10^–6 . , .

     

Metal dispersity and activity for methylcyclohexane dehydrogenation on Pt/NaY zeolite

By changing the conditions of calcination prior to reduction, three samples with different metal dispersity of Pt/NaY zeolite have been obtained. Their behavior in methylcyclohexane dehydrogenation shows an insensitive character if a second order mechanism with respect to the active site concentration is assumed.

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, , Pt NaY. , .

     

Reactivity of oxidized substances and its correlation with catalyst properties in deep oxidation reactions

In terms of the donor-acceptor interaction concept /1/ the relative reactivity (RR) of organic and inorganic compounds and its correlation with catalyst properties in deep oxidation reactions are treated. RR and relative activity of the catalysts are shown to change depending on the predominant character (acceptor or donor) of reactant-catalyst interaction.

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- /1/ (OPC) . , OPC .

     

Spectral properties and temperature-dependence of semiconductivity of various doped bismuth trioxide polycrystals

Several samples of Nb₂O₅-doped Bi₂O₃ and Y₂O₃-doped Bi₂O₃ were carefully prepared and sintered at 700° for 3 hours. Extensive measurements were carried out on these samples, including X-ray diffraction spectra, infrared absorption spectra and the temperature-dependence of the DC-electrical conductivity in the solid state. The results obtained were discussed, correlated and interpreted. Finally, the optimum compositions were established and recommended for doped-Bi₂O₃ in the electronics industry.

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Zusammenfassung Einige Proben von mit Nb₂O₅ und Y₂O₃ gedopten Bi₂O₃ wurden hergestellt und bei 700 °C 3 Stunden gesintert. Von den Proben wurden Röntgendiffraktogramme und IR-Absorptionsspektren aufgenommen und die Temperaturabhängigkeit der elektrischen Gleichstromleitfähigkeit im festen Zustand gemessen. Die erhaltenen Ergebnisse werden diskutiert, zueinander in Beziehung gesetzt und interpretiert. Optimale Zusammensetzungen werden ermittelt und für gedoptes Bi₂O₃ in der Elektronikindustrie empfohlen.

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Bi₂O₃, Nb₂O₅ Y₂O₃, 3 700°. , . . , .

     

A rapid method for catalyst testing. Zeolite catalysts for methanol conversion to hydrocarbon

A rapid method for testing catalysts is suggested, which permits a 30-fold reduction in the time of their examination. The method is recommended for studying catalytic processes taking place with either evolution or absorption of heat.

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- , Qj 30 . , .