Experimental study of the bifurcation diagram in the Belousov-Zhabotinskii reaction

In the citric acid-Mn²⁺–H₂SO₄–KBrO₃ system a hysteresis phenomenon in the switching on and off of the oscillations has been observed. The possible bifurcation diagrams of the system are discussed.

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-Mn⁺²–H₂SO₄–KBrO₃ . .

     

Catalytic properties of V?Mo?O systems in acrolein oxidation

Catalytic properties of V–Mo–O systems have been studied in acrolein oxidation. When catalysts are activated in reaction mixtures at 673 K, then a solid solution of molybdenum oxides in reduced vanadium oxides is formed, which is responsible for deep oxidation. Also, several compounds are produced, which by their activity and selectivity to acrylic acid formation are arranged in the sequences VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, and VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅, respectively.

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V–Mo–O . 673 K , , , : VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, : VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅.

     

Reduction kinetics of NiO-MoO3 catalysts

Reduction kinetics of NiO–MoO₃ catalysts in H₂ at 573–723 K has been studied. Reduction activation energies E_a have been determined. The degree of NiO–MoO₃ reduction is shown to increase with increasing NiO content.

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NiO–MoO₃ H₂ 573–723 . E NiO–MoO₃ . , NiO–MoO₃ NiO .

     

Kinetics of triphenylphosphite ozonide consumption in reaction with triphenylphosphite

Kinetic regularities of triphenylphosphite ozonide reaction with triphenylphosphite have been studied at T=–75°C to –40°C. The rate of ozonide consumption is estimated as W=k₁[(C₆H₅O)₃P·O₃]+k₂[(C₆H₅O)₃P·O₃][(C₆H₅O)₃P], where k₁=(2.03±0.39)×10^–5s^–1(–50°C), 1gk₂=(3.82±0.33)–(6.61±0.32)/gq dm³/mol s and =2.303RT kcal/mol.

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–75°C –40°C . : W=k₁[(C₆H₅O)₃P·O₃]+k₂[(C₆H₅O)₃P·O₃][(C₆H₅O)₃P], k₁=(2,03±0,39)·10^–5–1(–50°C); 1g k₂=(3,82±0,33)–(6,61±0,32)/ /·, =2,303·RT /

     

The kinetics of the thermal degradation of calcium carbonate

The decomposition of calcium carbonate fine powder in a flowing nitrogen atmosphere has been investigated by non-isothermal thermogravimetry at heating rates in the range, 10–50 deg min^–1. The analog percentage weight change record was digitized at 1 deg intervals. The resulting data, transformed into dimensionless extents of reaction and calculated rates of reaction, was then subjected to the Arrhenius, Friedman and Generalized Kissinger analyses, using a recently developed FORTRAN program system. The value ofn namely 0.39 ±0.04, resulting when the data is analyzed assuming an nth order reaction, strongly indicates that the most probable rate controlling step is a three-dimensional diffusion process (D4 mechanism), withE=172.4 kJ·mol^–1 andA=1.97·10⁴ K^–1·min^–1. Reasons for the wide disparity in previously reported kinetic data are discussed.

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Zusammenfassung Die Zersetzung von feinpulvrigem Calciumcarbonat im Stickstoffstrom wurde durch nicht-isotherme Thermogravimetrie bei Aufheizgeschwindigkeiten von 10–50 °C/min untersucht. Die analoge prozentuale Gewichtsverlustregistrierung wurde in Intervallen von einem Grad digitalisiert. Die erhaltenen, in solche eines dimensionslosen Reaktionsgradcs überführten Daten und berechnete Reaktionsgeschwindigkeiten wurden der Arrhenius-, der Friedmann- und einer verallgemeinerten Kissinger-Analyse unterzogen, wobei ein kürzlich aufgestelltes FORTRAN-Programm benutzt wurde. Der unter der Annahme einer Reaktion n-ter Ordnung fürn erhaltene Wert von 0.39 ±0.04 ist ein nachdrücklicher Hinweis darauf, daß der geschwindigkeitsbestimmende Schritt höchstwahrscheinlich ein dreidimensionaler Diffusionsprozeß (D4-Mechanismus) mitE=172.4 kJ·mol^–1 undA=1.97·10⁴ K^–1·min^–1 ist. Gründe für die weitreichende Verschiedenheit der bisher mitgeteilten kinetischen Daten werden diskutirt.

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10–50° . , , 1. , , , , , . n- , =0,39 ±0,04 , , e (4 ) E=172, 4 · ^–1 =1,97·10^{4 –1}·^–1. .

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To be presented at the 14th North American Thermal Analysis Society Conference, San Francisco, CA, September 15–18, 1985.     

The thermal decomposition of cerium(III) nitrate

The thermal decomposition of anhydrous Ce(NO₃)₃ has been studied. The thermal decomposition reaction is described by the second order kinetic equation, [1/(1–)]–1=kt. The apparent activation energy was determined asE _a=104 kJ mol^–1 while the enthalpy of the reaction was estimated asH _r=111.1 kJ mol^–1. The decomposition reaction differs from that observed for Nd(NO₃)₃.

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Zusammenfassung Die thermische Zersetzung von wasserfreiem Ce(NO₃)₃ wurde untersucht. Die thermische Zersetzung wird durch die Geschwindigkeitsgleichung zweiter Ordnung[1/(1–)]–1=kt, beschrieben. Für die scheinbare Aktivierungsenergie wurde ein Wert von 104 kJ mol^–1 und für die Enthalpie der Reaktion ein Wert von 111,1 kJ mol^–1 ermittelt. Die Zersetzungsreaktion unterscheidet sich von der für Nd(NO₃)₃.

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. : [1/(1–)]– 1=kt. a, 104 · ^–1, H _r, 111.1 · ^–1. .

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The authors wish to thank the Council for Scientific and Industrial Research and the University of Pretoria for financial assistance.     

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 .

     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Gas phase thermolysis of alkyl allyl ethers, thioethers and amines

The pyrolysis of cyclohexyl allyl ether and thioether has been studied in a stirred-flow reactor in the temperature range of 360–470 °C and pressures up to 10 Torr. The first order rate coefficients yielded the Arrhenius parameters log A=11.22±0.23, E_a=169±3 kJ mol^–1 and log A=10.42±0.12, E_a=140±3 kJ mol^–1, respectively. The mechanism of the pyrolysis of alkyl allyl ethers, thioethers and amines is discussed using literature data.

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360–470°C 10 . : log A=11,22±0,23, E_a=169±3 / log A=10,42±0,12, E_a=140±3 /, . , .

     

The role of excited states in the photolysis of n-butyraldehyde, II. Intersystem crossing quantum yields

Singlet triplet intersystem crossing quantum yields were determined for n-butyraldehyde, using the photosensitized cis-trans isomerization of piperylene to monitor the process. At room temperature and 313 nm, 0.58±0.05 and 0.72±0.05 were obtained for the triplet yield in the vapor phase and in isooctane, respectively.

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- - - . 0,58±0,05 0,72±0,05 313 .

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For Part I, see Ref. /1/     

Gasification in steam of a bituminous coal from Peñarroya (Cordoba,Spain) and of different samples prepared from it

The gasification with steam of a bituminous coal from Peñarroya (Cordoba, Spain) (H—O) and of several samples prepared from either by acid treatment (H—H, H—N, H—F and H—F(3)) or by thermal treatment (H—O—C) was studied under both dynamic and isothermal conditions (10 deg/min and 40 min at 1000°).It was found that only for the samples prepared by hydrofluoric acid treatment, H-F and H—F(3), did the gasification effected under such experimental conditions take place in a complete manner.

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Zusammenfassung Die Dampfvergasung von bituminöser Kohle (H—O) (Penarroya, Cordoba, Spanien) und von daraus durch Säurebehandlungen (H—H, H—N, H—F und H-F(3)) oder thermische Behandlung (H—O—C) hergestellten Proben wurde unter dynamischen und isothermen Bedingungen (10 °/min und 40 min bei 1000°) untersucht. Es wurde festgestellt, daß nur die durch Flußsäurebehandlung hergestellten Proben (H—F und H—F(3)) unter den experimentellen Bedingungen vollständig vergasbar sind.

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(10°/ 40 1000°) () , . , , , .

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The authors are grateful to the CAICYT of Spain for the financial support on Project No. 0794/82.     

Effect of electronic interaction between metal and support: How the nature of Ru/Al2O3 is modified

It is a well known fact that when supported on different supports, a transition metal may show different catalytic behavior. In some cases it is claimed that the differences in the acidity of supports are due to this phenomenon. In this work, by adding increasing amounts of MgO to Al₂O₃, the number of acid sites and hence the acidity of Al₂O₃ were monotonically decreased. The behavior of Ru supported on these mixed supports was investigated with IR, and it is concluded that the interaction between metal and acid sites on the surface is the most important factor for the changing properties.

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, , . . Al₂O₃ MgO Al₂O₃. Ru -, , -.

     

Calculation of the rate of SO2 oxidation to SO3

Approximate equation to calculate the effectiveness factor of catalyst for SO₂ oxidation to SO₃ has been derived. Calculated data agree well with those predicted by a quasi-homogeneous model.

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. .

     

Thermal studies on the cubic spinel Fe2MoO4

The cubic spinel Fe₂MoO₄ was studied in air by DTA, DTG, TG and X-ray in the temperature interval 298–1173 K. From these studies, it was concluded that above the Néel temperature Fe₂MoO₄ undergoes an irreversible crystalline phase transition from cubic to tetragonal at 623 K, wherec/a is 1.022. Above 723 K, surface oxidation followed by bulk oxidation of the spinel occurs. At 948 K, after about half the total weight gain due to oxidation, a compound is formed which was confirmed by X-ray as ferrimolybdite, Fe₂O₃·3–4 MoO₃, indicating that in Fe₂MoO₄ the Mo⁴⁺ is more readily oxidized than the Fe²⁺. Above 940 K, further oxidation of Fe²⁺ and Mo⁴⁺ into their respective oxide occurs. About 13 % of the MoO₃ vaporizes, and the rest melts at 1028 K.

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Zusammenfassung Das kubische Spinell Fe₂MoO₄ wurde in Luft im Temperaturbereich von 298 bis 1173 K durch DTA, DTG, TG und Röntgen untersucht. Aus diesen Studien wurde gefolgert, daß oberhalb der Neel Temperature ein irreversibler kristalliner Phasenübergang des Fe₂MoO₄ aus der kubischen in die tetragonale Form bei 623 K stattfindet, wobeic/a=1.022 beträgt. Oberhalb von 725 K findet eine Oberflächenoxidierung des Spinels statt, der eine allgemeine Oxidation folgt. Bei 948 K, nachdem etwa die Hälfte der infolge der Oxidation auftretenden Gewichtszunahme erfolgte, wird eine durch Röntgen als Ferrimolybdit bestätigte Verbindung gebildet (Fe₂O₃·3–4 MoO₃), welche zeigt, daß in Fe₂MoO₄ das Mo⁴⁺ leichter oxidiert wird als das Fe²⁺. Oberhalb von 940 K erfolgt eine weitere Oxidation von Fe²⁺ und Mo⁴⁺ zu ihren entsprechenden Oxiden. Etwa 13% des MoO₃ verdampft und das übrige schmilzt bei 1028 K.

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, , Fe₂MoO₄ 298–1173 . , Fe₂MoO₄ 623 , / 1.022. 723 , , . 948 Fe₂O₃. 3–4₃, . , Fe₂MoO₄ Mo⁴⁺ , Fe²⁺. 940 Fe²⁺ Mo⁴⁺ . 13% MoO₃ , 1028 .

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The author wishes to thank the Chemistry Division of BARC for helping with the high-temperature X-ray pattern.     

Catalytic desulfurization of ethanethiol over zinc-forms of NaX zeolites

Zinc exchanged zeolite X was found to catalyze effectively the dehydrosulfurization of ethanethiol. The catalytic activity correlated linearly with the degree of ion exchange and increased with the reaction temperature. The role of zinc cations in the reaction examined is discussed and suggestions concerning the reaction mechanism are put forward.

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X, Zn, . . .

     

Discrimination of active sites for ethylene homologation and ethylene metathesis on molybdena silica catalyst

Active sites for ethylene homologation (3C₂H₄2C₃H₆) and ethylene metathesis (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) were discriminated by adding platinum to a reduced molybdena silica catalyst, and the former was presumed to be composed of several molybdenum species, while the latter was presumed to be composed of one molybdenum species.

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(3C₂H₄2C₃H₆) (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) . , , .

     

Electron transfer in solutions of tungstovanadophosphoric heteropoly compounds

Redox properties of some isomers of tungstovanadophosphoric heteropoly anions have been studied. Rate constants of electron transfer from -1, 2, 3-PW₉V ₂ ^V V^IVO ₄₀ ^7– to PW₁₁V^VO ₄₀ ^4– (k=1.1±0.2)×10² dm³/mol s) and from PW₁₀V^VV^ivO ₄₀ ^6– to -1,2,3-PW₉V ₃ ^V O ₄₀ ^6– (k=1.4±0.2)×10² dm³/mol s) have been measured in 30% CH₃COOH at pH 3 and 20°C.

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- . PW₁₁V^VO₄₀ ^4– -1,2,3-PW₉V ₂ ^V V^ivO₄₀ ^7– (k=(1,1±0,2)·10^{2 3}/·), -1,2,3-PW₉V ₃ ^V O₄₀ ^6– PW₁₀V^vV^ivO₄₀ ^6– (k=(1,4±0,2)·10^{2 3}/·) pH=3 30%- CH₃COOH 20°C.

     

Glass transition and crystallization effects demonstrated by thermal analysis of liquid-quenched ternary glasses Te80Ge20−xA x V (AV=Sb,Bi)

In DSC studies of liquid-quenched ternary chalcogenide glasses Te₈₀Ge_20–xA _x ^V (A^V=Sb, Bi), the characteristic temperatures (glass transition and crystallization temperatures) were determined. Changes in the thermal stabilities of these glasses, depending on the element A (Sb, Bi) from group V of the periodic table and on its content in the alloy were evaluated. Moreover, the effect of changes in the glass composition on the glass formation ability expressed by the parameter K_g1 was determined.

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Zusammenfassung In DSC-Untersuchungen abgeschreckter ternärer Chalkogenidgläser des Typs Te₈₀Ge_20–xA _x ^v (A^x=Sb, Bi) wurden die charakteristischen Temperaturen (die GlasÜbergangs- und Kristallisationstemperaturen) bestimmt. Die Änderungen der Thermostabilität dieser Gläser wurden in Abhängigkeit von dem Element A (=Sb, Bi) aus der V Gruppe der Periodensystems und von seinem Gehalt in der Legierung ausgewertet. Ausserdem wurde der Einfluß der Änderungen in der Glaszusammensetzung auf die Glasbildungsfähigkeit, ausgedrückt durch den Parameter K_g1, bestimmt.

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Résumé On a déterminé par analyse calorimétrique différentielle (DSC) les températures caractéristiques (températures de transition vitreuse et de cristallisation), des verres ternaires à chalcogénures formés par trempe à partir du liquide, du type Te₈₀Ge_20–xA _x ^v (A^v=Sb, Bi). On a évalué la variation de la stabilité thermique de ces verres en fonction de l'élément A (=Sb, Bi) du Vème groupe du tableau périodique et de sa teneur dans l'alliage. De plus, on a déterminé l'effet des variations de la composition du verre sur la capacité de formation du verre qui s'exprime par le paramètreK _g1.

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Te₈₀Ge_20–xA _x ^v (A^v=Sb, Bi), , . A(=Sb,Bi) . , K _gl, .

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Research supported by the U. S. National Science Foundation under Grant No. GF 421 76     

Influence of substituents on rate constants for recombination of tertiary peroxy radicals

A linear correlation between the logarithm of rate constant (2k_t) for recombination of tertiary peroxy radicals (ROO)^* and ^* constants of substituents R was found to be 1g 2k_t=lg 2k _t ^° . The calculated values are 1g 2k _t ^° =4.59±0.08 and ^*=5.56±0.35.

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I (2k_t) (ROO) R: 1g 2k_t=lg 2k _t ^° . , 1g 1g 2k _t ^° =4,59±0,08 =5,56±0,35

     

Molecular isotope exchange of14CO in surface carbonyl complexes of rhodium

Molecular isotope exchange of CO with¹⁴CO for Rh₆(CO)₁₆/Sn(II)–SiO₂, Rh₆(CO)₁₆/Al₂O₃, Rh(I)(CO)₂/Al₂O₃, Rh₄(CO)₁₂/Al₂O₃ carbonyl complexes of rhodium has been studied. Estimates of the activation energies and a mechanism of the CO exchange are suggested.

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, (Rh₆(CO)₁₆/Sn(II)–SiO₂, Rh₆(CO)₁₆/Al₂O₃, Rh^I(CO)₂/Al₂O₃, Rh₄(CO)₁₂/Al₂O₃), ¹⁴CO. CO .