Kinetics of aluminium hydroxide dehydration

Non-isothermal thermogravimetric analysis was used for determination of the kinetics of aluminium hydroxide dehydration in an air atmosphere and for processing of the experimental results by the method due to Chatterjee.Aluminium hydroxide dehydration proceeds according to the following mechanism: Al(OH)₃AlOOH + H₂O 2 AlOOHAl₂O₃ + H₂OBoth reactions proceed in the diffusion region, the first up to 526 K and the second up to 700 K, and the corresponding activation energy values are 15.7 and 0.2 kJ/mole, respectively.

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Zusammenfassung Die nicht-isotherme thermogravimetrische Analyse wurde zur Bestimmung der Kinetik der Dehydration von Aluminiumhydroxid in Luft-Atmosphäre eingesetzt und die Methode von P. K. Chatterjee zur Verarbeitung der Versuchsergebnisse angewendet.Der Dehydratisierungsvorgang von Aluminiumhydroxid verläuft nach folgendem Mechanismus: Al(OH)₃AlOOH + H₂O 2 AlOOHAl₂O₃ + H₂OBeide Reaktionen spielen sich in der Diffusionszone ab, die erstere bis zur Temperatur von 526 K und die zweite bis zur Temperatur von 700 K. Die entsprechenden Aktivierungsenergien sind 15.70 kJ/Mol für die erste und 0.20 kJ/Mol für die zweite Reaktion.Bei kontinuierlicher Erhöhung der Temperatur über 526 K im ersten und über 700 K im zweiten Fall werden die Geschwindigkeiten dieser Reaktionen durch kristallchemische Umwandlungen begrenzt und die Aktivierungsenergie beträgt 116.97 kJ/Mol für die erste und 91.92 kJ/Mol für die zweite Reaktion.

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Résumé On détermine la cinétique de la déshydratation de l'hydroxyde d'aluminium dans l'air, par thermogravimétrie non-isotherme, en dépouillant les résultats suivant la méthode proposée par P. K. Chatterjee.Le processus de la déshydratation de l'hydroxyde d'aluminium s'effectue suivant le mécanisme: Al(OH)₃AlOOH + H₂O 2AlOOHAl₂O₃ + H₂OLes deux réactions ont lieu par diffusion, la première jusqu'à la température de 526 K et la seconde jusqu'à 700 K, les valeurs correspondantes des énergies d'activation étant 15.70 kJ · mol^–1 pour la première et 0.20 kJ · mol^–1 pour la seconde réaction.Lors d'une élévation continue de la température au-dessus de 526 K dans le premier cas et au-dessus de 700 K dans le deuxième cas, les vitesses de ces réactions deviennent limitées en raison des transformations cristallochimiques et les valeurs des énergies d'activation sont 116.97 pour la première et 91.92 kJ · mol^–1 pour la seconde réaction.

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, — . : Al(OH)₃AlOOH + H₂O 2 AlOOHAl₂O₃ + H₂O , 526 , — 700 . 15,70 0,20 / . 526 700 — , - , , 116,97 91,92 /.

     

Conversion of C1?C2 alkanes over manganese catalysts reoxidized by carbon dioxide and oxygen

Reoxidation of Mn-containing catalysts by oxygen and carbon dioxide in the conversion of C₁–C₂ alkanes has been studied. Reoxidation of these catalysts by carbon dioxide and oxygen added at a certain ratio permits to obtain optimum degree of surface oxidation, ensuring the high selectivity of conversion of C₁–C₂ alkanes to C₂H₄.

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Mn- C₁–C₂. , Mn- , C₁–C₂ C₂H₄.

     

Temperature programmed reduction studies of nonpyrophoric Raney nickel catalysts

Temperature programmed reduction studies have revealed that the surface of nonpyrophoric Raney nickel catalysts is covered by readily reduceable nonstoichiometric metaloxygen structures. A method is suggested to calculate kinetic reaction parameters on the basis of analyzing the shape of one of the TPR curves.

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, - . , -.

     

Proton transfer to palladium during phenylacetylene hydrogenation in ethanol

Exchange processes over palladium during the liquid-phase hydrogenation of phenylacetylene have been studied by successive substitution of starting substances by deuterated products. It has been revealed that on the catalyst surface a proton transfer to unsaturated substance, gas phase and solvent takes place. Rates of the processes have been calculated.

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. , , . .

     

A method for preliminary estimation of solid oxidation kinetics and mechanism

The possibility of preliminary estimation of the oxidation kinetics and mechanism using the quantity t_o from the exponential kinetic rate equation is discussed.

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, t_o .

     

M?ssbauer spectroscopic studies of the interaction between iron(III) and molybdenum(VI) oxides

At 400°C an appreciable interaction between the title oxides is observed, resulting in iron molybdate formation

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400°C .

     

Catalytic performance in hydrodesulfurization of thiophene and ir investigation of Co and no adsorption over Co?Mo/Al2O3 and Ru?Co?Mo/Al2O3 catalysts

A new Ru–Co–Mo/Al₂O₃ catalyst has been prepared by impregnation of Ru salt as a secondary promoter onto Co–Mo/Al₂O₃ catalyst, and it was found that the Ru–Co–Mo/Al₂O₃ exhibited higher activity than Co–Mo/Al₂O₃ in hydrodesulfurization of thiophene to hydrocarbons. Ir studies on Ru–Co–Mo/Al₂O₃ revealed that the Co and NO adspecies increased significantly in intesnities and displayed a bathochromic shift in frequencies, as compared with Co–Mo/Al₂O₃.

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Ru–Co–Mo/Al₂O₃ Ru, , Co–Mo/Al₂O₃. Co–Mo/Al₂O₃. CO NO, Co Mo, Co–Mo/Al₂O₃. , Mo , Mo³⁺ Mo³⁺ Co Ru–Co–Mo/Al₂O₃.

     

Preparation and characterization of iron(II) complexes of ethylene glycol

Nine iron(II) ethylene glycol sulphate complexes were prepared. Their compositions were determined by standard analytical methods. They were characterized by means of temperature-dependent magnetic susceptibility and Mössbauer spectroscopic measurements. On the basis of the patterns of their thermal decompositions, the complexes could be classified into three groups.

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Zusammenfassung Neun Eisen(II)-ethylenglykol-sulfat-Komplexe wurden dargestellt. Die Zusammensetzung dieser Komplexe wurde nach analytischen Standardmethoden bestimmt. Die Verbindungen wurden durch Messungen der temperaturabhängigen magnetischen Susceptibilität sowie mittels Mössbauer-Spektroskopie charakterisiert. Nach dem Verhalten bei der thermischen Zersetzung konnten diese Komplexe in drei Gruppen klassifiziert werden.

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, . . , .

     

Calorimetric measurements of adsorption power for active centers of aluminosilicate catalysts

Direct calorimetric measurements for the interaction energy of cumene and benzene with active centers of an aluminosilicate catalyst have been carried out to determine the potential energies of the centers catalyzing selective cracking with minimum coke formation. Kinetics of cumene cracking has been examined.

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. , .

     

Chain transfer mechanism and kinetics in radical telomerization of ethylene with bromalkanes

Rate constants for chain transfer via bromoalkanes of various structure are estimated for primary, secondary and tertiary alkyl radicals and isokinetic dependences are shown to exist for their activation parameters. Isokinetic temperatures are calculated.

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, . . .

     

Epoxy polymers: Glass transition/cure degree correlation

The correlation between the glass transition temperature,T _g , and the cure degree, , of epoxy polymers has been analysed on the basis of an extension of the Vogel-Tamman-Fulcher equation for the viscosity of polymers and glasses.A physical meaning has been given to the coefficients of the series expansion of the functionT _g=T _g ().This analysis allows one to verify that the experimental (T _g ,) data support the conclusion that, in the case of thermoset polymers, the ideal glass transition temperature,T _o, appearing in the VTF equation, is larger thanT _g .This conclusion may be supported by the thermodynamic interpretation ofT ₀ as the temperature at which the excess entropy of the systems tends to vanish: in the case of partially cured thermosets;T ₀ would represent the minimum temperature at which the system becomes able to enhance its cure degree.

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Zusammenfassung Die Korrelation zwischen der Glasumwandlungs-temperaturT _g und dem Aushärtungsgrad von Epoxidpolymeren wurde analysiert, und zwar basierend auf einer Erweiterung der Vogel-Tamman-Fulcher-Gleichung für die Viskosität von Polymeren und Gläsern. Den bei der Reihenentwicklung der FunktionT _g =T _g () auftretenden Koeffizienten wurde eine physikalische Bedeutung zugeschrieben. Diese Analyse ermöglicht nachzuweisen, daß die experimentellen Daten (T _g ), die Schlußfolgerung stützen, daß im Falle von hitzehärtbaren Polymeren die in der VTF-Gleichung auftretende sogenannte ideale GlasumwandlungstemperaturT ₀ höher alsT _g ist. Diese Konklusion wird auch durch die thermodynamische Interpretation vonT ₀ gestützt, nämlich als die Temperatur, bei der die Überschußentropie des Systems gegen Null geht: im Falle von teilweise ausgehärteten hitzehärtbaren Polymeren würdeT ₀ die minimale Temperatur darstellen, bei der eine Erhöhung des Aushärtungsgrades des Systems einsetzt.

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T _g () - - . qT _g =T _g (). T _g , T ₀, -- , T _g . T ₀, , . ,T ₀ , .

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Work supported by the Progetto Finalizzato Chimica Fine e Secondaria of the Italian C.N.R., grant No. 84.01304.95     

Phase formation in Na2O?MnOx catalysts for oxidative dimerization of methane

Na₂O–MnO_x catalysts of different composition, pretreated in air or nitrogen at 1020 and 1170 K, have been investigated in oxidative dimerization of methane. Under the reaction conditions -NaMnO₂ and -Na_0.7Mn_2+y are formed as catalytically active phases.

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Na₂O–MnO_x , 1020 1170 K, . -NaMnO₂ -Na_0,7Mn_2+y.

     

Effect of the dielectric constant on the reactivity of alkyl and polychloroalkyl radicals in addition and substitution reactions

Generalized data for the effect of reaction medium on the elementary steps of radical homo-and cotelomerization of olefins with carbon tetrachloride are generalized.

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.

     

Ausbrennen von Kohlenstoffhaltigen,in den Ziegelrohstoff Eingepressten Stoffen

Zusammenfassung Die Kinetik der Ausbrennung organischer Stoffe im Ziegelscherben wird verfolgt und erläutert. Die Möglichkeiten der Beeinflussung des energetischen Aufwandes unter Nutzung moderner analytischer Methoden sind festzustellen. Bei einem diffusen Ausbrennen ist die Dichte und Durchlässigkeit des Scherbens massgebend. Praktische Anwendungsmöglichkeiten verschiedener auszubrennender Stoffe in unterschiedlichen Rohstoffen der Ziegelindustrie.

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The kinetics of burn-out of organic materials in bricks has been followed and explained. It is to establish that using new analytical methods the energy consumption can be influenced. The diffuse burn-out is determined by the density and permeability of bricks. There is a possibility for practical use of the results in the brick-industry with the different compounds to be burnt out from various raw materials.

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$ . , . . .

     

Time dependence of the rate constant in the free radical oxidation in solid phase

ESR studies of oxidation kinetics of ethyl and dimethylpentyl radicals have been performed in glassy deuterium-containing alcohols, toluene-d₈ and in glassy 2,4-dimethylpentane-h₁₆, respectively. The kinetics is interpreted by assuming time-dependent reaction rate constant.

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, -d₈ 2,4--h₁₆. .

     

Samarium hydroxide as catalyst in hydrogen evolution

Hydrogen evolution on a platinum cathode taking place in Na₂SO₄ as electrolyte, is catalyzed by the formation of samarium hydroxide deposited on platinum. It is shown by voltammetric experiments that the quantity of adsorbed hydrogen is greater with samarium than without it and the H₂O reduction reaction is an irreversible process due, presumably, to a reaction between the adsorbed hydrogen and samarium hydroxide.

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Na₂SO₄, , . , , H₂O .

     

A kinetic study of the regeneration of new AlPO4-supported nickel catalysts

A kinetic study of the regeneration of a series of AlPO₄, SiO₂ and AlPO₄–SiO₂ supported nickel catalysts poisoned with n-butanethiol (nBSH) has been carried out using 1-hexene hydrogenation as the test reaction. The regeneration capacity of catalysts fits the expression , where r_A/r _A ^o is the regeneration capacity, _s the specific poisoning coefficient and a constant for each series of supported catalysts, Ni/SiO₂, Ni/AlPO₄ and Ni/AlPO₄–SiO₂ (5–20 wt.%), respectively.

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AlPO₄, SiO₂ AlPO₄–SiO₂, -, , 1- . , r_A/r _A ^o , _s - : Ni/SiO₂, Ni/AlPO₄ Ni/AlPO₄–SiO₂ (5–20 .%), .

     

Lithium phosphate catalyst, III. New supported catalyst

Some new non-stoichiometric Li₃PO₄ supported on -Al₂O₃, -Al₂O₃, TiO₂ and SiO₂ are described as catalysts. The catalysts are used in the isomerization of propene oxide. The catalyst supported on SiO₂ is more active and selective to allyl alcohol than the catalysts described in the literature till now.

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, Li₃PO₄, -Al₂O₃, -Al₂O₃, TiO₂ SiO₂, . . , , SiO₂.

     

Simple catalytic mechanism permitting a multiplicity of catalyst steady states

The conditions of the existence of several steady states for a three-step mechanism, viz. a catalytic trigger (consecutive), are discussed.

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- ().