Activation of hydrocarbons in the oxidative dimerization of methane over alkaline earth metals

Oxidative dimerization of methane over alkaline earth metal oxides and phosphates has been studied. The ratedetermining step is heterolytic C–H bond dissociation of methane on surface basic sites of the catalysts.

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- . , C–H .

     

Preparation,spectral and thermal studies of neodymium zirconyl oxalate hexahydrate

Neodymium zirconyl oxalate (NdZrOX) is prepared and characterized by chemical analysis and ir spectral studies. Its thermal decomposition has been investigated by using DTA, TG, DTG, X-ray diffraction and ir spectroscopy. On the basis of thermogravimetry and isothermal studies a probable mechanism for the decomposition is proposed. The decomposition proceeds mainly through three stages: i) dehydration between RT-413 K, ii) decomposition of oxalate between 413–943 K and iii) decomposition of the carbonate between 1028–1235 K to give a mixed oxide. The ir spectra and X-ray diffraction studies are made for identification of the intermediates. X-ray diffraction studies of the end product indicates that it belongs to cubic crystal system witha=11.520 Å.

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Zusammenfassung Neodymzirkonyloxalat (NdZrOX) wurde dargestellt und durch chemische Analyse und IR-spektroskopische Untersuchungen charakterisiert. Die thermische Zersetzung dieser Verbindung wurde mittels DTA. TG, DTG, Röntgendiffraktometrie und IR-Spektroskopie untersucht. Basierend auf Ergebnisse der Thermogravimetrie und isothermer Methoden wird ein möglicher Zersetzungsmechanismus vorgeschlagen. Die Zersetzung verläuft im wesentlichen über drei Stufen: i) Dehydratisierung zwischen Zimmertemperatur und 413 K, ii) Zersetzung des Oxalats zwischen 413 und 943 K und iii) Zersetzung des Carbonats zwischen 1028 und 1235 K unter Bildung eines Mischoxides. IR-spektroskopische und röntgendiffraktometrische Untersuchungen wurden zur Identifizierung der Zwischenprodukte ausgeführt. Die röntgendiffraktometrische Untersuchung des Endproduktes ergibt eine kubische Zelle mita= 11.520 Å.

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-. , , , . . , , : / 413 , / 413943 / 1028–1235 . - . - , =11.520 Å.

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One of the authors (VBR) is grateful to CSIR (India) for the senior research fellowship.     

Toluene disproportionation and coke formation over fluorided alumina and hydrogen-mordenite

Toluene transformation was investigated on a fluorided alumina and a protonic mordenite under hydrogen (0.8, 12 bar) and under nitrogen (12 bar). Hydrogen pressure considerably improves the catalytic stability of H-mordenite by inhibiting the formation of coke. Moreover, hydrogen eliminates part of the coke deposited by reaction under nitrogen, and regenerates the activity of the mordenite. On the contrary, hydrogen has no effect in the case of fluorided alumina. The particular behavior of the mordenite is attributed to its very strong acidity.

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(0,8, 12 ) (12 ). -, . , , , . , - . .

     

The structures and thermal decomposition of cupric mono,di and trichloracetates

Magnetic moment measurements and ultra-violet diffuse reflectance spectroscopy have been used to investigate the structure of the chloroacetates of copper(II). These studies indicate that cupric monochloroacetate dihydrate is dimeric and cupric trichloracetate tetrahydrate is monomeric. Cupric dichloracetate tetrahydrate forms an intermediate case. The thermal decomposition of these compounds under nitrogen has been studied using thermogravimetry and differential thermal analysis, together with analysis of the products of the decomposition. The major organic product formed in the thermal decomposition of the mono- and dichloracetates is the corresponding chlorinated acetic acid; the solid inorganic product is cuprous chloride. Thermal decomposition of the trichloracetate yields cupric chloride and a mixture of trichloracetic acid and trichloracetyl chloride.

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Zusammenfassung Messungen des magnetischen Momentes sowie diffuse UV-Remissionspektroskopie wurden zur Untersuchung der Struktur der Kupfer(II)-chloracetate eingesetzt. Die Ergebnisse deuten darauf hin, daß Kupfermonochloracetat-Dihydrat dimer und Kupfertrichloracetat-Tetrahydrat monomer ist. Das Kupferdichloracetat-Tetrahydrat bildet hierbei eine Zwischenstufe. Die thermische Zersetzung dieser Verbindungen wurde in Stickstoffatmosphäre unter Anwendung der Thermogravimetrie und Differentialthermoanalyse untersucht, bei gleichzeitiger Analyse der Zersetzungsprodukte. Das bei der thermischen Zersetzung des Mono- und Dichloracetats gebildete organische Hauptprodukt ist die entsprechende chlorierte Essigsäure; der feste anorganische Rückstands das Kupfer(I)-chlorid. Die thermische Zersetzung des Trichloracetats ergibt Kupfer(II)-chlorid sowie eine Mischung von Trichloressigsäure und Trichloracetylchlorid.

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Résumé La mesure du moment magnétique et la spectroscopie de réflexion diffuse dans l'U. V. sont utilisées pour étudier la structure des chloroacétates de cuivre (II). Les résultats indiquent que le monochloroacétate de cuivre (II) dihydraté est dimère et que le trichloroacétate de cuivre (II) tétrahydraté est monomère. Le dichloroacétate de cuivre (II) tétrahydraté représente un cas intermédiaire. La décomposition de ces composés dans l'azote a été suivie par thermogravimétrie et analyse thermique différentielle, en analysant simultanément les produits de décomposition. Le principal produit organique formé lors de la décomposition thermique des mono et dichloroacétates est l'acide chloroacétique correspondant; le produit solide inorganique est le chlorure de cuivre (I). La décomposition thermique du trichloroacétate fournit le chlorure de cuivre (II) et un mélange d'acide trichloracétique et de chlorure trichloroacétylique.

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(II). , (II) , (II) - . (II) . , , . , - , , (I). (II) (II) .

     

Photooxygenation of 9-methyl-1,2,3,4-tetrahydrocarbazole: A kinetic study

The reaction of the singlet oxygen with 9-methyl-1,2,3,4-tetrahydrocarbazole has been undertaken to give a benzazonine derivative in good yield. Rose-bengal supported on an anionic resin was used as heterogeneous photosensitizing agent. Kinetic evaluation has been made for the additon of singlet oxygen to the indole ring at room temperature.

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9--1,2,3,4- . , , . .

     

Trapping adsorption of carbon monoxide located between carbon dioxide adsorbed on magnesium oxide

Carbon monoxide adsorbed on MgO is strongly trapped by the adsorbed carbon dioxide, increasing the heat of adsorption from 85.4 to 184.1 kJ/mol. The trapped CO is thought to be captured by two or three adsorbed CO₂ and becomes less active to react with oxygen.

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, MgO, , 85,4 184,1 /. , CO CO₂ .

     

Study of the adsorption properties of a natural Hungarian mordenite and its ion-exchanged derivatives

The texture and adsorption properties of a natural, Hungarian mordenite were investigated by electron microscopy and BET adsorption measurements. The properties of the ion-exchanged adsorbents were characterized by CO₂ and SO₂ isotherms. The measurements were evaluated on the basis of the pore-filling theory of Dubinin. We have found that at 20°C the H⁺-form of mordenite interacts preferably with CO₂, while on the Na⁺- and Ca²⁺-derivatives stronger adsorption of SO₂ takes place. This fact accounts for their applicability as selective adsorbents.

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, . CO₂ SO₂. . , 20°C H⁺- CO₂, Na⁺- Ca²⁺- SO₂ . .

     

Adsorption of carbon monoxide and oxygen on Pt(110)

Adsorption of CO and O₂ on Pt(110) was studied by XPS, LEED and TDS methods to elucidate the role of O_ads states and structural rearrangements of the surface under the action of CO_ads in the appearance of self-oscillations in the rate of CO oxidation on Pt(110).

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, CO O₂ Pt(110) O CO CO Pt(110).

     

Calorimetric study of dinitrogen adsorption at 310 K on a chromia/silica catalyst

The energetics of dinitrogen adsorption on 310 K on a chromia catalyst has been investigated by adsorption calorimetry. Two types of heats have been detected and assigned to a least two different interactions with Cr^II sites of the catalyst.

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310 . , , - , Cr^II .

     

Relation between the catalytic and acidic properties of zeolite catalysts

Influence of the strength and concentration of non protic centers on the catalytic activity of metal-zeolite catalysts in isomerization of n-butane has been studied. A relationship between the specific activity and the center strength is suggested.

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-. , .

     

Kinetics of oxidation of acrolein on a vanadium-molybdenum oxide catalyst

A kinetic study has shown that, in the range of low conversions, the reaction rate depends only on the partial pressure of oxygen. Comparison of the oxidation of acrolein and I-deuteroacrolein suggests that the splitting of the H–CO bond is not rate-limiting.

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, , , . 1- , H–CO .

     

Kinetics of oxidation of carbonyl compounds by peroxomonosulfate. Formaldehyde, formic acid and formate anion

Kinetics of oxidation of formaldehyde, formic acid and formate anion by peroxomonosulfate (PMS) were studied. Formaldehyde is oxidized both by HSO ₅ ^– and SO ₅ ^2– , whereas formic acid and formate ion are oxidized by SO ₅ ^2– alone. The kinetic results show that the formaldehyde is 10³ times more reactive than formic acid, which in turn reacts 10² times faster than formate anion. Mechanisms are discussed in terms of the kinetic results.

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, . HSO ₅ ^– , SO ₅ ^2– , SO ₅ ^2– . , . 10³ , , , , . 10² , . .

     

Influence of carbonate upon adsorption and isomerization of n-butenes on zeolite ZnA. Some conclusions from an infrared study

Upon the formation of carbonates inside zeolite ZnA, weakly bound species of adsorbed n-butenes are observed together with a significant change in the catalytic behavior.

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. ZnA - .

     

Impregnation of alumina with palladium tetrahalide anionic complexes

The difference in reactivity of PdCl ₄ ^2– and PdBr ₄ ^2– species versus the Al₂O₃ hydrous surface was explained according to the trans-effect theory. It has important consequences on Pd uptake rates and impregnation profiles.

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PdCl ₄ ^2– PdBr ₄ ^2– Al₂O₃ . Pd .

     

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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. .

     

Mechanism of methane photooxidation on V/SiO2 catalyst

CH₄ photooxidation on V/SiO₂ catalyst in the presence of gaseous oxygen has been studied by the mass-spectometric method. It has been established that CO₂ forms due to the interaction of CH₄ with surface oxygen anions bonded to vanadium ions. Photodecomposition of V⁴⁺O ₂ ^– species formed in O₂ adsorption on reduced vanadium ions leads to the reoxidation of the latter.

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- CH₄ V/SiO₂ . , CO₂ CH₄ , . V⁴⁺O ₂ ^– O₂ , .

     

Recombination of polyatomic ester peroxy radicals in solution

Termination rate constants of peroxy radicals of seven polyatomic esters in benzene and perflouorooctane media have been measured by pulse photolysis. Recombination of peroxy radicals for all esters examined proves to be diffusion controlled. Reactivity of peroxy radicals in the termination reaction grows with increasing number of ester groups.

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. . .

     

Kinetics and mechanism of homogeneous catalytic oxidation of pyrocatechol in aqueous solutions containing Cu(II) and histidine

Kinetic studies of pyrocatechol oxidation by oxygen in weakly acidic aqueous solutions containing pyrocatechol, Cu(II) ions and histidine, indicate that the reaction involves mixed copper-pyrocatechol histidine complexes. The proposed mechanism of the process agrees with the kinetic relationships obtained.

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, , Cu(II) . , . , -.

     

Influence of the amount of structurally decomposed Y zeolite on the activity of platinum hydrocracking catalysts

On the basis of n-decane transformation, the activity and selectivity of platinum catalysts containing HNaY, as a component of the carrier, were compared. The catalysts differed in the amount of the preserved crystalline structure of the Y-zeolite.

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- , HNaY . Y.

     

On the dioximine complexes of transition metals

Twelve new complexes NH₄[Co(DH)₂(SO₃)(amine)]·t H₂O (DH ₂=dimethylglyoxime) have been synthesized and characterized. Their i.r. spectra show the SO₃ to be co-ordinated to the Co atom through the S atom. The thermal decompositions of a series of derivatives of this type have been investigated with a derivatograph. The first process is an endothermic dehydration reaction, occurring in a single stage or in two successive ones. The loss of the crystallization water is followed by another endothermic reaction, without a clear stoichiometry, which is referred to as deamination. At higher temperatures, exothermic pyrolysis processes occur. From the TG curves, kinetic parameters have been derived for the dehydration and deamination reactions.

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Zusammenfassung Zwölf neue Komplexe der allgemeinen Formel NH₄[Co(DH)₂(SO₃)(amin)]·t H₂O (DH=Dimethylglyoxim) wurden synthetisiert und charakterisiert. Die IR-Spektren zeigen, daß SO₃ über das S-Atom koordinativ an das Co-Atom gebunden ist. Die thermische Zersetzung einer Reihe von Derivaten dieses Typs wurde mittels eines Derivatographen untersucht. Der erste Prozeß ist die in einem einzigen oder in zwei aufeinander folgenden Schritten verlaufende endotherme Dehydratisierung. Auf die Abgabe des Kristallwassers folgt eine andere endotherme Reaktion unklarer Stöchiometrie, die als Deaminierung bezeichnet wird. Bei höheren Temperaturen verlaufen exotherme Pyrolyseprozesse. Aus den TG-Kurven wurden kinetische Parameter für die Dehydratisierung und die Deaminierung bestimmt.

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NH₄Co(DH)₂(SO₃)(a)]·tH₂O, DH ₂ — . , . . , . «». . .