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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, , , .

     

Thorough study of bromide control in bromate oscillators, III. Simulation by the oregonator model of the behavior of reacting BZ systems perrturber by mercury (II) ions

The behavior of the bromate-maloni acid-cerium (III) oscillator in the presence of mercury (II)-a bromide-removing ion-can be simulated by the Oregonator model if the dynamics of bromocomplex-formation and dissociation reactions is taken into account.

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- - (III) (II)- - , .

     

Kinetics of Fe3+ and Cu2+ sorption by fibrous polyampholite

The kinetics of Fe³⁺ and Cu²⁺ sorption from sulfate salt solutions by fibrous polyampholite have been studied.

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Fe³⁺ Cu²⁺ , .

     

Hydrogenation of benzene on sulfide catalysts in the presence of thiophene

The principles of benzene hydrogenation have been studied with sulfide catalysts NI/MS₂, Ni/SiO₂, M/SiO₂ and (Ni, M)/SiO₂ (M=Mo, W) obtained via metal complex precursors or by impregnation. In bimetallic catalysts active sites of benzene hydrogenation are formed upon reduction of the active component for thiophene hydrogenolysis.

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Ni/MS₂, Ni/SiO₂, M/SiO₂, (Ni,M)/SiO₂, M=Mo W, , . , .

     

Investigation of thermooxidative stability of oils by thermal analysis methods

Two base oils, obtained on a laboratory scale, were investigated with a derivatograph and by means of DSC. The sensitivities of the oils to some antioxidants were also examined. The high thermooxidative stability of the oil obtained from a preoxidized atmospheric crude residue was confirmed.

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Zusammenfassung Zwei im Labormaßstab hergestellte Rohöle wurden mit einem Derivatographen und mittels DSC untersucht. Die Empfindlichkeit der Öle gegenüber Antioxidanten wurde ebenfalls geprüft. Es wurde eine hohe thermooxidative Stabilität des aus einem präoxidierten atmosphärischen Rohstoffrestes erhaltenen Öls nachgewiesen.

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, . . , .

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The authors are grateful to the Institute of Petroleum Technology for the DSC measurements.     

Mechanism of ascorbic acid oxidation by molecular oxygen in aqueous pyridine catalyzed by CO2+, Ni2+, Mn2+ and Zn2+

Data on the radical non-chain mechanism of ascorbic acid oxidation by molecular oxygen catalyzed by Co²⁺, Ni²⁺, Mn²⁺ and Zn²⁺ ions are reported.

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Co²⁺, Ni²⁺, Mn²⁺ Zn²⁺.

     

Positions of steady states in two-component chemical systems

The general kinetic equation for two-component chemical systems is analyzed. It is shown that the positions of steady states in concentration spaces can be detected by a qualitative analysis of the chemical mechanism.

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. , .

     

Physico-chemical properties of catalysts: Thermal analysis,infrared spectroscopy,X-ray diffraction and magnetic susceptibility of the vanadates of zinc,manganese and silver

Thermal characteristics of the vanadates of zinc, manganese and silver have been studied by DTA and TG techniques and the different transition products thus obtained have been characterised by IR, X-ray diffraction and magnetic susceptibility data. Chemical analyses indicate the following compositions of these vanadates: (1) Zn₂V₂O₇.5H₂O, (2) Zn₃(VO₄)₂.3H₂O, (3) Mn(VO₃)₂.2H₂O and (4) Ag₃VO₄. The DTA curves indicate that zinc pyrovanadate undergoes endothermic changes at 110–195, 265, 365, 440, 660° and one exothermic change at 485°. This system is diamagnetic which becomes completely paramagnetic after 660°. Zinc orthovanadate exhibits a number of endothermic peaks at 300, 470, 700, 815 and 930° respectively. This system is feebly paramagnetic and retains this property up to 930°. Manganese metavanadate undergoes endothermic changes at 240, 280–590, 830 and 880° respectively. This vanadate is paramagnetic and paramagnetism increases appreciably at 590° and remains constant up 830°. Silver orthovanadate exhibits three endothermic changes at 180, 455 and 640°, respectively.

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Zusammenfassung Die thermischen Charakteristika der Vanadate von Zink, Mangan und Silber wurden durch DTA- und TG-Methoden untersucht und die auf diese Weise erhaltenen verschiedenen Übergangsprodukte durch Daten aus IR-, Röntgen- und magnetischer Susceptibilität charakterisiert. Die chemische Analyse deutet auf folgende Zusammensetzung dieser Vanadate: 1) Zn₂V₂O₇.5H₂O, 2) Zn₃(VO₄)₂.3H₂O, 3) Mn(VO₃)₂.2H₂O und 4) Ag₃VO₄. Die DTA-Kurven zeigen endotherme Veränderungen des Zink-pyrovanadats bei 110–195, 265, 365, 440 und 660° und eine exotherme Veränderung bei 485°. Dieses System ist diamagnetisch und wird nach 660° vollständig paramagnetisch. Zink-orthovanadat zeigt eine Anzahl exothermer Peaks bei 300, 470, 700, 815, bzw. 930°. Dieses System ist schwach paramagnetisch und behält diese Eigenschaft bis zu 930°. Im Manganmetavanadat vollziehen sich endotherme Veränderungen bei 240, 280–590, 830 und 880°. Dieses Vanadat is paramagnetisch, der Pararnagnetismus steigt zusehends bei 590° und bleibt bis zu 830° konstant. Silberorthovanadat zeigt drei endotherme Veränderungen bei 180, 455 bzw. 640°.

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Résumé On a étudié par ATD et TG les caractéristiques thermiques des vanadates de zinc, de manganèse et d'argent. La caractérisation des divers produits de transition ainsi obtenus a été effectuée à partir des données fournies par IR, rayons X et susceptibilité magnétique. Les analyses chimiques indiquent les compositions suivantes de ces vanadates: (1) Zn₂V₂O₇.5H₂O, (2) Zn₃(VO₄)₂.3H₂O, (3) Mn(VO₃)₂.2H₂O et (4) Ag₃VO₄. Les courbes ATD du pyrovanadate de zinc montrent des effets endothermiques à 110–195, 265, 365, 440 et 660° ainsi qu'un phénomène exothermique à 485°. Ce corps est diamagnétique; il devient complètement paramagnétique au-dessus de 660°. L'orthovanadate de zinc donne des pics endothermiques à 300, 470, 700, 815 et 930°. Il est faiblement paramagnétique jusqu'à 930°. Le métavanadate de manganèse est le siège de phénomènes endothermiques à 240, 280–590, 830 et 880°. Il est paramagnétique et son paramagnétisme augmente de manière appréciable à 590° pour rester constant jusqu'à 830°. L'orthovanadate d'argent montre trois effets endothermiques à 180, 455 et 640°.

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, . - , . : Zn₂V₂O₇·5H₂O, Zn₃(VO₄)₂ · 3H₂O, Mn(VO₃)₂· 2H₂O Ag₃VO₄. , 110–195°, 265, 365,440 660° 485°. , 660° . 300, 470, 700, 815 930°. 930°. 240, 280–590, 830 880°. , 590° 830°. 180, 455 640°.

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The authors are grateful to the Physical Research Wing and Catalyst Research and Development Section, F. C. I., Sindri and also the Analytical Physics Division and Catalyst Section, I.I.P., Dehradun (India) for their help in getting TG and X-ray patterns of the catalysts studied.     

Kinetics and mechanism of oxidation of sulfaguanidine by peroxydisulfate ion

Results of the kinetic studies of peroxydisulfate ion oxidation of sulfaguanidine are discussed. N,N'-bis(guanyl)azoxybenzene-p,p'-disulfonamide has been identified as the main oxidation product. On the basis of product identification and kinetic studies a radical mechanism is proposed.

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. N,N'- () -, '- . , .

     

Kinetics of thermal decomposition of diacyl peroxides in the presence of aerosil

In the presence of aerosil the thermal decomposition of the polymeric peroxide of sebacic acid is enhanced proportionally to the filler weight fraction in the reaction system. This is attributed to the interaction of peroxide groups with acidic groups on the aerosil surface and their decomposition according to a nonradical mechanism unlike the homolytic radical decomposition in solution.

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, , . .

     

Kinetic parameters of the thermal decompositions of nitritonickelates(II)

Kinetic parameters of thermal decomposition of compounds of general formulaM ₂ ^I M ^II[Ni(NO₂)₆], whereM ^I= K⁺, Rb⁺ or Cs⁺ andM ^II= Ca²⁺, Sr²⁺ or Ba²⁺, were investigated on the basis of the respective thermal curves. Calculations of the reaction order and activation energy carried out by the Coats-Redfern method and by Doyle's method (modified by Zsakó) gave similar results, The reaction order is 2 for all the compounds investigated. In the group of potassium salts the activation energy increases fromM ^II=Ca²⁺ toM ^II=Ba²⁺. In the groups of rubidium and caesium salts, the lowest activation energy is observed whenM ^II=Sr²⁺. Such behaviour of the nitritonickelates is explained in terms of structures and the principle of maximum density.

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Zusammenfassung Die kinetischen Parameter der thermischen Zersetzung von Verbindungen der allgemeinen FormelM ₂ ^I M ^II [Ni(NO₂)₆] (M ^I= K⁺, Rb⁺ oder Cs⁺ und M^II = =Ca²⁺, Sr²⁺ oder Ba²⁺) wurden auf Grund der entsprechenden thermischen Kurven untersucht. Die an Hand der Coats-Redfern Methode und der durch Zsakó modifizierten Doyleschen Methode durchgeführten Berechnungen der Reaktionsordnung und der Aktivierungsenergie ergaben ähnliche Resultate. Die Reaktionsordnung ist 2 für sämtliche untersuchten Verbindungen. In der Gruppe der Kaliumsalze steigt die Aktivierungsenergie vonM ^II=Ca²⁺ in RichtungM ^II=Ba²⁺ an. In der Gruppe der Rubidium- und Caesiumsalze wird die niedrigste Aktivierungsenergie beiM ^II=Sr²⁺ beobachtet. Dieses Verhalten der Nitritonickelate wird durch die Strukturen und das Prinzip der maximalen Dichte erklärt.

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₁ ^{2 II}[Ni(NO₂)₆], ^I= ⁺, Rb⁺Cs⁺,a ^II= ²⁺,8r²⁺²⁺. , - ( ), . 2. ^{+ 2+}. ^II=S²⁺. .

     

A thermal decomposition study of some nickel(II)thioureachloride complexes

TG/DTA and Thermal Degradation Mass spectrometry (TDMS) data are presented for a series of nickel(II)thiourea chloride complexes: NiL₄Cl₂:L=thiourea or methyl-, dimethyl-, tetramethyl-, di-n-butyl, naphthyl-, ethylene- or allylthiourea. Two different thermal decomposition mechanisms are proposed for these complexes, and it is apparent that the thermal decomposition mechanism adopted by a particular complex depends on the structure of the relevant thiourea ligand and not on the nature of the halide ligand or on the existence of geometrical isomerism for these complexes.

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Zusammenfassung Durch TG, DTA und thermodegradative Massenspektrometrie (TDMS) von Nickel(II)-thioharnstoff-chlorid-Komplexen, NiL₄Cl₂ (L=Thioharnstoff oder Methyl-, Dimethyl-, Tetramethyl-, Di-n-butyl-, Naphthyl-, Vinyl- oder Allylharnstoff), erhaltene Daten werden angegeben. Zwei verschiedene Mechanismen werden für die thermische Zersetzung vorgeschlagen. Es ist offensichtlich, daß der Mechanismus, nach der die thermische Zersetzung eines gegebenen Komplexes verläuft, von der Struktur des relevanten Thioharnstoffliganden und nicht von der Natur des Halidliganden oder vom Vorliegen einer geometrischen Isomerie abhängt.

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/ - NiL₄Cl₂, L= , -, -, -, ---, -, - . . , .

     

Interaction between propene and CoNaX zeolite and exchange of propene hydrogens

Interaction of propene with CoNaX and NaX zeolites and exchange of propene hydrogens with CoNaX zeolite was studied at the temperature of the IR beam and at 300°C by means of IR and MS analysis. In addition, the heats of adsorption were measured. The structure of adsorbed propene complexes was found to be influenced by the presence of Co²⁺ ions. The mechanism of the exchange is discussed and the properties of the OH groups of HY, HX and CoNaX zeolites are compared.

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CoNaX NaX CoNaX 300°C . . , Co²⁺ . OH , CoNaX .

     

Influence of physically adsorbed oxygen on the separation of electron-hole pairs on anatase irradiated by visible light

ESR studies on the formation and properties of O ₂ ^– and [O^–·O₂] ion-radicals under photo-irradiation of oxidized anatase have been performed. The role of physically adsorbed oxygen in the separation of electrone-hole pairs is shown.

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- O ₂ ^– [O^–·O₂], . - .

     

Autocatalysis in the formose reaction

It has been found that carbohydrates naturally present in ppm quantities in paraformaldehyde are the cause of the autocatalysis in the formose reaction of paraformaldehyde solutions. Paraformaldehyde sublimed into Ca(OH)₂ suspension was not transformed to sugars by formose reaction, only to methanol and formate by Cannizzaro reaction. A minute trace of glycolaldehyde — 3 ppm — was sufficient to initiate conventional autocatalysis. A formose reaction scheme in which formaldehyde reacts only with sugars by aldol condensation but not with itself is proposed.

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, , .. . , Ca(OH)₂, , , . — 3 .. — . , , .

     

Free-radical pyrolysis of ethanal in the presence of mono-or diolefins: Addition and hydrogen transfer mechanisms

The effects of mono-and diolefins on ethanal pyrolysis are summarized and discussed. It is shown that an addition and a hydrogen transfer mechanism, separately or together, may account for the experimental results obtained with various mono- and diolefins.

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- . , , , , - .

     

Adsorption-desorption hysteresis in porous networks

As a result of computer experiments with model porous networks, the factors (other than pore shape and size distribution) determining the form of the adsorption-desorption hysteresis loop have been elucidated.

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, - - .

     

Thermal investigation of polyols

The thermal behaviour of D-mannitol, dulcitol, D-sorbitol, the semihydrate of D-sorbitol, L-arabitol, xylitol and ribitol was investigated by means of differential thermal analysis and a derivatograph. All these polyols are stable up to 200–250°. The endothermic peaks on the DTA curves at lower temperatures are due to melting. These effects are not accompanied by an increase in the electric conductivity. The hexitols decompose endothermally at boiling above 200–250°, the majority of the decomposition products boil out, and the residue is oxidized. The beginning of the decomposition of the pentitols is accompanied by an exothermic peak.

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Zusammenfassung Das thermische Verhalten von D-Mannitol, Dulcitol, D-Sorbitol, vom Semihydrat des D-Sorbitol, von L-Arabitol, Xylitol und Ribitol wurde differentialthermoanalytisch und derivatographisch untersucht. Diese Polyole waren bis 200–250° stabil. Die endothermische Spitze der DTA-Kurve bei niedrigerer Temperatur ist dem Schmelzen zuzuschreiben, welches durch kein Erhöhen der elektrischen Leitfähigkeit begleitet ist. Hexitole zersetzen sich endotherm in ähnlicher Weise beim Sieden über 200–250°, der größte Teil der Zersetzungsprodukte entfernt sich und der Rückstand wird oxydiert. Der Zersetzungsbeginn der Pentitole ist von einem exothermen Effekt begleitet.

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Résumé On a suivi par ATD et à l'aide d'un derivatograph le comportement thermique des polyalcools suivants: D-mannitol, dulcitol, D-sorbitol, D-sorbitol hémihydraté, L-arabitol, xylitol et adonitol. Tous sont stables jusqu'à 200–250°C. Le pic endothermique qui apparaît sur la courbe d'ATD à plus basse température est dû à la fusion. Celle-ci ne s'accompagne pas d'un accroissement de la conductivité électrique. Les hexitols se décomposent endothermiquement avec ébullition simultanée au-dessus de 200–250° et élimination de la majeure partie des produits de décomposition; le résidu est oxydé. La décomposition des pentitols s'accompagne au début d'un effet exothermique.

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-, , -, -, L- , ( ). 200–250°. , . 200–250° , , ( ). .

     

Dissociative adsorption of oxygen and hydrogen, and the formation of hydroxyl groups on the surface of Cu, Ag, Ni, Pd and Pt

By the semi-empirical interacting bonds method, the heats of oxygen and hydrogen adsorption in a dissociative form on the (100) face of Cu, Ag, Ni, Pd and Pt have been calculated. It has been shown that most stable are the multiply bonded adsorption forms. For the different bonding states, the heat of hydroxyl group formation from O₂ and H₂ varies but slightly. The calculated values are compared with the experimental data.

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(100) Cu, Ag, Ni, Pd, Pt. , . - H₂ O₂. .

     

Catalytic properties of nitrides in ammonia synthesis

Ammonia synthesis on nitrides CeN, UN_1.70 and iron catalyst CA-1 has been examined at pressures of up to 100 bar. Reaction kinetics is described by the Temkin-Pyzhev equation. Activation energy for all samples is similar and equals about 200 kJ/mol. Specific catalytic activity of nitrides is lower than that of the iron catalyst by a factor of 3–4 for uranium and 10 for cerium.

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100 CeN, UN_{1, 70} CA-1. -. 200 /. : 3–4 10 .