Steady state kinetic equation for SO2 oxidation on vanadium catalysts

From the analysis of the detailed reaction mechanism and taking into account vanadium complex formation processes, a steady state kinetic equation has been derived to describe experimental data in a wide range of reaction conditions.

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, .

     

IR-spectroscopic studies of strength and concentration of acid centers on V2O5/Al2O3 catalysts

The strength of protonic sites and the concentration of acid centers in V₂O₅/Al₂O₃ catalysts have been estimated according to pyridine and ammonium adsorption.

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V₂O₅/Al₂O₃.

     

Effect of nickel on the hydrogenating activity of MoS2

The activating effect of nickel on MoS₂ impregnated with an aqueous solution of Ni(CH₃COO)₂ and sulfided has been established to be proportional to the amount of active nickel incorporated as Ni²⁺ cations in the MoS₂ lattice. MoS₂ capacity for active nickel is limited and determined by the preparation method of the parent MoS₂.

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MoS₂ ( Ni(CH₃COO)₂, ) Ni²⁺, . MoS₂ «» .

     

Ligand exchange between bis-acetylacetonato cobalt(II) and organotin compounds SnR2Cl2 (R=Ph, Et), II. Mechanism of ligand exchange between acetylacetonate complexes of Co(II)

Ligand exchange between the compounds Co(AA)₂Py₂ and Co(AA)Clpy_x (x=1 or 3) formed in the, system, CO(AA)₂–SnR₂Cl₂(R=Ph, Et) in chloroform with pyridine has been established to be catalyzed by SnR₂Cl₂. An interpretation of the catalytic action of SnR₂Cl₂ is suggested.

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, Co(AA₂py₂ Co(AA)Clpy_x (x=1 3) (Co(AA)₂–SnR₂Cl₂ (R=Ph, Et) , SnR₂Cl₂. SnR₂Cl₂.

     

Asymmetric hydrogenation of tryptophan precursors catalyzed by rhodium-DIOP complexes

Z-2-benzamido(acetamido)-3-(3-indolyl)-2-propenoic acids were hydrogenated with neutral and cationic rhodium(I) complexes containing the chiral diphosphine (–) or (+)–2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)-butane [(–) or (+)–DIOP].

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Z-2- ()-3-(3-)-2- () (I), (–) (+)-2,3--2,3--1,4- ()-.

     

Thermogravimetry of copper and copper oxides (Cu2O-CuO)

The thermogravimetry of mixtures of metallic copper and copper oxides was studied. The experiments were performed by heating the samples in air to 700–800° to transform all the components to copper(II) oxide, and continuing the heating in nitrogen to 1050–1100° when the dissociation of copper(II) oxide to copper(I) oxide is complete. The identification of the components and their quantitative determination were carried out by determining the shape, size, and ratio of the segments of the curves obtained during the heating. The method can be used for quantitative analysis of mixtures of copper and/or copper oxides.

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Zusammenfassung Gemische von metallischem Kupfer und Kupferoxiden wurden thermogravimetrisch untersucht. Zur Überführung aller Komponenten in Kupfer(II)-oxid erhitzte man sie in Luft auf 700–800°, um daraufhin bis zur vollständigen Dissoziation des Kupfer-(II)-oxids zu Kupfer(I)-oxid unter Stickstoff die Temperatur bis auf 1050–1100° zu steigern. Die Identifizierung der Komponenten und ihre quantitative Bestimmung erfolgten durch die Form, Größe und die Verhältnisse der verschiedenen Abschnitte der erhaltenen Kurven. Diese Methode ist zur quantitativen Bestimmung von Gemischen aus Kupfer und Kupferoxid sowie von Kupferoxiden geeignet.

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Résumé Étude thermogravimétrique de mélanges du cuivre métallique et d'oxydes de cuivre. Les échantillons sont d'abord chauffés dans l'air jusqu'à 700–800° jusqu'à ce que tous les constituants soient transformés en oxyde de cuivre(II); le chauffage est ensuite poursuivi dans l'azote jusqu'à 1010–1100°, où la dissociation de l'oxyde de cuivre(II) en oxyde de cuivre(I) est complète. Les constituants ont été identifiés et dosés en utilisant la forme, la dimension et les proportions des différentes parties des courbes pendant le chauffage. La méthode peut être utilisée pour l'analyse quantitative de mélanges de cuivre et ou d'oxydes de cuivre.

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. 700–800: ( (), 1050–1100° [ () (I)]. , , . / .

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The author wishes to acknowledge the financial assistance provided by the Technion — Israel Institute of Technology.The author wishes also to thank Dr. R. F. Tylecote (University of Newcastle Upon Tyne, England) for very helpful comments and useful discussions of this investigation and to Mrs. N. Leder for chemical analyses.     

Thermal and photochemical stability of polystyrene and its blends with polyvinyl chloride

The influence of some irregularities in polystyrene (PS) and polyvinyl chloride (PVC) chains on their thermal stability was investigated. UV irradiation caused an increase in the content of these irregularities in the polymers. It was found that the presence of carbonyl groups and crosslinking of the polymer chains hamper the thermal dehydrochlorination of PVC and the total decomposition of both polymers. On the other hand, weak peroxy linkages (which facilitate degradation processes) and conjugated double bonds decrease the temperature of total decomposition of PS and PVC blends.

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Zusammenfassung Es wurde der Einfluß von Unregmlmäßigkeiten in Polystyrol (PS)- und Polyvinylchlorid (PVC)-Ketten auf deren thermische Stabilität untersucht. UV-Bestrahlung verursacht ein Ansteigen des Gehaltes an Unregelmäßigkeiten in den Polymeren. Es wurde festgestellt, daß die Gegenwart von Carbonylgruppen und Querverbindungen der Polymerketten die thermische Dehydrochlorierung von PVC und eine vollständige Zersetzung beider Polymere verhindern. Andererseits senken Peroxidverknüpfungen (die die Degradierungsvorgänge erleichtern) und konjugierte Doppelbindungen die Temperatur für eine vollständige Zersetzung von PS und PVC Gemischen.

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. - . , . , , , .

     

Thermal and photochemical stability of polystyrene and its blends with polyvinyl chloride I.

The influence of a 1–20% content of PVC in PS films on their thermal stability was investigated. It was found that the thermal stabilities of these blends are higher than that of either of the two pure polymers. This indicated the mutual stabilizing effects of these polymers on each other. The effect is significant when the PVC content in the blends is 1–5%. A higher amount of PVC causes either no significant change or a lowering of the thermal stability. The miscibility of the polymer components in the blends clearly has an important influence on the course of the thermal processes.

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Zusammenfassung Der Einfluß von 1–20% PVC in PS-Filmen auf deren thermische Stabilität wurde untersucht. Es wurde festgestellt, daß die thermische Stabilität dieser Gemische höher ist, als die der beiden reinen Polymere für sich. Dies verdeutlicht den gegenseitigen Stabilisierungseffekt der beiden Polymere. Zu einem signifikanten Effekt kommt es bei einem PVC Gehalt der Gemische von 1–5%. Ein höherer Gehalt an PVC führt entweder zu keiner signifikanten Veränderung oder zu einer Abnahme der thermischen Stabilität. Die Mischbarkeit der Polymerkomponenten des Gemisches verfügt eindeutig über einen wichtigen Einfluß auf den Ablauf der thermischen Prozesse.

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() 1 20%. , , . 1–5%. . .

     

Kinetics and mechanism of the decomposition of pyrite under conventional and quasi-isothermal — quasi-isobaric thermoanalytical conditions

The kinetics and mechanism of the thermal decomposition of pyrite were examined by the method of quasi-isothermal and quasi-isobaric thermogravimetry (Q-TG). It emerged that by means of this technique the overlapping partial processes of the complicated oxidation and decomposition reactions of pyrite can be separated and studied independently from one another. It was found that the partial reactions FeS₂=FeS +S and Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ are endothermic processes taking place quasiisothermally and leading to equilibrium, while the oxidation FeS+O₂=Fe₂O_3–x(SO₄)_x is an exothermic process which takes place in an oscillating manner in a rather broad temperature interval.

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Zusammenfassung Autoren untersuchten die Kinetik und den Mechanismus der thermischen Zersetzung von Pyrit durch quasi-isotherme und quasi-isobare Thermogravimetrie (Q-TG). Es stellte sich heraus, daß sich überlagernde Teilprozesse der komplizierten Oxydations- und Zersetzungsprozesse von Pyrit mit Hilfe dieser Technik absondern und unabhängig voneinander untersuchen lassen. Es wurde festgestellt, daß die Teilreaktionen FeS₂=FeS+S und Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ endotherme Prozesse sind, die quasi-isotherm verlaufen und zu einem Gleichgewicht führen, während die Oxydation FeS+O₂=Fe₂O_3–x(SO₄)_x ein exothermer Prozeß ist, der oszillierend in einem ziemlich breiten Temperaturintervall verläuft.

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(Q-) . . , FeS₂=FeS+S Fe₂O_3–x(S₂O₄)_x=Fe₂O₃+SO₃ , . FeS+O₂ =Fe₂O_3–x(SO₄)_x , .

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The authors thank Prof. E. Pungor for valuable discussions, and Mrs. M. Kiss and Miss I. Fabian for their technical assistance.     

Acetoxylation of olefins catalyzed by a palladium(II)-heteropolyacid system

The catalytic acetoxylation of ethylene and propylene occurs under the action of oxygen in the presence of Pd(II)+HPA-6, where HPA-6 is the heteropolyacid H₉PMo₆V₆O₄₀. In addition to the products of acetoxylation (alkenyl and allyl acetates), oxidation products (acetaldehyde and acetone) are also formed. The selectivity of acetoxylation increases upon the addition of NaOAc.

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— — Pd(II)+-6, -6 H₉PMo₆V₆O₄₀. (- ) — . NaOAc.

     

Kinetics and mechanism of the oxidation of p-aminobenzoic acid by periodate ion in aqueous medium

Kinetic results of the oxidation of p-aminobenzoic acid by periodate ion in aqueous medium are discussed. A suitable mechanism based on kinetic evidence and product analysis is proposed.

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- . , .

     

NO adsorption on tin(IV) oxide

The adsorption of NO on SnO₂ has been studied in the temperature range from 0 to 86°C, at pressures from 0.4 to 3.5 Torr. The adsorption isotherms are described by the Freundlich equation. The rate of adsorption obeys the Roginskii-Zeldovitch equation and decreases with increasing temperature. The reduction of SnO₂ with carbon monoxide results in a drop in the adsorption rate and in the amount of adsorbed NO.

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NO SnO₂ 0°–86°C 0,4–3,5 . . - . SnO₂ NO.

     

Aromatization of propylene and butadiene over MoO3?SiO2 and WO3?SiO2 catalysts

The activity of various MoO₃–SiO₂ and WO₃–SiO₂ catalysts for the aromatization of propylene and butadiene has been investigated. The results obtained show a comparatively high aromatization activity of the catalysts for propylene to benzene and toluene. The direct conversion of butadiene to ethylbenzene, using WO₃ on acid treated silica, is considered to be an alternative reaction pathway to the known metathesis step to ethylene and benzene.

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MoO₃–SiO₂ WO₃–SiO₂ . . , WO₃ .

     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .

     

Identifiability classes in reaction kinetics

Some difficulties of eliciting reliable rate constants from experimental data are considered. Different classes of ill-posed estimation problems are given and demonstrated by simple examples.

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. .

     

On the initial treatment of kinetic data

The kinetic methods usually employed to determine reaction orders involve some sort of mathematical approximation and provide values approximate and very often discrepant. Three methods are reported to determine accurate reaction orders without introducing approximations.

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, , , , . .

     

Investigation of n-heptane conversion over Pt?Al2O3 catalysts under gradientless reforming conditions

The rates of the total and individual directions of n-heptane conversion in reforming over platinum-on-alumina catalysts were shown to be independent of dilution with hydrogen. They can be described by simple equations following from kinetic concepts in ideal adsorbed layers.

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, - , .

     

Synthesis of benzothiophenes in gas phase from aromatic hydrocarbons and carbon disulfide

A way of synthesis of benzothiophenes, in the gas phase, employing a monosubstituted aromatic compound, carbon disulfide as sulfur source and a Kearby type aluminium orthophosphate as catalyst, has been studied. The best yields in benzothiophene (53%) were reached when vinylbenzene was employed, in a very selective reaction.

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, , , , . (53%) .

     

Investigation of kinetics and mechanism of maleic anhydride interaction with pentachlorinated phosphorus

Kinetics and mechanism of the interaction of maleic anhydride with pentachlorinated phosphorus have been studied. Kinetic parameters of a model making it possible to control this reaction have been calculated.

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, , .

     

Chemisorption of H2, O2 and CO on bimetallic catalysts Rh?Ag/Al2O3

Comparison of adsorptive properties of Rh–Al₂O₃ catalysts in relation to H₂, O₂ and CO as adsorbates points to different surface interactions between the adsorbates and metallic surface of the catalysts. The differences may result from the changing composition of bimetal surface in relation to the catalyst composition and/or from the changing stoichiometry of surface interactions of the adsorbates.

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H₂, O₂ CO Rh–Ag/Al₂O₃ . , , () .