Computation in kinetics V. A new KINDC computational method. Comparative study with other computer programs for kinetic treatment

A new KINDC kinetic computational method is proposed that offers a greatly improved version of the KILET program. A comparative study is made of its performance and those of the most recent computational methods reported in the literature.

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, KINDC, KILET. .

     

Influence of the gas phase on metallic reference electrodes used in work function measurements

Contact potential differences between electrodes of Pt, Au and Ta of different surface finishing were measured by the dynamic condenser method in propylene and oxygen. Propylene is irreversibly adsorbed, thus changing the work function. This renders the electrodes unsuitable as standard electrodes for work function measurements on catalysts in the atmosphere of hydrocarbons, but they may be used in adsorption studies on oxygen.

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Pt, Au Ta . , , . , .

     

Modification effect of Cu upon Pt In Pt?Cu?Al2O3 catalysts

In Pt–Cu–Al₂O₃ catalysts Cu might display either Electronic Ligand Effect or Ensemble Effect, depending on the preparation method of catalysts. For catalysts with Pt added before Cu, the latter exhibits an Electronic Ligand Effect. However, for catalysts with Cu added before Pt or with co-added Pt and Cu, Cu mainly demonstrates an Ensemble Effect.

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Pt–Cu/Al₂O₃ , . Pt Cu, , .

     

Measurement of adsorption heats of nitrogen on metal nitrides

Adsorption heats q and activation energies of the nitrogen exchange on several metal nitrides have been compared. For the systems capable of changing readily their composition upon varying conditions, the isotope exchange is suggested to be the most reliable method of the determination of q.

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. , , , .

     

n-Pentane isomerization in a continuous-flow reactor on Pt/Al2O3 catalysts modified by adsorbed bismuth and palladium

Isomerization of n-pentane has been studied in a continuous-flow reactor at atmospheric pressure on Pt/Al₂O₃ catalysts modified by adsorbed bismuth and palladium. Lower activity and higher selectivity have been obtained on a catalyst modified by bismuth. Both activity and selectivity have decreased on a catalyst modified by palladium. After oxygen treatment the Pd–Pt/Al₂O₃ catalyst showed the most pronounced change in catalytic properties and its stability was lower than that of the unmodified Pt/Al₂O₃ catalyst.

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- , Pt/Al₂O₃, . , . , , . Pd–Pt/Al₂O₃ , Pt/Al₂O₃.

     

Interaction of super-finely dispersed Al powders with water

Interaction of super-finely dispersed Al powders (SFDP) with water is characterized by the presence of a considerable section on the kinetic curves, where the conversion rate is maximum and its degree is as high as =0.5–0.7. It is suggested that the essential factor accounting for the conversion kinetics and the phase composition of its products is the self-heating of Al particles.

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() , , () 0,5–0,7. , .

     

Study of well-characterized Pt?Ru/C catalysts by oxygen electroreduction

A series of well characterized Pt–Ru bimetallic catalysts supported on graphite has been studied by means of the electroreduction of oxygen in a supporting electrolyte of 1 N H₂SO₄. A synergetic effect is observed when the activity per gram of catalyst is considered. However, this effect disappears when the activity values are corrected by the active surface area.

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Pt–Ru, , 1N H₂SO₄. 1- , . , , .

     

Anwendung thermometrischer Methoden auf die Untersuchung von oxydationsmechanismen aromatischer Amine

Zusammenfassung An Hand von Oxydationsreaktionen einiger aromatischer Amine, deren mechanismus bekannt ist, wurde gezeigt, daß enthalpiometrische Titrationskurven in bedeutenden mass zur Formulierung des Reaktionsmechanismus beitragen und auf diese Weise eine wichtige Ergänzung der spektrophotometrischen, potentiometrischen, chromatographischen und weiteren Methoden bilden. In einigen Fällen ist deren Gebrauch unersetzbar.

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In the oxidation reactions of some aromatic amines with known mechanisms, it was shown that the enthalpimetric titration curves could provide considerable help in the determination of the mechanisms, acting as an important complement for spectrophotometry, potentiometry, chromatography and other methods. In some cases the method proved irreplaceable.

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, , , , , . .

     

Modelling of quantitative DTA equipment I. Electric analog approach

For an electric model, relationships have been established as a function of the DTA baseline shift, the intensity of the signal, the slope of the leading edge, the heating rate, the thermal resistance of the heating disc built into the DTA apparatus, the contact resistance between the disc and the sample holders, and the heat resistance between the two measuring sites. Some of the relationships obtained supported knowledge acquired earlier by other approaches, and some furnished new information. The limits of use of this simple model are indicated.

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Zusammenfassung Unter Anwendung eines elektrischen Modells wurden Zusammenhänge als Funktion der Verschiebung der Basislinie der DTA, der Signalintensität, der Steile der Leitkante, der Aufheizgeschwindigkeit, des Wärmewiderstandes der in das DTA-Gerät eingebauten Heizscheibe, des Kontaktwiderstandes, zwischen Scheibe und Probenbehälter und des Wärmewiderstandes zwischen den beiden Meßstellen ermittelt. Ein Teil der erhaltenen Zusammenhänge bestätigte von anderen Annäherungen her bereits vorliegende Kenntnisse, ein anderer Teil lieferte neue Informationen. Auf die Grenzen und der Nutzen dieses einfachen Modells wurden hingewiesen.

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Résumé A l'aide d'un modèle électrique, on a établi des relations décrivant l'influence de la dérive de la ligne de base ATD, de l'intensité du signal, de la pente du bord du pic, de la vitesse de chauffage, de la résistance thermique du disque de chauffage incorporé dans l'appareil ATD, de la résistance de contact entre le disque et les porte-échantillons et enfin, de la résistance thermique entre les deux points de mesure. Une partie des relations obtenues confirme les connaissances déjà acquises par d'autres approches, l'autre partie fournit des renseignements nouveaux. Les limites d'utilisation de ce modèle simple sont indiquées.

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, , , , , , , . , — . .

     

Formation of hexagonal MoO3 upon the decomposition of silica-supported ammonium paramolybdate

Upon the decomposition of silica-supported ammonium paramolybdate, hexagonal MoO₃ is formed at 300–350 °C. Irreversible transformation of hexagonal to rhombic MoO₃ is observed with increasing calcination temperature. The hexagonal MoO₃ structure is probably stabilized by the insertion of ammonium and silicon ions into the lattice of molybdenum trioxide.

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, , 300–359 °C . MoO₃ . MoO₃, , MoO₃.

     

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 .

     

Catalytic properties of Ni/WS2 samples in thiophene hydrogenolysis

The interaction of diallylnickel with WS₂ produces catalysts whose activity is 10–50 times higher than that of the parent sulfide. The atomic catalytic activity referred to supported nickel is independent of the catalyst type and the sulfur removed in temperature programmed reduction.

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, WS₂ , 10–50 . , , .

     

Kinetic and mechanistic studies on the oxidation of arginine and histidine by chloramine-T in hydrochloric acid medium

The oxidation of amino acids by chloramine-T (CAT) in HCl medium at 30°C indicates simultaneous catalysis by H⁺ and Cl^– ions in the HCl concentration range of 0.04–0.12 M. The reaction is first order with respect to concentrations [CAT], [H⁺] and [arginine], but zero order with respect to [histidine]. The rate depends also on Cl^– concentration following 0.7th order. At HCl concentrations >0.12 M, the rate equation is:w=k[CAT] [amino acid]^0.6 and is independent of the [Cl^–]. A suitable mechanism has been suggested.

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-T (CAT) HCl (30°C) H⁺, Cl^– [HCl]=0,04–0,12M. [CAT], [H⁺] [] []. [Cl^–]^0,7. [HCl]>0,12M =k · [CAT][]^0,6 [Cl^–]. .

     

Influence of carbon support pretreatment on properties of Pd/C catalysts

Preoxidation of the surface of carbon support was found to increase the dispersity of palladium and activity of Pd/C catalysts obtained by reduction of supported Pd(OAc)₂, in hydrogenation of olefins. Probable reasons for this effect are discussed.

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, Pd/C , Pd(OAc), . .

     

Effect of alkali metal ions on the catalytic of Pd/SiO2?AlPO4 systems

The effect of different alkali metal hydroxides on the metallic dispersity and catalytic activity of SiO₂–AlPO₄ (8020, by mass) supported palladium catalysts has been studied. The reduction by hydrogen transfer of benzylideneacetone and styrene (using cyclohexene and n-octanol, respectively, as hydrogen donors) and the liquid phase reduction of cyclohexene at low pressure (5 bar) in a Parr type reactor have been used as test reactions to follow changes in the catalytic activity.

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(SiO₂–AlPO₄/8020 ). ( n-, , , (5 ) .

     

ESR identification of formation stages for TiCl3 particles in catalysts for isoprene polymerization

The analysis of ESR spectra from the system TiCl₄+ TIBA in solution under defreezing from 77 to 200 K permitted to identify formation stages of TiCl₃ particles. At first well-ordered Ti ₂ ⁷⁺ structures, and upon subsequent reduction [Ti ₂ ⁶⁺ ]_n are formed. It is the crystallization of the latter that produces TiCl₃ particles.

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TiCl₄+ 77 200 K TiCl₃: Ti ₂ ⁷⁺ , -[Ti ₂ ⁶⁺ ]_n, TiCl₃.

     

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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. .

     

Interaction of monochlorinated phenols with granular activated carbon

The validity of an empirical model to estimate the adsorption affinity of a solute from its acidity constant (pKa) was confirmed through study of the adsorption of monochlorinated phenols on granular activated carbon.Neglecting possible adsorbate fragmentation, simplified desorption kinetic data were obtained for the massive thermal release of the investigated solutes. The resulting non-isothermal kinetic parameters confirm that thermal cleaning of the adsorbent surface is a phase-boundary controlled process involving the interruption of physical interactions according to the calculated activation energy values.

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Zusammenfassung Die Gültigkeit eines empirischen Modells zur Abschätzung der Adsorptionsaffinität eines gelösten Stoffes auf Grund der Aciditätskonstante (pKa) wurde durch Untersuchung der Adsorption von monochlorierten Phenolen an granulierter Aktivkohle bestätigt. Unter Vernachlässigung einer möglichen Adsorbatfragmentierung wurden vereinfachte kinetische Daten für die thermische Desorption der untersuchten gelösten Stoffe erhalten. Die erhaltenen, nichtisothermen kinetischen Parameter zeigen, daß die thermische Säuberung der Adsorbentoberfläche ein phasengrenzflächenkontrollierter Prozeß ist, bei dem physikalische Wechselwirkungen entsprechend den berechneten Werten der Aktivierungsenergie aufgehoben werden.

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, K_a. , . , , , « », .

     

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- . , , . .

     

Effect of medium composition on the monooxygenase activity of immobilized hemin in aniline oxidation

The effect of the composition of the reaction medium on the rate of aniline oxidation to p-aminophenol by hydrogen peroxide on hemin immobilized on -propylimidazole-modified silica has been studied. Organic solvent additives (alcohols, esters and nitriles) are shown to increase the reaction rate. The observed effect is attributed to the decrease of the medium dielectric constant.

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- , , --. , (, , ) . .