Influence of the entropy factor on the equilibrium and kinetics of chemisorption

A correction to the model of uniform heterogeneous surface has been introduced. This correction extends the limits of application to processes with entropy changes of the adsorbent. On the basis of the model thus corrected a kinetic equation has been deduced, which takes into account the role of the entropy factor. The presence of a compensation effect in chemisorption kinetics is supported theoretically.

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- , , . , . .

     

Neighboring amide group participation in ester aminolysis in aprotic solvents

The piperidinolysis of 8-quinolyl-, p-nitrophenyl-, o-, and p-piperidinocarbonylphenyl acetates in acetonitrile and in chlorobenzene was studied at 25°C. The strictly second order kinetic behaviour and the weaks solvent-dependence of the rate of the reaction of o-piperidinocarbonylphenyl acetate indicate anchimeric assistance by the o-amide group, and support the suggestion that amide groups of hydrophobic enzyme active sites may act as general base catalysts.

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8--, --, - - 25°C. - - , .

     

Catalytic oxidative hydrolysis of H2PO2? anions in the presence of RhCl3

Kinetics of H₂ evolution in the RhCl₃–NaH₂PO₂–HCl–H₂O system has been studied. As found by³¹P NMR, Rh(I) complexes with the Rh–P(OH)₂O^– bond are formed and play the role of catalysts in the subsequent H₂ evolution reaction.

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H₂ RhCl₃–NaH₂PO₂–HCl–H₂O. ³¹P Rh(I) Rh–P(OH)₂O^–, H₂.

     

Kinetics of methanol synthesis in the presence of low-temperature catalyst

The kinetics of methanol synthesis performed in a flow circulation installation in the presence of low-temperature copperzinc-aluminium catalyst has been investigated. The application of a power kinetic equation describing the surface chemical interaction on an exponentially inhomogeneous surface is established. The effect of the volume rate and the temperature is studied and the presence of a compensation effect is proved. A possibility of determination of the temperature and the volume rate, under which conditions the side-reactions do not affect the main one, is shown on the basis of the kinetic investigations.

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-- - . - - . . , .

     

Kinetics and mechanism of the oxidation of bis(acetylacetonato)-cobalt(II) by cumene hydroperoxide in the presence of pyridine

Stoichiometric reaction of bis(acetylacetonato) cobalt(II) with cumene hydroperoxide in chloroform solutions containing added pyridine has been studied by the PMR method.

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() Co(II) , .

     

A new method to determine the distance of electron tunneling transfer and its application to recombination of paramagnetic radiation deffects in CaO

A new method to determine the distance of electron tunneling transfer between paramagnetic reagents based on simultaneous analysis of both kinetic and ESR data is suggested. This method has been used to estimate the tunneling distance and the parameters characterizing the rate of tunneling for finely dispersed CaO.

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, - . CaO , .

     

Differential-thermal and thermogravimetric analysis of some gagates from Bulgaria

The thermal behaviour of three gagates (Bulgaria) was investigated by DTA and TG. The characteristic endo- and exoeffects and the sequence of the thermal stabilities are established.

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Zusammenfassung Das thermochemische Verhalten von drei Gagaten (Bulgarien) wurde mittels DTA und TG untersucht. Die charakteristischen endo- und exothermen Effekte und die Reihenfolge der thermischen Stabilitäten wurden ermittelt.

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(). - .

     

Investigation of changes in catalyst for conversion by means of steam during use in an industrial reactor

A study was made of the changes in the active component of a commercial catalyst for methane reforming by means of steam, as a function of its duration of use and of its position in an industrial reactor. The samples for examination were taken after 3, 8, 9 and 20 months of catalyst use, and from seven different levels in the reformer tube, ranging from the top to the bottom.DTA, TG, IR spectroscopy, X-ray diffraction and surface area determination were used to follow the catalyst changes.

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Zusammenfassung Veränderungen der aktiven Komponente eines kommerziellen Katalysators zur Methanreformierung mittels Wasserdampf wurden in Abhängigkeit von der Betriebsdauer und der Lage im industriellen Reaktor untersucht. Proben für die Untersuchung wurden nach 3-, 8-, 9- und 20-monatiger Betriebsdauer aus 7 verschiedenen Höhen vom Boden bis zum Kopf des Reformer-Rohres entnommen. Veränderungen des Katalysators wurden mittels DTA, TG, IR-Spektroskopie, Röntgendiffraktometrie und Oberflächenmessungen verfolgt.

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, - , @2 . 3, 8, 9 20 -, -. , , , , , .

     

Distribution of components in the rare earth ammonia synthesis catalysts and effect of additives

The distribution of components in the HG-1 ammonia catalyst promoted by rare earth oxide (successfully developed by the authors) was analyzed by electron microprobe photography. The results enable us to explain the effect of additives upon the activity as well as the remarkably high lifetime of catalyst.

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HG-1, ( ) , . , .

     

A method for the treatment of experimental data. Kinetic system comprising two irreversible first order consecutive reactions

A method is proposed for the treatment of data from a kinetic system comprising two irreversible first order consecutive reactions (ABC). It is based on the solving of contrary propositions for an ordinary differential equation.

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(ABC). .

     

Kinetics of SO2 oxidation on K2S2O7?V2O5 catalyst in non-steady conditions

Studies of SO₂ oxidation on a molten component of vanadium catalysts in non-steadystate conditions indicates that the kinetics agree fairly well with an oxidation-reduction mechanism. In the low temperature range (<790 K) tetravalent vanadium can be partially crystallized.

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. , - . ( 790 ) .

     

Heterogenized rhodium complexes as hydrogen transfer catalysts

Cationic rhodium(I) norbornadiene complexes with polystyrene-immobilized imidazole, tetramethylbiimidazole or phosphine ligands in the presence of potassium hydroxide catalyze hydrogen transfer from isopropanol to acetophenone and 1-hexene. [Rh(NBD) (poly-PPh₂)₂] ClO₄ complexes are particularly efficient for the reduction of acetophenone, but slow decomposition to rhodium metal is observed.

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(I) , , , 1-. [Rh(NBD) (-PPh₂)₂]ClO₄ , .

     

Influence of pore diffusion on the rate of n-heptane conversion on a Pt/Al2O3 catalyst under reforming conditions

Under reforming conditions, the rate of n-heptane conversion on a large Pt/Al₂O₃ catalyst grain, in contrast to that in the kinetic region, depends on the hydrogen to hydrocarbon mole ratio. The rate equation for the reaction on a large grain agrees well with the experimental results obtained by a gradientless method under pressure.

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- , , : . , .

     

Kinetics of gas phase hydrochlorination of acetylene over a mercury catalyst

The kinetics of gas phase hydrochlorination of acetylene over a mercury catalyst has been studied. The kinetic equation is in agreement with the experimental data of various authors.

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. .

     

Spectroscopic and thermoanalytical characterization of standard substances for the identification of reaction products on iron electrodes

The in situ spectroscopic investigation of electrochemical, and especially corrosion processes in iron requires well-characterized reference substances. It has been found that the application of spectroscopic methods alone is not sufficient for the detection of impurities in certain phases. Thermoanalytical methods have therefore additionally been used to detect impurities and to optimize the preparation methods. Infrared and Raman spectra and thermoanalytical data on-FeOOH,-FeOOH,-FeOOH,-FeOOH and on amorphous iron(III) hydroxide sol are reported.

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Zusammenfassung Die in situ-Untersuchung von elektrochemischen und speziell von Korrosionsprozessen an Eisen mit spektroskopischen Methoden erfordert gut charakterisierte Standardsubstanzen. Es zeigte sich, daß die spektroskopische Charakterisierung allein nicht ausreicht, um Verunreinigungen in definierten Phasen zu erkennen. Deshalb wurden zusätzlich thermoanalytische Untersuchungsmethoden zur Auffindung von unreinen Substanzen und zur Optimierung der Präparationsmethoden angewandt. Es werden IR- und Ramanspektroskopische sowie thermoanalytische Daten von-, -, - und-FeOOH sowie eines amorphen Eisen(III) hydroxidsols berichtet.

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in situ , , , . , . , , . , -FeOOH,-FeOOH,-FeOOH,-FeOOH .

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We gratefully acknowledge the financial support given by the Fonds zur Förderung der wissenschaftlichen Forschung of Austria. We also thank Prof. A. Otto (Düsseldorf) and Prof. H. Kuzmany (Wien) for measuring the Raman spectra; thanks are also due to Prof. R. Kellner (Wien) for his kind permission to use the FTIR equipment.     

Role of rhenium in bimetallic reforming catalysts

The influence of rhenium on the behavior of a Pt/Al₂O₃ catalyst was studied in n-hexane reaction by means of dilution of the catalyst bed with Re/Al₂O₃. Parallel to activity, selectivity and ageing data obtained in slug pulse and continuous flow reactors, the amount of the surface carbon formed during the reaction was determined and its reactivity in hydrogen atmosphere was also studied. It is suggested that in the presence of rhenium due to the increase in the amount of hydrogen available for hydrogen consuming reactions including hydrodepolymerization of the carbonaceous surface overlayer, the routes of ageing processes are changed, resulting in lower carbon content on the catalyst and less pronounced catalyst deactivation.

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Pt/Al₂O₃ -, Re/Al₂O₃. , , , , . , , , , , , , .

     

Mössbauer study of the thermal decompositions of alkaline earth tris(oxalato)ferrates(III)

The thermal decompositions of alkaline earth tris(oxalato)ferrates(III) (Mg, Ca, Sr and Ba) have been studied by Mössbauer spectroscopy and other techniques. During the thermal decomposition, dehydration occurs first, followed by reduction to iron(II) species, and oxides and ferrites (MFe^IIIO₄) are then formed at higher temperature. In the case of strontium tris(oxalato)ferrate(III), strontium ferrite (SrFe^IVO₄) is formed at 700°.

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Zusammenfassung Die thermische Zersetzung von Tris(oxalato)ferraten(III) der Erdalkalimetalle (Mg, Ca, Sr, Ba) wurde durch Mössbauer-Spektroskopie und andere Techniken untersucht. Im Verlaufe der thermischen Zersetzung verläuft zunächst die Dehydratisierung, gefolgt von der Reduktion zu Eisen(II)-Species. Oxide und Ferrite (MFe^IIIO₄) werden danach bei höheren Temperaturen gebildet. Strontium-tris(oxalato)-ferrat(III) geht bei 700 °C in Strontiumferrit (SrFe^IVO₄) über.

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() () , , ë . , , MFe^IIIO₄. 700° SrFe^IVO₄.

     

Reactions of isoflavone and 2-hydroxyisoflavanone with sodium ethoxide in anhydrous ethanol

Recent observation /1,4/ on the existence and unreactivity of IV under basic conditions, as well as its part in the inhibitory effect on the decomposition into deoxybenzoin is unequivocally proved by comparing the decompositions of I and VI. It is also shown that the decomposition of I is detemined neither by the character of the solvent nor by the nucleophilic character of the reactant, but by the possibility of the formation of IV.

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IV , I VI. , I . , , IV.

     

Study on the thermal behaviours of homo- and copolymers of styrene,MA and AN by thermogravimetry

The thermal behaviours of polystyrene (PS), polymethylacrylate (PMA), polyacrylonitrile (PAN), polystyrene-co-methylacrylate [P(S: MA)](alternate and random), polystyrene-co-acrylonitrile [P(S: AN)] (alternate) and a terpolymer of styrene, methylacrylate and acrylonitrile [P(S: MA: AN)] are discussed on the basis of non-isothermal thermogravimetric studies. The thermal stabilities of the copolymers have been found to be intermediate between of those of the individual homopolymers. The stability of the [P(S: AN)] copolymer is higher than those of the individual homopolymers. The activation energy values are also in accordance with the thermal behaviours of these polymers.

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Zusammenfassung Basierend auf nicht-isotherme thermogravimetrische Untersuchungen wurde das thermische Verhalten von Polystyrol [PS], Polymethacrylat [PMA], Polyacrylnitril [PAN], Polystyrol-co-methacrylat [P(S: MA)] (alternierend und random), Polystyrolco-acrylnitril [P(S: AN)] (alternierend) sowie eines Mischpolymeren von Styrol, Methacrylat und Acrylnitril [P(S: MA: AN)] untersucht. Die thermische Stabilität der Kopolymeren liegt zwischen denen der individuellen Homopolymeren. Die thermische Stabilität des Kopolymeren [P(S: AN)] ist höher als die der individuellen Homopolymeren. Die Werte der Aktivierungsenergie sind ebenfalls in Übereinstimmung mit dem thermischen Verhalten dieser Polymere.

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

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Presented at the 3rd National Symposium on Thermal Analysis held at VSSC, Trivandrum (India), November, 1981     

Partial oxidation of methane on Cr2O3/Al2O3

The oxidation of methane on supported chromia was studied at temperatures varying between 423 and 743 K and CH₄/O₂ ratios between 1 and 9 in a differential reactor. The main reaction products observed were carbon monoxide and formaldehyde. The rates of reaction obey a power law expression.

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, 423 743 CH₄/O₂ 1 9, . . .