Acidity and catalytic activity of polyfunctional zeolite catalysts in the benzene-propene-diisopropylbenzene system

Studies on the effect of the acidity of polyfunctional zeolite catalysts on their activity in benzene alkylation by propene and its transalkylation by diisopropylbenzene (DIPB) have revealed that alkylation and transalkylation of aromatics proceed on catalytic centers of different acidity.

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. , .

     

Catalytic deactivation dynamics of zeolites in multicycle processes

Catalytic deactivation dynamics of zeolites in multicycle processes has been calculated. It has been revealed that in naphthalene sorption on NaX zeolites surface deactivation is predominant with its similarity criterion close to unity and a high fraction of deactivation. Calculated data for several multicycle processes are given.

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. , NaX . .

     

ESR studies on stabilized cool flame of propylene

In the oxidation of propylene a sharp change in the concentration of radicals, observed when passing from the slow reaction region to cool flames, indicates the chain character of the cool flame. Unlike propane and butane, the temperature dependence of the radical concentration and the maximum self-heating are practically unchanged within 603–663 K.

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. , . , 603–663 , .

     

Oxidation of propene over various doped tungsten oxides

The oxidation of propene was studied on several tungsten oxides which contained small amounts of Ti, Ta, Nb and Sn. Only the Sn-containing specimen was found to be selective in the conversion of propene to acrolein. The catalytic results are correlated with crystal structures determined by electron microscopy.

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, Ti, Ta, Nb Sn. , , Sn, . , .

     

Effect of catalyst surface modification on pentachlorobutene-1 oxidation to dichloromaleic anhydride

Modification of V–P–O catalyst surface by reaction products changes the reaction course and increases its catalytic activity in pentachlorobutene-1 oxidation to dichloromaleic anhydride.

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V–P–O . -1 .

     

Thermogravimetric and EPR study of the vacuum thermal decomposition of some zinc and copper(II) chromates

The thermal decompositions in vacuum of the compounds ZnCrO₄, ZnCrO₄·3.5 Zn(OH)₂·H₂O and CuCrO₄ have been investigated using a combination of various techniques: TG, EPR, IR and X-ray.While the TG and X-ray data confirm the final formation of Cu(I) and Zn chromites with the spinel structure resulting from the spontaneous thermal reduction of the Cr(VI) ions, EPR reveals the progressive formation and decay of the following intermediate paramagnetic species: Cr(V) ions and Cr(III) species either dispersed in theM(II) oxide bulk and/or clustered in a Cr₂O₃-like phase, or finally ordered in the chromite phase formed at high temperature.The paramagnetic species which appear, as well as their temperature ranges of stability, are strongly dependent on the nature of theM(II) ion and the Cr(III)/M(II) ratio.The successive detection of these intermediates by EPR yields some detailed information about the decomposition mechanisms of the chromates.

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Zusammenfassung Die thermische Zersetzung der Verbindungen: ZnCrO₄, ZnCrO₄·3.5 Zn(OH)₂ · H₂O und CuCrO₄ in Vakuum wurde unter Anwendung der Kombination verschiedener Techniken, wie TG, EPR, IR und Röntgen, untersucht.Während die TG- und Röntgen-Daten die schließlich erfolgende Bildung der Chromite von Cu (I) Zn mit der aus der spontanen thermischen Reduktion der Cr (VI)-Ionen hervorgehenden Spinellstruktur bestätigen, zeigt EPR die progressive Bildung sowie den Zerfall der folgenden intermediären paramagnetischen Species: Cr(V)-Ionen und Cr(III)-Species entweder in der Masse desM (II)-Oxids dispergiert und/oder in einer Cr₂O₃ ähnlichen Phase eingeschlossen oder aber endlich in der bei hoher Temperatur gebildeten Chromitphase geordnet.Sowohl die auftretenden paramagnetischen Species als auch der Temperaturbereich, in welchem sie stabil sind, hängen stark von der Beschaffenheit desM (II)-Ions und des Verhältnisses Cr(III) (M/II) ab.Der schrittweise Nachweis dieser Zwischenprodukte durch EPR erbringt einige eingehende Informationen über die Zersetzungsmechanismen der Chromate.

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ZnCrO₄₄, ZnCrO₄. 3.5 Zn(OH)₂·H₂O CuCrO₄, , , , , . , Cr(VI). : Cr(V) Cr(III), , Cr₂O₃, , . (II) Cr(III)/()II). .

     

Unimolecular decomposition of CF3OF-calculation by reduced Kassel integral in factorized form

The fall-off curves were calculated for the unimolecular decomposition of the trifluoromethyl hypofluorite at 475.8, 496.9 and 507.3 K by means of the Reduced Kassel Integral in Factorized Form.

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475,8,496,9 507,3 .

     

Alumina as a nickel catalysts support for steam reforming of hydrocarbons

The coking resistance of six alumina supported nickel catalysts in n-butane steam reforming mainly depends on the average size of nickel crystallites. Thus, by using suitable preparative methods, it is possible to produce good, coking resistant nickel catalysts even with Al₂O₃ support.

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Al₂O₃ -, , . . ., , - Al₂O₃.

     

Dehydrocyclization of 1-heptene-1-14C over chromia on non-acidic alumina

The dehydrocyclization of 1-heptene-1-¹⁴C has been investigated over a chromia on nonacidic alumina catalyst with the aim of determining the¹⁴C distribution in the ring of the toluene product. As high as 80% of the¹⁴C was consistently found in the methyl position as predicted for direct six-carbon ring formation.

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1--1-C¹⁴ , , C¹⁴ . 80%- C¹⁴ , .

     

Quantitative thermogravimetry of multicomponent zeolite-bearing rocks

A quantitative thermoanalytical determination of mixture compositions is extremely difficult if there is a partial or full overlapping of the temperature ranges of the thermal transformations, and a proximity of the quantitative characteristics of the weight changes is also observed. A method of quantitative analysis of such a system is offered, based on the calculation of differences in the regularity of rate variation of the thermal transformations of the separate mixture components. The principle of distinguishing temperature intervals with maximum differentiation of thermal effects and methods of calculation of the quantitative mixture composition is shown. Examples of determination of the mineral compositions of zeolite-bearing rock are given.

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Zusammenfassung Eine quantitative thermoanalytische Beschreibung der Zusammensetzung eines Gemisches ist äusserst schwer, wenn die Temperaturbereiche der thermischen Zersetzungen teilweise oder vollständig überlappen und auch die quantitativen Charakteristika der Gewichtsänderungen nahe bei einander liegen. Eine Methode der quantitativen Analyse eines solchen Systems wird gezeigt, die auf der Berechnung der Unterschiede der Regelmässigkeit der Geschwindigkeitsänderung bei der thermischen Umsetzung der einzelnen Komponenten des Gemisches beruht. Das Prinzip der Unterscheidung von Temperaturbereichen unter maximaler Differenzierung der thermischen Effekte, sowie die Methode zur Berechnung der quantitativen Zusammensetzung des Gemisches werden beschrieben. Beispiele zur Bestimmung der Zusammensetzung der Mineralstoffe in zeolithaltigem Gestein werden gegeben.

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Résumé La détermination quantitative de la composition d'un mélange est très difficile par les méthodes thermoanalytiques si les intervalles de température où s'effectuent les transformations se chevauchent partiellement ou totalement et si les variations pondérales sont proches les unes des autres. Pour effectuer l'analyse quantitative d'un tel système, on présente ici une méthode qui repose sur le calcul des modifications de la vitesse de transformation des composants individuels du mélange. On décrit le principe suivant lequel on effectue la distinction des intervalles de température avec une différenciation maximale des effets thermiques ainsi que les méthodes permettant de calculer la composition du mélange. Le dosage des constituants présents dans des roches à zéolites est donné comme exemple.

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, , . , . . .

     

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 substituent on the mechanism of oxidation of anilines by acidic iodate. A kinetic study

The nature of the substituent is found to exhibit a profound influence on the mechanism of oxidation of anilides by iodate. The process appears to be smooth with electron-releasing groups, while it involves consecutive reactions with electron-withdrawing groups. Azobenzenes and quinones are obtained as the major products with electron-releasing and withdrawing groups, respectively.

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. - , - . -, .

     

Usefulness of kinetic parameters in investigations of thermal decompositions of solids

The theoretical curves in the coordinates a vs. time for isothermal, and avs. temperature for non-isothermal experiments are calculated as functions of three kinetic parameters: activation energyE, pre-exponentical factorA and theg() function describing the mechanism of thermal decomposition of solids. The results show that conclusions not taking into consideration all three parameters can lead to information of little value concerning the mechanism of the decomposition and kinetic calculations. A correlation between non-isothermal and isothermal experiments, important for determination of the thermal stabilities of the compounds, is impossible without a knowledge of theg() function.

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Zusammenfassung Theoretische Umsatzkurven gegent für isotherme bzw gegen Temperatur für nichtisotherme Versuchsführung wurden berechnet in Abhängigkeit von den drei kinetischen Parametern AktivierungsenergieE, PräexponentialfaktorA und derg()-Funktion, die den Mechanismus der Zersetzung von Festkörpern beschreibt. Die Ergebnisse zeigen, dass Schlussfolgerungen, die nicht alle drei Parameter berücksichtigen, zu, Ergebnissen von geringer Aussagekraft bezüglich des Zersetzungsmechanismus und der kinetischen Interpretation führen. Eine Korrelation nicht-isothermer und isothermer Experimente, die für die Bestimmung der thermischen Stabilität der Verbindungen wichtig ist, ist ohne Kenntnis der Funktiong() unmöglich.

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- - : , - g(), . , , , . , g().

     

Infrared spectroscopic study of the interaction between furan and a vanadium oxide catalyst

The results of the infrared spectroscopic study of the interaction between furan and a vanadium oxide catalyst permit to suppose that the intermediates in furan oxidation are surface succinyl oxide and maleates.

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, , , - .

     

Deactivation of reforming catalysts. Coke formation on metallic and acidic centers

To check coke formation on metallic (Pt^o) and acidic (Al₃₊) centers of Pt/Al₂O₃ and Pt–Sn/Al₂O₃ catalysts, the application of IR spectroscopy of adsorbed CO for detecting Pt^o–CO (2070 cm^–1) and Al³⁺–CO (2190 cm^–1) bonds has been substantiated. Decrease in the number of active Pt^o and Al³⁺ centers is shown to correlate with that in the dehydrogenation rate of cyclohexane and in the isomerization rate of heptane, respectively.

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(Pt^o) (Al³⁺) Pt/Al₂O₃ Pt–Sn/Al₂O₃ - CO Pt^o–CO (2070 ^–1) Al³⁺–CO (2190 ^–1). , Pt^o , Al³⁺- .

     

Pt(alizarine)2 complex adsorbed on titanium dioxide as a sensitizer in photocatalytic evolution of dihydrogen

Pt(alizarine)₂ complex adsorbed on the surface of titanium dioxide has been found to cause spectral sensitization of the photocatalytic activity of TiO₂. Adsorption of the complex provides simultaneously sensitization of the photoprocess and catalysis of dark steps of dihydrogen formation.

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, Pt()₂ TiO₂. , , .

     

Catalysis of thiophene hydrogenolysis by bimetallic sulfide catalysts of different compositions

The activity of sulfide catalysts M_I/SiO₂, M_I/WS₂, (M_I,W)/SiO₂ and (Ni,M_II)/SiO₂ (M_I is a first row transition metal, and M_II=Nb, Mo, W or Re) in the thiophene hydrogenolysis reaction has been studied. Activities of mono- and bimetallic catalysts are found to change in the same manner depending upon the nature of M_I. The formation of a sulfide bimetallic species (SBMS) is suggested.

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M_I/SiO₂, M_I/WS₂, (M_I,W)/SiO₂ (Ni, M_II)/SiO₂, M_I — , M_II–Nb, Mo, W, Re. - M_I. .

     

Thermogravimetric study of the C + SiO2 reaction

The kinetics of the reaction of one-to-one molar mixtures of crystalline silica and carbon powder were studied using thermogravimetric analysis. The resulting kinetic data was evaluated using simple kinetic and mass transport models. A two-stage reaction mechanism consisting of three stoichiometric reactions can adequately be used to describe the global reaction phenomena. Both the first and second stages of reaction were found to be influenced by diffusion mass transfer within the reacting bed of solids.

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Zusammenfassung Mittels Thermogravimetrie wurde die Reaktionskinetik der Reaktion von kristallinem Siliziumdioxid und Kohlenstoffpulver im Molverhältnis 11 untersucht. Die kinetischen Angaben wurden mittels einfachen kinetischen und Stofftransportmodellen ausgewertet. Zu einer adäquaten Beschreibung der gesamten Reaktionserscheinung kann ein Zweischrittereaktionsmechanismus bestehend aus drei stöchiometrischen Reaktionen benutzt werden. Sowohl der erste als auch der zweite Reaktionsschritt wird durch diffusiven Stofftransport innerhalb des Reaktionsbettes beeinflußt.

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, 11. - . , , . , .

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This paper is based on the doctoral dissertation of the senior author.