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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, , , .

     

Reaction routes for hydrogenation of acetylene-ethylene mixtures using a double labelling method

Hydrogenation of C₂H₂:C₂H₄ mixtures using a double labelling method has been studied. Both in the presence and absence of ethylene the rate of acetylene hydrogenation on its partial pressure proceeds through a maximum and the rate is higher when ethylene is added. Using¹⁴C–C₂H₂ it was demonstrated that at low acetylene partial pressures the main route of acetylene hydrogenation was the formation of ethane and C₄ hydrocarbons. Using¹⁴C–C₂H₄ it was also shown that at certain acetylene partial pressures the formation of ethane from ethylene completely ceased. Different surface species are suggested and a reaction mechanism is proposed.

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C₂H₂:C₂H₄, . , , . C¹⁴–C₂H₂, , C₄. C¹⁴–C₂H₄, , . .

     

Methanol oxidation on copper-oxide catalysts

Complete oxidation of methanol on CuO and CuO/Al₂O₃ catalysts has been studied. The main kinetic parameters have been determined. A possible mechanism and the nature of the rate-determining step are discussed.

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CuO CuO/Al₂O₃. . .

     

Vapor phase oxidation of methylpyridines on zeolite catalysts

It has been established that zeolites containing Pd and Cu ions catalyze the vapor phase oxidation of methylpyridines. In oxidation of 2-methylpyridine on PdCuNa-mordenite at 375 °C the yield of 2-pyridinecarbaldehyde is 40 % of its theoretical values.

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, , Pd Cu, . 2- PdCuNa- 2- 375°C 40% .

     

Interaction and exchange of propene with OH groups of HX zeolites

The interaction of C₃H₆ and the exchange of C₃D₆ with a HX zeolite dehydroxylated to various degrees was studied at the temperature of the IR beam and at 300 °C. The exchange was followed by the analysis of the gas phase (MS) and the solid phase (IR). The properties of HX and HY zeolites were compared.

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C₃H₆ C₃D₆ 300 °C HX . () () . HX HY .

     

Improved deactivation profile observed for Pt/H-chabazites and Pt/H-Y zeolite

The presence of small platinum crystallites in the framework of protonic offretite, erionite and Y-zeolite causes an improved deactivation profile during n-butane conversion and reflects a stronger shape-selectivity compared to the analogous behavior of the monofuctional (protonic) zeolites.

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, - - () .

     

Nature of the adsorption centers of oxide catalysts and the direction of propylene conversion

According to the analysis of spectral data on adsorbed propylene forms, an attempt has been made to establish a relationship between the nature of olefin adsorption center, the adsorbed form during precatalysis and the direction of conversion.

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, .

     

Mechanism of catalysis and factors responsible for oxide catalyst activity in deep oxidation reactions

A general scheme for the deep oxidation mechanism on oxide catalysts including stepwise and concerted mechanisms as well as their mutual transformations is suggested. The principal factor responsible for the activity in the concerted mechanism region is the rate of oxygen binding. For the stepwise mechanism the main factor is the rate of catalyst interaction with oxidizable reactant.

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, . , . .

     

Dispersity and reducibility of the molybdenum oxide phase in SiO2, SiO2?Al2O3 and γ-Al2O3 supported molybdena catalysts

XRD, isothermal and temperature-programmed reduction (TPR) experiments were carried out with SiO₂, SiO₂–Al₂O₃ and -Al₂O₃ supported catalysts. Molybdena is in a more disperse state on supports containing more alumina and it is more reducible on SiO₂–Al₂O₃ than on SiO₂ or -Al₂O₃. TPR curves were shown to reflect connections between reduction kinetics and dispersity.

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-, , SiO₂, SiO₂–Al₂O₃ -Al₂O₃. , , SiO₂–Al₂O₃ SiO₂ -Al₂O₃. .

     

The thermoanalytical determination of deactivation types of cation-exchanger catalyst's

The dependence of the thermal decomposition of a cation-exchanger catalyst on its deactivation type has been ascertained, and thermal analysis has been suggested as a diagnostic method for the determination of the condition of such a catalyst.

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Zusammenfassung Die Abhängigkeit der thermischen Zersetzung eines Kationaustauscher-Katalysators von seinem Inaktivierungstyp wurde bewiesen und die Thermoanalyse als diagnostische Methods für die Bestimmung des Zustandes eines solchen Katalysators vorgeschlagen.

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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)- - , .

     

Decomposition of cumene hydroperoxide in the presence of 1,5,9-cyclododecatriene catalyzed by MoO2 (ACAC)2: A kinetic study

The kinetics of decomposition of cumene hydroperoxide in the presence of 1,5,9-cyclododecatriene, catalyzed by MoO₂(acac)₂ has been studied at constant temperature (303 K) and at atmospheric pressure. The influence of substrate, catalyst and product concentrations on the rate has been established. The rate and equilibrium constants have been calculated.

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1,5,9-. MoO₂(acac)₂. , .

     

Thermal degradation of some polymers based on ethylene glycol dimethacrylate

Thermogravimetric analysis and pyrolysis in combination with gas chromatography were used to study the thermal behaviour of some cross-linked polymers of ethylene glycol dimethacrylate. The investigated polymers show a complex thermal degradation mechanism. The complexity of the reaction increases together with increase of the ethylene glycol chain in the macromolecule and with increase of the pyrolysis temperature. At low temperature, the thermal decomposition products of the analyzed polymers are mainly the constituent monomers. At high temperatures, besides the monomer, other decomposition products are formed as a result of thermal cracking reactions, i.e. secondary reactions of decomposition and recombination.

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Zusammenfassung Zur Untersuchung des thermischen Verhaltens einiger quervernetzter Polymere auf Äthylenglykoldimetacrylatbasis wurden thermogravimetrische Analyse und Pyrolyse in Zusammenhang mit der Gaschromatographie angewendet. Die untersuchten Polymere zeigten einen komplexen thermischen Zersetzungsmechanismus. Die Komplexizität der Reaktion nimmt mit Zunahme der Anzahl der Äthylenglykolketten im Makromolekül und mit Zunahme der Pyrolysentemperatur gleichermaßen zu. Bei niedrigeren Temperaturen stellen die Hauptzerfallsprodukte der analysierten Polymere hauptsächlich deren Monomere dar. Bei höheren Temperaturen werden als Ergebnis thermischer Krackreaktionen, z. B. sekundäre Zersetzungs- und Rekombinationsreaktionen, neben den Monomeren auch andere Zersetzungsprodukte gebildet.

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. . . . , , , .

     

Catalytic activity of high-silicon TsVK and Y type zeolites

Conversion of paraffins on TsVK and Y zeolites follow a similar mechanism yielding the same intermediates. Low selectivity of Y zeolites with respect to aromatic hydrocarbons is attributed to the strong adsorption of these hydrocarbons on zeolites. It is assumed that the centers of strong adsorption are Al³⁺ ions in cationic positions in zeolite.

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, . . , Al³⁺ .

     

Electron microscopic and chemisorption studies of the dispersity of supported rhodium catalysts of various compositions

The dispersity and size distribution of metal particles in mono- and bimetallic rhodiumcontaining catalysts prepared via decomposition of SiO₂- and Al₂O₃-supported complexes and impregnation of the support by inorganic metal compounds have been studied.

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, SiO₂ Al₂O₃ .

     

Effect of free phosphine on the reactivity of phosphine-containing rhodium(I) complexes

The photolysis products of SO₂-pentane-NO mixtures are N₂O, H₂O and a compound designated as RNO. Kinetic data obtained by OC method confirm the previously proposed scheme of photolysis. Also studied was the photolysis of SO₂, NO and cyclohexane mixtures. From comparison of spectral characteristics of RNO and its analog 2-methyl-2-nitrosopropane, the probable structure of RNO is suggested.

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SO₂--NO N₂O, H₂O , RNO. , , . SO₂ NO . RNO 2--2- RNO.

     

Catalytic isomerization of olefins on BeO, I

The catalytic activity of BeO for the double bond shift of 1-pentene has been investigated. The maximum activity was exhibited by samples calcined at 1173 K. The effect of pyridine, CO₂ and CCl₄ on the activity was also studied. Lewis acid-base site pairs appear to be active for the isomerization.

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BeO 1- . , 1173 . , CO₂ CCl₄ . - .

     

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, , . , .

     

M?ssbauer spectroscopic studies of the state of Pt?Sn/Al2O3 catalyst for hydrocarbon conversion

Mössbauer spectroscopic studies of the state of Pt–Sn catalyst for hydrocarbon conversion supported on prechlorinated -Al₂O₃ indicate that, unlike nonchlorinated Al₂O₃, this system is much more reduced and besides Pt₃Sn–PtSn₂, its surface contains sigfificant amounts of Sn(II) and Sn(IV) chlorides bonded to the surface.

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Pt–Sn , -Al₂O₃. , Al₂O₃, Pt–Sn Pt₃Sn–PtSn₂ Sn(II) (IV), .

     

Reactivity of oxidized substances and its correlation with catalyst properties in deep oxidation reactions

In terms of the donor-acceptor interaction concept /1/ the relative reactivity (RR) of organic and inorganic compounds and its correlation with catalyst properties in deep oxidation reactions are treated. RR and relative activity of the catalysts are shown to change depending on the predominant character (acceptor or donor) of reactant-catalyst interaction.

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- /1/ (OPC) . , OPC .