Adsorption heats of acrolein and acrylic acid on promoted V?Mo?O catalysts

Adsorption heats of acrolein and acrylic acid on promoted V–Mo–O catalysts for selective oxidation of acrolein have been measured by the calorimetric technique. It has been established that modification changes the energy characteristics of the interaction of acrolein and acrylic acid with catalyst surface.

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- . , .

     

Radical addition of methyldichlorosilane to vinyl acetate

The GC-MS method was used to identify the addition products of methyldichlorosilane to vinyl acetate. Radiation-induced addition of methyldichlorosilane to vinyl acetate produces 2-methyldichlorosilylethyl ethyl ether. The reaction follows a radical-chain mechanism. The ratio of the rate constants of methyldichlorosilyl radical addition to C=C and C=O to vinyl acetate amounts to 0.4±0.1 (303 K).

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- . , - 2- . , C=C C=O 0,4±0,1.

     

Highly active supported palladium catalysts for selective hydrogenation of conjugated dienes into olefins

Products of the interaction of PdCl₂ with oxide-supported tertiary aliphatic amines were found to be extremely active in the selective hydrogenation of conjugated dienes into olefins. Promoting action of molecular oxygen on their activity has been established.

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, , . .

     

The relationship between the structures of Cu(II) complexes and their chemical transformations

The paper presents the results of a study of M ₂ ^I M ^II(SO₄)₂ compounds withM ^I= K, Rb, Cs or Tl, andM ^II=Cu or Ni, in the interval from room temperature to the melting temperature. All the compounds studied show endo- or exothermic excursions in their DTA curves, corresponding to phase transitions connected with colour changes of the compounds. For M ₂ ^I Cu(SO₄)₂, whereM ^I is K or Tl, several modifications could be prepared at laboratory temperature, probably distortion isomers. No modifications of this type could be prepared, however, for M ₂ ^I Ni(SO₄)₂ compounds.

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Zusammenfassung Die Ergebnisse einer Untersuchung von M ₂ ^I M ^II(SO₄)₂-Verbindungen Cs, Tl;M ^II=Cu, Ni) im Temperaturbereich von Raum- bis Schmelztemperatur werden beschrieben. Alle untersuchten Verbindungen zeigen in ihren DTA-Kurven mit Farbänderungen einhergehende, durch Phasenumwandlungen bedingte endo- und exotherme Peaks. Bei Laboratoriumstemperatur konnten verschiedene Modifikationen von M ₂ ^I Cu(SO₄)₂ (mitM ^I gleich K oder Tl) hergestellt werden, wobei es sich wahrscheinlich um Distorsionsisomere handelt. Keine Modifikationen dieses Typs konnten jedoch für M ₂ ^I Ni(SO₄)₂ erhalten werden.

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M ₂ ^I M ^II(SO₄)₂, ¹-, Rb, Cs Tl, aM ¹¹-Cu Ni, . - -, , . M ₂ ^I Cu(SO₄)₂, ¹- l, , , , . , M _i ² Ni(SO₄)₂ .

     

Kinetics and mechanism of oxidation of methanol by acid bromate

The kinetics of oxidation of methanol by bromate ion in hydrochloric acid medium has been investigated. A mechanism consistent with the experimental observations is suggested.

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. , .

     

An evolved gas analysis study of the reduction of nickel oxide by hydrogen

The reduction of NiO by H₂ was followed by conventional thermogravimetry and a new evolved gas analysis approach which follows the course of the reaction by measuring the H₂O content of the gas stream. Excellent correspondence is observed between the two techniques for simultaneous measurements. Heating rates between 0.5 and 10° min^–1 shift the temperature of the reaction as does changing the surface area of the NiO. These shifts are discussed in terms of the Neel temperature (T _N) of NiO and the thermal history of the sample. No correlation between reaction rate andT _N is observed under dynamic conditions. Preheating the sample in vacuum at 130° has a marked effect on shape of the DTG and EGA curves.

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Zusammenfassung Die Reduktion von NiO durch H₂ wurde durch konventionelle Thermogravimetrie und eine neue Analyse des entwickelten Gases untersucht, welche den Reaktions-ablauf durch Messung des H₂O-Gehalts des Gasstromes verfolgt. Eine ausgezeichnete Übereinstimmung beider Techniken wird bei simultanen Messungen beobachtet. Aufheizgeschwindig keiten zwischen 0.5 und 10° min^–1 verschieben die Temperatur der Reaktion und verändern die Oberfläche des NiO. Diese Verschiebungen werden auf Grund der Neel-Temperatur (T _N) des NiO und der thermischen Vergangenheit der Probe erörtert. Unter dynamischen Bedingungen wird keine Korrelation zwischen der Reaktionsgeschwindigkeit undT _N beobachtet. Das Vorwärmen der Probe im Vakuum bei 130° zeigt einen deutlichen Einfluß auf die Form der DTG und EGA Kurven.

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() ( ), H₂O . . 0.5 10° , . (T _N) . T _N. 130° - -.

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Presented at the 11th Annual NATAS Meeting, New Orleans, LA, Oct. 19–21, 1981.

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The authors are grateful to Mr. F. Schrey for measurements of the surface area.     

Explodator and bistability

It is shown that the Explodator model of the BZ reaction can show bistability in CSTR. Conditions for multistationarity are formulated.

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, - CSTR. .

     

Synergetic effects in combined catalytic oxidation-epoxidation of cyclohexene

Catalytic properties of a mechanical mixture of SiO₂-iminodiacetatechromium(III)+V₂O₅/SiO₂ have been studied. A synergetic effect in the combined catalytic oxidation-epoxidation of cyclohexene, observed at about 40 wt.% V₂O₅, is due to the autocatalytic character of the combined process.

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Cr(III), - . 40% . - . , .

     

Benzene hydrogenation on nickel/honeycomb catalysts

Monolithic supported nickel catalysts were investigated in benzene hydrogenation between 100 and 280 °C. The conversion of benzene to cyclohexane reaches a maximum around 210 °C with a maximum yield at a ratio p^oH₂/p^oBz=3. The experimental results and some kinetic aspects are discussed.

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100 280 °C. 210 °C p^oH₂/p^oB=3. .

     

Ammonia adsorption on the surface of Ni(II)-, Cu(II)-and Co(II)-phthalocyanine

Ammonia adsorption on the surface of Ni(II)–, Cu(II)- and Co(II)-phthalocyanine has been studied by means of reflection spectroscopy. Ammonia bonds to the metal ions in the surface layers of phthalocyanines preferably in octahedral coordination. In the case of Co(II)-phthalocyanine the trivalent state of cobalt is stabilized. Close similarity between coordination in liquid phase and adsorption on the surface is observed.

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- , , . , - . Co (II)- . .

     

Formaldehyde base catalysis by NaX zeolite

Reactions of formaldehyde to produce formose sugars at 95°C in aqueous solutions were studied over a trickle bed of NaX Zeolite spheres. When effluent pH was in the range of 5 to 7, a rapid irreversible catalyst deactivation from an initial 50% conversion occurred. The catalyst was destroyed in less than five hours by formic acid produced by the undesired Cannizzaro reaction. Incorporation of 0.86 mol NaOH/mol HCHO at 1.21 LHSV into the combined feed to the reactor maintained the effluent pH in the range of 10 to 12. Conversion of HCHO fell only from 95 to 92% in three hours, and selectively to Cannizzaro reaction was reduced to approximately 25%.

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, , 95°C , NaX. pH 5÷7, , 50%- . , 5 . . 0,86 NaOH 1 HCHO 1,21 pH 10÷12. HCHO 95 92%, 25%.

     

Thermal study of date kernels via TG and DTA

Thermal analyses was performed on Egyptian date kernels to assess the value of the products as possible sources of valuable compounds. It also furnished technical data necessary for determination of the optimum degree of temperature for the design and operation of units for the pyrolytic processing of date kernels.Two different sets of experiments were carried out, involving thermogravimetry (TG) and differential thermal analysis (DTA).The TG results revealed a purely kinetically controlled, first-order reaction. The activation energy and the Arrhenius constant were 8.17 kJ/mol and 0.0115 min^–1, respectively.The DTA results indicated the nature of the reactions involved in the pyrolysis and the corresponding products.

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Zusammenfassung Ägyptische Dattelkerne wurden thermisch untersucht, um die Möglickkeit einer Verwendung als Quellen für wertvolle Verbindungen zu ergründen. Außerdem wurden technische Daten ermittelt, die zur Festlegung der Optimumtemperatur für die Gestaltung und den Betrieb der Geräte zur pyrolytischen Behandlung von Dattelkernen benötigt werden. Es wurden zwei Versuchsreihen durchgeführt, bei denen einerseits Thermogravimetrie (TG) und andererseits Differentialthermoanalyse (DTA) Anwendung fand. Die TG Ergebnisse eröffnen eine rein kinetisch kontrollierte Reaktion erster Ordnung. Die Aktivierungsenergie und die Arrheniuskonstante betrugen 8,17 kJ/mol bzw. 0,0115 min^–1. DTA Resultate gaben Auskunft über den Charakter und Reaktionsprodukte der Reaktionen bei der Pyrolyse.

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, , . , . , . . , , 8,17 -^–1 0,0115 ^–1. , .

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The authors wish to express their sincere appreciation to Prof. Dr. S. G. Serag El-Din, Professor of the Chemical Engineering Department, Cairo University, and Dr. H. H. Abou El-Naga, Manager of Analytical and Research Centre, Misr Petroleum Company, for their sincere and helpful co-operation.     

Benzoylation of toluene by benzoic anhydride on solid superacid catalysts

Acylation was carried out by using two kinds of solid superacid catalyst, SO ₄ ^2– /ZrO₂ and Nafion-H. The reaction was expressed by reversible first-second order kinetics. The SO ₄ ^2– /ZrO₂ catalyst was superior to Nafion-H and could be reactivated by treating with sulfuric acid.

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SO ₄ ^2– /ZrO₂ Nafion-H. - . SO ₄ ^2– /ZrO₂ , Nafion-H .

     

Comparative selectivities of two copper-based catalysts: Mixed Cu?Cr and Cu?Al oxides for allylic alcohol reactions in the presence of molecular hydrogen

In the presence of mixed copper-chromium (aluminium) oxide, allylic alcohols react with molecular hydrogen and lead to several primary products. This is due to the simultaneous presence of two active sites in the mixed oxides. Copper species (Cu⁺) are responsible for hydrogenation (HYD) and the chromium (Cr³⁺) (aluminium [Al³⁺]) species for the isomerization (I) and the hydrodeoxygenation (HDO) reactions. However, the stronger acidic character of Al³⁺, compared with Cr³⁺, entails some differences evidenced by the HYD/(I+HDO) and HDO/I ratios.

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- () , . . (Cu⁺ (), (Cr³⁺) ( Al³⁺) (), (). , Al³⁺ Cr³⁺ , /(+) /.

     

Influence of the particle size of metal in the hydrogenolysis of n-butane on carbon supported iron catalysts

The hydrogenolysis of n-butane on different carbon supported iron catalysts has been studied. Changes in activity, product distribution, apparent activation energy and frequency factor were found to be a function of particle size. This behavior is explained as a change in the reaction mechanism, which also leads to the isomerization of n-butane in the case of catalysts with higher dispersity.

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- . , , . , - .

     

Kinetic study of the permanganate oxidation of DL-valine in acidic media

The kinetics of permanganic oxidation of DL-valine in a concentrated sulfuric acid medium (3.0–5.0 M) has been studied by spectrophotometry. The rate law found shows that the reaction is autocatalyzed by Mn(II) ions. The influence of the reagent and Mn(II) concentrations and acidity of the medium has been analyzed. A reaction mechanism is proposed according to the experimental results.

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DL- (3,0–5,0 M) . Mn(II). Mn(II) . .

     

The danger of inadvertent heterogeneous catalysis when studying solution kinetics

Reactions in solution can be heterogeneously catalyzed not only by conductance or e. m. f. electrodes but also by precipitates formed during the titration of qliquots. Attempts to follow a Menschutkin reaction by Volhard titrations revealed serious errors caused by the catalysis of a side reaction by insoluble silver salts.

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Investigation of the interaction between zinc oxide and phosgene

It has been shown that in the interaction of zinc oxide and phosgene, the most active are the samples having oxygen vacancies. A mechanism for this process is suggested.

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, , . .

     

Kinetics of propylene oxidation in the region of negative temperature coefficients of the rate

Kinetic regularities in the consumption of initial reactants and the accumulation of propylene oxidation products has been studied in the region of negative temperature coefficients of the maximum reaction rate (T=648–723 K). It has been revealed that for prolynene-enriched mixtures (C₃H₆:O₂=3:1) at P-20.66 kPa, the reaction rate is practically independent of the temperature, whereas for poor mixtures (C₃H₆:O₂=1:5) it decreases with increasing temperature.

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a (T=648–723K). , (C₃H₆:O₂=3:1) P=20,66 , (C₃H₆:O₂=1:5) .

     

Activation of hydrocarbons in the oxidative dimerization of methane over alkaline earth metals

Oxidative dimerization of methane over alkaline earth metal oxides and phosphates has been studied. The ratedetermining step is heterolytic C–H bond dissociation of methane on surface basic sites of the catalysts.

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- . , C–H .