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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. , .

     

A study of thermal preparation OF c-Mn2P4O12

With the application of thermogravimetry under quasi-isothermal-isobaric conditions, the reaction course of the calcination of Mn(H₂PO₄ · H₂O to give dimanganese cyclotetraphosphate has been studied. Isothermal calcination was also carried out in an electric furnace at various temperatures (200 min). The reaction products were analyzed by chromatography, IR and NMR spectrocopy, and X-ray diffraction analysis. The compositions of the calcinates were determined through extraction with various inorganic and organic solvents.

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Zusammenfassung Der Verlauf der Dimangan-cyclotetraphosphat ergebenden Kalzinierung von Mn(H₂PO₄)₂ · H₂O wurde thermogravimetrisch unter quasi-isothermen-isobaren Bedingungen untersucht. Isotherme Kalzinierung wurde auch im elektrischen Ofen (200 min) bei verschiedenen Temperaturen ausgeführt. Die Reaktionsprodukte wurden chromatographisch, IR- und NMR-spektroskopisch sowie röntgendiffraktometrisch analysiert. Die Zusammensetzung der kalzinierten Produkte wurde via Extraktion mit verschiedenen anorganischen und organischen Lösungsmitteln bestimmt.

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Mn(H₂PO₄ · H₂O. . . - , - - . .

     

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)- . .

     

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. .

     

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 .

     

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.     

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) . .

     

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 .

     

Combined use of calorimetric and adsorption kinetic methods for the study of the mechanisms of catalytic processes

Consideration is given to the main results obtained in studies based on calorimetric methods at high temperatures (above room temperature) of the following aspects of the mechanisms of catalytic and sorption processes on powder catalysts: 1) relation between chemisorption and dissolution of gases in the subsurface layers of solids; 2) influence of surface-adsorbed substance on the adsorption of another substance from the gas phase; 3) nature of intermediate species formed during catalytic processes on the catalyst surface. Results are presented of the application of calorimetric methods to measuring the enthalpy change of polymerization in a dry system: gaseous monomer — solid catalyst — solid polymer, and to investigating the mechanisms of such processes. Anomalous solubility of gases in the subsurface layers of solids has been shown to be significant for the mechanism of nucleation during phase transitions in solids.

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Zusamenfassung Die wichtigsten Ergebnisse der auf kalorimetrischen Methoden bei hohen Temperaturen (über Raumtemperatur) beruhenden Untersuchungen der Mechanismen von katalytischen und Sorptionsprozessen an pulverförmigen Katalysatoren werden behandelt: 1) Zusammenhang zwischen Chemisorption und Lösung von Gasen in den Schichten von Festkörpern unterhalb der Oberfläche; 2) Einfluß der an der Oberfläche adsorbierten Substanz auf die Adsorption einer anderen Substanz aus der Gasphase; 3) Beschaffenheit der während des katalytischen Vorgangs an der Katalysator-Oberfläche entstandenen Intermediärteilchen.Ergebnisse der Anwendung der kalorimetrischen Methode zur Messung der Enthalpie-Änderungen der Polymerisation im trockenen System: gasförmiges Monomer — fester Katalysator — festes Polymer und zur Untersuchung der Mechanismen solcher Vorgänge werden mitgeteilt. Es wurde gezeigt, daß die anomale Löslichkeit von Gasen in den Schichten unterhalb der Oberfläche von Festkörpern für den Mechanismus der Keimbildung während des Phasenüberganges in Festkörpern von Bedeutung ist.

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Résumé On examine les principaux résultats obtenus lors des études effectuées à l'aide de méthodes calorimétriques à hautes températures (au-dessus de la température ambiante), sous les aspects suivants du mécanisme des réactions catalytiques et de Sorption sur des catalyseurs en poudre: 1) relation entre la chimisorption et la dissolution des gaz dans les sous-couches superficielles des solides, 2) influence d'une substance adsorbée en surface sur l'adsorption d'une autre substance de la phase gazeuse, 3) nature des particules intermédiaires formées lors de la réaction catalytique à la surface du catalyseur. Les résultats de l'application de la méthode calorimétrique à la mesure des variations d'enthalpie au cours de la polymérisation en système «sec» sont présentés: monomère gazeux — catalyseur solide — polymère solide, ainsi que ceux relatifs à l'étude du mécanisme de ces réactions. On montre que la solubilité anormale des gaz dans les sous-couches superficielles des solides joue un rôle important sur le mécanisme de la nucléation lors des transitions de phases dans les solides.

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, ( ) : 1) : 2) ; 3) , . » « — . .

     

Testing the photocatalytic activity of cyanogen-and thiocyanogen-based inorganic polymers

The photocatalytic properties of some cyanogen-and thiocyanogen-based inorganic polymers, such as paracyanogens containing different metals (Hg, Ag, Cu), polythiocyanogens of different iodine contents, polycyanogen and poly (cyanogenthiocyanate), have been tested in two systems. Cu-containing paracyanogen and the iodine-poor polythiocyanogens catalyze the photoreduction of methylviologen under visible light, furthermore the Cu-containing paracyanogen catalyzes the photoreduction of water to hydrogen under UV irradiation.

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, , , , (Hg, Ag, Cu), , (), . , , , , , , -.

     

Iron-chromium catalysts in the conversion of methanol with water vapor

The catalytic properties of iron-chromium catalysts in methanol conversion with water vapor were studied. The activity of the catalysts is shown to depend on the method of preparation and their Cr₂O₃ content. The Cr₂O₃ admixture is found to play the role of a stabilizer of the active surface.

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. Cr₂O₃. Cr₂O₃ .

     

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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, , . .

     

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 .

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

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, - , , () . .

     

Oxide catalyst for the combustion of organic compounds in industrial waste gases

An oxide catalyst for combustion of organic compounds in exhaust gases from plastics plants has been developed. As the active catalyst phase, cupric cobaltate is supported on -Al₂O₃ carrier. Its catalytic activity in the test reaction of propylene oxidation was compared with that of the platinum catalyst used so far. The results show that the new catalyst can replace platinum in the above process.

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. (II) -Al₂O₃. . , .

     

Ethylene oxidation by lithium nitrate in the presence of palladium acetate in acetic acid

Data are reported on variations of the gas phase volume and product accumulation in ethylene oxidation by lithium nitrate in acetic acid solutions, catalyzed by palladium acetate. An assumption is made on the routes of nitrate ion reduction.

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, , . -.

     

Modification of catalytic properties of silica-supported rhodium

A sharp change in the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion has been found for catalysts prepared via interaction between Rh(CO)₂Cl₂ and silica modified by Sn, Pb, Mo and W ions.

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, Rh(CO)₂Cl₂ , Sn, Pb, Mo W, , , -.

     

Study of the steps of acrolein oxidation over a vanadium-molybdenum catalyst

Acrolein is oxidized to acrylic acid over a V–Mo catalyst by lattice oxygen, while the formation of CO₂ also involves gas phase oxygen. The steady state of catalyst reduction is about 5% monolayer and is characterized by an oxygen binding energy of 61 kcal/mol.

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V–Mo- , CO₂ . 5% 61 /.