Nonsteady-state oxidation of propylene on supported silver catalysts

Nonsteady-state epoxidation of propylene on silver has been studied to establish the reason for the low catalyst activity and selectivity that appear to be due to side reactions of the formation of hydrogen-deficient deposits.

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Studies on the catalytic oxidation of propylene on ferric molybdate

Ferric molybdate is less selective in the partial oxidation of propylene than bismuth molybdate. Its catalytic behavior is similar to that observed on other transition metal molybdates. The intrafacial nature of the reaction is established through kinetic and adsorption measurements.

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The effect of ethanol on the catalytic oxidation of methanol on silver

Thermal desorption, radioactive indicators, and a kinetic method involving frozen radicals were used to study the catalytic oxidation of methanol in the presence of ethanol on silver. The increase in the yield of aldehydes in the combined oxidation of these alcohols on silver is related to a change in the nature of the adsorption and homogeneous steps of this reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1174–1176, May, 1990.     

Gas-chromatographic study of the retention of components of the reaction of the catalytic oxidation of propylene on porous polymers

The gas-chromatographic retention of oxygen, carbon dioxide, propane, propylene, water, propylene oxide, acrolein, acetone, and acetaldehyde on polar and nonpolar adsorbents was studied. A procedure was proposed for the gas-chromatographic determination of gaseous and liquid components of the reaction of the catalytic oxidation of propylene using one column.     

Prediction of the catalytic action of oxide catalysts in allyl oxidation of propylene

Concepts are described according to which an efficient catalyst of propylene oxidation to acrolein should contain oxygen of two types — nucleophilic and electrophilic. This can be ensured by a combination of an amphoteric oxide and an oxide of a high-valent element. The distribution of the products of allyl oxidation also depends on the collective properties of a catalyst.

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Modifying action of carbon dioxide in catalytic oxidation of ethylene on silver

Carbon dioxide exerts a strong inhibitory effect on oxygen adsorption and complete oxidation of ethylene on silver but has little effect on the rate of ethylene oxidation to ethylene oxide.

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Influence of silver dispersity on its specific catalytic activity in ethylene oxidation

Specific catalytic activity for massive (powders and films) and supported (Ag/SiO₂) silver catalysts have been studied in ethylene oxidation. It has been found to be approximately constant for metal particles whose size is above 30 nm.

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Bi-Mo-Nb复合氧化物的结构与对丙烯氧化的催化活性

本文用XRD, IR, Raman, SEM和ESR等方法研究了系列氧化物Bi~2Mo~3-3XNb~2xO~12-4X(X=0.00, 0.02, 0.05, 0.10, 0.15, 0.20, 0.25) 的结构和对丙烯氧化的催化活性。结果表明, 在X<0.25范围内, 催化剂基本保持典型的α-Bi~2Mo~3O~12结构, 少量Nb^5+的掺杂, 可取代晶格中的Mo^6+, 产生氧空位,无序分布的氧空位的浓度先随X值的增加而增加, 当X=0.15时达到最大值, 催化剂对丙烯氧化的催化活性与这种氧空位的浓度成正比, 反应遵循Redox机理。     

Molecular orbital study of anthracene photo-oxidation

The light stimulated interaction of anthracene and oxygen was studied by the MO (molecular orbital) method. Using the principle of orbital symmetry conservation, the interactions anthracene-oxygen in the ground and first excited states and in various geometric arrangements were classified as symmetry allowed or forbidden. The results indicate that the photo-oxidation of anthracene is catalysed by transition metals.     

Molecular orbital study of cobalt-oxygen interaction

A modified CNDO-UHF procedure is used to discuss cobalt-oxygen interactions in CoO and [CoO₂]^q (q = −1, 0, +1, +2, +3). The cobalt orbitals that contribute most to the bonding in these systems are the 4s and 3d orbitals with relatively little contribution from the 4p orbitals. The ground state of CoO is calculated to be a²π with a π hole localized in the 3d orbitals. The dioxygen activation in the CoO₂^q systems is described in terms of the local electron configuration of the O₂(π) antibonding orbitals together with the charge, Mulliken bond order and bond length of coordinated O₂. The distortion properties are described in terms of the thermodynamic stability difference and the energy barrier for the peroxo to superoxo transformation. The CoO₂ systems studied were classified into two groups depending on the degree of dioxygen activation and distortion properties. The lowest activation energy calculated to break the O-O bond corresponded to 69 kcal mol⁻¹, suggesting that dissociative chemisorption of O¹ on a single Co atom is not a likely process.     

Molecular orbital study on the active center of lactate dehydrogenase

In the active site of lactate dehydrogenase important roles are given to aminoacids His195 and Arg171. The coenzyme nicotinamide adenine dinucleotide (NAD) is required in oxidized form (NAD⁺) for the enzymatic oxidation of the substrate L-lactate. Molecular orbital methods CNDO /2, INDO , and EHT were applied to the study of the model of active center of lactate dehydrogenase. An energetically preferred arrangement of the models of His195, Arg171, NAD⁺, and lactate was found. Possible biochemical aspects of these arrangements are discussed.     

The heterogeneous catalytic oxidation of propylene in the presence of singlet oxygen in the reaction mixture

Three methods for the introduction of singlet oxygen into the reaction mixture were tested, including thermal generation of singlet oxygen on the catalyst itself, the introduction of singlet oxygen from an external source, and photogeneration of singlet oxygen on the catalyst. Zeolites with admixtures of Mo, Bi, V, and Ni and SiO₂ with deposited Mo, V, and Bi were used. Common to all reactions was an increase in the yield of deep oxidation products in the presence of singlet oxygen. A sharp increase in the yield of mild oxidation products was observed in the oxidation of propylene on a Bi/SiO₂ catalyst. The generation of singlet oxygen under irradiation at 240–260 nm was found to cause deep oxidation only. Mild oxidation products could only form under the action of total mercury lamp light.     

Effect of iodine-containing promoter on the catalytic activity of silver in the course of ethylene glycol oxidation

Surface morphology and catalytic properties of electrolytic silver crystals in partial oxidation of ethylene glycol into glyoxal were studied.     

Dependence of the catalytic properties of cobalt molybdate in propylene oxidation on the surface reduction and oxygen bond energy

The dependences of the tate of partial propylene oxidation and of oxygen bond energy on the degree of cobalt molybdate reduction has been investigated by pulse and caloremetric methods. It has been found that upon reduction, the selectivity to acrolein and the oxygen bond energy increase. The steady state under the conditions examined is characterized by 22% surface reduction and the presence of uniform oxygen with a bond energy of about 85 kcal/mol.

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Molecular orbital study of the conformational properties of phenothiazines

The conformation of the side-chain attached to N₁₀ of the phenothiazine ring system is investigated by the molecular orbital PCILO method. It is shown that this conformation depends on the folding of the ring along the S-N central axis. The theoretical results are in very satisfactory agreement with the available X-ray crystallographic data on chlorpromazine, thiethylperazine, diethazine and mopazine.

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Zusammenfassung Die Konformation der Seitenkette am N₁₀ des Phenothiazinringsystems wird mit der PCILO-Methode untersucht. Es wird gezeigt, daß diese Konformation von der Stellung des Rings entlang der zentralen S-N Achse abhängt. Die theoretischen Ergebnisse stimmen sehr gut mit den vorhandenen kristallographischen Daten von Chlorpromazin, Thiethylperazin, Diethazin und Mipazin überein.

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Résumé La conformation de la chaîne latérale partant du N₁₀ du noyau phenothiazinique est étudiée par la méthode PCILO. Les résultats montrent que cette conformation dépend notablement du degré de pliage de la molécule le long de l'axe S-N central. Les prédictions théoriques sont en excellent accord avec les données expérimentales provenant de l'étude cristallographique de la chlorpromazine, la thiethylperazine, la diethazine et la mopazine.

     

Molecular orbital study of molecular nitrogen fixation

The model systems of molecular nitrogen fixation [N₂ + H]?, [N₂ + H]⁺, [N₂ + H]^?, [N₂ + H₂], [N₂ + H₂]⁺, and [N₂ + H₂]^? were studied by the semiempirical INDO method. The study was based on the formal analogy between the catalytic reactions and the photochemical, radical, and ionic reactions on the other side. Symmetrical and donor-acceptor properties of necessary catalytic systems were proposed using the dependence of energy characteristics and electron structure on reaction coordinate. On the basis of this MO study we have proposed the appropriate symmetry types of catalysts for each of acceptable models of nitrogen fixation. For one of the proposed systems there was realised a model MO computation with explicit inclusion of atoms of transition metals (Fe, V).     

Kinetic fluorimetric determination of silver by its catalytic effect on the oxidation of pyridoxal nicotinylhydrazone by potassium peroxidisulphate

Summary The oxidation of pyridoxal nicotinylhydrazone by potassium peroxidisulphate, catalysed by traces of silver(I), has been studied and used for the kinetic determination of this ion. The reaction is followed spectrofluorimetrically by measuring the rate of change in the fluorescence intensity (_ex 365, _em 450 nm). The calibration graph is linear in the silver range 60–720 ng/ml. The variables affecting the method have been optimized and the tolerance levels of foreign ions determined. The solvent extraction method with dithizone is used to eliminate interferences in the determination of silver in synthetic samples.

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Kinetisch-fluorimetrische Bestimmung von Silber auf der Grundlage seiner katalytischen Wirkung bei der Oxydation von Pyridoxal-nikotinylhydrazon durch Kaliumperoxydisulfat

Zusammenfassung Die durch Silberspuren katalysierte Oxydation wurde untersucht und für deren kinetische Bestimmung verwendet. Die Reaktion wird spektrofluorimetrisch ausgewertet, indem man das Ausmaß der Veränderung der Fluoreszenzintensität (_ex=365, _em=450 nm) bestimmt. Die Eichkurve verläuft für 60–720 ng Ag/ml linear. Die das Verfahren beeinflussenden Reaktionsbedingungen wurden optimiert und die Toleranzgrenzen fremder Ionen bestimmt. Störfaktoren bei der Silberbestimmung in synthetischen Proben wurden durch Extraktion mit Dithizon beseitigt.

     

Molecular mechanics study of zirconocenium catalyzed isospecific polymerization of propylene

Stereocontrol energy (ΔE⁰) is investigated as a measure of enantioselectivity of ansa-zircoocenium catalyst in propylene polymerization; it was calculated with MM2 (molecular mechanics) force field using π complex (°C) and transition state (TS) geometries obtained by ab initio molecular orbital methods. Both rac-ethylenebis (1-η⁵-indenyl) - ( 1 ) and rac-ethylenebis (1-η⁵-4,5,7,8-tetrahydroindenyl) ( 2 ) zirconocenium species are isospecific in either the π-complexes or the transition states. The stereoselectivity is greater if there is α-agostic interaction; it is lowered in the cases of β and γ agostic interactions. The ¹³C-NMR steric pentad distribution indicates the poly(propylene) to be much less stereoregular than that predicted by ΔE⁰. Following the occurrence of a regiochemical insertion error, the addition of another monomer via any mode is prohibitively unfavorable. The catalyst suffers loss of stereospecificity as temperature of polymerization increases. Insertion via transition states involving different agostic interactions could be one explanation for the observed loss. © 1995 John Wiley & Sons, Inc.     

Epoxidation of propylene over silver sponge catalysts

The oxidation of propylene with air on silver catalysts of macropore structure has been studied both in a flow and an open recirculation reactor. Under strictly isothermal conditions, avoiding the local overheating of the catalyst, propylene oxide was produced with a selectivity as high as about 50%.

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