Determination of hydroxyl groups and/or water on the surface of oxide catalysts by a pulse chromatographic method

A pulse chromatographic method based on the reaction of gaseous dimethylzinc tetrahydrofura nate was developed for the determination of surface hydroxyl groups and/or adsorbed water in solid porous materials. The procedure is rapid and gives results comparable to other methods. Some heterogeneous catalysts and supports have been analyzed.

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, , / , . , . .

     

A Thermal study of the precipitates formed in ammonia neutralization of acidic solutions of dissolved phlogopite

The precipitates containing mainly iron, aluminium and magnesium hydroxides, obtained from phlogopite dissolved in nitric acid by means of the neutralization procedure with ammonia, have been investigated by thermal analysis (TG, DTG and DTA). According to the present study, which is part of a larger investigation into the chemical utilization of Finnish mica minerals, the formation of solid solutions between iron and aluminium hydroxides in silt increases with an increasing neutralization temperature. Nitrogen exists mainly in the form of nitrate in silts, and magnesium forms mixed hydroxides with aluminium, which causes a separation between the iron hydroxide and magnesium aluminium hydroxide phases.

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Zusammenfassung Die von in Salpetersäure gelöstem Phlogopit durch Neutralisierung mit Ammoniak erhaltenen, hauptsächlich Eisen-, Aluminium- und Magnesiumhydroxid enthaltenden Niederschläge wurden thermoanalytisch (TG, DTG und DTA) untersucht. In der vorliegenden Arbeit, die Teil einer grossangelegten Untersuchung zur chemischen Nutzung finnischer Glimmermineralien ist, wird gezeigt, dass die Bildung fester Lösungen von Eisen- und Aluminiumhydroxiden in Schluff mit zunehmender Neutralisationstemperatur ansteigt. Stickstoff kommt in Schluff hauptsächlich in Form von Nitraten vor, und Magnesium bildet Mischhydroxide mit Aluminium, was eine Trennung der Eisenhydroxidphase von der Magnesium-Aluminium-Hydroxidphase bewirkt.

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, , , . . , , . , , , , .

     

Oxidizing supported reagents, III. Oxidation of alcohols by new supported K2Cr2O7 reagents

Several new supported K₂Cr₂O₇ reagents are used in the oxidation of secondary alcohols. The influence of the number of active sites and the nature of solid support on the yield is discussed. The influence of the structure of alcohol on the yield of ketone is analyzed.

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K₂Cr₂O₇ . . .

     

Catalytic conversion of dimethylsulfide to methylmercaptan

The effect of reaction conditions on the methylmercaptan formation from dimethylsulfide in H₂S catalyzed by -Al₂O₃ has been studied. The reaction is first order with respect to dimethylsulfide. It has been revealed that the maximum activity in this reaction is observed for the catalysts whose surface contains a large number of aprotonic acid centers and moderate-strength basic sites.

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-Al₂O₃. , . . , , .

     

Phase equilibria in the V2O5-FeVMoO7 system

The progress of the reactions of water with brownmillerite (C₄AF⁺) and its mixtures with gypsum (C¯SH₂) and calcium sulphoaluminate (C₄A₃¯S) was investigated by means of calorimetric measurements in situ and X-ray diffractometry to determine the reaction heat and the conversion of the solid reactants as functions of time up to 50 h. The rapid reaction of C₄AF with water and the modifying effect of sulphates on the composition of the hydrated phases were confirmed. The presence of sulphates causes the induction period during the reactions of aluminium and iron-containing clinker phases with water. These phenomena are important technologically too, especially in cements with increased contents of C₄AF and of sulphate-yielding phases (C¯SH₂ and C₄A₃¯S).

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Zusammenfassung Der Verlauf der Hydratation von Brownmillerit Ca₄AF^* bzw. seinen Mischungen mit Gips (C¯SH₂) und Calcium-sulfat-aluminat (C₄A₃¯S) wurde durch kalorimetrische Messungen in situ und Röntgendiffraktometrie verfolgt, um die Abhängigkeit der Reaktionswärme und des Umsatzes der festen Reaktanden von der Zeit (bis 50 h) zu bestimmen. Die schnelle Reaktion von C₄AF mit Wasser und der modifizierende Effekt der Sulfate auf die Zusammensetzung der hydratisierten Phase wird bestätigt. Die Anwesenheit von Sulfat bewirkt eine Induktionsperiode bei der Reaktion von alumimum- und eisenhaltigen Klinkerphasen mit Wasser. Diese Erscheinungen sind von technischer Bedeutung, insbesondere für Zemente mit erhöhtem Gehalt an C₄AF und sulfatbildenden Phasen wie C¯SH₂ und C₄A₃¯S.

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(4 · l23 · Fe2O3) (4 · 3l23 · SO3) ( 50 ). . - . , , - .

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Dedicated to F. Hanic, D. Sc. on the occasion of his 60th birthday     

XPS and chemisorption studies of the surface layer of Pd?Ag catalysts for CO oxidation

XPS and chemisorption studies of the surface composition of a Pd–Ag alloy (5% Pd) before and after its application in CO oxidation have been performed. It is shown that in a freshly prepared sample the bulk and surface layer compositions are the same. High-temperature treatment of the catalyst in the reaction medium leads to a thermodynamic equilibrium between surface and bulk.

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Pd–Ag Pd 5% CO . , . .

     

Thermal decompositions of complexes of metal ions with riboflavin

Two kinds of complexes of riboflavin with Zn(II), Co(II), Cu(II), Fe(III), Mg(II) and Ca(II) were synthesized, having metal: ligand molar ratios of 11 and 21. When heated, these complexes first lose water. Their thermal degradation in static air atmosphere starts at temperatures higher than, equal to, or lower than that observed for free riboflavin degradation. The rates and stages of pyrolysis were related to the structures of the complexes.

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Zusammenfassung Es wurden zwei verschiedenartige Komplexe von Riboflavin mit Zn(II), Co(II), Cu(II), Fe(III), Mg(II) und Ca(II) mit einem molaren Metall-Ligandenverhältnis von 11 und 21 dargestellt. Beim Erhitzen geben diese Komplexe zuerst Wasser ab. Ihre thermische Zersetzung beginnt in unbewegter Luftathmosphäre bei einer Temperatur, die entweder mit der für die Zersetzung freien Riboflavins übereinstimmt, größer oder kleiner als diese ist. Die Abschnitte und Geschwindigkeit der Pyrolyse werden mittels der Struktur der Komplexe erläutert.

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, , , : 11 21. . , . .

     

Novel evidence for the selective behaviour of tungsten carbide in liquid phase heterogeneous catalytic hydrogenation

Liquid (aqueous) phase catalytic hydrogenation of compounds containing two oxo-groups in -position (biacetyl, glyoxal, alloxan) was studied in the presence of tungsten carbide catalyst. It has been shown that only one of the oxo-groups is affected in the course of the process and is transformed into a >CH–OH group. Comparative studies carried out in the presence of platinum catalyst attest the selective behaviour of tungsten carbide.

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- - (, , ). , >C=O >CH–OH, . .

     

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.

     

A differential scanning calorimetric study of some phenol derivatives

Differential scanning calorimetry has been applied to derive the fusion enthalpies and entropies of series of mono and dimethylphenols, mono and dichlorophenols, and mono and dinitrophenols.

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Zusammenfassung DSC wurde verwendet zur Ermittlung der Schmelzenthalpie und Entropie der Reihen von Mono- und Dimethylphenolen, Mono- und Dichlorphenolen, Mono- und Dinitrophenolen.

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- , - , - .

     

Silylation of porous glass supported platinum catalysts

Effect of silylation with hexamethyldisilazane on adsorption and catalytic properties of porous glass-supported platinum catalysts has been studied. Catalytic activity decreases markedly with an increase in surface coverage by trimethylsilyl groups for all the following reactions examined: hydrogenation of benzene, dehydrogenation of cyclohexane and dehydrocyclization of n-hexane.

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, . , : , -.

     

Thermal analysis of poly(methyl methacrylate)-copper composite

Thermal characteristics of the composites of poly(methyl methacrylate) and copper are reported, including the order of reaction and activation energy of the major second stage of pyrolysis. The randomly-distributed metal particles in the polymer matrix can form paths for heat transfer which determine the mechanism of thermal degradation.

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Zusammenfassung Die thermischen Charakteristika der Verbindungen von Polymethylmethacrylat mit Kupfer werden zusammen mit der Reaktionsordnung und der Aktivierungsenergie der grösseren zweiten Stufe der Pyrolyse beschrieben. Die zufallsbestimmt verteilten Metallpartikel in der Polymermatrix können Wege des Wärmetransfers formen, welche den Mechanismus der thermischen Zersetzung bestimmen.

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Résumé On décrit les caractéristiques thermiques de composites du polyméthylméthacrylate avec le cuivre, parmi lesquelles l'ordre de réaction et l'énergie d'activation de la seconde étape de la pyrolyse qui est la principale. Les particules du métal distribuées au hasard dans la matrice du polymère peuvent constituer des voies pour le transfert de chaleur qui déterminent le mécanisme de la dégradation thermique.

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, . , .

     

The thermal properties of carbon-silica adsorbents (carbosils) prepared by methylene chloride pyrolysis

The thermal properties of complex carbon-silica adsorbents (carbosils) were investigated using differential thermal analysis. The adsorbents were prepared by pyrolysis of methylene chloride. Pyrolysis reaction on silica surface was carried out at different temperatures (400–700 °C) and at different pressures of CH₂Cl₂ vapours. Thermal analysis was carried out in air atmosphere. The following parameters characterizing the properties of the adsorbents were determined: carbon content, specific surface area, carbon layer thickness, pore volume, mean pore radius, differential of heats of adsorption ofn-hexane and benzene, and micrographs. The correlation between topography and morphology of carbon deposits (dependent on the parameters of the pyrolysis process) and the courses of DTA and TG curves corresponding to individual carbosils have been determined.

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Zusammenfassung Mittels DTA wurden die thermischen Eigenschaften von komplexen Kohlenstoff-Silikaadsorptionsmitteln (Carbosil) untersucht. Die Adsorptionsmittel wurden durch Pyrolyse von Methylenchlorid gefertigt. Die Pyrolyse wurde an der Oberfläche von Silika bei verschiedenen Temperaturen (400–700 °C) und bei verschiedenen CH₂Cl₂-Drücken durchgeführt. Die Thermoanalyse geschah in Luftatmosphäre. Folgende Parameter zur Charakterisierung der Eigenschaften der Adsorbenten wurden ermittelt: Kohlenstoffgehalt, spezifische Oberfläche, Kohlenstoffschichtdicke, Porenvolumen, Porendurchmesser, Ableitung der Adsorptionswärme vonn-Hexan und Benzol sowie Oberflächenmikrogramme. Es konnte der Zusammenhang zwischen Topografie und Morfologie der Kohlenstoffablagerungen (abhängig von den Parametern des Pyrolysevorganges) sowie dem Verlauf der DTA- und TG-Kurven der entsprechenden Carbosile festgestellt werden.

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- (). . (400–700°) . . : , , , , - , . , , .

     

Intermediate oxygen-containing compounds in oxidative condensation of methane over sodium-manganese catalysts

CH₂O conversion over sodium-manganese oxide and oxychloride catalysts in methane dehydrodimerization have been studied under unsteady-state conditions at high temperatures (600–750 °C). It has been established that formaldehyde conversions produce deep oxidation (CO, CO₂), condensation (C₂H₄, C₂H₆) and methanation products through CH₃O^– formation and decomposition.

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(600–750°C) CH₂O - . , (CO, CO₂) (C₂H₄, C₂H₆), , CH₃O^–.

     

Relaxation of the rate of o-xylene oxidation to phthalic anhydride on vanadium catalysts

Based on numerical analysis of experimental data, the main ideas of the reaction mechanism have been confirmed and kinetic principles of the non-steady=state reaction have been determined.

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, .

     

Analysis of thermal desorption spectra of oxygen desorbed from rhodium

Thermal desorption spectra of oxygen desorbed from rhodium have been analyzed in terms of models accounting for the effect of lateral interactions between adsorbed particles and of their diffusion into the bulk of metal on the desorption kinetics of O₂. Complex configuration of these spectra is ascribed to the processes of formation/decomposition of surface Rh oxides and the diffusion of particles into the near-surface layers of metal and back to the surface.

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- , O₂ . - O₂ Rh - .

     

Preparation and properties of supported vanadium-phosphorus catalysts studied by chemical analysis and ESR

The preparation of vanadium-phosphorus catalysts is described, showing the considerable influence of phosphorus on the concentration of V⁴⁺ ions. The oxidation properties were studied by chemical analysis and electron spin resonance. Moreover, ESR spectra show a strong influence of moisture on the structure of the catalysts.

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- , V⁺⁴. , . , , .

     

Kinetics of the catalytic transformation of isobutene into methacrylonitrile with NO on supported nickel oxide aerogel

Kinetic studies of the nitroxidation of isobutene by NO show that the reaction follows a redox mechanism in the temperature range of 300–400°C. This mechanism implies an interaction between dehydrogenated isobutene -allyl radical and atomic nitrogen due to the decomposition of NO by the reduced catalyst, which is then reoxidized.

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NO , 300–400°C. - , NO , .

     

Flavonoids of Ammothamnus lehmannii. Structure of lehmannin and of ammothamnidin

The new flavanon lehmannin (I) has been isolated from the roots ofAmmothamnus lehmannii Bunge. On the basis of chemical transformations and with the aid of physicochemical characteristics it has been established that compound (I) has the structure of 2,4,7-trihydroxy-8-(2-isopropenyl-5-methylhex-4-enyl)flavanone. The alkaline cleavage of lehmannin gave ammothamnidin (V). The structure proposed previously for the chalcone ammothamnidin has been corrected. It has been shown that it has the structure of 2,2-4,4-tetrahydroxy-3-(2-isopropenyl-5-methylhex-4- enyl)chalcone. A comparative study of the¹³C NMR spectra of a number of flavanones has revealed an empirical law permitting the prediction of the presence or absence of substituents (OH and OCH₃) at C-2 from the value of the chemical shift of the signal of the C-2 carbon atom.Institute of the Chemistry of Plant Substances of the Uzbek SSR Academy of Sciences, Tashkent. I. P. Pavlov Samarkand State Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 516–524, July–August, 1987.     

Effect of preparation method of nickel-zeolite catalysts on their catalytic properties

The effect of the carrier-gas (H₂, N₂, CO₂ and air) and the influence of additives (H₂S and water vapors) in the activation of Ni- and Cr-containing zeolites on their catalytic activity have been studied in toluene disproportionation.

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- (H₂, N₂, CO₂ ) (H₂S ) , Ni Cr, .