Sulfur poisoning of Pt/Al2O3 catalysts, I. Determination of sulfur coverage by infrared spectroscopy

In the case of Pt/Al₂O₃ catalysts, a spectroscopic method was proposed to determine the amount of sulfur irreversibly bonded to platinum. Sulfate contamination of Pt/Al₂O₃ samples does not affect the metal properties for reduction temperatures lower than 300°C. Hydrogen treatment at 500°C reduces the sulfate groups into hydrogen sulfide which poisons platinum. This poisoning is strongly dependent on the metal loading. Irreversibly held sulfur sulfur corresponds to a S/Pt_s ratio close to 0.44.

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, , Pt/Al₂O₃, . Pt/Al₂O₃ 300°C. 500°C , . ⤠ . S/Pt_s, 0,44.

     

Thermal effects of contamination,adsorbed water and annealing on the DTA of powdered quartz

During the grinding of quartz, water is adsorbed from the atmosphere, but this water gave no detectable thermal effect on DTA because it was evolved uniformly up to 1000°. However, in conjunction with an iron contaminant, the adsorbed water was involved in an oxidation reaction causing noticeable thermal effects for quartz powdered in a vibration mill constructed of steel parts. When powdered so finely that the - inversion peak at 573° had disappeared, annealing caused a partial redevelopment of the peak but recrystallization of disrupted quartz was too small an effect to give any detectable exothermic peak on DTA.

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Zusammenfassung Während des Vermahlens von Quartz wird Wasser aus der Atmosphäre adsorbiert, jedoch ergab dieses Wasser keinen nachweisbaren thermischen Effekt in der DTA, da es bis zu 1000° gleichmässig freigesetzt wird. Im Zusammenhang mit einer Eisen-Verunreinigung wurde jedoch das adsorbierte Wasser in eine Oxidationsreaktion einbezogen, welche beim in einer aus Stahlteilen gefertigten Vibrationsmühle zerpulvertem Quartz nachweisbare thermische Effekte verursachten. Wenn so fein pulverisiert wurde, daß der --Inversions-Peak bei 573° verschwunden war, verursachte eine Wärmebehandlung eine teilweise Wiederentwicklung des Peaks, jedoch war die Rekristallisation des zerstörten Quartzes zu geringfügig um einen nachweisbaren exothermen Peak in der DTA-Kurve zu ergeben.

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Résumé Lors du broyage du quartz, il se produit une adsorption de l'eau atmosphérique mais cette eau ne donne pas d'effet thermique décelable par ATD car elle se dégage régulièrement jusqu'à 1000°. Cependant, en présence de fer comme contaminant, l'eau adsorbée intervient dans une réaction d'oxydation qui donne des effets thermiques perceptibles dans le cas de quartz pulvérisé dans un vibrobroyeur en acier. Si le quartz est en poudre assez fine pour que le pic d'inversion - à 573° disparaisse, le recuit provoque la réapparition partielle du pic. La recristallisation du quartz est cependant trop faible pour donner un effet exothermique décelable par ATD.

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, , 1000°. , , . - 573° , , , - .

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We are grateful to the Science Research Council for supporting this work.     

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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, , . .

     

Phase composition of an iron-bismuth-molybdenum catalyst for propylene ammoxidation

The phase composition of a selective Fe–Bi–Mo oxide catalyst changes under the influence of the reaction medium in the ammoxidation of propylene. It represence a heterogeneous mixture of bismuth and iron(II) molybdates.

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. .

     

Kinetics of the formation and decomposition of hydroperoxide in the oxidation of 8-pentadecanone

Kinetic parameters for the decomposition of 8-pentadecanone ketohydroperoxides in the oxidized ketone medium and the effect of caprylic acid on the rate and mechanism of hydroperoxide decomposition have been studied. The decomposition of hydroperoxide into molecular products follows mainly the ionic mechanism.

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8- . . , .

     

Inhomogeneity of strong Lewis acid centers on Al2O3 surface

Specificity of the bands at 1630–1620 cm^–1 in IR spectra of coordinatively bonded pyridine has been studied. Three strong Lewis-type acid centers have been revealed on Al₂O₃ surface.

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- 1630–1620 ^–1.

     

Image processing using the Briggs-Raucher oscillating chemical reaction

Some images obtained by illuminating the Briggs-Raucher oscillating chemical reaction are illustrated. This reaction gives more distinct and contrasty images than the Belousov-Zhabotinskii reaction.

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-. , , -.

     

Thermal decomposition of palladium-imidazole complexes

Two Pd-imidazole complexes have been synthesized following the reaction of PdCl₂ and imidazole at 12 and 14 metal ligand ratios. Elemental and thermogravimetric analytical data obtained from these compounds illustrate that they have the formulae Pd(IMDAH)₂Cl₂ · 4H₂O and Pd(IMDAH)₃Cl₂ (IMDAH = imidazole), respectively. The mechanism of thermal decomposition for these complexes in air involves initial dissociation of H₂O and IMDAH ligands in the 120–340 °C range, subsequent dissociation of the chloride atoms to form PdO in the 530–570 °C range, and finally formation of Pd metal at 820–840 °C.

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Zusammenfassung In einer Reaktion von PdCl₂ mit Imidazol wurde bei einem metall-Ligandenverhältnis von 12 bzw. 14 zwei Pd-Imidazolkomplexe dargestellt. Auf Grund der Ergebnisse von Elementaranalyse und Thermogravimetrieuntersuchungen besitzen die Verbindungen die Formeln Pd(IMDAH)₂Cl₂·4H₂O bzw. Pd(IMDAH)₃Cl₂ (IMDAH=Imidazol). Der Mechanismus der thermischen Zersetzung dieser Komplexe in Luft umschliesst eine anfängliche Dissoziation (Abgabe von Wasser und IMDAH-Liganden) im Temperaturbereich 120–340 °C, gefolgt von der Bildung von PdO unter Abspaltung der Chloratome bei 530–570 °C sowie die letztendliche Bildung von metallischem Pd bei 820–840 °C.

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, 12 14, . , d()₂l₂· 4₂ d()₃l₂. 120–340°, 530–570°. 820–840°.

     

Spectral dependence of photocatalytic CO oxidation on rutile

In the region of intrinsic rutile adsorption, CO oxidation follows a redox mechanism via the interaction of CO with O^– ion-radicals, and the photocatalytic activity is determined by the density of 2p states close to the top of the valence band.

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CO CO - O^–, 2- .

     

Hydrodemetallation and the promoter effect of vanadium compounds on a Co?Mo/Al2O3 hydrodesulfurization catalyst

The effect of the vanadium compounds [VO(phthalocyanine)], [VO(salen)] [salen=N,N-ethylenebis(salicylideneiminate)], petroporphyrins, and metal-free phthalocyanine on the hydrodesulfurization of thiophene over a Co/Mo/Al₂O₃ catalyst (350°C, 1 atm) is described. The compound [VO(salen)], which decomposes, acts as a promoter at low V (0.1–0.2 wt. %); the other compounds deactivate the catalyst, an effect which is due to the whole molecule binding to the catalyst in the same way as a nitrogen base.

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[VO()], [VO()] [=N,N-- ()], , , Co–Mo/Al₂O₃ (350°C, 1). [VO()], , V (0,1–0,2 . %-); , , .

     

Observation of a peculiar phenomenon in the cerium-ion-catalyzed Belousov-Zhabotinskii oscillator with acetylacetone in CSTR mode

The cerium-ion-catalyzed Belousov-Zhabotinskii reaction with acetylacetonate as the organic substrate was investigated in flow reactor (CSTR) mode. Most behavior observed could be readily rationalized in terms of the Oregonator model of the Belousov-Zhabotinskii reaction. However, at high acetylacetone concentrations (>0.07 M) and rapid flow rates, the system behaved peculiarly. Large-amplitude oscillations in the response of a Ag/AgBr electrode appeared while the response of a shiny platinum electrode was flat, suggesting the absence of oscillations in redox potential. This phenomenon was reproducible and disappeared when the flowrate was decreased.

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, , - . -. , (>0,07 M) . Ag/AgBr, , -. .

     

Thermal conductivity of cemented carbides

The hypothetical salts Li₄SiN₂O and Li₇SiN₃O were sought in the course of studies on the reactions of Li₂SiN₂ and Li₅SiN₃ with lithium oxide, and of LiSiNO with lithium nitride.

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Zusammenfassung In einer Reihe von Studien der Reaktionen von Li₂SiN₂ und Li₅SiN₃ mit Lithiumoxid bzw. LiSiNO mit Lithiumnitrid wurde nach den hypothetischen Salzen Li₄SiN₂O und Li₇SiN₃O gesucht.

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Li₂SiN₂ Li₅SiN₃ LiSiNO Li₄SiN₂O Li₇SiN₃O.

     

Product selectivity and qualitative reaction scheme for the dehydrogenation and hydrogenolysis of n-butane over supported ruthenium at high temperature

The dehydrogenation and hydrogenolysis of n-butane (n-C₄) over a Ru–Al₂O₃ catalyst (0.849 w/w% Ru) have been studied at 490°C at different time factors. Some runs have also been made on pure -Al₂O₃ at 490°C and on Ru-black at temperatures between 100 and 490°C, feeding n-butane and hydrogen. The analysis of the selectivity vs. time factor allows to prove that the initial reactions taking place are n-C₄ dehydrogenation to 1-butene and 2-butenes and skeletal isomerization to isobutane. The initial molar selectivity to the n-butenes reaches about 70%. A qualitative reaction scheme is proposed.

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- (-C₄) Ru–Al₂O₃ (0,849 .% Ru) 490°C . -Al₂O₃ 490°C Ru- 100–490°C - . , -C₄ 1- 2- . - 80%. .

     

Methane synthesis from CO/H2O mixture on supported nickel catalysts, I. Influence of the support on the catalytic properties

The behavior of some supported Ni catalysts for methane synthesis from CO and steam in correlation with the specific metal-support interactions is discussed.

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CO . .

     

Hydrogenation of toluene over Pt and Pt?Cu alloys in NaY

The hydrogenation of toluene is performed over small Pt and Pt–Cu particles in a NaY zeolite. For toluene hydrogenation the T.O.N. of Pt and Pt alloyed with Cu are very different at room temperature but at high temperature (530 K) they are of the same order of magnitude.

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Pt Pt–Cu NaY. ( ) Pt Pt, , , , (530 K) .

     

Triterpene glycosides of Gypsophila trichotoma III. Structure of trichoside B

Summary The structure of trichoside B — a gypsogenin tetraoside fromGypsophila trichotoma Wend. — has been established. The glycosidic carbohydrate chain is O--D-glucopyranosyl-(1 3)-O--D-glucuronopyranosyl and the acyloside chain is O--D-glucopyranosyl-(1 4)-O--D-galactopyranosyl.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 431–434, July–August, 1971.     

Syntheses and properties of mixed dinuclear copper(II) complexes with heterocyclic dithiocarbamates and a cyclic octadentate tertiary amine

Five new Cu^II complexes of general formula [Cu₂(Rdtc)tpmc](ClO₄)₃, (1)–(5), where tpmc and Rdtc ^– refer to N,N,N,N-tetrakis(2-pyridylmethyl)-1,4,8,11-teraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc) or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. Elemental analyses, conductometric and magnetic measurements, u.v./vis, i.r., e.p.r. and mass spectroscopy have been employed to characterize them. The complexes adopt an exo coordination of Cu^II ions and tpmc. The dithiocarbamate ion joins both the sulphur and the copper atoms acting as a bridging ligand The presence of different heteroatoms in the piperidine ring influences the (C=N) and (C=S) vibrations which decrease in the order of the complexes: Pipdtc>N-Mepipdtc>Pzdtc>Morphdtc>Timdtc ligands. Attention has been paid to the detailed mechanism of the mass spectral fragmentation of the complexes. The g _eff factors of the complexes have been also estimated by e.p.r. spectra. Finally, the complexes obtained demonstrate microbiologycal activity against some bacteria.