Interaction between metal and support: Effects of support acidity on adspecies of co over Ru

Supported Ru/X catalysts (X: SiO₂, Al₂O₃, SiO₂·Al₂O₃, HY) have been investigated by IR and TPR (temperature programmed reduction). Due to interaction between Ru and Lewis or Brönsted sites of the support, the Ru sites become electron-deficient. Stronger acidity of the support makes the Ru sites more electron-deficient, and as a result, adspecies of Ru⁺ (CO)₄ or Ru⁺(CO)₂ can occur more easily.

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Ru/X (X:SiO₂, Al₂O₃, SiO₂·Al₂O₃, HY) - . Ru . , Ru⁺(CO)₄ Ru⁺(CO)₂.

     

Oxidation of propylene to acrylic acid on a Fe?Mo?Bi oxide system

Data obtained in a flow reactor show that iron(III) molybdate doped by bismuth can oxidize propylene to acrylic acid directly in one step. Part of the catalyst works in a partially reduced form and in the preparation of the catalyst the surface acidity must be controlled.

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, , (III), , . .

     

Thermal stability of substituted poly-xylylenes

The insertion of meta units in the chain of poly-p-xylylene decreases both the onset temperature of oxidative degradation and the rate of decomposition.Functionalization of the polymer with chlorine and sulphonic groups makes the chain more resistant to high temperature treatments, notwithstanding the low stability of the substituent groups.

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Zusammenfassung Die Einführung von Metaeinheiten in die Kette von Poly-p-xylen setzt sowohl die Einsetztemperatur des oxydativen Abbaues als auch die Zersetzungsgeschwindigkeit herab. Die Einführung von Chlor und Sulfogruppen erhöht trotz der geringen Stabilität der Substituenten die Temperaturbeständigkeit der Kette.

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- -- . , .

     

Li/MgO catalysts. III. Effect of precursor salts on the catalytic activity in methane oxidative coupling

Oxidative coupling of methane has been studied on Li/MgO catalysts prepared from three different MgO precursors and from lithium carbonate or nitrate. In samples prepared from Li₂CO₃, the persistence of this on the support surface favors formation of carbon oxides.

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Li/MgO, MgO . , Li₂CO₃, .

     

Radiochromatographic studies of isobutylene oxidation over SnO2

Radiochromatographic studies of isobutylene oxidation over SnO₂ confirm the formation of carbon dioxide from the products of oxidative olefin condensation.

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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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, . . .

     

Kinetics of methane conversion over microspherically grained nickel-alumina catalysts

Kinetics of methane conversion in a fluidized bed of microspherically grained nickel-alumina catalyst has been studied at pressures from 0.3 to 3.1 MPa. The rate equation shows that the reaction is inhibited by H₂O.

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0,3 3,1 . , .

     

Oxygen diffusion in Me2O?V2O5 melts

The anodic and cathodic polarization of a platinum electrode in K₂O–V₂O₅ melt have been studied. The dissolved oxygen is shown to be ionized. Diffusion coefficients of oxygen in K₂O–V₂O₅ and Na₂O–V₂O₅ melts at various temperatures and K/V ratios are presented.

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K₂O–V₂O₅. , . K₂O–V₂O₅, Na₂O–V₂O₅ K/V.

     

Surface hydration of crystalline and amorphous silicas

The surface properties of three SiO₂ samples, one crystalline (quartz) and two amorphous, with a large difference in particle size, have been investigated by thermal analysis, adsorption calorimetry and infrared spectroscopy. The variation in the silanol group population upon thermal treatment has been followed via the evolution of the i.r. bands at 3745–3750 cm^–1 (free hydroxyl groups) and 3650-3550 cm^–1 (adjacent pairs of SiOH) and the evolution of the heat of adsorption of water with coverage on the outgassed samples.The adsorption capacities increase in the sequence high surface area amorphous sample T=673 K) brings about dehydroxylation leaving only isolated silanols on the high surface area amorphous silica, and partial dehydroxylation of the low surface area material. Quartz is totally hydrophilic, as its regular structure probably stabilizes the hydroxyl layers at the surface.

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Zusammenfassung Die Oberflächeneigenschaften von einer kristallinen (Quarz) und zwei amorphen SiO₂-Proben mit großen Unterschieden in der Partikelgröße wurden durch thermische Analyse, Adsorptionskalorimetrie und Infrarotspektroskopie untersucht. Bei thermischer Behandlung eintretende Veränderungen in der Silanolgruppenpopulation wurden durch Messung der IR-Banden bei 3745–3750 cm^–1 (freie Hydroxylgruppen) und 3650–3550 cm^–1 (benachbarte SiOH-Paare) und der Adsorptionswärme von Wasser an ausgeheitzten Proben untersucht. Die Adsorptionskapazitäten nehmen in folgender Reihenfolge ab: amorphe Probe mit großer Oberfläche > amorphe Probe mit geringer Oberfläche > Quarz. Dehydroxylierung der Oberfläche hat zunehmenden hydrophoben Charakter (Gestalt der Isothermen, Adsorptionswärme kleiner als Kondensationswärme von Wasser) zur Folge. Bei der gleichen thermischen Behandlung (673 K) werden bei amorphen Siliciumdioxid mit großer Oberfläche eine nur isolierte Hydroxylgruppen zurücklassende Dehydroxylierung und bei Material mit kleiner Oberfläche eine teilweise Dehydroxylierung beobachtet. Quarz ist vollkommen hydrophyl, da die reguläre Struktur wahrscheinlich die Hydroxylschichten an der Oberfläche stabilisiert.

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, , (), — . 3745–3750 ^–1 ( ) 3650–3550 ^–1 ( SiOH), . < < . ( , ). (T=673 K) . , , , .

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This research was supported by the Ministry of Public Education within a national programme relating to the structure and reactivity of surfaces.     

Dilution effect on catalytic pyrolysis of hydrocarbons

It is shown that unlike thermal pyrolysis, the rate of catalytic pyrolysis is greatly affected by dilution of hydrocarbons with inert gases. The nature of this effect has been analyzed.

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, . .

     

Interaction of super-finely dispersed Al powders with water

Interaction of super-finely dispersed Al powders (SFDP) with water is characterized by the presence of a considerable section on the kinetic curves, where the conversion rate is maximum and its degree is as high as =0.5–0.7. It is suggested that the essential factor accounting for the conversion kinetics and the phase composition of its products is the self-heating of Al particles.

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() , , () 0,5–0,7. , .

     

Chemical oscillations in the uncatalyzed bromate oxidation of hydroquinone and nitrophenols

Chemical oscillatory behavior in the uncatalyzed bromate oxidation of hydroquinone and nitrophenols is reported. The reaction is strongly inhibited by stirring. Effect of one-electron redox couples (EZ catalysts) on the system is described.

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. . - ( EZ) .

     

Convenient synthesis of 5′-methyl-2′-desoxyuridines

A convenient method has been developed for the synthesis of 5-methyl-2-desoxyuridines. Chlorination of 5-O-benzoyl-5-methyluridines with a mixture of Ph₃P and CCl₄ in DMF affords the 2-desoxy-2-chloro-derivatives, which are then reduced with tributyltin hydride. The crystalline 5-O-benzoyl-5-methyl-2-desoxyuridines were obtained in overall yields of 40–60%. In a similar way, 5-O-benzoyluridine has given 5-O-benzoyl-2-desoxyuridine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 246–248, February, 1989.     

Toluene disproportionation and coke formation over fluorided alumina and hydrogen-mordenite

Toluene transformation was investigated on a fluorided alumina and a protonic mordenite under hydrogen (0.8, 12 bar) and under nitrogen (12 bar). Hydrogen pressure considerably improves the catalytic stability of H-mordenite by inhibiting the formation of coke. Moreover, hydrogen eliminates part of the coke deposited by reaction under nitrogen, and regenerates the activity of the mordenite. On the contrary, hydrogen has no effect in the case of fluorided alumina. The particular behavior of the mordenite is attributed to its very strong acidity.

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(0,8, 12 ) (12 ). -, . , , , . , - . .

     

Kinetics of Cr(VI) and V(V) oxidation of trans-stilbene and indene

Title reactions are acid catalyzed and strongly dependent on the permittivity of the medium. With Cr(VI) indene reacts faster than trans-stilbene, but with V(V), trans-stilbene reacts faster than indene. The mechanism is discussed.

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. Cr(VI) , -, V(V) - , . , .

     

Enthalpies de melange du systeme antimoine-tellure a 909,30 K, 911,85 K et 917,95 K

Thermodynamical data on Sb-Te system at 909,30 K, 911,85 K and 917,95 K. The integral molar enthalpies of formation of liquid Sb-Te alloys were measured at three temperatures by drop calorimetry.Partial molar enthalpies of formation of these alloys, referring to the pure liquid constituants, and enthalpie of formation at 298 K of the compound Sb₄₀₅Te₅₉₅ were deduced.

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Zusammenfassung Thermodynamische Daten, des Systemes Sb-Te bei 909,30, 911,85 und 917,95 K. Mittels Drop-Kalorimetrie wurden die integralen molaren Bildungsenthalpien von flüssigen Sb-Te Legierungen bei drei verschiedenen Temperaturen gemessen. Die partiellen molaren Bildungsenthalpien dieser Legierungen, bezogen auf die reinen flüssigen Komponenten sowie die Bildungsenthalpie der Verbindung Sb_0.405Te_0.595 bei 298 K wurden abgeleitet.

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Sb-Te 909,30; 911,85 917,95 . , Sb_0.4050.595 298 .

     

Thermal decomposition of 10-molybdo-2-vanadosilicic heteropolyacid:29Si and51V-NMR study

Thermal decomposition of 10-molybdo-2-vanadosilicic heteropolyacid has been studied by²⁹Si and⁵¹V-NMR method.²⁹Si-NMR MAS spectra of solid samples indicate that the HPA begins to decompose at T<300°C and the decomposition is complete at 300–400°C.

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²⁹Si ⁵¹V Si–Mo-V () 12- . ²⁹Si MAS , 300°C 300–400°C.

     

Thermal and spectral studies on some tetrachloroaurates of 8-alkyltheophylline derivatives

Tetrachloroaurates of 8-ethyl-, 8-isopropyl-, 8-propyl- and 8-pentyltheophylline were synthesized and studied by¹H-NMR, TG and DSC techniques. The metal is not coordinated to the 8-alkyltheophylline derivatives and forms a salt-like structure.

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Zusammenfassung Tetrachloroaurate von 8-Äthyl-, 8-Isopropyl-, 8-Propyl- und 8-Pentyltheophillin wurden synthetisiert und mittels¹H-NMR, TG und DSC untersucht. Die 8-Alkyltheophillin-Derivate sind nicht koordinativ an das Metall gebunden, es liegt vielmehr eine salzartige Struktur vor.

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8--, 8--, 8-- 8- , . , 8- .

     

Hydrocarbon hydrogenolysis on nickel-tin catalysts

Hydrogenolysis of ethane, n-hexane and cyclohexane has been studied on nickel-kieselguhr catalysts modified by organic and inorganic compounds of tin. Tin additives decrease nickel reactivity with respect to C–C dissociation, which is ascribed to the formation of surface intermetallides on the catalyst.

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, - - , . . C–C .

     

Influence of substituents on rate constants for recombination of tertiary peroxy radicals

A linear correlation between the logarithm of rate constant (2k_t) for recombination of tertiary peroxy radicals (ROO)^* and ^* constants of substituents R was found to be 1g 2k_t=lg 2k _t ^° . The calculated values are 1g 2k _t ^° =4.59±0.08 and ^*=5.56±0.35.

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I (2k_t) (ROO) R: 1g 2k_t=lg 2k _t ^° . , 1g 1g 2k _t ^° =4,59±0,08 =5,56±0,35