Structural studies of nickel-based Raney catalysts

Electron microscopy and Mössbauer spectroscopy studies of nickel-based Raney catalysts have revealed that the catalysts are formed through the successive aggregation of their structural elements. Catalyst particles are covered by a thin layer of nickel oxide.

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. , . .

     

SIMS studies of water vapor adsorption on polycrystalline rhodium

Studies of water vapor adsorption on polycrystalline Rh at T>315 K and P=(2–4)×10^–2 Pa indicate that water is adsorbed dissociatively to O_ads and O_ads through a molecularly adsorbed species. Desorption activation energy is 46 and 69 kJ/mol for molecular and dissociative species, respectively.

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Rh (2–4)·10^–2 . , O OH - . 46 /, -69 /.

     

Kinetics of heterogeneous catalytic hydroformylation of propylene on rhodium-cobalt catalysts. Reaction mechanism

Steady-state kinetics of combined heterogeneous catalytic hydrogenation and hydroformylation of propylene on Rh–Co-containing catalysts has been studied at atmospheric pressure and T=140–170 °C. A reaction mechanism is suggested. The kinetic model adequately describes all observations.

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- Rh–Co- 140–170 °C. . , .

     

Thermal studies on the cubic spinel Fe2MoO4

The cubic spinel Fe₂MoO₄ was studied in air by DTA, DTG, TG and X-ray in the temperature interval 298–1173 K. From these studies, it was concluded that above the Néel temperature Fe₂MoO₄ undergoes an irreversible crystalline phase transition from cubic to tetragonal at 623 K, wherec/a is 1.022. Above 723 K, surface oxidation followed by bulk oxidation of the spinel occurs. At 948 K, after about half the total weight gain due to oxidation, a compound is formed which was confirmed by X-ray as ferrimolybdite, Fe₂O₃·3–4 MoO₃, indicating that in Fe₂MoO₄ the Mo⁴⁺ is more readily oxidized than the Fe²⁺. Above 940 K, further oxidation of Fe²⁺ and Mo⁴⁺ into their respective oxide occurs. About 13 % of the MoO₃ vaporizes, and the rest melts at 1028 K.

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Zusammenfassung Das kubische Spinell Fe₂MoO₄ wurde in Luft im Temperaturbereich von 298 bis 1173 K durch DTA, DTG, TG und Röntgen untersucht. Aus diesen Studien wurde gefolgert, daß oberhalb der Neel Temperature ein irreversibler kristalliner Phasenübergang des Fe₂MoO₄ aus der kubischen in die tetragonale Form bei 623 K stattfindet, wobeic/a=1.022 beträgt. Oberhalb von 725 K findet eine Oberflächenoxidierung des Spinels statt, der eine allgemeine Oxidation folgt. Bei 948 K, nachdem etwa die Hälfte der infolge der Oxidation auftretenden Gewichtszunahme erfolgte, wird eine durch Röntgen als Ferrimolybdit bestätigte Verbindung gebildet (Fe₂O₃·3–4 MoO₃), welche zeigt, daß in Fe₂MoO₄ das Mo⁴⁺ leichter oxidiert wird als das Fe²⁺. Oberhalb von 940 K erfolgt eine weitere Oxidation von Fe²⁺ und Mo⁴⁺ zu ihren entsprechenden Oxiden. Etwa 13% des MoO₃ verdampft und das übrige schmilzt bei 1028 K.

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, , Fe₂MoO₄ 298–1173 . , Fe₂MoO₄ 623 , / 1.022. 723 , , . 948 Fe₂O₃. 3–4₃, . , Fe₂MoO₄ Mo⁴⁺ , Fe²⁺. 940 Fe²⁺ Mo⁴⁺ . 13% MoO₃ , 1028 .

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The author wishes to thank the Chemistry Division of BARC for helping with the high-temperature X-ray pattern.     

Kinetics of oxidation of octacyanomolybdate(V) ion by thiosulfate

The oxidation of thiosulfate by octacyanomolybdate(V) in the pH range of 4,0 to 5,1 is catalyzed by alkali metal ions and shows first order dependence on the concentrations of thiosulfate, octacyanomolybdate(V) and alkali metal ions and is independent of the hydrogen ion concentration. A mechanism for the reaction is proposed.

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(V) pH=4,0–5,1 . , (V) . . .

     

Studies of Cu?Ni supported catalysts for enantioselective hydrogenation

The effect of support content and composition of supported metal phase on the crystallite size, phase composition and catalytic properties of supported Ni and Cu–Ni catalysts has been investigated. It has been established that with increasing metal content, crystallite sizes and enantioselectivity increase. Copper added to Ni catalysts decreases metal phase dispersity and enantioselectivity.

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, , - . , . є .

     

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 - .

     

Thermogravimetric study of the C + SiO2 reaction

The kinetics of the reaction of one-to-one molar mixtures of crystalline silica and carbon powder were studied using thermogravimetric analysis. The resulting kinetic data was evaluated using simple kinetic and mass transport models. A two-stage reaction mechanism consisting of three stoichiometric reactions can adequately be used to describe the global reaction phenomena. Both the first and second stages of reaction were found to be influenced by diffusion mass transfer within the reacting bed of solids.

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Zusammenfassung Mittels Thermogravimetrie wurde die Reaktionskinetik der Reaktion von kristallinem Siliziumdioxid und Kohlenstoffpulver im Molverhältnis 11 untersucht. Die kinetischen Angaben wurden mittels einfachen kinetischen und Stofftransportmodellen ausgewertet. Zu einer adäquaten Beschreibung der gesamten Reaktionserscheinung kann ein Zweischrittereaktionsmechanismus bestehend aus drei stöchiometrischen Reaktionen benutzt werden. Sowohl der erste als auch der zweite Reaktionsschritt wird durch diffusiven Stofftransport innerhalb des Reaktionsbettes beeinflußt.

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, 11. - . , , . , .

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This paper is based on the doctoral dissertation of the senior author.     

Hydrogenation reactions over alkali metal doped MgO, II

The hydrogenation of benzene, styrene and isoprene over magnesia doped with sodium and potassium vapors has been studied. Neither system displays a catalytic activity towards benzene hydrogenation. The initial rate, turnover number and time of halfdecay for styrene and isoprene hydrogenation have been determined.

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, . . , .

     

m-Xylene conversion over dealuminated Y zeolites studied by the pulse method

m-Xylene conversion was studied over dealuminated Y type zeolites in hydrogen forms, SiO₂ to Al₂O₃ ratios were varied from 4.86 to 12.95.

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- . SiO₂/Al₂O₃ 4,86 12,95.

     

Quantitative parameters by thermoanalytical methods

The conditions and premises of the kinetic evaluation of thermoanalytical curves on the basis of chemical kinetics are demonstrated, and the limits of their availability are pointed out. For reactions with an unclear structural and chemical course, some appropriate definitions of terms are proposed.The possibilities of the use of the inflection points of the reaction rate versus time curve are presented. New methods of determination of kinetic parameters are described, including the ratio of the degrees of reactionx, the ratio of the reaction ratesx and the ratio of the tangent slopesx at these points.

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Zusammenfassung Bedingungen und Voraussetzungen der kinetischen Auswertung thermoanalytischer Meßkurven auf der Basis der chemischen Kinetik werden dargestellt, gleichzeitig wird auf die Grenzen ihrer Gültigkeit hingewiesen. Für Reaktionen mit unklarem chemischem oder strukturellem Ablauf werden geeignete neue Bezeichnungen definiert.Die Möglichkeit zur Verwendung der Wendepunkte der Kurve Reaktionsgeschwindigkeit gegen Zeit vorgestellt. Neue Methoden werden beschrieben, die zur Bestimmung kinetischer Parameter das Verhältnis der Umsätzex ₁ x ₂, das Verhältnis der Reaktionsgeschwindigkeitenx ₁/x ₂, und das Verhältnis der Tangentensteigungenx ₁/x ₂ an den Wendepunkten verwenden.

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. . . — . , (x), () () .

     

Hydrogenolysis of n-butane on Ni-Pd/SiO2 catalysts

Supported Ni-Pd/SiO₂ catalysts of different Ni and Pd composition were studied in n-butane hydrogenolysis. The reaction rate, selectivity towards methane, ethane and propane were determined. On the basis of these data the relationship between the size and composition of the active center and the possibility of surface segregation of one of the components is discussed.

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Ni-Pd/SiO₂ Ni Pd -. , . .

     

Properties of highly dispersed supported catalysts in hydrogenation reactions

Pt/sol and Pt/support catalysts with 6–15 Å Pt particles have been established to be low active in the hydrogenation of propargyl alcohol, butyn-l-ol-3 and dimethylethynylcarbinol. The specific catalytic activity significantly rises with increasing d_Pt above 15 Å and after the thermal treatment of highly dispersed catalysts in a hydrogen flow.

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, -30 -- 6–15 Å , -1, -3 . d_Pt>15 Å .

     

On the mechanism of propylene oxidation over gallium-molybdenum oxide catalysts

The products of selective oxidation are shown to be formed via a stepwise mechanism with participation of surface allylic complexes. A successive transformation of -allyl to -allyl and further to acrolein is possible. The products of complete oxidation may be formed through surface carbonate-carboxylate complexes via either a stepwise mechanism involving the catalyst's oxygen, or a concerted mechanism with the participation of molecular oxygen.

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, . - -, . - , .

     

Kinetics and mechanism of the permanganate oxidation of trans-crotonic acid

The kinetics and intermediates of the permanganate oxidation of trans-crotonic acid have been investigated in the pH range of 0.5–5.0 using the stoppedflow technique. The formation of manganese(III) as a short-lived intermediate has been established. The reaction is first order with respect to both MnO ₄ ^– and crotonic acid (crotonate). The resolved rate constants at 25°C are 730 and 410 M^–1 sec^–1 for the acid and the anion, respectively. The reaction mechanism is discussed.

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pH=0,5–5,0, . (III) . MnO ₄ ^– , (). 25°C 730 410 M^{–1 –1} , . .

     

Formation of O2? ion-radicals on reduced anatase. Influence of adsorbed CO on the stabilization of O2?

ESR studies of O₂ adsorption on reduced anatase have been performed. The amount of O ₂ ^– species is determined by adsorbed surface oxygen and their parameters are changed by CO adsorption.

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O₂ . , O ₂ ^– , CO.

     

Strong H2 chemisorption on Al2O3 or SiO2 supported group VIII metals

Following hydrogen treatments at high temperature a decrease in hydrogen chemisorption at room temperature is observed in almost all group VIII elements supported on SiO₂ or Al₂O₃. The effect is attributed to self inhibition by strongly chemisorbed hydrogen on the metals.

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VIII , SiO₂ Al₂O₃. .

     

Heterogeneous reactions of solid nickel(II) complexes

The influence of different modes of preparation on the stoichiometry of thermal decomposition of isothiocyanatonickel(II) complexes with ammonia was studied. It was found that the complex Ni(NCS)₂(NH₃)₄ (I) prepared by heterogeneous reaction undergoes decomposition in two steps (–2 NH₃, –2 NH₃), while for complex II, of the same composition but prepared by homogeneous reaction from solution, the decomposition proceeds in three steps (–1 NH₃, –1 NH₃, –2NH₃). Electronic and infrared absorption spectra were used for the study of the spectral properties of the starting complex. It was found that the different stoichiometries of thermal decompositions of complexes I and II do not cause differences in the bonding strength of the ammonia molecules (chemical factor); this effect is rather brought about by physical factors such as different imperfections of the crystal lattice.

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Zusammenfassung Der Einfluß der Herstellung auf die Stöchiometrie der thermischen Zersetzung von Amin-Komplexen des Isothiocyanatonickels wurde studiert. Der Zerfall des Komplexes Ni(NCS)₂(NH₃)₄ (I), hergestellt durch heterogene Reaktion, verlief in zwei Etappen (–2 NH₃, –2 NH₃). Beim selben Komplex (II), hergestellt durch homogene Reaktion in Lösung, wurden jedoch drei Etappen beobachtet (–1 NH₃, –1 NH₃, –2 NH₃). Die Eigenschaften des Ausgangsproduktes wurden durch Elektronen- und IR-Spektroskopie untersucht. Das unterschiedliche thermische Verhalten ist nicht auf eine verschiedene Bindungsstärke der NH₃ Moleküle, sondern auf physikalische Ursachen, wie z. B. Unregelmässigkeiten im Kristallgitter zurückzuführen.

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Résumé On a étudié l'influence des diverses méthodes de préparation sur la stoechiométrie de la réaction de décomposition thermique des complexes de l'isothiocyanate de nickel(II) avec l'ammoniac. On a établi que le complexe Ni(SCN)₂(NH₃)₄, (I), préparé rar réaction hétérogène, subit une décomposition en deux étapes (–2NH₃, –2NH₃), tandis que le complexe (II), de même composition, mais préparé par réaction homogène, à partir de solutions, se décompose en trois étapes (–1NH₃,–1NH₃, –2NH₃). Les propriétés spectrales du complexe initial ont été étudiées par absorption électronique et infrarouge. On a trouvé que les différences de stoechiométrie des réactions de décomposition thermique des complexes (I) et (II) n'apportaient pas de différences entre les énergies de liaison des molécules d'ammoniac (facteur chimique). C'est plutôt à des facteurs physiques, comme les différentes imperfections du réseau cristallin, que cet effet serait dû.

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(II) . , Ni(NCS)₂(NH₃)₄ (I), , (–2NH₃,–2NH₃). , II , , (–1 NH₃,–1 NH₃ –2NH₃). . , I II ( ), , .