Mechanism and kinetics of the hydrogenation of CO with the formation of paraffins and olefins on an iron catalyst

A kinetic model is proposed for the hydrogenation of CO on a Fe/Al₂O₃ catalyst, based on a mechanism of parallel formation of paraffins and olefins. The model satisfactorily describes the experimental data on the dependence of the total rate of conversion of CO to hydrocarbons and the selectivity with respect to paraffins on the composition of the reaction mixture. It was shown that in the case of olefins the successive steps of their hydrogenation, which make a substantial contribution to the distribution of reaction products, must be taken into consideration.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Nauki Prospekt, Kiev 252039, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 2, pp. 118–123, March–April, 1996. Original article submitted May 22, 1995.     

Effect of the nature of the metal oxide on selective transformation of methane under unsteady conditions in the absence of oxidant in the gaseous phase

The catalytic transformation of methane into higher hydrocarbons was studied under unsteady conditions on oxides of various metals (Pb, Fe, Nb, Ti, Cd, Mo, Mg, Zn, Zr, Bi, Mn), and also on Sr-, La-, Y-, and Mn-containing oxides of perovskite structure. It is shown that the effectiveness of the catalysts not only depends on their chemical composition, but also is determined to a considerable degree by the specific surface of the oxides. L. V. Pisarzhevskii Institute of Physical Chemistry, Academy of Sciences of Ukraine, 252039 Kiev, Prosp. Nauki, 31, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 2, pp. 91–95, March–April, 1997.     

Effects of adsorbed bismuth on Si(001) surface electronic states

It is shown that depositing Bi on an Si(001) surface fills the free broken-bond surface states, whose concentration decreases linearly as the bismuth coating 8 increases up to _st, = 0.6 monolayer. The bismuth desorption activation energy is constant < _st, (E_d = 2.77 ± 0.1 eV) and decreases for > _st.Taras Shevachenko Kiev National University, ul. Vladimirskaya 64, 252601 Kiev-17, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 168–171, May–June, 1996. Original article submitted September 19, 1995.     

Mechanism of oxygen effect on hyrogenation rate of CO over palladium catalysts

Acceleration of CO hydrogenation by oxygen over palladium catalysts can be accounted for by competing reactions taking place in the CO-H₂O₂ system.

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, CO O₂ , CO–H₂–O₂.

     

Influence of oxygen on catalytic properties of supported palladium catalysts in CO hydrogenation

It has been established that the addition of oxygen to synthesis gas has a positive effect of the activity and selectivity of supported palladium catalysts in methanol synthesis. The degree of the effect of oxygen depends on the chemical nature of the support and the conditions of catalysis, preceding the addition of oxygen to the reaction mixture. The probable causes for the influence of oxygen on the catalytic properties of palladium, supported on oxide supports, have been discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 557–563, September–October, 1989.     

Influence of the composition of perovskites based on SrMnO<Subscript>3</Subscript> on their catalytic properties in the oxidative coupling of methane

The oxidative coupling of methane (OCM) in a periodic regime over the SrMnO₃ and its derivatives has been investigated. It has been established that partial replacement of the strontium ion by alkali metal ions leads to an increase in both catalytic activity and in selectivity with respect to higher hydrocarbons. Comparison of the results obtained in the present work with those obtained earlier for catalysts based on SrCoO₃ led to the conclusion that the Co-containing catalysts were preferable to the Mn-containing catalysts for carrying out oxidative coupling of methane in a periodic regime.__________Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 41, No. 1, pp. 30–34, January–February, 2005.     

Liquid Entrainment from the Meniscus of a Liquid Wedge by a Moving Horizontal Plate

A hydrodynamic model is proposed for smear formation during the drawing of a film from the meniscus of a limited-volume liquid wedge. It was assumed that the regime of the flow is capillary and the characteristic time of the film formation is small compared to the characteristic time of the change in the meniscus curvature. At small time intervals, the film thickness was determined according to the Landau–Levich–Derjaguin method. At large time intervals, the curvature of the meniscus is described by a linear differential equation for the dynamics of the liquid wedge volume. Under these conditions, the film thickness changes along the plate according to a linear law with the tangent coefficient depending on the capillary number according to a power law, and the profile of the longitudinal section of the smear is close to a right triangle.     

Mutual effect of benzene and maleic acid anhydride in their adsorption on V2O5?MoO3 catalysts

TPD studies have revealed that benzene and maleic anhydride are adsorbed on different active sites of the V₂O₅–MoO₃ catalyst.

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, - .

     

Influence of composition of reaction mixture on selectivity in oxidation of aromatic compounds on oxide catalysts

A general outline is given of a kinetic model of oxidation of a hydrocarbon under the conditions of coexistence on the catalyst surface of sections of different oxidation levels. An analytical dependence has been obtained of the selectivity of the process and conversion on the composition of the reaction mixture. A qualitative agreement has been established between the theoretical and experimental dependences of selectivity and conversion on the ratio of the benzene and oxygen concentrations in the reaction mixture.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 105–108, January–February, 1985.     

Limiting phenomena and multiplicity of steady states in gas-phase oxidation processes

It was found that in a chain-branching oxidation reaction of hydrogen at low pressures, there is a concentration range of the reagents over which there are three steady states: the boundaries of this range determine the positions of the limiting transitions between the regions of slow and rapid occurrence of the process. The dependences of the position of the limiting transitions in noncatalytic oxidation reactions of hydrogen and of oxidation of CO on platinum metals on the rate constants of the elementary stages of these processes have been compared. At different ratios of the rate constants of the heterogeneous-homogeneous catalytic process, the dependences of the reaction rate on the concentration of the reagent may contain a break, or may have the form of a loop or hystereses, both clockwise and counterclockwise.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 1, pp. 28–33, January–February, 1987.