Partial kinetic models in the H2?O2 system

Using the concepts of maximum mechanism and non-equilibrium free energy, some partial kinetic models of hydrogen oxidation have been found by means of solving a direct kinetic problem. It is shown that the basic difference in the kinetic models of ignition is the initial period of the process (induction period) while the mechanism of the well-developed process slightly depends on the initial conditions and remains mainly the same for the parameters under study.

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H₂–O₂ ( ) . , ( ), , .

     

Influence of the crystallite size of platinum of the course of hydrogenolysis of ethane and propane over Pt/Al2O3 catalysts

The effect of the degree of platinum crystallite size on the reaction rate, selectivity and activation energy of ethane and propane hydrogenolysis has been studied in the range of platinum crystallite size of 1.7–4.0 nm. In the same range of Pt crystallite size, the activation energy of both processes shows a clear minimum. The decrease in Pt crystallite size bellow 3.0 nm brings about rapid changes in the selectivity of propane hydrogenolysis.

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( ) , -. 1,7–4,0 , .

     

Isomerization of olefins on Ta2O5 catalysts

The double bond and skeletal isomerization of olefins was investigated on Ta₂O₅ catalysts calcined at different temperatures. A remarkable minimum of catalytic activity and surface acidity (as characterized by pyridine adsorption) was found at 600°C calcination temperature. A further peculiarity of Ta₂O₅ catalyts was found in the exceptionally low surface OH coverage (0.01–0.3 OH nm^–2). Pyridine is a total poison, water is a partial poison, whereas CO₂ has no effect on the catalytic activity.

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Ta₂O₅, . ( ) 600°C. Ta₂O₅ OH (0,01–0,3 OH nm^–2). , CO₂ - .

     

V2O5/TiO2 oxidation catalysts, IV. Adsorption of acrolein on sodium-containing systems

Adsorption of acrolein on vanadia/titania catalysts fits a polymerization kinetics if Na–V compounds are not present or the vanadium content is lower than that corresponding to formation of a monolayer of vanadia on the titania support.

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, Na–V .

     

Dispersity and reducibility of the molybdenum oxide phase in SiO2, SiO2?Al2O3 and γ-Al2O3 supported molybdena catalysts

XRD, isothermal and temperature-programmed reduction (TPR) experiments were carried out with SiO₂, SiO₂–Al₂O₃ and -Al₂O₃ supported catalysts. Molybdena is in a more disperse state on supports containing more alumina and it is more reducible on SiO₂–Al₂O₃ than on SiO₂ or -Al₂O₃. TPR curves were shown to reflect connections between reduction kinetics and dispersity.

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-, , SiO₂, SiO₂–Al₂O₃ -Al₂O₃. , , SiO₂–Al₂O₃ SiO₂ -Al₂O₃. .

     

Interaction of methanol with hydrogen sulfide in the presence of K2WO4/Al2O3

Kinetic data show that in the presence of K₂WO₄/Al₂O₃, methanethiol is largely produced by the reaction of H₂S with metanol and partly with dimethyl ether. Dimethyl sulfide is formed during the interaction of methanethiol with methanol, of H₂S with dimethyl ether and as a result of methanethiol disproportionation. Methane and carbon oxides are the decomposition products of methanethiol and dimethyl sulfide and of methanol and dimethyl ether, respectively.

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, K₂WO₄/Al₂O₃ H₂S — . , H₂S . , — .

     

On the deactivation of Fe2O3?MoO3/SiO2 catalysts in the oxidation of methanol to formaldehyde

The deactivation behavior of Fe₂O₃–MoO₃/SiO₂ catalysts with different Fe₂O₃+MoO₃ content in the oxidation of methanol to formaldehyde is investigated. A simplified reaction-deactivation kinetic model is presented and used to compare and discuss the different behaviors.

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Fe₂O₃–MoO₃/SiO₂ Fe₂O₃+MoO₃ . : -.

     

Effect of electronic interaction between metal and support, II. TPD, TPR and chemisorption studies on Ru/Al2O3?MgO catalysts

TPD, TPR and chemisorption were used to characterize Ru/Al₂O₃–MgO catalysts. It is suggested that the acidity of support may influence the properties of catalysts significantly.

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, Ru/Al₂O₃–MgO. , .

     

On the occurrence of competitive mechanisms in the transformation of butadiene into maleic anhydride with air on MoO3?TiO2 catalysts

Unusual variations of selectivity are observed in the catalytic oxidation of butadiene on MoO₃–TiO₂ catalysts. A maximum of selectivity in furan and maleic anhydride is obtained at 400°C, since the oxidation of crotonaldehyde, dihydrofuran and furan are selective at all temperatures. Competitive oxidation of furan and crotonaldehyde proved that the aldehyde cannot be the unique intermediate for furan and maleic anhydride formation. Two mechanisms, involving various adsorbed species of butadiene, occur depending on the temperature and explain the decrease of the selectivity below 400°C.

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MoO₃–TiO₂ . 400°C, , . , . , , , 400°C.

     

Influence of rare earth ions on CO oxidation over Ln2NiO4 oxides (Ln=La, Pr or Nd)

CO oxidation was studied over Ln₂NiO₄ compounds in an all-glass static recirculatory system. The reactions were performed at an initial total pressure of 50±2 Torr, in the temperature interval 340–450°C. The apparent activation energy was found to decrease from La to Nd. A correlation between activity and binding energy of oxygen in the compound as well as with the tolerance factor is observed. The role of rare earth ions in these catalysts is discussed.

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CO Ln₂NiO₄ , . 50±2 340–450°C. La Nd. , . .

     

Comparative study of the catalytic properties of V2O5, Nb2O5 and Ta2O5 in the oxidation of methanol to formaldehyde

The selectivity of the oxides under consideration to the oxidation of methanol to formaldehyde is shown to increase in the sequence V₂O₅–Nb₂O₅–Ta₂O₅. The same sequence corresponds to the decrease in specific activity. The activation energy of the reaction is 12 kcal/mol for V₂O₅, 14 kcal/mol for Nb₂O₅ and 22 kcal/mol for Ta₂O₅.

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, V₂O₅–Nb₂O₅–Ta₂O₅. . : V₂O₅ 12 /, Nb₂O₅ 14 / Ta₂O₅ 22 /.

     

V2O5/TiO2 oxidation catalysts. I. Preparation and characterization by XRD and IR spectroscopy

V₂O₅/TiO₂ systems have been prepared by reacting VO-(acetylacetonate)₂ with differently hydroxylated TiO₂ supports. When the OH population is increased, a larger vanadia content, but well dispersed, is achieved. The presence of sodium ions leads to the formation of Na–V bronze crystallites, decreasing the dispersity of the supported phase.

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V₂O₅/TiO₂ VO()₂ TiO₂, . OH V₂O₅, , , . Na–V, .

     

Infrared studies of CO2(CO)8 adsorption on zeolites Y

Co₂(CO)₈ sublimed onto the surface of HY, CeY, CoY and two dealuminated forms of NaY zeolite is converted at room temperature to Co₄(CO)₁₂ and other surfacebound cobalt carbonyl species. The reaction proceeds in a different way on each of the above zeolites, depending also on their pretreatment.

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Co₂(CO)₈, HY, CeY, CoY NaY, Co₄(CO)₁₂ - . - .

     

Kinetics and selectivity of the oxidation of alkanes in Cl2?H2O and Cl2?Hg2+?H2O solutions

Relative oxidation rate constants of several normal, iso-, cyclo-and methylcycloalkanes have been measured in Cl₂–H₂O and Cl₂–Hg²⁺–H₂O solutions at 343K. The selectivity of C–H bond dissociation in both systems is the same. HOCl is assumed to be the active species for the two systems.

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Cl₂–H₂O Cl₂–Hg²⁺–H₂O 343 , -,- ; C–H . , HOCl.

     

Pt catalyst for the liquid-phase epoxidation of cyclohexene with an O2/H2 mixture

Conditions are found for the preparation of Pt catalysts providing the formation of epoxy-derivative in the reaction of cyclohexene with an O₂/H₂ mixture.

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Pt .

     

Calorimetric studies of adsorptive properties of metallic carbides and nitrides of transition elements. Adsorption of H2, CO and O2 on titanium nitrides

Adsorption heats of hydrogen, oxygen and carbon monoxide on titanium nitrides have been measured calorimetrically in the temperature range from 473 to 673 K. With increasing Me/N ratio, the adsorption heat of oxygen grows.

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, 473–673 . Me/N.

     

Hydrogenation of CO2 on Fe/carbon catalysts

The hydrogenation of CO₂ on activated carbon-supported iron catalysts has been carried out at atmospheric pressure and using a H₂/CO₂ ratio of 4. The specific activities for this reaction are lower than those obtained for the Fischer-Tropsch synthesis using the same catalysts. CO and CH₄ are the only products obtained in the hydrogenation of CO₂ under the experimental conditions used. The apparent activation energies determined for the production of CO are lower than those for the production of CH₄.

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CO₂ , , H₂/CO₂=4. , - . CO CH₄ , CO₂ . - CO , CH₄.

     

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. .

     

Acidity of SiO2, SiO2?Al2O3 and γ-Al2O3 supports and supported molybdena catalysts

Acidity of SiO₂, -Al₂O₃ and SiO₂–Al₂O₃ supports and supported Mo-catalysts in oxidized and reduced state are characterized by IR-spectroscopic and gravimetric pyridine (py) adsorption measurements. Differences in surface acidities are interpreted as results of differences in chemical compositions, molybdena-support interactions and molybdena dispersities.

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SiO₂, -Al₂O₃ SiO₂–Al₂O₃, Mo -- . , .

     

Electronic state of the active site of A V?P?O/SiO2 catalyst in oxidation of chlorine-containing hydrocarbons

V⁴⁺ ions in slightly associated states are supposed to play the role of V–P–O/SiO₂ active sites. V⁴⁺ ions are reduced to V³⁺ during deactivation of the V–P–O/SiO₂ catalyst.

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V–P–O/SiO₂ V⁴⁺ . V–P–O/SiO₂ V⁴⁺ V³⁺.