Kinetic studies of Pt/Al2O3 catalyst pellets with nonuniform activity

Catalysts with nonuniform distribution of the catalytically active component (Pt) over their porous support (Al₂O₃) have been studied. A nonuniform activity distribution changes not only the reaction rate but also the kinetics can be different on these catalysts.

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(Pt) (Al₂O₃). , , .

     

Influence of the preparation method on the pore spectrum of Pt?Cr/Al2O3 and Pt?Sn/Al2O3 catalysts

It is shown that, in contrast to classical impregnation methods, in bimetallic catalyst production the texture of the carrier is stabilized by introducing the promoting ion on the surface of Pt/Al₂O₃ with vapors of CrO₂Cl₂ or SnCl₄. This is shown by a relatively slower decrease of the specific area and the volume of the pores upon calcination.

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, Pt/Al₂O₃- CrO₂Cl₂ SnCl₄ . .

     

IR-spectroscopic studies of strength and concentration of acid centers on V2O5/Al2O3 catalysts

The strength of protonic sites and the concentration of acid centers in V₂O₅/Al₂O₃ catalysts have been estimated according to pyridine and ammonium adsorption.

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V₂O₅/Al₂O₃.

     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .

     

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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. .

     

Ab initio investigation of the electron structure in bis-Cu+ acetylene and vinylidene complexes

[Cu(-C₂H₂)₂]⁺, [Cu(-CCH₂)₂]⁺ and [Cu(-C₂H₂) (-CCH₂]⁺ complexes have been studied by the ab initio double-zeta basis set method. It has been established that all calculated compounds are stable to decomposition into two C₂H₂ molecules and Cu⁺ cation and into one C₂H₂ molecules and the respective monocomplex. Calculation results suggest the possibility of intramolecular acetylene-vinylidene rearrangement in the coordination sphere of Cu⁺.

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ab initio : [Cu(-C₂H₂)₂]⁺, [Cu(-CCH₂)₂]⁺, [Cu(-C₂H₂) (-CCH₂)]⁺. C₂H₂ Cu⁺ C₂H₂ . - Cu⁺.

     

Liquid-phase hydrogenation on new AlPO4?SiO2 supported rhodium catalysts

The liquid-phase catalytic hydrogenation of various organic compounds was carried out using new rhodium catalysts supported on AlPO₄–SiO₂ (2080 wt. %) system, in methanol as solvent, under low hydrogen pressure (0.55 MPa) and at 293 K. Neither alkene isomerization nor hydrogenolysis products were detected in any of the cases.

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AlPO₄–SiO₂ (2080 . %), , , (0,55 MPa) 293 . , .

     

Steady state kinetic equation for SO2 oxidation on vanadium catalysts

From the analysis of the detailed reaction mechanism and taking into account vanadium complex formation processes, a steady state kinetic equation has been derived to describe experimental data in a wide range of reaction conditions.

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, .

     

Hydrogen pressure dependence of the reaction of neopentane with hydrogen over Pd/SiO2 and Pt/SiO2 catalysts

H₂ pressure influences in different ways the reaction rates of neopentane conversion over Pd/SiO₂ and Pt/SiO₂ catalysts. It seems that on Pt/SiO₂ both isomerization and hydrogenolysis involve a common surface intermediate (probably an adalkyl), whereas on Pd/SiO₂ the hydrogenolysis goes via more dehydrogenated species than those involved in isomerization.

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H₂ Pt/SiO₂ Pd/SiO₂. , Pt/SiO₂ (, ), Pd/SiO₂ , .

     

V2O5/TiO2 oxidation catalysts, III. Oxidation of CO on pure and sodium-doped systems

The activity of vanadia/titania catalysts in CO oxidation has been tested and found to be of the same order as that observed for unsupported vanadia; the simultaneous presence of vanadium-sodium compounds cancels the activity, probably because of the elimination of labile V=0 species at surface defects.

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V₂O₅/TiO₂ CO, V₂O₅; - , , V=0 .

     

IR spectra of oxygen adsorbed on SnO2

IR spectra of oxygen adsorbed on SnO₂ with and without lattice defects have been studied. At low temperatures oxygen is adsorbed on defect SnO₂ in two forms of O ₂ ^– . This supports the earlier results obtained by ESR. The low-temperature forms of adsorbed oxygen (unrevealed in ESR spectra) were detected on defectless SnO₂. High-temperature forms of adsorbed oxygen appear in the IR-spectra as bands due to vibrations of the cation-oxygen bond.

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- SnO₂. , O ₂ ^– , . SnO₂ .

     

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- . . , .

     

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 -. , . .

     

Hreels studies of Hads effect on NO adsorption on Pt(111)

HREELS studies of NO molecular adsorption on clean and hydrogen covered Pt(111) have revealed that a reversible transition between bridge (₁) and on-top (₂) states of NO_ads is realized in the (NO+H₂)/Pt(111) system. In the presence of H_ads the adsorption of NO in the ₁ state is inhibited and the main state of NO_ads is ₂. Upon heating the layer (₂-NO_ads+H_ads) hydrogen desorption is accompanied by on-top to bridge state conversion.

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NO Pt(III). , (NO+H₂)/Pt(III) (₁) (₂) NO. H NO ₁ , , ₂ NO. (₂-NO+H) NO .

     

Effect of nickel on the hydrogenating activity of MoS2

The activating effect of nickel on MoS₂ impregnated with an aqueous solution of Ni(CH₃COO)₂ and sulfided has been established to be proportional to the amount of active nickel incorporated as Ni²⁺ cations in the MoS₂ lattice. MoS₂ capacity for active nickel is limited and determined by the preparation method of the parent MoS₂.

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MoS₂ ( Ni(CH₃COO)₂, ) Ni²⁺, . MoS₂ «» .

     

Phase composition of a selective V2O5?Fe2O3 catalyst of methanol oxidation to formaldehyde

Redispersion of Re/SiO₂ catalysts during air-aging at ambient temperature has been confirmed by TEM analysis. The splitting of large primary crystallites (>10 nm) under the influence of the strain energy of the oxide layer formed on the Re surface has been proposed to explain the observed phenomenon.

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Re/SiO₂ . , Re(>10 nm), , .

     

Kinetics and mechanism of the decomposition of pyrite under conventional and quasi-isothermal — quasi-isobaric thermoanalytical conditions

The kinetics and mechanism of the thermal decomposition of pyrite were examined by the method of quasi-isothermal and quasi-isobaric thermogravimetry (Q-TG). It emerged that by means of this technique the overlapping partial processes of the complicated oxidation and decomposition reactions of pyrite can be separated and studied independently from one another. It was found that the partial reactions FeS₂=FeS +S and Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ are endothermic processes taking place quasiisothermally and leading to equilibrium, while the oxidation FeS+O₂=Fe₂O_3–x(SO₄)_x is an exothermic process which takes place in an oscillating manner in a rather broad temperature interval.

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Zusammenfassung Autoren untersuchten die Kinetik und den Mechanismus der thermischen Zersetzung von Pyrit durch quasi-isotherme und quasi-isobare Thermogravimetrie (Q-TG). Es stellte sich heraus, daß sich überlagernde Teilprozesse der komplizierten Oxydations- und Zersetzungsprozesse von Pyrit mit Hilfe dieser Technik absondern und unabhängig voneinander untersuchen lassen. Es wurde festgestellt, daß die Teilreaktionen FeS₂=FeS+S und Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ endotherme Prozesse sind, die quasi-isotherm verlaufen und zu einem Gleichgewicht führen, während die Oxydation FeS+O₂=Fe₂O_3–x(SO₄)_x ein exothermer Prozeß ist, der oszillierend in einem ziemlich breiten Temperaturintervall verläuft.

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(Q-) . . , FeS₂=FeS+S Fe₂O_3–x(S₂O₄)_x=Fe₂O₃+SO₃ , . FeS+O₂ =Fe₂O_3–x(SO₄)_x , .

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The authors thank Prof. E. Pungor for valuable discussions, and Mrs. M. Kiss and Miss I. Fabian for their technical assistance.     

Kinetics of Co?Mo/Al2O3 catalyst reduction

According to kinetic studies on the reduction of commercial Co–Mo/Al₂O₃ and model catalysts in H₂ at 523–773 K, the kinetic curves for the reduction process have been determined. The reduction rate is shown to be higher for the commercial catalyst. Activation energies E_act for the reduction of several forms of Mo and Co in Co–Mo/Al₂O₃ catalysts are presented.

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H₂ 523–773 . , : Mo Co .