Temperature-programmed reduction of bimetallic Ir?Fe/Al2O3 catalysts

Investigations on the temperature-programmed reduction of 3% Ir–Fe/Al₂O₃ catalysts after their oxidation at different temperatures T_ox have been carried out. A substantial promoting effect of iridium on the reducibility of iron has been observed for all the investigated catalysts, at T_ox applied.

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- 3% Ir–Fe/Al₂O₃ (T_ox). T_ox.

     

Sulfuration of Pt/Al2O3, Pt?Re/Al2O3 and Pt?Ir/Al2O3 catalysts

Three reforming catalysts Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃ have been sulfurated by H₂S and tested by their activities in benzene hydrogenation. By treatment at 500°C under hydrogen flow only a part of the initial activity of the non-sulfurated catalyst is retained. So only a part of the adsorbed sulfur is easily removed in these conditions. The remaining sulfur for each of the catalysts (Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃) gives the same atomic ratio of 0.5 sulfur atom per accessible metallic atom.

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Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃ . 500°C H₂ . . ., . (Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃) 0,5.

     

Temperature-programmed reduction and oxidation of bimetallic catalysts Rh?Ag/Al2O3

Investigations of temperature-programmed reduction and oxidation of bimetallic catalysts Rh–Al₂O₃ seem to indicate that there are no strong interactions between rhodium and silver. Bimetallic catalysts rather show the additive properties of individual components, i. e. rhodium and silver.

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- Rh–Al/Al₂O₃ . , .

     

Temperature-programmed reduction and oxidation of bimetallic Pd?Ni/Al2O3 catalysts

Temperature-programmed reduction and oxidation of bimetallic catalysts Pd–Ni/Al₂O₃ seem to indicate phase segregation of palladium and nickel oxides and alloying of palladium and nickel in the process of reduction of oxidized catalysts.

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- Pd–Ni/Al₂O₃ , .

     

Temperature-programmed reduction of CuO?NiO/Al2O3 catalysts

Reducibility of NiO/Al₂O₃ and CuO–NiO/Al₂O₃ catalysts has been studied by the TPR method within the temperature range 293–873 K. The results suggest that the copper content essentially does not influence the reducibility of NiO/Al₂O₃.

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NiO/Al₂O₃ CuO–NiO/Al₂O₃ TPR 293–873 . , NiO/Al₂O₃.

     

Temperature-activated hydrogen adsorption on Ir/Al2O3

A strongly temperature-activated character of hydrogen sorption on supported iridium has been observed. Activated hydrogen sorption as a function of temperature grows, at first, rapidly and its further, relatively gentle increase is probably due to a spillover effect.

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. , , , , .

     

CO oxidation over CuCr/Al2O3 catalysts in presence of SO2

Poisoning of variously prepared CuCr/Al₂O₃ catalysts having different compositions by sulfur dioxide has been studied. Comparative values for a decrease in the catalyst activities have been obtained.

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CO .

     

Temperature-programmed desorption of carbon monoxide from 3% Ir?Fe/Al2O3 catalysts

An increase in percentage of iron in 3% Ir–Fe/Al₂O₃ brings about a considerable decrease in desorptive effects of CO and small qualitative changes in TPD spectra, suggesting the predominant role of iridium, slightly modified by the presence of iron.

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3%- Ir–Fe/Al₂O₃ CO . , , .

     

Temperature-programmed hydrogen desorption from water on bimetallic catalysts Ir?Fe/Al2O3

Desorption of hydrogen liberated in the process of water decomposition on bimetallic catalysts (3% Ir–Fe/Al₂O₃) at linear temperature growth was observed. In the case of iridium the amounts of desorbing hydrogen are relatively small, whereas for iron they are many times greater.

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, 3% Ir–Fe/Al₂O₃ . , , .

     

Sulfurization of Pt/Al2O3?Cl catalysts. IV. Adsorption sites of H2S on Al2O3, Al2O3?Cl and Pt/Al2O3?Cl

Chemisorption of H₂S on Al₂O₃, Al₂O₃–Cl and Pt/Al₂O₃–Cl has been studied by gravimetry and IR spectroscopy. The influence of the amount of Cl on the H₂S adsorption equilibrium value and the nature of the adsorption sites at low and high coverages are discussed.

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H₂S Al₂O₃, Al₂O₃–Cl Pt/Al₂O₃–Cl . Cl H₂S, .

     

Investigation of Pd?Pb/Al2O3 catalysts by temperature-programmed reduction

Temperature-programmed reduction has been used to characterize, a series of Pd–Pb/Al₂O₃ catalysts. Oxidation and thermal decomposition of bimetallic Pb–Pb/Al₂O₃ catalysts in a stream of argon leads to segregation of individual oxides. Reduction of PdO–PbO/Al₂O₃ occurs at the same temperature as that found for PdO/Al₂O₃ and PbO/Al₂O₃. TPR measurement after isothermal reduction at 823 K and reoxidation point to bimetallic interaction between palladium and lead atoms only for small percentages of palladium.

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- () Pd–Pb/Al₂O₃. PdO–Pb/Al₂O₃ . PdO–PbO/Al₂O₃ PdO/Al₂O₃ PbO/Al₂O₃. - 823 — .

     

Partial oxidation of methane on Cr2O3/Al2O3

The oxidation of methane on supported chromia was studied at temperatures varying between 423 and 743 K and CH₄/O₂ ratios between 1 and 9 in a differential reactor. The main reaction products observed were carbon monoxide and formaldehyde. The rates of reaction obey a power law expression.

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, 423 743 CH₄/O₂ 1 9, . . .

     

Investigation of the acidity of Ni/Al2O3 and Ni/SiO2?Al2O3 catalysts

Acidity of Ni-modified alumina and silica-alumina catalysts was determined using n-butylamine titration and pyridine adsorption methods. Strong influence of Ni²⁺ ions on the Brönsted acidity of silicaalumina was observed. Improved Brönsted acidity of such system was confirmed by the results of the test reaction.     

Reduction kinetics of Mo/Al2O3 catalysts

Studies of the reduction kinetics of MoO₃ and Al₂O₃–MoO₃ catalysts in H₂ at 523–823 K indicate that molybdenum is present in Al₂O₃/MoO₃ in three forms: as Mo⁶⁺ in the Al₂O₃ lattice and as MoO₃ and Al₂(MoO₄)₃ phases. Activation energies of reduction E_act determined according to the Avrahmy-Erofeev equation, are reported.

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MoO₃ Al₂O₃–MoO₃ H₂ 523–823 . Al₂O₃–MoO₃ : Mo⁶⁺ Al₂O₃ MoO₃ Al₂(MoO₄)₃, . -.

     

Cyclohexane dehydrogenation over Pt-Dy/Al2O3 catalysts

The conversion of cyclohexane dehydrogenation over Pt–Dy/Al₂O₃ has been studied with a pulsed microcatalytic reactor. Two interesting experiments utilizing CS₂ and thiophene poisoning Pt/Al₂O₃ and Pt–Dy/Al₂O₃ for cyclohexane dehydrogenation are shown and the reaction mechanism is described. The kinetic parameters of cyclohexane dehydrogenation have been calculated. Correlation of the catalytic behavior with the properties of active sites is also discussed.     

A model of reduction mechanism of rhenium in Re/Al2O3 catalysts

In Re/Al₂O₃ there exist a monolayer type of Re and a second one which is inserted in the alumina lattice. The latter is reduced by a two-step mechanism including Re(IV) species.

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Re/Al₂O₃ , . , Re(IV).

     

Fischer-Tropsch synthesis over Ru/Al2O3 catalysts

Fischer-Tropsch syntheses (FTS) were carried out in a slurry phase over Ru/Al₂O₃ catalysts using hexadecane as a solvent. The outcome of the FTS was dependent on the oxide support, calcination temperature, synthesis gas composition and sulfur content. The addition of Mn/Na to Ru/Al₂O₃ was effective in raising the initial activity and C5+ selectivity, but after 20 hours, the performance of the modified catalyst was similar to that of the unmodified catalyst. An additional investigation involving the use of fresh vs used catalysts demonstrated that an agglomeration of the metallic Ru, at least in part, does occur during the reaction.     

Temperature-programmed reduction (TPR) of Co?Ni/Al2O3 catalysts

Reducibility of Co–Ni/Al₂O₃ catalysts has been studied by the TPR method in the temperature range 293–900 K. Results seem to indicate alloying of cobalt and nickel in the process of reduction of the bimetallic systems.

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Co–Ni/Al₂O₃ 293–900 K. .

     

X-ray study of Re/Al2O3 and Re+Pt/Al2O3 catalysts using synchrotron radiation

Uning synchrotron radiation, L_III rhenium absorption spectra have been studied for Re/Al₂O₃ and Re+Pt/Al₂O₃ catalysts obtained by impregnation. For individual rhenium compounds a linear dependence between the shift of absorption edge and the state of rhenium oxidation has been found. The absorption spectra of reduced catalysts are significantly broadened as compared with those of individual compounds of the same valency. This points to the presence of rhenium compounds in different oxidation states.

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L_III- , Re/Al₂O₃ Re+Pt/Al₂O₃, . . . .