The dehydrogenation of cyclohexane on an AP-64 industrial platinum catalyst subjected to plasma chemical treatments

The influence of glow discharge plasma in oxygen and argon and high-frequency discharge plasma in hydrogen on the activity of the AP-64 (Pt/γ-Al₂O₃) catalyst in the dehydrogenation of cyclohexane was studied. The catalytic experiments were performed in a flow unit and under static conditions in a vacuum. Under flow conditions, catalyst treatment with plasmas in O₂ and Ar decreased the yield of benzene by ～50% but strengthened temperature hysteresis because of the formation of active carbon on the surface of the catalyst. Under static conditions, argon plasma and high-frequency discharge H₂ plasma multiply increased the rate of the reaction because of an increase in the number of active centers, whereas an oxygen plasma decreased the rate of the reaction by two times because of an increase in activation energy. The determination of the order of the reaction led us to suggest that the stage scheme of the reaction did not change after plasma chemical catalyst treatments.     

The influence of plasma chemical treatment of nickel and nickel-rhenium catalysts deposited on sibunite on their activity in dehydrogenation

The dehydrogenation of isopropanol was studied at 440–680 K to find that the activity of the Ni(1 wt %)/sibunite catalyst decreased after annealings and quenchings and was stabilized after subsequent treatment with an (I) O₂ glow-discharge or (II) H₂ high-frequency plasma. Treatments of both kinds decreased the activity of the catalyst below the Curie point (633 K) and increased it over the paramagnetic temperature range (635–680 K). The treatment of the (1 wt % Ni–1 wt %Re)/sibunite and (2 wt % Ni–2 wt % Re)/sibunite catalysts with plasma II weakly influenced their activity, whereas treatment with plasma I substantially increased it. The kinetic reaction parameters on the (2 wt % Ni–2 wt % Re)/sibunite catalyst were found to depend on the duration of treatment with plasma II. Treatment with plasma I much more effectively changed the state of the surface of all the catalysts studied than treatment with plasma II.     

Synthesis and properties of a platinum catalyst supported on plasma chemical silicon carbide

A CO oxidation catalyst based on β–SiC and Pt nanoparticles has been synthesized and studied. The average size of Pt clusters on the surface of the plasma-chemical silicon carbide nanoparticles is close to 4 nm. It has been found that the rate of the CO oxidation reaction at low concentrations (100 mg/m³) in air at room temperature over the catalyst based on platinum and silicon carbide nanoparticles is 60–90 times that over a platinum black-based catalyst with a specific surface area of 30 m²/g. The Pt/SiC catalyst containing 12 wt % Pt has been found to provide the maximum CO oxidation rate.     

Effect of plasmochemical treatment of platinum catalyst on dispersity of metal phase and its catalytic activity

We studied how treatment of 0.64 wt % Pt/SiO₂ catalyst with a glow-discharge plasma in O₂ and a high-frequency plasma in H₂ (HF H₂) influences the cyclohexane dehydrogenation reaction. The effect of plasmochemical treatment on the average diameter of platinum particles was established by the method of X-ray diffraction analysis. It was found that oxygen plasma increases the surface area of the metal by ∼15% and diminishes activity by raising the activation energy and reducing the number of active centers per unit surface of the metal. The HF H₂ plasma increases the reaction rate constant many times over, due to the number of active centers per unit surface of the metal rising sharply while the size of the Pt particles remains unchanged.     

Rhodium-technetium catalysts in the dehydrogenation of cyclohexane

The catalytic properties of a Rh-Tc/support (-Al₂O₃, SiO₂, or MgO) system in the dehydrogenation of cyclohexane have been investigated. A nonadditive increase in the catalytic activity of bimetallic catalysts in comparison with monometallic systems has been established. This effect depends on the ratio of the amounts of the supported metals and on the nature of the support. Diffuse reflectance spectra showed the presence of ionic forms of the metals in the bimetallic catalysts. Analysis of the catalytic and optical properties allowed one to draw the conclusion that the synergistic effect is explained by the formation of Rh_xTc_y clusters.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1563–1566, September, 1994.     

Note on the kinetics of dehydrogenation of cyclohexane

Kinetic data available for Pt and Ni suggest doubts about the acceptance of the method applied by V.I. Anikeev et al. [1] as basis for Kinetic Laws for cyclohexane dehydrogenation on Pd/C catalysts.

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Pt Ni , . . . [1] Pd/C.

     

Hydrogenation of CO2 conjugated with dehydrogenation of cyclohexane over an intermetallic catalyst

Transformations of carbon dioxide catalyzed by the hydride form of [TiFe_0.95Zr_0.03Mo_0.02]H_x, by the industrial Pt/Al₂O₃ catalyst, and by a mixture of the above materials were studied. Study of the thermal desorption of H₂ showed the presence of two forms of absorbed hydrogen, namely, the weakly bound hydrogen, which is evolved from the intermetallic structure on heating to 430 °C under Ar, and the strongly bound hydrogen (SBH), which remains in the intermetallic compound at higher temperatures (up to 700 °C). In a carbon dioxide medium, the SBH enters into selective CO₂ reduction to give CO at 350—430 °C and 10—12 atm. The selectivity of the formation of CO reaches 80—99% for conversion of CO₂ between 50—70%, the SBH being consumed almost entirely for the reduction of CO₂. In the presence of the mixed catalyst, conjugate reactions proceed efficiently; dehydrogenation of cyclohexane yields hydrogen, which is consumed for CO₂ hydrogenation.     

Cyclohexane dehydrogenation on a copper-platinum catalyst

The reaction of the dehydrogenation of cyclohexane on a copper-platinum catalyst supported by silica gel (1 wt % Pt + 0.15 wt % Cu)/SiO₂ was studied. The state of the catalyst surface was investigated using X-ray photoelectron spectroscopy. It was established that under both flow and static conditions, the activity of the copper-platinum catalyst is higher than the activity of a catalyst containing 1 wt % Pt/SiO₂. The rise in activity as a result of the introduction of copper, due to a decrease in the activation energy, is explained by an increase in the fraction of carbon in the composition of active centers localized on particles of neutral (Pt _m ⁰) and positively charged (Pt _n ^+δ) platinum, and by the formation of centers with increased activity as a result of the adsorption of Cu^+δ on particles of Pt _m ⁰. It was demonstrated that treating the copper-platinum catalyst with the plasma of a glow discharge in argon and oxygen increases its activity, while treatment in high-frequency H₂ plasma reduces it. The indicated changes in the activity are associated with the alteration of the activation energies and the number of active centers, revealed by X-ray photoelectron spectroscopy, that depend on changes in the catalyst surface composition.     

The properties of supported rhenium catalysts in the dehydrogenation of cyclohexane

The 2 % Re/sibunite catalyst is more active than 2 % Re/-Al₂O₃ and 2 % Re/-Al₂O₃ catalysts in the dehydrogenation of cyclohexane into benzene (T = 350 °C,w = 0.5 h–1). The substitution of NH₄ReO₄ by HReO₄ in the preparation of the catalyst enhances its activity by a factor of 1.3. Treatment with HNO₃ or oxalic acid increases the selectivity by a factor of 1.2 and 1.35, respectively, the overall conversion of cyclohexane being 32–40 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2119–2121, August, 1996.     

The influence of plasma chemical treatments on the activity of the Li3Fe2(PO4)3 catalyst in butanol-2 transformations

The influence of plasma chemical treatments in oxygen, hydrogen, and argon on the catalytic activity of Li₃Fe₂(PO₄)₃ was studied for the example of butanol-2 transformations. Plasma chemical treatment was found to be an effective method for increasing catalyst activity and changing its selectivity. The character of activation depends on the selection of the plasma-forming gas. The highest activity in the dehydration of butanol-2 was observed after treating the catalyst in hydrogen under glow discharge conditions.     

Isomerization and dehydrogenation of cyclohexane on chromium oxide

Conclusions A study was made of the reactions for the dehydrogenation and isomerization of cyclohexane under the conditions of their joint progress on unsupported chromium oxide. The obtained data indicate that these processes progress on different active portions of the catalyst surface.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 921–922, May, 1966.     

Synergistic effect between Sn and K promoters on supported platinum catalyst for isobutane dehydrogenation

Catalytic dehydrogenation of isobutane has recently received considerable attention because of the increasing demand for isobutene.In this study,the synergistic effect between Sn and K on PtSnK/γ-Al2O3 catalysts has been investigated by changing the content of Sn.It was found that with the presence of potassium,suitable addition of Sn could not only increase the metal dispersion,but also reduce the catalyst acidity.In these cases,the synergistic effect could also strengthen the interactions between the metal and support,which resulted in an increase in both catalytic activity and stability.In our experiments,Pt-0.6SnK/Al catalyst exhibited the lowest deactivation rate (12.4%) and showed a selectivity to isobutene higher than 94% at the isobutane conversion of about 45.3% after running the reaction for 6 h.However,with the excessive loading of Sn,surface property of active sites and the interactions between metal and support were changed.As a result,the initial optimal ratio between the metallic function and acid function would be destroyed,which was disadvantageous to the reaction.