Promoting effect of Pt in Ni-based catalysts for CH4 reforming

The effect of Pt/Ni ratio on the surface properties and catalytic behavior of bimetallic PtNi catalysts for reforming of methane with CO₂ was studied. The TPR, FTIR of adsorbed CO and XPS data showed that introduction of a small amount of Pt (0.3 – 0.5 wt.%) into the Ni catalyst leads to a decrease of the NiO size, its easy reduction and a uniform distribution of the nickel metal particles.     

Propane formation by aqueous-phase reforming of glycerol over Pt/H-ZSM5 catalysts

Solid acid supports such as H-ZSM5, H-Mordenite, γ-Al₂O₃, USY and Beta catalysts were modified with Pt. These Pt/oxide catalysts were found to be active for propane formation through aqueous reforming of glycerol in the presence of hydrogen. The reforming reactions, possibly, proceeded through reaction cycles of dehydration on acid sites and hydrogenation on Pt sites over the catalysts.     

Charge state and activity of Pt/C catalysts in oxygen reduction reaction

Electrochemical experiments with a rotating disk electrode are used to measure specific catalytic activity of Pt/C structures in the oxygen reduction reaction at the density of Pt nanoparticles on the glassy carbon support surface below one monolayer. The specific activity maximum is found at the coverage of about 0.4 monolayer. An explanation of the observed dependence is suggested that is based on consideration of the relationship between the surface density and charge state of the system of metallic catalyst particles. A numeric model is developed that describes charge transfer in the catalyst structure due to the difference in the work functions between the metal nanoparticles and support with account for the discrete nature of the nanoparticle charging and their mutual polarization. Calculations show that the carbon support coverage by Pt particles of about 0.4 monolayer corresponds to the largest amount of charged particles with the maximum energy of electrons, which provides the maximum catalyst activity and explains the dependence observed in the experiment.     

Oxidized platinum surface in Pt/Al2O3 reforming catalysts: IR studies

The influence of halide ions on the state of dispersed Pt in oxidized catalysts has been investigated, adsorbed CO being used as a probe. Charged platinum complexes form upon catalyst oxygenation, with CO bands at 2130, 2150, 2165, 2170 and 2180 cm^–1. Composition of the complexes depends on the oxidation temperature and the nature of the halide ion.     

Catalytic properties of metallic and electron-deficient platinum in reforming over Pt/Al2O3 catalysts

The activity of Pt/Al₂O₃ catalysts with various contents of metallic (Pt^o) and electron-deficient (Pt) platinum has been examined in dehydrocyclization of n-heptane and dehydrogenation of cyclohexane. In the former case it is proportional to the number of surface Pt atoms and in the latter case it is proportional to the BET surface of metallic platinum Pt^o.

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(Pt^o) (Pt) - . , Pt, — Pt^o.

     

Effect of pretreatment conditions on the activity and selectivity of Pt/Al2O3 reforming catalysts

The optimal reduction conditions for Pt/Al₂O₃ vary depending on whether the catalyst is fresh or lined-out and chlorine is present or absent. Optimal pretreatment conditions proposed by previous workers for fresh catalysts therefore have no meaning for industrial reformers since reforming catalysts spend most of their life under line-out conditions. Results from this work lend support to the strong hydrogen chemisorption theory.

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Pt/Al₂O₃ , , . , , , , .. . .

     

Tap study of the impact of the oxidation state of Pt/PrCeZrO and Pt/GdCeZrO catalysts on their reactivity in the partial/deep oxidation of methane

The temporal analysis of products (TAP) technique coupled with the oxygen TPD was used to elucidate the effects of the Pt-supported fluorite-like doped ceria–zirconia oxide chemical composition and the type of pretreatment on their oxygen bonding strength, mobility, and reactivity as related to catalytic properties in the partial oxidation of methane into synthesis gas. A rapid evolution of hydrogen under CH₄ pulse observed for oxidized catalysts agrees with the direct route of the methane selective oxidation into syngas. This route is favored by the Pt-support interaction and a moderate bonding strength of surface oxygen species along with a high lattice oxygen mobility.     

Ethanol steam reforming on Ni/Al2O3 catalysts: effect of the addition of Zn and Pt

Ni-based catalysts supported on Zn-modified alumina were investigated in the ethanol steam reforming reaction. A commercial γ-alumina was impregnated with different amounts of zinc nitrate (0, 2, 5, 10, 15, 20 wt.% on Zn basis), calcined, and then impregnated with nickel nitrate aqueous solutions. The samples were characterized by a number of techniques: N(2) adsorption at 77 K, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray fluorescence (XRF), and temperature-programmed reduction (TPR). Their catalytic behavior in the ethanol steam reforming reaction was studied at 873 K, with a H(2)O/ethanol ratio of 5:1. Two effects of the presence of Zn were detected. On the one hand, zinc modifies the surface structure and the surface chemistry of the catalysts by formation of zinc aluminates, and on the other hand, zinc oxide can be reduced to metallic zinc under reaction conditions, thus modifying the catalytic properties of the active phase. The presence of Zn increases the ethanol conversion to gaseous compounds as compared with the catalyst supported on the Zn-free commercial alumina. The addition of a small amount of Pt (1 wt.%) causes a beneficial effect in the reaction. When Ni catalysts were used without a previous reduction treatment, ethylene was formed in high amounts; however, the Pt-Ni catalysts need no reduction pre-treatment to achieve high H(2) yields (close to 70%) and showed a high stability versus time on stream because of the control of the production of ethylene, a coke precursor.     

Investigation of n-heptane conversion over Pt?Al2O3 catalysts under gradientless reforming conditions

The rates of the total and individual directions of n-heptane conversion in reforming over platinum-on-alumina catalysts were shown to be independent of dilution with hydrogen. They can be described by simple equations following from kinetic concepts in ideal adsorbed layers.

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, - , .

     

X-ray diffraction studies of the state of components in Pt?Ce/Al2O3 catalysts

X-ray diffraction studies of supported Ce/Al₂O₃ and Pt–Ce/Al₂O₃ catalysts have shown that besides a bulk phase CeO₂ a product of the interaction with the support cerium aluminate having a perovskite structure, is usually formed. Platinum in unreduced modified samples forms an oxide and is statistically distributed in the perovskite phase of cerium aluminate. After reduction, only half of the metal is in the metallic state with a particle size of 10 Å.

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, CeO₂, - . . 10 Å.

     

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, . . . .

     

Degradation of Pt/C catalysts in start-stop cycling tests

The stability of highly disperse 50 wt % Pt catalysts deposited on carbon supports with various porosity and morphology is tested in accelerated oxidative experiments in the potential range of 1–1.5 V (RHE) in 0.1 M HClO₄ solution. The electrochemically active surface area of platinum (S _Pt) is determined based on the charge of adsorbed hydrogen by the cyclic voltammetry (CVA) method. The specific activity per mass unit (the mass catalytic activity (MCA)) and the electrochemically active surface area of the active component (surface catalytic activity (SCA)) are determined in the oxygen electroreduction reaction (OERR) by the method of rotating disk electrode (RDE). It is shown that the catalyst degradation is mainly due to the growth of Pt particles and the corrosion of the carbon support. It is found that under these cycling conditions, the rate of the S _Pt decline depends inversely on the cycle number throughout the cycling interval (up to 60000 cycles) for all catalysts, which points to the quadratic dependence of the degradation rate on S _Pt. Two regions are revealed in the MCA and SCA dependences on the cycle number, In the first region (from 0 to 8–10 thousand cycles), a sharp decrease in MCA and SCA is observed for all catalysts, which can be associated with the restructuring or passivation of the Pt particle surface due to the oxide formation on oxidative cycling. In the second region, the relative stabilization of MCA and the linear increase in SCA are observed for all catalysts without exception. The linear increase in SCA is due to the growth of Pt particles and the size effect. It is shown that carbonization of the carbon support leads to enhancement of its cycling stability.     

Modern state of the catalytic reforming of petrol fractions. Experience of manufacture and industrial exploitation of reforming catalysts of the PR series

Analysis of the modern state of catalytic reforming is performed. Comparative assessment of the efficiency of various technologies of the process is given and their distribution in Russia and abroad is shown. Experience of the modernization of reforming installations with periodic catalyst regeneration is summarized. The state of manufacture of reforming catalysts in our country and accumulated experience of the development of catalysts of the PR series are presented. Results of industrial exploitation of new domestic reforming catalysts are shown. On this basis comparative assessment of Russian and imported catalysts is given. Original Russian Text D.I. Kiryanov, M.D. Smolikov, V.V. Pashkov, A.G. Proskura, E.V. Zatolokina, I.E. Udras, A.S. Belyi, 2007, published in Russkii Khimicheskii Zhurnal, 2007, Vol. 51, No. 4, pp. 60–68.     

Hydrocarbon conversion over Pt?Re/Al2O3-ZSM-5 bifunctional catalysts. II. Sulfur resistance of Pt?Re/Al2O3 modified with ZSM-5

The sulfur resistance of Pt–Re/Al₂O₃-ZSM-5 catalyst has been investigated for normal heptane reforming. It was found that while sulfur acts as a poison for Pt–Re/Al₂O₃, it can play an important role in activity maintenance and aromatics production when ZSM-5 zeolite is present.

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Pt–Re/Al₂O₃-ZSM-5 -. , , Pt–Re/Al₂O₃, ZSM-5.

     

X-ray spectral investigation by synchrotron radiation of supported Re/SiO2 and (Re+Pt)/SiO2 catalysts prepared via triethoxyrhenium

Using synchrotron radiation L_III absorption spectra of rhenium in Re/SiO₂ and (Re+Pt)/SiO₂ catalysts prepared via triethoxyrhenium have been studied. The conclusion has been drawn that reduced catalysts contain lowvalent rhenium ions and their composition is more uniform than that of the previously examined catalysts Re/Al₂O₃ and (Re+Pt)/Al₂O₃ prepared by a conventional impregnation technique.

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L_III- Re/SiO₂ (Re+Pt)/SiO₂, . , , Re/Al₂O₃ (Re+Pt)/Al₂O₃, .