Kinetics of methanation of carbon dioxide on a nickel catalyst

The kinetics of hydrogenation of CO₂ to methane on an NKM-4A nickel-containing catalyst was studied in a wide range of change of partial pressures of hydrogen and carbon dioxide at 498–543 K. It was shown that when hydrogen is replaced by deuterium in the reaction, a reverse kinetic isotope effect is observed. The kinetic equation of the reaction was derived and a stepwise scheme is proposed which includes the involvement of oxygen-containing intermediates in the process without preliminary dissociation of CO₂.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 26, No. 5, pp. 620–624, September–October, 1990.     

Specific action of nickel-zeolite catalysts in the methanation of carbon monoxide

The effect of nickel distribution in zeolites on their activity in CO methanation, determined by the state of nickel on the outer zeolite surface, indicates that nickel inside the zeolite cavities is inactive. Under the effect of the reaction medium, an increase in the average size of nickel particles does not change the catalyst activity.

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CO, . , . , .

     

A study of the methanation reaction with simple nickel on amorphous carbon catalysts

Homologation of n-pentane and cyclopentane results in formation of benzene on Ru, Os, Re and Ir/SiO₂ catalysts. Formation of benzene can be explained by the insertion of carbene into terminal vinilic carbon followed by C₆-dehydrocyclization.

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- , Ru, Os, Re Ir/SiO₂ . C₆-.

     

Effect of hydrogen sulfide on the activity of nickel catalysts for methanation

The resistance of 14 different nickel catalysts to H₂S poisoning in CO₂ methanation was examined. Experiments were carried out in a quartz reactor of special design, utilizing the methods of temperature difference measurement (DTA) and chromatographic analysis of outlet gases.

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14 H₂S CO₂. , .

     

Hydrogenation of carbon monoxide over technetium catalysts

Supported Tc catalysts are active in CO hydrogenation, their activity depending on the nature of the support. The reaction proceeds predominantly toward methane formation. All catalysts studied yielded very little C₂ and C₃ hydrocarbons. The thermal desorption data indicate that the CO strongly bound to the substrate is responsible for CH₄ formation.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1507–1511, July, 1992.     

Preferential oxidation of carbon monoxide on supported gold catalysts

Catalyst precursors containing 1% Au were synthesized by the impregnation of Al₂O₃ and CeO₂-Al₂O₃ supports with an aqueous solution of HAuCl₄ followed by drying, treatment with aqueous ammonia for the removal of chlorine residues, and final drying at 90°C. The oxidation of CO in gas containing ～1 vol % O₂, ～1 vol % CO, 60 vol % H₂, and the balance N₂ on the activated catalysts was studied. In a number of experiments, to 18 vol % water was added to the gas mixture. The activation of precursors by the initial gas was studied. It was found that the prolonged storage of a precursor in air made its activation difficult to perform. The 1%Au/Al₂O₃ catalyst activated by the gas mixture stably operated in the preferential oxidation of CO at room temperature with the occurrence of the reaction in the mode of catalyst surface ignition (a hot spot at the bed inlet) under a change in the feed gas flow rate by a factor of 3. The effect of the presence of additional CO₂ (to 39 vol %) on the oxidation of H₂ was studied: the catalyst activity decreased. Because the reaction of CO₂ reduction to CO did not occur, the effect can be due to the adsorption of CO₂ on gold. The effect of the addition of water vapor to the feed gas was studied with the use of 1%Au/CeO₂-Al₂O₃ as an example. The exo/endo effects related to the adsorption/desorption of water on the catalyst surface were detected upon steam supply and shutoff at a bed temperature of 100–150°C. It was noted that the addition of water vapor to a certain level favorably affected the selectivity (decreased the residual concentration of CO). The boundary water concentration, at which the effect became negative, depended on catalyst bed temperature. The higher was the bed temperature, the greater amount of water could be added until the manifestation of a negative effect.     

Robust nickel silicate catalysts with high Ni loading for CO2 methanation

CO₂ is the main component of greenhouse gases and also an important carbon source. The hydrogenation of CO₂ to methane using Ni-based catalysts can not only alleviate CO₂ emissions but also obtain useful fuels. However, Ni-based catalysts face one major problem of the sintering of Ni nanoparticles in the process of CO₂ methanation. Thus, this work has synthesized a series of efficient and robust nickel silicate catalysts (NiPS−X) with different nickel content derived from nickel phyllosilicate by the hydrothermal method. It was found that the Ni loading plays a critical role in the structure and catalytic performance of the NiPS−X catalysts. The catalytic performance gradually increases with the increase of Ni loading. In particular, the highly dispersed NiPS-1.6 catalyst with a high Ni loading of 34.3 wt% could obtain the CO₂ conversion greater than 80%, and the methane selectivity was close to 100% for 48 h at 330 °C and the GHSV of 40,000 mL g⁻¹ h⁻¹. The excellent catalytic property can be assigned to the high dispersion of Ni nanoparticles and the strong interaction between the active component and the carrier, which is derived from a unique layered silicate structure with lots of nickel phyllosilicate and a large number of Lewis acid sites.     

Kinetic model of catalytic oxidation of carbon monoxide on nickel

A mechanism is proposed for describing the previous disclosed multiplicity of equilibrium states in the oxidation of carbon monoxide on metallic nickel. In contrast to the known mechanism for oxidation of CO oh platinum metals it includes a nonlinear stage of carbon monoxide adsorption and a linear stage of oxygen adsorption. A kinetic model has been obtained and stage velocity constants have been found, providing a basis for obtaining a quantitative agreement between the calculated and experimental relations between the reaction velocity and the reagent concentrations. Opinions are stated in relation to the causes for evolution of the CO oxidation reaction from platinum metals to nickel.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 83–87, January–February, 1986.     

Effect of nickel oxide additive on properties of catalysts used in the reaction of selective oxidation of carbon monoxide

Effect of nickel oxide additives on the oxidation selectivity of carbon monoxide in the presence of hydrogen was studied for the widely recognized system constituted by copper and cerium oxides. It was shown that a significant positive effect is observed upon introduction of the nickel-containing additive (??0.3%) due to the electron-donor effect of nickel oxide. It was demonstrated that the catalyst of composition NiO/CuO/CeO₂/Al₂O₃ shows high selectivity in the reaction of CO oxidation.     

New catalysts for the oxidation of carbon monoxide

Catalytic activity of binary and multicomponent semiconductors of the ZnSe-CdTe system prepared in a form of powders and nanofilms in CO oxidation was studied by pulsed flow and circulation flow methods. The conditions of maximal CO conversion were determined from the results of investigation of individual and joint adsorption of the reactants in a broad temperature range, and the specific activity of the catalysts was determined by the specific reaction rate at the specified temperature and composition of the reaction mixture. A noticeable catalytic transformation of CO on the semiconductors under study (up to 78.5%) was noted as low as room temperature. It was concluded that the oxidation of CO and adsorption of the CO + O₂ mixture proceeds mainly by the collisional mechanism. It was noted that the high activity of studied catalysts already at room temperature (the (ZnSe)_0.05(CdTe)_0.95 solid solution possessed the highest activity) and the absence of high-cost metals in their composition allow us to recommend them as low-temperature, relatively low-cost catalysts for the neutralization of CO (carbon monoxide).     

Characteristics of methanation of carbon monoxide on a nickel-aluminum-calcium catalyst at atmospheric and elevated pressures

Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 254–255, March–April, 1988.     

Kinetics of the total oxidation of para-xylene and its mixtures with carbon monoxide over supported copper catalysts

The kinetics of the total oxidation of para-xylene and its mixtures with CO over alumina-supported copper catalysts has been investigated at atmospheric pressure in the temperature range from 200 to 270°C. The reactions over the catalysts 10%CuO/γ-Al₂O₃ and (10%CuO + 20%CeO₂)/γ-Al₂O₃ obey the same kinetic equations in fractional rational form. These equations imply that the reactions occur at medium surface coverages of adsorbed substances and differ only in numerical values of constants. The simultaneous oxidation of para-xylene and CO reveals a complicated mutual influence associated with the formation of new intermediates inducing a change in the kinetics of the process.     

Reaction mechanism of CO methanation on nickel catalysts,as studied by isotopic and nonstationary methods

Kinetic isotope effects were measured upon the replacement of hydrogen by deuterium in the reaction of carbon monoxide methanation on nickel catalysts supported on TiO₂ and γ-Al₂O₃. Data on the mechanism of the process were obtained with the use of a nonstationary method. A step-scheme was proposed, in which the interaction of oxygen-containing compounds with hydrogen is a slow step of the process.     

Reaction of hydride complexes of nickel with carbon monoxide

Conclusions When the hydride complexes of nickel (Ph₃P)₃Ni(H)Br and [(Ph₃P)₃Ni(H)(CH₃CN)]⁺BF₄ ^– are reacted with CO, the Ni-H bond is cleaved and carbonyl complexes of Ni(0) are formed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1919–1920, August, 1981.     

Cooligomerization of carbon monoxide with cyclic olefins on supported palladium catalysts

The cooligomerization of CO with cyclic olefins, such as norbornene, 5-vinyl-2-norbornene, and dicyclopentadiene, in toluene in the presence of supported palladium catalysts containing 2,2’-bipyridine as a ligand is studied. It is shown that, during copolymerization, opening of the double bond in a ring occurs, while in the case of 5-vinyl-2-norbornene, vinyl bond C=C is not involved in the reaction. When ethylene is added to the reaction mixture, it does not participate in polymer-chain growth. The yield of the process is commensurable with the yield attained in the case of a homogeneous catalytic system, and the conversion of olefins is as high as 47%. The copolymers in the solid state occur in the form of spiroketal structures that, during dissolution, transform into ketone structures to different extents.     

纳米银催化剂上CO氧化反应研究进展

纳米Ag催化剂由于具有独特的物理和化学性质,在很多反应中受到了越来越多的关注,尤其对低温催化一氧化碳氧化反应.近年来,银催化剂表现出较高的催化活性、稳定性以及良好的应用前景,能够在常温下将CO氧化为CO2.本文结合本课题组的研究进展,从制备方法、载体、预处理、第二组分、其它气氛和催化反应机理等方面对Ag基催化剂上CO氧化反应进行了系统的讨论和总结.