Nickel catalysts based on porous nickel for methane steam reforming

The influence of synthesis conditions on the phase composition and texture of porous nickel supports as plates with a magnesium oxide underlayer were investigated by X-ray diffraction, low-temperature nitrogen absorption, and electron microscopy combined with X-ray microanalysis. Nickel catalysts supported on these plates were studied. Thermal treatment of Mg(NO₃)₂ in nitrogen yields a magnesium oxide underlayer with a small specific surface area (support I). The replacement of nitrogen with hydrogen leads to a larger surface area (support II). The formation of MgO is accompanied by the incorporation of Ni²⁺ cations from the oxide film into the underlayer. Upon subsequent reduction with hydrogen or under the action of the reaction medium, these cations form fine crystallites of nickel. The supports having an oxide underlayer show a higher activity in methane steam reforming than the initial metallic nickel. Nickel catalysts on supports I and II show similar activities. The activity of the catalysts was stable throughout 50-h-long tests; no carbon deposits were detected by TEM.     

Synthesis of neutral nickel catalysts for ethylene polymerization--the influence of ligand size on catalyst stability

A facile synthesis of nickel salicylaldimine complexes with labile dissociating ligands is described. In addition to producing highly active ethylene polymerization catalysts, important insights into the effect of ligand size on catalyst stability and information on the mechanism of polymerization are provided.     

Promotion of nickel catalysts for the steam reforming of methane

The influence of additives (Cu, Fe and Al₂O₃) on the textural and catalytic properties of nickel in steam reforming of methane is described. The effects of structural promoting by Al₂O₃ and of electronic promoting by copper are reported. The rate of steam reforming of methane was measured in a gradientless reactor at atmospheric pressure.

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(Cu, Fe Al₂O₃) . Al₂O₃ . .

     

Influence of particle size on the stoichiometry of chemisorption of oxygen on supported nickel catalysts

It has been found that the stoichiometry of adsorption of oxygen on nickel supported on silica is linearly correlated to the particle size of the metal. It is shown that the combined use of hydrogen and oxygen chemisorption at room temperature allows to determine both the dispersity and reduction degree of nickel.

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, . , , .

     

Effect of the support on the coking of nickel catalysts in hydrocarbon steam reforming

Experiments on the coking rates of variously prepared nickel catalysts on TiO₂, Al₂O₃ and MgO in n-butane steam reforming show that changes in the relative coking rate at a rising steam excess in the gas phase depend mainly on the kind of support. The results obtained are accounted for by changes in the electron density at the site of nickel crystallite contact with the surface of various supports.

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, TiO₂, Al₂O₃ MgO, - , , , , , . .

     

Alumina as a nickel catalysts support for steam reforming of hydrocarbons

The coking resistance of six alumina supported nickel catalysts in n-butane steam reforming mainly depends on the average size of nickel crystallites. Thus, by using suitable preparative methods, it is possible to produce good, coking resistant nickel catalysts even with Al₂O₃ support.

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Al₂O₃ -, , . . ., , - Al₂O₃.

     

Reinforced nickel catalysts for steam reforming of methane to synthesis gas

XRD, mercury porosimetry, low-temperature nitrogen adsorption and electron microscopy were used to study peculiarities of the formation of reinforced composite nickel catalysts. The catalysts were prepared by sintering powdered metallic nickel with a supported nickel catalyst (GIAP-3 or NIAP-18) applied to a reinforcing stainless steel gauze. It was found that a metal matrix, in the pores of which supported catalyst particles were distributed, was formed in the composite catalysts. The NIAP-18-based catalyst exceeded the GIAP-3-based catalyst in activity toward the methane steam reforming. The NIAP-18-based catalyst was as active as the Cr₂O₃-doped NIAP-18-based catalyst, but showed a worse coke-resistance. A chromium oxide additive increased the activity of the GIAP-3-based catalyst.     

Stability and activity of carbon nanofiber-supported catalysts in the aqueous phase reforming of ethylene glycol

Nickel, cobalt, copper and platinum nanoparticles supported on carbon nano-fibers were evaluated with respect to their stability, catalytic activity and selectivity in the aqueous phase reforming of ethylene glycol (230 C, autogenous pressure, batch reactor). The initial surface-specific activities for ethylene glycol reforming were in a similar range but decreased in the order of Pt (15.5 h1 ) >Co(13.0 h1 ) >Ni(5.2 h1 ) while the Cu catalyst only showed low dehydrogenation activity. The hydrogen molar selectivity decreased in the order of Pt (53%)>Co(21%)>Ni (15%) as a result of the production of methane over the latter two catalysts. Over the Co catalyst acids were formed in the liquid phase while alcohols were formed over Ni and Pt. Due to the low pH of the reaction mixture, especially in the case of Co (as a result of the formed acids), significant cobalt leaching occurs which resulted in a rapid deactivation of this catalyst. Investigations of the spent catalysts with various techniques showed that metal particle growth is responsible for the deactivation of the Pt and Ni catalysts. In addition, coking might also contribute to the deactivation of the Ni catalyst.     

Effect of initial concentration on stability of panipenem in aqueous solution

The effect of initial panipenem (CAS No. 87726-17-8) concentration on its degradation in an aqueous solution was investigated. The degradation of panipenem followed pseudo-first-order kinetics at all the pH values tested. However, in an acidic solution, the degradation rate increased with the initial panipenem concentration. On the other hand, in an alkaline solution, the degradation rate was not affected by its initial concentration. In an acidic solution, the plots of the first-order rate constants versus initial panipenem concentrations showed a linear relationship. Theoretically, the first-order rate constant is independent of the initial concentration, and therefore, the results suggested unusualness. We investigated the results obtained under acidic conditions in detail to find a very complex reaction mechanism: panipenem and its degradation products are factors causing the unusual increase in the degradation rate. Moreover, it was shown that the dissociation of the carboxyl group played an important role in the degradation of panipenem.     

负载Ni催化剂上低温甘油蒸汽重整制氢

采用等体积浸渍法制备了Al₂O₃、CeO₂、TiO₂及MgO负载Ni催化剂,考察了它们对甘油蒸汽重整制氢反应的催化性能。采用X射线衍射、N₂吸附、透射电镜及H₂程序升温还原等方法对催化剂进行了表征。结果表明,载体对Ni催化剂的活性有显著影响。在400 ℃下Ni/CeO₂的催化活性明显好于其他催化剂,活性次序为Ni/CeO₂> Ni/Al₂O₃ > Ni/TiO₂ ~ Ni/MgO。Ni/CeO₂也具有好的稳定性,反应20 h未见活性下降,甘油转化率70%,氢气收率69.2%。这与CeO₂的本性及其与活性组分的相互作用有关。Al₂O₃具有较大的比表面积与孔体积,有利于CO吸附及甲烷化反应的进行,使得Ni/Al₂O₃催化剂在较高温度下具有很高的甘油转化率85.7%,但H₂选择性较差。由于MgO载体与活性组分强的相互作用而生成NiMgO₂固溶体,导致Ni/MgO低温活性差。     

Effect of crystallite size on the intercalation pseudocapacitance of lithium nickel vanadate in aqueous electrolyte

This work describes lithium nickel vanadate (LiNiVO₄) as a pseudocapacitor electrode material for the first time. The micro and nano-sized LiNiVO₄ are synthesized via mechanochemical reaction and hydrothermal reaction followed by calcination, respectively. The phase purity, surface morphology and microstructure of the LiNiVO₄ synthesized by both methods are analysed by X-ray diffraction and scanning electron microscopy techniques. The lithium ion intercalation-extraction behaviour of the LiNiVO₄ electrode material is investigated in 1 M LiOH electrolyte solution. The results demonstrate an improved capacitive performance for nano-sized LiNiVO₄ electrode synthesized via hydrothermal reaction due to the collective effect of small size and additional redox sites. The nanocrystalline LiNiVO₄ electrode exhibits a high specific capacitance of 456.56 F g^?1 at a current density of 0.5 A g^?1. The cycle stability test reveals exceptional capacitance retention of 99.60% even after 1000 cycles owing to the unique structural feature which permit intercalation mechanism. These findings demonstrate the significance of lithium transition metal vanadate-based electrode material in the development of lithium ion intercalation pseudocapacitors.     

负载Ni催化剂用于乙二醇蒸汽重整制氢催化性能研究

采用等体积浸渍法和共沉淀法制备了Ni催化剂,在固定床反应器上考察了Ni负载量、焙烧温度、反应温度等因素对乙二醇低温重整制氢反应活性和选择性的影响。应用X射线衍射、氮物理吸附、H₂程序升温还原等技术对负载型Ni催化剂进行了表征。结果表明,共沉淀法制备的Ni/CeO₂催化剂具有较小的NiO颗粒与CeO₂载体颗粒粒径,催化活性较高。添加少量氧化钴到Ni/CeO₂催化剂中可使H₂收率达72.6%,EG转化率达93.1%。在CeO₂中添加Al₂O₃能提高负载Ni催化剂的活性,乙二醇转化率达94.0%,H₂收率达67.0%;但添加SiO₂则使其活性明显变差。     

Effect of particle size in the hydrogenation of crotonaldehyde on supported Pt and Pt-Sn catalysts

The present work reports the effect of metal particle size on the selectivity to crotyl alcohol (S_UOL) in the liquid phase hydrogenation of crotonaldehyde over SiO₂ and a-Al₂O₃-supported Pt and Pt-Sn catalysts. It was demonstrated that, for the monometallic catalysts, a higher particle size led to a higher S_UOL, while for the bimetallic catalysts, this effect was not so important.     

Effect of particle size on the desorption and dissociation of CO from carbon-supported iron catalysts

A series of carbon-supported iron catalysts has been prepared from Fe(CO)₅ and, by different reduction temperature, metallic dispersions from 0.11 to 1 have been obtained. Temperature-programmed desorption experiments over Fe/active carbon catalysts show that the temperature for maximum desorption rate of CO decreases with an increase in the average iron particle size. Also it has been observed that the temperature for the reaction of CO on iron surface is a function of metal particle size.

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, Fe(CO)₅, 0,11 1. Fe/ , , , CO, . , , CO , .

     

Effect of particle size of activated clay on the adsorption of paraquat from aqueous solution

This paper describes the effect of particle size on the process of paraquat adsorption from aqueous solution onto an activated clay surface at 25 degrees C and initial pH 11.0. Measurements of the pore properties of the clay adsorbents with three different particle sizes (0.053-0.074 mm, 0.037-0.053 mm, and <0.037 mm) were carried out. The rates and isotherms of adsorption have been also investigated by batch methods under the controlled conditions. From the experimental results obtained, the adsorption process can be well described with the pseudo-second order model and Freundlich model for adsorption kinetics and adsorption isotherm, respectively. In addition, the effect of the particle size of the clay adsorbent on the adsorption kinetics was found to be of considerable significance; namely, the rate constant (k) of paraquat adsorption by the clay adsorbent decreased with increasing particle size. It was concluded that the pore properties (i.e., surface area and total pore volume) and particle size of the clay adsorbent played a significant role in determining adsorption capacity and adsorption rate, respectively.     

Synthesis of supports for reforming catalysts

The formation of surface defects in γ-Al₂O₃ obtained by pseudoboehmite calcination and plasticized with monobasic, dibasic, and tribasic organic acids is reported. The efficiency of catalysts in reforming reactions depends on the defectivity of the support.     

Hydrogen production via steam reforming of bio-oil model compounds over supported nickel catalysts

The steam reforming of four bio-oil model compounds(acetic acid,ethanol,acetone and phenol) was investigated over Ni-based catalysts supported on Al2O3 modified by Mg,Ce or Co in this paper.The activation process can improve the catalytic activity with the change of high-valence Ni(Ni2O3,NiO) to low-valence Ni(Ni,NiO).Among these catalysts after activation,the Ce-Ni/Co catalyst showed the best catalytic activity for the steam reforming of all the four model compounds.After long-term experiment at 700°C and the S/C ratio of 9,the Ce-Ni/Co catalyst still maintained excellent stability for the steam reforming of the simulated bio-oil(mixed by the four compounds with the equal masses).With CaO calcinated from calcium acetate as CO2 sorbent,the catalytic steam reforming experiment combined with continuous in situ CO2 adsorption was performed.With the comparison of the case without the adding of CO2 sorbent,the hydrogen concentration was dramatically improved from 74.8% to 92.3%,with the CO2 concentration obviously decreased from 19.90% to 1.88%.     

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. , .