• Title, Summary, Keyword: hydrogen reduction

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Activation of Spinel Phase Magnetite by Hydrogen Reduction (스피넬상 마그네타이트의 수소환원에 의한 활성화)

  • 류대선;이동석;이풍헌;김순태
    • Journal of the Korean Ceramic Society
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    • v.37 no.6
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    • pp.559-563
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    • 2000
  • To decompose carbon dioxide, magnetite was synthesized with 0.2M-FeSO4$.$7H2O and 0.5 M-NaOH by coprecipitation. The deoxidized magnetite was prepared from the magnetite by hydrogen reduction for 1, 1.5, 2 hr. The degree of hydrogen reduction and the decomposition rate of carbon dioxide were investigated with hydrogen reduction time. The crystal structure of the magnetite was identified spinel structute by the X-ray powder diffractions. After magnetite was reduced by hydrogen, magnetite reduced by hydrogen become new phae(${\alpha}$-Fe2O3, ${\alpha}$-Fe) and spinel type simultaneously. After decomposing of carbon dioxide at 350$^{\circ}C$, new phse(${\alpha}$-Fe2O3, ${\alpha}$-Fe) were removed and the spinel type only existed. The specific surface area of the synthesized magnetite was 46.69㎡/g. With the increase of the hydrogen reduction time, the grain size, the hydrogen reduction degree and the decomposition rate of carbon dioxide was increased.

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The Effect of Composition on Hydrogen Reduction Behavior of Ball-milled WO3-CuO Nanocomposite Powders (볼밀링한 WO3-CuO 나노복합분말의 조성에 따른 수소환원 거동)

  • Jung Sung-Soo;Kang Yun-Sung;Lee Jai-Sung
    • Journal of Korean Powder Metallurgy Institute
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    • v.13 no.3
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    • pp.205-210
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    • 2006
  • The effect of Cu content on hydrogen reduction behavior of ball-milled $WO_3$-CuO nanocomposite powders was investigated. Hydrogen reduction behavior and reduction percent(${\alpha}$) of nanopowders were characterized by thermogravimetry (TG) and hygrometry measurements. Activation energy for hydrogen reduction of $WO_3$ nanopowders with different Cu content was calculated at each heating rate and reduction percent(${\alpha}$). The activation energy for reduction of $WO_3$ obtained in this study existed in the ranging from 129 to 139 kJ/mol, which was in accordance with the activation energy for $WO_3$ powder reduction of conventional micron-sized.

Hydrogen Reduction Behavior of Oxide Scale in Water-atomized Iron Powder (수분사 Fe 분말의 산화물 및 이의 수소가스 환원거동)

  • Shin, Hea-Min;Baik, Kyeong-Ho
    • Journal of Korean Powder Metallurgy Institute
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    • v.21 no.6
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    • pp.422-428
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    • 2014
  • In this study, the reduction kinetics and behaviors of oxides in the water-atomized iron powder have been evaluated as a function of temperature ranging $850-1000^{\circ}C$ in hydrogen environment, and compared to the reduction behaviors of individual iron oxides including $Fe_2O_3$, $Fe_3O_4$ and FeO. The water-atomized iron powder contained a significant amount of iron oxides, mainly $Fe_3O_4$ and FeO, which were formed as a partially-continuous surface layer and an inner inclusion. During hydrogen reduction, a significant weight loss in the iron powder occurred in the initial stage of 10 min by the reduction of surface oxides, and then further reduction underwent slowly with increasing time. A higher temperature in the hydrogen reduction promoted a high purity of iron powder, but no significant change in the reduction occurred above $950^{\circ}C$. Sequence reduction process by an alternating environment of hydrogen and inert gases effectively removed the oxide scale in the iron powder, which lowered reduction temperature and/or shortened reduction time.

Reaction of Potassium 2-Thexyl-1,3,2-dioxaborinane Hydride with Selected Organic Compounds Containing Representative Functional Groups

  • Jin Soon Cha;Sung Eun Lee
    • Bulletin of the Korean Chemical Society
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    • v.13 no.5
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    • pp.531-537
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    • 1992
  • The approximate rates and stoichiometry of the reaction of excess potassium 2-thexyl-1,3,2-dioxaborinane hydride(KTDBNH) with 55 selected compounds containing representative functional groups under standardized conditions (tetrahydrofuran, TEX>$0^{\circ}C$, reagent : compound=4 : 1) was examined in order to define the characteristics of the reagent for selective reductions. Benzyl alcohol and phenol evolve hydrogen immediately. However, primary, secondary and tertiary alcohols evolve hydrogen slowly, and the rate of hydrogen evolution is in order of $1^{\circ}$> $2^{\circ}$> $3^{\circ}$. n-Hexylamine is inert toward the reagent, whereas the thiols examined evolve hydrogen rapidly. Aldehydes and ketones are reduced rapidly and quantitatively to give the corresponding alcohols. Cinnamaldehyde is rapidly reduced to cinnamyl alcohol, and further reduction is slow under these conditions. The reaction with p-benzoquinone dose not show a clean reduction, but anthraquinone is cleanly reduced to 9,10-dihydro-9,10-anthracenediol. Carboxylic acids liberate hydrogen immediately, further reduction is very slow. Cyclic anhydrides slowly consume 2 equiv of hydride, corresponding to reduction to the caboxylic acid and alcohol stages. Acid chlorides, esters, and lactones are rapidly and quantitatively reduced to the corresponding carbinols. Epoxides consume 1 equiv hydride slowly. Primary amides evolve 1 equiv of hydrogen readily, but further reduction is slow. Tertiary amides are also reduced slowly. Both aliphatic and aromatic nitriles consume 1 equiv of hydride rapidly, but further hydride uptake is slow. Analysis of the reaction mixture with 2,4-dinitrophenylhydrazine yields 64% of caproaldehyde and 87% of benzaldehyde, respectively. 1-Nitropropane utilizes 2 equiv of hydride, one for hydrogen evolution and the other for reduction. Other nitrogen compounds examined are also reduced slowly. Cyclohexanone oxime undergoes slow reduction to N-cyclohexylhydroxyamine. Pyridine ring is slowly attacked. Disulfides examined are reduced readily to the correponding thiols with rapid evolution of 1 equiv hydrogen. Dimethyl sulfoxide is reduced slowly to dimethyl sulfide, whereas the reduction of diphenyl sulfone is very slow. Sulfonic acids only liberate hydrogen quantitatively without any reduction. Finally, cyclohexyl tosylate is inert to this reagent. Consequently, potassium 2-thexyl-1,3,2-dioxaborinane hydride, a monoalkyldialkoxyborohydride, shows a unique reducing characteristics. The reducing power of this reagent exists somewhere between trialkylborohydrides and trialkoxyborohydride. Therefore, the reagent should find a useful application in organic synthesis, especially in the field of selective reduction.

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Hydrogen Induced Reduction of Fe- and Co-Oxides with Addition of Ni and Pd (철과 코발트 산화물의 수소 환원에 니켈 및 팔라듐 첨가의 효과)

  • Kim, Jong-Pal
    • Transactions of the Korean hydrogen and new energy society
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    • v.22 no.1
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    • pp.35-41
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    • 2011
  • Temperature programmed reduction experiments for Fe- and Co-oxides were performed and weight losses were carefully measured to calculate the extent of reduction. Addition of nickel and palladium affected the reduction by lowering the DTG peak temperature. Reduction experiments for the oxides on alumina were also studied and the effect of nickel and palladium addition was confirmed. And that was explained by means of increased adsorption of hydrogen and increased diffusion ability of the surface hydrogen.

Influence of the Water Vapor Content on the Hydrogen Reduction Process of Nanocrystalline NiO

  • Jung, Sung-Soo;An, Hyo-Sang;Lee, Jai-Sung
    • Korean Journal of Metals and Materials
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    • v.48 no.4
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    • pp.315-319
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    • 2010
  • In this study, the hydrogen reduction behavior of ball-milled NiO nanopowder was investigated depending on the partial pressure of water vapor. The hydrogen reduction behavior was analyzed by thermogravimetry and hygrometry under heating to 873 K in hydrogen. In order to change the partial pressure of the water vapor, the dew point of hydrogen was controlled in the range of 248 K~293 K by passing high-purity hydrogen through a saturator that contained water. Interestingly, with the increase in the dew point of the hydrogen atmosphere, the first step of the hydrogen reduction process decreased and the second step gradually increased. After the first step, a pore volume analysis revealed that the pore size distribution in the condition with a higher water vapor pressure shifted to a larger size, whereas the opposite appearedat a lower pressure. Thus, it was found that the decrease in the pore volume during the chemical reaction controlled process at a dew point of 248 K caused a reduction in retardation in the diffusion controlled process.

Synthesis and Properties of Fe-Ni Nano-sized Powders using Metal Nitrates (금속질산염을 이용한 Fe-Ni 나노분말의 제조 및 특성)

  • Joo, Min-Hee;Oh, Sung-Tag
    • Journal of Korean Powder Metallurgy Institute
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    • v.16 no.3
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    • pp.191-195
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    • 2009
  • The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate have been investigated. $Fe_2O_3$/NiO composite powders were prepared by chemical solution mixing of Fe- and Ni-nitrate and calcination at $350^{\circ}C$ for 2 h. The calcined powders were hydrogen-reduced at $350^{\circ}C$ for 30 min. The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate were analyzed by TG in air and hydrogen atmosphere, respectively. TG and XRD analysis for hydrogen-reduced powders revealed that the $Fe_2O_3$/NiO phase transformed to $FeNi_3$ phase at the temperature of $350^{\circ}$. The activation energy for the hydrogen reduction, evaluated by Kissinger method, was measured as 83.0 kJ/mol.

High Purity Hydrogen Production by Redox Cycle Operation (산화-환원 싸이클 조업에 의한 고순도 수소생성)

  • Jeon, Bup-Ju;Park, Ji-Hun
    • Transactions of the Korean hydrogen and new energy society
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    • v.21 no.5
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    • pp.355-363
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    • 2010
  • High purity hydrogen, 97-99 vol.%, with CO at just ppm levels was obtained in a fixed bed of iron oxide employing the steam-iron cycle operation with reduction at 823K and oxidation in a steam-$N_2$ mixture at 773K TGA experiments indicated that temperature of the reduction step as well as its duration are important for preventing carbon build-up in iron and the intrusion of $CO_2$ into the hydrogen product. At a reduction temperature of 823K, oxide reduction by $H_2$ was considerably faster than reduction by CO. If the length of the reduction step exceeds optimal value, low levels of methane gas appeared in the off-gas. Furthermore, with longer durations of the reduction step and CO levels in the reducing gas greater than 10 vol.%, carbidization of the iron and/or carbon deposition in the bed exhibited the increasing pressure drop over the bed, eventually rendering the reactor inoperable. Reduction using a reducing gas containing 10 vol.% CO and a optimal reduction duration gave constant $H_2$ flow rates and off-gas composition over 10 redox reaction cycles.

Mo Powders Fabricated from MoO3 by Reduction in Hydrogen Gas

  • Hong, Seonghoon;Lee, Changsup;Oh, Changsup;Kil, Sangcheol;Kim, Yongha
    • Korean Journal of Metals and Materials
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    • v.50 no.6
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    • pp.445-448
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    • 2012
  • We studied the effect of temperature and reaction time by investigating the various temperatures and reaction times in the reduction of molybdenum oxide ($MoO_3$) to molybdenum (Mo) powder in hydrogen gas. We also studied the effect of the reaction of reduction according to the various hydrogen gas flow rates. We surveyed the reduction from molybdenum oxide to molybdenum powder in hydrogen gas and checked two temperature ranges, one from $400^{\circ}C$ to $600^{\circ}C$ and the other from $700^{\circ}C$ to $900^{\circ}C$. We found that the reaction ratio of molybdenum oxide increased with an increasing temperature and also increased with an increasing reaction time, but hydrogen gas did not influence the reduction ratio of molybdenum oxide. We examined molybdenum powders fabricated by ball milling for two hours, using with X-ray diffraction (XRD) and a scanning electron microscopy (SEM).

Effect of Sulfate Reduction on the Hydrogen Competition among Dechlorination, Methane Production, and Sulfate Reduction (황산염 환원반응이 탈염소화, 메탄생성 및 황산염 환원 간 수소경쟁에 미치는 영향)

  • Lee, Il-Su;Bae, Jae-Ho
    • Journal of Korean Society of Environmental Engineers
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    • v.27 no.6
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    • pp.635-641
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    • 2005
  • Batch experiments were performed to evaluate the effect of sulfate reduction on methane production and reductive dechlorination, both compete for hydrogen with sulfate reduction. Dechlorination was inhibited by sulfate reduction at lower hydrogen concentration because their threshold values for hydrogen are similar (2 nM). Unlike methane production mainly inhibited transformation of cDCE to ethene, sulfate reduction inhibited the initial dechlorination step, PCE reduction into cDCE as well as cDCE dechlorination. The presence of sulfate eliminated methanogens as hydrogen competitor because of its high threshold value of 10 nM. When sulfate coexisted with PCE, dechlorination efficiency was not affected by the increase of seed concentration as both dechlorination and sulfate reduction were stimulated simultaneously by the increased seeding culture.