• New & Renewable Energy
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• v.9 no.1
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• pp.51-59
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• 2013

Tantalum carbide crystallites which is to be used for $H_2$ fuel cell has been synthesized via a temperature-programmed reduction of $Ta_2O_5$ with pure $CH_4$. The resultant Ta carbide crystallites prepared using two different heating rates and space velocity exhibit the different surface areas. The $O_2$ uptake has a linear relation with surface area, corresponding to an oxygen capacity of $1.36{\times}10^{13}\;O\;cm^{-2}$. Tantalum carbide crystallites are very active for hydrogen production form ammonia decomposition reaction. Tantalum carbides are as much as two orders of magnitude more active than Pt/C catalyst (Engelhard). The highest activity has been observed at a ratio of $C_1/Ta^{{\delta}+}=0.85$, suggesting the presence of electron transfer between metals and carbon in metal carbides.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.6
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• pp.269-273
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• 2012

Ammonia decomposition over titanium carbides were investigated using eight different samples which have been synthesized by TPR (temperature-programmed reduction) method of titanium oxide ($TiO_2$) with pure $CH_4$. The resulting materials which were synthesized using wo different heating rates and space velocity exhibited the different surface areas. These results indicated that the structural properties of these materials have been related to heating rates and space velocity employed. The titanium carbides prepared in this study proved to be active for ammonia decomposition, and the activity changed with the particle size/surface area. These showed the relationship between ammonia decomposition activity and the different active species. Compared to molybdenum carbide, the titanium carbides were one order of magnitude less active, suggesting the correlation between the activity difference and the degree of electron transfer between metals and carbon in metal carbides.

• Journal of Powder Materials
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• v.27 no.3
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• pp.193-197
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• 2020

Porous Cu-14 wt% Co with aligned pores is produced by a freeze drying and sintering process. Unidirectional freezing of camphene slurry with CuO-Co₃O₄ powders is conducted, and pores in the frozen specimens are generated by sublimation of the camphene crystals. The dried bodies are hydrogen-reduced at 500℃ and sintered at 800℃ for 1 h. The reduction behavior of the CuO-Co₃O₄ powder mixture is analyzed using a temperature-programmed reduction method in an Ar-10% H₂ atmosphere. The sintered bodies show large and aligned parallel pores in the camphene growth direction. In addition, small pores are distributed around the internal walls of the large pores. The size and fraction of the pores decrease as the amount of solid powder added to the slurry increases. The change in pore characteristics according to the amount of the mixed powder is interpreted to be due to the rearrangement and accumulation behavior of the solid particles in the freezing process of the slurry.

• Journal of Powder Materials
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• v.25 no.4
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• pp.322-326
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• 2018

The hydrogen reduction behavior of $MoO_3-CuO$ powder mixture for the synthesis of homogeneous Mo-20 wt% Cu composite powder is investigated. The reduction behavior of ball-milled powder mixture is analyzed by XRD and temperature programmed reduction method at various heating rates in Ar-10% $H_2$ atmosphere. The XRD analysis of the heat-treated powder at $300^{\circ}C$ shows Cu, $MoO_3$, and $Cu_2MoO_5$ phases. In contrast, the powder mixture heated at $400^{\circ}C$ is composed of Cu and $MoO_2$ phases. The hydrogen reduction kinetic is evaluated by the amount of peak shift with heating rates. The activation energies for the reduction, estimated by the slope of the Kissinger plot, are measured as 112.2 kJ/mol and 65.2 kJ/mol, depending on the reduction steps from CuO to Cu and from $MoO_3$ to $MoO_2$, respectively. The measured activation energy for the reduction of $MoO_3$ is explained by the effect of pre-reduced Cu particles. The powder mixture, hydrogen-reduced at $700^{\circ}C$, shows the dispersion of nano-sized Cu agglomerates on the surface of Mo powders.

• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.1008-1014
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• 2012

The amount of domestic carbon dioxide emissions is more than 600 million tons/year. The emitted $CO_2$ should be captured and stored, however, suitable storage sites have not been found yet. A lot of researches on the conversion of captured carbon dioxide to useful carbon source have been conducted. The purpose of this study is to convert stable carbon dioxide to useful resources using less energy. For this purpose reducing gas and metallic oxide (activator) are required. Hydrogen was used as reducing gas and cobalt ferrite was used as activator. Considering that activator has different physical properties depending on synthesis methods, activator was prepared by hydrothermal synthesis and solid method. Decomposition characteristics of carbon dioxide were investigated using synthesized powders. Temperature programmed reduction/oxidation (TPR/TPO) and thermogravimetric analyzer (TGA) device were used to observe the decomposition characteristics of carbon dioxide. Activator prepared by solid method with 5 and 10 wt% CoO content showed an excellent performance. In TGA experiments with samples prepared by the solid method, reduction by hydrogen was 29.0 wt% and oxidation by $CO_2$ was highest in 27.5 wt%. 95% of adsorbed $CO_2$ was decomposed with excellent oxidation-reduction behaviors.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3387-3390
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• 2013

Catalytic gasification of mandarin waste residue was carried out using direct and indirect catalyst-contact methods for the first time. In the indirect method, non-catalytic reaction in a reactor was followed by catalytic upgrading of vapor product in another reactor. Two different catalysts, $Ni/{\gamma}-Al_2O_3$ and $Ni/CeO_2-ZrO_2$, were employed. $CeO_2-ZrO_2$ support was prepared using hydrothermal synthesis in supercritical water. The catalysts were characterized by $H_2$-temperature programmed reduction and Brunauer-Emmett-Teller analyses. Under the condition of equivalent ratio (ER) = 0, the indirect catalyst-contact method led to a higher gas yield than the direct method. Under ER = 0.2, the yield of biogas obtained over $Ni/CeO_2-ZrO_2$ was higher than that obtained over $Ni/{\gamma}-Al_2O_3$. Also, the coke formation of $Ni/CeO_2-ZrO_2$ was lower than that of $Ni/{\gamma}-Al_2O_3$. Such results were attributed to the higher reducibility and better lattice oxygen mobility of $Ni/CeO_2-ZrO_2$, which were advantageous for partial oxidation reaction.

• Clean Technology
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• v.21 no.4
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• pp.248-256
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• 2015

MnO₂ was prepared by a hydrothermal process method in the range of 120-200 ℃ and 0.5-5 h, calcined at 300 ℃ after induction of precipitation using KMnO₄ and MnCl₂･4H₂O, and its catalytic activity was compared for CO oxidation. The catalysts were characterized using by X-ray diffraction, N₂-sorption, scanning electron microscopy, and temperature programmed reduction of H₂ or CO. The crystalline structure of pure α-MnO₂ or hybrid α/β-MnO₂ was controlled by the preparation conditions. The pure α-MnO₂ showed better catalytic activity and thermal stability than hybrid α/β-MnO₂. Especially, α-MnO₂ prepared at 150 ℃ for 1 h has the highest specific surface area 214 m² g^-1, reducibility and labile lattice oxygen species analyzed by H₂, CO-TPR, respectively. It also showed the best CO oxidation activity in both conditions of temperature programmed and isothermal reaction. The results came from the physicochemical properties of catalysts like the crystalline structure, specific surface area, reducibility and lattice oxygen species, and which are correlated with catalytic performance.

• Journal of Hydrogen and New Energy
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• v.21 no.1
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• pp.50-57
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• 2010

Stepwise production of syn-gas and hydrogen from methane on ferrite based media added with yttria-stabilized zirconia (YSZ) was carried out using a fixed bed infrared reactor. In this study, all M-ferrite (M=Co, Cu, Mn and Ni) media were prepared by co-precipitation method, and there the YSZ was added as a binder to improve thermal stability, reactivity, and resistance against carbon deposition. Most of the ferrite media containing YSZ showed the good redox property for temperature programmed reduction/oxidation (TPR/O) tests. Notably, the Cu-substituted ferrite medium with YSZ showed the great resistance against carbon deposition as well as the good reactivity for the stepwise production of syngas and hydrogen. Furthermore, it also showed the good durability without significant deactivation during five repeated cyclic tests.