• Title/Summary/Keyword: Low Temperature Metal Catalyst

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Study on Pressure-dependent Growth Rate of Catalyst-free and Mask-free Heteroepitaxial GaN Nano- and Micro-rods on Si (111) Substrates with the Various V/III Molar Ratios Grown by MOVPE

  • Ko, Suk-Min;Kim, Je-Hyung;Ko, Young-Ho;Chang, Yun-Hee;Kim, Yong-Hyun;Yoon, Jong-Moon;Lee, Jeong-Yong;Cho, Yong-Hoon
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.180-180
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    • 2012
  • Heteroepitaxial GaN nano- and micro-rods (NMRs) are one of the most promising structures for high performance optoelectronic devices such as light emitting diodes, lasers, solar cells integrated with Si-based electric circuits due to their low dislocation density and high surface to volume ratio. However, heteroepitaxial GaN NMRs growth using a metal-organic vapor phase epitaxy (MOVPE) machine is not easy due to their long surface diffusion length at high growth temperature of MOVPE above $1000^{\circ}C$. Recently some research groups reported the fabrication of the heteroepitaxial GaN NMRs by using MOVPE with vapor-liquid-solid (VLS) technique assisted by metal catalyst. However, in the case of the VLS technique, metal catalysts may act as impurities, and the GaN NMRs produced in this mathod have poor directionallity. We have successfully grown the vertically well aligned GaN NMRs on Si (111) substrate by means of self-catalystic growth methods with pulsed-flow injection of precursors. To grow the GaN NMRs with high aspect ratio, we veried the growth conditions such as the growth temperature, reactor pressure, and V/III molar ratio. We confirmed that the surface morphology of GaN was strongly influenced by the surface diffusion of Ga and N adatoms related to the surrounding environment during growth, and we carried out theoretical studies about the relation between the reactor pressure and the growth rate of GaN NMRs. From these results, we successfully explained the growth mechanism of catalyst-free and mask-free heteroepitaxial GaN NMRs on Si (111) substrates. Detailed experimental results will be discussed.

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Preparation of Pt Catalysts for 2-propanol Dehydrogenation using Sol-gel Method (솔-젤법을 이용한 2-propanol 탈수소화 반응 Pt 촉매의 제조)

  • Lee, Yeong-Kweon;Lee, Hwaung;Song, Hyung Keun;Na, Byung-Ki
    • Korean Chemical Engineering Research
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    • v.45 no.4
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    • pp.328-334
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    • 2007
  • Chemical heat pump system of 2-propanol/acetone/hydrogen is most suitable to the recovery of waste heat of power plant. various types of 5 wt% Pt-alumina catalysts were prepared for 2-propanol dehydrogenation using sol-gel method. The characteristics and the dehydrogenation reaction rate of each catalyst were investigated. Pt-alumina xerogel catalyst has excellent reaction rate and good durability in comparison with the existing alumina supported Pt catalysts. Pt-alumina aerogel catalyst had the highest reaction rate in all prepared catalysts, but sufficient aging time was necessary to maintain its reaction rate. A potential advantage of the aerogel catalyst is the fact that the high temperature heat treatment is not required. Without heat treatment or with low temperature heat treatment, the Pt-alumina aerogel catalyst has excellent reaction rate as well as durability and this gives us the economic advantage. Alumina xerogel supported Pt catalyst prepared by incipient wetness method showed good reaction rate, and had good mechanical strength. Blank alumina xerogel prepared by sol-gel method can be used for the support of metal catalysts.

Evaluation of Thermal Catalytic Decomposition of Chlorinated Hydrocarbons and Catalyst-Poison Effect by Sulfur Compound (염소계 탄화수소의 열촉매 분해와 황화합물에 의한 촉매독 영향 평가)

  • Jo, Wan-Kuen;Shin, Seung-Ho;Yang, Chang-Hee;Kim, Mo-Geun
    • Journal of Korean Society of Environmental Engineers
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    • v.29 no.5
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    • pp.577-583
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    • 2007
  • To overcome certain disadvantages of past typical control techniques for toxic contaminants emitted from various industrial processes, the current study was conducted to establish a thermal catalytic system using mesh-type transition-metal platinum(Pt)/stainless steel(SS) catalyst and to evaluate catalytic thermal destruction of five chlorinated hydrocarbons[chlorobenzene(CHB), chloroform(CHF), perchloroethylene (PCE), 1,1,1-trichloroethane(TCEthane), trichloroethylene(TCE)]. In addition, this study evaluated the catalyst poison effect on the catalytic thermal destruction. Three operating parameters tested for the thermal catalyst system included the inlet concentrations, the incineration temperature, and the residence time in the catalyst system. The thermal decomposition efficiency decreased from the highest value of 100% to the lowest value of almost 0%(CHB) as the input concentration increased, depending upon the type of chlorinated compounds. The destruction efficiencies of the four target compounds, except for TCEthane, increased upto almost 100% as the reaction temperature increased, whereas the destruction efficiency for TCEthane did not significantly vary. For the target compounds except for TCEthane, the catalytic destruction efficiencies increased up to 30% to 97% as the residence time increased from 10 sec to 60 sec, but the increase of destruction efficiency for TCEthane stopped at the residence time of 30 sec, suggesting that long residence times are not always proper for thermal destruction of VOCs, when considering the destruction efficiency and operation costs of thermal catalytic system together. Conclusively, the current findings suggest that when applying the transition-metal catalyst for the better destruction of chlorinated hydrocarbons, VOC type should be considered, along with their inlet concentrations, and reaction temperature and residence time in catalytic system. Meanwhile, the addition of high methyl sulfide(1.8 ppm) caused a drop of 0 to 50% in the removal efficiencies of the target compounds, whereas the addition of low methyl sulfide (0.1 ppm), which is lower than the concentrations of sulfur compounds measured in typical industrial emissions, did not cause.

The Study of CO2 Gasification of Low Rank Coal Impregnated by K2CO3, Mn(NO3)2, and Ce(NO3)3 (저급석탄에 K2CO3와 Mn(NO3)2 및 Ce(NO3)3이 CO2-석탄 가스화 반응에 미치는 영향)

  • Park, SangTae;Choi, YongTaek;Shon, JungMin
    • Applied Chemistry for Engineering
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    • v.22 no.3
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    • pp.312-318
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    • 2011
  • We have investigated the kinetics and catalytic activity of $CO_2$-lignite gasification with various metal precursors as catalysts. $K_2CO_3$, $Mn(NO_3)_2$, and $Ce(NO_3)_3$ were used and impregnated on a coal using an evaporator. The gasification experiments were carried out with the low rank coal loaded with 5 wt% catalyst at the temperature range from $700{\sim}900^{\circ}C$ and atmospheric pressure with the $N_2-CO_2$ reactant gas mixture. The catalytic effect on the gasification rate of the low rank coal with $CO_2$ was determined by the thermogravimetric analyzer. It was observed that the low rank coal reached the complete carbon conversion regardless of the kinds of catalysts at $900^{\circ}C$ from the results of TGA. The catalytic activity was ranked as 5 wt% $K_2CO_3$ > 5 wt% $Mn(NO_3)_2$ > 5 wt% $Ce(NO_3)_3$ > Non-catalyst at $900^{\circ}C$. The gasification rate increased with increasing the temperature. The activation energy of the catalytic gasification with 5 wt% $K_2CO_3$ was 119.0 kJ/mol, which was the lowest among all catalysts.

Supercritical Water Gasification of Low Rank Coal with High Moisture Content (고함수 저등급 석탄의 초임계수 가스화 특성)

  • Yoon, Sang Jun;Lee, Jae Goo;Ra, Ho Won;Seo, Myung Won
    • Transactions of the Korean hydrogen and new energy society
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    • v.24 no.4
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    • pp.340-346
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    • 2013
  • Study on clean and efficient utilization technology for low rank coal with high moisture content is actively ongoing due to limited reserves of petroleum and of high grade coal and serious climate change caused by fossil fuel usage. In the present study, supercritical water gasification of low rank coal was performed. With increasing reaction temperature, content of combustible gases such as $H_2$ and $CH_4$ in the syngas increased while the $CO_2$ content decreased. As the reaction pressure increased from 210 to 300 bar, the $CO_2$ content in the syngas increased while the hydrocarbon gas content decreased. The $H_2$ and $CH_4$ content in the syngas increased slightly with pressure. With the addition of Pd, Pt, and Ru catalysts, it was possible to improve the production of $H_2$. Moreover, the increase of active metal content in the catalyst increased the $H_2$ productivity. The Ru catalyst shows the best performance for increasing the $H_2$ content in the syngas, while decreasing the $CO_2$ content.

Low-temperature Oxidation of Odor Compounds over La-based Perovskite Catalyst (란탄 기반 페롭스카이트 촉매를 이용한 악취 유발 물질의 저온 산화 반응)

  • Bang, Yong-Ju;Seo, Jeong-Gil;Lee, Gi-Chun;Park, Chan-Jung;Kim, Hyung-Tae;Song, In-Kyu
    • Korean Chemical Engineering Research
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    • v.49 no.2
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    • pp.168-174
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    • 2011
  • Various La-based perovskite catalysts were prepared by a Pechini method, and they were applied to the low-temperature oxidation of odor compounds exhausted from waste food treatment process for effective deodorization. Quantitative and qualitative analyses of exhausted gas were conducted to measure the amount of major odor compounds with respect to operation time. A standard odor sample composed of major odor compounds was then prepared for use as a feed for oxidation reaction system. Various transition metal(M)-substituted La-based perovskite catalysts ($LaMO_{3}$: M=Cr, Mn, Fe, Co, and Ni) were prepared and applied to the oxidation of odor compounds in order to investigate the $LaNiO_3$ catalyst showed the best catalytic performance. Pt-substituted perovskite catalysts ($LaNi_{1-x}Pt_{x}O_{3}$: x=0, 0.03, 0.1, and 0.3) were then prepared for enhancing the catalytic performance. It was found that $LaNi_{0.9}Pt_{0.1}O_{3}$ catalyst served as the most efficient catalyst. Supported perovskite catalysts ($XLaNi_{0.9}Pt_{0.1}O_{3}/Al_{2}O_{3}$: X=perovskite content(wt%), 0, 10, 20, 30, 40, 50, and 100) were finally applied for the purpose of maximizing the catalytic performance of perovskite catalyst in the low-temperature oxidation reaction. Catalytic performance of $XLaNi_{0.9}Pt_{0.1}O_{3}/Al_{2}O_{3}$ catalysts showed a volcano-shaped curve with respect to perovskite content. Among the catalysts tested, $20LaNi_{0.9}Pt_{0.1}O_{3}$/$Al_{2}O_{3}$ catalyst exhibited the highest conversion of odor compounds of 88.7% at $180^{\circ}C$.

Electrochemical Analysis of CuxCo3-xO4 Catalyst for Oxygen Evolution Reaction Prepared by Sol-Gel Method (Sol-Gel법을 이용한 CuxCo3-xO4 산소 발생 촉매의 합성 및 전기화학 특성 분석)

  • Park, Yoo Sei;Jung, Changwook;Kim, Chiho;Koo, Taewoo;Seok, Changgyu;Kwon, Ilyeong;Kim, Yangdo
    • Korean Journal of Materials Research
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    • v.29 no.2
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    • pp.92-96
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    • 2019
  • Transition metal oxide is widely used as a water electrolysis catalyst to substitute for a noble metal catalyst such as $IrO_2$ and $RuO_2$. In this study, the sol-gel method is used to synthesize the $Cu_xCo_{3-x}O_4$ catalyst for the oxygen evolution reaction (OER),. The CuxCo3-xO4 is synthesized at various calcination temperatures from $250^{\circ}C$ to $400^{\circ}C$ for 4 h. The $Cu_xCo_{3-x}O_4$ synthesized at $300^{\circ}C$ has a perfect spinel structure without residues of the precursor and secondary phases, such as CuO. The particle size of $Cu_xCo_{3-x}O_4$ increases with an increase in calcination temperature. Amongst all the samples studied, $Cu_xCo_{3-x}O_4$, which is synthesized at 300?, has the highest activity for the OER. Its onset potential for the OER is 370 mV and the overpotential at $10mA/cm^2$ is 438 mV. The tafel slope of $Cu_xCo_{3-x}O_4$ synthesized at $300^{\circ}C$ has a low value of 58 mV/dec. These results are mainly explained by the increase in the available active surface area of the $Cu_xCo_{3-x}O_4$ catalyst.

Properties of ZnO nanostructures by metal deposited on Si substrates (Metal 증착한 Si 기판 상의 ZnO 나노 구조 특성)

  • Jang, Hyeon-Gyeong;Jung, Mi-Na;Park, Seung-Hwan;Shin, Dae-Hyeon;Yang, Min;Yao, Takafumi;Chang, Ji-Ho
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • v.9 no.1
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    • pp.1034-1037
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    • 2005
  • The variation of shapes and related properties of ZnO nanostructures grown on the metal pattern and Si substrate have been investigated. Ni, Cr metal patterns were formed on Si (111) substrates by e-beam evaporation, and ZnO nanostructures were fabricated on it by using thermal evaporation of Zn powder in air. Growth temperature was controlled from 500 $^{\circ}$C to 700 $^{\circ}$C. When the growth temperature was relatively low, no considerable effect was found. However, UV emission intensity decreased, and Green-emission intensity, which is regarded as originated from the defect state in the ZnO nanostructure, increased as growth temperature increase. Also, the variation of nanostructure shape at high temperature (700 $^{\circ}$C) is understood in terms of the enhanced incorporation of metal vapor during the nanostructure formation.

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Hydrogenation Properties on MgHx-Sc2O3 Composites by Mechanical Alloying (MgHx-Sc2O3 복합재료의 수소화 특성)

  • Kim, Kyeong-Il;Kim, Yong-Sung;Hong, Tae-Whan
    • Transactions of the Korean hydrogen and new energy society
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    • v.21 no.2
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    • pp.81-88
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    • 2010
  • Hydrogen energy applications have recognized clean materials and high energy carrier. Accordingly, Hydrogen energy applies for fuel cell by Mg and Mg-based materials. Mg and Mg-based materials are lightweight and low cost materials with high hydrogen storage capacity. However, commercial applications of the Mg hydride are currently hinder by its high absorption/desorption temperature, and very slow reaction kinetics. Therefore one of the most methods to improve kinetics focused on addition transition metal oxide. Addition to transition metal oxide in $MgH_x$ powder produce $MgH_x$-metal oxide composition by mechanical alloy and it analyze XRD, EDS, TG/DSC, SEM, and PCT. This report considers kinetics by transition metal oxide rate and Hydrogen pressure. In this research, we can see behavior of hydriding/dehydriding profiles by addition catalyst (transition metal oxide). Results of PCI make a excellent showing $MgH_x$-5wt.% Sc2O3 at 623K, $MgH_x$-10wt.% $Sc_2O_3$ at 573K.

Characterization of dissociation catalysts for waste plastics (폐플라스틱 분해 촉매의 특성)

  • Kim, Moon-Chan;Lee, Cheal-Gyu
    • Analytical Science and Technology
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    • v.23 no.4
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    • pp.383-388
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    • 2010
  • Catalytic dissociation reaction was studied in order to transform waste plastics to oil by using noble metal supported catalysts. XRD, SEM, and GC/MSD analysis were performed to find the crystalline structure and shape, and product distribution. Generally, dissociation reaction occurs at low temperature compared to pyrolysis. Dissociation reaction has advantage of gasoline yield with respect to pyrolysis which products mainly $C_1\simC_4$. The result of dissociation reaction, gasoline was obtained much as a product. $C_5\simC_{11}$ compounds were produced as a gasoline product on Pt-zeolite among noble metal catalysts at $340^{\circ}C$. The conversion of dissociation reaction of waste plastics on the prepared catalyst was above 70% over $340^{\circ}C$.