• Title/Summary/Keyword: reaction active energy.

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Recent Developments of Metal-N-C Catalysts Toward Oxygen Reduction Reaction for Anion Exchange Membrane Fuel Cell: A Review

  • Jong Gyeong Kim;Youngin Cho;Chanho Pak
    • Journal of Electrochemical Science and Technology
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    • v.15 no.2
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    • pp.207-219
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    • 2024
  • Metal-N-C (MNC) catalysts have been anticipated as promising candidates for oxygen reduction reaction (ORR) to achieve low-cost polymer electrolyte membrane fuel cells. The structure of the M-Nx moiety enabled a high catalytic activity that was not observed in previously reported transition metal nanoparticle-based catalysts. Despite progress in non-precious metal catalysts, the low density of active sites of MNCs, which resulted in lower single-cell performance than Pt/C, needs to be resolved for practical application. This review focused on the recent studies and methodologies aimed to overcome these limitations and develop an inexpensive catalyst with excellent activity and durability in an alkaline environment. It included the possibility of non-precious metals as active materials for ORR catalysts, starting from Co phthalocyanine as ORR catalyst and the development of methodologies (e.g., metal-coordinated N-containing polymers, metal-organic frameworks) to form active sites, M-Nx moieties. Thereafter, the motivation, procedures, and progress of the latest research on the design of catalyst morphology for improved mass transport ability and active site engineering that allowed the promoted ORR kinetics were discussed.

Effect of Pressure and Solvent Dielectric Constant on the Kinetic Constants of Trypsin-Catalyzed Reaction. (Trypsin 반응에 대한 용매의 유전상수 및 압력의 영향)

  • Park, Hyun;Chi, Young-Min
    • Microbiology and Biotechnology Letters
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    • v.28 no.1
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    • pp.26-32
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    • 2000
  • Electrostatic forces contribute to the high degree of enzyme transition state complementarity in enzyme catalyzed reaction and such forces are modified by the solvent through its dielectric constant and polar properties. The contributions of electrostatic interaction to the formation of ES complex and the stabilization of transition state of the trypsin catalyzed reaction were probed by kinetic studied with high pressure and solvent dielectric constant. A good correlation has been observed between the increase of catalytic efficiency of trypsin and the decrease of solvent dielectric constant. Activation volume linearly decreased as the dielectric constant of solvent decreased, which means the increase in the reaction rae. Moreover, the decrease of activation volume by lowering the solvent dielectric constant implies a solvent penetration of the active with and a reduction of electrostatic energy for the formation of dipole of the active site oxyanion hole. When the 야electric constant of the solvents was lowered to 4.7 unit, the loss of activation energy and that of free energy of activation were 2.262 KJ/mol and 3.169 KJ/mol, respectively. The results of this study indicate that the high pressure kinetics combined with solvent effects can provide unique information on enzyme reaction mechanisms, and the controlling the solvent dielectric constant can stabilize the transition state of the trypsin-catalyzed reaction.

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Solvent Effect on Preservation and Inversion of the Chirality in the Processes of Nucleophilic Substitution Reaction of Organic Compound bearing Optical Activity Resolution (광학활성 분리능을 갖는 유기화합물의 친핵성치환반응에서 키랄성의 유지 및 반전에 미치는 용매효과)

  • Lee, Yong-Hee;Lee, Young-Sei
    • Journal of the Korean Society of Industry Convergence
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    • v.7 no.3
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    • pp.299-303
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    • 2004
  • A systematic investigation for the reactivity and solvent effect was studied on the reaction of optical resolving agents with the optically active assistant compounds. The reaction rate constants of the nucleophillic substitution reactions were determined by means of conductometric method The linear solvent energy relationship based on the solvent parameters and the thermodynamic parameters was discussed on the reactions of various physiological active compounds and optical resolving agents The reaction mechanism was discussed from the kinetic results compared with the optical purity.

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Recent Progress in the Identification of Active Sites in Pyrolyzed Fe-N/C Catalysts and Insights into Their Role in Oxygen Reduction Reaction

  • Sa, Young Jin;Kim, Jae Hyung;Joo, Sang Hoon
    • Journal of Electrochemical Science and Technology
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    • v.8 no.3
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    • pp.169-182
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    • 2017
  • Iron and nitrogen codoped carbon (Fe-N/C) catalysts have emerged as one of the most promising replacements for state-of-the-art platinum-based electrocatalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells. During the last decade, significant progress has been achieved in Fe-N/C catalysts in terms of ORR activity improvement and active site identification. In this review, we focus on recent efforts towards advancing our understanding of the structure of active sites in Fe-N/C catalysts. We summarize the spectroscopic and electrochemical methods that are used to analyze active site structure in Fe-N/C catalysts, and the relationship between active site structure and ORR activity in these catalysts. We provide an overview of recently reported synthetic strategies that can generate active sites in Fe-N/C catalysts preferentially. We then discuss newly suggested active sites in Fe-N/C catalysts. Finally, we conclude this review with a brief future outlook.

Potential Energy Surfaces for the Reaction Al + O2→ AlO + O

  • Ledentu, Vincent;Rahmouni, Ali;Jeung, Gwang-Hi;Lee, Yoon-Sup
    • Bulletin of the Korean Chemical Society
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    • v.25 no.11
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    • pp.1645-1647
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    • 2004
  • Potential energy surfaces for the reaction Al + $O_2{\to}$AlO + O have been calculated with the multireference configuration interaction (MRCI) method using molecular orbitals derived from the complete active space selfconsistent field (CASSCF) calculations. The end-on geometry is the most favourable for the reaction to take place. The small reaction barrier in the present calculation (0.11 eV) is probably an artefact related to the ionicneutral avoided crossing. The charge analysis implies that the title oxidation reaction occurs through a harpooning mechanism. Along the potential energy surface of the reaction, there are two stable intermediates of $AlO_2(C_{{\infty}v}$ and $C_{2v}$) at least 2.74 eV below the energy of reactants. The calculated enthalpy of the reaction (-0.07 eV) is in excellent agreement with the experimental value (-0.155 eV) in part due to the fortuitous cancellation of errors in AlO and $O_2$ calculations.

Synthesis and characterization of NiFe2O4 nanoparticle electrocatalyst for urea and water oxidation (요소 산화반응을 위한 NiFe2O4 나노파티클 촉매 합성 및 특성 분석 )

  • Ki-Yong Yoon;Kyung-Bok Lee;Dohyung Kim;Hee Yoon Roh;Sung Mook Choi;Ji-hoon Lee;Jaehoon Jeong;Juchan Yang
    • Journal of the Korean institute of surface engineering
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    • v.56 no.4
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    • pp.243-249
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    • 2023
  • Urea oxidation reaction (UOR) via electrochemical oxidation process can replace oxygen evolution reaction (OER) for green hydrogen production since UOR has lower thermodynamic potential (0.37 VRHE) than that of OER (1.23 VRHE). However, in the case of UOR, 6 electrons are required for the entire UOR. For this reason, the reaction rate is slower than OER, which requires 4 electrons. In addition, it is an important challenge to develop catalysts in which both oxidation reactions (UOR and OER) are active since the active sites of OER and UOR are opposite to each other. We prove that among the NiFe2O4 nanoparticles synthesized by the hydrothermal method at various synthesis temperatures, NiFe2O4 nanoparticle with properly controlled particle size and crystallinity can actively operate OER and UOR at the same time.

Effect of Support in HI Decomposition Reaction using Pt Catalyst (Pt 촉매를 이용한 HI분해반응에서 지지체에 따른 영향)

  • Ko, Yun-Ki;Park, Chu-Sik;Kang, Kyoung-Soo;Bae, Ki-Kwang;Kim, Young-Ho
    • Journal of Hydrogen and New Energy
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    • v.22 no.4
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    • pp.415-423
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    • 2011
  • HI decomposition step certainly demand catalytic reaction for efficient production of hydrogen in SI process. Platinum catalyst can apply to HI decomposition reaction as well as hydrogenation or dehydrogenation. Generally, noble metal is used as catalyst which is loaded form for getting high dispersion and wide active area. In this study, Pt was loaded onto zirconia, ceria, alumina, and silica by impregnation method. HI decomposition reaction was carried out under the condition of $450^{\circ}C$, 1atm, and $167.76h^{-1}$ (WHSV) in a fixed bed reactor for measuring catalytic activity. And property of a catalyst was observed by BET, TEM, XRD and chemisoption analysis. On the basis of experimental results, we discussed about conversion of HI according to physical properties of the loaded Pt catalyst onto each support.

Electrocatalytic activity of carbon-supported near-surface alloys (NSAs) for electrode reaction of fuel cell (연료전지 전극 반응을 위한 카본 담지 표면 합금의 전기촉매 활성)

  • Park, In-Su;Sung, Yung-Eun
    • New & Renewable Energy
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    • v.2 no.4 s.8
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    • pp.64-69
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    • 2006
  • There is a worldwide interest in the development and commercialization of polymer electrolyte membrane fuel cells [PEMFCs] for vehicular and stationary applications. One of the major objectives is the reduction of loaded electrode materials, which is comprise of the Pt-based noble metals. In this paper, a novel chemical strategy is described for the preparation and characterization of carbon-supported and surface-alloys, which were prepared by using a successive reduction process. After preparing Au colloid nanoparticles, the supporting of Au colloid nanoparticles occurred spontaneously in the carbon black-dispersed aqueous solution. Then nano-scaled active materials were formed on the surface of carbon-supported Au nanoparticles. The structural and electrochemical analyses indicate that the active materials were deposited on the surface of Au nanoparticles selectively and that an alloying process occurred during the successive reducing process. The carbon-supported & surface-alloys showed the higher electrocatalytic activity than those of the particle-alloys and commercial one [Johnson-Matthey] for the reaction of methanol and formic acid oxidation. The increased electrocatalytic activity might be attributed to the effective surface structure of surface-alloys, which have a high utilization of active materials for the surface reaction of electrode.

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Effect of Physico-chemical Properties of Pt/TiO2 Catalyst on CO Oxidation at Room Temperature (Pt/TiO2 촉매의 물리화학적 특성이 CO 상온산화 반응에 미치는 영향 연구)

  • Kim, Sung Chul;Kim, Geo Jong;Hong, Sung Chang
    • Applied Chemistry for Engineering
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    • v.29 no.6
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    • pp.657-662
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    • 2018
  • In this study, the effect of $Pt/TiO_2$ catalysts on the CO oxidation reaction at room temperature was investigated using various $TiO_2$ supports with different physical properties to compare and evaluate $Pt/TiO_2$ catalysts. Physicochemical properties of the catalyst were alanyzed using XPS, CO-chemisorption, BET, and CO-TPD. As a result, when the active particle diameter was smaller, while the metal dispersion and surface area were larger, the CO room temperature oxidation reaction was better. These physical properties increased the number of active sites, causing the target material to increase the adsorption amount of CO. In addition, when the $O_2$-consumption increased, the CO-room temperature oxidation reaction activity increased due to the excellent oxygen-transferring ability.

Optimization of Cu/CeO2 Catalyst for Single Stage Water-Gas Shift Reaction: CeO2 Production Using Cerium Hydroxy Carbonate Precursor and Selection of Optimal Cu Loading (단일 수성가스 전이 반응용 Cu/CeO2 촉매 최적화: 수산화탄산세륨 전구체를 이용한 CeO2 제조 및 최적 Cu 담지량 선정)

  • HEO YU-SEUNG;JEONG, CHANG-HOON;PARK, MIN-JU;KIM, HAK-MIN;KANG, BOO MIN;JEONG, DAE-WOON
    • Journal of Hydrogen and New Energy
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    • v.32 no.6
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    • pp.455-463
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    • 2021
  • In this study, CeO2 support is synthesized from cerium hydroxy carbonate prepared using precipitation/digestion method using KOH and K2CO3 as the precipitants. The Cu was impregnated to CeO2 support with the different loading (Cu loading=10-40 wt. %). The prepared Cu/CeO2 catalysts were applied to a single stage water gas shift (WGS) reaction. Among the prepared catalysts, the 20Cu/CeO2 catalyst contained 20 wt.% of Cu showed the highest CO conversion (Xco=68% at 400℃). This result was mainly due to a large amount of active sites. In addition, the activity of the 20 Cu/CeO2 catalyst was maintained without being deactivated for 100 hours because of the strong interaction between Cu and CeO2. Therefore, it was confirmed that 20 Cu/CeO2 is a suitable catalyst for a single WGS reaction.