• Korean Journal of Materials Research
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• 제33권2호
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• pp.29-46
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• 2023

The electrochemical reduction of carbon dioxide (CO₂) to value-added products is a remarkable approach for mitigating CO₂ emissions caused by the excessive consumption of fossil fuels. However, achieving the electrocatalytic reduction of CO₂ still faces some bottlenecks, including the large overpotential, undesirable selectivity, and slow electron transfer kinetics. Various electrocatalysts including metals, metals oxides, alloys, and single-atom catalysts have been widely researched to suppress HER performance, reduce overpotential and enhance the selectivity of CO₂RR over the last few decades. Among them, single-atom catalysts (SACs) have attracted a great deal of interest because of their advantages over traditional electrocatalysts such as maximized atomic utilization, tunable coordination environments and unique electronic structures. Herein, we discuss the mechanisms involved in the electroreduction of CO₂ to carbon monoxide (CO) and the fundamental concepts related to electrocatalysis. Then, we present an overview of recent advances in the design of high-performance noble and non-noble singleatom catalysts for the CO₂ reduction reaction.

• Journal of the Korean Society of Combustion
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• 제4권2호
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• pp.63-74
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• 1999

The effects of EGR and premixedness on NO formation have been numerically investigated. The flame structure is classified into three categories; premixed flame($=1)$, rich/lean premixed flame(${\alpha}=0.6$ and 0.8) and diffusion flame(${\alpha}=0$). NO formation/destruction mechanisms are assorted to thermal, reburn and Fenimore mechanisms. The temperature of unburned gas is arranged to 298 and 500 K to have access to the condition in a real internal combustion engine. The results show that all three NO formation/destruction reaction rates in the fuel rich flame zone could be decreased by EGR for rich/lean premixed flames, while those in the fuel lean flame zone are not significantly changed. Near the stagnation plane, however, only the thermal NO reaction rate is decreased. The contribution of reburn and Fenimore mechanisms for the net NO production becomes less significant as the premixedness of a flame increases. The larger amount of NO reduction with EGR is expected under the higher temperature and/or higher fuel/air premixedness conditions due to the increased contribution of the thermal mechanism. The role of Fenimore and reburn mechanisms could be important for rich premixed and diffusion flames; therefore, the effect of EGR on NO reduction could vary with fuel/air premixedness. The premixedness of a partially premixed flame changes the flame structure and could affect the NO production characteristics.

• Bulletin of the Korean Chemical Society
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• 제11권4호
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• pp.281-286
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• 1990

The kinetics and mechanism of reduction of Cu(II) with an excess D-penicillamine have been examined at pH = 6.2 and 0.60M in ionic strength. The reaction at the initial stage is biphasic with a rapid complexation process to give "red" transient complex of $[Cu(II)(pen)_2]^2$- that is partially reduced to another transient "brown" intermediate. The "brown" intermediate is finally reduced to diamagnetic "yellow" complex, $[Cu(I)(Hpen)]_n$. The final reduction process is pseudo-first order in ["brown" transient] disappearance $with {\kappa} = {{\kappa}_{3a} + {\kappa}_{3b}[pen]^{2-}},$ where ${\kappa}_{3a} = (5.0{\pm}0.8){\times}10^{-3}sec^{-1}$ and ${\kappa} = (0.14{\pm}0.02) M^{-1}sec^{-1}$ at $25^{\circ}C$. The activation parameters for the $[H_2pen]$-independent and $[H_2pen]$-dependent paths are ${\Delta}H^{\neq} = (52{\pm}5)kJmol^{-1},$ and ${\Delta}S^{\neq} = ( - 27{\pm}3)JK^{-1}mo^{l-1},$ and ${\Delta}H^{\neq} = (56{\pm}2)kJmol^{-1}$ and ${\Delta} S^{\neq} = ( - 18{\pm}0.7)JK^{-1}mol^{-1}$ respectively. The nature of "brown" intermediate is not clearly identified, but this intermediate seems to be in the mixed-valence state, judging from the kinetic and spectroscopic informations.

• Korean Journal of Metals and Materials
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• 제50권10호
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• pp.745-751
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• 2012

The Kroll process for magnesium reduction of titanium tetrachloride is used for mass production of titanium sponge. The present study was conducted in a lab scale reactor to develop a better understanding of the mechanism of titanium sponge formation in the Kroll reactor with respect to reaction degrees and the feeding rate of $TiCl_4$. The $MgCl_2$ produced during the initial stage of the reaction was not sunk into the molten magnesium, but covered the surface of the molten magnesium. As a result, subsequently fed $TiCl_4$ reacted with Mg exposed on the edge of molten $MgCl_2$ in the crucible. Therefore, titanium sponge grew toward the center of the crucible from the edge. The temperature of the molten magnesium increased remarkably with the increasing feeding rate of $TiCl_4$. Consequently, fed $TiCl_4$ reacted at the upper side of the crucible with evaporated Mg, and produced titanium on the upper surface of the crucible wall, which increased considerably with the feeding rate of $TiCl_4$.

• Journal of Mechanical Science and Technology
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• 제20권1호
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• pp.1-12
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• 2006

This work reviews the effects of catalyst formulation and exhaust gas composition on soot oxidation in CDPF (Catalytic Diesel Particulate Filter). DOC's (Diesel Oxidation Catalysts) have been loaded with Pt catalyst (Pt/$Al_{2}O_3$) for reduction of HC and CO. Recent CDPF's are coated with the Pt catalyst as well as additives like Mo, V, Ce, Co, Fe, La, Au, or Zr for the promotion of soot oxidation. Alkali (K, Na, Cs, Li) doping of metal catalyst tends to increase the activity of the catalysts in soot combustion. Effects of coexistence components are very important in the catalytic reaction of the soot. The soot oxidation rate of a few catalysts are improved by water vapor and NOx in the ambient. There are only a few reports available on the mechanism of the PM (particulate matter) oxidation on the catalysts. The mechanism of PM oxidation in the catalytic systems that meet new emission regulations of diesel engines has yet to be investigated. Future research will focus on catalysts that can not only oxidize PM at low temperature, but also reduce NOx, continuously self-cleaning diesel particulate filters, and selective catalysts for NOx reduction.

• Advances in Traditional Medicine
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• 제8권3호
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• pp.286-294
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• 2008

We have studied the possible mechanism of anti-asthmatic action of ethanolic extracts of dried seeds of Lepidium sativum (EXLS, 400 mg/kg) using various experimental models. EXLS produced an increase in the Pre-Convulsion Dyspnoea time induced by histamine and acetylcholine aerosol, a significant reduction in the elevated leucocyte counts in the Broncho-Alveolar Lavage fluid of sensitized guinea-pigs and reduction in the paw edema volume as compared to the control rats. Treatment with EXLS also produced decrease in the elevated histamine release from the sensitized guinea-pig lungs. The anti-asthmatic anti-inflammatory responses of EXLS was supported by improvement in microscopic changes like infiltration of inflammatory cells, submucosal edema, epithelial desquamation and reduced lumen size of the bronchi. The $pD_2$ values of histamine in tracheal chain and taenia-coli were significantly greater and that in lung strip was lower in the sensitized animals as compared to control. Treatment of sensitized guinea pigs with EXLS significantly decreased $pD_2$ values of histamine in all three preparations. Our data suggest the prevention of hyper-responsiveness in bronchial smooth muscles and inhibition of the immediate hypersensitive reaction, histamine release in the lungs and the infiltration of various inflammatory cells as the possible mechanisms of anti-asthmatic activity of EXLS.

• The Journal of Engineering Geology
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• 제17권1호
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• pp.143-150
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• 2007

AMD (Acid mine drainage) from disused mines is one or the most significant pollutant problems to make harmful effect to human health. We demonstrated the mechanism of resolution and adsorption reaction for arsenic, manganese and zink from the soil and mine tailings which were located in the vicinity of a disused mine in Kyoungnam area. The resolution experiments were carried with a column test f3r 45 days continuously. Metal chemical forms in water were changed with the condition of solution pH and ORP (oxidation-reduction potential). Metal chemical forms affected on the reaction of resolution and adsorption of metals in water environments. Even though the sampling was carried in very closed location, there was significant different results of pollution level and ORP changes in terms of column operations. Hence It was important to note the pH and ORP in AMD to evaluate a risk assessment and a soil management using monitoring metals. When we operate AMD management with the mechanism of resolution and adsorption it can be achieved better economic solution.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3607-3617
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• 2012

In this paper, the study of various ortho- and meta-substituted Magnolol derivatives is presented. The reaction enthalpies related to three antioxidant action mechanisms HAT, SET-PT and SPLET for substituted Magnolols have been calculated using DFT/B3LYP method in gas-phase and water. Calculated results show that electron-withdrawing substituents increase the bond dissociation enthalpy (BDE), ionization potential (IP) and oxidation/reduction enthalpy (O/RE), while electron-donating ones cause a rise in the proton dissociation enthalpy (PDE) and proton affinity (PA). In ortho- position, substituents show larger effect on reaction enthalpies than in meta-position. In comparison to gas-phase, water attenuates the substituent effect on all reaction enthalpies. In gas-phase, BDEs are lower than PAs and IPs, i.e. HAT represents the thermodynamically preferred pathway. On the other hand, SPLET mechanism represents the thermodynamically favored process in water. Results show that calculated enthalpies can be successfully correlated with Hammett constants (${\sigma}_m$) of the substituted Magnolols. Furthermore, calculated IP and PA values for substituted Magnolols show linear dependence on the energy of the highest occupied molecular orbital ($E_{HOMO}$).

• Korean Journal of Pharmacognosy
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• 제50권3호
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• pp.175-184
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• 2019

Mast cells are crucial as effector cells in the immediate-type allergic reaction. Lentinus edodes has been the popular edible mushroom in oriental countries and reported to have immunomodulatory, anti-tumor, anti-atherogenic, anti-viral, and anti-allergic activities. However, the roles of L. edodes in mast cell-mediated anaphylactic reaction have not been fully elucidated. In this research, we have demonstrated the effects of the methanol extract of L. edodes (MELE) on mast cell-mediated anaphylaxis-like and anaphylactic reactions. MELE suppressed systemic anaphylaxis-like reaction, plasma histamine levels, and ear swelling response in mice treated with compound 48/80. MELE also suppressed passive systemic and cutaneous anaphylaxis mediated by anti-dinitrophenyl IgE. In accordance with these findings, MELE dose-dependently decreased histamine release from RPMC evoked by compound 48/80 or the antigen-antibody reaction. To clarify the mechanism of degranulation system, intracellular cAMP levels as well as calcium influx in RPMC was evaluated. In compound 48/80-treated RPMC, MELE blocked calcium uptake into the cells. In addition, MELE elevated the intracellular cAMP content and significantly attenuated compound 48/80-induced cAMP reduction in RPMC. Taken together, we propose the clinical use of MELE in mast cell-mediated immediate-type allergic diseases.

• Bulletin of the Korean Chemical Society
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• 제35권11호
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• pp.3143-3155
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• 2014

This tutorial review provides a general account of the electrochemical behavior of quinones and their various applications. Quinone electrochemistry has been investigated for a long time due to its complexity. A simple point of view is developed that considers the relative stability of the reduced quinone species and the values of the first and second reduction potentials. The 9-membered square scheme in buffered aqueous solutions is explained and semiquinone radical stability is discussed in this context. Quinone redox reaction has also been employed in various studies. Diverse examples are presented under three broad categories defined by the roles of quinone: molecular tool for physical chemistry, versatile electron mediator, and charge storage for energy conversion devices.