• Journal of Electrochemical Science and Technology
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• 제13권3호
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• pp.354-361
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• 2022

In a direct methanol fuel cell system (DMFC), one of the drawbacks is methanol crossover. Methanol from the anode passes through the membrane and enters the cathode, causing mixed potential in the cell. Only Pt-based catalysts are capable of operating as cathode for oxygen reduction reaction (ORR) in a harsh acidic condition of DMFC. However, it causes mixed potential due to high activity toward methanol oxidation reaction of Pt. To overcome this situation, developing Pt-based catalyst that has methanol tolerance is significant, by controlling reactant adsorption or reaction kinetics. Pt/C decorated with phosphate ion was prepared by modified polyol method as cathode catalyst in DMFC. Phosphate ions, bonded to the carbon of Pt/C, surround free Pt surface and block only methanol adsorption on Pt, not oxygen. It leads to the suppression of methanol oxidation in an oxygen atmosphere, resulting in high DMFC performance compared to pristine Pt/C.

• 한국지하수토양환경학회지:지하수토양환경
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• 제25권1호
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• pp.62-73
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• 2020

PAHs commonly found in industrial sites such as manufactured gas plants (MGP) are potentially toxic, mutagenic and carcinogenic, and thus require immediate remediation. In-situ chemical oxidation (ISCO) is known as a highly efficient technology for soil and groundwater remediation. Among the several types of oxidants utilized in ISCO, persulfate has gained significant attention in recent years. Peroxydisulfate ion (S₂O₈^2-) is a strong oxidant with very high redox potential (E⁰ = 2.01 V). When mixed with Fe²⁺, it is capable of forming the sulfate radical (SO₄^-·) that has an even higher redox potential (E⁰ = 2.6 V). In this study, the influence of various iron activators on the persulfate oxidation of PAHs in contaminated soils was investigated. Several iron sources such as ferrous sulfate (FeSO₄), ferrous sulfide (FeS) and zero-valent iron (Fe(0)) were tested as a persulfate activator. Acenaphthene (ANE), dibenzofuran (DBF) and fluorene (FLE) were selected as model compounds because they were the dominant PAHs found in the field-contaminated soil collected from a MGP site. Oxidation kinetics of these PAHs in an artificially contaminated soil and the PAH-contaminated field soil were investigated. For all soils, Fe(0) was the most effective iron activator. The maximum PAHs removal rate in Fe(0)-mediated reactions was 92.7% for ANE, 83.0% for FLE, and 59.3% for DBF in the artificially contaminated soil, while the removal rate of total PAHs was 72.7% in the field-contaminated soil. To promote the iron activator effect, the effects of hydroxylamine as a reducing agent on reduction of Fe³⁺ to Fe²⁺, and EDTA and pyrophosphate as chelating agents on iron stabilization in persulfate oxidation were also investigated. As hydroxylamine and chelating agents (EDTA, pyrophosphate) dosage increased, the individual PAH removal rate in the artificially contaminated soil and the total PAHs removal rate in the field-contaminated soil increased.

• 한국토양환경학회지
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• 제5권3호
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• pp.3-15
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• 2001

본 연구에서는 증류수와 인공지하수, 그리고 지하수를 대상으로 오존의 분해거동(오존의 자가분해, pH의 영향, 용해도)과 오존산화공정에 의한 디젤의 분해(디젤의 분해, TCE와 PCE의 분해, 수산화라디칼 scavenger의 영향, pH의 영향, 오존/과산화수소의 영향)를 조사하였다. 증류수와 지하수내에서 오존의 자가분해는 모두 2차 반응속도식을 보였고, 증류수(반감기 37.5 분)에서보다 지하수(반감기 14.7분)에서 훨씬 빠르게 오존이 분해되었으며, 알칼리성 조건하에서 두 액상에서 모두 오존의 분해는 촉진되었다. 또한 오존산화공정의 사용은 TCE와 PCE, 그리고 디젤에 대해 높은 산화처리속도를 나타내었다. 비록 지하수내에 존재하는 hydroxyl radical scavenger는 디젤의 분해에서 억제제로 작용하였지만, 높은 pH조건과 과산화수소의 첨가는 지하수내에서 디젤을 분해시키는 데 중요한 촉진제로서 작용하였다. 그러므로 오존산화공정은 디젤로 오염된 지하수를 처리하는 데 효과적으로 적용될 것이라 판단된다.

• 한국자동차공학회논문집
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• 제20권6호
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• pp.73-82
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• 2012

The main and side reactions of the three selective catalytic reduction (SCR) reactions with ammonia over a vanadium-based catalyst have been investigated using synthetic gas mixtures in the temperature range of $170{\sim}590^{\circ}C$. The three SCR reactions are standard SCR with pure NO, fast SCR with an equimolar mixture of NO and $NO_2$, and $NO_2$ SCR with pure $NO_2$. Vanadium based catalyst has no significant activity in NO oxidation to $NO_2$, while it has high activity for $NO_2$ decomposition at high temperatures. The selective catalytic oxidation of ammonia and the formation of nitrous oxide compete with the SCR reactions at the high temperatures. Water strongly inhibits the selective catalytic oxidation of ammonia and the formation of nitrous oxide, thus increasing the selectivity of the SCR reactions. However, the presence of water inhibits the SCR activity, most pronounced at low temperatures. In this study, the experimental results are analyzed by means of a dynamic one-dimensional isothermal heterogeneous plug-flow reactor (PFR) model according to the Eley-Rideal mechanism.

• Rapid Communication in Photoscience
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• 제3권4호
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• pp.70-72
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• 2014

Visible-light irradiation of MeCN solution containing di(hydroxo)metallo(tetraphenyl)porphyrin complex $(tppM(OH)_2$: 1a; $M=Sb(V)^+Br^-$, 1b; $M=P(V)^+Cl^-$, 1c; M=Ge(IV)) and 2-mercaptoethanol (2-ME) as a substrate under aerated condition gave bis(2-hydroxyethyl)disulfide (2-HEDS) as an oxidative product of 2-ME. It is indicated that the oxidation of 2-ME should proceed with a photocatalytic process by 1, because the turn over number (TON) for the formation of 2-HEDS was over unit. The TON was determined to be 642 as a maximum value when 1a was used as a sensitizer. The formation of 2-HDES was extremely slow under argon atmosphere. The fluorescence of 1 was not quenched by 2-ME at all, and the free energy change (${\Delta}G$) with electron transfer (ET) from 2-ME to excited triplet state of $1(^31^*)$ was estimated as a negative value. The quenching rate constant ($k_r$) of $^31^*$ by 2-ME, obtained by the kinetics for the formation of 2-HEDS, strongly depends on ${\Delta}G$. These findings indicate that 1-sensitized oxidation was initiated by photoinduced ET from 2-ME to $^31^*$ to generate both radical cation of 2-ME ($2-ME^{+\bulle}$) and porphyrin radical anion ($1^{-\bulle}$), resulting that the formation of 2-HEDS can be proceeded by the dimerization of $2-ME^{+\bulle}$, and through a catalytic cycle due to returning to 1 by the ET from $1^{-\bulle}$ to molecular oxygen.

• Nuclear Engineering and Technology
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• 제45권2호
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• pp.211-218
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• 2013

Large quantities of irradiated graphite waste from graphite-moderated nuclear reactors exist and are expected to increase in the case of High Temperature Reactor (HTR) deployment [1,2]. This situation indicates the need for a graphite waste management strategy. Of greatest concern for long-term disposal of irradiated graphite is carbon-14 ($^{14}C$), with a half-life of 5730 years. Fachinger et al. [2] have demonstrated that thermal treatment of irradiated graphite removes a significant fraction of the $^{14}C$, which tends to be concentrated on the graphite surface. During thermal treatment, graphite surface carbon atoms interact with naturally adsorbed oxygen complexes to create $CO_x$ gases, i.e. "gasify" graphite. The effectiveness of this process is highly dependent on the availability of adsorbed oxygen compounds. The quantity and form of adsorbed oxygen complexes in pre- and post-irradiated graphite were studied using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Xray Photoelectron Spectroscopy (XPS) in an effort to better understand the gasification process and to apply that understanding to process optimization. Adsorbed oxygen fragments were detected on both irradiated and unirradiated graphite; however, carbon-oxygen bonds were identified only on the irradiated material. This difference is likely due to a large number of carbon active sites associated with the higher lattice disorder resulting from irradiation. Results of XPS analysis also indicated the potential bonding structures of the oxygen fragments removed during surface impingement. Ester- and carboxyl-like structures were predominant among the identified oxygen-containing fragments. The indicated structures are consistent with those characterized by Fanning and Vannice [3] and later incorporated into an oxidation kinetics model by El-Genk and Tournier [4]. Based on the predicted desorption mechanisms of carbon oxides from the identified compounds, it is expected that a majority of the graphite should gasify as carbon monoxide (CO) rather than carbon dioxide ($CO_2$). Therefore, to optimize the efficiency of thermal treatment the graphite should be heated to temperatures above the surface decomposition temperature increasing the evolution of CO [4].

• Korean Chemical Engineering Research
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• 제44권6호
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• pp.636-643
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• 2006

연속식 SCWO 반응기를 이용하여 DMMP의 초임계수 산화반응을 반응온도 $440{\sim}540^{\circ}C$, 반응압력 242 bar, 체류시간 10~26 초, 과잉산소량 -40~200％의 조건 하에서 수행하였다. 반응온도 $540^{\circ}C$에서 DMMP 분해율은 99.7% 이상으로 높았으며, DMMP의 농도가 증가함에 따라 DMMP 분해율은 증가하였다. 산화제 농도 변화에 따른 분해율은 양론비 이하에서는 현저하게 영향을 받았으나, 양론비 이상에서는 큰 차이가 없었다. DMMP 분해율이 85% 이상인 30개의 실험결과로부터 DMMP의 초임계수 산화반응 속도식을 도출하였다. Pre-exponential factor는 $(1.10{\pm}0.76){\times}10^6$, 반응 활성화에너지는 $90.66{\pm}3.87kJ/mol$, DMMP와 산소에 대한 반응차수는 각각 $1.02{\pm}0.03$, $0.32{\pm}0.03$로 모델에 의한 예측값과 실험값은 잘 일치하였다.

• 한국표면공학회지
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• 제34권6호
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• pp.585-591
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• 2001

니오비움 첨가 지르코늄 합금(Zr-1%Nb)의 고온 수증기에서 산화속도에 관한 연구를 수행하였다. 산화온도는 $700-1200^{\circ}C$이다. 대기압수증기에서 산화될 때, Zr -1%Nb은 2차법칙을 따르는 것으로 나타났으며, 이는 $900^{\circ}C$이하에서 3차법칙을 따르는 지 르칼로이 -4와 상이한 형태를 보이고 있다. $900^{\circ}C$이상에선 산화속도가 지르칼로이 -4보다 약간 낮으며, 산화후 금속층의 경도가 증가하였다. 경도증가로 보아 인성의 감소가 예상되며, 따라서 니오비움 첨가 지르코늄 합금의 사고시 안전성에 대한 주의가 요구된다.

• 한국환경보건학회지
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• 제27권1호
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• pp.1-7
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• 2001

Ammonia is used in the manufacture of fertilizers, refrigerants, stabilizers and many household cleaning agents. These wide applications resulted in ammonia contamination in water. Ammonia can be removed from water by physical, biological, and chemical methods. Ozonation is effictive in the treatment of water with low concentration of ammonia. This study is undertaken to provide kinetic data for the ozonation of ammonia with or without hydrogen peroxide. The results were as follows; The destruction rate of ammonia increased gradually with the influent hydrogen peroxide concentration up to 0.23 mM and inhibited in the range of 0.23~11.4mM, and the maximum removal rate of ammonia achieved at 0.23mM of hydrogen peroxide, and the overall kinetics was first order. The combination effect of hydrogen and ozone to oxide ammonia in aqueous solution was better than ozone alone. The reacted ammonia was converted completely to nitrate ion.

• Natural Product Sciences
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• 제10권2호
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• pp.80-84
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• 2004

Rosmarinic acid and its methyl ester, isolated from the ethyl acetate soluble fraction of the methanolic extract of Salvia miltiorrhiza Bunge (Labiatae), were found to inhibit the oxidation of L-tyrosine catalyzed by mushroom tyrosinase with the $IC_{50}$ values of 16.8 and $21.5\;{\mu}M$, respectively. It was comparable with kojic acid, a well-known tyrosinase inhibitor, with an $IC_{50}$ of $22.4\;{\mu}M$. The inhibitory kinetics analyzed by the Lineweaver-Burk plots, were found rosmarinic acid and its methyl ester to be competitive inhibitors with $K_i\;of\;2.4{\times}10^{-5}\;and\;1.5{\times}10^{-5}\;M$, respectively.