• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3660-3665
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• 2011

CO-tolerant PtMo/C alloy electrocatalyst was prepared by a colloidal method, and its electrocatalytic activity toward CO oxidation was investigated. Electrochemical study revealed that the alloy catalyst significantly enhanced catalytic activity toward the electro-oxidation of CO compared to Pt/C counterpart. Cyclic voltammetry suggested that Mo plays an important role in promoting CO electro-oxidation by facilitating the formation of active oxygen species. The effect of Mo on the electronic structure of Pt was investigated using X-ray absorption spectroscopy to elucidate the synergetic effect of alloying. Our in-depth spectroscopic analysis revealed that CO is less strongly adsorbed on PtMo/C catalyst than on Pt/C catalyst due to the modulation of the electronic structure of Pt d-band. Our investigation shows that the enhanced CO electrooxidation in PtMo alloy electrocatalyst is originated from two factors; one comes from the facile formation of active oxygen species, and the other from the weak interaction between Pt and CO.

• Korean Journal of Soil Science and Fertilizer
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• v.26 no.3
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• pp.204-214
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• 1993

The purpose of this study was to elucidate the chemical changes and formation of sulfur minerals following reduction and subsequent oxidation of the acid sulfate soils derived from the fluvio-marine plains in Gimhae area. Changes in pH, Eh and water soluble $SO_4$, Fe, Al, K, na and Ca were determined in the soil under the reduced and oxidized conditions. These chemical properties were related to the formation of the pyrite and jarosite, the major sulfur minerals in the acid sulfate soils. On incubation, suspension pH tended to increase with decreaseing Eh in the reduction periods. Jarosite formation was favored by maintaining continuous low pH(below 4.0) and high Eh(above 400mV) during the oxidation periods, however, the conditions were not favorable for the soils with $Ca(OH)_2$. Water soluble K increased by reduction but decreased by oxidation, while the jarosite of the soil with $Ca(OH)_2$ was dissolved even under the oxidation conditon, resulting in rapid increase of water soluble K. The water soluble Ca decreased rapidly, indicating that gypsum was formed with $Ca(OH)_2$ during the oxidation periods. The formation of jarosite was favored by the oxidation condition, and hindered by the reduction condition. But the formation of pyrite was favored by reduction and hindered by oxidation. When the troll was treated with $Ca(OH)_2$, Jarosite was dissolved in both oxidized and reduced conditions.

• Journal of Hydrogen and New Energy
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• v.30 no.4
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• pp.320-329
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• 2019

This study was performed by the numerical approach to investigate chemical behaviors of homogeneous syngas ($CO/H_2$) with nitric monoxide (NO) in pressurized oxy-fuel conditions. Hydrogen had a dominant effect to the ignition delay time of syngas due to the fast chemistry of its oxidation. Combustion was promoted by NO at the low temperature region. It was by the additional heat release through NO oxidation and production and consumption of major radicals related to the ignition. Two stage ignition behavior was shown in the pressurized condition by the accumulation of $H_2O_2$ produced from $HO_2$ radical. Additional NO oxidation was induced by the pressurized oxy-fuel condition to produce $NO_2$.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.4
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• pp.402-408
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• 2005

This investigation aimed at selecting the optimum catalyst and reaction conditions used in Fenton oxidation for landfill leachate treatment and was carried out at ambient temperature using a lab-scale experiment. The investigation led to the following results: 1) The optimum pH and dose for each iron catalyst were as follows: $Fe^{2+}\;=\;1,200\;mg/L$, $H_2O_2\;=\;1,200\;mg/L$, initial pH=3.0; $Fe^{3+}\;=\;1,200\;mg/L$, $H_2O_2\;=\;1,500\;mg/L$, initial pH=4.5; $Fe^0\;=\;1,200\;mg/L$, $H_2O_2\;=\;900\;mg/L$, initial pH=4.0, respectively. 2) The progress of Fenton oxidation could be instrumentally monitored by measuring redox potential evolution during leachate oxidation, thus, indicating the possibility of an on-line process monitoring. 3) A simple acid-base titration of Fenton-treated leachate proved that a relevant fraction of by- products formed during the treatment was made of acidic compounds in the optimum reaction condition for each catalyst used, thus demonstrating that the higher the extent of Fenton oxidation the greater was the amount of acids formed. 4) With the aim of selecting the optimum catalyst among $Fe^0$, $Fe^{2+}$ and $Fe^{3+}$, removal efficiency of each parameter in the optimum reaction conditions was considered. Although $Fe^{3+}$ was higher than other catalysts($Fe^0$, $Fe^{2+}$) in removal efficiency, $Fe^0$ was a optimum catalyst with a view of cost effectiveness.

• Biotechnology and Bioprocess Engineering:BBE
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• v.5 no.1
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• pp.48-52
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• 2000

An autotrophic sulfur oxidizer, Thiobacillus sp. ASWW-2, was isolated from activated sludge, and its sulfur oxidation activity was characterized. Thiobacillus sp. ASWW-2 could oxidize elemental sulfur on the broad range from pH 2 to 8. When 5-50 g/L of elemental sulfur was supplemented as a substrate, the growth and sulfur oxidation activity of Thiobacillus sp. ASWW-2 was not inhibited. The specific sulfur oxidation rate of strain ASWW-2 decreased gradually until sulfate was accumulated in medium up to 10 g/L. In the range of sulfate concentration from 10 g/L to 50 g/L, the sulfur oxidation rate could keep over $2.0g-S/g-DCW{\cdot}d$. It indicated that Thiobacillus sp. ASWW-2 has tolerance to high concentration of sulfate.

• Journal of Environmental Science International
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• v.18 no.11
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• pp.1225-1234
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• 2009

The aim of this research was to apply experimental design methodology in the optimization condition of electrochemical oxidation of Rhodamine B(RhB). The reactions of electrochemical oxidation were mathematically described as a function of parameters amounts of current, NaCl dosage, pH and time being modeled by the use of the central composite design, which was used for fitting quadratic response surface model. The application of response surface methodology using central composite design(CCD) technique yielded the following regression equation, which is an empirical relationship between the removal efficiency of RhB and test variable in actual variables: RhB removal (%) = 3.977 + 23.279$\cdot$Current + 49.124$\cdot$NaCI - 5.539$\cdot$pH - 8.863$\cdot$time - 22.710$\cdot$Current$\cdot$NaCl + 5.409$\cdot$Current$\cdot$time + 2.390$\cdot$NaCl$\cdot$time + 1.061$\cdot$pH$\cdot$time - $0.570{\cdot}time^2$. The model predicted also agree with the experimentally observed result($R^2$ = 91.9%).

• Environmental Engineering Research
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• v.11 no.2
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• pp.84-90
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• 2006

UV-catalytic oxidation technique was applied for the treatment of bio-refractory character of the leachate, which is generally present in the form of adsorbable organic halogens (AOX). Destruction of AOX was likely to be governed by pH adjustment, quantitative measurement of oxidants, and the selection of oxidation model type. Peroxide induced degradation ($UV/H_2O_2$) facilitated the chemical oxidation of organic halides in acidic medium, however, the system showed least AOX removal efficiency than the other two systems. Increased dosage of hydrogen peroxide (from 0.5 time to 1.0 time concentration) even did not contribute to a significant increase in the removal rate of AOX. In ozone induced degradation system ($UV/O_3$), alkaline medium (pH 10) favored the removal of AOX and the removal rate was found 11% higher than the rate at pH 3. Since efficiency of the $UV/O_3$ increases with the increase of pH, therefore, more OH-radicals were available for the destruction of organic halides. UV-light with the combination of both ozone and hydrogen peroxide ($UV/H_2O_2$ 0.5 time/$O_3$ 25 mg/min) showed the highest removal rate of AOX and the removal efficiency was found 26% higher than the removal efficiency of $UV/O_3$. The system $UV/H2O_2/O_3$ got the economic preference over the other two systems since lower dose of hydrogen peroxide and relatively shorter reaction time were found enough to get the highest AOX removal rate.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.7
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• pp.549-556
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• 2009

In situ chemical oxidations (ISCO) are technologies for destruction of many contaminants in soil and groundwater, and persulfate has been recently studied as an alternative ISCO oxidant. Trichloroethylene (TCE) and tetrachloroethylene (PCE) were chosen for target organic compounds. The objective of this study is to demonstrate the influence of initial pH (3, 6, 9, 12), oxidant concentrations (0.01, 0.05, 0.1, 0.3, 0.5 M), and contaminants concentrations (10, 30, 50, 70, 100 mg/L) on TCE/PCE degradation by persulfate oxidation. The maximum TCE/PCE degradation occurred at pH 3, and the removal efficiencies with this pH condition were 93.2 and 89.3%, respectively. The minimum TCE/PCE degradation occurred at pH 12, and the removal efficiencies were 55.0 and 31.2%, respectively. This indicated that degradation of TCE/PCE decreased with increasing the initial pH of solution. Degradation of TCE/PCE increased with increasing the concentration of persulfate and with decreasing the concentration of contaminants (TCE/PCE). The optimum conditions for TCE/PCE degradation were pH 3, 0.5 M of persulfate solution, and 10 mg/L of contaminant concentration. At these conditions, the first-order rate constants ($k_{obs}$) for TCE and PCE were 1.04 and 1.31 $h^{-1}$, respectively.

• Corrosion Science and Technology
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• v.19 no.1
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• pp.43-50
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• 2020

In this study, the effects of KCl(s) and K₂SO₄(s) on the oxidation characteristics of 2.25Cr-1Mo steel were investigated for 500 h in 10O₂ + 10CO₂ (vol%) gas environmen at 650 ℃. Oxidation kinetics were characterized by weight gain, oxide layer thickness, and fitted models for the experiment data were proposed. The fitted models presented considerable agreement with the experimental data. The oxide layer was analyzed using the scanning electron microscope, optical microscope, and energy dispersive X-ray spectroscopy. The oxidation kinetics of 2.25Cr-1Mo steel with KCl and K₂SO₄ coatings showed significantly different oxidation kinetics. KCl accelerated the oxidation rate very much and had linear oxidation behavior. In contrast, K₂SO₄ had no significant effect, which had parabolic kinetics. The oxide layer was commonly composed of Fe₂O₃, Fe₃O₄, and FeCr₂O₄ spinel. KCl strongly accelerated the oxidation rates of 2.25Cr-1Mo steel in the high-temperature oxidation environment. Conversely, K₂SO₄ had little effect on the oxidation rates.

• Bulletin of the Korean Chemical Society
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• v.27 no.12
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• pp.2023-2027
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• 2006

Dibenzyl sulfide was oxidized at the a-carbon to yield benzaldehyde in the presence of $Pd(NO_3)_2$. Oxygen itself could not oxidize the sulfide directly, instead the nitrato ligand of the palladium complex transferred oxygen to dibenzyl sulfide to form benzaldehyde. The X-ray crystal structure of the intermediate complex, cis-[$Pd(NO_3)_2${$S(CH_2C_6H_5)_2$}$_2$], revealed that the nitrato ligand was unidentate. Para-substituted dibenzyl sulfides I, $(YC_6H_4CH_2)_2S $wherein Y = $OCH_3$, $CH_3$, Cl, CN, or $NO_2$, were synthesized and reacted with palladium nitrate, and those with electron-donating substituents (Y = $OCH_3$ and $CH_3$) were good substrates for the oxidation reaction with palladium nitrate. Thus, the reaction mechanism of the oxygen transfer was proposed to include nucleophilic benzylic carbon.