• Applied Chemistry for Engineering
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• v.25 no.4
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• pp.418-424
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• 2014

The improved thermal stability and anti-oxidation properties of Lyocell fiber were studied based on flame retardant treatment by using NaCl/$H_3PO_4$ solution. The optimized conditions of flame retardant treatment were studied on various maxing ratio of NaCl and $H_3PO_4$ and the mechanism was proposed through experimental results of thermal stability anti-oxidation. The IPDT (integral procedural decomposition temperature), LOI (limited oxygen index) and $E_a$ (activation energy) increased 23, 30 and 24% respectively via flame retardant treatment. It is noted that thermal stability and anti-oxidation improved based on char and carbon layer formation by dehydrogenation and dissociation of C-C bond resulting the hindrance of oxygen and heat energy into polymer resin. The optimized conditions for efficient flame retardant property of Lyocell fiber were provided using NaCl/$H_3PO_4$ solution and the mechanism was also studied based on experimental results such as IDT (initial decomposition temperature), IPDT, LOI and $E_a$.

• Fire Science and Engineering
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• v.29 no.2
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• pp.25-32
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• 2015

The improved thermal stability and anti-oxidation properties of lyocell fiber were studied based on flame retardant treatment by using $Na_3PO_4$ solution. The optimized conditions of flame retardant treatment were studied on various concentrations of $Na_3PO_4$ and the mechanism was proposed through experimental results of thermal stability and anti-oxidation. The integral procedural decomposition temperature (IPDT), limiting oxygen index (LOI) and activation energy ($E_a$) increased 30, 160% respectively via flame retardant treatment. It is noted that thermal stability and anti-oxidation improved based on char and carbon layer formation by dehydrogenation and dissociation of C-C bond resulting the hindrance of oxygen and heat energy into polymer resin. The optimized conditions for efficient flame retardant property of lyocell fiber were provided using $Na_3PO_4$ solution and the mechanism was also studied based on experimental results such as initial decomposition temperature (IDT), IPDT, LOI and $E_a$.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.1939-1945
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• 2009

Kinetic investigations on the oxidation of pyrazine and four 2-substituted pyrazines viz., 2-methylpyrazine, 2-ethylpyrazine, 2-methoxypyrazine and 2-aminopyrazine by bromamine-B (BAB) to the respective N-oxides have been studied in HCl$O_4$ medium at 303 K. The reactions show identical kinetics being first-order each in $[BAB]_o\;and\;[pyrazine]_o$, and a fractional- order dependence on $[H^+]$. Effect of ionic strength of the medium and addition of benzenesulfonamide or halide ions showed no significant effect on the reaction rate. The dielectric effect is positive. The solvent isotope effect was studied using $D_2$O. The reaction has been studied at different temperatures and activation parameters for the composite reaction have been evaluated from the Arrhenius plots. The reaction showed 1:1 stoichiometry and the oxidation products of pyrazines were characterized as their respective N-oxides. Under comparable experimental conditions, the oxidation rate of pyrazines increased in the order: 2-aminopyrazine > 2-methoxypyrazine > 2-ethylpyrazine > 2-methylpyrazine > pyrazine. The rates correlate with the Hammett $\sigma$ relationship and the reaction constant $\rho$ was found to be -0.8, indicating that electron donating centres enhance the rate of reaction. An isokinetic temperature of $\beta$ = 333 K, indicated that the reaction was enthalpy controlled. A mechanism consistent with the experimental results has been proposed in which the rate determining step is the formation of an intermediate complex between the substrate and the diprotonated species of the oxidant. The related rate law in consistent with observed results has been deduced.

• Journal of environmental and Sanitary engineering
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• v.15 no.3
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• pp.88-93
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• 2000

The objective of this study was to depict the kinetic behavior of the platinum catalyst for the deep oxidation of VOCs and their mixture. The oxidation characteristics of VOCs, which were benzene, toluene, and styrene, was studies on a 0.5% $Pt/{\gamma}-Al_2O_3$ catalyst. The reactivity increases in order benzene>toluene>styrene. In mixtures, remarkable effects on reaction rate and selectivity have been evident ; the strongest inhibiting effect was shown by styrene and increases in a reverse order with respect to that of reactivity. The reaction model reveals that there is a competition between the two reactants for the oxidized catalyst. Thus, the nontoxic catalytic oxidation process was suggested as the new VOCs control technology.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.164-164
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• 2013

Among multicomponent nanostructures, hybrid nanocatalysts consisting of metal nanoparticle-semiconductor junctions offer an interesting platform to study the role of metal-oxide interfaces and hot electron flows in heterogeneous catalysis. In this study, we report that hot carriers generated upon photon absorption significantly impact the catalytic activity of CO oxidation. We found that Pt-CdSe-Pt nanodumbbells exhibited a higher turnover frequency by a factor of two during irradiation by light with energy higher than the bandgap of CdSe, while the turnover rate on bare Pt nanoparticles didn't depend on light irradiation. We also found that Pt nanoparticles deposited on a GaN substrate under light irradiation exhibit changes in catalytic activity of CO oxidation that depends on the type of doping of the GaN. We suppose that hot electrons are generated upon the absorption of photons by the semiconducting nanorods or substrates, whereafter the hot electrons are injected into the Pt nanoparticles, resulting in the change in catalytic activity. We discuss the possible mechanism for how hot carrier flows generated during light irradiation affect the catalytic activity of CO oxidation.

• Journal of the Korean Chemical Society
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• v.38 no.4
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• pp.302-308
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• 1994

Homogeneous catalytic oxidation of hydrazobenzene was investigated by employing pentadentate Schiff base complexes such as [Co(II)(Sal-DPT)(H$_2$O)] and [Co(II)(Sal-DET)(H$_2$O)] in oxygen-saturated methanol solvent. The oxidation product of hydrazobenzene(H$_2$AB) was trans-azobenzene(trans-AB). The rate constants of oxidation reaction measured by UV-visible spectrophotometry were observed as $6.06{\times}10^{-3}sec^{-1}$ for [Co(II)(Sal-DPT)(H$_2$O)] and $2.50{\times}10^{-3}sec^{-1}$ for [Co(II)(Sal-DET)(H$_2$O)]. The mechanism of oxidation reaction for H$_2$AB by homogeneous activated catalysts has been proposed as following. H$_2$AB + Co(II)(L)(H$_2$O) + O$_2$ $\rightleftharpoons^K_{MeOH}Co(III)(L)O_2{\cdot}H_2AB + H_2O\longrightarrow^{k}Co(II)(L) + trans-AB + H_2O_2$ (L: Sal-DPT and Sal-DET)

• Applied Chemistry for Engineering
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• v.10 no.2
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• pp.212-217
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• 1999

Porous alumina membrane with asymmetrical structure was prepared by anodic oxidation under constant DC current mode in aqueous solution of sulfuric acid. In order to produce membrane with improved properties, the aluminium plate was pre-treated with thermal oxidation, chemical polishing and electrochemical polishing before anodic oxidation. The thickness and pore diameter of the membrane were controlled by current density and charge density, respectively. The upper layer of 20 nm under of pore diameter was produced under very low current density while the lower layer of 36 nm pore diameter was produced under higher current density. The thickness of the membrane was about $80{\sim}90{\mu}m$ and that of the upper layer was $6{\mu}m$. We found that the mechanism of gas permeation through the membrane depended on Knudsen diffusion.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.253-258
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• 2012

The effects of active sites and valence states were investigated over $Pd/TiO_2$ catalyst on simultaneous oxidation of $CH_4$ and CO. The Pd species (PdO) crystallite size increased with increasing Pd loadings, which results in enhancement of the activity of $CH_4$ oxidation. Different results from the activity of $CH_4$ and CO oxidation were shown to be dependent on the Pd valence state on the surface of the catalyst prepared through a thermal treatment. XRD and $H_2-TPR$ analysis confirmed that $Pd^{2+}$species was predominated in the calcination catalyst, while $Pd^0$species was predominated in the reduction catalyst. Additionally, it could be found that the valence state of Pd was a more important factor on the catalytic activity than that of factors as the surface area and pore volume. The reaction mechanism of $CH_4$ and CO followed by the valence state of Pd could be identified using FT-IR analysis.

• Applied Chemistry for Engineering
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• v.31 no.4
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• pp.368-376
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• 2020

In this study, an analysis on the reaction characteristics of a catalyst using platinum (Pt) as an active oxidation metal catalyst for controlling SO₂ was performed. Pt/TiO₂ catalyst was prepared by using Pt as various precursor forms on a titania (TiO₂) support, and used for the experiment. There was no difference in performance of SO₂ oxidation according to Pt valence states such as Pt²⁺ or Pt⁴⁺ on Pt/TiO₂, and Pt chloride species such as PtCl_x reduces SO₂ oxidation performance. In addition, as a result of analyzing the valence state of the catalyst before and after the SO₂ oxidation reaction by XPS analysis, a decrease in lattice oxygen and an increase in surface chemisorbed oxygen after the SO₂ oxidation reaction were confirmed. Therefore it can be suggested that the oxidation reaction of SO₂ when using the Pt/TiO₂ catalyst is the major one following the Mar-Van Krevelen mechanism where the reaction of lattice oxygen corresponding to PtOx and the oxidation-reduction reaction by oxygen vacancy occur. Overall, it can be confirmed that the oxygen species of PtOx (Pt²⁺ or Pt⁴⁺) present on the catalyst acts as a major active site.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.97-105
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• 1998

Antioxidation mechanism of Al metal powders on $Al_2O_3-C$ refractory was investigated in temperature range from 800 to $1400^{\circ}C$. The addition of 5 wt% Al metal powders suppressed the oxidation of carbon in $Al_2O_3$-C sample. The carbons were distributed uniformly on the surface and the interface of the $Al_2O_3$-C-Al. Reaction products of $Al_4C_3$ and AIN were found with a composition of Al-C at temperatures between 800 and $1200^{\circ}C$ and transformed to $Al_2O_3$ above $1400^{\circ}C$. Cavity structures related to the to the formation of $Al_4C_3$ were observed for the AI-C after heating at $1000^{\circ}C$ ofr 1 hour. Thermodynamic mechanism was considered to discuss the formation $Al_4C_3$, AlN and their transformation to $Al_2O_3$, which leads to the effect of oxidation resistance.