• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.304-304
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• 2010

The study on the catalytic oxidation of carbon monoxide (CO) to carbon dioxide ($CO_2$) using the noble metals has long been the interest subject and the recent progress in nanoscience provides the opportunity to develop new model systems of catalysts in this field. Of the noble metal catalysts, we selected ruthenium (Ru) as metal catalyst due to its unusual catalytic behavior. The size of colloid Ru NPs was controlled by the concentration of Ru precursor and the final reduction temperatures. For catalytic activity of CO oxidation, it was found that the trend is dependent on the size of Ru NPs. In order to explain this trend, the surface oxide layer surrounding the metal core has been suggested as the catalytically active species through several studies. In this poster, we show the influence of surface oxide on Ru NPs on the catalytic activity of CO oxidation using chemical treatments including oxidation, reduction and UV-Ozone surface treatment. The changes occurring to UV-Ozone surface treatment will be characterized with XPS and SEM. The catalytic activity before and after the chemical modification were measured. We discuss the trend of catalytic activity in light of the formation of core-shell type oxide on nanoparticles surfaces.

• Applied Chemistry for Engineering
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• v.16 no.2
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• pp.206-211
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• 2005

Mediated electrochemical oxidation (MEO) of polyethylene glycols (PEGs) of molecular weight of 1000, 4000 and 20000, was carried out on both platinum (Pt) and titanium-iridium electrodes in 8.0 M nitric acid solution containing 0.5 M Fe(II) and Co(II) ion. The electrochemical parameters such as current densities, kinds of electrode, electrolyte concentration and removal efficiency were investigated in both Fe(III)/Fe(II) and Co(III)/Co(II) redox systems. The PEGs was decomposed into carbon dioxide by MEO in Fe(III)/Fe(II) and Co(III)/Co(II) redox system during 180 min and 210 min at the current density of $0.67A/cm^2$ on the Pt electrode. Removal efficiency of PEGs by MEO was better in Co(III)/Co(II) redox system than Fe(III)/Fe(II) redox system, indicating mediated electrochemical removal efficiency was 100%.

• Journal of Hydrogen and New Energy
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• v.24 no.5
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• pp.353-358
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• 2013

To develop preferential CO oxidation reaction (PROX) catalyst for small scale hydrogen generation system, supported Pt catalysts have been applied for the target reaction. The supports were systematically changed to optimize supported Pt catalysts. $Pt/Al_2O_3$ catalyst showed the highest CO conversion among the catalysts tested in this study. This is due to easier reducibility, the highest dispersion, and smallest particle diameter of $Pt/Al_2O_3$. It has been found that the catalytic performance of supported Pt catalysts for PROX depends strongly on the reduction property and depends partly on the Pt dispersion of supported Pt catalysts. Thus, $Pt/Al_2O_3$ can be a promising catalyst for PROX for small scale hydrogen generation system.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.339-339
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• 2010

The metallic nanoparticles (Pt, Au, Ag. Cu, etc.) supported on ceria-titania mixed oxide exhibit a high catalytic activity for the water gas shift reaction ($H_2O\;+\;CO\;{\leftrightarrow}\;H_2\;+\;CO_2$) and the CO oxidation ($O_2\;+\;2CO\;{\leftrightarrow}\;2CO_2$). It has been speculated that the high catalytic activity is related to the easy exchange of the oxidation states of ceria ($Ce^{3+}$ and $Ce^{4+}$) on titania, but very little is known about the ceria titanium interaction, the growth mode of metal on ceria titania complex, and the reaction mechanism. In this work, the growth of $CeO_x$ and Au/$CeO_x$ on rutile $TiO_2$(110) have been investigated by Scanning Tunneling Microscopy (STM), Photoelectron Spectroscopy (PES), and DFT calculation. In the $CeO_x/TiO_2$(110) systems, the titania substrate imposes on the ceria nanoparticles non-typical coordination modes, favoring a $Ce^{3+}$ oxidation state and enhancing their chemical activity. The deposition of metal on a $CeO_x/TiO_2$(110) substrate generates much smaller nanoparticles with an extremely high activity. We proposed a mechanism that there is a strong coupling of the chemical properties of the admetal and the mixed-metal oxide: The adsorption and dissociation of water probably take place on the oxide, CO adsorbs on the admetal nanoparticles, and all subsequent reaction steps occur at the oxide-admetal interface.

• Membrane and Water Treatment
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• v.13 no.4
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• pp.191-199
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• 2022

In industrial production, the development of traditional polyamide nanofiltration (NF) membrane was limited due to its poor oxidation resistance, complex preparation process and high cost. In this study, a composite NF membrane with high flux, high separation performance, high oxidation resistance and simple process preparation was prepared by the method of dilute solution dip coating. And the sulfonated polysulfone was used for dip coating. The results indicated that the concentration of glycerin, the pore size of the based membrane, the composition of the coating solution, and the post-treatment process had important effects on the structure and performance of the composite NF membrane. The composite NF membrane prepared without glycerol protecting based membrane had a low flux, when the concentration of glycerin increased from 5% to 15%, the pure water flux of the composite NF membrane increased from 46.4 LMH to 108.2 LMH, and the salt rejection rate did not change much. By optimizing the coating system, the rejection rate of Na₂SO₄ and PEG1000 was higher than 90%, the pure water flux was higher than 40 LMH (60psi), and it can withstand 20,000 ppm.h NaClO solution cleaning. When the post treatment processes was adjusted, the salt rejection rate of NaCl solution (250 ppm) reached 45.5%, and the flux reached 62.2 LMH.

• Archives of Metallurgy and Materials
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• v.66 no.4
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• pp.997-1000
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• 2021

In this study, a novel composite was fabricated by adding the Hafnium diboride (HfB₂) to conventional WC-Co cemented carbides to enhance the high-temperature properties while retaining the intrinsic high hardness. Using spark plasma sintering, high density (up to 99.4%) WC-6Co-(1, 2.5, 4, and 5.5 wt. %) HfB₂ composites were consolidated at 1300℃ (100℃/min) under 60 MPa pressure. The microstructural evolution, oxidation layer, and phase constitution of WC-Co-HfB₂ were investigated in the distribution of WC grain and solid solution phases by X-ray diffraction and FE-SEM. The WC-Co-HfB₂ composite exhibited improved mechanical properties (approximately 2,180.7 kg/mm²) than those of conventional WC-Co cemented carbides. The high strength of the fabricated composites was caused by the fine-grade HfB₂ precipitate and the solid solution, which enabled the tailoring of mechanical properties.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.863-870
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• 1999

The catalytic performance of Co-Mn-Br system was performed in the 2,6-dimethylnaphthalene(DMN) oxidation at relatively mild reaction conditions such as $160^{\circ}C$ and $6kg/cm^2$. Experiments were conducted using a $2{\ell}$ batch reactor with varying the concentrations of catalysts. The reaction route of DMN oxidation was considered by measuring the concentration of intermediate species. As the intermediate species, 2-formyl-6-naphthoic acid, 2-methyl-6-naphthoic acid and 2-hydroxymethyl-6-methylnaphthalene are found. It was found that the yield of 2,6-naphthalene dicarboxylic acid(NDA) is largely dependent on the Co and Br concentrations. In addition, it was observed that color-b was closely related with Mn concentration in this experimental range. The burning loss of solvent could be reduced by controlling the concentration of Mn and Br. Addition of small amount of Ce and Cu compounds led to increase the NDA yields and decrease the burning amount of solvent.

• Clean Technology
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• v.2 no.1
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• pp.60-68
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• 1996

The oxidation of carbon monoxide of low concentration on the natural manganese dioxide (NMD) has been investigated in a fixed bed reactor. The experimental variables were concentration of oxygen (500ppm~99.8%) and carbon monoxide (500ppm~10000ppm) and catalyst temperature ($50{\sim}750^{\circ}C$). The NMD(Natural Manganese Dioxide) has been characterized by temperature - program reduction(TPR) using 2.4% $CO/H_2$ as a reducing agent, thermogravimetric analysis (TGA), and reduction of NMD by 2.4% $CO/H_2$. It was found that the NMD catalyst activity on the unit area was greater than the $MnO_2$ catalyst for oxidation of CO at the same temperature. The thermal stability of oxidation activity was considered to be maintained when the NMD was heated to $750^{\circ}C$. The TGA, reduction by CO, and TPR of the NMD showed that the NMD had active lattice oxygen which was easily liberated on heating in the absence and low concentration of oxygen. The reaction order in CO is 0.701 between 500~3500ppm and almost zero between 3500~10000ppm of CO.

• Korean Journal of Materials Research
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• v.14 no.3
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• pp.163-167
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• 2004

TiAl(La)N thin films were oxidized in vacuum of about 7 Pa to reduce the oxidation of WC-Co as a substrate. The oxidation rate constants of the thin films were quantified by an assumption of parabolic oxidation. Increasing AI content significantly decreased the parabolic oxidation rate constant. A simultaneous addition of AI and La was more effective to reduce the oxidation rate. The parabolic oxidation rate constant of $Ti_{0.66}$ $Al_{0.32}$ $La_{ 0.02}$N thin film at 1273 K showed about ten times lower than that of TiN. The addition of a small amount of La with Al induced the preferential formation of dense $\alpha$ $-Al_2$$O_3$ film in oxide film, leading to the abrupt reduction of oxidation rate.