• Applied Chemistry for Engineering
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• v.4 no.2
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• pp.308-317
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• 1993

The study is related to the synthesis of acrylic acid by selective oxidation of acrolein on Mo-V-W multicomponent mixed oxide catalysts. Mo-V-W-O(WVM), Mo-V-O/Mo-W-O(VM/WM), Mo-W-O/Mo-V-O(WM/VM) and mechanical mixtures of Mo-V-O and Mo-W-O(M-VM+WM) were prepared and characterized by BET, XRD, SEM and EPMA. Catalytic activity of these catalysts was tested in a continuous fixed bed reactor. In WVM catalysts small amount of tungsten added to VM increased surface area and selectivity of acrylic acid, but excess amount of tungsten decreased reaction rate of acrolein and selectivity. VM/WM catalysts, VM supported on WM, showed higher activity and selectivity than WM/VM catalysts where WM is supported on VM. Phase cooperation between WM and VM was observed in mechanical mixture of WM and VM and they showed higher yield than WM or VM.

• Applied Chemistry for Engineering
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• v.5 no.2
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• pp.295-304
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• 1994

$Mo-V-O/SnO_2$(VM/Sn) and $SnO_2/Mo-V-O$(Sn/VM) catalysts have been prepared and characterized by XRD, BET, SEM and TPD of ammonia. The catalytic reaction of acrolein oxidation with these catalysts, in a continuous-flow fixed-bed reactor, showed that they had higher conversion of acrolein and higher yield of acrylic acid than those of Mo-V-O itself. The origin of the observed synergy studied by TPD, TPR and TPO is explained by the cooperation of $SnO_2$ and Mo-V-O at their interfaces where electrons flow from Mo-V-O phase to $SnO_2$ and $SnO_2$ produces spill-over oxygens, which, by being transported onto the surface of Mo-V-O, reoxidize the partially reduced active sites.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.348-351
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• 2012

The effect of the addition of Cu on the catalytic activity of the $Mn/CeO_2-ZrO_2$ catalyst for the low-temperature SCR reaction of NO was investigated. Three different amounts of Cu, 5, 10, and 15 wt%, were impregnated on the $Mn/CeO_2-ZrO_2$ catalyst. The characteristics of the synthesized catalysts were examined by BET, XRD, XPS, and $H_2-TPR$ analyses. The de-NOx efficiency of the Cu-added catalysts increased with the amount of Cu. When 15 wt% Cu was impregnated, the deNOx efficiency was the highest, reaching as high as 99%. The increased deNOx efficiency is attributed to the enhanced reducing power stemming from the interaction between Mn and Cu on the catalyst surface.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.70.1-70.1
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• 2012

In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies of SOFC cathode materials will be discussed in this presentation. The mixed conducting perovskites (ABO3) containing rare and alkaline earth metals on the A-site and a transition metal on the B-site are commonly used as cathodes for solid oxide fuel cells (SOFC). However, the details of the oxygen reduction reaction are still not clearly understood. The information about the type of adsorbed oxygen species and their concentration is important for a mechanistic understanding of the oxygen incorporation into these cathode materials. XPS has been widely used for the analysis of adsorbed species and surface structure. However, the conventional XPS experiments have the severe drawback to operate at room temperature and with the sample under ultrahigh vacuum (UHV) conditions, which is far from the relevant conditions of SOFC operation. The disadvantages of conventional XPS can be overcome to a large extent with a "high pressure" XPS setup installed at the BESSY II synchrotron. It allows sample depth profiling over 2 nm without sputtering by variation of the excitation energy, and most importantly measurements under a residual gas pressure in the mbar range. It is also well known that the catalytic activity for the oxygen reduction is very sensitive to their electrical conductivity and oxygen nonstoichiometry. Although the electrical conductivity of perovskite oxides has been intensively studied as a function of temperature or oxygen partial pressure (Po2), in-situ measurements of the conductivity of these materials in contact with the electrolyte as a SOFC configuration have little been reported. In order to measure the in-plane conductivity of an electrode film on the electrolyte, a substrate with high resistance is required for excluding the leakage current of the substrate. It is also hardly possible to measure the conductivity of cracked thin film by electrical methods. In this study, we report the electrical conductivity of perovskite $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ (LSC) thin films on yttria-stabilized zirconia (YSZ) electrolyte quantitatively obtained by in-situ IR spectroscopy. This method enables a reliable measurement of the electronic conductivity of the electrodes as part of the SOFC configuration regardless of leakage current to the substrate and cracks in the film.

• Journal of the Korean Ceramic Society
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• v.47 no.5
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• pp.401-406
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• 2010

For the lower-temperature preparation of calcium monoaluminate(CA, C:CaO, A:$Al_2O_3$) clinker which is hard to synthesize purely within its melting point, an equimolar hydrate was obtained and then used as a starting raw material of clinker burning. The hydrate was prepared from a mixture of waste oyster shell and industrial aluminium hydroxide by heating to $1200^{\circ}C$, grinding and mixing with water. The hydrate was composed of amorphous aluminium hydroxide and $C_3AH_6$(H:$H_2O$) formed by resolution-precipitation mechanism of the system C-A-H. By heating the hydrate, nearly pure and porous calcium monoaluminate clinker was formed at $1400^{\circ}C$ which is fairly lower temperature than that of its melting point. The formation of calcium monoaluminate was performed mainly by the reaction between amorphous alumina and $C_{12}A_7$ caused by the decomposition of $C_3AH_6$. The immediate and earlier formation of $C_{12}A_7$ seemed to be accelerated by not only high surface area and instability of the thermally decomposed hydrate but also the catalytic effect of water decomposed from the hydrate. The final calcium monoaluminate clinker was very porous because of the influence of highly porous shape of the thermally decomposed hydrate.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.267-271
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• 2020

Cerium oxide (ceria, CeO₂) is one of the most wide-spread oxide supporting materials for the precious metal nanoparticle class of heterogeneous catalysts. Because ceria can store and release oxygen ions, it is an essential catalytic component for various oxidation reactions such as CO oxidation (2CO + O₂ 2CO₂). Moreover, reduced ceria is known to be reactive for water activation, which is a critical step for activation of water-gas shift reaction (CO + H₂O → H₂ + CO₂). Here, we apply van der Waals-corrected density functional theory (DFT) calculations combined with U correction to study the mechanism of water chemisorption on CeO₂(111) surfaces. A stoichiometric CeO₂(111) and a defected CeO₂(111) surface showed different water adsorption chemistry, suggesting that defected CeO₂ surfaces with oxygen vacancies are responsible for water binding and activation. An appropriate level of water-ceria chemisorption energy is deduced by vdW-corrected non-local correlation coupled with the optB86b exchange functional, whereas the conventional PBE functional describes weaker water-ceria interactions, which are insufficient to stabilize (chemisorb) water on the ceria surfaces.

• Journal of Korean Society on Water Environment
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• v.34 no.6
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• pp.621-631
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• 2018

In this study, catalyst was made through incipient wetness method using palladium (Pd) as noble metal, indium (In) as secondary metal, and montmorillonite (MK10) and Al pillared montmorillonite (Al-MK10) as supporters. The nitrate reduction rate of the catalysts was measured by batch experiments where H2 gas was used as reducing agent and formic acid as pH controller. Transmission electron microscopy (TEM) equipped with energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were all used to determine the elemental distribution of Pd, In, Al, and Si on catalysts. It was observed that Al pillaring increased the Al/Si elemental composition ratio and point of zero charge of MK10, but decreased its BET specific surface area and pore volume. The nitrate reduction rate of Al-MK10 Pd/In was 2.0 ~ 2.5 times higher than that of MK10 Pd/In using artificial groundwater (GW) in ambient temperature and pressure. Nitrate reduction rates in GW were 1.2 ~ 1.7 times lower than those in distilled deionized water (DDW). Nitrate reduction rates in acidic conditions were higher than those in neutral condition in both GW and DDW. The amount of produced NH3-N over degraded NO3- at acid conditions was lower than that of neutral condition. Even though the leaching of Pd after reaction was measured in DDW it was not detected when both Al-MK10 Pd/In and MK10 Pd/In were used in GW. The modification of montmorillonite as a supporter significantly increased the reductive catalytic activities of nitrates. However, the ratio of producing ammonia by-products to degraded nitrates in ambient temperature and pressure was similar.

• Clean Technology
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• v.24 no.3
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• pp.198-205
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• 2018

This study investigated the influence of catalyst preparation on the activity of $Co-CeO_2$ catalyst for $N_2O$ decomposition. $Co-CeO_2$ catalysts were synthesized by co-precipitation and incipient wetness impregnation. In order to estimate the performance of the as prepared catalysts, direct catalytic $N_2O$ decomposition test was carried out under $250{\sim}375^{\circ}C$. As a result, the catalyst prepared by co-precipitation (CoCe-CP) showed an enhanced performance on $N_2O$ decomposition reaction even in the presence of $O_2$ and/or $H_2O$, whereas the impregnation catalyst (CoCe-IM) did not. In order to investigate the difference in catalytic activity, characterization such as XRD, BET, TEM, $H_2-TPR$, $O_2-TPD$, and XPS was conducted. It is confirmed that the particle size and specific surface area were changed depending on the catalyst preparation method and the synthesis process influenced the physical properties of the catalysts. In addition, the improvement in the activity of the catalyst prepared by co-precipitation is due to the enhanced reduction from $Co^{3+}$ to $Co^{2+}$ and the improved oxygen desorption rate. However, it has been confirmed that the surface electron state and binding energy, which are related to $N_2O$ decomposition, do not change depending on the preparation method.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.4
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• pp.609-617
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• 2000

This study is aimed at investigating an effect of HCl gas on selective reduction of NOx over a CuHM and $V_2O_5-WO_3/TiO_2$ catalyst. SCR process is the most effective method to remove NOx, but catalyst can be deactivated by the acidic gas such as HCl gas which is also included in flue gas from the incinerator. In dry condition of flue gas, the CuHM catalyst treated by HCl gas has shown higher NO removal activity than the fresh catalyst. The activity of the catalyst can be restored by treating at $500^{\circ}C$. On the contrary. $V_2O_5-WO_3/TiO_2$ catalyst is obviously deactivated by HCl and the deactivation increases in proportion to the concentration of HCl gas. The deactivated catalyst is not restored to it's original activity by heat treatment for regeneration. In wet flue gas stream, the CuHM catalyst has shown lower activity than fresh catalyst and $V_2O_5-WO_3/TiO_2$ catalyst was severely deactivated by HCl treatment. The activity loss of catalysts are mainly due to the decrease of Br$\ddot{o}$nsted acid site on the catalyst surface by $NH_3$ TPD. The change of BET surface area of CuHM catalyst after the reaction isn't observed but $V_2O_5-WO_3/TiO_2$ catalyst is observed. The amount of $Cu^{{+}{+}}$ and $V_2O_5$ is decreased after the reaction. From these results, it is expected that CuHM catalyst should be better than $V_2O_5-WO_3/TiO_2$ catalyst for its application to the incineration of flue gas.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.10
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• pp.957-964
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• 2010

The deactivated catalyzed diesel particulate filter-trap (DPF) was remanufactured by ultrasonic wave treatment with various prepared solutions, followed by active component re-impregnation, and the emission control performance and surface properties of remanufactured DPF were studied at various remanufacturing conditions. The proper ultrasonic wave cleaning time at various prepared solutions and optimal re-impregnation amounts of active component for the best emission control performance of DPF were investigated and its performance tests were also carried out with various temperatures for the conversions of CO, THC (total hydrocarbon) and PM (particulate matter) by catalytic reaction test unit using bypass gas from the diesel engine dynamo system. It was found that the emission control performance of DPF remanufactured with the high-temperature air washing, ultrasonic wave cleaning at acid/base solutions and active component re-impregnation method was recovered to 95% level of its activity compared to that of the fresh DPF, which was caused by removing the deactivating materials from the surface of the DPF, through the analyses of performance test and their surface characterization by Optical microscope, EDX, ICP, TGA, and porosimeter.