• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.2
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• pp.177-182
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• 2015

The NOx emissions from diesel engines and industrial boilers are a major cause of environmental pollution. The selective catalytic reduction of urea is an aftertreatment technology that is widely used for the reduction of NOx emissions. The objective of this study was to investigate the characteristics of the thermal decomposition of a urea aqueous solution using laboratory-scale experimental equipment under conditions similar to those of marine diesel engines. A 40 wt. urea aqueous solution was used in this study. It was found that the total conversion rate varied with the inflow gas conditions and flow rates of the urea aqueous solution. In addition, there were conversion rate differences between NH3 and HNCO. At inflow gas temperature conditions of $210^{\circ}C$ and $250^{\circ}C$, the $NH_3$ conversion rate was found to be higher than that of the HNCO, depending on the residence time.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.125-132
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• 2012

Urea-SCR system, which converts nitrogen oxides to nitrogen and water in the presence of a reducing agent, usually AdBlue urea solution, is known as one of the powerful NOx reduction systems for mobile as well as stationary applications. For its consistent and reliable operation in mobile applications, such various problems as transient injection, ammonia slip, and freezing in cold weather have to be resolved. In this work, therefore, numerical study on three-dimensional unsteady heating problems were analyzed to understand the melting and heat transfer characteristics such as urea liquid volume fraction, temperature profiles and generated natural convection behavior in urea solution by using the commercial software Fluent 6.3. After validating by comparing numerical and experimental data with pure gallium melting phenomena, numerical experiment for urea melting is conducted with three different coolant heating models named CH1, 2, and 3, respectively. Finally, it can be found that the CH3 model, in which more coolant is concentrated on the lower part of the urea tank, has relatively better melting capability than others in terms of urea quantity of $1{\ell}$ for start-up schedule.

• Journal of Powder Materials
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• v.21 no.2
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• pp.119-123
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• 2014

Pt has been widely used as catalyst for fuel cell and exhausted gas clean systems due to its high catalytic activity. Recently, there have been researches on fabricating composite materials of Pt as a method of reducing the amount of Pt due to its high price. One of the approaches for saving Pt used as catalyst is a core shell structure consisting of Pt layer on the core of the non-noble metal. In this study, the synthesis of Pt shell was conducted on the surface of $TiO_2$ particle, a non-noble material, by applying ultraviolet (UV) irradiation. Anatase $TiO_2$ particles with the average size of 20~30 nm were immersed in the ethanol dissolved with Pt precursor of $H_2PtCl_6{\cdot}6H_2O$ and exposed to UV irradiation with the wavelength of 365 nm. It was confirmed that Pt nano-particles were formed on the surface of $TiO_2$ particles by photochemical reduction of Pt ion from the solution. The morphology of the synthesized Pt@$TiO_2$ nano-composite was examined by TEM (Transmission Electron Microscopy).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.922-926
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• 2002

In this paper, in order to investigate the catalytic effect of the sludge exhausted from waterworks as heating temperature for NOx removal, we measure NO, $NO_2$ concentration as increasing temperature of sludge pellets and applying high voltage to sludge pellets in a quartz-glass reactor at the same time. NO initial concentration is 100ppm balanced with air gas in a mixing chamber. The gas flow is 5[l/min] and the heating temperature of sludge pellets in a quartz-glass reactor is adjusted from $200[^{\circ}C]$ $400[^{\circ}C]$ to investigate the effect of sludge pellets for removal NOx$(NO+NO_2)$ as increasing temperature. $BaTiO_3$ pellets is filled in a packed-bed reactor for corona discharge to measure how much NOx$(NO+NO_2)$ is removed after generating $NO_2$ from the packed-bed reactor. AC[60Hz] voltage is supplied to the reactor for discharge. In the result, $NO_2$ concentration is decreased by sludge pellets without heating temperature for sludge pellets in case of sludge pellets done heat treatment, however NO concentration is almost the same to be compared NO initial concentration. As increasing heating temperature for sludge pellets, $NO_2$ adsorbed on the sludge surface done heat treatment is converted to NO by the thermal energy, so NO concentration is extremely increased by reduction decomposition of $NO_2$. Finally, We think the sludge is possible to use for reduction catalysts, however we need to study more about the possibility and endurance of sludge as catalysts for NOx removal.

• Applied Chemistry for Engineering
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• v.3 no.1
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• pp.24-34
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• 1992

Recent studies dealing with the fundamental understanding and applications of bimetallic catalysts are discussed. Bimetallic catalysts have had a major industrial impact, specifically for the reforming of petroleum naphtha, for the hydrogen reduction of carbon monoxide, and for the three way catalytic converter system. The action of the bimetallic catalysts in these reactions may be interpreted in terms of ensembles, electronic influences and surface structure. Various combinations of metal pairs have been considered in order to evaluate the role played by the added metals. For catalyst selectivity control, the possibility of surface enrichment of one element has been recognised. More generally, the influence of preparative variables on the formation of supported catalysts has been clarified, In particular by temperature programmed reduction (TPR). Information on the structure of bimetallic catalysts has been obtained with chemical probes, such as chemisorption and reaction rate measurement and physical probes, such as extended X-ray absorption fine structure (EXAFS), scanning transmission electron microscopy (STEM) and Xe-NMR.

• Journal of the Korea Organic Resources Recycling Association
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• v.7 no.2
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• pp.93-104
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• 1999

Existing composting system was improved to have a high performance for organic degradation, deodorization and energy reduction. Compared with conventional devices, this developed system uses the heat recovered from platinum catalytic tower by three times heat exchange in which 65% of exhaust gas was recirculated. Evaporation of water was made easy by maintaining negative pressure in entire system. It was possible for reaction to be maintained steadily by microorganism agent. The optimum mixing volume ratio of garbage to sawdust was 15:1 contrary to 20:1 in conventional one. Moreover, aerobic condition was maintained efficiently. Effects obtained by using a inner circulation system were as follows. It was possible to reduce the ammonia causing offensive odor and verified that consumption of electricity cut down to 1/3 with reduction of exhaust gas inflowing. According to this inner circulation, the optimum air flow was $0.44m^3$ to 100kg treatment capacity. The electricity consumption was changed in proportion to inflowing air volume.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.24-30
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• 2010

In this study, numerical experiments were carried out to estimate the SCR De-NOx performance in DOC plus SCR systems. The SCR De-NOx phenomena are described by Langmuir-Hinshelwood reaction scheme. After validating the present approach by comparing the present results with the experimental results, such various parameters as space velocity, $H_2O$ concentration, $NO_2$/NOx ratio and relative volume of DOC are explored to increase the SCR De-NOx performance. The results indicate that SCR De-NOx performance largely depends on space velocity and $NO_2$/NOx ratio, especially below $200^{\circ}C$. SCR De-NOx performance is seriously affected by relative volume of DOC with SCR due to increasing in $NO_2$/NOx ratio at below $250^{\circ}C$.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.512-518
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• 2008

The present work studied the selective catalytic reduction (SCR) of NO to $N_2$ by $NH_3$ over $V/TiO_2$ focusing on NOx control for the stationary sources. The SCR process depends mainly on the catalyst performance. The reaction characteristics of SCR with $V/TiO_2$ catalysts were closely examined at low and high temperature. In addition, adsorption and desorption characteristics of the reactants on the catalyst surface were investigated with ammonia. Seven different $TiO_2$ supports containing the same loading of vanadia were packed in a fixed bed reactor respectively. The interaction between $TiO_2$ and vanadia would form various non-stoichiometric vanadium oxides, and showed different reaction activities. There were optimum calcination temperatures for each samples, indicating different reactivity. It was finally found from the $NH_3-TPD$ test that the SCR activity was nothing to do with $NH_3$ adsorption amount.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.6
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• pp.192-199
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• 2008

The key issues for the reduction technologies of the exhaust gas from diesel engine being developed are to reduce particulate matters and NOx. The SCR system is known to be one of the most efficient and stable technologies to remove NOx through the mixing of NOx and urea solution. In the present research, the effects of mixer configurations of SCR system have been investigated to enhance the SCR performance. First, a Schlieren technique is employed to visualize the mixing characteristics of urea solution and exhaust gas. The results show that a mixer is essential to obtain proper fluid mixing. In addition, numerical studies have been made to understand the mixing characteristics through the comparison of the mal-distribution index of concentration at the several locations of the diffuser. In particular, the effects of number of blade and mixer angles on mixing characteristics were studied. The results show that the blade angle has a larger effect on the mixing characteristics than the number of blades.

• 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.