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- 검색키워드
- 저자 : Yukwon Jeon (검색결과 24 건)
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Jeon, Yukwon,Kim, Heeseon,Lee, Chanmin,Lee, Sunghun,Song, Soonho,Shul, Yong-gun Elsevier 2017 Fuel Vol.207 No.-
<P><B>Abstract</B></P> <P>The purpose of this work is to investigate proper hydrogen production methods from methane through the parametric study for the highly active and stable nanofibrous perovskite catalyst. A ruthenium doped lanthanide chromate (LaCr<SUB>0.8</SUB>Ru<SUB>0.2</SUB>O<SUB>3</SUB>) micro-fibrous perovskite catalyst is prepared and fixed to focus on the effect of reaction environments such as steam, partial oxidation and autothermal conditions. Temperatures, H<SUB>2</SUB>O/C and O<SUB>2</SUB>/C ratios were occasionally changed for the investigation of the effects and the optimization conditions. At the same perovskite catalyst system, the reaction at the autothermal atmosphere is the most effective conditions in terms of both CH<SUB>4</SUB> conversion and H<SUB>2</SUB> production, which was comparable to the theoretical calculations. It is found that conversion increases with oxygen at even low temperature while the H<SUB>2</SUB> productivity increases with much stable behavior at steam condition. These are more obvious at the elevated temperature with each optimized H<SUB>2</SUB>O and O<SUB>2</SUB> amounts for high activity by low activation energy. Time-on-stream runs conducted on these three reactions with each optimized conditions of 50h at 800°C, H<SUB>2</SUB>O/C=3 and O<SUB>2</SUB>/C=0.5. The perovskite micro-fiber catalyst at autothermal condition shows excellent CH<SUB>4</SUB> conversion of over 95%, H<SUB>2</SUB> production of around 70%, and even H<SUB>2</SUB>/CO of over 4. On the other hand, the reactivity at the steam condition is lower and even slow. The durability at the partial oxidation condition starts to decrease after 10h due to the instability of the perovskite at the extremely oxidative concentration which causes a relatively high coke formation. Therefore, it is worthwhile in suggesting proper autothermal reaction conditions for the highly active and stable perovskite catalyst like LaCr<SUB>0.8</SUB>Ru<SUB>0.2</SUB>O<SUB>3</SUB> micro-fibers.</P> <P><B>Graphical abstract</B></P> <P>The perovskite microfiber catalysts were introduced for the application to the methane reforming at reaction environments such as steam, partial oxidation and autothermal conditions. The purpose of this work is to investigate proper hydrogen production methods from methane through the parametric study for the highly active and stable nanofibrous perovskite catalyst.</P> <P>[DISPLAY OMISSION]</P>
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Jeon, Yukwon,Myung, Jae-ha,Hyun, Sang-hoon,Shul, Yong-gun,Irvine, John T. S. Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.8
<P>An efficient cathode for solid oxide fuel cells (SOFC) is mainly determined by the oxygen reduction reaction (ORR) activity of mixed materials. We demonstrate a new microstructure design through a nanofibrous electrode based on a unique corn-cob structure. A one-step process to produce corn-cob ceramic nanofibers of La0.8Sr0.2MnO3(LSM) and Y2O3-stabilized ZrO2(YSZ) is introduced using an electrospinning system equipped with a coaxial nozzle. From the microscope analysis, perfect corn-cob nanofibers are finely produced with a diameter of 350 nm for the core and nanoparticles (30-40 nm) stacked on the surface similar to a core-shell structure. The cathode fabricated using nanofibers with LSM outside and YSZ inside (YSZ@LSM) shows the best maximum power density of 1.15 W cm<SUP>−2</SUP>at 800 °C with low polarization resistance, which is higher than that of the reverse core and shell positions (LSM@YSZ) and even the commercial LSM-YSZ. This better outcome is more prominent at elevated temperatures due to its accelerated catalytic activity. Therefore, insight into the key factors that enhance ORR activity and single cell performance is obtained in terms of not only the nanofibrous core@shell structure but also more reaction active sites from the optimum catalyst position at the designed corn-cob nanofiber based cathodes.</P>
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Jeon, Yukwon,Chi, Won Seok,Hwang, Jusoon,Kim, Do Hyun,Kim, Jong Hak,Shul, Yong-Gun Elsevier 2019 Applied Catalysis B Vol.242 No.-
<P><B>Abstract</B></P> <P>We developed a new class of acid-base bifunctional heterogeneous catalyst, which can be used in the transesterification of rapeseed oil for highly efficient biodiesel production. A simple Keggin-type HPA (heteropoly acid) functionalization on the surface of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles, through an imidazolium medium, results in the bifunctional heterogeneous catalysts. The hybrid materials exhibit a novel hierarchically core-shell nanostructure, which provides a large surface area and interconnectivity, leading to a thin-wrinkled HPA shell at the surface of rhombic dodecahedral ZIF-8 core crystals. A strong ON hybrid bonding through an electrostatic effect in the hybrid materials demonstrates a strong interaction between the Keggin and imidazole units, which is one of the main driving forces of hybrid materials formation. Additionally, the transformation of the HPA/ZIF-8 ratio in the hybrid materials changes the acidity and basicity, thereby affecting catalyst activity. We used these bifunctional core-shell materials as environmentally friendly heterogeneous catalysts in the transesterification of rapeseed oil with methanol to produce a high-quality biodiesel. Of particular interest, the HPA-functionalized ZIF-8 catalyst with a proper HPA/ZIF-8 ratio shows a high FAME conversion of 98.02% along with high recyclability because of the sufficiently large surface area and bi-functionality of strong acidity. Furthermore, the HPA-functionalized ZIF-8 catalyst shows a high reaction efficiency of the benzyl alcohol oxidation process, indicating a great potential of our catalyst to a wide range of applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bifunctional heterogeneous catalyst was prepared using HPA functionalization on ZIF-8 nanoparticles. </LI> <LI> HPA/ZIF-8 materials showed core-shell structure with large surface area and interconnectivity. </LI> <LI> A high FAME conversion of 98.02% along with high recyclability was obtained. </LI> <LI> A high reaction efficiency of the benzyl alcohol oxidation process was also achieved. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The core-shell structured heteropoly acid (HPA)-functionalized zeolitic imidazolate frameworks-8 (ZIF-8) nanoparticles were used as acidic and basic bifunctional, highly-porous, heterogeneous catalysts for efficient biodiesel production.</P> <P>[DISPLAY OMISSION]</P>
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Jeon, Yukwon,Ji, Yunseong,Cho, Yong Il,Lee, Chanmin,Park, Dae-Hwan,Shul, Yong-Gun American Chemical Society 2018 ACS NANO Vol.12 No.7
<P>Well-designed electronic configurations and structural properties of electrocatalyst alter the activity, stability, and mass transport for enhanced catalytic reactions. We introduce a nanofibrous oxide-carbon composite by an in situ method of carbon nanofiber (CNF) growth by highly dispersed Ni nanoparticles that are exsoluted from a NiTiO<SUB>3</SUB> surface. The nanofibrous feature has a 3D web structure with improved mass-transfer properties at the electrode. In addition, the design of the CNF/TiO<SUB>2</SUB> support allows for complex properties for excellent stability and activity from the TiO<SUB>2</SUB> oxide support and high electric conductivity through the connected CNF, respectively. Developed CNF/TiO<SUB>2</SUB>-Pt nanofibrous catalyst displays exemplary oxygen-reduction reaction (ORR) activity with significant improvement of the electrochemical surface area. Moreover, exceptional resistance to carbon corrosion and Pt dissolution is proven by durability-test protocols based on the Department of Energy. These results are well-reflected to the single-cell tests with even-better performance at the kinetic zone compared to the commercial Pt/C under different operation conditions. CNF/TiO<SUB>2</SUB>-Pt displays an enhanced active state due to the strong synergetic interactions, which decrease the Pt d-band vacancy by electron transfer from the oxide-carbon support. A distinct reaction mechanism is also proposed and eventually demonstrates a promising example of an ORR electrocatalyst design.</P> [FIG OMISSION]</BR>
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Catalytic activity and characterization of V2O5/γ-Al2O3 for ammoxidation of m-xylene system
설용건,Yukwon Jeon,Sung wook Row,Altansukh Dorjgotov,Sang Duek Lee,Kyeongseok Oh 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.8
An ammoxidation of m-xylene was evaluated in a fixed-bed reactor using V2O5 on various oxides. Catalysts were prepared by wet impregnation method. At first, the loading of V2O5 was varied from 5 wt% to 20 wt% on γ-Al2O3support to estimate the most effective amount of V2O5. Second, the effect of catalyst supports was examined at 10 wt%loading of V2O5. V2O5/TiO2 and V2O5/SiO2 catalysts were employed to compare the ammoxidation reaction with V2O5/γ-Al2O3. Most catalytic activity was observed when γ-Al2O3 was used as a support. Careful characterization was followed by physicochemical techniques, such as BET measurement, X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). The results provided the clue that monolayer V2O5 was favorably dispersed on the surface of γ-Al2O3 up to 10 wt%, which led to the highest yield of isophthalonitrile (IPN).
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Ulziidelger Byambasuren,Yukwon Jeon,Dorjgotov Altansukh,Yunseong Ji,Yong-Gun Shul 한국탄소학회 2016 Carbon Letters Vol.17 No.-
Nitrogen (N)-doped ordered mesoporous carbons (OMCs) with a dual transition metal system were synthesized as non-Pt catalysts for the ORR. The highly nitrogen doped OMCs were prepared by the precursor of ionic liquid (3-methyl-1-butylpyridine dicyanamide) for N/C species and a mesoporous silica template for the physical structure. Mostly, N-doped carbons are promoted by a single transition metal to improve catalytic activity for ORR in PEMFCs. In this study, our N-doped mesoporous carbons were promoted by the dual transition metals of iron and cobalt (Fe, Co), which were incorporated into the N-doped carbons lattice by subsequently heat treatments. All the prepared carbons were characterized by via transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). To evaluate the activities of synthesized doped carbons, linear sweep was recorded in an acidic solution to compare the ORR catalytic activities values for the use in the PEMFC system. The dual transition metal promotion improved the ORR activity compared with the single transition metal promotion, due to the increase in the quaternary nitrogen species from the structural change by the dual metals. The effect of different ratio of the dual metals into the N doped carbon were examined to evaluate the activities of the oxygen reduction reaction.
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Lee, Chanmin,Jeon, Yukwon,Kim, Taehyen,Tou, Akihiro,Park, Joo-Il,Einaga, Hisahiro,Shul, Yong-Gun Elsevier 2018 Fuel Vol.212 No.-
<P><B>Abstract</B></P> <P>The catalytic combustion of soot and CO is one of the key technologies required to meet rigorous emission standards. Recently, solid solution materials have been employed in heterogeneous catalysts because of their remarkable intrinsic activities and good stabilities. However, the low number of contact points between soot particles and the catalyst remains a challenge to enhancing catalytic performance. Thus, we herein report the preparation of Ce-ZrO<SUB>2</SUB> solid solution nano-fibrous web catalysts with a hierarchical structure using an electrospinning method, where Ag particles were loaded onto the surface of the Ce-ZrO<SUB>2</SUB> webs. X-ray diffraction, scanning transmission electron microscopy, and energy dispersive spectroscopic studies allowed us to investigate the morphological and crystal structures of the prepared Ce-ZrO<SUB>2</SUB> and Ag/Ce-ZrO<SUB>2</SUB> web catalysts. Moreover, the relationship between the Ce/Zr ratio and activated oxygen is discussed based on X-ray photoelectron spectroscopy results. Following the catalytic oxidation of soot and CO using our novel materials, we found that the Ce<SUB>0.67</SUB>Zr<SUB>0.33</SUB>O<SUB>2</SUB> web exhibited higher catalytic activities than the Ce<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> and Ce<SUB>0.33</SUB>Zr<SUB>0.67</SUB>O<SUB>2</SUB> webs, respectively. In addition, Ag/Ce<SUB>0.67</SUB>Zr<SUB>0.33</SUB>O<SUB>2</SUB> exhibited enhanced catalytic activity compared with the pristine Ce<SUB>0.67</SUB>Zr<SUB>0.33</SUB>O<SUB>2</SUB> for the oxidation of both soot (e.g., 500°C vs. 544°C at 50% conversion) and CO (e.g., 282°C vs. 408°C at 50% conversion). It therefore appeared that our proposed Ce-ZrO<SUB>2</SUB> solid solution nano-fibrous web catalysts bearing Ag particles exhibited superior redox properties and enhanced surface areas, and as such, are promising candidates for use in the oxidation of both soot and CO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ce-ZrO<SUB>2</SUB> solid-solution oxide fibrous webs were synthesized by electrospinning. </LI> <LI> Ag particles were deposited to improve catalytic activity. </LI> <LI> Ag/Ce<SUB>0.67</SUB>Zr<SUB>0.33</SUB>O<SUB>2</SUB> exhibited superior catalytic activity to other sample. </LI> <LI> Redox property of Ag and enhanced surface areas improved the catalytic oxidation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Synthesis of Durable Small-sized Bilayer Au@Pt Nanoparticles for High Performance PEMFC Catalysts
Dorjgotov, Altansukh,Jeon, Yukwon,Hwang, Jeemin,Ulziidelger, Byambasuren,Kim, Hyeong Su,Han, Byungchan,Shul, Yong-Gun Elsevier 2017 ELECTROCHIMICA ACTA Vol.228 No.-
<P><B>Abstract</B></P> <P>Design of small-sized Au@Pt core-shell nanocatalysts with high activity and stability is crucial area for a wide range of electronic and chemical devices. Here, we report a novel reduction method using UV treatment at room temperature by a weak reducing agent of H<SUB>2</SUB>O<SUB>2</SUB> enabling to produce carbon-supported small Au nanoparticles as the core of Pt shells. Different thicknesses of Pt layers are deposited on the Au to configure small-sized core@shell nanocatalysts. We acquire superior catalytic activity of Au@Pt catalysts toward cyclic voltammetry analysis and oxygen reduction reaction (ORR) via atomic level control of the particle size and the electronic structure. Underlying mechanism of the ORR activity is described from the aspect of compressive strain caused by shorter Au-Au distance than the bulk counterpart. The thickness of the Pt shell is shown to play an important role in stabilizing the nanocatalyst. Using density functional theory (DFT) calculations we validate the experimental outcomes. Top-quality power density above 2Wcm<SUP>−2</SUP> at low Pt loading (0.1mgcm<SUP>−2</SUP>) is achieved by a bilayer small-size Au@Pt core-shell catalyst with an excellent durability over 10,000 cycles by ADT, which is, indeed, beyond the recent DOE targets for a proton exchange membrane fuel cell system.</P>
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