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Kim, Kyeounghak,Yoo, Jeong Do,Lee, Siwon,Bae, Minseok,Bae, Joongmyeon,Jung, WooChul,Han, Jeong Woo American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.18
<P>Ceria (CeO2) is an attractive catalyst because of its unique properties, such as facile redoxability and high stability. Thus, many researchers have examined a wide range of catalytic reactions on ceria nanoparticles (NPs). Among those contributions are the reports of the dopant-dependent catalytic activity of ceria. On the other hand, there have been few mechanistic studies of the effects of a range of dopants on the chemical reactivity of ceria NPs. In this study, we examined the catalytic activities of pure and Pr, Nd, and Sm-doped CeO2 (PDC, NDC, and SDC, respectively) NPs on carbon monoxide (CO) oxidation. Density functional theory (DFT) calculations were also performed to elucidate the reaction mechanism on rare-earth (RE)-doped CeO2(111). The experimental results showed that the catalytic activities of CO oxidation were in the order of CeO2 > PDC > NDC > SDC. This is consistent with the DFT results, where the reaction is explained by the Mars-van Krevelen mechanism. On the basis of the theoretical interpretation of the experimental results, the ionic radius of the RE dopant can be used as a simple descriptor to predict the energy barrier at the rate-determining step, thereby predicting the entire reaction activity. Using the descriptor, a wide range of RE dopants on CeO2(111) were screened for CO oxidation. These results provide useful insights to unravel the CO oxidation activity on various oxide catalysts.</P>
Kim, Hyun-seok,Seo, Yu Seon,Kim, Kyeounghak,Han, Jeong Woo,Park, Youmie,Cho, Seonho SPRINGER SCIENCE + BUSINESS MEDIA 2016 NANOSCALE RESEARCH LETTERS Vol.11 No.1
<P>Under various concentration conditions of reducing agents during the green synthesis of gold nanoparticles (AuNPs), we obtain the various geometry (morphology and size) of AuNPs that play a crucial role in their catalytic properties. Through both theoretical and experimental approaches, we studied the relationship between the concentration of reducing agent (caffeic acid) and the geometry of AuNPs. As the concentration of caffeic acid increases, the sizes of AuNPs were decreased due to the adsorption and stabilizing effect of oxidized caffeic acids (OXCAs). Thus, it turns out that optimal concentration exists for the desired geometry of AuNPs. Furthermore, we investigated the growth mechanism for the green synthesis of AuNPs. As the caffeic acid is added and adsorbed on the surface of AuNPs, the aggregation mechanism and surface free energy are changed and consequently resulted in the AuNPs of various geometry.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-016-1393-x) contains supplementary material, which is available to authorized users.</P>
Different catalytic behaviors of Pd and Pt metals in decalin dehydrogenation to naphthalene
Kim, Kyeounghak,Oh, Jinho,Kim, Tae Wan,Park, Ji Hoon,Han, Jeong Woo,Suh, Young-Woong Royal Society of Chemistry 2017 Catalysis Science & Technology Vol.7 No.17
<▼1><P>Decalin is more easily dehydrogenated on Pt catalyst than Pd while the dehydrogenation of tetralin is more facile on Pd than Pt.</P></▼1><▼2><P>The catalytic dehydrogenation from decalin to tetralin to naphthalene is usually performed over supported Pd or Pt catalysts at a high temperature due to the endothermic nature of the reaction. However, the mechanistic studies of the catalytic activity and selectivity are not still sufficient to understand the dehydrogenation reaction on these metal surfaces. In this study, we mechanistically investigated the dehydrogenation reaction of decalin to tetralin to naphthalene on Pd and Pt catalysts using density functional theory (DFT) calculations combined with experimental validation. We firstly explored the relative energy profile of the entire elementary steps of the dehydrogenation reaction. Our theoretical results demonstrate that the conversion of decalin to tetralin on the Pt catalyst is energetically more preferred to that on Pd. On the other hand, Pd exhibits an energetically more favored reaction pathway in the conversion of tetralin to naphthalene than Pt. It is found that the difference in the catalytic activity and selectivity between Pd and Pt originates from the different structural and chemical characteristics of the metals. Our experimental results also support that decalin is more easily dehydrogenated over Pt/C while the dehydrogenation of tetralin is more facile over Pd/C.</P></▼2>
Mun, Yeongdong,Kim, Kyeounghak,Kim, Seongbeen,Lee, Seunghyun,Lee, Seonggyu,Kim, Sujeong,Choi, Wonyong,Kim, Soo-kil,Han, Jeong Woo,Lee, Jinwoo Elsevier 2018 Applied Catalysis B Vol.236 No.-
<P><B>Abstract</B></P> <P>Electrochemical CO<SUB>2</SUB> reduction reaction (CO<SUB>2</SUB>RR) has attracted a lot of interest as a highly potential CO<SUB>2</SUB> utilization system. Due to the high overpotential in CO<SUB>2</SUB>RR, an effective catalyst is required. We report a metal-organic hybrid catalyst (Co-PPy-C), which consists of Co and polypyrrole, as a highly active electrocatalyst for CO<SUB>2</SUB>RR. Co-PPy-C exhibited high Faradaic efficiency and metal mass activity for CO production at low overpotential region. By density functional theory calculations, it was revealed that the catalytic site is the Co surface on which the deprotonated pyrrolic functionality in polypyrrole is adsorbed, and that the facile production of CO from CO<SUB>2</SUB> is due to the CO adsorption on the Co being weakened by the charge transfer from the Co surface to the polypyrrole. This work reports a new and active non-noble metal catalyst for CO<SUB>2</SUB>RR, and provides the strategy of hybridization of metal and organic material to modify or enhance the catalytic activity of metal for CO<SUB>2</SUB>RR.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A hybrid catalyst of Co and polypyrrole converted CO<SUB>2</SUB> to CO electrochemically. </LI> <LI> Polypyrrole weakened the CO adsorption on the Co surface by electron transfer. </LI> <LI> CO production was fast and highly selective in spite of the non-nobility of Co. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Jo, Yong-Ryun,Koo, Bonjae,Seo, Min-Ji,Kim, Jun Kyu,Lee, Siwon,Kim, Kyeounghak,Han, Jeong Woo,Jung, WooChul,Kim, Bong-Joong American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.16
<P>A precise control of the size, density, and distribution of metal nanoparticles dispersed on functional oxide supports is critical for promoting catalytic activity and stability in renewable energy and catalysis devices. Here, we measure the growth kinetics of individual Co particles ex-solved on SrTi<SUB>0.75</SUB>Co<SUB>0.25</SUB>O<SUB>3-δ</SUB> polycrystalline thin films under a high vacuum, and at various temperatures and grain sizes using in situ transmission electron microscopy. The ex-solution preferentially occurs at grain boundaries and corners which appear essential for controlling particle density and distribution, and enabling low temperature ex-solution. The particle reaches a saturated size after a few minutes, and the size depends on temperature. Quantitative measurements with a kinetic model determine the rate limiting step, vacancy formation enthalpy, ex-solution enthalpy, and activation energy for particle growth. The ex-solved particles are tightly socketed, preventing interactions among them over 800 °C. Furthermore, we obtain the first direct clarification of the active reaction site for CO oxidation-the Co-oxide interface, agreeing well with density functional theory calculations.</P> [FIG OMISSION]</BR>
Kwon, Ohhun,Kim, Kyeounghak,Joo, Sangwook,Jeong, Hu Young,Shin, Jeeyoung,Han, Jeong Woo,Sengodan, Sivaprakash,Kim, Guntae The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.33
<P><I>In situ</I> exsolved nanoparticles on metal oxide materials have received much attention in catalysis due to their well socketed structure and high catalytic activity. Recently, the demand for active nanoparticles with multiple functionalities in catalysis has increased, so exsolutions of intermetallic nanoparticles could be an effective strategy to meet the requirements. Herein, for the first time, we report exsolved Co-Ni alloy nanoparticles and their Gibbs free energy of alloy formation in a PrBaMn1.7Co0.1Ni0.2O5+δ layered double perovskite. These exsolved alloy nanoparticles have a high catalytic performance for fuel oxidation in fuel cells and in the dry reforming of methane. Furthermore, we probed the mechanism of the alloy formation in the exsolution using density functional theory (DFT). The theoretical calculations reveal that the Gibbs free energy of the surface alloy formation (Δ<I>G</I>aggr_surface) is more favorable than that of the bulk alloy formation (Δ<I>G</I>aggr_bulk), indicating that Co and Ni are exsolved separately from the bulk, and then aggregate to form a Co-Ni alloy on the surface.</P>
Mun, Yeongdong,Lee, Seonggyu,Kim, Kyeounghak,Kim, Seongbeen,Lee, Seunghyun,Han, Jeong Woo,Lee, Jinwoo American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.15
<P>Replacement of Pt-based oxygen reduction reaction (ORR) catalysts with non-precious metal catalysts (NPMCs) such as Fe/N/C is one of the most important issues in the commercialization of proton exchange membrane fuel cells (PEMFCs). Despite numerous studies on Fe/N/C catalysts, a fundamental study on the development of a versatile strategy is still required for tuning the kinetic activity of a single Fe-N<SUB>4</SUB> site. Herein, we report a new and intuitive design strategy for tuning and enhancing the kinetic activity of a single Fe-N<SUB>4</SUB> site by controlling electron-withdrawing/donating properties of a carbon plane with the incorporation of sulfur functionalities. The effect of electron-withdrawing/donating functionalities was elucidated by experimentation and theoretical calculations. Finally, the introduction of an oxidized sulfur functionality decreases the d-band center of iron by withdrawing electrons, thereby facilitating ORR at the Fe-N<SUB>4</SUB> site by lowering the intermediate adsorption energy. Furthermore, this strategy can enhance ORR activity without a decrease in the stability of the catalyst. This simple and straightforward approach can be a cornerstone to develop optimum NPMCs for application in the cathodes of PEMFCs.</P> [FIG OMISSION]</BR>
Kang, Shin Wook,Kim, Kyeounghak,Chun, Dong Hyun,Yang, Jung-Il,Lee, Ho-Tae,Jung, Heon,Lim, Jung Tae,Jang, Sanha,Kim, Chul Sung,Lee, Chan-Woo,Joo, Sang Hoon,Han, Jeong Woo,Park, Ji Chan Elsevier 2017 Journal of catalysis Vol.349 No.-
<P><B>Abstract</B></P> <P>Highly-loaded and well-dispersed Fe<SUB>5</SUB>C<SUB>2</SUB> nanoparticles within ordered mesoporous carbon CMK-3 (Fe<SUB>5</SUB>C<SUB>2</SUB>@CMK-3) were prepared via a simple melt infiltration method. They were successfully applied to high-temperature Fischer-Tropsch synthesis, and showed high CO conversion (91%) and activity (5.1×10<SUP>−4</SUP> mol<SUB>co</SUB> g<SUB>Fe</SUB> <SUP>−1</SUP> s<SUP>−1</SUP>) as well as good selectivity (38wt%) for gasoline-range hydrocarbons (C<SUB>5</SUB>–C<SUB>12</SUB>). The catalytic property of Fe<SUB>5</SUB>C<SUB>2</SUB>@CMK-3 was newly interpreted, based on theoretical data obtained by computational simulations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Fe<SUB>5</SUB>C<SUB>2</SUB>@CMK-3 catalyst was designed for gasoline-range hydrocarbon production. </LI> <LI> The catalyst showed high stability and activity for Fischer-Tropsch synthesis. </LI> <LI> The catalytic property of Fe<SUB>5</SUB>C<SUB>2</SUB>@CMK-3 was interpreted by computational simulations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>