How Pt-ceria interacts under reductive and oxidative environment: the origin of improved thermal stability of Pt-ceria compared to ceria

이재하,유영석,( Xiaojun Chan ),김태진,김도희 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.0

When precious metal is loaded on ceria, they interact strongly with each other, so high metal dispersion is obtained. Many catalytic reactions, including automotive catalytic reaction and water-gas-shift reaction, utilize such strong metal support interaction between precious metal and ceria to attain high catalytic activity. Therefore, understanding how precious metal interacts with ceria becomes crucial in order to properly design catalytic reaction system. In the present work, Pt-ceria interaction was analyzed in various aspects. Special attention is paid to investigating the effects of Pt loadings and oxidative thermal treatment on metal support interaction. Consistent with previous reports, Pt is found to strongly interact with reducible surface oxygen (and surface oxygen vacancies) of ceria. Metal support interaction guaranteed high metal dispersion as well as the enhanced thermal stability of the ceria support.

귀금속 촉매를 이용한 수소혼합가스에 포함된 일산화탄소의 선택적 산화반응

임미숙,김동현 한국화학공학회 2002 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.40 No.3

Alumina, ceria 그리고 ceria가 10wt% 담지된 alumina를 담체로 한 Pt, Ru, Pt-Ru 이원금속(bimetallic)촉매 상에서 일산화탄소의 선택적 산화반응에 대한 연구를 진행하였다. 실험은 대기압, 50-400℃온도 영역에서 행하였다. Ceria는 금속표면에 산소를 원활히 공급함으로써 Pt촉매의 활성을 증가시키는 역할을 하였으며, 순수한 ceria에 담지된 Pt촉매가 ceria를 포함한 alumina를 담체로 한 Pt촉매보다 저온 활성이 증가하였다. 금속 전구체로 염화물을 사용하는 경우, 촉매표면에 잔존하는 Cl로 인해 산소의 mobility가 감소하고 활성이 저하되는 것으로 나타났다. Ru 또한 150℃ 이하의 저온에서 우수한 활성을 나타내었다. Pt-Ru 이원금속(bimetallic)촉매의 제조과정에서 소성과정 없이 300℃에서 환원과정만을 거친 촉매는 소성과정을 거친 촉매보다 더 좋은 활성을 보였는데 이것은 소성과정이 합금형성을 방해하기 때문인 것으로 판단된다. The selective oxidation of CO in hydrogen mixture was studied over Pt, Ru, and Pt-Ru bimetallic catalysts supported on alumina, ceria, or alumina impregnated with 10wt% ceria. The experiments were conducted at atmospheric pressure and in the temperature range of 50-400℃. Ceria was found to significantly promote the catalytic activity of the Pt catalysts by supplying oxygen to the metal interface, particulary at low temperatures where Pt alone was inactive. The Pt supported on pure ceria exhibited better low-temperature activity than the Pt supported on the alumina impregnated with ceria. When using chlorine compound as the metal precursor, the residual chlorine present on the catalyst was found to inhibit the oxygen mobility of the ceria to lower the catalytic activity. Ru also exhibited excellent low-temperature activities at temperatures lower than 150℃. As to the preparation methods for the Pt-Ru bimetallic catalysts, the catalyst directly reduced under hydrogen at 300℃ without prior calcination exhibited better activity than the bimetallic catalysts prepared with a calcination step, indicating hat the calcination step may hinder the formation of the alloy phase.

Stable ceria-based electrolytes for intermediate temperature-solid oxide fuel cells via hafnium oxide blocking layer

Kim, You-Dong,Yang, Ja-Yoon,Lee, John-In,Saqib, Muhammad,Shin, Ji-Seop,Shin, Minjae,Kim, Jung Hyun,Lim, Hyung-Tae,Park, Jun-Young Elsevier 2019 Journal of Alloys and Compounds Vol.779 No.-

<P><B>Abstract</B></P> <P>The electronic loss of ceria-based electrolytes is caused by the reduction of ceria at low oxygen partial pressure for intermediate temperature-solid oxide fuel cells. To address this issue, a thin hafnium oxide layer is deposited at the interface between the anode and electrolyte using a magnetron sputtering system, based on the hypothesis that the stability of ceria electrolytes in the anode side can be controlled as a function of the reducibility of the ceria surface. The performance of ceria-based cells (Nd<SUB>0.1</SUB>Ce<SUB>0.9</SUB>O<SUB>2-δ</SUB>; NDC, Sm<SUB>0.2</SUB>Ce<SUB>0.8</SUB>O<SUB>2-δ</SUB>; SDC) is investigated by varying the HfO<SUB>2</SUB> film thickness on the same ceria-based substrate. The range of thickness of the HfO<SUB>2</SUB> film is 121–686 Å for 6–30 min with the deposition rate of 0.38 Å‧S<SUP>−1</SUP>. The open-circuit voltages and power densities of NDC- and SDC-based cells are measured at 600–700 °C as a function of HfO<SUB>2</SUB> film thickness. It is clearly observed that open-circuit voltages and the maximum power densities of both cells increase with the increasing of thickness of HfO<SUB>2</SUB> film until a film thickness of 600 Å is reached. This indicates that the HfO<SUB>2</SUB> layer effectively prevents the electron transfer through the electrolytes by the reduction of ceria. Furthermore, the NDC-cell with the HfO<SUB>2</SUB> film shows a stable performance under a constant current density operation of 130 h at 650 °C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Develop highly conductive and stable ceria-based electrolytes for IT-SOFCs via HfO<SUB>2</SUB> blocking layer. </LI> <LI> A thin hafnium oxide layer is deposited at the interface between the anode and electrolyte using a sputtering. </LI> <LI> OCVs and the maximum power densities of cells increase with the increasing of thickness of HfO<SUB>2</SUB> film. </LI> <LI> The HfO<SUB>2</SUB> layer effectively prevents the electron transfer through the electrolytes by the reduction of ceria. </LI> </UL> </P>

Low temperature synthesis of Nafion/Ceria nanocomposite through self-assembly process

( Irshad Mobina ),김주영 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

A relatively low temperature synthesis of nano-structured Nafion/CeO₂ composites was carried out without any heat treatment and surfactant. Through self-assembled structure of Nafion in the solution, colloidally stable solutions, where ceria nanoparticles were dispersed in the presence of Nafion, could be prepared. Obtained ceria/Nafion solutions were casted to prepare ceria/Nafion nanocomposite films. Formation of ceria nanoparticles in the solutions and the nanocomposite films were characterized by SEM, TGA, and EDS analysis. Also, type of Nafion, amount of ceria precursors, and weight ratio of ceria/Nafion was changed to study their effect on the dispersibility and size of ceria nanoparticles in the solutions and the nanocomposite films.

[Retraction]Size measurement and characterization of ceria nanoparticles using asymmetrical flow field-flow fractionation (AsFlFFF)

Kim, Kihyun,Choi, Seong-Ho,Lee, Seungho,Kim, Woonjung The Korean Society of Analytical Science 2019 분석과학 Vol.32 No.5

As the size of semiconductors becomes smaller, it is necessary to perform high precision polishing of nanoscale. Ceria, which is generally used as an abrasive, is widely used because of its uniform quality, but its stability is not high because it has a high molecular weight and causes agglomeration and rapid precipitation. Such agglomeration and precipitation causes scratches in the polishing process. Therefore, it is important to accurately analyze the size distribution of ceria particles. In this study, a study was conducted to select dispersants useful for preventing coagulation and sedimentation of ceria. First, a dispersant was synthesized and a ceria slurry was prepared. The defoamer selection experiment was performed in order to remove the air bubbles which may occur in the production of ceria slurry. Dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) were used to determine the size distribution of ceria particles in the slurry. AsFlFFF is a technique for separating nanoparticles based on sequential elution of samples as in chromatography, and is a useful technique for determining the particle size distribution of nanoparticle samples. AsFlFFF was able to confirm the presence of a little quantities of large particles in the vicinity of 300 nm, which DLS can not detect, besides the main distribution in the range of 60-80 nm. AsFlFFF showed better accuracy and precision than DLS for particle size analysis of a little quantities of large particles such as ceria slurry treated in this study.

불규칙 입자형상을 갖는 세리아 안정화 지르코니아 세라믹스의 제조

강현희,이종국 한국세라믹학회 1999 한국세라믹학회지 Vol.36 No.4

Hihg-toughened ceria-stabilized tetragonal zirconia ceramics with irregular grain shape and undulated grain boundary was prepared by ceria doping. Irregularity of grain shapes was increased with the amount of doped ceria. But in case of the large amount of doped ceria grain boundary was migrated to the reverse direction of DIGM. Ceria-stabilized zirconia ceramics annealed at 1650$^{\circ}C$ for 2h after twice dippings into cerium nitrate solu-tion of 0.2M and sintering at 1500$^{\circ}C$ for 2h showed the highest grain boundary length with a value of 23.6$\mu\textrm{m}$ Ceria concentration difference between convex and concave sides in irregular grains was observed over 1 mol% but not observed in normal grains, Specimens with normal grain shape showed intergranular fracture mode whereas the specimens with irregular grain shape showed transgranular fracture mode.

Effect of Particle Size of Ceria Coated Silica and Polishing Pressure on Chemical Mechanical Polishing of Oxide Film

김환철,임형미,김대성,이승호 한국전기전자재료학회 2006 Transactions on Electrical and Electronic Material Vol.7 No.4

Submicron colloidal silica coated with ceria were prepared by mixing of silica and nano ceria particles and modified by hydrothermal reaction. The polishing efficiency of the ceria coated silica slurry was tested over oxide film on silicon wafer. By changing the polishing pressure in the range of 140~420 g/cm2 with the ceria coated silica slurries in 100~300 nm, removal rates, WIWNU and friction force were measured. The removal rate was in the order of 200, 100, and 300 nm size silica coated with ceria. It was known that the smaller particle size gives the higher removal rate with higher contact area in Cu slurry. In the case of oxide film, the indentation volume as well as contact area gives effect on the removal rate depending on the size of abrasives. The indentation volume increase with the size of abrasive particles, which results to higher removal rate. The highest removal rate in 200 nm silica core coated with ceria is discussed as proper combination of indentation and contact area effect.

Size measurement and characterization of ceria nanoparticles using asymmetrical flow field-flow fractionation (AsFlFFF)

Kihyun Kim,Seong-Ho Choi,Seungho Lee,Woonjung Kim 한국분석과학회 2019 분석과학 Vol.32 No.5

As the size of semiconductors becomes smaller, it is necessary to perform high precision polishing of nanoscale. Ceria, which is generally used as an abrasive, is widely used because of its uniform quality, but its stability is not high because it has a high molecular weight and causes agglomeration and rapid precipitation. Such agglomeration and precipitation causes scratches in the polishing process. Therefore, it is important to accurately analyze the size distribution of ceria particles. In this study, a study was conducted to select dispersants useful for preventing coagulation and sedimentation of ceria. First, a dispersant was synthesized and a ceria slurry was prepared. The defoamer selection experiment was performed in order to remove the air bubbles which may occur in the production of ceria slurry. Dynamic light scattering (DLS) and asymmetrical flow fieldflow fractionation (AsFlFFF) were used to determine the size distribution of ceria particles in the slurry. AsFlFFF is a technique for separating nanoparticles based on sequential elution of samples as in chromatography, and is a useful technique for determining the particle size distribution of nanoparticle samples. AsFlFFF was able to confirm the presence of a little quantities of large particles in the vicinity of 300 nm, which DLS can not detect, besides the main distribution in the range of 60-80 nm. AsFlFFF showed better accuracy and precision than DLS for particle size analysis of a little quantities of large particles such as ceria slurry treated in this study.

Role of the Surface Chemistry of Ceria Surfaces on Silicate Adsorption

Seo, Jihoon,Lee, Jung Woo,Moon, Jinok,Sigmund, Wolfgang,Paik, Ungyu American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.10

<P>Ceria nanoparticles (NPs) have been widely explored as a promising material in various fields. As synthesized under various physicochemical conditions, it exhibits the different surface chemistry. Here, the role of hydroxyl and nitrate group on ceria surface, formed under various physicochemical conditions, for the silicate adsorption was experimentally and theoretically investigated based on the adsorption isotherms and theoretical analyses using density functional theory (DFT) calculation. Experimental results acquired from adsorption isotherms with Freundlich model indicated that the nitrate group shows a much higher affinity with silicate than the hydroxyl groups. These phenomena were demonstrated through the theoretical approaches that exhibit the binding energy of the NO<SUB>3</SUB>–ceria (−4.383 eV) on the SiO<SUB>2</SUB> surface being much higher than that of the OH–ceria (−3.813 eV). In good agreement with the experimental and the theoretical results based on adsorption properties, the results of chemical mechanical planarization (CMP) also show that the nitrate groups significantly enhance the removal of SiO<SUB>2</SUB> than the hydroxyl groups. The results investigated in this study will provide researchers, studying the ceria NPs, with guidelines on the importance of exploring the surface chemistry of ceria.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-10/am500816y/production/images/medium/am-2014-00816y_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am500816y'>ACS Electronic Supporting Info</A></P>

강화상 나노입자의 용액 반응성이 구리 도금 박막에 미치는 영향

박지은,오민주,김이슬,이동윤,Park, Jieun,Oh, Minju,Kim, Yiseul,Lee, Dongyun 한국재료학회 2013 한국재료학회지 Vol.23 No.12

To understand how reactivity between reinforcing nanoparticles and aqueous solution affects electrodeposited Cu thin films, two types of commercialized cerium oxide (ceria, $CeO_2$) nanoparticles were used with copper sulfate electrolyte to form in-situ nanocomposite films. During this process, we observed variation in colors and pH of the electrolyte depending on the manufacturer. Ceria aqueous solution and nickel sulfate ($NiSO_4$) aqueous solutions were also used for comparison. We checked several parameters which could be key factors contributing to the changes, such as the oxidation number of Cu, chemical impurities of ceria nanoparticles, and so on. Oxidation number was checked by salt formation by chemical reaction between $CuSO_4$ solution and sodium hydroxide (NaOH) solution. We observed that the color changed when $H_2SO_4$ was added to the $CuSO_4$ solution. The same effect was obtained when $H_2SO_4$ was mixed with ceria solution; the color of ceria solution changed from white to yellow. However, the color of $NiSO_4$ solution did not show any significant changes. We did observe slight changes in the pH of the solutions in this study. We did not obtain firm evidence to explain the changes observed in this study, but changes in the color of the electrolyte might be caused by interaction of Cu ion and the by-product of ceria. The mechanical properties of the films were examined by nanoindentation, and reaction between ceria and electrolyte presumably affect the mechanical properties of electrodeposited copper films. We also examined their crystal structures and optical properties by X-ray diffraction (XRD) and UV-Vis spectroscopy.