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Tuning the base properties of Mg–Al hydrotalcite catalysts using their memory effect

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Journal of Energy Chemistry 2020年第7期29卷 229-236,I0008页

作者： Dahye Kwon ji Yeon Kang Suna An Inchan Yang ji chul jung Department of Chemical Engineering Myongji UniversityYongin 17058Republic of Korea

Herein,the relationship between the structure and base properties of Mg–Al hydrotalcite catalysts was comprehensively investigated in relation to heat treatment and rehydration processes,which are well known as memory effects of *** structure of Mg–Al hydrotalcites changed from layered double hydroxide(LDH)to mixed metal oxide and subsequently to a spinel structure during heat treatment,and it was returned from mixed metal oxide to a LDH structure by *** on various characterizations,we successfully proposed a detailed mechanism of memory *** also confirmed that the Mg–Al hydrotalcites had weak or strong base sites and that their base properties could be systematically tuned by heat treatment and *** prepared Mg–Al hydrotalcites were applied to a model reaction,isomerization of glucose to fructose,as base *** the catalysts tested,the rehydrated Mg–Al hydrotalcite efficiently produced fructose due to its appropriate base and structure *** finally concluded that the base sites of Mg–Al hydrotalcites can be designed as desired by heat treatment and ***,through systematic design of the base sites of Mg–Al hydrotalcites,these can be promising catalysts for various heterogeneous reactions over base catalysts,giving excellent catalytic performances.

关键词： Mg–Al hydrotalcite Structure Base properties Heat treatment Rehydration

Oxidative coupling of methane over LaAlO3 perovskite catalysts prepared by a co-precipitation method: Effect of co-precipitation pH value

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Journal of Energy Chemistry 2019年第8期28卷 1-8,I0001页

作者： Yujin Sim jihoon Yoo Jeong-Myeong Ha ji chul jung Department of Chemical Engineering Myongji UniversityYongin 17058 Republic of Korea Clean Energy Research Center Korea Institute of Science and TechnologySeoul 02792 Republic of Korea

Oxidative coupling of methane(OCM) was conducted over LaAlO3X catalysts that were prepared by a coprecipitation method using different co-precipitation pH values(X = 6–10). The aim is to investigate the effect of p H values on the catalytic activity of La AlO3 catalysts in this reaction. The results showed that the co-precipitation pH value affected greatly on the formation of chemical species of precipitate precursors in the co-precipitation step, leading to different phases of the finally obtained LaAlO3 *** the co-precipitation pH value increased up to 8, the lanthanum-related phases such as La2 O3 and La(OH)3 were gradually formed as by-products, preventing the formation of LaAlO3 perovskite crystalline structure and facilitating the formation of oxygen vacancies on catalyst surface. However, at pH value of9 or higher, the lanthanum content in the precipitate precursor was increased greatly. Not LaAlO3 perovskite but lanthanum-related phases were developed as main phases, reducing their catalytic activities in this reaction. Among LaAlO3 catalysts, the one prepared at pH = 8 showed the highest C2 yield due to its well-developed oxygen vacancies and electrophilic lattice oxygen. Therefore, the co-precipitation pH value strongly affected the LaAlO3 catalyst activity in OCM reaction. A precious pH control should be required to prepare various perovskite catalysts for the OCM.

关键词： LaAlO3 Perovskite Oxidative coupling of methane Co-precipitation pH value

Oxygen vacancy engineering for tuning the catalytic activity of LaCoO_(3) perovskite

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Journal of Rare Earths 2024年第3期42卷 506-514,I0003页

作者： Jeong Hyun Cho Minjae Kim Inchan Yang Kyung Tae Park Chang Houn Rhee Hai Woong Park ji chul jung Department of Chemical Engineering Myongji UniversityYongin 17058Republic of Korea Institute of Advanced Composite Materials Korea Institute of Science and TechnologyWanju-gunJeollabuk-do 55324Republic of Korea Iron&Steel Process Engineering Research Group POSCOPohang 37859Republic of Korea Hydrogen Research Center Research Institute of Industrial Science&Technology(RIST)Pohang 37673Republic of Korea

Herein, we attempted to engineer oxygen vacancies on the surface of LaCoO_(3) perovskite through simple post-treatments(acid or reductive thermal treatments). Acid treatment induces oxygen vacancies through the selective etching of the La cations, whereas thermal treatment in a reducing atmosphere generates oxygen vacancies by directly removing lattice oxygen. The characterization results confirm that the number of surface oxygen vacancies, which are crucial in various catalytic oxidation reactions,considerably increases in the LaCoO_(3) catalysts treated with acid or reducing gas. Acid treatment enriches the oxygen vacancies while maintaining the structure of the LaCoO_(3) catalysts, which can not be achieved through reductive thermal treatment. Therefore, the acid treatment is considered a promising technique for oxygen vacancy engineering of perovskite catalysts for tuning their catalytic activities. Furthermore,the catalytic activities of the posttreated LaCoO_(3) catalysts for CO oxidation were evaluated and are noted to be considerably better than those of the pristine LaCoO_(3) catalyst due to their abundant oxygen vacancies. Consequently, we conclude that the oxygen vacancies of perovskite catalysts can be effectively engineered via two simple methods and play a significant role in CO oxidation.

关键词： LaCoO_(3)perovskite Acid treatment Reductive thermal treatment Oxygen vacancy CO oxidation Rare earths

Bifunctionality of Cu/ZnO catalysts for alcohol-assisted low-temperature methanol synthesis from syngas:Effect of copper content

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Journal of Energy Chemistry 2017年第3期26卷 373-379页

作者： Ilho Kim Gihoon Lee Heondo Jeong Jong Ho Park ji chul jung Department of Chemical Engineering Myongji University Korea Institute of Energy Research

Alcohol-assisted low-temperature methanol synthesis was conducted over Cu/ZnO;catalysts while varying the copper content（X）. Unlike conventional methanol synthesis, ethanol acted as both solvent and reaction intermediate in this reaction, creating a different reaction pathway. The formation of crystalline phases and characteristic morphology of the co-precipitated precursors during the co-precipitation step were important factors in obtaining an efficient Cu/ZnO catalyst with a high dispersion of metallic copper,which is one of the main active sites for methanol synthesis. The acidic properties of the Cu/ZnO catalyst were also revealed as important factors, since alcohol esterification is considered the rate-limiting step in alcohol-assisted low-temperature methanol synthesis. As a consequence, bifunctionality of the Cu/ZnO catalyst such as metallic copper and acidic properties was required for this reaction. In this respect, the copper content（X） strongly affected the catalytic activity of the Cu/ZnO;catalysts, and accordingly, the Cu/ZnO;.5 catalyst with a high copper dispersion and sufficient acid sites exhibited the best catalytic performance in this reaction.

关键词： Low-temperature methanol synthesis Alcohol-assisted Bifunctionality Cu/ZnO catalysts Copper content

Formation Mechanism of Chunky Graphite and Its Preventive Measures

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Journal of Materials Science & Technology 2008年第3期24卷 289-295页

作者： Hideo Nakae Sanghoon jung Ho-chul Shin Department of Materials Science and Engineering Waseda University National Institute of AIST Corporate Res.and Dev.Div. Hyundai.Kia Motors

The formation mechanism of chunky graphite has been reviewed and studied. The study consisted of a unidirectional solidification method, a small droplet method and a furnace cooling method. Four kinds of iron samples were prepared, namely, the pure Fe-C, Fe-C-S, Fe-C-Ce and Fe-C-Si-Ce alloys, and three kinds of nickel samples, namely the Ni-C, Ni-C-S and Ni-C-Mg alloys. The results of the unidirectional solidification of the Ni-C alloys showed that spheroidal graphite is not observed in the continuous solidified region, in which only flake-like graphite is observed, while spheroidal graphite is usually observed in the quenched liquid region. The existence of spheroidal graphite in the solidified phase is recognized only in the discontinuous growth mode of the Ni-C-Mg alloy solidified at 150 mm/h. This means that the spheroidal graphite is directly crystallized from the melt and entrapped by the flake-like chunky graphite that is formed by the continuous growth mode. In the small droplet method, a small piece of the Fe-C or Fe-C-Ce sample was melted on a pure graphite plate then cooled at a different cooling rate in a He-3%H2 atmosphere. The graphite in the Fe-C-Ce alloy is usually spherical. Nevertheless, the graphite morphology of the final solidified area changed from spherical to chunky and chunky to ledeburite with an increase in the cooling rate. This means that the chunky graphite is formed in the residual liquid region by the solidification into Fe-graphite system. The sample was cooled in a furnace, and the graphite morphology changes from spherical to chunky and chunky to ledeburite with the decrease in the Si content. These phenomena can be confirmed by the cooling curves of these samples.

关键词： Chunky graphite Spheroidal graphite Solidification Cooling curve

Antiphospholipid syndrome with renal and splenic infarction after blunt trauma:A case report

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World Journal of Clinical Cases 2022年第26期10卷 9404-9410页

作者： Na-A Lee Eui-Sung Jeong Hyun-Seok Jang Yun-chul Park ji-Hyoun Kang jung-chul Kim Young-Goun Jo Division of Trauma Department of SurgeryChonnam National University Medical School and HospitalGwangju 61469South Korea Division of Rheumatology Department of Internal MedicineChonnam National University Medical School and HospitalGwangju 61469South Korea

BACKGROUND In trauma patients,bleeding is an immediate major *** the same time,there are few cases of acute vascular occlusion after blunt trauma,and it is unclear what assessment and diagnosis should be considered for these ***,we describe a patient diagnosed with antiphospholipid syndrome after a hypercoagulable workup for acute renal and splenic vascular occlusion due to blunt *** SUMMARY A 20-year-old man was admitted to the emergency department with abdominal pain after hitting a tree while riding a sled 10 h *** had no medical *** investigations revealed occlusion of the left renal artery with global infarction of the left kidney and occlusion of branches of the splenic artery with infarction of the central portion of the *** revascularization of the left renal artery occlusion through percutaneous transluminal angioplasty failed due to difficulty in passing the wire through the total *** the presence of acute multivascular occlusions in a young man with low cardiovascular risk,additional laboratory tests were performed to evaluate *** results suggested a high possibility of antiphospholipid *** with a subcutaneous injection of enoxaparin was started and changed to oral warfarin after two *** diagnosis was confirmed,and he continued to visit the rheumatology outpatient clinic while taking *** A hypercoagulable workup can be considered in trauma patients with acute multivascular occlusion,especially in young patients with low cardiovascular risk.

关键词： Wounds and injuries Wounds Nonpenetrating Antiphospholipid syndrome Renal artery obstruction Splenic infarction Case reports

Discovering High-Quality Threaded Discussions in Online Forums

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Journal of Computer Science & Technology 2014年第3期29卷 519-531页

作者： jung-Tae Lee Min-chul Yang Hae-Chang Rim Department of Computer and Radio Communications Engineering Korea UniversitySeoul 136-713Korea

Archives of threaded discussions generated by users in online forums and discussion boards contain valuable knowledge on various topics. However, not all threads are useful because of deliberate abuses, such as trolling and flaming, that are commonly observed in online conversations. The existence of various users with different levels of expertise also makes it difficult to assume that every discussion thread stored online contains high-quality contents. Although finding high-quality threads automatically can help both users and search engines sift through a huge amount of thread archives and make use of these potentially useful resources effectively, no previous work to our knowledge has performed a study on such task. In this paper, we propose an automatic method for distinguishing high-quality threads from low-quality ones in online discussion sites. We first suggest four different artificial measures for inducing overall quality of a thread based on ratings of its posts. We then propose two tasks involving prediction of thread quality without using post rating information. We adopt a popular machine learning framework to solve the two prediction tasks. Experimental results on a real world forum archive demonstrate that our method can significantly improve the prediction performance across all four measures of thread quality on both tasks. We also compare how different types of features derived from various aspects of threads contribute to the overall performance and investigate key features that play a crucial role in discovering high-quality threads in online discussion sites.

关键词： online forum discussion board thread quality

Dually-functionalized Ni-rich layered oxides for high-capacity lithium-ion batteries

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Journal of Materials Science & Technology 2021年第27期86卷 70-76页

作者： ji Won Kim Kwangeun jung Taeeun Yim Department of Chemistry Incheon National University119 Academy-roYeonsu-guIncheon 22012Republic of Korea

Layered lithium nickel-cobalt-manganese oxides(NCM)have been highlighted as advanced cathode materials for lithium-ion batteries(LIBs);however,their low interfacial stability must be overcome to ensure stable cycling performance of the *** this work,we propose a one-step surface modification method that uses a task-specific precursor,N,N,N,N-tetraethylsulfamide(NTESA),to improve interfacial stability of Ni-rich NCM cathode *** unstable surface properties of Ni-rich NCM cathode material are improved by embedding an artificial cathode-electrolyte interphase(CEI)layer on the cathode surface by heat treatment of the Ni-rich NCM cathode material with an NTESA precursor at low *** material analyses indicate that this approach allows the formation of amine-and sulfone-functionalized CEI layers on the surface of Ni-rich NCM cathode material without changing the layered structure of the cathode ***-functionalized Ni-rich NCM cathode materials exhibit improved cycling retention after 100 cycles:for example,a cell cycled with a 3.0 NTESA-modified NCM811 cathode presents the highest retention ratio of 88.3%,whereas a cell cycled with a non-functionalized NCM811 cathode suffers from rapid fading of the cycling performance(68.4%).Our additional SEM,XPS,and EIS analyses indicate that electrolyte decomposition is suppressed during electrochemical cycling,thereby leading to smaller increases in the internal ***-MS analyses of the cycled anodes also indicate that the NTESA-based artificial CEI layer inhibits the dissolution of transition metal components from the Ni-rich NCM cathode materials,thereby contributing to an improved overall electrochemical performance of the cell.

关键词： Lithium-ion battery Cathode Cathode-electrolyte interphase N,N,N,N-Tetraethylsulfamide Electrochemical performance

Comparison of the meibomian gland dysfunction in patients with chronic ocular graft-versus-host disease and Sjogren's syndrome

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International Journal of Ophthalmology(English edition) 2019年第3期12卷 393-400页

作者： Won Choi Jun Young Ha Ying Li jung Han Choi Yong Sok ji Kyung chul Yoon Department of Ophthalmology and Research Institute of Medical Sciences Chonnam National University Medical School and Hospital

AIM: To investigate the abnormalities in the meibomian gland in patients with dry eye disease(DED) associated with chronic ocular graft-versus-host disease(coGVHD) in comparison with Sj?gren's syndrome(SS), a major form of aqueous deficient DED and meibomian gland dysfunction(MGD), a common cause of evaporative ***: A total 135 eyes of 135 subjects included in this study: patients with DED associated with coGVHD(n=30), patients with SS(n=35), patients with MGD(n=35), and normal controls(n=35). All participants completed the Ocular Surface Disease Index(OSDI) questionnaire, ocular surface examination [Schirmer test, tear film breakup time(TFBUT), and ocular surface staining], and meibomian gland assessment [meiboscore(gland dropout detected on meibography using infrared camera of the Keratograph 5 M), meibum expressibility score(MES), meibum quality score(MQS), lid margin abnormality]. In addition, correlations of meibomian gland characteristics with ocular surface parameters as well as disease severity score were investigated in coGVHD ***: The coGVHD group showed significantly higher meiboscore, MES, and MQS than the other 3 groups(all P<0.05). In the coGVHD group, parameters of meibomian gland showed a significant correlation each other and those of ocular surface. The correlation between meibomian gland parameters and severity score of co GVHD was also established(meiboscore, r=0.62; MES, r=0.47; MQS, r=0.47; lid margin abnormality score, r=0.55; all P<0.05).CONCLUSION: Patients with DED associated with co GVHD show poorer gland morphology and worse glandfunction than other types of DED. In addition, meibomian gland damage is not only associated with ocular surface damage but also disease severity of coGVHD.

关键词： chronic ocular graft-versus-host disease Sjogren's syndrome dry eye disease meibomian gland dysfunction meibography