전이 금속 산화물 지지체와 귀금속 간의 금속-지지체 상호작용을 활용한 촉매 활성 증진

학위논문(박사)--서울대학교 대학원 :공과대학 화학생물공학부,2020. 2. 김도희.By manipulating metal-support interaction between PGMs and metal-oxide supports, the catalysts chemical properties could be modulated and their catalytic performances could be significantly improved. In addition, it is most desirable both in academic and industrial perspectives to control the metal-support interaction in a simple but effective manner. In this context, in this thesis, the metal-support interaction was studied under both oxidizing and reducing environments. Based on the understanding of the interaction under various environments, three different simple but effective strategies were devised to improve catalytic performances. The interaction between Pt and CeO2 under reducing and oxidizing conditions were extensively investigated. According to Raman spectroscopy, Pt species are strongly bonded on CeO2 surface by forming Pt-O-Ce bond under the oxidizing condition. Interestingly, Pt-O-Ce bonds became more resistive to the reducing treatment when the oxidation temperature increased from 500 oC to 800 oC. Under the reducing condition, the amount of CO chemisorbed on CeO2 is almost equal to that on Pt/CeO2, implying that Pt atoms are located on the oxygen vacancy generated on reduced CeO2 surface. The textural properties of Pt/CeO2 were maintained from the oxidative treatment at high temperature as high as 1000 oC. However, the thermal stability of Pt/CeO2 greatly decreased when Pt-O-Ce bonds are selectively removed. Therefore, it can be concluded that Pt-O-Ce bonds play the critical role in improving the thermal stability of Pt/CeO2. The CO oxidation ability of Pt/CeO2 catalysts can be greatly improved by weakening the metal-support interaction between Pt and CeO2 by decreasing the defect concentration of CeO2 surface before loading Pt. The defect concentration of CeO2 surface could be readily decreased by the thermal treatment of CeO2 at high-temperature. In short, Pt/(800C)CeO2 was prepared by the thermal treatment of CeO2 at 800 oC before loading Pt. Pt/(800C)CeO2 maintained the much higher Pt dispersion than Pt/γ-Al2O3 after the thermal aging at 800 oC, indicating its excellent thermal resistance against Pt sintering. In addition, the CO oxidation rate of Pt/(800C)CeO2 was order-of-magnitude higher than that of Pt/CeO2. The temperature for 50 % conversion of CO oxidation of Pt/(800C)CeO2 was 76 oC lower than that of Pt/CeO2. Particularly, Pt/(800C)CeO2 accomplished ~100% CO conversion below 150 oC. Such enhanced activity is explained by the formation of PtO2 species that interact weakly with CeO2. Similarly to Pt/CeO2 catalysts, the CO oxidation abiltiy of Pt/TiO2 catalysts could be improved by weakening the metal-support interaction between Pt and TiO2 by using S-doped TiO2 (S-TiO2) as the suppoort. The temperature for 50 % conversion of CO oxidation of Pt/S-TiO2 was 50 oC lower than that of Pt/TiO2. Especially, Pt(4)/S-TiO2 accomplished ~100% CO conversion below 150 oC. Such improvement in activity is explained by the formation of large Pt clusters on S-TiO2 with more metallic character. The catalytic performance could be also improved by modifying the geometry of catalysts to facilitate the metal-support interaction. The type of catalysts with Pt nanoparticles (NP) encapsulated in CeO2 over-layers (Pt in CeO2) were successfully prepared by applying the controlled reductive treatments. Pt NP are covered by CeO2 over-layers as revealed by HAADF-STEM images and CO chemisorption. While Pt on CeO2 exhibits good high temperature Water-Gas-Shift reaction (HT-WGSR) activity, Pt sites also catalyze the formation of CH4 as by-product, which places the limitation on the use of Pt/CeO2 as HT-WGSR catalyst. On the contrary, the CH4 production was successfully inhibited on Pt in CeO2 while high WGS activity was maintained. Interestingly, thin CeO2 over-layers could catalyze WGSR while thick CeO2 over-layers could not. This is attributed to the high concentration of oxygen vacancies on thin CeO2 over-layers that aided the formation of catalytically active monodentate formate intermediates. Detailed CO chemisorption, XPS and in-situ DRIFT studies unraveled the catalytic properties of CeO2 over-layers formed by controlled reductive treatments.전이 금속 산화물 지지체와 귀금속 간의 금속-지지체 상호작용(metal-support interaction)을 조절함으로써 촉매의 화학적 특성을 조절하고 촉매 성능을 크게 개선할 수 있다. 이러한 맥락에서, 이 논문에서는 우선 metal-support interaction이 산화 및 환원 분위기에서 어떻게 작동하는지 연구하였다. 또한, metal-support interaction을 세가지 다른 효과적인 방법으로 조절하여, 촉매 성능(일산화탄소 산화 반응(CO oxidation)과 수성 가스 전이 반응(Water-Gas-Shift reaction; WGSR))을 개선하는데 성공하였다. 본 논문에서는 우선, 환원 및 산화 분위기에서 플래티넘(Pt)과 세리아(CeO2)가 어떻게 상호작용하는지를 연구하였다. 라만 분광법(Raman spectroscopy)에 따르면, Pt은 산화 분위기에서 Pt-O-Ce 결합을 형성함으로써 CeO2 표면에 강하게 결합한다. 흥미롭게도, 산화 온도가 500 oC에서 800 oC로 증가하면 Pt은 CeO2와 더 강하게 상호작용하였다. 또한, 환원 분위기에서, CeO2에 화학-흡착한 일산화탄소(carbon monoxide; CO) 양은 Pt/CeO2에 화학-흡착한 CO 양과 동일하였다. 이는 Pt이 환원된 CeO2 표면에 생성된 산소 결함(oxygen vacancy)에 위치함을 의미한다. Pt/CeO2의 표면적은 산화 분위기에서 1000 oC에 노출되어도 큰 변화 없이 유지되었다. 그러나 Pt-O-Ce 결합이 선택적으로 제거되면, 고온 처리 후 Pt/CeO2의 표면적은 크게 감소하였다. 따라서, Pt-O-Ce 결합이 Pt/CeO2의 열-안정성을 향상시키는 데 중요한 역할을 한다고 결론 내릴 수 있었다. Pt을 담지하기 전에 CeO2 표면의 결함 농도(defect concentration)를 감소시키면, Pt과 CeO2 사이의 상호작용이 약해지고, Pt/CeO2 촉매의 CO oxidation 활성은 증가한다. CeO2 표면의 defect concentration는 CeO2를 고온-열처리하면 감소한다. 따라서, 800 oC에서 CeO2를 열처리하고 Pt을 담지하여 촉매를 제조하였다 (Pt/(800C)CeO2.) Pt/(800C)CeO2는 800 oC에서 열처리 후, Pt가 담지 된 감마 알루미나 촉매(Pt/γ-Al2O3)보다 높은 Pt 분산도를 유지하여 Pt 소결에 대한 우수한 열 저항성을 보였다. 또한, Pt/(800C)CeO2 촉매는 Pt/CeO2 촉매보다 76 oC 더 낮은 온도에서 CO를 전부 산화 하였다. 이러한 촉매 활성 향상은 CeO2와 약하게 상호작용하는 산화 플래티넘(PtO2)의 형성에 기인한다. Pt/CeO2 촉매와 유사하게, Pt과 티타니아(TiO2) 사이의 상호작용을 약화시키면, Pt가 담지 된 TiO2(Pt/TiO2) 촉매의 CO oxidation 활성을 증진할 수 있다. Pt를 황이 도핑 된 TiO2(S-TiO2)에 담지하면(Pt/S-TiO2), Pt는 TiO2 표면과 더 약하게 상호작용하고, 더 많은 금속 특성을 가지는 커다란 Pt 클러스터가 형성된다. Pt/S-TiO2 촉매는 Pt/TiO2 촉매보다 50 oC 더 낮은 온도에서 CO를 전부 산화 하였다. 마지막으로, 촉매의 기하학적 구조를 바꿔줌으로써 특정한 metal-support interaction을 유도하여 촉매 성능을 개선할 수 있다. 제어 된 환원 처리를 적용하여, Pt 나노 입자가 CeO2 과층에 갇힌 촉매(Pt in CeO2)를 제조하는 데 성공하였다. Pt가 기상에 노출된 Pt/CeO2 촉매(Pt on CeO2)는 우수한 고온 WGSR 활성을 나타내지만, Pt가 부산물로서 메탄(CH4)의 형성을 촉진한다는 문제가 있다. 반면에, Pt in CeO2 촉매는 Pt가 노출되어 있지 않아서 CH4이 생성되지 않았고, 높은 고온 WGSR 활성도 나타내었다. 흥미롭게도, 얇은 CeO2 과층은 WGSR 활성이 있었지만, 두꺼운 CeO2 과층은 WGSR 활성이 없었다. Pt의 영향으로 얇은 CeO2 과층에는 oxygen vacancy 농도가 높았는데, oxygen vacancy가 WGSR 반응의 중간체인 한 자리 폼산염(monodentate formate)의 형성을 촉진하기 때문에 얇은 CeO2 과층에서만 우수한 WGSR 활성이 나타난 것으로 분석된다.Chapter 1. Introduction 1 1.1. Necessities to study the control of metal-supporting interactions in heterogeneous catalysts 1 1.2. CO oxidation 3 1.3. Water-Gas-Shift reaction 4 1.4. Objectives 5 Chapter 2. How Pt interacts with CeO2 under the reducing and oxidizing environments at elevated temperature? The origin of improved thermal stability of Pt/CeO2 compared to CeO2 7 2.1. Introduction 7 2.2. Experimental 10 2.3. Results 14 2.3.1. Position of Pt on CeO2 under oxidizing and reducing condition 14 2.3.2. The role of Pt-O-Ce bond in the thermal stability of CeO2 24 2.3.3. Pt-CeO2 interaction under the oxidizing environment 32 2.4. Discussion 36 Chapter 3. Weakening the metal-support interaction to improve catalytic activities of PGM supported catalysts (Pt/CeO2&Pt/TiO2) 40 3.1. Introduction 40 3.2. Experimental 44 3.3. Results 52 3.3.1. The CO oxidation ability of Pt(2)/CeO2 and CeO2 52 3.3.2. The influence of the change in Pt-CeO2 interaction induced by the thermal treatment of CeO2 prior to the Pt loading 54 3.2.2.1. The influence on the Pt sintering behavior 54 3.3.2.2. The influence on the CO oxidation ability 56 3.2.2.3. The relationships between the Pt dispersion and the CO oxidation ability 59 3.3.3 Chemical states of the Pt species on CeO2, (800C)CeO2 and γ-Al2O3 supports 67 3.3.3.1 Investigation of the chemical states of Pt species by CO chemisorption 67 3.3.3.2. Investigation of the chemical states of Pt species by XP spectroscopy 71 3.3.3.3. Investigation of the chemical states of Pt species by H2-TPR 75 3.3.4. S dopants on TiO2 surface weakens the Pt-TiO2 interaction and improves the CO oxidation ability of Pt/TiO2 catalysts 78 Chapter 4. Synthesis of Pt nanoparticles encapsulated in CeO2 over-layers by controlled reduction treatment to suppress CH4 formation in high-temperature Water-Gas-Shift reaction 84 4.1. Introduction 84 4.2. Experimental 87 4.3. Results 92 4.3.1. Synthesis of Pt in CeO2 with the controlled reductive treatment 92 4.3.2. Comparison of WGSR activity and CH4 yield of Pt on CeO2 and Pt in CeO2 catalysts 100 4.3.2.1. WGSR activity 100 4.3.2.2. CH4 yield 102 4.3.2.3. R and NC treatments at other temperatures 104 4.3.3. Why only Pt(2)/CeO2 800NC has the WGSR activity, not Pt(2)/CeO2 800R? 112 Chapter 5. Summary and Conclusions 122 Bibliography 125 국 문 초 록 133Docto

압력을 제어하는 소프트 리소그래피를 이용한 폴리머 싱글모드 광도파로의 설계 및 제작에 관한 연구

학위논문(석사) -- 서울대학교대학원 : 융합과학기술대학원 융합과학부 나노융합전공, 2013. 8. 김창순.본 연구에서는 잔여층이 없는 코어 패턴을 가진 폴리머 싱글모드 광도파로를 설계 및 제작하였다. Effective index method와 finite element meth를 이용하여 싱글모드의 조건을 구해냈고, 이를 활용해 광도파로의 구조를 설계하였다. 소프트 리소그래피 공정에 압력을 조절하는 과정을 추가함으로써, 1550 nm영역에 적합한 잔여층이 없는 채널 형태의 싱글모드 제작하였다. 포토리소그래피 공정을 이용한 포토레지스트(SU-8) 패턴을 마스터 몰드로 이용하였고, 복제몰드로 PDMS를 이용함으로 압력에 따라 광도파로의 코어 모양을 바꿀 수 있게 하였다. 3.25 kg/cm2 이상의 압력을 인가함으로 전파손실의 원인이 되는 잔여층을 제거 할 수 있었고, 그 이상의 압력에서 코어 패턴의 변화를 고찰함으로 fundamental mode에 적합한 광도파로를 만들어 낼 수 있었다. 그럼으로 싱글모드 광도파로를 제작함에 있어 발생되는 두 가지 제약을 해결했다. 먼저 광도파로 코어를 제작하는 단계에 있어 포토리소그래피 공정을 사용하지 않기 때문에 감광성 물질을 사용해야 하는 한계를 벗어날 수 있었다. 또한 수 마이크로 크기의 사각형 형태의 광도파로를 성공적으로 제작함으로 싱글모드 조건을 만족하기 위한 코어와 클래딩의 굴절를 차이를 넓힐 수 있었다. 광도파로의 광학적 특성은cut-back method를 이용하여 전파손실 측정하고, 코어에 가이드 된 빛을CCD 카메라를 이용해 IR 이미지를 확인함으로 파악하였다. 싱글모드 광도파로의 정확한 전파손실 측정을 위해 piezo-stage, detector을 이용한 피드백 알고리즘 이용하여 구성하고, 자동정렬 시스템을 구축함으로 데이터의 신뢰도를 높였다. Chem optics사의 Zpu13-430, Zpu13-44을 이용하여 광도파로를 제작하였고, 이를 SEM, OM 이미지를 통해 확인하였다. 광도파로는 0.18~0.20 dB/cm 의 전파손실을 나타냈고, 1550 nm의 빛을 효과적으로 가이드하였다.In this study, we investigate the design of a polymer single mode waveguide which does not have residual layer of core pattern. The single mode conditions were calculated using effective index method and finite element method. We fabricated polymer single mode waveguide (λ = 1550 nm) based on the design using soft lithography and additional pressure control. The master mold and replica mold consist of negative photoresist (SU-8) and PDMS, respectively. By applying a pressure of 3.43 kg/cm2 on PDMS, we eliminate the residual layer of core that brings about an additional propagation loss. In addition, we fabricated an appropriate waveguide for the fundamental mode by identifying the shape of core, especially in the higher pressure region. We resolve two critical constraints. The first problem is limitation of material which is used in core pattern of single mode waveguide by the photolithography method. The other constraint is the small difference between refractive indices of the core and cladding to satisfy single mode conditions of waveguide. These constraints are resolved using soft lithography with additional pressure control. We successfully demonstrate fabrication of rectangular waveguide in several micrometers using this method. Thus, it enables us to apply various other materials, and we extend the required index contrast of core and cladding layers. The optical characteristics of the waveguide were evaluated in terms of propagation loss and IR image from the detector of guided light at 1550nm. The propagation loss was measured using cut-back method. For the improvement of data accuracy, we use the novel feed-back algorithm that composed of piezo-stage and IR detector. We also built an auto-alignment system. The waveguide was fabricated using Zpu13-430 and Zpu13-440 which were purchased from Chem Optics, and we observed it using microscopes. These waveguides show a propagation loss of 0.18~0.20 dB/cm and can effectively guide light at 1550 nm.Abstract ⅰ Contents ⅳ List of schemes and figures ⅵ 1.Introduction 1 1.1 Optoelectronic circuits and optical waveguides 1 1.2 Lithography technology for polymer waveguide 3 1.3 Rectangular polymer waveguide with single mode conditions 5 2. Optical waveguide theory and design 7 2.1 Guided mode in optical waveguide 7 2.2 Effective index method at rectangular waveguide 8 2.3 Simulation and design of rectangular waveguide 16 3. Fabrication 24 3.1 Material and characterization 24 3.2 Photoresist mold and PDMS stamp 25 3.3 Rectangular waveguide with non-residual core layer 31 3.4 Preparation of SEM samples 34 4. Set-up for optical characteristic of waveguide 35 4.1 Set-up for waveguide propagation loss measurement 35 4.2 Algorithm of automatic alignment system 40 5. Results and Discussion 44 5.1 Rectangular single mode waveguide with non-residual core layer 44 5.2 Optical characteristic of waveguide 50 6. Conclusion 54 Reference 56 초록(국문) 60석

Inhibition of Radiation-Induced PFN2 by Exosomal miR-3065-5p : A Mechanism to Limit Lung Cancer Aggressiveness

Profilin-2 (PFN2), a cytoskeletal regulator associated with tumor aggressiveness, has been implicated in radiation-induced tumor progression in lung adenocarcinoma (LUAD). This study aimed to elucidate whether exosomal miR-3065-5p regulates PFN2 expression and modulates tumor-promoting responses following irradiation. Integrated proteomic and microRNA array analyses of irradiated A549 cells identified PFN2 as a radiation-inducible protein and miR-3065-5p as its potential upstream suppressor. Functional assays revealed that radiation increased PFN2 expression both intracellularly and within secreted exosomes, which in turn enhanced proliferation, migration, and angiogenesis- related gene expression in recipient tumor and endothelial cells. Exosome-mediated PFN2 transfer significantly promoted aggressive phenotypes through a bystander effect, particularly in PFN2-low models such as EKVX cells. Treatment with a miR-3065-5p mimic suppressed PFN2 expression, reduced exosome-mediated endothelial activation and transmigration, and inhibited tumor cell motility and proliferation. In vivo, administration of the mimic attenuated tumor growth, decreased Ki-67 expression, and suppressed angiogenesis in an A549 xenograft model. These findings suggest that radiation-induced downregulation of miR-3065-5p promotes PFN2-driven tumor progression via exosomal signaling, and that restoring miR-3065-5p levels may offer a promising strategy to mitigate adverse microenvironmental effects of radiotherapy in LUAD. Key words: NSCLC, profilin-2, PFN2, miR-3065-5p, radiotherapy, radiation induced tumor progressionDocto

Optimal all-to-all-broadcasting algoritms on meshes and recursive circulants

학위논문(석사) - 한국과학기술원 : 전산학과, 1994.2, [ 42 p. ]한국과학기술원 : 전산학과

다각형에서의 가시기반 경로계획 알고리즘

학위논문(박사) - 한국과학기술원 : 전산학과, 1999.8, [ ii, 104 p. ]Path planning in an environment cluttered with obstacles is a basic problem in computational geometry and robotics. Recently, researches on the visibility-based path planning algorithms have attracted much attention, where the robot (or a person) has visibility. These researches divides into two categories: online navigations and pursuit-evasions. In online navigation problems, the robot has to find a target or explore the environment without knowing the geometry of the obstacles. In pursuit-evasions, the robot with visibility has to find a mobile target. In this thesis, we deal with various versions of the visibility-based path planning problems. These problems are natural extensions of the well-known geometric problems including the shortest path problem and watchman route problem and the art gallery problems. In the first part, we consider an online navigation problem, called online kernel-search problem. The online kernel-search problem is for a mobile robot with 360° visibility to move from a starting point s to the closest kernel point κ within an unknown star-shaped polygon. The goal is to minimize the ratio of the distance traveled by the robot to the length of the shortest s-t path. Icking and Klein first introduced this problem and presented a very intuitive strategy and showed that their strategy is 5.331-competitive. We show that their strategy is, in fact, π+1(?4.14)-competiive. Since it is known that their strategy is no better than (π+1)-competitive, our new analysis is tight. Next, we present a new simple strategy that is $1+2\sqrt{2};(＜ 3.829)$-competitive. In the second part, we consider visibility-based pursuit-evasion problems stated as follows: given a polygonal region, a searcher with visibility, and an {\em unpredictable} intruder that is arbitrarily faster than the searcher, plan the motion of the searcher so as to see the intruder. In particular, we mainly discuss about the following question. Given a simple polygon with a door (i.e.,...한국과학기술원 : 전산학과

Clinically amyopathic dermatomyositis presenting with isolated facial edema complicated by acute respiratory failure: a case report

Background In clinically amyopathic dermatomyositis, the hallmark cutaneous manifestations are the key to diagnosis. We report a case of clinically amyopathic dermatomyositis which presented with facial edema as the sole cutaneous manifestation and was later complicated by acute respiratory failure leading to death. Case presentation A 58-year-old woman presented with edema of the face that had developed approximately one year ago. There was no weakness in the extremities, and the serum creatine kinase level was within normal range. On MRI, there was diffuse edematous change in the bilateral masticator and extra-ocular muscles, accompanied by subcutaneous fat infiltration in the face. A shared decision was made to defer muscle biopsy in the facial muscles. The facial swelling almost resolved with medium-dose glucocorticoid therapy but relapsed in days at glucocorticoid doses lower than 15 mg/day. Combination therapy with either azathioprine, mycophenolate, or methotrexate was not successful in maintaining clinical remission, and the swelling became more severe after relapses. A US-guided core-needle biopsy was subsequently performed in the right masseter muscle. On pathologic examination, there was a patchy CD4 + T cell-dominant lymphoplasmacytic infiltration in the stroma, necrosis of the myofibrils and prominent perifascicular atrophy. Based on those findings, a diagnosis of clinically amyopathic dermatomyositis was made. Therapy with gamma-globulin was not effective in maintaining remission. In the sixth week after starting rituximab, she presented to emergency room with altered mental state from acute respiratory failure. Despite treatment with antibiotics, glucocorticoid pulse, cyclosporin, and polymyxin B-immobilized fiber column direct hemoperfusion, she died three weeks later from persistent hypoxemic respiratory failure. Conclusions This case showed the full spectrum and severity of internal organ involvement of dermatomyositis, although the patient presented exclusively with subcutaneous edema limited to the head. The prognosis may be more closely associated with a specific auto-antibody profile than the benign-looking initial clinical manifestation. Close follow-up of lung involvement with prophylactic treatment for Pneumocystis pneumonia and prompt implementation of emerging therapeutic regimens may improve the outcome