중형기공성 니켈-알루미나-지르코니아 촉매 상에서 에탄올의 수증기 개질 반응을 통한 수소 생산

학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2017. 2. 송인규.As a renewable energy, hydrogen has received much attention on the basis of their potential contribution to the sustainable energy development. High energy density and environmental compatibility is main advantages of hydrogen utilization. Hydrogen production technologies can be classified into thermal processes, electrolyte processes, and photolytic processes. Although splitting of water through photo-catalysis and electrolysis is known as an ultimate method for hydrogen production, most hydrogen production is based on LNG (liquefied natural gas) reforming process which is still based on non-renewable fossil fuel system. Therefore, development of hydrogen production technology using renewable source is required to attain sustainability and fuel flexibility. In this situation, hydrogen production by bio-derived liquids reforming has been studied, which is the most viable renewable hydrogen pathway in the near future. Among the bio-derived liquids, ethanol is the most feasible source for hydrogen production in the near term due to its non-toxicity, storage facility, and biodegradable nature. Moreover, bio-ethanol can be used as a source for SOFC vehicle which has potential to become an alternative transportation in the future. As a consequence, ethanol steam reforming is a promising technology for hydrogen production which is expected to mitigate the environmental problems. For steam reforming of ethanol, Ni-based catalyst has been extensively used as a non-noble metal catalyst due to its low cost and high activity in C-C cleavage reaction. In general, Ni/Al2O3 catalyst has been widely employed for steam reforming of ethanol, because Al2O3 has large surface area and strong metal-support interaction with Ni particles. However, Al2O3 support with acidic nature induces ethanol dehydration, leading to coke formation. Therefore, many attempts have been made to increase both catalytic activity and durability of Ni/Al2O3 catalysts through modification of supporting materials. Alkaline earth metal oxides such as MgO and CaO have been used as promoters because they can suppress coke deposition by neutralizing acid sites of Al2O3. Addition of lanthanide oxides can also increase the catalytic activity by promoting gasification reaction of dissolved carbon species on the surface of nickel catalysts. Among various metal oxides, ZrO2 is known to be the effective promoter for Ni/Al2O3 catalysts in the steam reforming of ethanol, because ZrO2 can not only enhance the stability of the catalysts but also promote adsorption and dissociation of water on the surface of nickel catalysts. In this work, in order to achieve efficient catalyst for steam reforming of ethanol, mesoporous nickel-alumina-zirconia catalysts were designed by various catalyst compositions and preparation methods, including epoxide-driven sol-gel method, P123-assissted sol-gel method, supercritical CO2 drying method, and copper addition. First of all, a series of mesoporous nickel-alumina-zirconia xerogel catalysts (denoted as Ni-AZ-X) with different Zr/Al molar ratio (X) were prepared by a single-step epoxide-driven sol-gel method, and they were applied to the hydrogen production by steam reforming of ethanol. Surface area of Ni-AZ-X catalysts decreased with increasing Zr/Al molar ratio due to the lattice contraction of ZrO2 caused by the incorporation of Al3+ into ZrO2. Interaction between nickel oxide species and support (Al2O3-ZrO2) decreased with increasing Zr/Al molar ratio through the formation of NiO-Al2O3-ZrO2 composite structure. Acidity of reduced Ni-AZ-X catalysts decreased with increasing Zr/Al molar ratio due to the loss of acid sites of Al2O3 by the addition of ZrO2. Among the catalysts tested, Ni-AZ-0.2 (Zr/Al = 0.2) catalyst with an intermediate acidity exhibited the best catalytic performance in the steam reforming of ethanol. A series of mesoporous nickel-alumina-zirconia xerogel catalysts (denoted as XNiAZ) with different nickel content (X, wt%) were prepared by a single-step epoxide-driven sol-gel method. All the XNiAZ catalysts exhibited a well-developed mesoporous structure and they dominantly showed an amorphous NiO-Al2O3-ZrO2 composite phase, leading to high dispersion of NiO. Nickel surface area and reducibility of XNiAZ catalysts showed volcano-shaped trends with respect to nickel content. Among the catalysts tested, 15NiAZ catalyst with the highest nickel surface area exhibited the best catalytic performance in the steam reforming of ethanol. A mesoporous nickel-alumina-zirconia aerogel (Ni-AZ) catalyst was prepared by a single-step epoxide-driven sol-gel method and a subsequent supercritical CO2 drying method. For comparison, a mesoporous alumina-zirconia aerogel (AZ) support was prepared by a single-step epoxide-driven sol-gel method, and subsequently, a mesoporous nickel/alumina-zirconia aerogel (Ni/AZ) catalyst was prepared by an incipient wetness impregnation method. Although both catalysts retained a mesoporous structure, Ni/AZ catalyst showed lower surface area than Ni-AZ catalyst. From TPR, XRD, and H2-TPD results, it was revealed that Ni-AZ catalyst retained higher reducibility and higher nickel dispersion than Ni/AZ catalyst. In the hydrogen production by steam reforming of ethanol, Ni-AZ catalyst with superior textural properties, high reducibility, and high nickel surface area showed a better catalytic performance than Ni/AZ catalyst. A series of mesoporous nickel-alumina-zirconia xerogel (denoted as X-NAZ) catalysts were prepared by a P123-assisted epoxide-driven sol-gel method under different P123 concentration (X, mM), and they were applied to the hydrogen production by steam reforming of ethanol. All the catalysts retained a mesoporous structure. Pore volume of the catalysts increased with increasing P123 concentration. Nickel surface area and ethanol adsorption capacity of X-NAZ catalysts exhibited volcano-shaped trends with respect to P123 concentration. Among the catalysts tested, 12-NAZ catalyst with the highest Ni surface area and the largest ethanol adsorption capacity showed the best catalytic performance in the steam reforming of ethanol. A series of mesoporous copper-nickel-alumina-zirconia (XCNAZ) xerogel catalysts with different copper content (X, wt%) were prepared by a single-step epoxide-driven sol-gel method, and they were applied to the hydrogen production by steam reforming of ethanol. All the calcined XCNAZ catalysts retained a mesoporous structure, and their surface area increased with increasing copper content. Metal-support interaction of XCNAZ catalysts decreased with increasing copper content due to the electronic effect. Nickel surface area and ethanol adsorption capacity of the catalysts exhibited volcano-shaped trends with respect to copper content. Among the catalysts, 0.2CNAZ catalyst exhibited the highest nickel surface area and the largest ethanol adsorption capacity. Catalytic performance in the steam reforming of ethanol over XCNAZ catalysts showed a volcano-shaped trend with respect to copper content. This result was well matched with the trend of nickel surface area. Among the catalysts tested, 0.2CNAZ catalyst with the highest nickel surface area showed the highest hydrogen yield. In summary, various physicochemically-modified nickel-alumina-zirconia catalysts were designed and they were applied to the hydrogen production by steam reforming of ethanol in this study. In order to elaborate the effect of physicochemical properties of catalyst on catalytic performance in the steam reforming of ethanol, several characterizations such as N2 adsorption-desorption, XRD, TPR, TEM, XPS, H2-TPD, EtOH-TPD, and in-situ FT-IR analyses were conducted. It was concluded that nickel surface area served as a crucial factor determining the catalytic performance in the hydrogen production by steam reforming of ethanol.Chapter 1. Introduction 1 1.1. Hydrogen energy 1 1.2. Hydrogen production and utilization 3 1.3. Steam reforming of ethanol 8 1.4. Objective 15 Chapter 2. Experimental 19 2.1. Preparation of catalysts 19 2.1.1. Preparation of mesoporous nickel-alumina-zirconia xerogel catalyst with various zirconium/aluminum molar ratio 19 2.1.2. Preparation of mesoporous nickel-alumina-zirconia xerogel catalyst with various nickel content 22 2.1.3. Preparation of mesoporous nickel-alumina-zirconia aerogel catalyst by carbon dioxide supercritical drying 23 2.1.4. Preparation of mesoporous nickel-alumina-zirconia xerogel catalyst by P123-assisted sol-gel method 26 2.1.5. Preparation of mesoporous copper-nickel-alumina-zirconia xerogel catalyst with various copper content 28 2.2. Characterization 30 2.2.1. Physicochemical properties 30 2.2.2. Crystalline structure 30 2.2.3. Metal-support interaction 30 2.2.4. Acid property 31 2.2.5. Morphological feature 32 2.2.6. Hydrogen chemisorption studies 32 2.2.7. Ethanol adsorption-desorption studies 33 2.2.8. Carbon deposition on used catalysts 34 2.3. Hydrogen production by steam reforming of ethanol 35 Chapter 3. Results and Discussion 38 3.1. Mesoporous nickel-alumina-zirconia xerogel catalyst with various zirconium/aluminum molar ratio 38 3.1.1. Textural properties of calcined catalysts 38 3.1.2. Crystalline structures of calcined catalysts 41 3.1.3. Reducibility and metal-support interaction 43 3.1.4. Characterization of reduced catalysts 45 3.1.5. Catalytic performance in the steam reforming of ethanol 50 3.2. Mesoporous nickel-alumina-zirconia xerogel catalyst with various nickel content 56 3.2.1. Textural properties of calcined catalysts 56 3.2.2. Crystalline structure and reducibility 59 3.2.3. Characterization of reduced catalysts 63 3.2.4. Catalytic performance in the steam reforming of ethanol 66 3.2.5. Effect of total feed rate on the catalytic performance 74 3.3. Mesoporous nickel-alumina-zirconia aerogel catalyst prepared by carbon dioxide supercritical drying 76 3.3.1. Textural properties of calcined catalysts 76 3.3.2. Crystalline structure and reducibility 80 3.3.3. Characterization of reduced catalysts 83 3.3.4. Catalytic performance in the steam reforming of ethanol 90 3.3.5. Effect of reaction temperature on catalytic performance 95 3.4. Mesoporous nickel-alumina-zirconia xerogel catalyst prepared by P123-assisted sol-gel method 100 3.4.1. Textural properties of calcined catalysts 100 3.4.2. Crystalline structure and reducibility 103 3.4.3. Characterization of reduced catalysts 105 3.4.4. Ethanol adsorption study on the reduced catalysts 112 3.4.5. Catalytic performance in the steam reforming of ethanol 116 3.5. Mesoporous copper-nickel-alumina-zirconia xerogel catalyst with various copper content 123 3.5.1. Characterization of calcined catalysts 123 3.5.2. Characterization of reduced catalysts 129 3.5.3. Ethanol adsorption study on the reduced catalysts 137 3.5.4. Catalytic performance in the steam reforming of ethanol 142 Chapter 4. Conclusions 147 Bibliography 151 초 록 163Docto

Optimal scheduling of drug treatment for HIV infection : receding horizon control using continuous dose control

Thesis (master`s)--서울대학교 대학원 :전기·컴퓨터공학부,2003.Maste

The Failure of Controlling Government Bureaucracy: A Case Study of the Korean National Intelligence Services Political Intervention in the 2012 Presidential Election

이 연구는 2012년 제18대 대통령 선거 당시 국가정보원이 온라인 공간에서 특정 정당 및 정치인을 지지 및 반대하는 활동으로 정치적 중립 의무를 위반하였던 사건을 분석한다. 파당적 행위가 한 정부 조직의 정상업무로 간주될 수 있었던 논리와 방식을 문헌 분석과 재판 참여관찰을 통해 귀납적으로 도출하였다. 분석 결과, 사건의 발생 조건은 과거부터 정권안보 업무를 수행해왔던 국정원의 운영이 여전히 불투명한 현실, 집권성이 강한 국정원에 대통령 최측근이 기관장으로 부임하면서 대통령과의 권력거리가 밀접해진 상황, 그리고 대북 사이버심리전이라는 선례 없는 새 업무의 내용과 기준이 여전히 모호한 상황 등으로 볼 수 있었다. 이러한 조건 속에서 국정원의 정치개입 활동이 작동했던 방식은 국정원장의 추상적 정치개입 지시가 조직위계에 따라서 구체적인 업무지침이 되었고, 외주화 및 실적 평가, 대량 확산기술의 사용 등 효율적 업무실행 체계가 운영되면서 정상 업무로 취급되었다. 또한 정치개입 활동을 정당화한 논리는 국가 안보의 절대시, 국정원은 첩보기관으로서 타 기관과 다르다는 예외주의, 업무 범위의 지나친 확장 해석으로 볼 수 있었다. 그 결과 국정원의 사이버심리전 활동은 국정원 내부에서는 정상적인 업무 활동으로 간주되었고 이로써 국정원은 정치적 요구에 과잉 부응하고 전문직업적 중립 의무는 부차적･방계적 의무로 축소하면서 비파당적 중립성 유지에 실패하였던 것이다. 즉, 제도적 차원에서외부통제 없는 독점적 지위, 행정수반의 강한 지배권이, 조직적 차원에서는 위계적 명령복종 구조와 왜곡된 조직정체성, 업무내용의 모호성이 정치적 중립을 어렵게 한 요인으로 볼 수 있었다.Although political neutrality is one of the most fundamental principles of modern government bureaucracy, it is often violated in reality. This study shows the failure where the Korean government bureaucracy was involved in partisan politics during the 2012 Korean presidential election. It turned out that Korean National Intelligence Service (KNIS) influenced public opinion by posting political comments on the internet. These comments supported a candidate from the ruling party and criticized candidates from the opposition. Some agents of the Psychological Operations Group of the KNIS conducted such political actions under orders from the head of the KNIS and claimed that these activities were not illegal and even were part of their official tasks responding to cyber terror attacks from North Korea. However, they were later convicted of violating their duty of political neutrality in an election. Through qualitative analysis, this study determined why they abused their power and how they conducted these partisan activities. It also suggests the organizational and institutional conditions of failure to control bureaucracys power in the context of Korean government

A Qualitative Study on the Political Neutrality of Civil Servants: The Experience of Middle-and-Lower-Ranking Civil Servants in Local Government

본 논문은 지방자치가 실시되면서 지방자치단체의 정치적 중립성 훼손 우려가 높아지는 가운데, 공무원들이 정치적 중립과 관련하여 어떠한 경험들을 했는지, 그 경험의 차원들을 밝혀내고자 하였다. 그리고 현재 상황에서 논의해야 할 정치적 중립에 관한 토론을 제시하는데 목적을 두었다. 질적 분석을 통해 찾아낸 정치적 중립의 차원들은 선거 개입과 동원, 고위 공무원의 재 량권 행사, 노조를 통한 집단적 활동, 각종 매체를 통한 의견 표명, 인맥의 적극적인 동원과 활용, 불합리한 명령에 대한 복종 등과 같이 6가지였다. 정치적 중립에 대한 공무원들의 판단은 단순히 규범적인 수준에 머물지 않고 다층적이었으며, 각각의 범주에 대한 경험들 역시 상호 모순적이었다. 정치적 중립을 명확히 규정하는 것이 쉽지 않았지만 이 연구는 6개 범주 안에 공통으로 작용하는 2가지 담론이 있다는 것을 발견하였다. 첫째는 정치적 중립이라는 것이 정치와 행정의 관계를 설명하기 보다는 행정 내부의 위계적 승진구조를 표현하는 담론이라는 것이며, 둘째는 지방자치의 제도화 과정에서 나타나는 신엽관제의 흐름 때문에 중하위직 공무원의 정체성이 흔들리고 전문성이 위협 받고 있다는 것이다. 담론을 토대로 정치적 중립이 훼손되는 것을 막기 위해서는 단체장이나 기관장에게 주어진 과도한 인사권을 견제할 수 있는 장치를 설계해야 한다는 시사점을 제시할 수 있었다

An Exploratory Analysis of Collective Responsibility and its Determinants: Focused on South Koreas Public Officials

정부 조직에서 다수의 구성원들이 여러 단계를 거치며 수행한 업무가 해롭거나 비난 받을 결과를 도출했을 때, 공직자는 구성원으로서 집단적 책임감을 느낄 것인가. 이 연구는 집단적・복합적으로 수행된 결과에 대해, 법적 잘못을 저지르지 않은 공직자가 구성원으로서의 책임감을 느끼고 문제해결을 위하여 희생을 감수하려는 지를 분석하였다. 공직자의 책임회피에 대한 사회적 비판이 높아지는 현 상황에서, 공직자의 집단적 책임감은 관료제의 수동성과 무관심을 극복하고 적극적인 행정을 제공할 토대가 될 수 있다. 공직자 373명을 대상으로 한 설문조사 결과, 응답자들은 어느 정도 긍정적인 수준의 집단적 책임감을 나타내었다. 더불어 공직자 개인이 지닌 공익에 대한 헌신과 자기희생 성향이 높을 때, 업무처리의 자율성이 높을 때, 업무상의 개인적 책임소재가 명확할 때, 공직자의 집단적 책임감이 높았다. 반면에 집단주의적 조직문화는 영향을 미치지 못하는 것을 발견하였다. 이러한 결과는 공직자의 책임회피가 불명료한 책임의 경계와 낮은 자율성 구조에서 발생하기 쉽고, 집단주의적인 분위기가 구성원에게 조직생활의 안정감을 줄 수 있을지라도 책임을 공유하는데 별다른 영향을 미치지 못함을 보여준다. 개인적 책임이 명료할 때 집단적 책임감이 강화될 수 있으며, 스스로 결정을 내리도록 존중될 때 공직자가 집단적 결과를 수용하고 조직문제를 적극적으로 개선하려는 태도가 나타날 수 있음을 시사한다.Do public officials feel morally responsible for organizational results when they are faced with the problem of many hands -the difficulty of assigning responsibility in organizations in which many different individuals contribute to decisions and policies (Thompson, 2014)? This study explored how public officials perceived and responded to organizational failures in terms of collective responsibility using survey results gathered from South Koreas central and local government officials. The major findings follow. First, public officials in general have an intention of taking collective responsibility for organizational consequences even if they do not have legal responsibility. Second, public officials tend to take collective responsibility if they have a high level of self-sacrifice and commitment to the public interest. They are also likely to take collective responsibility when they have a high degree of autonomy and when they have a clear-cut line of individual responsibility in their task. However, collectivist organizational culture has no statistically significant influence on their perception of collective responsibility.이 논문은 대한민국 교육부와 한국연구재단의 지원을 받아 수행된 연구임(NRF-2016S1A3A2924956)

A Consideration of the Anticipatory Accountability of Government Bureaucracy

이 연구는 정부 관료제가 문제 예방에 무능력한 체계라는 사회적 비판에 직면하여, 예방의 실패는 관료적 예측이 무능하고 역량이 부족하기보다는 예견되는 바를 선제적으로 조치하기 어렵게 만드는 조직적 행태와 제약 때문일 것이라고 전제하였다. 예견되는 실패를 최소화해야 할 정부의 예기적 책무성(anticipatory accountability)을 탐색하기 위하여, 조직의 실패가 예견 가능했다는 인식이 어느 정도 존재하는지, 그러한 인식이 조직 내 책임회피 행태에 영향을 받고 있는지를 중심으로 공무원 설문조사를 수행하였다. 분석 결과는 다음과 같다. 첫째, 응답자의 약 43%가 조직의 실패를 예견할 수 있었다고 응답하여 예견된 실패 현상이 있음을 추론할 수 있었다. 둘째, 예견 가능한 문제의 실패 원인으로 개인의 문제의식과 이견을 표출하기 어려운 조직 분위기를 가장 중요하게 꼽았으며, 전문지식과 자원의 부족으로 인한 예견의 어려움은 상대적으로 낮게 평가하 였다. 셋째, 조직 내 지시로의 책임회피 행태가 강하다고 인식할수록 조직실패가 예견 가능했다는 인식이 높게 나타났다. 이는 지시에 복종하는 계층적 책임을 다하면 자신의 의무를 다한 것이 라는 책임회피적인 인식이 문제의 사전 해결을 제한할 수 있음을 의미한다. 공무원이 지시와 다른 자신의 의견을 부담 없이 표현할 수 있는 제도의 마련이 문제의 예방 차원에서도 중요하다는 것을알 수 있었으며, 이에 근거하여 정부의 예기적 책무성을 높일 수 있는 몇 가지 방안을 제안하였다

Emotional Response of Civil Servants to New Public Management Reform: An Application of Q-Methodology

본 연구는 신공공관리적 행정개혁으로 인한 공무원의 경험과 그 대응모습이 어떠한지를 분석하였다. 신공공관리적 행정개혁의 대표적 제도인 성과급제도를 사례로 공무원 대응의 실제와 논리를 파악하고 그 유형을 나누어 보았다. 선행연구에서 공무원의 대응을 인지적 차원 중심으로 분석해왔다면 본 연구는 경쟁과 차별보상 상황이 공무원들의 정서적 상태에도 중요한 영향을 미쳤을 것으로 가정하고 대응의 정서적 차원을 함께 분석하였다. Q방법론과 인터뷰를 통한 분석결과, 공무원들의 상이한 반응을 발견하였는데 일부는 성과급제도가 정치적 상징의 의미로 충분하다며 축소재평가하고 있었고, 다른 일부는 기회주의적으로 인정할 현실질서로 여기면서 부정적 정서로부터 거리를 두려하였으며, 또 다른 일부는 무력감, 박탈감, 위화감 등에 강하게 정서이입하고 있었다. 본 연구결과는 공무원들의 대응이 다차원적 특성이 있음을 보여주며 대응의 다양성에 기반한 인사관리의 필요성을 제시한다. Over the last decade, the Korean government has been trying to achieve high performance with the introduction of New Public Management reform measures. Pay for performance seems to be a representative case of NPM reform initiatives. This study has the intention of analyzing how pay for performance has been accepted by civil servants under the traditional hierarchical government bureaucracy. In particular, it examines their multi-dimensional responses including cognitive and emotional aspects. For this purpose, it develops a substantive model based on Q methodology. The research results show that civil servants experience negative emotions such as a sense of powerlessness, a sense of incongruity, and a sense of deprivation when pay for performance is implemented. Moreover it reveals that the responses of the civil servants can be divided into three types: the symbolic rationalizing type, the opportunity recognizing type, and the alienated opposing type. The first type emphasizes the symbolic meaning of the NPM reform and rationalizes the informal operation of pay for performance. They seem to reappraise pay for performance positively. The second type recognizes and accepts its benefits although they experience negative emotions. They tend to be opportunistic and try to avoid and ignore their emotions. The third type shows cynical hostility to pay for performance and realizes that they lose their strong bonds and become alienated. They are able to empathize with the negative emotions. Therefore, this study shows that civil servants cope with these emotions in three different ways: positively reappraising emotions, keeping distance from them, and empathizing with them. We should consider that negative emotions are at the center of civil servants` responses to pay for performance