Surface morphology dependent catalytic reaction on model catalyst and real catalyst = 모델 촉매 및 실제 촉매에서 표면 형상에 따른 촉매활성 반응 메커니즘 연구

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Reconstruction of Besocke-Beetle Type STM The Scanning Tunneling Microscope (STM) is one of the most powerful instrument to visualize the re-al space two dimensional surfaces as atomic resolution. We constructed the Besocke-Beetle type STM which has good vibration resistivity, high resonant frequencies, and simple coarse approach system. We elucidated the principles and construction procedure in this dissertation. The evaluation of construction was conducted by Ge(100) clean surface with atomic scale. Step Induces Dehydrogenation and Stabilization of Formic Acid on Cu(775) Surface Dissociation of formic acid on Cu surface has been intensively studied because the formate ($HCOO^{\ast}$) has been regarded as key intermediate of methanol synthesis and water gas shift (WGS) reaction on $Cu/ZnO/Al_2O_3$ industrial catalyst. According to the recent investigations, step surface is regarded as active sites of those reactions. Thus, characterization of peak position has to be needed. We figured out the dissociation features of formic acid on step edge of Cu(775) surface as well as the corresponding peak position. As a result, formate species form the link structure with interaction between formate on step and on terrace which link structure stabilizes the formate on terrace. Higher desorption temperature at 480 K compared to desorp-tion on terrace (~380 K) also supports this stabilization. One significant observation is the formate transfer from terrace to step in order to reduce the desorption energy. Mechanism of the Surface Hydrogen Induced Conversion of $CO_2$ to Methanol at Cu(111) Step Sites $Cu/ZnO/Al_2O_3$ is an industrially important heterogeneous catalyst for the conversion of $CO_2$ to methanol, which is in world-wide demand and to solve the activation mechanism of catalytically inactive $CO_2$. Recent studies have achieved numerous improvements in active site of catalysts for this process which can be described as 'active copper with step sites' decorated with $ZnO_x$. In spite of these improvements, the mechanism of this process is still unknown, and even its initial stage remains unclear. In this study, we simplified the catalytic system to bare Cu(111) and Cu(775) surfaces in order to systematically determine the mechanistic effects of step sites. The reaction was conducted by using a $CO_2/H_2$ gas mixture at 1 Torr at various temperatures and characterized with infrared reflection absorption spectroscopy (IRRAS). The initial activation of $CO_2$ was found to occur only with the co-adsorption of hydrogen; it cannot on its own be converted into other activated species. This co-adsorbed hydrogen induces the dissociation of $CO_2$ and converts it into CO, surface oxygen ($O^{\ast}$), and surface hydroxyl ($HO^{\ast}$). These species are subsequently converted to carbonate ($CO_3^{\ast}), bicarbonate ($HCO_3^{\ast}$), and formate ($HCOO^{\ast}$). One significant observation is that the number of these formate species on step sites continuously decreases with increases in the number of $CH_2$ species during step wise heating. And continuous reaction is obtained from formate transfer from terrace to step. In addition, instantaneous feature of methoxy ($CH_3O^{\ast}$) was also observed during the evacuation process. These phenomena strongly indicate that formate is an essential intermediate, especially on steps, for the conversion of $CO_2$ to methanol, and that the reduction in its level during this process is due to step-by-step hydrogena-tion. Enhancement of Photo-oxidation Activities Depending on Structural Distortion of Fe-Doped $TiO_2$ Nanoparticles To design a high-performance photocatalytic system with $TiO_2$, it is necessary to reduce the band gap and enhance the absorption efficiency. The reduction of the band gap to the visible range was investigated with reference to the surface distortion of anatase $TiO_2$ nanoparticles induced by varying Fe doping concentrations. Fe-doped $TiO_2$ nanoparticles ($Fe@TiO_2$) were synthesized by a hydrothermal method and analyzed by various surface analysis techniques such as transmission electron microscopy, Raman spectroscopy, X-ray diffraction, scanning transmission X-ray microscopy, and high-resolution photoemission spectroscopy. We observed that Fe doping over 5 wt% gave rise to a distorted structure, i.e., $Fe_2Ti_3O_9$, indicating numerous $Ti^{3+}$ and oxygen-vacancy sites. The $Ti^{3+}$ sites act as an electron trap sites to deliver the electron to $O_2$ as well as introduce the dopants level inside the band gap, resulting in a significant increase in the photocatalytic oxidation reaction of thiol (-SH) of 2-aminothiophenol to sulfonic acid ($SO_3H$) under ultraviolet and visible light illumination.
Advisors
Kwak, Juhyounresearcher곽주현researcher
Description
한국과학기술원 :화학과,
Publisher
한국과학기술원
Issue Date
2016
Identifier
325007
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 화학과, 2016.2,[viii, 72 p. :]

Keywords

STM; IRRAS; formate; 2-Aminothiophenol; Step site; Methanol; photo-oxidation; Band gap; 주사터널링현미경; 표면적외선분광기; 이산화탄소; 포메이트; 타이타니아; 2-아미노싸이오페놀; 스텝 위치; 메탄올; 광산화반응; 밴드갭

URI
http://hdl.handle.net/10203/242140
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=669295&flag=dissertation
Appears in Collection
CH-Theses_Ph.D.(박사논문)
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