카드뮴 첨가된 α형 산화철에 의한 일산화탄소의 촉매산화 반응연구

이성한,김용록,김돈,정원양,김규홍,최재시 연세대학교 자연과학연구소 1983 學術論文集 Vol.11 No.-

α형 산화철에 카드뮴을 4mol%, 8mol% 및 12mol%로 각각 첨가시켜 외성영역의 특성을 갖는 산화물들을 제조하였다. 이 산화물들을 촉매로한 일산화탄소의 산화반응 속도론적 연구를 통하여 본산화물의 결함구조, CO 산화반응에 대한 촉매성 및 불순물 첨가효과등을 조사하였다. 또한 450℃에서 O_2 및 CO를 여러압력으로 도입시켜 Cd-doped α-Fe_2O_3의 전기전도도를 측정하고 이를 반응속도론적 데이타와 결부시켜 본산화물상에서 CO 의 산화반응 메카니즘과 율속단계를 제안하였다. 반응온도범위 350~460℃에서 산출된 활성화에너지는 10.1~11.3kcal.mol^-1이었다. CO_2흡착에 의한 CO산화반응의 억제효과는 본실험의 반응온도 영역인 350~460℃에서는 나타나지 않았으며 CO 산화반응의 전반응속도 차수는 1.5차로서 일산화탄소에 대해서는 1차, 산소에 대해서는 0.5차임이 밝혀졌다. 반응속도론적 데이타와 전기전도도 데이타에 의해 본촉매의 활성은 카드뮴도프로 인해 생성된 산소공위(Vo"-2e^-)에 기인한 것이었다. 카드뮴의 첨가량이 증가할수록 반응속도는 증가하였으나 12mol% 이상의 카드뮴이 첨가된 산화철상에서는 반응속도가 크게 증가하지 않는 것으로 나타났다. CO와 O_2는 근본적으로 화학흡착하며 CO의 흡착자리는 격자산소(O^-2_(latt))와 기흡착원산소 (O^-_(ads)), 그리고 O_2의 흡착자리는 산소공위(Vo"-2e^-)로 밝혀졌다. The α-Ferric oxide containing 4, 8, and 12mol% with cadmium were prepared. The oxidation rates of carbon monoxide in the presence of these oxide systems were measured to investigate the defect structure, the catalytic activity for the oxidation of carbon monoxide, and the impurity effect. The conductivity was also measured at 450℃ under the various pressures of oxygen and carbon monoxide. From the agreement between the kinetic and conductivity data, the oxidation mechanism of carbon monoxide and the rate determining step on this oxide catalyst were suggested. In the temperature range from 350 to 460℃, the calculated activation energy for the CO oxidation over Cd-doped α-Fe_2O_3 systems were 10.1∼11.3kcal·mol^-1. The inhibition by an adsorbed CO_2 during the CO oxidation was not observed in the above temperature range. The overall reaction order for the CO oxidation is 1.5; the first order with respect to CO and the one-half order with respect to O_2. The catalytic activity of this oxide system is due to oxygen vacancies induced by Cd-doping. The oxidation rates increase with increasing the amount of dopant and above 12mol%, however, don't highly increased. CO and O_2 are essentially chemisorbed as ions and the adsorption sites for CO are the lattice oxygens (O^2-_(latt)) and prechemisorbed oxygens (O^-_(ads)), the adsorption site for O_2 is the oxygen vacancies (Vo¨-2e^-).

NiO-ZnO-Fe_2O_3 System의 물성에 관한 연구

최재시,김규홍,전종호,박광하 연세대학교 자연과학연구소 1984 學術論文集 Vol.13 No.-

NiO-Z_nO-Fe_2O_3계에 대하여, Solid Solution 을 이루는 적합한 조성관계와 여러가지 비율로 혼합한 페라이트에 대하여 자성, 전도성을 측정하였다. 각 시료의 비저항은 3×10^-6Ωcm이었고, α-Fe_2O_3, NiO, ZnO의 조성비가 50, 15, 35mol %인 페라이트가 가장 높은 μ와 Q값을 갖는다. physical-chemical properties and the best composition of the solid solution of the NiO-ZnO-Fe_2O_3 system were checked by Q-meter and electrometer. The resistivity of each sample is 3×10^-6Ωcm, and the best composition of nickel ferrite for radio frequency use is α-Fe_2O_3:NiO:ZnO=50:15:35(mol%).

금속산화물 반도체 In_2O_3 촉매에 의한 일산화탄소의 산화반응

이성한,허권,전종호,김규홍,최재시 연세대학교 자연과학연구소 1985 學術論文集 Vol.14 No.-

순수한 In_2O_3, 환원된 In_2O_3, 그리고 NiO를 도프시킨 In_2O_3를 촉매로하여 CO의 산화반응을 433-513K 온도영역에서 실시하였다. 새로 도입된 시료상에서 산화반응은 촉매활성이 다른 두 영역을 나타내었다. 초기반응 단계에서는 Roginsky-Zcldovich 속도식에 잘 일치하며 활성화 에너지는 37.2kJ mol^-1이고, 촉매활성이 일정하게 나타나는 두번째 반응단계에서는 전반응차수가 1차이며 활성화 에너지는 27.2kJ·mol^-1로서 CO_2에 의한 억제효과를 나타내었다. CO_2trap을 사용한 결과 전반응 차수는 1.5차로서 CO에 대해 1차, O_2에 대해 0.5차의 의존성을 보였다. 결정내의 산소결함농도가 반응속도를 증가시킬 수 있는 요인으로 밝혀졌으며 CO의 흡착자리는 격자산소(O^2-_0)이고 O_2의 흡착자리는 촉매의 처리과정과 제조과정에 의해 형성된 산소공위 (V^x_o)로서 밝혀졌다. 반응속도론적 데이타와 전기전도도 데이타를 결부시켜 산화반응 메카니즘을 제안하였으며 산소공위가 반응속도에 미치는 효과및 산소공위에 O_2가 흡착하는 과정이 속도결정단계임을 설명하였다. A kinetic study of CO oxidation on pure, reduced, and NiO-doped Indium Sesquioxide systems was carried out in the temperature range of 433-513 K. Catalytic oxidation showed two step regions. First initial step of fresh sample followed the Roginsky-Zeldovich kinetics with the apparent activation energy of 37.2 kJ.mol^-1. The second step which showed a constant activity was found to be the approximate first order kinetics with the apparent activation energy of 27.2 kJ.mol^-1 and then the inhibition by produced CO_2 was observed. By use of CO_2 trap, however, the oxidation kinetics was found to be the first order with respect to CO and the one-half order to O_2. The rate determining step was considered as the adsorption process of oxygen on the surface of catalyst. The site for CO adsorption was the lattice oxygen (O_o^2-) and the site for O_2 adsorption was the oxygen vacancy formed by vacuum activation, hydrogen reduction, and NiO doping. It was believed that the oxygen vacancy was responsible for the catalytic activity for CO oxidation.

Syntheses and Properties of the High-Tc Superconductive Bi_{2-x}Mo_xSr_2Ca_2Cu_3O_y$ System

Keu Hong Kim,Jong Tae Lim,Seung Koo Cho,Byoung Chan Kwak,Don Kim,Jae Shi Choi Korean Chemical Society 1990 Bulletin of the Korean Chemical Society Vol.11 No.1

The superconducting properties have been studied for high-Tc superconductors of the $Bi_{2-x}Mo_xSr_2Ca_2Cu_3O_y$ system (x = 0.03-0.30). The crystal structure is pseudo tetragonal with the average lattice parameters a = 5.38 ${\AA}$, b = 5.44 ${\AA}$ and c = 30.6 ${\AA}$. All samples exhibit superconductivity with Tc offset at 79 K and Tc onset at 90-115 K. The Tc onset point decreases with increasing x, but the Tc offset points are nearly the same for all samples. Scanning electron micrographs show a special growth behavior of the grains with a plate shape. It is suggested that the decrease in Tc onset points with substitution of Mo for Bi is due to the decrease in lattice parameters and to the p-orbital of Mo. It is concluded that Mo does not play a crucial role in the superconducting transition of the $Bi_2Sr_2Ca_2Cu_3O_y$ system.

Kinetics and Mechanism of the Oxidation of Carbon Monoxide on CoO-$\alpha-Fe_2O_3$ Catalysts

Kim, Keu Hong,Choi, Jae Shi,Kim, Young Bae Korean Chemical Society 1987 Bulletin of the Korean Chemical Society Vol.8 No.5

The oxidation of carbon monoxide by gaseous oxygen on 0.53, 1.02, and 1.51 mol $\%$CoO-doped $-Fe_2O_3$ catalysts has been investigated in the temperature range from 340 to 480$^{\circ}C$ under various CO and $O_2$ partial pressures. The oxidation rates have been correlated with 1.5-order kinetics; the 0.5-order with respect to $O_2$ and the first-order with respect to CO. In the above temperature range, the activation energy is 0.34 $\pm$ 0.01 eV${\cdot}$$mol^{-1}$. The electrical conductivity of 0.53, 1.02, and 1.51 mol %CoO-doped $\alpha$-$Fe_2O_3$ has been measured at 350$^{\circ}C$ under various $P_{CO}and $P_{O_2}$. From the conductivity data it was found that $O_2$ was adsorbed on Vo formed by doping with CoO, while CO appeared essentially to be chemisorbed on the lattice oxygen of the catalyst surface. The proposed oxidation mechanism and the dominant defect were supported by the agreement between the kinetic data and conductivities.

Electronic Localization Due to Fluorine in $YBa_2Cu_3O_xF_y$ Superconducting Materials

Keu Hong Kim,Don Kim,Seung Koo Cho,Yong Wook Choi,Jong Sik Park,Jae Shi Choi Korean Chemical Society 1990 Bulletin of the Korean Chemical Society Vol.11 No.3

High-Tc superconducting materials, $YBa_2Cu_3O_xF_y$ with $x{\leq}6.89\;and\;0.25{\leq}y{\leq}0.35$, were prepared and Studied by X-ray diffraction, magnetic susceptibility and resistivity measurement. Under given conditions, reproducible resistivities were obtained, which increased with increase in the amount of fluorine. The introduced fluorine atoms were found to be localized in pyramidal Cu-O units rather than in Cu-O chains. It is suggested that the localized fluorine atom increases the electronic lolcalization of the superconducting electrons.

Catalytic Activity of $Nd_{1-x}Sr_xCoO_{3-y}$ on the Oxidation of Carbon Monoxide

Kim, Keu-Hong,Kim, Seong-Han,Lee, Dong-Hoon,Kim, Yoo-Young,Choi, Jae-Shi Korean Chemical Society 1991 Bulletin of the Korean Chemical Society Vol.12 No.1

The catalytic activity of $Nd_{1-x}Sr_xCoO_{3-y}$, $0{\leq}x{\leq}0.75$ and $0.001{\leq}y{\leq}0.103$, on the oxidation of carbon monoxide has been investigated from the structure analyses of the catalysts by X-ray diffraction and infrared spectroscopy and the measurements of the oxidation and adsorption rates of carbon monoxide. The catalytic activity is found to be correlated with Sr substitution (x) and nonstoichiometry (y). The oxidation power of carbon monoxide increases continuously with increasing Sr substitution without oxygen, but increases with Sr substitution up to x = 0.25 and then is almost constant at larger x values up to x = 0.75 with oxygen. This change of catalytic activity is explained by the oxidation-reduction properties of the catalyst due to the variation of nonstoichiometry.

Dopping Effect of Fluorine Atom on the Superconductivity of $YBa_2Cu_3O_{7-x}F_y$

Kim, Keu-Hong,Cho, Seun- Koo,Kim, Yoo-Young,Park, Jong-Sik,Choi, Mu-Yong Korean Chemical Society 1990 Bulletin of the Korean Chemical Society Vol.11 No.5

The normal and fluorinated high-Tc superconducting materials, $YBa_2Cu_3O_{7-x}F_y$with $0.25{\leq}x{\leq}0.55\;and\;0.00{\leq}y{\leq}0.30$, were synthesized to investigate the dopping effect of fluorine atom on the superconductivity of Y123 and studied by X-ray diffraction analysis and electron probe microanalysis, resistivity and thermopower measurements, and polarized micro-Raman spectroscopy. The reproducible micro-Raman spectra were recorded and analyzed. The coherent assignments could be suggested for the spectra of normal and fluorinated samples. The fluorine atoms introduced were found to be substituted for oxygen in pyramidal Cu-O units rather than in Cu-O chains. The unit cell parameters were decreased upon the substitution of oxygen by fluorine atom. From the decreasing cell parameters and Tc, the increasing thermopower, and the possible assignments of the vibrational modes, it could be suggested that the dopping of fluorine atom localizes the superconducting electrons in Y123.

Transport Mechanisms of Holmium Sesquioxide-Yttrium Sesquioxide System

Kim, Keu-Hong,Choi, Jae-Shi,Park, Sung-Ho,Won, Hui-Jun Korean Chemical Society 1985 Bulletin of the Korean Chemical Society Vol.6 No.1

Electrical conductivites of polycrystalline yttrium sesquioxides containing 1.6 and 3.2 mol % of holmium sesquioxdes have been measured from 650 to $1050^{\circ}C$ under oxygen partial pressures of $1{\times}10^{-5}$ to $2{\times}10^{-1}$ atm. Plots of log conductivity vs. 1/T at constant oxygen partial pressures are found to be linear away from the two inflection points. The low- and high-temperature dependences of conductivity show different defect structures of yttrium sesquioxide. The plots of log conductivity vs. log $PO_2$ are found to be linear at $PO_{2'}$s of $10^{-5}$ to $10^{-1} atm. The electrical conductivity dependences on $PO_2$ are found to be $1}5.3$ at $950-1050^{\circ}C$, $\frac{6}{1}$ at $800-950^{\circ}C$ and ($\frac{6.2}{1}$) - ($\frac{6.5}{1}$) at $650-800^{\circ}C$, respectively. The defect structures and conduction mechanisms have been suggested.

Transport Mechanisms and Defect Structures of the System $\alpha$-Fe$_2O_3$-CoO

Kim, Keu-Hong,Lee, Sung-Han,Choi, Jae-Shi Korean Chemical Society 1986 Bulletin of the Korean Chemical Society Vol.7 No.5

The electrical conductivity of the system ${\alpha}-Fe_2O_3-CoO$ was measured in the temperature range 200-1000$^{\circ}C$ and PO$_{2}$ range 10$^{-7}-2{\times}10^{-1}$ atm. Possible defect models were suggested on the basis of conductivity data, which were measured as a function of temperature and of oxygen partial pressure. The observed activation energies were 0.50 eV and 1.01 eV in the low- and high-temperature regions, respectively. The observed conductivity dependences on PO$_{2}$ were ${\sigma}\;{\alpha}\;PO_2^{-1/6}$ in the PO$_{2}$ range $10^{-7}-10^{-4}$ atm and ${\sigma}\;{\alpha}\;PO_2^{-1/4}$ at PO$_{2}$ 's of $10^{-4}-2{\times}10^{-1}$ atm at temperatures from 300-1000$^{\circ}C$. An extrinsic electron conduction due to an Vo defect and an intrinsic electron conduction due to an Fei' defect were suggested at different temperature and oxygen partial pressure regions, respectively.