• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제4권2호
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• pp.95-102
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• 2000

Methane combustion over perovskite-type oxides prepared using the malic acid method was investigated. To enhance the catalytic activity, the perovskite oxides were modified by the substitution of metal into their A or B site. In addition, the reaction conditions, such as the temperature, space velocity, and partial pressure of the methane were varied to understand their effect on the catalytic performance. With the LaCoO3-type catalyst, the partial substitution of Sr or Ba into site A enhanced the catalytic activity in the methane combustion. With the LaBO3(B=Co, Fe, Mn, Cu)-type catalyst, the catalytic activities were exhibited in the order of Co>Fe Mn>Cu. Futhermore, the partial substitution of Co into site B enhanced the catalytic activity, whereas an excess amount of Co decreased the activity. The surface area and catalytic activity of the perovskite catalysts prepared using the malic acid method showed higher values than those prepared using the solid reaction method. The catalytic activity was enhanced with decreased methane concentration and with a decrease in the space velocity.

• 청정기술
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• 제18권3호
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• pp.259-264
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• 2012

페롭스카이트형 산화물을 능금산법으로 합성하여 TG/DTA, XRD, XPS, TEM 및 $H_2$-TPR 등에 의해 특성분석을 하였고, 벤젠의 연소반응에서의 활성을 조사하였다. 대부분의 촉매들은 페롭스카이트 결정구조를 잘 가지고 있었으며 15에서 70 nm의 크기를 나타내었다. $LaMnO_3$ 촉매가 가장 높은 활성을 보여주었고 $350^{\circ}C$에서 거의 100%의 전환율을 나타내었다. 반응활성을 증가시키기 위해 페롭스카이트 산화물의 A-와 B-위치에 다른 금속이온의 치환을 행하였다. $LaMnO_3$ 촉매의 A-위치에 Sr을 일부분 치환시키면 벤젠의 전환율이 증가하였다. 또한, B-위치에 Co 및 Cu 이온의 치환 역시 촉매 활성을 증가시켰고, $LaMn_{1-x}B_xO_3$ (B = Co, Fe, Cu)형 페롭스카이트에서 촉매활성은 Co > Cu > Fe의 순서로 감소하였다.

• Journal of Microbiology and Biotechnology
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• 제9권1호
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• pp.62-69
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• 1999

In order to investigate the critical amino acid residues involved in the catalytic activities of $\beta$-cyclodextrin glucanotransferase ($\beta$-CGTase) excreted by Bacillus firmus var. alkalophilus, the amino acid residues in $\beta$-CGTase were modified by various site-specific amino acid modifying reagents. The cyclizing and amylolytic activities of $\beta$-CGTase were all seriously reduced after treatment with Woodward's reagent K (WRK) modifying aspartic/glutamic acid, N-bromosuccinimde (NBS) modifying tryptophan, and diethylpyrocarbonate (DEPC) modifying histidine residues. The roles of tryptophan and histidine residues in $\beta$-CGTase were further investigated by measuring the protection effect of various substrates during chemical modification, comparing protein mobility in native and affinity polyacrylamide gel electrophoresis containing soluble starch, and comparing the $K_m$ and $V_{max}$ values of native and modified enzymes. Tryptophan residues were identified as affecting substrate-binding ability rather than influencing catalytic activities. On the other hand, histidine residues influenced catalytic ability rather than substrate-binding ability, plus histidine modification had an effect on shifting the optimum pH and pH stability.

• 대한화학회지
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• 제34권4호
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• pp.360-369
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• 1990

보로실리케이트와 HZSM-5 제올라이트 및 이들의 골격에 철이 일부 치환된 촉매를 제조하여 메탄올의 전환반응에서 촉매성질을 조사하였다. 산점의 세기와 양이 생성물 분포에 미치는 영향을 암모니아의 승온 탈착곡선으로부터 얻어진 산성도와 연관지어 고찰하였다. 강한 산점이 적은 보로실리케이트 촉매에서는 프로필렌 선택도가 높았으나, 강한 산점이 많은 HZSM-5 제올라이트 촉매에서는 방향족 화합물의 선택도가 높았다. 약한 산점이 전환반응에 기여하는지 여부는 확인되지 않았으나, 생성물 선택도는 강한 산점의 양과 관련지어 설명할 수 있었다. 철의 치환으로 약한 산점이 많아졌으나, 전화율이나 올레핀 선택도에는 영향이 없었다.

• 한국대기환경학회지
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• 제14권1호
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• pp.25-33
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• 1998

We have studied the reduction of NO by propane over perovskite-type oxides prepared by malic acid method. The catalysts were modified to enhance the activity by substitution by substitution of metal into A or B site of perovskite oxides. In addition, the reaction conditions, such as temperature, $O_2$ concentration, space velocity have been studed. In the $LaCoO_3$ type catalyst, the partial substitution of Ba, Sr into A site enhanced the catalytic activity in the reduction of NO. In the $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3(x=0 \sim 1.9)$ catalyst, the partial substitution of Fe into B site enhanced the conversion of NO, but excess amount of Fe decreased the conversion of NO. The surface area and catalytic activity of perovskite catalysts prepared by malic acid method showed higher values than those of solid reaction method. In the $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$ catalyst, the conversion of NO increased with increasing $O_2$ concentration and contact time. The introduction of water into reactant feed decreased the catalytic activity.

• BMB Reports
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• 제32권6호
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• pp.599-604
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• 1999

A highly conserved amino acid, glutamic acid (Glu), present at position 152 in the catalytic domain of the human immunodeficiency virus type 1 (HIV-1) integrase (IN) protein has been known to be critical for enzymatic function since substitution of Glu 152 with other residues results in a complete loss of enzymatic activities. In order to better understand the role of Glu 152 as a conserved residue in enzymatic action, intragenic second site mutations have been introduced around residue 152 of a mutant IN (E152A), and their biochemical properties were analyzed in terms of enzymatic activities. Disintegration activities were found to be significantly restored in several second site mutant INs, while integration activities were only recovered weakly. However, endonucleolytic activities were not discovered in all the mutant INs. These findings indicate that the second site mutations can partially restore that catalytic structure of the active site disturbed by the E152A mutation and lead to the regaining of integration and disintegration activities. In addition, it is also suggested that endonucleolytic activity requires a more accurate structure of the catalytic site than that for the integration and disintegration activities.

• Bulletin of the Korean Chemical Society
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• 제22권3호
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• pp.263-266
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• 2001

Isopropylation of phenol with 2-propanol has been carried out over Na-exchanged ZSM-5 zeolites to determine the effect of catalyst acidity on phenol conversion and product selectivity. The acid type and strength of the catalyst such as Lewis, weak and strong Bronsted acid sites are measured by pyridine adsorbed XPS and the catalytic properties are interpreted in terms of the acid properties. The active site and mechanism for the reaction are suggested based on evidence of study from the reactant adsorbed FT-IR.

• 미생물학회지
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• 제29권4호
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• pp.209-214
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• 1991

The PRD1 DNA polymerase is a small multi-functional enzyme containing conserved amino acid sequences shared by family B DNA polymerases. Thus the PRD1 DNA polymerase provides an useful model system with which to study structure-functional relationships of DNA polymerase molecules. In order to investigate the functional and structural roles of the highly conserved amino acid sequences, we have introduced three mutations into a conserved amino acid of the PRD1 DNA polymerase. Genetic complememtation study indicated that each mutation inactivated DNA polymerase catalytic activity.

• 한국환경과학회지
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• 제13권7호
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• pp.619-626
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• 2004

We have studied the catalytic combustion of soot particulates over perovskite-type oxides prepared by malic acid method, The catalysts were modified to enhance the activity by substitution of metal into A or B site of perovskite oxide. In addition, the reaction conditions such as temperature and $O_2$ concentration were investigated. The partial substitution of alkali metals into A site in the $LaMnO_3$ catalyst, enhanced the catalytic activity in the combustion of carbon particulate and the activity was shown in the order: Cs > K > Na. For the $La_{1-x}Cs_{x}MnO_{3}$ catalysts, the catalytic activity showed the maximum value with x=0.3 but no more increase on the catalytic activity was shown with x > 0.3. For the $La_{0.8}Cs_{0.2}MnO_{3}$ catalyst, the substitution of Fe or Ni increased the ignition temperature. The ignition temperature decreased with an increase of $O_2$ concentration, however, no more increase in the catalytic activity was shown with $O_2$ concentration > 0.2. The introduction of NO into reactants showed no effect on the catalytic activity.

• Advances in nano research
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• 제12권3호
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• pp.291-300
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• 2022

The behavior of hydrogen species on the surface of the catalyst during the Lewis acid transformation to form Brønsted acid sites over the spherical silica-supported WO_x catalyst was investigated. To understand the structure-activity relationship of Lewis acid transformation and hydrogen bonding interactions, we explore the potential of using the in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) with adsorbed ammonia and hydrogen exposure. From the results of in situ DRIFTS measurements, Lewis acid sites on surface catalysts were transformed into new Brønsted acid sites upon hydrogen exposure. The adsorbed NH₃ on Lewis acid sites migrated to Brønsted acid sites forming NH⁴⁺. The results show that the dissociated H atoms present on the catalyst surface formed new Si-OH hydroxyl species - the new Brønsted acid site. Besides, the isolated Si-O-W species is the key towards H-bond and Si-OH formation. Additionally, the H atoms adsorbed surrounding the Si-O-W species of mono-oxo O=WO₄ and di-oxo (O=)₂WO₂ species, where the Si-O-W species are the main species presented on the Inc-SSP catalysts than that of the IWI-SSP catalysts.