• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.183-188
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• 2008

We have studied the chemisorption of oxygen at room temperature on Fe layers deposited on Pt(111) substrates by using core-level X-ray photoelectron spectroscopy. It was found that the oxygen atoms are chemisorbed when the thickness of the Fe layers is not larger than 6 monolayers. Upon post-annealing, it was found that part of the chemisorbed atoms are desorbed at a temperature range 600 - 700 K, after which the intermixing between Fe and Pt atoms occurs. The overall trend of this intermixing was very similar to the Fe/Pt(111) surface without oxygen exposure. The remaining oxygen adatoms, the amount of which is about a half of the total, were found to be eventually desorbed from the surface upon post-annealing at 1000 K. The binding energy of this phase was higher than that of the oxygen atoms desorbed at lower temperatures by 1.3 eV.

• Bulletin of the Korean Chemical Society
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• v.9 no.1
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• pp.32-36
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• 1988

The isotherms of oxygen chemisorption on polycrystaline nickel surface are obtained at various temperatures between 298K and 523K from intensity measurernent of O 1s xps peaks, and the activation energy of the chemisorption is estimated as a function of the coverage. The activation energy extrapolated to zero coverage is found to be -5.9 kJ/mol. The negative activation energy can be taken as a strong implication of the propriety of a currently accepted chemisorption model, in which molecularly adsorbed precursor state is assumed to exist. The residence time of this precursor state is estimated by assuming a molecularly physisorbed state for the precursor state and assuming a pairwise interaction energy of Lennard-Jones 12-6 potential between an admolecule and each substrate nickel atom. The sticking coefficients are also calculated from the isotherms. The calculated results agree well with those obtained by others with different methods.

• Journal of the Korean Society of Safety
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• v.1 no.1
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• pp.21-26
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• 1986

Gas sensing materials for detecting inflammable gas such as alcohol, propane, acetic acid, carbon monoxide, hydrogen were developed by utiliting $MgO-Cr_2O_3-TiO_2$ system. Between 30$0^{\circ}C$ and 50$0^{\circ}C$, reversible chemisorption becomes dominant and the electrical canduction of P-type semiconductive with the gas chemisorption. The ceramic sensor exhibits a high sensitivity to particular reducing gas such as alcohol, whereas propane and butane have little effect on the resistivity. The time response of adsorption is estimated to be about 20 sec. On the other hand, the desorption process, which corresponds to oxidation due to oxygen adsorption, take more than 60 sec. Thus the ceramic sensor can be used as a alcohol sensor in an ambient aunosphere. As the oxygen concentration is increased from 0.1 to 10 precent($10^3-10^6ppm$), the resistance decreases rapidly but stabilizes at higher concentration.

• Journal of the Korean Chemical Society
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• v.19 no.6
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• pp.420-422
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• 1975

The chemisorption of hydrogen and carbon monoxide, as well as the hydrogen titration of prechemisorbed oxygen was studied at $110^{\circ}$C on evaporated platinum and platinum-tungsten films. The results suggest that hydrogen titration of prechemisorbed oxygen may be used to determine the platinum surface area of platinum-tungsten film.

• Korean Journal of Materials Research
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• v.1 no.4
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• pp.184-190
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• 1991

Oxygen chemisorption on single crystal ZrC(111) surface was studied by high-resolution electron energy loss and ultraviolet photoelectron spectroscopy. At a low amount of oxygen exposure, adsorbed oxygen atoms construct $(\sqrt{3}{\times}\sqrt{3})R30^{\circ}$ structure. On the other hand, oxygen adsorption changes into $1{\times}1$ structure as the amount of oxygen exposure increases. The adsorbed oxygen atoms show smaller vertical distance from the Zr topmost layer in the $1{\times}1$ structure than in the $(\sqrt{3}{\times}\sqrt{3})R30^{\circ}$ structure and approach to the bridge site rather than 3-fold hollow site. The two different oxygen adsorption behavior comes from the two different surface stales of the clean ZrC(111) surface.

• Korean Chemical Engineering Research
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• v.60 no.3
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• pp.459-467
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• 2022

Redispersion of Pt-Sn particles in Pt, PtSn catalyst which have been sintered by high temperature hydrogen reduction was investigated using oxygen treatment with various temperatures. The aim of this study was to understand the relationship between the catalytic activity for propane dehydrogenation reaction and the change in the physicochemical properties of the catalyst. X-ray diffraction analysis (XRD), CO pulse chemisorption, and H₂ temperature programmed reduction (H₂-TPR) were performed to investigate the state of active metal and interactions between particles of redispersed catalyst. It was confirmed that the dispersion and particle size of platinum, the crystal phase of the catalyst, and the reduction behavior were changed according to the oxygen treatment. As for the catalytic activity in propane dehydrogeantion, sintered PtSn catalyst treated with oxygen at 500 ℃ showed best activity and recovery of initial activity. It was confirm that catalyst after oxygen treatment at 500 ℃ showed high dispersion of Pt and decreased particle size as the results of CO pulse chemisorption and XRD of catalyst, and thus the redispersion of PtSn particles in sintered catalyst was occurred. Catalytic activity was recovered due to redispersion using oxygen treatment, and the activity recovery of the PtSn catalyst was higher than that of Pt catalyst.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.267-271
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• 2020

Cerium oxide (ceria, CeO₂) is one of the most wide-spread oxide supporting materials for the precious metal nanoparticle class of heterogeneous catalysts. Because ceria can store and release oxygen ions, it is an essential catalytic component for various oxidation reactions such as CO oxidation (2CO + O₂ 2CO₂). Moreover, reduced ceria is known to be reactive for water activation, which is a critical step for activation of water-gas shift reaction (CO + H₂O → H₂ + CO₂). Here, we apply van der Waals-corrected density functional theory (DFT) calculations combined with U correction to study the mechanism of water chemisorption on CeO₂(111) surfaces. A stoichiometric CeO₂(111) and a defected CeO₂(111) surface showed different water adsorption chemistry, suggesting that defected CeO₂ surfaces with oxygen vacancies are responsible for water binding and activation. An appropriate level of water-ceria chemisorption energy is deduced by vdW-corrected non-local correlation coupled with the optB86b exchange functional, whereas the conventional PBE functional describes weaker water-ceria interactions, which are insufficient to stabilize (chemisorb) water on the ceria surfaces.

• Bulletin of the Korean Chemical Society
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• v.13 no.1
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• pp.30-32
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• 1992

The apparent depth of space charge region on the ZnO $(10{\bar{1}}0)$ surface in chemisorption of oxygen has been estimated from the capacitance of two contacting faces. When the sample (donor concentration: $2.4{\times}10^{22}\;m^{-3}$) was evacuated at 773 K for 1 hr the depth reached to 40-100 ${\AA}$ depending on sample assembly. Admission of oxygen to the sample resulted in an increase of the depth to 3600 ${\AA}$ where the increment was greater at higher oxygen pressure between 6.6-1600 $N/m^2$. Admission of CO to the sample previously exposed to oxygen yields a decrease in the depth. The results of the measurement support that oxygen is adsorbed as an acceptor on ZnO $(10{\bar{1}}0)$.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.279-284
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• 1992

Oxygen adsorption on the single crystal NbC(111) surface was studied by high-resolution electron energy loss and ultraviolet photoelectron spectroscopy. On the NbC(111) surface, oxygen molecules as well as oxygen atoms were adsorbed. Oxygen atoms were located at the 3-fold hollow site of the NbC(111) surface with the frequency of 548c$m^{-1}$. It was found that oxygen molecules had vibrational frequency of 968c$m^{-1}$which was much lower than that of the free oxygen molecule. Also the work function of the NbC(111) surface has increased by adsorption of oxygen molecule. These suggest electron tranfer from the NbC(111) substrate to the 2p${pi}_g$ substrate of the oxygen molecule.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2219-2222
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• 2010

A density functional theory (DFT) study of $CO_2$ adsorption on barium oxide (BaO) adsorbents is conducted to understand the chemical activity of the oxygen site on the BaO (100) surface. This study evaluated the adsorption energies and geometries of a single $CO_2$ molecule and a pair of $CO_2$ molecules on the BaO (100) surface. A quantum calculation was performed to obtain information on the molecular structures and molecular reaction mechanisms; the results of the calculation indicated that $CO_2$ was adsorbed on BaO to form a stable surface carbonate with strong chemisorption. To study the interactive $CO_2$ adsorption on the BaO (100) surface, a pair of $CO_2$ molecules was bound to neighboring and distant oxygen sites. The interactive $CO_2$ adsorption on the BaO surface was found to slightly weaken the adsorption energy, owing to the interaction between $CO_2$ molecules.