• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.87-87
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• 2010

Adsorption and subsequent catalytic reactions of ethanol and acetaldehyde on chemically modified rutile TiO2(001) surfaces are probed by x-ray photoemission spectroscopy (XPS) using synchrotron radiation. TiO2 is a well-known photocatalyst for various catalytic reactions including oxidation of organic molecules. In this respect, the surface atomic structure has been found to play a vital role in determining the catalytic reactivity and selectivity of TiO2. In this study, we employ an atomically well-ordered reduced TiO2(001) surface which is prepared in a UHV chamber by repeated Ar+-sputtering and annealing (900 K) cycles. We systematically modify the surface by treating the surface with H2O or O2 at room temperature (RT). The catalytic reactivity of the surface-modified TiO2(001) is evaluated by dosing ethanol/acetaldehyde onto the surface at RT and by subsequent annealing to higher temperatures (400~600 K). XPS spectra of C 1s core level are intensively used to probe any change in the oxidation state of carbon atoms. We find that the reactivity as well as the saturation coverage are significantly affected by the RT-treatment of the TiO2 surface with H2O or O2. For both reactant molecules (ethanol/acetaldehyde), oxidation reactions are found to be enhanced on the O2-treated surface compared with the reduced or H2O-treated surfaces. Possibly reaction pathways are discussed based on the observed XPS spectra.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.2
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• pp.80-84
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• 2010

The temperature-programmed reduction of titanium oxide ($TiO_2$) with pure $CH_4$ was used for the preparation of titanium carbide crystallites. The synthesized materials had the different surface areas, indicating that the structural properties of these materials were strong functions of two different heating rates and space velocity employed. The titanium carbide crystallites were active for $NH_3$ decomposition. Since the reactivity varied with changes in the particle size, ammonia decomposition reactivity over the titanium carbides crystallites appeared to be related to the different active species. The reactivities of titanium carbide crystallites were two and three times lower than those of the vanadium and molybdenum carbide crystallites, respectively. These results suggested that the difference in activities might be related to the degree of electron transfer between metals and carbon.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.91-92
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• 2018

A glassy thin film was formed on the surface of the blast furnace slag. When blast furnace slag is used as an admixture of concrete, addition of alkali activators were required. However, alkali activators are not only dangerous as chemical products, but they are also difficult to use as expensive materials. Therefore, it is necessary to study the way of removal of the glassy thin film of blast furnace slag without the risk and cost increase. In this study, to solve this problem, experiment was carried out to improve the hydration reactivity by treatment the surface of blast furnace slag using arc discharge. Experimental results show that when the surface of the blast furnace slag was tratmented by arc discharge, the glassy thin film was destroyed. And the hydration reactivity was improved, the compressive strength was increased.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.267-267
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• 2012

$TiO_2$-Ni inverse catalysts were prepared using atomic layer deposition (ALD) process and catalytic $CO_2$ reforming of methane (CRM) reaction over catalysts (either bare Ni or $TiO_2$ coated-Ni particles) were performed using a continuous flow reactor at $800^{\circ}C$. $TiO_2$-Ni inverse catalyst showed higher catalytic reactivity at initial stage of CRM reactions at $800^{\circ}C$ comparing to bare Ni catalysts. Moreover, catalytic activity of $TiO_2$/Ni catalyst was kept high during 13 hrs of the CRM reactions at $800^{\circ}C$, whereas deactivation of bare Ni surface was started within 1hr under same conditions. The results of surface analysis using SEM, XPS, and Raman showed that deposition of graphitic carbon was effectively suppressed in a presence of $TiO_2$ nanoparticles on Ni surface, thereby improving catalytic reactivity and stability of $TiO_2$/Ni catalytic systems. We suggest that utilizing decoration effect of metal catalyst with oxide nanoaprticles is of great potential to develop metal-based catalysts with high stability and reactivity.

• Proceedings of the Korean Vacuum Society Conference
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• 1996.06a
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• pp.18-18
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• 1996

• Environmental Engineering Research
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• v.10 no.4
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• pp.174-180
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• 2005

Nano-sized iron was synthesized using borohydride reduction of $Fe^{3+}$ in aqueous solution. A wide range of synthesis conditions including varying concentrations of reagents, reagent feeding rate, and solution pH was applied in an aqueous system under anaerobic condition. The reactivity of nano-sized iron from each synthesis was evaluated by reacting the iron with TCE in batch systems. Evidence obtained from this study suggest the reactivity of iron is strongly dependent on the synthesis solution pH. The iron reactivity increased as solution pH decreased. More rapid TCE reduction was observed for iron samples synthesized from higher initial $Fe^{3+}$ concentration, which resulted in lower solution pH during the synthesis reaction. Faster feeding of $BH_4^-$ solution to the $Fe^{3+}$ solution resulted in lower synthesis solution pH and the resultant iron samples gave higher TCE reduction rate. Lowering the pH of the solution after completion of the synthesis reaction significantly increased reactivity of iron. It is presumed that the increase in the reactivity of iron synthesized at lower pH is due to less precipitation of iron (hydr)oxides or less surface passivation of iron.

• Proceedings of the Korean Vacuum Society Conference
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• 2004.08a
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• pp.181-181
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• 2004

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3196-3202
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• 2012

Post-synthesis is used to synthesize organic hybrid inorganic mesoporous sieves. In this method, the activity and structure of the base sieve are crucial to obtain the definable hybrid materials. The chemical and physical properties of the base can be largely changed either by the final step of its synthesizing processes, by template removal which is accomplished with the oxidative thermal decomposition (burning) method or by solvent extraction method. In this paper we compared two methods for the post-synthesis of organic hybrid MCM-48. When the template was extracted with HCl/alcohol mixture, the final product showed larger pore size, larger pore volume and better crystallinity compared to the case of the thermal decomposition. The reactivity of the surface silanol group of template free MCM-48 was also checked with an alkylsilylation reagent $CH_2=CHSi(OC_2H_5)_3$. Raman and $^{29}Si$ NMR spectra of MCM-48 in the test reaction indicated that more of the organic group was grafted to the surface of the sample after the template was removed with the solvent extraction method. Direct synthesis of vinyl-MCM-48 was also investigated and its characteristics were compared with the case of post-synthesis. From the results, it was suggested that the structure and chemical reactivity can be maintained in the solvent extraction method and that organic grafting after the solvent extraction can be a good candidate to synthesize a definable hybrid porous material.

• Journal of Energy Engineering
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• v.2 no.1
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• pp.114-122
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• 1993

A model describing the reaction rate and catalyst deactivation in a simplified reaction system was developed to investigate the significance of catalyst pore structure in terms of porosities, porosity ratios, and size ratios of reactants to pores. The model showed that the unimodal catalyst could give a better performance than the bimodal in certain circumstances and the crossover found in the reactivity curves resulted from a trade-off between surface area and diffusivity. Under the assumption of uniform coke buildup, the bimodal catalyst appeared to provide better resistance to deactation than unimodal catalyst.

• Journal of Energy Engineering
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• v.12 no.3
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• pp.231-240
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• 2003

Reactivity of Char-CO$_2$ gasification of five coals for power generation was investigated with PTGA in the temperature range 850∼1000$^{\circ}C$ and the pressure range 0.5∼2.0 MPa. The effect of coal rank, initial char characteristics and pressure on the reaction rate was evaluated for five chars. The reactivity of low lank coal char was better than that of high rank coal char, and this could be explained with the initial pore structure and surface area of char. Meso/macro-pores of char seems to markedly affect char reactivity by way of providing channels for diffusion of reactant gas into the reactive surface area. For the range of tested pressure, the reaction rate is proportional to CO$_2$ partial pressure and the reaction order ranges from 0.4 to 0.7 for five chars. The effect of total pressure on the reaction rate was small, and kinetic parameters, based on the unreacted core model, were obtained for five chars.