Ho-Geun Ahn

Complete oxidation of ethylene over supported gold nanoparticle catalysts.

Complete oxidation of ethylene was performed over supported noble metals or transition metals oxide catalysts and on monoliths under atmospheric pressure. Gold nanoparticles on Al2O3 or MxOy(M = Mo, Fe, Mn) were prepared by impregnation, coprecipitation, deposition, and dispersion methods. Nanoparticles prepared by impregnation method were irregular and very large above 25 nm, but those by coprecipitation and deposition method were uniformly nanosized at 4-5 nm. The gold nanoparticle were outstandingly active in catalyzing oxidation of ethylene. The activity order of these catalysts with preparation methods was deposition > coprecipitation > impregnation, and Au/Co3O4 prepared by deposition method showed the best performance in ethylene oxidation. The addition of gold particles to MxOy/Al2O3 catalyst enhanced the ethylene oxidation activity significantly. The main role of the gold nanoparticles apparently was to promote dissociative adsorption of oxygen and to enhance the reoxidation of the catalyst.

Visible-light-sensitive Na-doped p-type flower-like ZnO photocatalysts synthesized via a continuous flow microreactor

A Na-doped p-type flower-like ZnO photocatalyst (Na:ZnO) that is highly visible-light-sensitive in air at room temperature was synthesized by a continuous flow microreactor, where NaOH was used as both the precipitating and doping agent. The results of various characterization techniques (XPS, ICP, ToF-SIMS, XRD, and HRTEM) indicated that the Na ions have been successfully doped into the ZnO lattice. The Na:ZnO demonstrated a much higher photocatalytic degradation rate of methylene blue under simulated sunlight (λmax = 494 nm) than the rates obtained from commercially available TiO2 photocatalysts (P-25) and pure ZnO. This much enhanced rate is likely a result of increased surface defect sites associated with oxygen when Na replaces Zn in the crystal structure. A possible mechanism of the photocatalytic degradation of methylene blue on the Na:ZnO is suggested.

Adsorption-desorption characteristics of modified activated carbons for volatile organic compounds

Modification techniques for activated carbon were used to increase the removal capacity by surface adsorption and to improve the selectivity to volatile organic compounds (VOCs). Modified activated carbons (MACs) were prepared by modifying the purified activated carbon with various acids or bases. The effects of adsorption capacity and modified contents on the textural properties of the MACs were investigated. Furthermore, VOC adsorption and desorption experiments were carried out to determine the relationship between the adsorption capacity and the chemical properties of the adsorbents. High adsorption capacity for the selected VOCs was obtained over 1 wt%-H 3 PO 4 /AC (1wt%-PA/AC). As a result, MAC was found to be very effective for VOC removal by adsorption with the potential for repeated use through desorption by simple heat treatment.

Performance of double wash-coated monolith catalyst in selective catalytic reduction of NOx with propene

Abstract Highly dispersed Au/AI 2 O 3 and Pt/Al 2 O 3 catalysts were applied to the lower layer of double wash-coated monolith catalyst for selective catalytic reduction (SCR) of NOx with C 3 H 6 . H- mordenite, Cu-mordenite or MCM-41 was coated as the upper layer. The catalytic performance was investigated in the presence of oxygen. The double wash-coated catalysts were more active than the catalyst with only zeolite or without upper layer. Temperature window of the double wash-coated catalyst was broadened, and catalytic performance was remarkably improved. The role of each layer and a reaction mechanism were discussed. The combined noble metal monolith catalyst with zeolite was effective in removing NOx by SCR with hydrocarbons.

Water Quality of Streams and Riparian Vegetation at Rice Cultivation Area of Eastern Jeonnam

The characteristic of the quality of stream water and the riparian vegetation during rice cultivation in the rural area of the eastern Jeonnam province was surveyed from April to November, 2000. The water quality of the streams during rice cultivation was variable. The pH of these water bodies ranged from . Electro conductivity (EC) at each water body ranged from for Beogyo-cheoa for Boseong-cheon, for Songgwang-cheon, and for Isa-cheon. Total nitrogen and other parameters (K, Ca, Mg, Na, , SS) were higher at May (Boseong-cheon) through June (Songgwang-cheon, Isa-cheon) during the transplanting season than these same parameters at August October and November. Thirty weed species of sixteen families were found in the survey areas of Songgwang-cheon, Boseong-cheon Isa-cheon and Beolgyo-cheon. Nine annual weeds, four biennial weeds, and seventeen perennial weeds were found, several different life forms were identified. Of those species three were submerged, two were free floating, five were emerged, and twenty were water-side weeds.

Effect of ultra-fine gold particle addition to metal oxides in ethylene oxidation

Oxidation of ethylene was carried out over alumina-supported metal oxide catalysts and highly dispersed gold catalysts, respectively, under atmospheric pressure. The ethylene was completely oxidized to produce carbon dioxide and water with both metal oxide and gold catalysts. The activity of gold catalyst prepared by deposition method was much higher than that of supported metal oxide catalysts. Ultra-fine gold particles on Co3O4 were more active than on Al2O3. Fe2O3/Al2O3 and MnO2/Al2O3 catalysts were more active than MoO3/Al2O3 catalyst. The activity of the supported metal oxide catalysts was greatly enhanced by addition of gold particles. It was therefore considered that gold particles promote dissociative adsorption of oxygen and the adsorbed oxygen reacts with adsorbed ethylene on support adjacent to the active site.

Study on Conversion of Carbon Dioxide to Methyl Alcohol over Ceramic Monolith Supported CuO and ZnO Catalysts

Methyl alcohol is one of the basic intermediates in the chemical industry and is also being used as a fuel additive and as a clean burning fuel. In this study, conversion of carbon dioxide to methyl alcohol was investigated using catalytic chemical methods. Ceramic monoliths (M) with were used as catalyst supports. Monolith-supported CuO-ZnO catalysts were prepared by wash-coat method. The prepared catalysts were characterized by using ICP analysis, TEM images and XRD patterns. The catalytic activity for carbon dioxide hydrogenation to methyl alcohol was investigated using a flow-type reactor under various reaction temperature, pressure and contact time. In the preparation of monolith-supported CuO-ZnO catalysts by wash-coat method, proper concentration of precursors solution was 25.7% (w/v). The mixed crystal of CuO and ZnO was well supported on monolith. And it was known that more CuO component may be supported than ZnO component. Conversion of carbon dioxide was increased with increasing reaction temperature, but methyl alcohol selectivity was decreased. Optimum reaction temperature was about under 20 atm because of the reverse water gas shift reaction. Maximum yield of methyl alcohol over CuO-ZnO/M catalyst was 5.1 mol% at and 20 atm.

The Properties of HfO 2 Thin Films by DC/RF Magnetron Sputtering and Thermal Evaporation Method

[ ] thin film were prepared in order to clarify optimum conditions for growth of the thin film depending upon process, and then by changing a number of deposition conditions and heat treatment conditions variously, structural and electrical characteristics were measured. Thereby, optimum process variables were derived. For the manufacture of the , Cu, In and Se were deposited in the named order. Among them, Cu and In were deposited by using the sputtering method in consideration of their adhesive force to the substrate, and the DC/RF power was controlled so that the composition of Cu and In might be 1:1, while the annealing temperature having an effect on the quality of the thin film was changed from to at intervals of .ℊ攀Ѐ㘱〻ጀ䵥摩捩湥⁡湤⁨敬慴栀

Preparation of Styrenated Phenol Over SO2−4/ZrO2 Catalyst in a Large-Scale Synthesis Process

Styrenated phenols (SPs) are usually synthesized by the reaction of styrene and phenol under acid catalysts. SPs with a high content of di-styrenated phenol (DSP) can be used to prepare styrenated phenol alkoxylate (SP-A). Therefore, in this study, a scale-up process for synthesizing SPs with high DSP content which can be used for synthesis of SP-A was studied. The solid catalyst used in this study was prepared by impregnation method. SO2-₄ was impregnated on a SO2-₄/ZrO₂ catalyst in an aqueous 1 M H₂SO₄ solution. The prepared catalysts were characterized by NH3-TPD. Catalytic activity was examined by measuring the conversion of phenol and styrene in a liquid-phase batch reactor. Almost 100% conversion of both phenol and styrene over 5-SO2-₄/ZrO₂ catalyst was obtained at a reaction temperature of 80 °C and a reaction time of 6 h. The amount of catalyst to the reactants was 2 wt%. Under the same reaction conditions, the selectivity of MSP, DSP, and TSP was 12.4%, 64.5%, and 23.1% respectively.

A Synthesis of Alkoxylates from Styrenated Phenols and Ethylene Carbonate Over KOH/La2O3 Catalysts

Styrenated phenol alkoxylates (SP-A) are prepared from styrenated phenols (SP) and ethylene oxide (EO) under a homogeneous base catalyst. However, to use EO that is difficult to handle, a high-pressure reaction device capable of reaction process control should be used. Additionally, the homogeneous base catalyst requires a neutralization process to remove the remaining catalyst after the reaction, and it is difficult to separate the catalysts and the product. Therefore, in this study, the separation of product and catalyst by using KOH/La₂O₃ catalyst was facilitated in the production of SP-A. Also, it was possible to produce SP-A under atmospheric pressure reaction conditions using EC. The mean molecular weight of SP-A varied depending on the reaction conditions, and the size of the mean molecular weight could be arbitrarily controlled by changing the reaction conditions.