Un-Yeon Hwang

Effect of molar ratio of KOH to Ti-isopropoxide on the formation of BaTiO3 powders by hydrothermal method

Abstract Nano-crystalline BaTiO 3 powders were prepared using acylated titanium and barium acetate with hydrothermal method. The solution pH given by the molar ratio of KOH to Ti-isopropoxide was found to have an important effect on the size, morphology, and crystallinity of BaTiO 3 powders. FT-IR and Raman analyses showed that there were still some Ba–OAc bonds in the structure of as-prepared powders formed from the low pH alkaline solution. As hydrothermal aging time increased, the crystal structure of as-prepared powders was continuously transformed from amorphous to crystalline BaTiO 3 powders with breakage of Ba–OAc bonds and elimination of acetyl groups in the powders. When the solution pH was high, most of the acetyl groups bonded to Ba or Ti atoms were eliminated rapidly by hydrolysis in the solution. As a consequence, crystalline BaTiO 3 directly precipitated from homogeneous solution via condensation reaction between –Ba–OH and –Ti–OH bonds without subsequent hydrothermal reaction.

H2/CO2 separation characteristics of γ-Al2O3 membrane by aging stage in sol-gel process

Abstractγ-AlO(OH) sol solution was prepared by aluminum isopropoxide as an initial material. γ-Al2O3 membrane on the α-Al2O3 support was continuously made through coating and thermal treatment from the α-AlO(OH) sol. Previous work [Yoo et al., 1997] has shown that the aging stage in the sol preparation process mainly affects the characterization of γ-Al2O3 particles as well as γ-AlO(OH) sol. Based on this fact, the γ-Al2O3 membrane was prepared with two aging conditions in the present study. The separation characteristics experiment of the H2/CO2 mixture was performed on these membranes. As a result of the study, the mechanism of gas transport on the two membranes was proved as Knudsen diffusion. The ideal separation factor was reached at the value of the calculated Knudsen separation factor; however, permeability increased and selectivity decreased selectivity according to the aging.

A Study on the Effects of pH and Ni/Mo Mole Ratio during Wet Impregnation on the Characteristics and Methane Dry Reforming Reactivity of Activated Charcoal Supported Ni-Mo Carbide Catalyst

Abstract >> Activated charcoal supported nickel molybdenum carbide (carburized Ni-Mo/AC) catalysts were prepared by wet-impregnation followed by temperature-programmed carburization using 20% CH 4 /H 2 gas. The effects of pH and initial Ni/Mo mole ratio during wet-impregnation step on the characteristics of the carburizedNi-Mo/AC catalysts were investigated using ICP, XRD, XPS, BET and CO 2 -TPD techniques, and correlated withthe catalytic activity of the carburized Ni-Mo/AC in methane dry reforming reaction. Comparison of the resultsof methane dry reforming reaction kinetics with the results of characterization of the carburized Ni-Mo/AC catalystshowed that the catalytic activity in methane dry reforming reaction was higher at higher initial Ni/Mo mole ratioor at lower pH(3~natural value). This phenomenon was related to the crystal size of metallic Ni in the carburizedNi-Mo/AC catalyst. Key words : Nickel molybdenum carbide(니켈 몰리브덴 카바이드), Wet-impregnation(습식담지), Carburization(침탄), pH(수소이온농도지수), Initial Ni/Mo mole ratio(초기 Ni/Mo 몰비)