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Jhung, Sung ,Hwa,Jin, Taihuan,Hwang, Young ,Kyu,Chang, Jong-San WILEY-VCH Verlag 2007 Chemistry Vol.13 No.16
<P>Microporous materials, such as silicalite-1 and VSB-5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW–MW, MW–CE, CE–MW, and CE–CE (in the order of nucleation-crystal growth). In the case of synthesis by MW–CE or CE–MW, the heating modes were changed for the second step just after the appearance of X-ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW–MW<MW–CE≈CE–MW<CE–CE synthesis. The fast crystal growth and small crystal size observed in the synthesis from microwave-nucleated precursor can be explained in terms of the fact that the microwave-nucleated samples have higher population of nuclei with smaller size than the samples nucleated by conventional heating.</P> <B>Graphic Abstract</B> <P>Microwave synthesis: Microporous materials can be synthesized under microwave irradiation very efficiently. This work demonstrates that the effect of microwave irradiation appears to be much more significant on the nucleation step compared to crystal growth even though the microwave method accelerates both steps of the syntheses (see figure: MW: microwave irradiation, CE: conventional electric heating). <img src='wiley_img/09476539-2007-13-16-CHEM200700098-content.gif' alt='wiley_img/09476539-2007-13-16-CHEM200700098-content'> </P>
Jhung, Sung-Hwa,Lee, Jin-Ho,Lee, Jong-Min,Lee, Ji-Hye,Hong, Do-Young,Kim, Myong-Woon,Chang, Jong-San Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.4
The Pt/C and Pd/C catalysts were prepared from conventional chloride precursors by adsorption or precipitation-deposition methods. Their activities for hydrogenation reactions of cyclohexene and acetophenone were compared with those of commercial catalysts. The Pt/C and Pd/C catalysts obtained from the adsorption procedure reveal higher hydrogenation activity than commercial catalysts and the catalysts prepared by the precipitation-deposition method. Their improved performances are attributed to the decreased metal crystallite sizes of Pt or Pd formed on the active carbon support upon the adsorption of the precursors probably due to the same negative charges of the chloride precursor and the carbon support. Under the preparation conditions studied, the reduction of the supported catalysts using borohydrides in liquid phase is superior to a gas phase reduction by using hydrogen in the viewpoint of particle size, hydrogenation activity and convenience.
Size Control of Silicone Particles Using Sonochemical Approaches
Jhung, Sung-Hwa,Yoo, Ki-Cheon,Hwang, Young-Kyu,Chang, Jong-San Korean Chemical Society 2007 Bulletin of the Korean Chemical Society Vol.28 No.12
Particle size of silicones can be controlled by changing the reaction conditions such as temperature and concentrations of water and tetramethoxysilane (TMOS). Alternatively, the use of ultrasound radiation is also an elegant technique to decrease the particle size. Small silicone particles can be obtained at low temperature from diluted reagent containing TMOS, especially under the powerful ultrasound radiation. The size control may be explained by the rate of particle growth rather than that of nucleation.
Jhung, Sung ,Hwa,Yoon, Ji ,Woong,Lee, Ji ,Sun,Chang, Jong-San Wiley - VCH Verlag GmbH & Co. KGaA 2007 Chemistry Vol.13 No.22
<P>Several zeolites, such as faujasite, mordenite, and ZSM-5, with various aluminum contents have been used to analyze the effect of aluminum or cation concentration (strength of electrostatic field) on hydrogen adsorption at low temperature. Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (−ΔH<SUB>ads</SUB>), surface coverage, and micropore occupancy increase with increasing aluminum content of a zeolite. Zeolites with a higher amount of aluminum favorably adsorb hydrogen at relatively low pressures. For zeolites with similar aluminum contents, the adsorption capacity, isosteric heat of adsorption, surface coverage, and micropore occupancy are in the order of mordenite>ZSM-5>faujasite, probably due to differing pore sizes and the presence or absence of pore intersections. This work demonstrates that zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake.</P> <B>Graphic Abstract</B> <P>Hydrogen adsorption on zeolites: Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (−ΔH<SUB>ads</SUB>), surface coverage, and micropore occupancy increase when increasing the aluminum content of a zeolite (see figure). For zeolites with similar aluminum contents, the adsorption capacities are in the order of mordenite>ZSM-5>faujasite. Zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake. <img src='wiley_img/09476539-2007-13-22-CHEM200700148-content.gif' alt='wiley_img/09476539-2007-13-22-CHEM200700148-content'> </P>
Liquid Phase Oxidation of Xylenes: Effects of Water Concentration and Alkali Metals
Jhung, Sung-Hwa,Lee, Ki-Hwa,Park, Youn-Seok Korean Chemical Society 2002 Bulletin of the Korean Chemical Society Vol.23 No.1
A facile and precise batch oxidation reaction system allows continuous monitoring of the oxidation rate and cumulated oxygen conversion of xylenes, and the side reactions to carbon monoxide and carbon dioxide may also be studied. The oxidation reaction can be analyzed precisely with the rate and amount of oxygen consumed. The reaction reveals that 4-carboxybenzaldehyde is an unstable intermediate of p-xylene oxidation as the reaction proceeds instantaneously from p-toluic acid to TPA (terephthalic acid). The alkali metals accelerate oxidation, even though they retard the reaction initially. The oxidation rate increases with decreasing water concentration. However, in the later part of reaction, the reactivity decreases a bit if the water concentration is very low. This retarding effect of water can be overcome partly by the addition of potassium. The oxidation of o-xylene, compared with the oxidation of p-xylene and m-xylene, proceeds quite fast initially, however, the oxidation rate of xylene isomers in the later stage of reaction is in the order of p-xylene > mxylene > o-xylene.
Low Temperature Adsorption of Hydrogen on Nanoporous Materials
Jhung, Sung-Hwa,Yoon, Ji-Woong,Kim, Hye-Kyung,Chang, Jong-San Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.7
Hydrogen adsorption on various porous materials have been studied with a volumetric method at low temperature in the pressure of 0-760 torr. Their hydrogen uptakes depend at least partly on microporosity rather than total porosity. However, it is also necessary to consider other parameters such as pore size and pore architecture to explain the adsorption capacity. The heat of adsorption and adsorption-desorption-readsorption experiments show that the hydrogen adsorption over the porous materials are composed of physisorption with negligible contribution of chemisorption. Among the porous materials studied in this work, SAPO-34 has the highest adsorption capacity of 160 mL/g at 77 K and 1 atm probably due to high micropore surface area, micropore volume and narrow pore diameter.
Precipitation of Manganese in the p-Xylene Oxidation with Oxygen-Enriched Gas in Liquid Phase
Jhung, Sung-Hwa,Park, Youn-Seok Korean Chemical Society 2002 Bulletin of the Korean Chemical Society Vol.23 No.3
The liquid phase oxidation of p-xylene has been carried out with oxygen-enriched gas, and the manganese component was precipitated probably via over-oxidation to $Mn^{4+}$. The precipitation increased with rising oxygen concentration in the reaction gas and occurred mainly in the later part of the oxidation. The activity of the reaction decreased, and the blackening of the product and side reactions to carbon dioxide increased with the degree of precipitation. Precipitation can be decreased with the addition of metal ions, such as cerium, chromium and iron.