http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
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.
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>
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.
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.
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.
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.
Phase transformations and phase-selective syntheses of aluminophosphate molecular sieves.
Jhung, Sung Hwa,Jin, Taihuan,Hwang, Jin-Soo,Chang, Jong-San American Scientific Publishers 2007 Journal of nanoscience and nanotechnology Vol.7 No.8
<P>A few aluminophosphate (AlPO) molecular sieves are synthesized hydrothermally under microwave irradiation and conventional electric heating. Less stable AlPO molecular sieves especially with large pore can be obtained preferentially in a short crystallization time because the inter-conversion of less stable phase into a more stable one is prohibited in short reaction time. The VFI transforms into AFI, and finally into APC, with the increase of reaction time since the relative stability is VFI < AFI < APC under the chosen reaction conditions. The relative stability can be explained with the pore size or by the framework density of each structure. Due to the rapid crystallization involved in the microwave method and instability of porous materials with large pore, these porous materials can be selectively synthesized by microwave irradiation. The synthesis of extra-large-pore VPI-5 using triethylamine is also reported for the first time, and the synthesized VPI-5 is very stable that can be dried at 100 degrees C at atmospheric pressure without the phase-transformation into AIPO-8.</P>