Dul-Sun Kim

Selective formation of formaldehyde from carbon dioxide and hydrogen over PtCu/SiO2

CO2 hydrogenation was carried out at 423 K and 600 KPa with PtCu/SiO2 catalyst. Formaldehyde rather than methanol was mainly produced, and platinum is believed to play an important role in the selective production of formaldehyde from CO2 hydrogenation. The optimum atomic ratio of Pt/Cu in the PtCu/SiO2 catalyst for the selective production of formaldehyde was 0.03. Copyright

Catalytic wet oxidation of reactive dyes with H2/O2 mixture on Pd-Pt/Al2O3 catalysts

The Pd–Pt/Al2O3 bimetallic catalysts showed extremely high activities toward the wet oxidation of the reactive dyes in the presence of 1% H2 together with excess oxygen. Palladium acted as a promoter to spillover the adsorbed H2 onto the surface of the oxidized Pt surface, and thereby the reducibility of the Pt increased greatly. The organic dye molecule had higher chance to adsorb on the reduced Pt surface under the competition with excess oxygen, which is an essential step for the catalytic wet oxidation (CWO). The Pd–Pt/Al2O3 catalysts also produced H2O2 from H2/O2 mixture, and the hydroxyl radical was formed through the subsequent decomposition of H2O2. Additional oxidation of the reactive dyes was obtained with hydroxyl radical. The extremely high activities of the Pd–Pt/Al2O3 catalysts were believed to be due to the combined effects of the faster redox cycle resulting from the increased reducibility of Pt surface and the additional oxidation of the reactive dyes with hydroxyl radical.

Structural characterization and electrochemical properties of Co3O4 anode materials synthesized by a hydrothermal method

Cobalt oxide [Co3O4] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co3O4 powder was also studied. Physical characterizations of Co3O4 are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m2/g, 76.1 m2/g, and 55.2 m2/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co3O4 particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li+ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co3O4 prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles.

Recovery from self-assembly: a composite material for lithium–sulfur batteries

A highly ordered mesoporous carbon, AlCMK, with an assembly of carbon rods and a bimodal pore system is used for sulfur encapsulation, and the AlCMK/S composite is observed to be able to accommodate volume expansion during a discharge process and recover its original structure when recharged. It is proved that the assembly structure of AlCMK makes it “breath” during the redox reaction of lithium and sulfur. Such a novel ability greatly benefits the maintenance of electrode construction during a repeated discharge–charge process. Moreover, a long heating time (e.g. 20 h) at 300 °C in a two-step melt diffusion method is found to contribute to the uniform dispersion of sulfur in the AlCMK carbon matrix. Using this featured composite, a Li–S cell retains 627 mA h g−1 after 450 cycles at 0.1 C-rate with a coulombic efficiency close to 100% and also shows good rate capability up to 5 C-rate, demonstrating a significant improvement of reversible capacity and cycle stability of Li–S cells.

Effect of Preparation Parameters of Sulfur Cathodes on Electrochemical Properties of Lithium Sulfur Battery

Sulfur cathodes were prepared by ball milling method with different types of electronic conductors and binders in different ball milling time. The sulfur cell with a cathode prepared in 45 min ball milling time gave an initial discharge capacity of 794 mAh/g with Super-P as an electronic conductor and poly(vinylidene fluoride) as a binder. The cathode with multi-walled carbon nanotube as an electronic conductor showed an initial discharge capacity of 944 mAh/g and a discharge capacity of 300 mAh/g after 20 cycles. Cathodes with poly(ethylene oxide) and poly(vinylidene fluoride) as binders showed different cycle performance.

Electrochemical properties of magnesium electrolyte with organic solvent

Three kinds of electrolytes are investigated to find out the proper electrolyte for magnesium battery. Propylene carbonate electrolyte using magnesium salt of Mg(ClO4)2 shows a higher ionic conductivity than that of dimethyl carbonate and tri(ethyleneglycol dimethyl)ether (TRGDME) but low decomposition potential. The TRGDME electrolyte with 0.5?M Mg(ClO4)2 has a higher ionic conductivity of 6 ? 10?4 ?S?cm?1 than that of dimethyl carbonate, but the decomposition voltage of the electrolyte is over 3.0?V which can be used for Mg/S cell.

76 Catalytic wet oxidation of dyehouse effluents with Cu/Al2O3 and Cu−Al pillared clay

Abstract Catalytic wet oxidation of real dyehouse effluents was performed in a batch reactor and a continuous flow pilot plant scale reactor by using Cu/Al2O3 and Al−Cu-PILC catalysts. Hydrogen peroxide was used as the oxidant. The removal of TOC and color was strongly related to the consumption of H2O2 and the subsequent formation of HO. Copper components in the catalysis especially in the Al−Cu-PILCs, showed successful activity toward complete removal of TOC and color. In addition the Al−Cu-PILC catalysts were extremely stable against copper leaching.

Manganese Doped LiFePO 4 as a Cathode for High Energy Density Lithium Batteries

Porous LiMn0.6Fe0.4PO4 (LMFP) was synthesized by a sol-gel process. Uniform dis- persion of the conductive carbon source throughout LMFP with uniform carbon coating was achieved by heating a stoichiometric mixture of raw materials at 600 o C for 10 h. The crystal structure of LMFP was investigated by Rietveld refinement. The surface structure and pore properties were investigated by SEM, TEM and BET. The LMFP so obtained has a high spe- cific surface area with a uniform, porous, and web-like nano-sized carbon layer at the surface. The initial discharge capacity and energy density were 152 mAh/g and 570 Wh/kg, respectively, at 0.1 C current density, and showed stable cycle performance. The combined effect of high porosity and uniform carbon coating leads to fast lithium ion diffusion and enhanced electro- chemical performance.

Mixed (Al-Cu) pillared clays as wet peroxide oxidation catalysts

Abstract Al-Cu pillared clays were prepared by direct introduction of Al-Cu pillaring solution into the dilute bentonite suspension. Al-Cu pillared clays had doo1 spacing of about 18 and had surface area of about 140m 2 /g or higher. Al-Cu pillared clays showed excellent activity toward the catalytic wet peroxide oxidation of reactive black 5. Complete removal of reactive black 5 could be achieved within 20min at atmospheric pressure and 80°C0C which are extremely milder operation condition when compared with the conventional catalytic wet oxidation process. The pillared clays were also stable against the leaching out of Cu.

Preparation of iron-doped titania-pillared clays and their application to selective catalytic reduction of NO with ammonia

TiO 2 -pillared clays were synthesized by pillaring TiO 2 onto the pure bentonite. As the pillaring agent was used a solution of paritially hydrolyzed Ti-polycation which had been prepared by adding TiCl 4 into HCl solution. Successful intercalation of TiO 2 could be achieved, and the physical properties such as d 001 spacing, surface area and pore volume were influenced by the concentration of HCl, TiCl 4 and Ti/clay ratio. The d 001 spacing and surface area of the TiO 2 -PILCs increased up to 29.8and 389m 2 /g. respectively. The pore volume also increased up to 0.25cm 3 /g which was significantly higher than 0.06 cm 3 /g of the unpillared clay. The N 2 adsorption isotherms showed the presence of both the micropores and mesopores in the pillared clays. TPD and FTIR analyses showed the wide presence of the BrOnsted acid site which is essential to the SCR of NO with NH 3 . When Fe 2 O 3 was incorporated into the TiO 2 -PILCs, the Bronsted acidity increased significantly, and even the complete conversion of NO could be achieved with the Fe 2 O 3 /TiO 2 s at the temperature window between 375-400°C.