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201.
In this work, we studied the characteristic variations of catalyst supports caused by mechanical milling and their electrochemical application in fuel cells. Two different catalyst supports, carbon black (XC-72R) and K20 (mesoporous carbon), were crushed and dispersed by mechanical milling using a bead mill. The bead mill operated with 0.3 μm zirconia beads at the rate of 3500 rpm for 30 min. The secondary particle size of the crushed catalyst supports ranged from around 0.1 μm to 10 μm. The secondary particle size of the catalyst supports after crushing represents a decrease of approximately 10% compared with that of raw catalyst supports. To confirm the role of the catalyst supports in the direct methanol fuel cell (DMFC), Pt and Ru were loaded onto these catalyst supports using an impregnation method. In the single cell test, Pt-Ru/XC-Bead and PtRu/K20-Bead showed power densities of 135 mW/cm2 and 144 mW/cm2 under air at 60 °C, respectively. The performance values of these catalysts, which were fabricated using reformed catalyst supports, were 10% to 20% higher than those of raw catalyst supports. As a result, the catalyst supports crushed by the bead mill helped to improve the electrochemical performance of the direct methanol fuel cell. 相似文献
202.
The synthesis of micron-sized polymer particles with a core-shell pomegranate-like morphology is presented. The proposed polymerization technique takes advantage of a reaction-induced micro-phase separation within a suspended organic liquid droplet containing monomer, a chemical initiator, a steric stabilizer, and a poor solvent for the polymer. With an increase in monomer conversion, the monomer droplet suspended in a continuous aqueous medium is transformed first into a micro-capsule with a thick pericellular membrane, and eventually into a polymer particle packed with 300-500 nm polymer sub-particles. The experimentally observed evolution of particle morphology indicates that the reaction pathway is strongly influenced by micro-phase separation and transport phenomena. In the first stage of polymerization, a pseudo-homogeneous polymerization takes place at the droplet surface, followed by a starved macro-dispersive polymerization in the inner region where polymer precipitates out from the solvent phase as nano-sized sub-particles. 相似文献
203.
Polystyrene/polythiophene (PSt/PTh) core/shell nanoparticles were successfully synthesized via a one-pot Fe3+-catalyzed oxidative and soap-free emulsion polymerization process. A small amount of sodium styrene sulfonate (NaSS) was used to maintain the colloidal stability of the PSt/PTh nanoparticles. Hydrogen peroxide (H2O2) and a trace of iron chloride (FeCl3) were used to carry out the free-radical polymerization of styrene and the oxidative polymerization of thiophene. The dual initiation characteristics of H2O2/FeCl3 in the PSt/PTh core/shell nanoparticle formation were investigated by observing the time-evolution of the particle morphology. In addition, photoluminescent property, particle size distribution, core/shell morphology and the formation mechanism of the PSt/PTh nanoparticles were studied by spectrofluorophotometery, dynamic light scattering (DLS), in-situ IR, zeta-potential, and time-evolution field-emission scanning electron microscope (FE-SEM) analyses. 相似文献
204.
Jung Ho Choi Dong Ryul Park Sunyoung Park In Kyu Song 《Korean Journal of Chemical Engineering》2011,28(11):2137-2141
Niobium-containing H6+x P2W18−x Nb x O62 (x=0, 1, 2, 3) Wells-Dawson heteropolyacids (HPAs) were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) in order to elucidate their redox properties. The HPAs formed two-dimensional well-ordered monolayer arrays on graphite surface and exhibited a distinctive current-voltage behavior called negative differential resistance (NDR) in their tunneling spectra. NDR peak voltage measured on HPA molecule was correlated with reduction potential and absorption edge energy determined by electrochemical method and UV-visible spectroscopy, respectively. NDR peak voltage of H6+x P2W18−x Nb x O62 Wells-Dawson HPAs appeared at less negative voltage with increasing reduction potential and with decreasing absorption edge energy. Oxidative dehydrogenation of isobutyraldehyde was also carried out as a model reaction to probe oxidation catalysis of the HPAs. The trend of NDR peak voltage of H6+x P2W18−x Nb x O62 Wells-Dawson HPAs was well consistent with the trend of yield for methacrolein. 相似文献
205.
Grace M. Nisola Arnel B. Beltran Dong Min Sim Dongjoo Lee Bumsuk Jung Wook-Jin Chung 《Journal of Polymer Research》2011,18(6):2415-2424
The gas transport behaviors of O2, N2, CO2 and CH4 were investigated in mixed matrix membranes (MMMs) prepared from polydimethylsiloxane (PDMS) filled with surface functionalized
silica (SiO2) nanoparticles. SiO2 surface modification was performed through silanization using chlorodimethyl silane. FTIR confirmed the presence of dimethyl
silane on SiO2 (Si-DMS) whereas elemental analysis showed 94.2% successful modification. Thermal gravimetric analysis revealed the improved
thermal stabilities of PDMS MMMs. Field emission scanning electron microscopy revealed the uniform distribution of Si-DMS
within the membrane. The effect of Si-DMS in gas permeabilities (P) was in contrast to the Maxwell model prediction. Enhanced
P values of all gases in PDMS MMMs (as compared to pure PDMS) were associated to the improvement in diffusion coefficients
(Dm) despite the reduction in gas solubility coefficients. The increase in Dm values was attributed to the higher free volumes in PDMS MMMs. However, slight declines (<8% of pure PDMS) in selectivities
were observed. Overall, PDMS MMMs have improved performances due to enhanced gas permeabilities. 相似文献
206.
Hye-Ju Jung Ji-Sook Hong Jeong-Kwon Suh 《Korean Journal of Chemical Engineering》2011,28(9):1882-1888
This study aimed to find a way to remove organic pollutants, phenol and humic acid in aqueous solutions using TiO2 spherical activated carbon (Ti-SPAC). The Ti-SPAC was manufactured by resin ion-exchange and a heating process. This method was very effective not only in creating TiO2 on the surface of the supports evenly, but also in making activated carbon that has highly-developed micro pores. To estimate whether Ti-SPAC has the proper features as a photocatalyst and adsorbent, it was examined in detail by X-ray patterns, SEM image, EDXS, BET, EPMA. The results proved that Ti-SPAC is a very useful material for treating wastewater by photocatalysis and absorption. 相似文献
207.
J. M. L. N. de Moura D. Maurer S. Jung L. A. Johnson 《Journal of the American Oil Chemists' Society》2011,88(10):1649-1658
Proof-of-concept for integrated, countercurrent, two-stage, enzyme-assisted aqueous extraction processing of soybeans was demonstrated on a pilot-plant scale (75 kg extruded flaked soybeans) where the protease used to demulsify the cream was recycled into upstream extraction stages. Oil, protein, and solids extraction yields of 98.0 ± 0.5%, 96.5 ± 0.4%, and 86.8 ± 0.5% were achieved by using the integrated countercurrent process. A three-phase horizontal decanter centrifuge efficiently separated the solids from the two liquid fractions (skim and cream). Fine separation between the two liquid fractions was important to reducing the volume of skim contaminating the cream fraction, thereby reducing the amount of enzyme used for cream demulsification and subsequent extraction. We were able to reduce enzyme use when moving from the laboratory to the pilot-plant scale, which reduced the degree of protein hydrolysis and improved cream demulsification. Enzyme-catalyzed cream demulsification was 91.6% efficient and 93.0% free oil recovery from cream was achieved by using the integrated approach. 相似文献
208.
Bi2S3 and Bi2S3/C nanocomposites prepared by high-energy mechanical milling were evaluated as electrode materials in lithium secondary batteries. For a Bi2S3/C nanocomposite, Bi2S3 nanocrystallites were well distributed in an amorphous carbon matrix. The reaction mechanism of the Bi2S3/C electrode was also examined during the first cycle. The Bi2S3/C nanocomposite anode showed superior electrochemical performance (ca. 500 mAh g−1 and 85% of the capacity retention over 100 cycles). 相似文献
209.
Dae Ho Lim Ji Hwa Jang Hae Ryong Jin Yong Kang Heon Jung Sang Done Kim Woo Hyun Kim 《Chemical engineering science》2011,(14):3145
Characteristics of heat transfer were investigated in a three-phase circulating fluidized bed whose diameter and height were 0.102 m (ID) and 2.5 m, respectively. Effects of gas and liquid velocities, particle size (0.5–3.0 mm), solid circulation rate (2.0–6.5 kg/m2 s), and surface tension (47.53–72.75×10−3 N/m) of liquid phase on the heat transfer coefficient were examined. It was found that the heat transfer coefficient (h) between the immersed vertical heater and the riser proper of the three-phase circulating fluidized bed increased with increase in gas and liquid velocities, but did not change considerably with a further increase in liquid velocity, even in the higher range. The value of heat transfer coefficient increased gradually with increase in the size of fluidized solid particles without exhibiting the local minimum, which represented that there was no bed contraction in three-phase circulating fluidized beds due to the higher liquid velocity. The heat transfer system could attain a stabilized condition more easily with increase in particle size. The value of heat transfer coefficient increased with increase in solid circulation rate in all the cases studied due to the increase of solid holdup in the riser. The value of heat transfer coefficient decreased with increase in surface tension of liquid phase, due to the decrease of bubbling phenomena and bubble holdup. The decrease in liquid surface tension could lead to an increase in elapsed time from which the temperature difference between the heater surface and the riser became an almost constant value. The experimentally obtained values of heat transfer coefficient were well correlated in terms of dimensionless groups as well as operating variables. 相似文献
210.
The transitional behaviours of emulsion polymerisation for styrene and butyl acrylate (BA) monomers from zero-one to pseudo-bulk regime were mechanistically investigated. A dynamic mathematical model, which incorporates cross-over mechanism from zero-one to pseudo-bulk kinetics was developed for emulsion polymerisation and compared with experimental data for conversion, particle size and molar mass. Particles smaller than cross-over size follow zero-one kinetics and particles greater than cross-over size, they follow pseudo-bulk kinetics. In our mechanistic approach, particles nucleated from micelles, grow until the cross-over size is attained, based on zero-one kinetics, and subsequently continue to grow based on pseudo-bulk kinetics. Key findings from our work are that the developed transitional model predictions agree reasonably with experimental data on process and product attributes such as conversion, average molecular weight, molecular weight distribution (MWD), average particle size and particle size distribution (PSD). Optimal strategies for semibatch operation was developed using reaction temperature and monomer feed rate as process variables with specified initial conditions. 相似文献