• Journal of Powder Materials
• /
• v.24 no.2
• /
• pp.96-101
• /
• 2017

Well-dispersed platinum catalysts on ruthenium oxide nanofiber supports are fabricated using electrospinning, post-calcination, and reduction methods. To obtain the well-dispersed platinum catalysts, the surface of the nanofiber supports is modified using post-calcination. The structures, morphologies, crystal structures, chemical bonding energies, and electrochemical performance of the catalysts are investigated. The optimized catalysts show well-dispersed platinum nanoparticles (1-2 nm) on the nanofiber supports as well as a uniform network structure. In particular, the well-dispersed platinum catalysts on the ruthenium oxide nanofiber supports display excellent catalytic activity for oxygen reduction reactions with a half-wave potential ($E_{1/2}$) of 0.57 V and outstanding long-term stability after 2000 cycles, resulting in a lower $E_{1/2}$ potential degradation of 19 mV. The enhanced electrochemical performance for oxygen reduction reactions results from the well-dispersed platinum catalysts and unique nanofiber supports.

• Bulletin of the Korean Chemical Society
• /
• v.28 no.11
• /
• pp.1996-2002
• /
• 2007

The redox behavior of a [Ni6(μ3-Se)2(μ4-Se)3(Fe(η 5-C5H4P-Ph2)2)3] (= [Ni-Se-dppf], dppf = 1,1-bis(diphenylphosphino) ferrocene) cluster was studied using platinum (Pt) and glassy carbon electrodes (GCE) in nonaqueous media. The cluster showed electrochemical activity at the potential range between +1.6 and ?1.6 V. In the negative region (0 to ?1.6 V), the cluster exhibited two-step reductions. The first step was one-electron reversible, while the second step was a five-electron quasi-reversible process. On the other hand, in the positive region (0 to +1.6 V), the first step involved one-electron quasi-reversible process. The applicability of the cluster was found towards the electrocatalytic reduction of CO2 and was evaluated by experiments using rotating ring disc electrode (RRDE). RRDE experiments demonstrated that two electrons were involved in the electrocatalytic reduction of CO2 to CO at the Se-Ni-dppf-modified electrode.

• Journal of Surface Science and Engineering
• /
• v.51 no.5
• /
• pp.332-336
• /
• 2018

Alkaline oxygen electrocatalysis, targeting anion exchange membrane alkaline-based metal-air batteries has become a subject of intensive investigation because of its advantages compared to its acidic counterparts in reaction kinetics and materials stability. However, significant breakthroughs in the design and synthesis of efficient oxygen reduction catalysts from earth-abundant elements instead of precious metals in alkaline media still remain in high demand. One of the most inexpensive alternatives is carbonaceous materials, which have attracted extensive attention either as catalyst supports or as metal-free cathode catalysts for oxygen reduction. Also, carbon composite materials have been recognized as the most promising because of their reasonable balance between catalytic activity, durability, and cost. In particular, heteroatom (e.g., N, B, S or P) doping on carbon materials can tune the electronic and geometric properties of carbon, providing more active sites and enhancing the interaction between carbon structure and active sites. Here, we focused on boron and nitrogen doped nanocarbon composit (BNC nanocarbon) catalysts synthesized by a solution plasma process using the simple precursor of pyridine and boric acid without further annealing process. Additionally, guidance for rational design and synthesis of alkaline ORR catalysts with improved activity is also presented.

• Applied Chemistry for Engineering
• /
• v.9 no.3
• /
• pp.355-360
• /
• 1998

Reduction activity of precious metal-loaded HZSM-5 for NO has been studied and was compared to that of Cu-HZSM-5 in the presence of excess oxygen. It was found that among the catalysts used in this study, Ru-HZSM-5 was the most active catalyst for the reduction of NO to $N_2$ in the absence of hydrocarbon reductant. The highest conversion obtained was 45%. No severe inhibition of water vapor to the reduction was observed. It is suggested that the higher catalytic activity of Ru-HZSM-5 may result from the better ability to oxidize NO to $NO_2$ in the presence of excess oxygen. A proposed reaction mechanism for the reduction of NO to $N_2$ in the presence of excess oxygen is that NO is oxidized to $NO_2$ on the surface of Ru-HZSM-5 catalyst and the adsorbed $NO_2$ on the surface is then decomposed to $N_2$. $NO_2$ is supposed to the reaction.

• Clean Technology
• /
• v.13 no.4
• /
• pp.266-273
• /
• 2007

The adsorption properties of the activated carbon-based adsorbents were studied to remove COS emitted from $SO_2$ catalytic reduction process on the integrated gasification combined cycle (IGCC) system in this work. Transition metal supported catalysts and mixed metal oxide catalysts were used for the $SO_2$ catalytic reduction. The mechanism of COS produced from the $SO_2$ reduction and the COS concentration s according to the reaction temperature were investigated. In this study, an activated carbon and a modified activated carbon doped with KOH were used to remove the very low concentration of COS effectively. The adsorption rate and the breakthrough time of COS were measured by a thermo gravity analyzer (TGA, Cahn Balance) and a fixed bed flow reactor equipped with GC-pulsed flammable photometric detector (PFPD), respectively. It was confirmed that the COS breakthrough time of the activated carbon doped with KOH was longer than that of an activated carbon. In conclusion, the modified-activated carbon having a high surface area showed a high adsorption rate of COS produced from the $SO_2$ reduction.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.19 no.5
• /
• pp.118-124
• /
• 2011

To reach the Euro-6 regulations of PM and $NO_x$ for light-duty diesel vehicles, it will be necessary to apply the CDPF and the de-$NO_x$ catalyst. The described system consists of a catalytic configuration, where the CDPF is placed downstream of the diesel engine and followed by a urea injection unit and a urea-SCR catalyst. One of the advantages of this system configuration is that, in this way, the SCR catalyst is protected from PM, and both white PM and deposits become reduced. In the urea-SCR system, the injection control of reductant is the most important thing in order to have good performance of $NO_x$ reduction. The ideal ratio of $NH_3$ molecules to $NO_x$ molecules is 1:1 based on $NH_3$ consumption and having $NH_3$ available for reaction of all of the exhaust $NO_x$. However, under the too low and too high temperature condition, the $NO_x$ reduction efficiency become slower, due to temperature window of SCR catalyst. And space velocity also affects to $NO_x$ conversion efficiency. In this paper, rig-tests were performed to evaluate the effects of $NO_x$ and $NH_3$ concentrations, gas temperature and space velocity on the $NO_x$ conversion efficiency of the urea-SCR system. And vehicle test was performed to verify control strategy of reductatnt injection. The developed control strategy of reductant injection was improved over all $NO_x$ reduction efficiency and $NH_3$ consumption in urea-SCR system. Results of this paper contribute to develop urea-SCR system for light-duty vehicles to meet Euro-5 emission regulations.

• Journal of Hydrogen and New Energy
• /
• v.9 no.1
• /
• pp.8-15
• /
• 1998

The catalytic hydrogenation of carbon dioxide has been studied for the fixation of carbon dioxide to mitigate global warming problems, but it needed hydrogen, which the price is still high. Recently, the electrochemical reduction of carbon dioxide has been drawn attractions because carbon dioxide could be converted to the valuable chemicals such as methane, ethane and alcohols electrochemically in the electrolyte solution using a catalytic electrode. This system is simple because the water electrolysis and hydrogenation take place at the same time using the surplus electricity at midnight. In this work, a continuous electrochemical reduction system was fabricated, which was composed of the reduction electrode (copper or perovskite type, $2{\times}2cm^2$), reference electrode(platinum, $2{\times}6cm^2$), standard electrode(Ag/AgCl), and potassium bicarbonate electrolyte solution saturated with carbon dioxide. The quality and quantity of the products and reduction current were analyzed, according to the electrolyte concentration and electrode type.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.4
• /
• pp.412-417
• /
• 2015

The IMO MEPC has been increasingly strengthening the emission standard for marine environment protection. In particular, nitrogen oxide (NOx) emissions of all ocean-going ships built from 2016 will be required to comply with the Tier-III regulation. In this study, a vanadia based SCR (Selective Catalytic Reduction) system developed for ship application was installed on a diesel engine for power generation of the training ship T/S SAENURI in Mokpo National Maritime University. For the present study, the exhaust pipeline of the generator diesel engine was modified to fit the urea SCR system. This study investigated the NOx reduction performance according to the two kind of injection method of urea solution (40%): Auto mode through the PLC (Programable Logic Control) and Manual mode. We were able to find the ammonia slip conditions when in manual mode method. So, the optimal urea injection quantity can be controlled at each engine load (25, 35, 50%) condition. It was achieved 80% reduction on nitrogen oxide. Furthermore, we found that the NOx reduction performance was better with the load up-down (while down to 25% from 50%) than the load down-up (while up to 50% from 25%) test.

• Resources Recycling
• /
• v.33 no.3
• /
• pp.30-37
• /
• 2024

In this study, we investigated the separability of vanadium and tungsten from spent SCR (Selective Catalytic Reduction) catalyst leach solution by reduction of vanadium and solvent extraction using Alamine 336 and conducted experiments to optimize process conditions. It is difficult to separate vanadium and tungsten due to their similar chemical behavior, but tungsten can be selectively extracted from acidic solution when vanadium extraction is prevented by reducing anionic pentavalent vanadium to cationic tetravalent vanadium. The results showed that NaHSO₃ was most suitable as a reducing agent, and the extraction efficiency of vanadium decreased and the separation efficiency increased as the amount of reducing agent added, reaction time, and temperature increased. When reducing NaHSO₃ 1.5 eq, 60 min, and 60℃, which are optimal conditions of reduction, vanadium and tungsten were effectively separated with vanadium extraction efficiency of 5.8%, tungsten extraction efficiency of 99%, and separation factor of vanadium and tungsten of 7,564.

• Applied Chemistry for Engineering
• /
• v.27 no.1
• /
• pp.92-100
• /
• 2016

Low-temperature conversion of nitrogen oxides using plasma-assisted hydrocarbon selective catalytic reduction of (HC-SCR) was investigated. Plasma was created in the catalyst-packed bed so that it could directly interact with the catalyst. The effect of the reaction temperature, the shape of catalyst, the concentration of n-heptane as a reducing agent, the oxygen content, the water vapor content and the energy density on $NO_x$ removal was examined. $NO_x$ conversion efficiencies achieved with the plasma-catalytic hybrid process at a temperature of $250^{\circ}C$ and an specific energy input (SIE) of $42J\;L^{-1}$ were 83% and 69% for one-dimensional Ag catalyst ($Ag\;(nanowire)/{\gamma}-Al_2O_3$) and spherical Ag catalyst ($Ag\;(sphere)/{\gamma}-Al_2O_3$), respectively, whereas that obtained with the catalyst-alone was considerably lower (about 30%) even with $Ag\;(nanowire)/{\gamma}-Al_2O_3$ under the same condition. The enhanced catalytic activity towards $NO_x$ conversion in the presence of plasma can be explained by the formation of more reactive $NO_2$ species and partially oxidized hydrocarbon intermediates from the oxidation of NO and n-heptane under plasma discharge. Increasing the SIE tended to improve $NO_x$ conversion efficiency, and so did the increase in the n-heptane concentration; however, a further increase in the n-heptane concentration beyond $C_1/NO_x$ ratio of 5 did not improve the $NO_x$ conversion efficiency any more. The increase in the humidity affected negatively the $NO_x$ conversion efficiency, resulting in lowering the $NO_x$ conversion efficiency at the higher water vapor content, because water molecules competed with $NO_x$ species for the same active site. The $NO_x$ conversion efficiency increased with increasing the oxygen content from 3 to 15%, in particular at low SIE values, because the formation of $NO_2$ and partially oxidized hydrocarbon intermediates was facilitated.