• Journal of Powder Materials
• /
• v.11 no.1
• /
• pp.28-33
• /
• 2004

In the present study, the focus is on the analysis of carbothermal reduction of the titanium-cobalt-oxygen based oxide powder by solid carbon for the optimizing synthesis process of ultra fined TiC/Co composite powder. The titanium-cobalt-oxygen based oxide powder was prepared by the combination of the spray drying and desalting processes using the titanium dioxide powder and cobalt nitrate as the raw materials. The titanium-cobalt-oxygen based oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under a flowing argon atmosphere. The changes in the phase structure and thermal gravity of the mixture during carbothermal reduction were analysed using XRD and TGA. The synthesized titanium-cobalt-oxygen based oxide powder has a mixture of $TiO_2$ and $CoTiO_3$. This oxide powder was transformed to a mixed state of titanium car-bide and cobalt by solid carbon through four steps of carbothermal reduction steps with increasing temperature; reduction of $CoTiO_3$ to $TiO_2$ and Co, reduction of $TiO_2$, to the magneli phase($Ti_nO_{2n-1}$, n>3), reduction of the mag-neli phase($Ti_nO_{2n-1}$, n>3) to the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases, and reduction and carburization of the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases to titanium carbide.

• Journal of Environmental Science International
• /
• v.12 no.9
• /
• pp.997-1004
• /
• 2003

The objective of this research was to test whether, under controlled laboratory conditions, hybrid SNCR/SCR process improves N $O_{x}$ removal efficiency in comparison with the SNCR only. The hybrid process is a combination of a redesigned existing SNCR with a new downstream SCR. N $O_{x}$ reduction experiments using a hybrid SNCR/SCR process have been conducted in simple NO/N $H_3$/ $O_2$ gas mixtures. Total gas flow rate was kept constant 4 liter/min throughout the SNCR and SCR reactors, where initial N $O_{x}$ concentration was 500 ppm in the presence of 5% or 15% $O_2$. Commercial catalysts, $V_2$ $O_{5}$ -W $O_3$-S $O_4$/Ti $O_2$, were used for SCR N $O_{x}$ reduction. The residence time and space velocity were around 1.67 seconds and 2,400 $h^{-1}$ or 6000 $h^{-1}$ in SNCR and SCR reactors, respectively. N $O_{x}$ reduction of the hybrid system was always higher than could be achieved by SNCR alone at a given value of N $H_{3SLIP}$. Optimization of the hybrid system performance requires maximizing N $O_{x}$ removal in the SNCR process. An analysis based on the hybrid system performance in this lab-scale work indicates that a equipment with N $O_{xi}$ =500 ppm will achieve a total N $O_{x}$ removal of about 90 percent with N $H_{3SLIP}$ $\leq$ 5 ppm only if the SNCR N $O_{x}$ reduction is at least 60 percent. A hybrid SNCR/SCR process has shown about 26∼37% more N $O_{x}$ reduction than a SNCR unit process in which a lower temperature of 85$0^{\circ}C$ turned out to be more effective.be more effective.

• Journal of Environmental Science International
• /
• v.22 no.1
• /
• pp.73-81
• /
• 2013

The present work has been devoted to the catalytic reduction of $N_2O$ by $H_2$ with $Pt/SiO_2$ catalysts at very low temperatures, such as $110^{\circ}C$, and their nanoparticle sizes have been determined by using $H_2-N_2O$ titration, X-ray diffraction(XRD) and high-resolution transmission electron microscopy(HRTEM) measurements. A sample of 1.72% $Pt/SiO_2$, which had been prepared by an ion exchange method, consisted of almost atomic levels of Pt nanoparticles with 1.16 nm that are very consistent with the HRTEM measurements, while a $Pt/SiO_2$ catalyst possessing the same Pt amount via an incipient wetness technique did 13.5 nm particles as determined by the XRD measurements. These two catalysts showed a noticeable difference in the on-stream $deN_2O$ activity maintenance profiles at $110^{\circ}C$. This discrepancy was associated with the nanoparticle sizes, i.e., the $Pt/SiO_2$ catalyst with the smaller particle size was much more active for the $N_2O$ reduction. When repeated measurements of the $N_2O$ reduction with the 1.16 nm Pt catalyst at $110^{\circ}C$ were allowed, the catalyst deactivation occurred, depending somewhat on regeneration excursions.

• Journal of ILASS-Korea
• /
• v.25 no.3
• /
• pp.132-138
• /
• 2020

N₂O is hazardous atmosphere pollution matter which can damage the ozone layer and cause green house effect. There are many other nitrogen oxide emission control but N₂O has no its particular method. Preventing further environmental pollution and global warming, it is essential to control N₂O emission from industrial machines. In this study, the thermal decomposition experiment of N₂O gas mixture is conducted by using cylindrical reactor to figure out N₂O reduction and NO formation. And CHEMKIN calculation is conducted to figure out reaction rate and mechanism. Residence time of the N₂O gas in the reactor is set as experimental variable to imitate real SNCR system. As a result, most of the nitrogen components are converted into N2. Reaction rate of the N₂O gas decreases with N₂O emitted concentration. At 800℃ and 900℃, N₂O reduction variance and NO concentration are increased with residence time and temperature. However, at 1000℃, N₂O reduction variance and NO concentration are deceased in 40s due to forward reaction rate diminished and reverse reaction rate appeared.

• Bulletin of the Korean Chemical Society
• /
• v.15 no.1
• /
• pp.53-57
• /
• 1994

A comparison study on asymmetric borane reduction of ketoxime ethers and N-substituted ketimines possesing C = N double bond mediated by the selected chiral oxazaborolidines (1-6) was investigated. Thus, an aromatic ketoxime O-alkyl ether acetophenone oxime O-methyl ether was reduced to the corresponding amine (1-phenylethylamine 8a) with optical yields, such as 58% ee with 1, 86% ee with 2, 3% ee with 3, 99% ee with 4, 60% ee with 5, and 73% ee with 6. However, the reduction of an aliphatic ketoxime derivative 2-heptanone oxime O-methyl ether provided low optical inductions (7-13% ee). For ketoxime O-trimethylsilyl ethers, the reduction of acetophenone O-trimethylsilyl ether afforded 8a with optical yields which were 90% ee with 1, 40% ee with 2, 2% ee with 3, 62% ee with 4, 5% ee with 5, and 60% ee with 6. The reduction of 2-heptanone O-trimethylsilyl ether also gave the product amine with low optical yields (10-40% ee). In the case of N-substituted ketimines, the reduction of acetophenone N-phenylimine afforded the corresponding amine with 79% ee, 78% ee, 9% ee, 73% ee, 78% ee and 67% ee using 1, 2, 3, 4, 5, and 6, respectively, whereas low optical inductions (5-18% ee) for 2-heptanone N-phenylimine were achieved.

• Korean Chemical Engineering Research
• /
• v.47 no.1
• /
• pp.96-104
• /
• 2009

In order to lower a reaction temperature with high conversions for simultaneous catalytic reduction of NO and $N_2O$ over Pd-Rh supported mixed metal oxide honeycomb catalysts, $H_2$ or CO was utilized as a reductant. When using the reductants, the effects of reaction conditions were examined in NO and $N_2O$ conversions, where reaction temperatures, concentrations of the reductants and oxygen and the concentration ratio of $N_2O$ to NO were varied. In using $H_2$ reductant, larger than 50% of NO and $N_2O$ conversions was observed at the temperatures below $200^{\circ}C$ in absence of $O_2$. In using CO reductant, NO and $N_2O$ conversions increased from the temperatures higher than $200^{\circ}C$ and $300^{\circ}C$, respectively. However, in use of both reductants, NO and $N_2O$ conversions decreased with increasing oxygen concentration. As a result, $H_2$ reductant could reduce simultaneously NO and $N_2O$ at relatively lower reaction temperature than CO. Also, NO and $N_2O$ conversions were less influenced by using $H_2$ reductant than CO one. Concentration ratio between NO and $N_2O$ did not affect their conversions regardless the type of reductants. Pretreatment of the catalyst in $H_2$ was more effective in simultaneous reduction of NO and $N_2O$ at low reaction temperature than that in $O_2$.

• Journal of Korean Society for Atmospheric Environment
• /
• v.33 no.6
• /
• pp.605-615
• /
• 2017

Efficient simultaneous reduction conditions for $NO_x$ and $NH_3$-slip was investigated in SCR (Selective Catalytic Reduction) process with load variation by applying dual catalysts (SCR catalyst, $NH_3$ decomposition catalyst) system. $N_2O$ formation characteristics were analyzed to look into possible undesirable reaction pathways. In the experiments of catalyst characteristics, various operational variables were tested for the combined catalytic system, such as $NH_3/NO_x$ ratio, temperature, oxygen concentration and $H_2O$. The reaction characteristics of $NO_x$, $NH_3$ and $N_2O$ were analyzed and optimal conditions could be evaluated for the combustion facility with varied load. In terms of $NO_x/NH_3$ simultaneous reduction and $N_2O$ formation suppression, optimal condition was considered NSR 1.2 and temperature $300^{\circ}C$. At this operational condition, $NO_x$ conversion was 98%, $NH_3$ reduction efficiency was 95%, generated $N_2O$ concentration 9.5 ppm with inlet $NO_x$ concentration of 100 ppm. In $NH_3-SCR$ process with $NH_3$ decomposition catalyst, $NO_x$ and $NH_3$ can be considered to be reduced simultaneously at limited conditions. The results of this study may be utilized as basic data at facilities requiring simultaneous $NO_x$ and $NH_3$ reduction for facilities with load variation.

• Applied Chemistry for Engineering
• /
• v.19 no.6
• /
• pp.624-628
• /
• 2008

Nitrous oxide ($N_2O$), known as one of the major greenhouse gases, is an important component of the earth's atmosphere, and gives rise to precursor of acid rain and photochemical smog. For the removal of $N_2O$ and other nitrogen oxides, the SCR reaction system with various reductants is widely used. This study is based on the results of experimental and theoretical examinations on the catalytic decomposition of sole nitrous oxide ($N_2O$) and selective catalytic reduction of $N_2O$ with $CH_4$ in the presence of oxygen using mixed metal oxide catalysts obtained from hydrolatcite-type precursors. When $CH_4$ is fed together with a reductant, it affects positively on the $N_2O$ decomposition activity. At an optimum ratio of $CH_4$ to $O_2$ mole ratio, the $N_2O$ conversion activity is enhanced on the SCR reaction with partial oxidation of methane.

• Korean Chemical Engineering Research
• /
• v.51 no.3
• /
• pp.313-318
• /
• 2013

In order to investigate the effect of $V_2O_5$ loading of $V_2O_5-WO_3/TiO_2$ catalyst on the NO reduction and the formation of $N_2O$, the experimental study was carried out in a differential reactor using the powder catalyst. The NO reduction and the ammonia oxidation were, respectively, investigated over the catalysts compose of $V_2O_5$ content (1~8 wt%) based on the fixed composition of $WO_3$ (9 wt%) on $TiO_2$ powder. $V_2O_5-WO_3/TiO_2$ catalysts had the NO reduction activity even under the temperature of $200^{\circ}C$. However, the lowest temperature for NO reduction activity more than 99.9% to treat NO concentration of 700 ppm appeared at 340 with very limited temperature window in the case of 1 wt% $V_2O_5$ catalyst. And the temperature shifted to lower one as well as the temperature window was widen as the $V_2O_5$ content of the catalyst increased, and finally reached at the activation temperature ranged $220{\sim}340^{\circ}C$ in the case of 6 wt% $V_2O_5$ catalyst. The catalyst of 8 wt% $V_2O_5$ content presented lower activity than that of 8 wt% $V_2O_5$ content over the full temperature range. NO reduction activity decreased as the $V_2O_5$ content of the catalyst increased above $340^{\circ}C$. The active site for NO reduction over $V_2O_5-WO_3/TiO_2$ catalysts was mainly related with $V_2O_5$ particles sustained as the bare surface with relevant size which should be not so large to stimulate $N_2O$ formation at high temperature over $320^{\circ}C$ according to the ammonia oxidation. Currently, $V_2O_5-WO_3/TiO_2$ catalysts were operated in the temperature ranged $350{\sim}450^{\circ}C$ to treat NOx in the effluent gas of industrial plants. However, in order to save the energy and to reduce the secondary pollutant $N_2O$ in the high temperature process, the using of $V_2O_5-WO_3/TiO_2$ catalyst of content $V_2O_5$ was recommended as the low temperature catalyst which was suitable for low temperature operation ranged $250{\sim}320^{\circ}C$.

• Environmental Engineering Research
• /
• v.10 no.5
• /
• pp.239-246
• /
• 2005

The effect of Pt addition over $V_2O_5-WO_3/TiO_2$ catalyst supported on PRO-66 was investigated for NO reduction in order to develop the catalytic filter working at low temperature. Catalytic filters, $Pt-V_2O_5-WO_3/TiO_2/PRD$, were prepared by co-impregnation of Pt, V, and W precursors on $TiO_2$-coated ceramic filter named PRD (PRD-66). Titania was coated onto the pore surface of the ceramic filter using a vacuum aided-dip coating method. The Pt-loaded catalytic filter shifted the optimum working temperature from $260-320^{\circ}C$(for the catalytic filter without Pt addition) to $190-240^{\circ}C$, reducing 700 ppm NO to achieve the $N_x$ slip concentration($N_x\;=\;NO+N_2O+NO_2+NH_3$) less than 20 ppm at the face velocity of 2 cm/s. $Pt-V_2O_5-WO_3/TiO_2$ supported on PRD showed the similar catalytic activity for NO reduction with that supported on SiC filter as reported in a previous study, which implies the ceramic filter itself has no considerable interaction for the catalytic activity.