• Title/Summary/Keyword: vanadium oxides

Search Result 52, Processing Time 0.031 seconds

Single crystal growth of syntheric emerald by reflux method of temperatute gradient using natural beryl (천연베릴을 이용한 온도구배 환류법에 의한 합성 Emerald 단결정 육성)

  • 최의석;김무경;안영필;서청교;안찬준;이종민
    • Journal of the Korean Crystal Growth and Crystal Technology
    • /
    • v.8 no.4
    • /
    • pp.532-538
    • /
    • 1998
  • Emerald ($3BeO{\cdot}Al_2O_3{\cdot}6SiO_2:Cr^{3+}$) single crystal was grown by temperature gradient reflux method with using Korean natural beryl. The flux of lithium-molibudenium-vanadium oxide system was made by means of mixing the 2 sort of flux which were differently melted $Mo_3-Li_2O$ and $V_2O_5-Li_2O$ each other. The optimum composition of flux was 3 mole ratio of molibudenium. vanadium oxides to lithium oxide ($(MoO_3+V_2O_5)/Li_2O$), flux additives were substituted more less then 0.2 mole% of $K_2O$ or $Na_2O$ to the $Li_2O$ amount. The melting concentration of mixing beryl material was 3~10% content to the flux, that of $Cr_2O_3$ color dopant was 1% to the beryl amount. In the crystal growing apparatus with temperature gradient in the 3 zone furnace which was separated into the block of melt, growth and return, the solution have got to circulate continuously between $1100^{\circ}C$ and $1000^{\circ}C$ in steady state. When thermal fluctuation was treated to during 2 hrs once on a day at 950~$1000^{\circ}C$ in growth zone, the supersaturation solution was maintained, controled and emerald single crystal can be grown large crystal which was prevented from the nucleation of microcrystallite. The preferencial growth direction of hexagonal columnar emerald single crystal was the c(0001) plane of botton side and vertical to the m(1010) plane of post side.

  • PDF

Photodecomposition of Concentrated Ammonia over Nanometer-sized TiO2, V-TiO2, and Pt/V-TiO2 Photocatalysts

  • Choi, Hyung-Joo;Kim, Jun-Sik;Kang, Mi-Sook
    • Bulletin of the Korean Chemical Society
    • /
    • v.28 no.4
    • /
    • pp.581-588
    • /
    • 2007
  • To enhance the photodecomposition of concentrated ammonia into N2, Pt/V-TiO2 photocatalysts were prepared using solvothermal and impregnation methods. Nanometer-sized particles of 0.1, 0.5 and 1.0 mol% V-TiO2 were prepared solvothermally, and then impregnated with 1.0 wt% Pt. The X-ray diffraction (XRD) peaks assigned to V2O5 at 30.20 (010) and Pt metal at 39.80 (111) and 46.20 (200) were seen in the 1.0 wt% Pt/ 10.0 mol% V-TiO2. The particle size increased in the order: pure TiO2, V-TiO2 and Pt/V-TiO2 after thermal treatment at 500 °C, while their surface areas were in the reverse order. On X-ray photoelectron spectroscopy (XPS), the bands assigned to the Ti2p3/2 and Ti2p1/2 of Ti4+-O were seen in all the photocatalysts, and the binding energies increased in the order: TiO2 < Pt/V-TiO2 < V-TiO2. The XPS bands assigned to the V2p3/2 (517.85, 519.35, and 520.55 eV) and V2p1/2 (524.90 eV) in the V3+, V4+ and V5+ oxides appeared over V-TiO2, respectively, while the band shifted to a lower binding energy with Pt impregnation. The Pt components of Pt/ V-TiO2 were identified at 71.60, 73.80, 75.00 and 76.90 eV, which were assigned to metallic Pt 4f7/2, PtO 4f7/2, PtO2 4f7/2, and PtO 4f5/2, respectively. The UV-visible absorption band shifted closer towards the visible region of the spectrum in V-TiO2 than in pure TiO2 and; surprisingly, the Pt/V-TiO2 absorbed at all wavelengths from 200 to 800 nm. The addition of vanadium generated a new acid site in the framework of TiO2, and the medium acidic site increased with Pt impregnation. The NH3 decomposition increased with the amount of vanadium compared to pure TiO2, and was enhanced with Pt impregnation. NH3 decomposition of 100% was attained over 1.0 wt% Pt/1.0 mol% V-TiO2 after 80 min under illumination with 365 nm light, although about 10% of the ammonia was converted into undesirable NO2 and NO. Various intermediates, such as NO2, -NH2, -NH and NO, were also identified in the Fourier transform infrared (FT-IR) spectra. From the gas chromatography (GC), FT-IR and GC/mass spectroscopy (GC/MS) analyses, partially oxidized NO and NO2 were found to predominate over V-TiO2 and pure TiO2, respectively, while both molecules were reduced over Pt/V-TiO2.

Uranium Occurrences, and Process Development for Recovering Uranium and Vanadium from Uranium Ore in Coaly Meta-Pelites in Ogcheon Terrain, Korea (I) (한반도(韓半島) 옥천대(沃川帶) 탄질이암층중(炭質泥岩層中)의 저품위(低品位) 우라늄광(鑛)의 부존상태(賦存狀態) 및 우라늄, 바나듐 회수공정개발연구(回收工程開發硏究) ( I ))

  • So, Chil-Sup;Choi, Cheong-Song
    • Economic and Environmental Geology
    • /
    • v.17 no.1
    • /
    • pp.35-47
    • /
    • 1984
  • Combined mineralogical and geochemical studies were made on two hundred eighty one representative samples from uraniferous coaly meta-pelites of the Ogcheon metamorphic terrain. Different mineral occurrence of the areas investigated should be taken into account for chemical processes for uranium extraction. Secondary uranium minerals identified are metauranocircite, metatorbernite and autunite. These are disseminated mostly on the laumontites which infused and filled secondary openings in the coaly matrix, and are often closely associated with iron oxides. The uranium distribution show distinctly log normal. Geochemical correlation coefficient of uranium and organic carbon displays +0.624~+0.796. The relationship of the major components to uranium can be expressed by the following regression equation: Log $(U_3O_8{\times}10^4)$=1.40117-0.00076 (quartz) -0.00118 (muscovite) +0.00235 (biotite) +0.00323 (other silicates) - 0.01114 (apatite) +0.01124 (hematite) +0.00149 (limonite) -0.01823 (opaques)+0.03049 (organic carbon). Uranium in the coaly meta-pelites of the Ogcheon Group was deposited together under same physico-chemical environmental conditions. There is a considerable variation in the ${\delta}^{34}S$ values (11.2~16.8 per mil) of the pyrites from the U-bearing meta-pelites, which implies sedimentary origin. The two U-bearing coaly rocks analyzed have ${\delta}^{13}C$ values between -16.88~-18.00 per mil, which suggests organic.

  • PDF

Numerical Modeling of Vanadia-based Commercial Urea-SCR plus DOC Systems for Heavy-duty Diesel Exhaust Aftertreatment Systems (바나듐 기반의 Urea-SCR과 DOC가 결합된 Heavy-Duty 디젤 배출가스 후처리 시스템의 SCR De-NOx 성능 향상에 관한 수치해석 연구)

  • Yun, Byoung-Kyu;Kim, Chong-Min;Kim, Man-Young;Cho, Gyu-Baek;Kim, Hong-Suk;Jeong, Young-Il
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.18 no.2
    • /
    • pp.24-30
    • /
    • 2010
  • In this study, numerical experiments were carried out to estimate the SCR De-NOx performance in DOC plus SCR systems. The SCR De-NOx phenomena are described by Langmuir-Hinshelwood reaction scheme. After validating the present approach by comparing the present results with the experimental results, such various parameters as space velocity, $H_2O$ concentration, $NO_2$/NOx ratio and relative volume of DOC are explored to increase the SCR De-NOx performance. The results indicate that SCR De-NOx performance largely depends on space velocity and $NO_2$/NOx ratio, especially below $200^{\circ}C$. SCR De-NOx performance is seriously affected by relative volume of DOC with SCR due to increasing in $NO_2$/NOx ratio at below $250^{\circ}C$.

Understanding of Growth Habits of $VO_2$ Film on Graphene and Their Effects on Metal to Insulator $Transition_2$

  • Yang, Jae-Hoon;Kim, Keun-Soo;Jang, A-Rang;Yang, Hyoung-Woo;Kang, Dae-Joon
    • Proceedings of the Korean Vacuum Society Conference
    • /
    • 2012.02a
    • /
    • pp.572-572
    • /
    • 2012
  • Growth of metal oxides on graphene may lead to a better understanding of delicate effects of their growth habits on their underlying physics. The vanadium dioxide ($VO_2$) is well known for its metal-to-insulator transition accompanied by a reversible first order structural phase transition at 340 K. This transition makes $VO_2$ a potentially useful material for applications in electrical and optical devices. We report a successful growth of $VO_2$ nanostructures on a graphene substrate via a vapor-solid transport route. As-grown $VO_2$ nanostructures on graphene were systematically characterized by field emission scanning electron microscopy, x-ray diffraction, Raman spectroscopy, FT-IR spectroscopy and high resolution transmission electron microscopy. These results indicate that the strain between $VO_2$ and graphene layers may be easily controlled by the number of underlying graphene layer. We also found that the strain in-between $VO_2$ and graphene layer affected its metal-to-insulator transition characteristics. This study demonstrates a new way for synthesizing $VO_2$ in a desired phase on the transparent conducting graphene substrate and an easy pathway for controlling metal-to-insulator phase transition via strain.

  • PDF

Characterization of V/TiO2 Catalysts for Selective Reduction (V/TiO2 촉매의 선택적 촉매 환원 반응특성 연구)

  • Lee, Sang-Jin;Hong, Sung-Chang
    • Applied Chemistry for Engineering
    • /
    • v.19 no.5
    • /
    • pp.512-518
    • /
    • 2008
  • The present work studied the selective catalytic reduction (SCR) of NO to $N_2$ by $NH_3$ over $V/TiO_2$ focusing on NOx control for the stationary sources. The SCR process depends mainly on the catalyst performance. The reaction characteristics of SCR with $V/TiO_2$ catalysts were closely examined at low and high temperature. In addition, adsorption and desorption characteristics of the reactants on the catalyst surface were investigated with ammonia. Seven different $TiO_2$ supports containing the same loading of vanadia were packed in a fixed bed reactor respectively. The interaction between $TiO_2$ and vanadia would form various non-stoichiometric vanadium oxides, and showed different reaction activities. There were optimum calcination temperatures for each samples, indicating different reactivity. It was finally found from the $NH_3-TPD$ test that the SCR activity was nothing to do with $NH_3$ adsorption amount.

Catalytic Technology for NOx Abatement using Ammonia (암모니아를 환원제로 이용한 NOx 저감 촉매 기술)

  • Park, Soon Hee;Lee, Kwan-Young;Cho, Sung June
    • Clean Technology
    • /
    • v.22 no.4
    • /
    • pp.211-224
    • /
    • 2016
  • Three way catalyst has been used extensively for the exhaust gas treatment for the internal combustion gasoline engine. While, numerous research efforts have been directed to develop various technologies for the abatement of exhaust gas from diesel engine. Diesel engine operating under lean condition produces large amount of NOx and the corresponding catalytic technology employing vanadium supported titania using ammonia has been commercialized for heavy duty vehicle. Recently, the Cu catalyst supported on zeolite has been investigated for NOx abatement using ammonia because of its critical importance for ultra low emission vehicle. The current review shows the recent trend in research and development for zeolite based copper catalysts, which are mainly used as catalysts for selective catalytic reduction using ammonia, are one of the aftertreatment technologies for effectively removing nitrogen oxides from diesel exhaust.

The Effect of Vanadium(V) Oxide Content of V2O5-WO3/TiO2 Catalyst on the Nitrogen Oxides Reduction and N2O Formation (질소산화물 환원과 N2O 생성에 있어서 V2O5-WO3/TiO2 촉매의 V2O5 함량 영향)

  • Kim, Jin-Hyung;Choi, Joo-Hong
    • 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 $250{\sim}320^{\circ}C$.

Spent SCR Catalyst Leach Liquor Processed for Valuable Metals Extraction by Solvent Extraction Technique (SCR 폐촉매 침출액으로부터 용매추출법에 의한 유가금속의 추출)

  • Sola, Ana Belen Cueva;Jeon, Jong-Hyuk;Lee, Jin-Young;Parhi, Pankaj Kumar;Jyothi, Rajesh Kumar
    • Resources Recycling
    • /
    • v.29 no.2
    • /
    • pp.55-61
    • /
    • 2020
  • Selective catalytic reduction (SCR) has been a promising technology to reduce the air pollution caused by nitrogen oxides (NOx) in several industries. The consumption of SCR catalysts increases every year as technology evolves, however those have a limited lifespan and usually end up in landfills after they deactivate. Currently, the most widely used catalyst for and stationary applications is V2O5-WO3/TiO2 which can contain around 50% wt V2O5 and 7-10% wt of WO3. The vast uses for both vanadium and tungsten and the worldwide interest in recycling methods that allow for the extraction of metals from secondary sources represent the major motivation for this research. The extraction time, pH dependency, extraction concentration studies were carried out using Aliquat 336 in exxol D80 as the extractant. It was determined that to optimize the extraction of both metals 30min of contact time with an organic phase containing 0.5mol/L of Aliquat 336 are needed at a slightly acidic pH (~5.0). In addition, counter McCabe-Thiele studies allowed us to determine that one stage is necessary for the removal of 99% of vanadium while 2 stages are necessary for the extraction of tungsten and counter current simulations proved that the theoretical approach was correct.

The Study of Reaction Characteristics of V/W/TiO2 Catalyst Using Se-TiO2 Support On NH3-SCR Reaction (Se-TiO2 지지체를 이용한 V/W/TiO2 NH3-SCR 촉매의 반응 특성 연구)

  • Lee, Yeon Jin;Won, Jong Min;Ahn, Suk Hyun;Hong, Sung Chang
    • Applied Chemistry for Engineering
    • /
    • v.32 no.6
    • /
    • pp.599-606
    • /
    • 2021
  • In this study, an experiment and a reaction characteristic study were conducted to enhance the reaction activity of V2O5/WO3/TiO2 at 300 ℃ or less by adding selenium to the support, in a selective catalytic reduction method using ammonia as a reducing agent to remove nitrogen oxides. Se-TiO2 and TiO2 were synthesized using the sol-gel method, and used as a support when preparing V2O5/WO3/TiO2 and V2O5/WO3/Se-TiO2 catalysts. The reaction activity of our catalyst was compared with that of a commercial catalyst. The denitration efficiency of the catalyst using TiO2 prepared by the sol-gel method was lower than that of the catalyst prepared using commercial TiO2, but was improved by the addition of selenium. Thus, the effect of selenium addition on the catalyst structure was analyzed using BET, XRD, Raman, H2-TPR, and FT-IR measurements and the effect of the increase in specific surface area by selenium addition and the formation of monomer and complex vanadium species on reaction characteristics were confirmed.