• Title, Summary, Keyword: $NO_x$ Conversion

Search Result 165, Processing Time 0.036 seconds

The Effect of an Oxidation Precatalyst on the $NO_x$ Reduction by $NH_3$-SCR Process in Diesel Exhaust ($NH_3$-SCR 방법에 의한 디젤 배기 내 De-$NO_x$ 과정에서의 DOC에 의한 영향과 저감 성능 변화)

  • Jung, Seung-Chai;Yoon, Woong-Sup
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.16 no.5
    • /
    • pp.68-76
    • /
    • 2008
  • Diesel $NO_x$ reduction by $NH_3$-SCR in conjunction with the effective oxidation precatalyst was analytically investigated. Physicochemical processes in regard to $NH_3$-SCR $NO_x$ reduction and catalytic NO-$NO_2$ conversion are formulated with detailed descriptions on the commanding reactions. A unified model is correctly validated with experimental data in terms of extents of $NO_x$ reduction by SCR and NO-$NO_2$ conversion by DOC. The present deterministic model based on the rate expressions of Langmuir-Hinshelwood reaction scheme finds a conversion extent directly. A series of numerical experiments concomitant with parametric analysis of the $NO_x$ reduction was conducted. $NO_x$ reduction is promoted in proportion to DOC volume ar lower temperatures and an opposite holds at lower space velocity and intermediate temperatures. $NO_x$ conversion is weakly correlated to the space velocity and the DOC volume at higher exhaust temperature. In DOC-SCR system, the $NO_x$ reduction efficiency depends on the $NH_3/NO_x$ ratio.

Conversion of NOx by Plasma-hydrocarbon Selective Catalytic Reduction Process (플라즈마-탄화수소 선택적 촉매환원공정을 이용한 질소산화물 저감 연구)

  • Jo, Jin-Oh;Mok, Young Sun
    • Applied Chemistry for Engineering
    • /
    • v.29 no.1
    • /
    • pp.103-111
    • /
    • 2018
  • A plasma-catalytic combined process was used as an attempt to improve the conversion efficiency of nitrogen oxides ($NO_x$) over a wide temperature range ($150{\sim}500^{\circ}C$) to cope with the exhaust gas whose temperature varies greatly. Since the catalytic $NO_x$ reduction is effective at high temperatures where the activity of the catalyst itself is high, the $NO_x$ reduction was carried out without plasma generation in the high temperature region. On the other hand, in the low temperature region, the plasma was created in the catalyst bed to make up for the decreased catalytic activity, thereby increasing the $NO_x$ conversion efficiency. Effects of the types of catalysts, the reaction temperature, the concentration of the reducing agent (n-heptane), and the energy density on $NO_x$ conversion efficiency were examined. As a result of comparative analysis of various catalysts, the catalytic $NO_x$ conversion efficiency in the high temperature region was the highest in the case of the $Ag-Zn/{\gamma}-Al_2O_3$ catalyst of more than 90%. In the low temperature region, $NO_x$ was hardly removed by the hydrocarbon selective reduction process, but when the plasma was generated in the catalyst bed, the $NO_x$ conversion sharply increased to about 90%. The $NO_x$ conversion can be maintained high at temperatures of $150{\sim}500^{\circ}C$ by the combination of plasma in accordance with the temperature change of the exhaust gas.

Removal of Nitrogen Oxides Using Hydrocarbon Selective Catalytic Reduction Coupled with Plasma (플라즈마가 결합된 탄화수소 선택적 촉매환원 공정에서 질소산화물(NOx)의 저감)

  • Ihm, Tae Heon;Jo, Jin Oh;Hyun, Young Jin;Mok, Young Sun
    • 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.

[ De-NOx ] Characteristics for Pt/γ-Alumina/Cordierite Foam Filter of Beads Shape (Pt/γ-Alumina/Cordierite 비드형 세라믹 폼 필터의 NOx 제거 특성)

  • Park, Jung-Wook;Park, Jay-Hyun;Park, Jai-Koo
    • Journal of Korean Society for Atmospheric Environment
    • /
    • v.23 no.3
    • /
    • pp.277-285
    • /
    • 2007
  • Porous cordierite beads, of which the average pore size was $130{\mu}m$ and porosity was about 80%, were prepared by the foaming method and then their application as support of the $Pt/{\gamma}-alumina$ catalyst for $NO_x$, reduction with propene was investigated. The pressure drop of a 2 mm porous beads filter was less than that of a 1 mm porous beads filter and the difference in pressure drop between these two increased as the flow rate increased. The catalytic activity of $Pt/{\gamma}-alumina$ washcoated on the porous bead was tested with varying Pt loading $(0.005{\sim}0.1g/cm^3),\;C_3H_6/NO$ mole ratio $(0.5{\sim}8)$, space velocity $(20,000{\sim}30,000h^{-1})$ and oxygen contents (1 and 8). Pt loading of $0.04g/cm^3$ showed the highest activity for $NO_x$ conversion. The $De-NO_x$, test was operated in the temperature range of $200{\sim}400^{\circ}C$ and the best operation temperature of the catalytic filter is about $250^{\circ}C$. As the C/N ratio increased, increase of the $NO_x$, conversion might result from the increase in exhaustion of the amount of oxygen by the reduction of hydrocarbon. $NO_x$ conversion at $20,000h^{-1}$ of space velocity shows a maximum 34% higher conversion than that at $30,000h^{-1}$. On condition that $O_2$ was 5%, space velocity was $20,000h^{-1}$ and the C/N ratio was 8, the $NO_x$ conversion exhibited a maximum of 40% at $250^{\circ}C$.

DeNOx by Hydrocarbon-Selective Catalytic Reduction on Ag-V/γ-Al2O3 Catalyst (Ag-V/γ-Al2O3 촉매상에서 탄화수소-Selective Catalytic Reduction에 의한 질소산화물 저감)

  • Kim, Moon-Chan;Lee, Cheal-Gyu
    • Applied Chemistry for Engineering
    • /
    • v.16 no.3
    • /
    • pp.328-336
    • /
    • 2005
  • In order to remove the NO contained in exhaust gas by the non-selective catalyst reduction method, the catalysts were prepared by varing the loading amount of Ag and V into ${\gamma}-Al_2O_3$. The conversion of $NO_x$ using the prepared catalysts was studied by varying the temperatures, $O_2$ concentrations and $SO_2$ concentrations using. The influence of the catalyst structure on $NO_x$ conversion was studied through the analysis of the physical properties of the prepared catalysts. In the case of $AgV/{\gamma}-Al_2O_3$ catalyst, the $NO_x$ conversion was lower than that of $Ag/{\gamma}-Al_2O_3$ at higher temperatures but higher than that of $Ag/{\gamma}-Al_2O_3$ at lower temperatures. Even though $SO_2$ was contained in the reaction gas, the $NO_x$ conversion did not decrease. Based on the analysis including XRD, XPS, TPR, and UV-Vis DRS before and after the experiments, the experimental results were examined. The results indicated that, $NO_x$ conversion decreased at higher temperatures since Ag oxide could not be maintained well due to the addition of V, whereas it increased at temperatures lower than $300^{\circ}C$ due to the catalytic action of V.

A Performance Modeling of the Lean NOx Trap Catalyst with GT-POWERTM (GT-POWERTM를 이용한 Lean NOx Trap 촉매 성능 모델링)

  • Kim, Hyunjun;Han, Manbae;Jeon, Ji-Yong;Kim, Tae-Min
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.21 no.6
    • /
    • pp.64-71
    • /
    • 2013
  • In this study we designed a lean $NO_x$ trap (LNT) model with $GT-POWER^{TM}$ program and then the LNT model was compared to the bench flow reactor test results. This model consists of 9 kinetic reactions to represent the main steps of NO oxidation, $NO_x$ adsorption, $NO_x$ release and then its reduction. The comparison was performed on the operating conditions at the space velocity of 50,000 1/hr and 80,000 1/hr with the temperature range of $200^{\circ}C{\sim}500^{\circ}C$ with the even spaced temperature step of $50^{\circ}C$. The experimental results show that the $NO_x$ conversion efficiency was enhanced by the temperature up to $350^{\circ}C$ and then decayed at higher temperatures. The LNT model predicts the similar trend of the $NO_x$ conversion efficiency to the experimental results below $350^{\circ}C$, but overestimates above $350^{\circ}C$. This overestimation comes from the higher reduction efficiency which was obtained by the different reduction gas composition such as $C_3H_6$ in the model to replace $CH_4$, $C_2H_4$ in the bench test.

DeNOx performance and characteristic study for transition metals doped iron based catalysts

  • Zhu, Lin;Zhong, Zhaoping;Yang, Han;Wang, Chunhua;Wang, Lixia
    • Korean Journal of Chemical Engineering
    • /
    • v.34 no.4
    • /
    • pp.1229-1237
    • /
    • 2017
  • Novel, environmentally-benign catalysts for selective catalytic reduction of $NO_x$ were prepared by citric method through introducing transition metal elements (Ce, Cu and Co) into iron oxide. The physical-chemical properties of different catalysts were investigated by the characterization technologies like $N_2$-physisorption, XRD, $NH_3/NO-TPD$ and $H_2-TPR$. The results indicated that the introduction of transition metal elements increased the specific surface area and adsorption ability for reactants ($NH_3$ and $NO_x$). The redox capacity for the doped catalysts was improved at the same time. These characteristics all contributed to the improvement of catalytic performance. The $CoFeO_x$ catalyst exhibited the widest temperature window for SCR reaction, and the $CeFeO_x$ catalyst showed the most obvious decline of $NO_x$ conversion with the elevation of temperature above $250^{\circ}C$. Water vapor inhibited the SCR activity at low temperatures and relieved the decline of $NO_x$ conversion at higher temperatures. Meanwhile, the formation of $N_2O$ was inhibited. The pretreatment of $SO_2$ leaded to the sulfation of the active species for different catalysts. The decline of redox capacity and the reduction of active nitrate adsorbed species accounted for the serious loss of SCR activity at low temperatures. The abundant surface acid sites brought by the sulfation process might be the main reason for good SCR activity in the medium temperature range.

An Experimental Study on Optimization of $NH_3$ Injection for the Selective Catalytic Reduction(SCR) System (선택적 환원 촉매(SCR)에서 암모니아($NH_3$) 분사량 최적화에 대한 실험적 연구)

  • Jang, Ik-Kyoo;Yoon, Yu-Bin;Park, Young-Joon;Lee, Seang-Wock;Cho, Yong-Seok
    • Proceedings of the KSME Conference
    • /
    • /
    • pp.2874-2879
    • /
    • 2008
  • The Selective catalytic reduction(SCR) system is a highly-effective device of $NO_x$ reduction for diesel engines. Generally, the ammonia($NH_3$) generated from a liquid urea-water solution is used for the reductant. 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 becomes lower, due to temperature window. And space velocity also affects to $NO_x$ conversion efficiency. This paper reviews a laboratory study to evaluate the effects of $NO_x$ and $NH_3$ concentrations, gas temperature and space velocity on the $NO_x$ conversion efficiency of the SCR system. The maximum conversion efficiency of $NO_x$ was indicated when the $NH_3$ to $NO_x$ ratio was 1.2 and the space velocity was $60,000\;h^{-1}$. The results of this paper contribute to improve overall $NO_x$ reduction efficiency and $NH_3$ slip.

  • PDF

Development of a variable resistance-capacitance model with time delay for urea-SCR system

  • Feng, Tan;Lu, Lin
    • Environmental Engineering Research
    • /
    • v.20 no.2
    • /
    • pp.155-161
    • /
    • 2015
  • Experimental research shows that the nitric oxides ($NO_X$) concentration track at the outlet of selective catalytic reduction (SCR) catalyst with a transient variation of Adblue dosage has a time delay and it features a characteristic of resistance-capacitance (RC). The phenomenon brings obstacles to get the simultaneously $NO_X$ expected to be reduced and equi-molar ammonia available to SCR reaction, which finally inhibits $NO_X$ conversion efficiency. Generally, engine loads change frequently, which triggers a rapid changing of Adblue dosage, and it aggravates the air quality that are caused by $NO_X$ emission and ammonia slip. In order to increase the conversion efficiency of $NO_X$ and avoid secondary pollution, the paper gives a comprehensive analysis of the SCR system and tells readers the key factors that affect time delay and RC characteristics. Accordingly, a map of time delay is established and a solution method for time constant and proportional constant is carried out. Finally, the paper accurately describes the input-output state relation of SCR system by using "variable RC model with time delay". The model can be used for a real-time correction of Adblue dosage, which can increase the conversion efficiency of $NO_X$ in SCR system and avoid secondary pollution forming. Obviously, the results of the work discover an avenue for the SCR control strategy.

Cerium-loaded MnOx/attapulgite catalyst for the low-temperature NH3-selective catalytic reduction

  • Xie, Aijuan;Zhou, Xingmeng;Huang, Xiaoyan;Ji, Liang;Zhou, Wenting;Luo, Shiping;Yao, Chao
    • Journal of Industrial and Engineering Chemistry
    • /
    • v.49
    • /
    • pp.230-241
    • /
    • 2017
  • A series of $MnO_2$/attapulgite (ATP) and n(Ce):n(Mn)/ATP (molar ratios) catalysts were prepared and investigated for the selective catalytic reduction of NO by $NH_3$ ($NH_3$-SCR) at low temperature. The results showed that the 7 wt % $MnO_2$/ATP exhibited the best $NO_x$ conversion (85% at $300^{\circ}C$) among all $MnO_2$/ATP catalysts of different mass ratios. The introduction of cerium enhanced the $NO_x$ conversion at low temperature, and so Ce-$MnO_x$/ATP can reach the highest $NO_x$ conversion (95% at $300^{\circ}C$). Meanwhile, the as-prepared catalysts were characterized by XRD, TEM, BET, $H_2$-TPR, $NH_3$-TPD, and XPS. It can be deduced from TEM, XRD, and BET, $MnO_x$ nanorods in this work mainly existed in the ${\beta}-MnO_2$, and cerium highly dispersed on the surface of ATP to form porous structure and thus improved the $deNO_x$ performance. Moreover, the study of $SO_2$ tolerance demonstrated that cerium can effectively inhibit $SO_2$ poison. XPS results illustrated that Ce could enhance $Mn^{4+}$ content on the surface of the catalyst and thus lead to high SCR activity. Therefore Mn(1):Ce(0.25)/ATP was proved to be an excellent catalyst for $NH_3$-SCR.