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1.
氮氧化物(NOx)是一种重要的大气污染物, 它造成严重的环境问题, 同时威胁人类健康. 以钢铁烧结烟气为代表的固定源和以柴油机尾气为代表的移动源是氮氧化物的主要来源. 氨气选择性催化还原法(NH3-SCR)是目前最有效且应用最广泛的NOx脱除技术. 然而, 无论是固定源还是移动源上NH3-SCR催化剂, 都不可避免地会被SO2毒化, 造成催化剂失活, 限制了NH3-SCR技术的进一步应用. 因此, 研究NH3-SCR催化剂的SO2中毒机制以及提高催化剂的抗硫性能至关重要. 我们对固定源脱硝的金属氧化物和移动源上脱硝的Cu基分子筛这两类不同催化剂体系的SO2中毒机制的研究进展进行了介绍, 并对这两种催化剂上提高抗硫性能改性方法的研究进展进行了评述, 为未来的研究提供了参考. 相似文献
2.
通过软化学途径合成了铈钛混合氧化物(CeO2-TiO2)载体材料, 并分别通过等体积浸渍法和机械研磨法负载磷钨酸(H3PW12O40)。采用FTIR、XRD、SEM和BET比表面积测定对CeO2-TiO2及负载型多酸催化剂进行了表征;考察了负载量、负载方法、吸附温度等因素对催化剂吸附NOx效率的影响;选取吸附性能最佳的催化剂进行了NOx催化分解实验, 探讨了NOx吸附-分解机理。结果表明:相对于等体积浸渍法, 机械研磨法更适合此类载体负载H3PW12O40, 其NOx吸附效率均高于H3PW12O40及载体本身;在0~60%的负载量范围内, 随着H3PW12O40负载量的增加, 负载型催化剂吸附NOx的效率呈上升趋势, 负载量为40%时NOx吸附效率最佳, 达90%;吸附过程中NOx与催化剂活性组分H3PW12O40发生作用, 生成NOH+, H3PW12O40二级结构中结晶水对催化剂吸附NOx有重要作用;当温度从150℃升至 450℃时, 被吸附的NOx发生分解, 分解产物的组成与N2的收率均受升温速率的影响, 升温速率越快, N2收率越高。向吸附分解NOx后的催化剂床层通入含有水蒸气的空气, 可有效补充NOx分解过程中H3PW12O40失去的结晶水, 从而恢复催化剂优良的NOx吸附分解性能, 实现催化剂的有效再生利用。 相似文献
3.
分别以La2O2CO3, CeO2, ZrO2和Al2O3为载体, 采用浸渍法制备了Ni基重整催化剂, 并以正十二烷模拟车载燃油进行催化重整反应以同时制备小分子碳氢化合物(HCs)和H2, 考察了其在4wt%Ag/Al2O3上选择性催化还原(HC-SCR)氮氧化物(NOx)的性能. 采用N2吸附-脱附、X射线粉末衍射、H2程序升温还原和热重等手段对Ni基催化剂进行了表征. 结果表明, 随着重整催化剂氧化还原性能增强, 产物中H2浓度增加, 可参与SCR反应的HCs含量减少, 从而导致重整-SCR耦合体系上NOx净化活性温度窗口向低温移动, NOx最高转化率降低. Ni/ZrO2+Ag/Al2O3耦合体系中H2/HCs符合SCR反应所需的最优比例, 在柴油车典型排气温度范围内表现出良好的NOx净化能力. 同时, 在Ni/ZrO2+Ag/Al2O3耦合体系上考察了其燃油重整-SCR的活性稳定性. 结果显示, 重整催化剂的耐久性有待进一步提高. 相似文献
4.
研究了低于300 ℃时两种氧化铈对稀燃阶段NOx存储性能的影响,催化剂由2%(w)Pt/Al2O3(PA)与CeO2-X(X=S,I)机械混合制备. X射线衍射(XRD),BET表面积和扫描电子显微镜(SEM)用于表征材料的物理结构. X射线光电子能谱(XPS)和H2程序升温还原(H2-TPR)用于表面Ce3+和活性氧定量. 原位漫反射傅里叶变换红外光谱(in-situ DRIFTS)用于分析表面NOx吸附物种. 相比于CeO2-I,CeO2-S 具有优良的物理化学性能,包括高比表面积、丰富的空隙结构、较高的抗老化能力及表面Ce3+浓度. 因而,Pt/Al2O3+CeO2-S 表现出优异的NOx存储能力. 此外,PA+CeO2-X(X=S,I)上存在Pt 与CeO2之间的相互作用,可提高表面氧物种的活性进而促进NO氧化及NOx存储. PA+CeO2-S上的这种相互作用要强于PA+CeO2-I. 研究表明,表面Ce3+浓度和活性氧含量对NOx存储起到重要作用. 然而经过水热处理后,Pt 与老化的氧化铈(ACS,ACI)之间的相互作用降低,并且两种氧化铈NOx存储性能显著下降. 另外,与PA+ACS(ACI)相比,PA+PACS(PACI)样品NOx存储能力得到改善,这归因于表面氧物种活性增加能促进硝酸盐的形成. 相似文献
5.
基于实验室对柴油车用V2O5-WO3/TiO2催化剂配方以及涂覆成型技术的大量研究,设计了一条产量为6000只/月的NH3选择性催化还原NOx (NH3-SCR)催化剂中试生产线,并对生产的催化剂产品进行了发动机台架测试. 结果表明,实验室制备的V2O5-WO3/TiO2粉体催化剂和生产线产品,在空速为50000 h-1和200-450 ℃条件下NOx转化率均可达80%以上;采用大尺寸堇青石载体涂覆后制备的V2O5-WO3/TiO2整体催化剂经实验室小样测试,在空速为10000-30000 h-1和250-450 ℃条件下NOx转化率也为80%以上. 发动机台架测试结果表明,该催化剂产品可使重型柴油机NOx排放达到国IV标准中欧洲稳态循环(ESC)和欧洲瞬态循环(ETC)排放限值的要求. 该生产线经适当调整后也可用于生产非钒基NH3-SCR整体催化剂,以满足未来钒基NH3-SCR催化剂更新换代的需求. 相似文献
6.
以经过浓硝酸和等离子体放电预处理后的多壁碳纳米管(MWCNTs)为载体, 锰氧化物(MnOx)为活性组分, 采用等体积浸渍法制备MnOx/MWCNTs 催化剂. 利用热重分析(TGA)、扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、程序升温还原/脱附(TPR/TPD)以及傅里叶变换红外(FTIR)光谱对催化剂进行表征, 探讨SO2对催化剂低温氨选择性催化还原(SCR)NOx活性的影响及SO2中毒机理. 结果表明, 低温下SO2对MnOx/MWCNTs 催化剂活性有明显毒化作用. 反应温度越高, SO2浓度越大, 催化剂SCR活性下降越快. 活性中心Mn原子硫酸化是催化剂失活的主要原因. 另外, 催化剂表面生成硫酸铵盐以及SO2对NO吸附的抑制作用也一定程度上造成了催化剂的失活. 相似文献
7.
采用溶胶-凝胶法制备了Ba1-xMxFeO3 (M=Mg, Ca, Sr; x=0, 0.1, 0.2)系列钙钛矿型NOx储存还原(NSR)催化剂, 考察碱金属元素Mg、Ca 和Sr 的掺杂对BaFeO3 钙钛矿NOx 储存和氧化性能的影响. 结果表明, 在250-400 ℃范围内Mg的掺杂提高了BaFeO3钙钛矿的NOx储存性能, 其中以Ba0.8Mg0.2FeO3样品的NOx储存性能最佳, 在温度350 ℃时NOx储存量高达1200 μmol·g-1以上, NO→NO2转化率为53.4%. 与BaFeO3比较,Ba0.8Mg0.2FeO3样品在250 ℃进行NOx储存时就出现了单齿硝酸盐, 并随储存温度的变化而变化, 它的数量与NOx储存量有相同的变化趋势. 傅里叶变换红外(FTIR)光谱结果表明, 与BaFeO3相比, Ba0.8Mg0.2FeO3样品NOx储存量增大的原因在于: 一方面, 形成了具有A位缺陷的钙钛矿结构, 产生大量能够用于储存NOx的氧空位; 另一方面, 未进入钙钛矿晶格的Mg元素可能以碱性氧化物的形式与NOx作用形成了单齿硝酸盐. 相似文献
8.
采用浸渍法模拟商业V2O5-WO3/TiO2脱硝催化剂的砷中毒,并对不同As/V摩尔比中毒的催化剂进行脱硝实验测试,发现随着As中毒程度加深,催化剂的NOx转化率随之降低.当测试温度为400℃时,新鲜V2O5-WO3/TiO2催化剂NOx转化率有96.45%,而当As/V摩尔比到0.2的时候,As中毒催化剂的NOx转化率降低至不足67%.采用XRD、BET、SEM、in situ DRIFTS和H2-TPR等多种表征方法对As中毒前后催化剂的物性结构、表面物质的存在形式以及氧化还原性能的对比研究,结果显示As2O3堵塞催化剂微孔结构,导致催化剂表面微孔数量的减少,As2O5涂覆催化剂表面,进而阻碍了气相成分参与多相催化反应;As的引入使得表面形貌略有变差,并未导致催化剂晶型的变化,且As及其化合物在催化剂表面分散度较高.As会与催化剂表面的羟基作用形成As-OH,抑制催化剂酸性,尤其对Lewis酸的抑制效果明显;As中毒后的催化氧化还原能力增强. 相似文献
9.
硫酸钙及硫酸铵气溶胶对二次有机气溶胶生成的影响 总被引:1,自引:0,他引:1
二次有机气溶胶(SOA)是大气光化学反应的产物, 也是城市和郊区大气中细粒子的主要成分. 本研究致力于考察高浓度无机气溶胶颗粒对SOA生成的影响. 实验系统采用2 m3的温控烟雾箱, 以干燥的CaSO4和(NH4)2SO4为无机种子气溶胶, 研究了间二甲苯/NOx/空气体系光氧化生成SOA的过程. 实验结果显示间二甲苯和NOx在紫外光照下会产生大量SOA, SOA产率可用单产物模型表征. CaSO4气溶胶的存在对SOA产率曲线没有明显的影响, 而(NH4)2SO4气溶胶的存在使气相半挥发性氧化产物的生成量增加36%, 显著地增加了SOA的产率. (NH4)2SO4粒子在含水有机物作用下显现的弱酸性可能是导致这一影响的主要原因. 该实验结果有助于更详尽地阐明中国颗粒物污染严重城市SOA的生成机理, 从而为进一步修正空气质量模型提供依据. 相似文献
10.
等离子体在同时去除NOx和碳烟催化反应中的作用 总被引:9,自引:0,他引:9
采用程序升温反应(TPR)技术,研究了等离子体辅助同时催化去除富氧柴油机尾气中NOx和碳烟(soot)的反应特性.研究结果表明,等离子体提高了同时去除NOx-soot的催化反应活性,降低了碳烟的燃烧温度,使碳烟起燃温度从300 ℃降到280 ℃,燃尽温度从425 ℃降到380 ℃;同时,等离子体辅助提高了NOx转化为N2的效率,使催化选择性从1.12%提高到1.53%.本文还分别研究了在NO和O2的环境中,有或没有等离子体作用下,碳烟在催化作用下的去除特性.等离子体作用使得NO在和O2共存、只有NO和只有O2存在的各种条件下,碳烟的催化燃烧活性都有不同程度的提高,促进了N2的生成.此外,本文也对等离子体辅助同时催化去除NOx-soot的机理进行了探讨. 相似文献
11.
Piezoelectric crystal detectors possess a good potential as sensors in Analytical Chemistry. Their specificity is excellent, provided a highly selective adsorbent layer is placed on the surface of the crystal. Sensitivity is also good, down to parts per trillion levels of atmospheric pollutants are detectable, with a large linear range up to parts per million. Specific detectors have been developed for organophosphorus compounds, toluene in printing plants, dynamite and explosives, CO, SO2, NOx, NH3, HCl and organochlorine compounds. Results on some of these detectors is presented herein. 相似文献
12.
Development and validation of passive samplers for atmospheric monitoring of SO2, NO2, O3 and H2S in tropical areas 总被引:1,自引:0,他引:1
Traditionally the monitoring of atmospheric pollutants is aimed at managing accidents and short-term actions for the protection of human health on local and regional scales. These monitoring networks required continuous measurements with high time resolution, involving costly equipment, operation and maintenance. More recent simulations with mathematical models and scenario-building on regional, continental and global scales, as well as studies of environmental personal exposure are demanding three main types of monitoring design, where need for special resolution surpasses the one of temporal resolution: remote places, where no electric power nor trained human resources are available; validation of dispersion simulation by mathematical modeling on regional to larger scales; indoor measurements where people are acting under noise restriction such as residences, school and hospitals. To meet these demands environmental passive samplers for atmospheric gaseous pollutants have been developed and applied for different situations and environments of Brazil. Passive samplers were developed based on molecular diffusion of gas through a static layer of air with fixed filters impregnated with a specific solution for SO2, NO2, O3 and H2S and used in the following situations: in remote forest area, urban areas with different characteristics - near the sea, with clean ocean air masses coming in and in areas under direct industrial influence. The passive samplers showed good performance when exposed to different types of areas and during different periods: accuracy of measurements, based on standard deviation, were within the recommended limit by the European Union of ± 25% for this type of device and precision below the maximum of 20% cited in the literature, with variation of 2.0 to 16% in the case of these work. The passive devices were able of measuring concentrations very low as those found in the Amazon region (0.58 ± 0.05 µg m− 3 SO2 and 1.10 ± 0.07 µg m− 3 NO2) and higher concentrations in industrial areas (20.0 ± 1.3 µg m− 3 SO2 e 21.0 ± 1.3 µg m− 3 NO2). 相似文献
13.
臭氧氧化结合湿法喷淋对玻璃窑炉烟气同时脱硫脱硝实验研究 总被引:2,自引:0,他引:2
采用臭氧氧化结合湿法喷淋对模拟玻璃窑炉烟气开展了同时脱硫脱硝实验研究.采用不同溶液(NaOH、Na2S)进行了喷淋实验.结果表明,保证溶液pH值在10以上,NaOH浓度对NOx脱除效率无影响,SO2的存在促进了NOx吸收.当O3/NO物质的量比为1.6、溶液NaOH浓度为0.5%时,NOx脱除效率可达70%,SO2脱除效率在99%以上.往喷淋液中添加Na2S,NOx脱除效率随Na2S浓度增加而提高,SO2的存在对NOx脱除效率无影响.当O3/NO物质的量比为1.2、溶液中NaOH浓度为0.5%、添加剂Na2S浓度为0.6%时,NOx脱除效率可达70%,SO2脱除效率在95%以上.60 min长时间运行实验证明,模拟烟气中的NOx经碱液和添加剂吸收后主要以NO-2的形式存在于喷淋液中,且NOx脱除效率不随溶液pH值的变化而变化. 相似文献
14.
《中国化学快报》2021,32(10):2963-2974
The simultaneous removal of SO2, NOx and Hg0 from industrial exhaust flue gas has drawn worldwide attention in recent years. A particularly attractive technique is selective catalytic reduction, which effectively removes SO2, NOx and Hg0 at low temperatures. This paper first reviews the simultaneous removal of SO2, NOx and Hg0 by unsupported and supported catalysts. It then describes and compares the research progress of various carriers, eg., carbon-based materials, metal oxides, silica, molecular sieves, metal-organic frameworks, and pillared interlayered clays, in the simultaneous removal of SO2, NOx and Hg0. The effects of flue-gas components (such as O2, NH3, HCl, H2O, SO2, NO, and Hg0) on the removal of SO2, NOx, and Hg0 are discussed comprehensively and systematically. After summarizing the pollutant-removal mechanism, the review discusses future developments in the simultaneous removal of SO2, NOx and Hg0 by catalysts. 相似文献
15.
Flow reactor experiments were performed to study moist CO oxidation in the presence of trace quantities of NO (0–400 ppm) and SO2 (0–1300 ppm) at pressures and temperatures ranging from 0.5–10.0 atm and 950–1040 K, respectively. Reaction profile measurements of CO, CO2, O2, NO, NO2, SO2, and temperature were used to further develop and validate a detailed chemical kinetic reaction mechanism in a manner consistent with previous studies of the CO/H2/O2/NOX and CO/H2O/N2O systems. In particular, the experimental data indicate that the spin‐forbidden dissociation‐recombination reaction between SO2 and O‐atoms is in the fall‐off regime at pressures above 1 atm. The inclusion of a pressure‐dependent rate constant for this reaction, using a high‐pressure limit determined from modeling the consumption of SO2 in a N2O/SO2/N2 mixture at 10.0 atm and 1000 K, brings model predictions into much better agreement with experimentally measured CO profiles over the entire pressure range. Kinetic coupling of NOX and SOX chemistry via the radical pool significantly reduces the ability of SO2 to inhibit oxidative processes. Measurements of SO2 indicate fractional conversions of SO2 to SO3 on the order of a few percent, in good agreement with previous measurements at atmospheric pressure. Modeling results suggest that, at low pressures, SO3 formation occurs primarily through SO2 + O(+M) = SO3(+M), but at higher pressures where the fractional conversion of NO to NO2 increases, SO3 formation via SO2 + NO2 = SO3 + NO becomes important. For the conditions explored in this study, the primary consumption pathways for SO3 appear to be SO3 + HO2 = HOSO2 + O2 and SO3 + H = SO2 + OH. Further study of these reactions would increase the confidence with which model predictions of SO3 can be viewed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 317–339, 2000 相似文献
16.
Hydrogen peroxide formation in the photooxidation of CO? NOx, ethene? NOx, and propene? NOx mixtures has been determined in the TVA 31 cubic meter smog chamber under the following conditions: [NOx] ca. 22–46 ppb; ethene = 0.22–1.1 ppm, [propene] = 0.12–0.97 ppm; [H2O] ca. 8 × 10?3 ppm. Ethene, propene, NO, NOx, PAN, HCHO, and CH3CHO were also monitored. Computer modeling was performed using the gas phase ethene and propene mechanism of the Regional Acid Deposition Model. There is good agreement between the model predicted and observed H2O2 concentrations. However, to successfully model all the propene? NOx experimental results, organic nitrate formation from the reaction of peroxy radicals with NO must be included in the mechanism. 相似文献
17.
An experimental investigation of the gas-phase photooxidation of toluene–NOx–air mixtures at part-per-million concentrations has been carried out in a 65-m3, outdoor smog chamber to assess our understanding of the atmospheric chemistry of toluene. In addition, six CO? NOx–air irradiations were conducted to characterize the chamber with regard to any wall radical sources. Measured parameters in the toluene–NOx experiments included O3, NO, NO2, HNO3, peroxyacetyl nitrate (PAN), CO, toluene, benzaldehyde, o-cresol, m-nitrotoluene, peroxybenzoyl nitrate (PBZN), temperature, relative humidity, aerosol size distributions, and particulate organic carbon. Predictions of the reaction mechanism of Leone and Seinfeld [7] are found to be in good agreement with the data under a variety of initial conditions. Additional simulations are used to investigate various mechanistic pathways in areas where our understanding of toluene chemistry is still incomplete. 相似文献
18.
《Arabian Journal of Chemistry》2014,7(5):695-700
The optical gas recognition capabilities of thin film layer of 4-[bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-amino]phenol deposed on quartz substrates were studied. The dynamic gas responses to the following analytes have been investigated as air pollutants (SO2, NO2, CO, CH4 and NH3). The spin-coated bispyrazole layer appears to have reversible response towards SO2 and a very low and irreversible response to NO2. The selectivity of the thin film based on bispyrazole layer with respect to other analytes was also examined and the present data show that the thin sensing layer in the presence of CO, CH4 and NH3 in low concentration does not influence its optical properties. 相似文献
19.
Xiaoyu Zhang Enyan Long Yile Li Jiaxiu Guo Lijuan Zhang Maochu Gong Minghua Wang Yaoqiang Chen 《天然气化学杂志》2009,18(2):139-144
Composite supports CeO2-ZrO2-Al2O3 (CZA) and CeO2-ZrO2-Al2O3-La2O3 (CZALa) were prepared by co-precipitation method. Palladium
catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from
natural gas vehicles (NGVs) operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties
of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction (XRD) and Raman spectroscopy
revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale
and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperature-programmed reduction (H2-TPR)
and oxygen storage capacity (OSC) measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite
supports. Catalytic activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO
and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the
three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as
excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. They also have significant potential in
industrial application because of their high performance and low cost. 相似文献