新型高效H2-SCR尖晶石型NiFe2O4催化还原NO

采用柠檬酸配位溶胶-凝胶法制备尖晶石型复合金属氧化物NiFe2O4,以H2为还原剂,在固定床反应器中考察了该催化剂催化还原NO的性能,并借助X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、比表面积测定(BET)、程序升温还原(TPR)和程序升温脱附(TPD)等方法对样品的晶体结构、形貌等特性进行了表征.结果表明.在空速4500 h-1,H2/NO浓度比为1,温度为400℃下,H2催化还原NO的效率可达97.8%,高H2/NO浓度比对NO转化率提升不大,高空速对其催化活性无明显影响.所制备的NiFe2O4催化剂具有典型的尖晶石结构,颗粒不规则,粒径大约为30—150 nm,并且具有良好的双官能团氧化还原性质.     

氧化锰八面体分子筛(OMS-2)负载Pd催化剂的制备及其CO催化氧化性能

通过前掺杂法(PI)和浸渍法(IM)制备了氧化锰八面体分子筛(Octahedral Molecular Sieves,OMS-2)负载Pd(Pd/OMS-2)催化剂.采用X射线衍射(XRD)、H2-程序升温还原(H2-TPR)和N2-吸附/脱附等技术对样品进行了表征,研究了不同制备方法和不同Pd负载量对Pd/OMS-2催化剂催化氧化CO性能的影响,通过与载体OMS-2的比较研究了Pd/OMS-2催化剂的稳定性.结果表明,前掺杂法制备的Pd/OMS-2-PI催化剂活性明显优于浸渍法制备的Pd/OMS-2-IM催化剂,其T100分别为75℃和175℃.这与Pd/OMS-2-PI催化剂中OMS-2载体与Pd之间存在强相互作用有关.Pd负载量明显影响Pd/OMS-2-PI催化剂的催化活性,3Pd/OMS-2-PI催化剂(Pd=3.0wt%)催化活性最高,这是由于Pd掺杂进入OMS-2晶格结构,能活化晶格氧,而随Pd含量进一步增加,部分Pd分布在OMS-2表面.稳定性结果表明,Pd/OMS-2-PI稳定性明显优于OMS-2载体本身,这可能与Pd掺杂进入催化剂晶格,能较好稳定OMS-2结构密切相关.     

Cu-SAPO-44的制备及氨选择性催化还原氮氧化物的性能

氨选择性催化还原(NH_3-SCR)是消除柴油车尾气NO_x的主要技术,Cu-微孔分子筛催化剂展现了优异的活性和稳定性.本文采用直接离子交换法(DIE)和传统离子交换法(CIE)分别制备了Cu-SAPO-44催化剂.X射线粉末衍射(XRD)表征发现,在CIE过程中,硝酸铵的交换导致了SAPO-44结晶度下降,因此,CIE样品的比表面积降低.氨气程序升温脱附(NH_3-TPD)表明,DIE样品比CIE样品拥有更多的酸性位和较强的NH_3吸附能力.同时,氢气程序升温还原(H2-TPR)表明,DIE样品更容易发生氧化还原反应.然而,电感耦合等离子体发射光谱仪(ICP-AES)测得的Cu含量,DIE样品远低于CIE样品.对比两者的脱硝活性,发现铜含量较低的DIE样品和铜含量较高的CIE样品在250℃均可达到98%的NO_x转化率和接近100%的N2选择性.动力学结果表明,DIE样品的本征活性(转换频率)略高于CIE样品.由此,Cu-SAPO-44催化剂在NH_3-SCR领域具有潜在的广阔应用前景.     

凹凸棒石负载CuO催化剂脱除气态Hg~0

利用固定床反应器在模拟烟气条件下研究了凹凸棒石(PG)负载CuO催化剂(CuO/PG)对气态Hg~0的脱除.考察了CuO负载量、反应温度、烟气成分、SO_2浓度以及空速等对CuO/PG脱除Hg~0的影响,并利用逐级化学提取和程序升温脱附实验分析了CuO/PG上吸附Hg的形态.结果表明,CuO/PG对Hg~0具有较高的脱除能力,明显高于载体PG,且随CuO负载量的增加而增强(1%—8%);在150—250℃温度范围内,温度升高,CuO/PG对Hg~0的脱除能力降低;HCl对CuO/PG脱除Hg~0具有显著的促进作用,O2具有促进作用,H2O和SO_2具有抑制作用,NO的作用不明显;在6000—15000 h~(-1)空速范围内,空速降低,CuO/PG表现出了更好的脱除Hg~0的能力.逐级化学提取和程序升温脱附实验结果证实,CuO/PG对Hg~0的脱除是吸附和催化氧化的共同作用,Hg~0被氧化为Hg~(2+)的化合物并吸附在CuO/PG上.     

Pd/Fe和Ni/Fe二元金属去除水体中莠去津的比较

对比Ni/Fe和Pd/Fe二元金属对莠去津的催化降解特性.结果表明,在相同反应条件下(C0=20.0mg·l-1,pH=3.0,金属添加量为1.0g),与Fe0相比,Pd/Fe对莠去津表现出比Ni/Fe更加明显的催化脱氯效果,反应75min,Fe0对莠去津的脱氯效率为7.09%,Ni/Fe达到99.11%,而Pd/Fe反应30min就能够100%还原莠去津.通过SEM,XRS和BET-N2测试,Pd以无定形状态分布在Fe0的表面,有利于比表面积的增大,Ni/Fe和Pd/Fe的比表面积分别为11.671和16.94m2·g-1;而且Pd/Fe对H2有非常强的吸附能力,1cm3的Pd在常温下能够吸附1000ml H2,最高能够达到2800ml.体系pH值对Ni/Fe和Pd/Fe催化莠去津的影响非常大,pH=2.0时, Pd/Fe反应15min能够100%降解莠去津;pH=3.0时,30min达到完全降解;pH=4.0和未调节pH条件下,75min的脱氯效率只有82.55%和46.5%.     

碳纳米管负载Pd基催化剂对水中2,4-二氯酚的催化加氢脱氯

对多壁碳纳米管(MWNTs)进行掺氮得到含氮的多壁碳纳米管N-MWNTs,分别以MWNTs和N-MWNTs为载体,采用浸渍法合成了催化剂Pd/MWNTs和Pd/N-MWNTs.使用透射电镜(TEM)、电感耦合等离子体发射光谱仪(ICP)、X射线衍射仪(XRD)、元素分析仪等对催化剂进行了表征,并对2,4-二氯酚(2,4-DCP)的液相催化加氢脱氯反应进行了研究.结果表明,Pd/N-MWNTs对2,4-DCP具有更高的催化活性;该反应体系的催化反应过程不受传质阻力的影响;2,4-DCP在催化剂上的加氢脱氯行为符合Langmuir-Hinshelwood模型,即2,4-DCP的还原脱氯受表面吸附所控制.     

Pd-Fe/C催化氯酚还原脱氯-氧化联合降解

以Pd和Fe为活性金属组分通过沉积沉淀法制备了负载型Pd-Fe/C双金属催化剂,针对氯酚类污染物进行催化还原脱氯和催化氧化的连续降解处理.通过ICP-MS、XRD和TEM对催化剂进行表征,证实0.5%Pd-0.5%Fe/C催化剂中活性金属组分Pd和Fe在载体表面分散性最好,催化剂比表面积达到718.8 m~2·g~(-1).在温和条件下,以水作为反应介质,研究了负载型Pd-Fe/C催化剂对4-氯苯酚(4-CP)和2,4-二氯苯酚(2,4-DCP)的连续降解过程和反应条件,以及催化剂的重复使用情况.考察了Pd和Fe的负载量及p H值对催化剂活性的影响,得到了最佳反应条件,以0.5%Pd-0.5%Fe/C为催化剂,20 min内完成4-CP和2,4-DCP的催化还原脱氯,产物都为苯酚;之后加酸调节pH=5,并加入H2O2继续进行催化氧化,苯酚被彻底降解为H_2O和CO_2,而且转化率在60 min内可以达到97.5%以上,从而实现4-CP和2,4-DCP的彻底降解.     

Ce0.7Zr0.3O2纳米棒的制备及其对柴油车尾气碳颗粒的催化净化性能

本研究以硝酸铈、硝酸锆为原料使用溶剂热合成法,制备了CeO₂-ZrO₂纳米棒催化剂(Ce_0.7Zr_0.3O₂(NR)),并用于柴油车尾气碳颗粒催化净化.催化活性检测证实:Ce_0.7Zr_0.3O₂(NR)纳米棒催化剂可有效净化柴油车尾气碳烟颗粒.在Ce_0.7Zr_0.3O₂(NR)存在下,碳颗粒净化率为10%、50%和90%时,所需温度分别仅为375℃、414℃和455℃,比商用Ce_0.7Zr_0.3O₂和Ce0.3Zr0.7O2催化剂性能更优.采用氮吸附-脱附、X射线光电子能谱(XPS)、H2程序升温还原(H₂-TPR)、X射线衍射(XRD)、拉曼光谱(Raman)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等技术对催化剂进行表征.XRD和Raman结果证实,Ce_0.7Zr_0.3O₂(NR)主要由立方相CeO₂构成,并掺杂了少量四方相氧化锆.SEM和TEM结果则显示,Ce_0.7Zr_0.3O₂(NR)催化剂颗粒明显由纳米棒堆积而成,特定的纳米形貌会影响其对碳颗粒的催化氧化活性.XPS结果证明Ce_0.7Zr_0.3O₂(NR)催化剂主要具有晶格氧、化学氧和表面吸附氧等氧物种;晶格氧是碳颗粒氧化的活性氧物种,其溢流到催化剂表面可与碳颗粒接触从而提高反应活性;化学氧和表面吸附氧均为表面氧物种,极易与表面固体碳颗粒直接接触,从而可在较低温度下促进碳颗粒的净化.H₂-TPR结果进一步证实了XPS结果,Ce_0.7Zr_0.3O₂(NR)催化剂的低温还原温度比商用Ce_0.7Zr_0.3O₂催化剂更低,且含有更多的易还原氧物种,这些低温易还原氧物种可以在较低温度下参与催化反应,促进柴油车尾气颗粒物的低温催化净化.     

Pd/TiO_2催化剂对三氯生的催化加氢脱氯研究

采用沉淀-沉积法制备不同载体的Pd负载型催化剂,采用透射电镜(TEM)、X-射线衍射(XRD)和电感耦合等离子体发射光谱(ICP-AES)对材料进行表征;并以所得材料为催化剂对三氯生(TCS)的催化加氢脱氯反应进行了研究.结果表明,Pd/TiO_2型催化剂在TCS加氢脱氯反应中具有较好的效果,反应活性随着Pd负载量的提高而增强.当反应物初始浓度为0.016 mmol·L~(-1),pH值为10,催化剂0.36%Pd/TiO_2用量为20mg时,TCS在70 min可以完成脱氯过程.碱性条件下,p H的升高不利于反应的进行.当催化剂用量在15—25 mg时,催化剂质量标化的反应初活性没有明显变化,表明催化反应过程不受传质阻力的影响.当反应物初始浓度在0.009—0.02 mmol·L~(-1)时,反应初活性随浓度的提高显著增加,但进一步增加反应物的浓度时初活性没有明显提高,因此,TCS在Pd/TiO_2催化剂上的脱氯行为符合Langmuir-Hinshelwood模型,表明TCS的加氢脱氯受表面吸附所控制.催化反应的过程中生成多种脱氯中间产物,反应的最终产物为2-羟基二苯醚.     

Pd/TiO2催化水体中四溴双酚A的电催化还原脱溴

以TiO₂、Al₂O₃、CeO₂和SiO₂为载体，采用浸渍法制备Pd基催化剂，并通过透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)和电感耦合等离子体发射光谱(ICP-OES)等手段对催化剂的结构进行了详细表征.以Pd/TiO₂为催化剂，研究四溴双酚A(TBBPA)在阴极池的电催化还原.结果表明，悬浮体系中Pd基催化剂的催化活性远高于固定体系；与其他载体相比，Pd/TiO₂的电催化还原活性最高；反应过程符合Langmuir-Hinshelwood模型，受控于TBBPA在催化剂表面的吸附过程；随着恒定电流和Pd负载量的增大，TBBPA电催化还原反应的初活性呈现火山型变化规律；经过5次循环使用，Pd/TiO₂催化剂仍能够完全去除TBBPA，具有良好的稳定性.     

长三角区域背景地区SO2和NOx本底特征

本研究对代表长三角区域背景地区的临安大气本底站2006-2007年的SO2和NOx数据进行分析,结果表明,实验期间,SO2和NOx年均浓度均无明显差异;SO2,NOx季节变化特点和一些城市地区的研究结果一致,都是在冬季浓度较高,夏季浓度较低,不同的是,在邻近临安本底站的上海市,SO2与NO2最高月浓度与最低月浓度的比值小于临安区域本底站SO2与NOx最高月浓度与最低月浓度的比值,说明背景地区污染物浓度更容易受到气象条件变化的影响;SO2和NOx小时浓度日变化和城市地区的双峰双谷型分布形态不同,呈现出单谷型分布形态,午后的14点左右,SO2和NOx小时浓度达到24 h中的最低值,SO2和NOx分别在凌晨0点左右和晚上20点左右达到24 h中的最大值.     

武汉城区NOx污染特征及其变化趋势

武汉城区大气中NOx的污染,一日中以早晨最重,下午最轻;一年中,冬季的浓度比夏季高出37.7%.交通稠密区和商业集中区大气中的NOx年日均浓度分别比郊区高5倍和4.3倍.统计研究的结果表明,九年间特别是近六年来,武汉城区大气中NOx年日均值呈上升趋势.从1984年～1989年,大气中的NOx日均浓度平均每年以7%的速度递增,其超标率平均每年以0.8%的速度递增.     

北京市与香河县大气臭氧及氮氧化合物的变化特征

于2005年春、夏之交,在北京市及河北省香河县两地同时开展了臭氧和氮氧化合物的连续监测.结果表明,香河县和北京市的臭氧统计日变化形式基本一致,北京市大气臭氧平均浓度比香河低,分别为28×10-9V/V和43×10-9V/V;大气中0x浓度北京市高于香河县,分别为72×10-9V/V和60×10-9V/V.观测期间,两地臭氧的月最高值出现时间一致,其中6月21日北京市的臭氧浓度最高达到200×10-9V/V,香河县也达到149×10-9V/V.在三次臭氧严重超标事件发生的前一天,两地都伴随有氮氧化合物的高浓度积累;南风时北京市和香河县的Ox浓度都比平均值高25%.     

大气光化学烟雾反应机理比较(Ⅰ)O3和NOx的比较

在相同初始和排放条件下,对四种应用较广的光化学烟雾反应机理(CB4-99,RADM2,RACM,SAPRC99)进行了比较.研究发现对于O3,在低VOCs/NOx时,四种机理模拟结果相关较小,平均相对标准偏差为7%,在高VOCs/NOx时,平均相对标准偏差为26%,差距较大;对于NOx,多数情况下RACM和RADM2的模拟结果较高,CB4-99和SAPRC99的模拟值偏低,其原因主要来源于不同机理中O3的生成对NOx及VOCs的敏感性不同而造成的.在用模式模拟O3和NOx时,应特别注意机理不同而带来的模拟结果差异.     

臭氧应用于烟气净化的研究进展

烟气中所含的二氧化硫(SO2),氮氧化物(NOx),重金属汞(Hg)等污染物都能对人体健康及周围环境产生危害.本文综述了臭氧法应用于烟气净化的研究进展、工业应用及反应机理,探讨了臭氧同时脱硫脱硝脱汞的主要影响因素,介绍了臭氧发生技术的研究现状,并对臭氧应用于烟气净化进行了经济性分析,认为臭氧法脱除烟气中的多种污染物具有广泛的应用前景.     

温度对等离子体与催化剂结合脱除Nox的影响

考察了温度对介质阻挡放电和CuZSM-5催化剂"一段法"结合脱除氮氧化物(NOx)的影响.实验表明,在250℃和300℃时,对于NO/N2,NO/O2/N2和 NO/C2H4/N2三个体系,"一段法"脱除NOx的活性都相对较低.在NO/O2/C2H4/N2体系中,250℃介质阻挡放电和CuZSM-5结合脱除NOx产生了明显的协同效应.在300℃,等离子体对脱除NOx起负作用.相对低温(150℃)时,等离子体的促进作用很小.电学实验表明,当反应温度由25℃升至450℃,"一段法"体系的李萨如(Lissajous)图形由平行四边形(25℃)逐渐变为椭圆形(450℃),表明较高温度时催化剂的介电性质发生了变化.原位发射光谱证明在不同温度下,"一段法"体系中等离子体气相产生的活性物种数量明显不同.     

NiB2O4 (B = Mn or Co) catalysts for NH3-SCR of NOx at low-temperature in microwave field

● Microwave-assisted catalytic NH₃-SCR reaction over spinel oxides is carried out. ● SCR reaction temperature is tremendously lowered in microwave field. ● NO conversion of NiMn₂O₄ is highly up to 90.6% at 70°C under microwave heating. Microwave-assisted selective catalytic reduction of nitrogen oxides (NO_x) was investigated over Ni-based metal oxides. The NiMn₂O₄ and NiCo₂O₄ catalysts were synthesized by the co-precipitation method and their activities were evaluated as potential candidate catalysts for low-temperature NH₃-SCR in a microwave field. The physicochemical properties and structures of the catalysts were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), N₂-physisorption, NO adsorption-desorption in the microwave field, H₂-temperature programmed reduction (H₂-TPR) and NH₃-temperature programmed desorption (NH₃-TPD). The results verified that microwave radiation reduced the reaction temperature required for NH₃-SCR compared to conventional heating, which needed less energy. For the NiMn₂O₄ catalyst, the catalytic efficiency exceeded 90% at 70 °C and reached 96.8% at 110 °C in the microwave field. Meanwhile, the NiMn₂O₄ also exhibited excellent low-temperature NH₃-SCR reaction performance under conventional heating conditions, which is due to the high BET specific surface area, more suitable redox property, good NO adsorption-desorption in the microwave field and rich acidic sites.     

锐钛矿{001}面TiO2纳米片对NOx的光催化氧化性能

以钛酸丁酯为前驱物,HF为形貌控制剂,采用水热法合成{001}面TiO2光催化材料.通过X射线衍射、紫外\可见光吸收光谱、扫描电镜及透射电镜等手段对样品形貌及结构进行表征,并在紫外光下考察其对NOx的光催化氧化活性.结果表明,{001}面TiO2具有良好的锐钛矿晶型,为{001}面暴露率约50%的纳米级片状结构,在紫外波段具有强烈的光吸收.经过碱液洗涤去除表面F离子后的{001}面TiO2与{101}面TiO2及P25相比,其对NOx去除效果显著.在催化反应达到平衡后,其NO转化率为{101}面TiO2的2倍及P25的3倍.并且NO去除量增加的同时NO2的相对生成量却减少,导致光催化反应进行得更彻底.     

Impacts of emissions and meteorological changes on China’s ozone pollution in the warm seasons of 2013 and 2017

O₃ increment is mainly caused by changes in meteorology rather than emissions. Emission reduction is effective to reduce O₃ nationwide, especially in summer. Strengthened NO_x controls are necessary to meet the ambient O₃ standard. We have quantified the impacts of anthropogenic emissions reductions caused by the Air Pollution Control Action Plan and changes in meteorological fields between 2013 and 2017 on the warm-season O₃ concentration in China using a regional 3D chemical transport model. We found that the impact on daily maximum eight-hour (MDA8) O₃ concentration by the meteorological variation that mostly increased O₃ was greater than that from emission reduction, which decreased O₃. Specifically, the control measures implemented since 2013 in China have reduced SO₂, NO_x, PM_2.5, and VOC emissions by 33%, 25%, 30%, and 4% in 2017, while NH₃ emissions have increased by 7%. The changes in anthropogenic emissions lowered MDA8 O₃ by 0.4–3.7 ppb (0.8%–7.6%, varying by region and month), although MDA8 O₃ was increased slightly in some urban areas (i.e. North China) at the beginning/end of warm seasons. Relative to 2013, the average 2 m temperature in 2017 shows increments in North, North-east, East, and South China (0.34℃–0.83℃) and decreases in Central China (0.24℃). The average solar radiation shows increments in North, North-east, and South China (7.0–9.7 w/m²) and decreases in Central, South-west, and North-west China (4.7–10.3 w/m²). The meteorological differences significantly change MDA8 O₃ by -3.5–8.5 ppb (-8.2%–18.8%) with large temporal variations. The average MDA8 O₃ was slightly increased in North, North-east, East, and South China. The response surface model suggests that the O₃ formation regime transfers from NO_x-saturated in April to NO_x-limited in July on average in China.     

Tailoring the simultaneous abatement of methanol and NOx on Sb-Ce-Zr catalysts via copper modification

● Cu addition enhances CH₃OH oxidation and alleviates its inhibitory effect on SCR. ● Cu addition improves the activation of SCR reactants in the presence of methanol. ● Damaged structure by more Cu addition decreases specific surface area and acidity. ● Excessive Cu addition would lead to the narrowing of SCR temperature window. Simultaneously removal of NO_x and VOCs over NH₃-SCR catalysts have attracted lots of attention recently. However, the presence of VOCs would have negative effect on deNO_x efficiency especially at low temperature. In this study, copper modification onto Sb_0.5CeZr₂O_x (SCZ) catalyst were performed to enhance the catalytic performance for simultaneous control of NO_x and methanol. It was obtained that copper addition could improve the low-temperature activity of both NO_x conversion and methanol oxidation, where the optimal catalyst (Cu_0.05SCZ) exhibited a deNO_x activity of 96% and a mineralization rate of 97% at 250 °C, which are around 10% higher than that of Cu free sample. The characterization results showed that copper addition could obviously enhance the redox capacity of the catalysts. As such, the inhibition effect of methanol incomplete oxidation on NO adsorption and NH₃ activation were then lessened and the conversion of surface formamide species were also accelerated, resulting in the rising of NO_x conversion at low temperature. However, excessive copper addition would damage the Sb-Ce-Zr oxides solid solution structure owing to Cu-Ce strong interactions, decreasing the surface area and acidity. Meanwhile, due to easier over-oxidation of NH₃ with more Cu addition, the temperature window for NO_x conversion would become quite narrow. These findings could provide useful guidelines for the synergistic removal of VOCs over SCR catalyst in real application.