Cu-Mg-Al催化剂上NOx储存及分解性能研究

采用共沉淀方法制备了Gu-Mg-Al水滑石混合氧化物催化剂,并对该催化剂及其前驱物进行了XRD表征.使用等温吸附、程序升温脱附以及C3H6程序升温表面反应分别考察了催化剂上NOx储存及分解反应性能.结果表明,由于Cu-Mg-Al催化剂中CuO组分发挥了NO氧化作用,促进了进气中NOx以硝酸盐方式吸附在催化剂上,因此该催化剂具有很好的NOx储存性能;在富燃条件下,C3H6能够显著降低催化剂上硝酸盐的热稳定性,在160～360 ℃温度范围内,这些硝酸盐会迅速分解成气态NOx,同时随着C3H6加入量的提高,C3H6也可以将少量气态NOx进行还原.     

碳负载富氧空位的NiCo2O4用于电催化还原硝酸盐

水体中硝酸盐是一种广泛存在的污染物,因此,开发用于水中硝酸盐还原的高效电催化剂受到广泛关注.采用溶胶-凝胶法耦合硼氢化钠还原法制备了碳负载富氧空位的NiCo₂O_4-x/C电催化剂,并研究其去除硝酸盐的性能.结果发现,在该体系中,耦合导电碳载体可改善半导体型电催化剂导电性,构建氧空位可促使原子H^*生成,最终实现硝酸盐高效还原.NiCo₂O_4-x/C阴极在电流密度为20 mA·cm^-2、pH=7的条件下,可于3 h内去除水中94.8%的NO₃^--N,相较于NiCo₂O₄及NiCo₂O₄/C阴极,NO₃^--N去除率分别提高了36.6%和12.2%.此外,NiCo₂O_4-x/C阴极在连续5次还原硝酸盐过程中性能并未有明显变化.结合掩蔽实验和电子顺磁共振波谱分析证实,NiCo₂O_4-x/C阴极除了可通过直接电子还原硝酸盐外,还可以通过生成原子H^*间接还原硝酸盐.通过对实际废水处理进一步验证其转化硝酸盐的性能,研究表明,NiCo₂O_4-x/C阴极可有效去除焦化废水生物出水中硝酸盐.     

基于光化学指标法的邯郸市臭氧生成敏感性

邯郸市近年来O₃污染状况越发严峻,2018年夏季（6~8月）,邯郸市O₃日最大8 h平均浓度为175μg·m^-3,超标天数达54 d,超标率59%,最高浓度达257μg·m^-3.本研究应用WRF-CMAQ模式系统和光化学指标法对邯郸市夏季O₃生成敏感性特征进行分析.结果表明,用H₂O₂/HNO₃表征O₃生成敏感性较其他指标在理论和模拟效果方面均更合适.基于精细化的源清单和网格分辨率,CMAQ对H₂O₂和HNO₃有较好的模拟效果.对H₂O₂/HNO₃的模拟结果显示,邯郸市VOCs控制区范围逐月减少,6月协同控制区范围占比最大,7月和8月以NO_x控制区为主.邯郸市各区县VOCs和NO_x排放量比值显著的空间差异,是O₃生成敏感性差别的主要原因.VOCs/NO_x<1.7的区域,其O₃生成趋向于受VOCs控制,邯郸南部VOCs/NO_x>6.9的区域,NO_x是O₃生成的主控因子,1.7x<6.9的区域更易受到VOCs和NO_x的协同控制.当HCHO/NO₂、O₃/HNO₃和O₃/NO_x过渡范围分别为0.35~0.6、20~35和10~25时,可以得到与H₂O₂/HNO₃较为一致的敏感性空间分布,H₂O₂/（O₃+NO₂）不能指示出与其他指标一致的结果,表明该指标可能不适用于邯郸市.     

超细煤粉在氧化条件下NOx的释放特性实验研究

采用DTG(热重/差热分析仪)和GC-MS(气相色谱质谱联用仪)对鹤岗煤超细化煤粉进行燃烧试验,分析了粒径、氧气浓度、升温速率对NO_x释放的影响.结果表明,不同粒径的鹤岗煤在氧气浓度为20％的燃烧条件下,NO_x的析出均为单峰曲线;粒径对煤粉燃烧NO_x释放有重要影响,超细化煤粉可以减少NO_x的排放;在5、10、20 ℃/min升温条件下,随升温速率的增大NO和NO₂的析出量也增加,并且NO的最大析出速率对应的温度随着升温速率的提高也提高;随着燃烧气氛氧气浓度的增高,NO_x的析出量相应增加,并且NO_x的最大析出速率对应温度相应降低.     

不同活性组分催化剂的氧化活性和热稳定性

采用流动法催化反应装置测定了蜂窝陶瓷负载催化剂同时催化氧化丙烷 ( C₃H₈)、丙烯 ( c₃H₆)和 CO的活性 ,考察活性组分 Pd和非贵金属氧化物、La改性、反应空速对起燃温度、热稳定性和动力学转化特征的影响 .结果显示 ,含 Pd催化剂上 C₃H₆和 CO的起燃温度比 C₃H₈低 ,1150℃高温老化对 C₃H₈氧化性能的影响比对 C₃H₆和 CO的小 .含稀土非贵金属氧化物的活性、热稳定性及动力学转化性能都比单 Pd催化剂低 ,添加 La能提高 2类催化剂的初活性和高温热稳定性 .     

基于观测数据的石家庄交通干线附近臭氧光化学敏感性分析

为确定石家庄东部郊区交通干线附近O₃生成光化学敏感性,利用2019年1月1日—2020年10月31日在线观测的NO_x、NO_y和O₃等数据计算并分析了O₃生成效率(OPE)及O₃光化学敏感性的NO_x临界浓度.结果表明:1交通干线附近O₃光化学敏感性存在季节差异,春季主要受VOCs控制,整体OPE为2.6±0.3,夏、秋季节主要受NO_x与VOCs协同控制,整体OPE分别为5.3±0.4和5.1±0.8;2NO_x体积分数>11×10^-9时,O₃生成主要为VOCs控制;NO_x体积分数介于6×10^-9~11×10^-9时,O₃生成主要受VOCs与NO_x协同控制;NO_x体积分数<6×10^-9时,O₃生成主要为NO_x控制;3O₃生成敏感性存在日变化特征,10:00之前O₃生成主要受VOCs控制,10:00—11:00是O₃生成由VOCs控制转变为VOCs和NO_x协同控制的过渡时段,12:00之后O₃生成主要由VOCs和NO_x协同控制,且午后14:00—16:00之间NO_x对O₃控制比例凸显.因此,石家庄O₃治理不但要重视NO_x与VOCs排放源的协同管控,尤其午后还需要对NO_x排放源进行分时段精细化管控.     

北京大气中NO、NO2和O3浓度变化的相关性分析

臭氧（O₃）是城市污染大气中的首要光化学污染物,其变化规律与氮氧化物(NO_x=NO+NO₂)关系密切.采用49C臭氧分析仪和42CTL氮氧化物分析仪对北京城区O₃和NO_x浓度进行了连续观测,时间为2004-08～2005-07.结果显示,O₃和OX（O₃+NO₂）浓度在午后15:00左右出现峰值,NO_x呈双峰态日变化,在07:00和23:00左右出现峰值.不同季节污染物的浓度变化存在差异,O₃和NO_x浓度分别在夏季和冬季达到最大.NO_x浓度存在100×10^-9(体积分数)的“分界点”,NO_x低浓度时以NO₂为主,NO_x高浓度时NO占大部分.OX区域贡献和局地贡献存在明显的季节变化,前者主要受区域背景O₃的影响,在春季最大,后者主要受局地NO_x光化学反应的制约,在夏季最强,同时OX组分呈现显著的昼夜差异.     

Effects of WOx modification on the activity, adsorption and redox properties of CeO2 catalyst for NOx reduction with ammonia

A series of WO₃/CeO₂ (WOx/CeO₂) catalysts were synthesized by wet impregnation of ammonium metatungstate on a CeO₂ support. The resulting solid acid catalysts were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy (UV-Vis), Raman spectroscopy (Raman), in-situ Fourier transform infrared spectroscopy (in-situ FT-IR) of ammonia adsorption, NH₃-TPD, H₂ temperature-programmed reduction (H₂-TPR), NH₃/NO oxidation and activity measurements for NOx reduction by NH₃ (NH₃-SCR). The results show that polytungstate (WOx) species are the main species of tungsten oxide on the surface of ceria. The addition of tungsten oxide enhances the Brönsted acidity of ceria catalysts remarkably and decreases the amount of surface oxygen on ceria, with strong interaction between CeO₂ and WOx. As a result, the N₂ selectivity of NH₃ oxidation and NH₃-SCR at high temperatures (> 300℃) is enhanced. Therefore, a wide working temperature window in which NOx conversion exceeds 80% (NOx conversion > 80%) from 200 to 450℃, is achieved over 10 wt.% WOx/CeO₂ catalyst. A tentative model of the NH₃-SCR reaction route on WOx/CeO₂ catalysts is presented.     

低温条件下Nano-MnOx上NH3选择性催化还原NO

采用流变相法制备了无载体Nano-MnO_x催化剂,在低温条件下(50～150℃)以NH₃为还原剂系统考察了氮氧化物的选择催化还原特性.结果表明,流变相法制备的Nano-MnO_x催化剂具有良好的低温催化活性.实验条件下,80℃即可获得98.25%的NO转化率,100～150℃内NO几乎完全转化;SO₂和H₂Ｏ会与NO和NH₃在催化剂表面产生竞争吸附,导致催化活性下降,但该影响是可逆的.经分析,较大的比表面积和较低的晶化度是Nano-MnO_x具有良好低温活性的2个主要原因.     

Mn含量对Mn/ZSM-5催化剂脱硝和SO2氧化性能的影响

为研究不同Mn含量对Mn基催化剂上SO₂氧化特性的影响,采用湿式浸渍法制备了一系列不同Mn含量的Mn/ZSM-5催化剂,并研究了这些催化剂上SO₂的氧化及脱硝特性,利用一系列表征手段研究了Mn/ZSM-5催化剂的物化特性和SO₂氧化机理.结果表明：①在标准SCR（选择性催化还原）反应中,随着Mn含量和温度的升高,SO₂氧化率先增后减,并在300℃时达最大值.②在快速SCR反应中,NO₂会直接氧化SO₂,提高了SO₂的氧化率,300℃时SO₂氧化率达到最高值（0.76%）.③脱硝性能试验表明,随着温度的升高,NO_x转化率呈先升后降的特征,在快速SCR反应中NO₂促进了氧化还原反应的进行,9Mn（Mn含量为9%）催化剂在250℃时NO_x转化率达最大值（96.58%）,远高于标准SCR反应的NO_x转化率.④表征结果表明,增加Mn含量提高了晶格氧和Mn⁴⁺的含量,使SO₂氧化率和NO_x转化率均增加;但过高的Mn含量会导致催化剂表面活性物质积聚,导致晶格氧和Mn⁴⁺含量下降,从而降低锰基催化剂的氧化还原性能.研究显示,在实际运行温度范围（150~400℃）内,应选择合适的Mn含量的催化剂,保证较高的脱硝效率,降低SO₂的氧化率.     

Adsorption removal of thiocyanate from aqueous solution by calcined hydrotalcite

A hydrotalcite with Mg/AI molar ratio 2 was prepared by co-precipitation method and was characterized by XRD, TG/DTA, Zeta potential and BET surface area. The hydrotalcite was calcined at 500℃, with the dehydration from interlayer, the dehydroxilation from the brucite-like layer and the decomposition of carbonate successively, transformed into the mixed oxide type. The removal of thiocyanate from aqueous solution by using the original hydrotalcite and calcined hydrotalcite （HTC-500） was investigated. The results showed that the thiocyanate adsorption capacity of calcined hydrotalcite was much higher than that of the original form. Calcined hydrotalcite was particularly effective at removing thiocyanate, and that the effective range of pH for the thiocyanate removal are between 5.5-10.0. The experimental data of thiocyanate removal fit nicely with Langmuir isotherm, and the saturated adsorption uptake was 96.2 mg SCN-/g HTC-500. The adsorption of thiocyanate by calcined hydrotalcite follows first-order kinetics. And the intercalation to the structure recovery for calcined hydrotalcite. But the presence of additional anions could affect the adsorption behavior of thiocyanate.     

NH3-SCR performance and the resistance to SO2 for Nb doped vanadium based catalyst at low temperatures

Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction(SCR)of NO.The results showed that the addition of Nb_2O_5could improve the SCR activity at low temperatures and the 6 wt.%additive was an appropriate dosage.The enhanced reaction activity of adsorbed ammonia species and the improved dispersion of vanadium oxide might be the reasons for the elevation of SCR activity at low temperatures.The resistances to SO_2of 3V6Nb/WTi catalyst at different temperatures were investigated.FTIR spectrum and TG-FTIR result indicated that the deposition of ammonium sulfate species was the main deactivation reason at low temperatures,which still exhibited the reactivity with NO above 200°C on the catalyst surface.There was a synergistic effect among NH_3,H_2O and SO_2that NH_3and H_2O both accelerated the catalyst deactivation in the presence of SO_2at 175°C.The thermal treatment at 400°C could regenerate the deactivated catalyst and get SCR activity recovered.The particle and monolith catalysts both kept stable NO_xconversion at 225°C with high concentration of H_2O and SO_2during the long time tests.     

UV/H2O2液相氧化净化烟气中NO的实验研究

采用UV/H₂O₂液相氧化技术净化气体中的NO,通过正交实验和单因素实验,研究了H₂O₂浓度、温度、初始pH值、NO浓度、光照条件、O₂含量和气体流量等因素对NO去除率的影响.结果表明,UV/H₂O₂液相氧化体系对NO有良好的净化效果,可以获得80%左右的NO去除率, 温度、H₂O₂浓度和初始pH值对NO去除率具有不同程度的影响,温度和H₂O₂浓度对NO去除率影响较大.单因素实验结果表明, 当H₂O₂浓度为0.2 mol/L、初始pH值为6～7时NO去除率较高;溶液中H₂O₂浓度过高或过低、溶液过酸或过碱均会抑制·OH的产生而不利于NO的去除;净化NO的最佳反应温度为40 ℃,低于一般湿法脱硝温度(50 ℃);NO的去除率随紫外光辐射强度和O₂含量的增加而升高;同时,NO的去除也受气液传质面积和气液传质系数的控制.     

贵金属/BaO催化剂上NOx的储存-还原

运用模拟配气方法考察了贵金属(Noble Metals,NM)/BaO催化剂的氮氧化物(NO_x)储存-还原性能. 采用热重-差热分析(TG-DTA)法对催化剂的NO_x吸附-脱附性能进行了研究. 结果表明:NO₂比NO更易于在催化剂上储存,O₂的存在极大地促进了NO_x储存反应的进行. 温度对催化剂上的NO_x储存行为有较大影响,在φ(O₂)为16%,φ(NO)为5×10-4的氧化气氛下,NO_x在NM/BaO上储存的适宜温度为300 ℃. 300 ℃下催化剂的NO_x吸附量可达15 mg/g,当温度升到600 ℃时,催化剂上的NO_x能够完全脱附. 使用H₂在催化剂上进行NO_x还原过程中,当φ(H₂)为1%或3%时,还原反应速率随温度的升高而变化;φ(H₂)为5%时,还原反应速率几乎不受温度影响.      

Catalytic reduction of nitric oxide with carbon monoxide on copper-cobalt oxides supported on nano-titanium dioxide

A series of copper-cobalt oxides supported on nano-titanium dioxide were prepared for the reduction of nitric oxide with carbon monoxide and characterized using techniques such as XRD, BET and TPR. Catalyst CuCoOx/TiO2 with Cu/Co molar ratio of 1/2, Cu- Co total loading of 30% at the calcination temperature of 350°C formed CuCo2O4 spinel and had the highest activity. NO conversion reached 98.9% at 200°C. Mechanism of the reduction was also investigated, N2O was mainly yielded below 100°C, while N2 was produced instead at higher temperature. O2 was supposed to accelerate the reaction between NOx and CO for its oxidation of NO to give more easily reduced NO2, but the oxidation of CO by O2 to CO2 decreased the speed of the reaction greatly. Either SO2 or H2O had no adverse impact on the activity of NO reduction; however, in the presence of both SO2 and H2O, the catalyst deactivated quickly.     

Performance and mechanism study for low-temperature SCR of NO with propylene in excess oxygen over Pt/TiO2 catalyst

A 0.5 wt.% Pt/TiO2 catalyst was prepared and used for the low-temperature selective catalytic reduction(SCR) of NO with C3 H6 in the presence of excess oxygen.The effects of Pt loading and O2 concentration on Pt/TiO2 catalytic performance for low-temperature SCR were investigated.It was found that optimal Pt loading was 0.5 wt.% and excess O2 favored low-temperature SCR of NOx.The mechanism of low-temperature SCR of NO with C3 H6 was investigated with respect to the behavior of adsorbed species over Pt/TiO2 at 150°C using in situ DRIFTS.The results indicated that surface nitrosyl species(Pt δ+-NO and Ti 3+-NO) and Pt 2+-CO are main reaction intermediates during the interactions of NO,C3 H6 and O2.A simplified NO decomposition mechanism for the low-temperature SCR of NO with C3 H6 was proposed.     

Co3O4纳米棒的制备及其对气相甲苯的催化氧化

采用低温水热法制备棒状纳米结构的Co3O4,通过加入少量的表面活性剂（聚乙烯吡咯烷酮简称PVP）,在95℃下低温反应,并调控制备过程的老化时间、溶液的pH这2个因素合成了棒状Co3O4纳米结构.X射线衍射（XRD）、透射电镜（TEM）表明制得的是呈立方晶体的Co3O4纳米棒,氢气程序升温还原（H2-TPR）、N2吸附脱附等表征手段表明老化时间和pH会影响Co3 O4纳米棒的尺寸、孔隙结构,进而影响其比表面积大小.采用气相甲苯作为目标物,运用气相色谱（GC）对Co3 O4的催化性能进行研究.结果表明在该实验中,调控老化时间和pH制得的Co3O4纳米棒只影响其低温降解效果,在温度低于260℃,活性最好的是pH=9,老化时间为12 h的催化剂;当温度高于260℃后,其降解曲线基本一致.     

Mechanism and catalytic performance for direct dimethyl ether synthesis by CO2 hydrogenation over CuZnZr/ferrierite hybrid catalyst

Direct synthesis of dimethyl ether(DME) by CO_2 hydrogenation has been investigated over three hybrid catalysts prepared by different methods:co-precipitation,sol-gel,and solid grinding to produce mixed Cu,ZnO,ZrO_2 catalysts that were physically mixed with a commercial ferrierite(FER) zeolite.The catalysts were characterized by N_2 physisorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),temperature programmed desorption of CO_2(CO_2-TPD),temperature programmed desorption of NH_3(NH_3-TPD),and temperature programmed H2 reduction(H_2-TPR).The results demonstrate that smaller CuO and Cu crystallite sizes resulting in better dispersion of the active phases,higher surface area,and lower reduction temperature are all favorable for catalytic activity.The reaction mechanism has been studied using in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS).Methanol appears to be formed via the bidentate-formate(b-HCOO) species undergoing stepwise hydrogenation,while DME formation occurs from methanol dehydration and reaction of two surface methoxy groups.     

Fe-MnOx-CeO2/ZrO2低温催化还原NO性能研究

以纳米ZrO2为载体,用浸渍法制备出Fe-MnOx-CeO2/ZrO2催化剂,考察了活性组分配比和助剂负载量对催化剂低温NH3选择性催化还原NO活性的影响,并对催化剂进行了XRD、SEM、EDS和BET表征;探讨了温度、H2O和SO2对Fe-MnOx-CeO2/ZrO2催化剂低温下NH3选择性催化还原NO的影响,结果表明,无SO2和H2O条件下,8%Fe-10%MnOx-CeO2/ZrO2催化剂具有良好的催化活性和稳定性.120℃时,催化剂的脱硝效率为85.23%,当温度升至180℃时,脱硝效率可达到92.0%.SO2和H2O共存条件下,催化剂易失活,采用傅立叶变换红外光谱对各反应阶段的催化剂进行了表征,对其失活机制进行深入研究,结果表明,催化剂失活的主要原因是催化剂表面硫酸铵盐的沉积和催化剂本身活性成分的硫酸盐化.     

Rh-Al-MCM-41上NO选择性催化还原的原位红外研究

利用气-固相固定床反应装置考察了Rh交换的Al-MCM-41在高气体空速条件下对贫燃NOx的选择性催化还原活性,考察了氧含量对其的影响。结果表明,在200000h~(-1)的气体空速、O_2/C_3H_6=20、603K时,NO转化率为74.3％。利用原位FTIR技术研究了该催化剂的表面吸附物种及表面程序升温反应行为,并结合实验观察探讨了贫燃条件下Rh-Al-MCM-41催化剂上NO的选择性催化还原机理。