陈浩辉,王亚洲,余 杰,邱 磊,尹一萌,王驰中,常化振*

助剂添加对CuO/TiO2催化剂NH3-SCO性能的影响研究

陈浩辉1,王亚洲2,余 杰1,邱 磊1,尹一萌1,王驰中1,常化振1*

(1.中国人民大学环境学院,北京 100872；2.北京市生态环境保护科学研究院,北京 100037)

采用浸渍法制备了一系列CuO-MO/TiO2(M=W, Zr, La)催化剂用于NH3选择性催化氧化(NH3-SCO),同时探究了SO2中毒对NH3氧化性能的影响.结果表明,过渡金属氧化物的添加使Cu/TiO2催化剂NH3转化率降低,但显著提高N2选择性.其中,WO3具有最好的促进效果,在300℃下催化剂N2选择性提高了36%.通过H2-TPR和NH3-TPD表征发现,WO3的添加增加了Cu/TiO2催化剂表面酸性位点的数量,促进NH3的吸附,但降低催化剂氧化还原性能,抑制NH3氧化为NO.经SO2中毒处理后,CuO-MO/TiO2催化剂N2选择性进一步提高,表征结果表明,酸性位点的增加和氧化氧化还原性的降低是提高催化剂N2选择性的关键.

Cu/Ti基催化剂；NH3选择性催化氧化；金属氧化物添加；SO2中毒

氨(NH3)是重要的化工原材料,同时也是有毒有害的工业气态污染物之一[1-2].NH3不仅会对人体健康产生危害,还会导致雾霾,光化学烟雾等各种环境问题[3-7].化肥的大量使用以及工业活动是NH3的主要排放来源.例如工业采用NH3或者尿素作为还原剂的选择性催化还原(SCR)脱硝过程中NH3逃逸的发生[8-9].因此,有效地去除NH3具有非常重要的意义.

吸附､吸收､催化燃烧、催化分解等多种方法已被应用于NH3的去除,但存在成本高,适用范围窄,容易产生二次污染物等问题.选择性催化氧化(SCO)被视为一种高效的NH3处理技术[10-11].催化剂是NH3-SCO技术的核心.目前用于选择性催化氧化NH3的催化剂可以分为三大类:(1)贵金属催化剂,如Ag, Pt, Pd, Ru, Au等0[12-18];(2)过渡金属氧化物催化剂,包括CuO, Fe3O4, Co3O4, MnO2, V2O5, CeO2等[19-25];(3)沸石分子筛催化剂,如Cu-ZSM-5, Pd-Y, Pt-ZSM-5和Fe-Beta等[26-30].虽然贵金属催化剂在低温(<300℃)表现出高的催化活性,但成本高,N2选择性较低.相比之下,过渡金属氧化物和分子筛催化剂因成本低,N2选择性高等优点得到广泛研究[31].

在过渡金属氧化物催化剂中,Cu基催化剂越来越受到关注.其低成本和较高的活性被证明是NH3-SCO反应的有前途的催化剂之一.

Il’chenko等[32]在1975年发现CuO可以将NH3催化氧化为N2和H2O.随着研究的深入,发现Cu物种的种类、晶体结构、载体种类以及载体形貌等都会影响NH3的氧化性能[30-33].如有研究者比较了Cu-Mg-Al-O混合金属氧化物与Cu/Al2O3催化剂,发现催化剂上形成的不同存在形式的氧化铜物种(高度分散的CuO物种和块状CuO物种)对NH3-SCO活性有较大影响[33].也有研究者将Cu负载在Al2O3上,发现类CuAl2O4相在NH3氧化反应中比CuO相更活跃[30]. CuO与载体Al2O3的相互作用也在其他研究中被提及[34-35]有研究者将CuO负载在TiO2上,发现CuO/TiO2催化剂N2选择性与Cu/Al2O3催化剂相似,但是CuO/TiO2催化剂在低温下活性更好[36-37].不同形貌CeO2负载的CuO催化剂上NH3-SCO的反应路径和中间物种有很大差异[38]. Cu基催化剂在高温下容易发生NH3的过氧化,所以其N2选择性的提高也令人关注.研究者们发现将W和La等助剂掺杂到CuO基催化剂上后,催化剂NH3转化率略微下降,但也使其N2选择性显著增高0[39-40].Zhang等通过研究不同比例的CuO-Fe2O3复合金属氧化物,发现Cu/Fe比例越高,催化剂NH3氧化活性越高,Cu/Fe比例越低,催化剂N2选择性越高[41].

基于此,本文采用浸渍法制备了过渡金属氧化物WO3, La2O3, ZrO2添加改性的CuO/TiO2基催化剂并将其用于选择性催化氧化去除NH3,发现金属氧化物的添加显著提高了Cu/Ti基催化剂N2选择性.结合XRD, NH3-TPD和H2-TPR等物化表征,对过渡金属氧化物添加提高CuO/TiO2催化剂NH3- SCO反应N2选择性的机制进行探究.此外,本研究还考察了SO2对CuO/TiO2基催化剂NH3-SCO活性和选择性的影响.

1 材料与方法

1.1 催化剂制备

采用浸渍法制备了CuO/TiO2和CuO-MO/TiO2(M=W, Zr, La)催化剂,具体步骤如下:称取4份一定质量的硝酸铜(Cu(NO3)2·3H2O),分别与相应质量的钨酸铵(H40N10O41W12·H2O),硝酸锆(Zr(NO3)4·5H2O),硝酸镧(La2(NO3)3·6H2O)一起溶于60mL去离子水中,搅拌0.5h.称取一定质量的TiO2(德固赛P25)粉末,倒入上述溶液中并搅拌2h.经80℃水浴加热至糊状,放入110℃的烘箱中烘干12h.取出研磨后放入马弗炉中500℃下煅烧4h,升温速率10℃/min.自然冷却至室温后取出,研磨压片,筛分出40～60目的催化剂颗粒.其中CuO, La2O3, ZrO2和WO3质量分数均为5wt%.

SO2处理催化剂制备:在200℃下进行,中毒气氛中各组分的体积分数分别为5×10-4NH3, 5×10-4SO2, 5×10-2H2O, 5×10-2O2, N2为平衡气,气体流量为200mL/min,中毒时间12h.催化剂再生处理为在400℃下热处理2h.

为了便于区分,本文中新鲜的催化剂记为CuM/ Ti-f, SO2处理后的催化剂记为CuM/Ti-p,再生后的催化剂记为CuM/Ti-r.

1.2 催化剂表征

通过X射线衍射(XRD)对样品的晶体结构进行分析,选用的X射线衍射仪型号为岛津公司的XRD-700粉末衍射仪.实验条件: Cu Kα(=1.5418Å, 2=10°～90°,扫描速率=10°/min).

在化学吸附仪(Micromeritics, ChemiSorb 2720TPx)上进行H2-TPR(H2temperature programmed reduction)表征,以对样品的氧化还原性进行分析.H2-TPR的测试步骤如下: (1)在Ar气氛下对样品进行350℃预处理,持续时间1h,以去除样品表面的杂质; (2)待样品冷却至室温后,切换气体为5% H2/Ar,控制气体流量为30mL/min,保持气氛和流量不变,基线稳定后,以10°C/min的升温速率从室温升至800℃,通过TCD检测仪得到H2-TPR结果.

用氨分析仪(EAA-30r-EP)进行NH3-TPD(NH3temperature programmed desorption)实验.样品首先在N2气氛中400℃预处理1h以去除表面杂质,自然降温至100℃后,在100℃条件下通入NH3/N2.吸附饱和后,N2吹扫1h,去除弱吸附物质.后以10℃/min的速度升温至400℃,记录出口气体中NH3的浓度,得到NH3的脱附温度曲线.

单位质量催化剂样品上NH3脱附量计算公式为:

式中:ads为NH3脱附量;des为TPD曲线的脱附峰面积;c为吹扫气体流量(mL/min);T为升温速率(℃/min);cat为催化剂质量(g).

1.3 催化剂活性测试

催化剂活性测试在固定床适应反应器(内径6mm)进行.每次测试所用催化剂质量为0.15g,气体流量200mL/min,体积空速(GHSV)为65000h-1.进气中NH3的体积均为5×10-4, O2的体积分数为5×10-2,平衡气为N2.出口气中各气体浓度由傅里叶红外检测器(Thermo Fisher Scientific iS50)检测,记数时会在每个温度点稳定0.5h.

NH3转化率计算公式为:

N2选择性计算公式为:

式中:下标“in”和“out”分别表示进口和出口处的NH3, NO, NO2, N2O等气体的浓度.

2 结果与讨论

2.1 NH3-SCO活性测试

4种新鲜催化剂NH3-SCO活性和选择性分别如图1(a)和图1(b)所示.Cu/Ti催化剂表现出高的NH3氧化活性,在250℃时,NH3的转化率接近90%,比已经报道的其他Cu基负载型催化剂活性高20～60%[35-36].经助剂添加后,催化剂的活性明显发生改变,NH3的转化率依次为:Cu/Ti>CuZr/Ti>CuLa/ Ti>CuW/Ti.表明3种助剂的添加均导致催化剂活性的降低,其中W对活性的影响最大.如图1(b)所示, Cu/Ti催化剂虽然具有良好的NH3氧化活性,但是表现出低的N2选择性,这可能与NH3氧化的副反应进行有关.值得注意的是3种助剂的添加虽然降低了NH3氧化活性,但显著提高了催化剂N2选择性.其中WO3添加的催化剂表现出最高的促进效果,在300℃时,催化剂N2选择性由50%提高到90%,与已经报道的Cu基催化剂300℃下的最高N2选择性基本持平[39].以上表明W, Zr, La添加可以显著提高Cu基催化剂N2选择性,抑制副反应的进行.

新鲜催化剂在300℃时各种产物的选择性分布如图1(c)所示.4种催化剂催化NH3氧化的产物除了N2外,均含有N2O, NO和NO2,且各催化剂3种氮氧化物的选择性差别较大.300℃时,CuW/Ti催化剂NO选择性最低,而其N2选择性最高;Cu/Ti催化剂NO选择性最高,其N2选择性最低.CuM/Ti催化剂NO选择性与N2选择性有一定的相关性.这可以用内部SCR(i-SCR)机理来解释[42].i-SCR机理认为NH3- SCO反应可分为两步: (1)NH3首先在催化剂表面转化为NO;(2)NH3与NO发生SCR反应将NO还原为N2和H2O. NO选择性低,可能是因为与NH3反应消耗的NO更多,产生的N2也更多,N2选择性提高.

反应条件:5×10-4NH3, 5×10-2O2, N2平衡气, GHSV=65000h-1

2.2 催化剂的物化表征

2.2.1 XRD 新鲜CuM/Ti催化剂的XRD结果如图2(a)所示.在Cu/Ti催化剂上只存在锐钛矿相TiO2和金红石相TiO2的衍射峰,没有观察到CuO的特征峰[43],表明Cu物种高度分散在催化剂表面.同时出现锐钛矿型TiO2和金红石型TiO2的衍射峰是因为本研究所选用的德固赛 P25TiO2药品属于混晶型,其锐钛矿和金红石的质量比重大致为79:21.在W, Zr, La添加后,催化剂的晶体结构无明显变化,且ZrO2, WO3, La2O3晶相均未检测到[44-46],表明添加的元素不改变催化剂的晶体结构.

2.2.2 H2-TPR 催化剂的氧化还原性能是影响NH3-SCO活性的重要因素[47].新鲜CuW/Ti, CuZr/Ti, CuLa/Ti, Cu/Ti催化剂的H2-TPR表征结果如图2(b)所示.

观察Cu/Ti催化剂的H2-TPR曲线,在190和282℃出现2个H2还原峰,分别归属于Cu2+和Cu+的还原[43].在助剂添加后,2个还原峰的位置发生了不同程度地改变.在CuZr/Ti催化剂上,Zr的加入促使Cu2+和Cu+的还原峰向低温偏移,表明Zr的添加可以促进Cu的还原,提高催化剂的氧化还原性.在CuW/Ti催化剂上,W的加入没有影响Cu+的还原,但是Cu2+的还原峰由190℃偏移至209℃,表明Cu2+的还原受到抑制.此外,在725℃出现一个H2还原峰,这归属于W6+的还原[48].在CuLa/Ti催化剂上,La的添加没有影响Cu2+的还原,但是显著影响了Cu+的还原.WO3和La2O3的添加导致催化剂的氧化性能降低,这可能是CuW/Ti和CuLa/Ti催化剂的NH3-SCO活性不如Cu/Ti催化剂的主要原因.而催化剂氧化能力的降低,有助于提高催化剂的N2选择性[39].之前的研究发现La2O3, ZrO2, WO3的添加可能有助于提高Cu基催化剂的NH3-SCR性能[49,51],即促进i-SCR机理中第二步NH3还原NO转化为N2和H2O的过程,进而提高催化剂的N2选择性.

2.2.3 NH3-TPD 如图3所示,助剂添加明显影响了NH3的吸附性能.在W和Zr添加后,NH3的脱附曲线向低温方向偏移,且脱附峰较Cu/Ti催化剂出现了宽化,表明添加的W和Zr能促进NH3的低温脱附,同时提高NH3的吸附能力.对于La添加的催化剂而言,NH3的脱附曲线向高温侧偏移,且脱附峰的面积出现降低,表明La的添加抑制了NH3在催化剂表面的吸附与脱附.

计算了4种催化剂的NH3的吸附量,结果如表1所示,明显地发现助剂添加可以改变NH3的吸附能力,尤其是CuW/Ti催化剂,表现出最高的NH3吸附能力.在i-SCR机理中,NH3首先先被氧化为NO, NO再与未转化的NH3反应转化为N2和H2O.催化剂的NH3吸附能力越强,越有利于这两步反应的进行.4种催化剂的NH3吸附能力顺序为CuW/Ti> CuZr/ Ti>Cu/Ti>CuLa/Ti,但N2选择性顺序为CuW/Ti> CuZr/Ti>CuLa/Ti>Cu/Ti,可能的原因如下:除CuW/Ti催化剂外,另外3种催化剂的NH3吸附量差别不大.根据图2(b)中H2-TPR的结果,Cu/Ti催化剂的氧化还原性能比CuLa/Ti催化剂更强,可能会促进NH3转化为NO.所以Cu/Ti催化剂上未转化的NH3的浓度比CuLa/Ti更低,导致与NO反应生产N2的NH3不足,降低了Cu/Ti催化剂的N2选择性. CuZr/Ti催化剂的氧化还原能力比Cu/Ti更强,但其NH3转化率却比Cu/Ti催化剂低.可能是催化剂的形貌等其他因素,抑制了CuZr/Ti催化剂的NH3转化能力,同时也提高了CuZr/Ti催化剂的N2选择性.

图3 CuM/Ti催化剂的NH3-TPD谱图

2.3 SO2的影响

2.3.1 SO2中毒后催化剂的NH3-SCO性能 经过SO2处理后的CuM/Ti催化剂的NH3-SCO活性和各种产物的选择性如图4(a)和图4(b)所示.之前的研究指出,催化剂经SO2中毒处理后,催化剂上的活性组分会被硫化形成金属硫酸盐.同时当处理气氛中存在NH3和H2O时,催化剂表面还会伴随硫酸氢铵/硫酸铵物种的沉积.如图4(a)所示,在SO2中毒处理后,4个催化剂的NH3氧化活性显著降低.在300℃下,催化剂基本无催化活性,这主要是由于金属硫酸盐以及硫酸氢铵/硫酸铵的形成导致.值得注意的是,通过观察中毒前后4种催化剂的N2选择性发现,相较于中毒前,中毒后的催化剂的N2选择性都出现了提高.其中CuLa/Ti-f催化剂的N2选择性的提高最为明显.表明SO2中毒处理能有效提高Cu基催化剂的N2选择性.

而从中毒后催化剂在400℃时的产物选择性上来看,4种中毒后催化剂的N2选择性均大于新鲜催化剂.4种中毒后的催化剂的NO､NO2和N2O的总选择性与NO选择性高低顺序保持一致.400℃下,NO选择性按从低到高排列,顺序为CuLa/Ti-p

反应条件:5×10-4NH3, 5×10-2O2, N2平衡气, GHSV=65000h-1

2.3.2 H2-TPR和NH3-TPD 中毒后CuM/Ti催化剂的H2-TPR谱图如图5(a)所示.观察到Cu/Ti-p催化剂,经SO2中毒处理后,归属于Cu2+和Cu+的特征峰消失,同时在350℃出现新的特征峰,这归属于硫酸铜物种[43].表明经SO2中毒处理后,形成的金属硫酸盐降低了催化剂的氧化还原性.对于助剂添加的催化剂而言,经过SO2的处理后,归属于Cu2+和Cu+的特征峰均消失,并伴随着硫酸铜物种的形成.此外,在CuZr/Ti-p和CuLa/Ti-p催化剂上除了观察到硫酸铜的特征峰(371和336℃)之外,还形成新的特征峰(409,410,530,603℃),这可能是由于其他金属硫酸盐的形成导致的,如硫酸锆、硫酸镧、硫酸钛[52-54].总之,SO2中毒处理后,金属硫酸盐的形成会导致催化剂氧化还原性的降低,而低的氧化还原性有利于提高催化剂的N2选择性[54].

中毒后催化剂的NH3-TPD谱图如图5(b)所示.相较于新鲜的催化剂,在SO2中毒处理后,四个催化剂的NH3的脱附曲线明显发生改变,主要表现为脱附温度窗口变宽并伴随着新的脱附峰的出现.SO2中毒后,会在催化剂上沉积硫酸氢铵/硫酸铵,部分活性位点也会被硫酸化形成金属硫酸盐.一般情况下,大部分硫酸氢铵/硫酸铵会在400℃前分解,硫酸铜会在637℃开始分解,而硫酸锆､硫酸镧和硫酸钨在800℃前不会分解[43,55-56].所以根据SO2处理及再生后催化剂的NH3吸附量,一定程度上能够反映催化剂形成的硫酸氢铵/硫酸铵的量的多少.结合H2-TPR的结果,进一步证明SO2中毒后催化剂上金属硫酸盐和硫酸氢铵/硫酸铵的形成.之前的研究指出形成的金属硫酸盐和硫酸氢铵/硫酸铵可以为催化剂提供新的酸性位点进而提高催化剂NH3吸附性能0.根据i-SCR机理,NH3转化的NO可以与NH3通过SCR的方式转化为N2和H2O,因此SO2中毒为催化剂提供了新的NH3吸附位点,进而提高了N2选择性,降低NO的生成.此外,表1中SO2处理后催化剂的NH3吸附量与N2选择性并不相符,因为中毒后催化剂表面沉积的硫酸氢铵/硫酸铵分解会产生NH3,所以中毒后催化剂的NH3-TPD结果并不能准确地反应催化剂的NH3吸附能力.

2.4 热再生后

2.4.1 热再生后催化剂的NH3-SCO性能 进一步考察了热再生对SO2中毒催化剂的影响,经过400℃热再生后的CuM/Ti催化剂的NH3-SCO活性如图6所示.结果显示,再生后催化剂的活性得到部分恢复,在300℃下,催化剂的NH3氧化活性与新鲜样品相当(除CuZr/Ti-r),表明热再生处理能有效去除催化剂表面部分金属硫酸盐和硫酸氢铵/硫酸铵等,实现催化剂活性的恢复.

图6 再生CuM/Ti催化剂的NH3-SCO活性

反应条件:5×10-4NH3, 5×10-2O2, N2平衡气, GHSV=65000h-1

2.4.2 H2-TPR和NH3-TPD 再生后CuM/Ti催化剂的H2-TPR和NH3-TPD谱图如图7(a)和图7(b)所示.再生后Cu/Ti, CuW/Ti, CuZr/Ti, CuLa/Ti催化剂部分金属硫酸盐的特征峰消失,且归属于Cu物种还原的特征峰出现,表明热再生处理导致金属硫酸盐的分解,伴随着活性位点的释放.在NH3-TPD中,经过再生处理后催化剂的酸性出现了降低,这是由于硫酸氢铵/硫酸铵和小部分金属硫酸盐的分解导致的.但是相较于新鲜样品,再生后的催化剂依然表现出高的NH3吸附性能.

3 结论

3.1 WO3, ZrO2和La2O3的添加能够显著提高Cu/Ti催化剂NH3-SCO反应的N2选择性.其中WO3使N2选择性提高了20%～40%,效果最好.这可能是因为WO3的添加降低了Cu/Ti催化剂的氧化性能,同时提高了其NH3吸附能力.

3.2 SO2中毒能够显著提高CuM/Ti催化剂对NH3的吸附能力.硫酸根的存在抑制了催化剂在低温下(250℃及以下)的NH3-SCO性能,却提高了其在高温下的N2选择性.

[1] Fujii H, Managi S. Economic development and multiple air pollutant emissions from the industrial sector [J]. Environmental Science and Pollution Research, 2016,23(3):2802-2812.

[2] Jablonska M, Molla Robles A. A comparative mini-review on transition metal oxides applied for the selective satalytic ammonia oxidation (NH3-SCO) [J]. Materials, 2022,15(14):4770.

[3] Gu B, Zhang L, ingenen R V, et al. Abating ammonia is more cost-effective than nitrogen oxides for mitigating PM2.5air pollution [J]. Science, 2021,374(6568):758-762.

[4] 陈 莉,樊 星,李 佳等.制备方法对SSZ-13负载Cu催化剂NH3-SCO性能的影响[J]. 中国环境科学, 2023,43(7):3378-3386. Chen L, Fan X, Li J, et al. Effect of preparation methods on NH3-SCO performance of SSZ-13 supported Cu catalysts [J]. China Environmental Science, 2023,43(7):3378-3386.

[5] Bai Z, Winiwarter W, Klimont Z, et al. Further improvement of air quality in China needs clear ammonia mitigation target [J]. Environmental Science & Technology, 2019,53(18):10542-10544.

[6] Wang F, Ma J, He G, et al. Nanosize effect of Al2O3in Ag/Al2O3catalyst for the selective catalytic oxidation of ammonia [J]. ACS Catalysis, 2018,8(4):2670-2682.

[7] Bao Z, Xu H, Li K, et al. Effects of NH3on secondary aerosol formation from toluene/NOphoto-oxidation in different O3formation regimes [J]. Atmospheric Environment, 2021,261:118603.

[8] Lan T, Deng J, Zhang F, et al. Unraveling the promotion effects of dynamically constructed CuO-OH interfacial sites in the selective catalytic oxidation of ammonia [J]. ACS Catalysis, 2022,12(7):3955- 3964.

[9] Peng L, Guo A, Chen P, et al. Ammonia abatement via selective oxidation over electron-deficient copper catalysts [J]. Environmental Science & Technology, 2022,56(19):14008-14018.

[10] Jabłońska M, R Palkovits. Copper based catalysts for the selective ammonia oxidation into nitrogen and water vapour—Recent trends and open challenges [J]. Applied Catalysis B: Environmental, 2016, 181:332-351.

[11] Ge S, Liu X, Liu J, et al. Synthesis of TiSn1-xO2mixed metal oxide for copper catalysts as high-efficiency NH3selective catalytic oxidation [J]. Fuel, 2022,314:123061.

[12] Decarolis D, Clark A H, Pellegrinelli T, et al. Spatial profiling of a Pd/Al2O3catalyst during selective ammonia oxidation [J]. ACS Catalysis, 2021,11(4):2141-2149.

[13] Wang F, He G, Zhang M, et al. Insights into the activation effect of H2pretreatment on Ag/Al2O3catalyst for the selective oxidation of ammonia [J]. ACS Catalysis, 2019,9(2):1437-1445.

[14] Gong J L, Ojifinni R A, Kim T S, et al. Selective catalytic oxidation of ammonia to Nitrogen on atomic oxygen precovered Au(111) [J]. Journal of American Chemical Society, 2006,128:9012-9013.

[15] Cui X, Chen L, Wang Y, et al. Fabrication of hierarchically porous RuO2–CuO/Al–ZrO2composite as highly efficient catalyst for ammonia-selective catalytic oxidation [J]. ACS Catalysis, 2014,4(7): 2195-2206.

[16] Zhang Q, Zhang T, Xia F, et al. Promoting effects of acid enhancing on N2selectivity for selectivity catalytic oxidation of NH3over RuO/TiO2: The mechanism study [J]. Applied Surface Science, 2020,500:144044.

[17] Svintsitskiy D A, Slavinskaya E M, Stonkus O A, et al. The state of platinum and structural features of Pt/Al2O3catalysts in the reaction of NH3oxidation [J]. Journal of Structural Chemistry, 2019,60(6):919- 931.

[18] Lan T, Zhao Y, Deng J, et al. Selective catalytic oxidation of NH3over noble metal-based catalysts: state of the art and future prospects [J]. Catalysis Science & Technology, 2020,10(17):5792-5810.

[19] Long R Q, Yang R T, Selective catalytic oxidation of ammonia to nitrogen over Fe2O3–TiO2prepared with a sol–gel method [J]. Journal of Catalysis, 2002,207(2):158-165.

[20] Wang Z, Qu Z, Quan X, et al. Selective catalytic oxidation of ammonia to nitrogen over ceria–zirconia mixed oxides [J]. Applied Catalysis A: General, 2012,411-412:131-138.

[21] Kwon D W, Lee S M, Hong S C. Influence of attrition milling on V/Ti catalysts for the selective oxidation of ammonia [J]. Applied Catalysis A: General, 2015,505:557-565.

[22] Wang H, Zhang Q, Zhang T, et al. Structural tuning and NH3-SCO performance optimization of CuO-Fe2O3catalysts by impact of thermal treatment [J]. Applied Surface Science, 2019,485:81-91.

[23] Shojaee K, Haynes B S, Montoya A. The catalytic oxidation of NH3on Co3O4(110): A theoretical study [J]. Proceedings of the Combustion Institute, 2017,36(3):4365-4373.

[24] Fung W K, Ledwaba L, Modiba N, et al. Choosing a suitable support for Co3O4as an NH3oxidation catalyst [J]. Catalysis Science & Technology, 2013,3(8):1905-1909.

[25] Qu Z, Fan R, Wang Z, et al. Selective catalytic oxidation of ammonia to nitrogen over MnO2prepared by urea-assisted hydrothermal method [J]. Applied Surface Science, 2015,351:573-579.

[26] Kim M S, Lee D W, Chung S H, et al. Oxidation of ammonia to nitrogen over Pt/Fe/ZSM5 catalyst: Influence of catalyst support on the low temperature activity [J]. J. Hazardous Materials, 2012,237- 238:153-160.

[27] Jabłońska M, Król A, Kukulska-Zajac E, et al. Zeolite Y modified with palladium as effective catalyst for selective catalytic oxidation of ammonia to nitrogen [J]. J. Catalysis, 2014,316:36-46.

[28] Boroń P, Chmielarz L, Gurgul J, et al. The influence of the preparation procedures on the catalytic activity of Fe-BEA zeolites in SCR of NO with ammonia and N2O decomposition [J]. Catalysis Today, 2014,235: 210-225.

[29] Akah A C, Nkeng G, Garforth A A. The role of Al and strong acidity in the selective catalytic oxidation of NH3over Fe-ZSM-5 [J]. Applied Catalysis B: Environmental, 2007,74(1/2):34-39.

[30] Gang L, Grondelle J V, Anderson B G, et al. Selective low temperature NH3oxidation to N2on coppe-based catalysts [J]. J. Cayalysis, 1999, 186:100-109.

[31] Jablonska M. Progress on noble metal-based catalysts dedicated to the selective catalytic ammonia oxidation into nitrogen and water vapor (NH3-SCO) [J]. Molecules, 2021,26(21):6461.

[32] Il'chenko N I, Golodets G I. Catalytic oxidation of ammonia I. Reaction kinetics and Mechanism [J]. Journal of catalysis, 1975,39: 57-72.

[33] Jabłońska M, Wolkenar B, Beale A M, et al. Comparison of Cu-Mg-Al-Oand Cu/Al2O3in selective catalytic oxidation of ammonia (NH3-SCO) [J]. Catalysis Communications, 2018,110:5-9.

[34] Yang M, Wu C, Zhang C, et al. Selective oxidation of ammonia over copper-silver-based catalysts [J]. Catalysis Today, 2004,90(3/4):263-267.

[35] Liang C, Li X, Qu Z, et al. The role of copper species on Cu/γ-Al2O3catalysts for NH3–SCO reaction [J]. Applied Surface Science, 2012,258(8):3738-3743.

[36] Bagnasco G, Peluso G, Russo G, et al. Ammonia oxidation over CuO/TiO2catalyst: selectivity and mechanistic study [J].3rdWorld Congress on oxidation catalysis, 1997,110:643-652.

[37] He S, Zhang C, Yang Y, et al. Selective catalytic oxidation of ammonia from MAP decomposition [J]. Separation and Purification Technology, 2007,58(1):173-178.

[38] Sun H, Wang H, Qu Z. Construction of CuO/CeO2catalysts via the ceria shape effect for selective catalytic oxidation of ammonia [J]. ACS Catalysis, 2023,13(2):1077-1088.

[39] Yang X, Li N, Zhang Y, et al. Insight into the role of WO3on catalytic performance over CuO-CeO2catalyst for NH3selective catalytic oxidation reaction [J]. Journal of Environmental Chemical Engineering, 2021,9(6):106621.

[40] Xie J, Jin Q, Fang D, et al., Effect of La/Ce modification over Cu based Y zeolite catalysts on high temperature selectivity for selective catalytic reduction with ammonia [J]. J. Cleaner Production, 2022, 362:132255.

[41] Zhang Q, Wang H, Ning P, et al. In situ DRIFTS studies on CuO-Fe2O3catalysts for low temperature selective catalytic oxidation of ammonia to nitrogen [J]. Applied Surface Science, 2017,419: 733-743.

[42] Boer M D, Huisman H M, Mos R J M, et al. Selective oxidation of ammonia to nitrogen over SiO2-supported MoO3catalysts [J]. Catalysis Today, 1993,17:198-200.

[43] Wang Y, Yi W, Yu J, et al. Novel methods for assessing the SO2poisoning effect and thermal regeneration possibility of MO-WO3/TiO2(M=Fe, Mn, Cu and V) Catalysts for NH3-SCR [J]. Environmental Science & Technology, 2020,54(19):12612-12620.

[44] Karthikeyan S, Raj A D, Irudayaraj A A, et al. Effect of temperature on the properties of La2O3nanostructures [J]. Materials Today: Proceedings, 2015,2(3):1021-1025.

[45] Cumbrera F L, Sponchia G, Benedetti A, et al. Some crystallographic considerations on the novel orthorhombic ZrO2stabilized with Ta doping [J]. Ceramics International. 2018,14:10362-10366.

[46] Adhikari S, Sarkar D, Maiti H S. Synthesis and characterization of WO3spherical nanoparticles and nanorods [J]. Materials Research Bulletin, 2014,49:325-330.

[47] Liu W, Long Y, Tong X, et al. Transition metals modified commercial SCR catalysts as efficient catalysts in NH3-SCO and NH3-SCR reactions [J]. Molecular Catalysis, 2021,515:111888.

[48] Yu L, Zhong Q, Zhang S, et al. A CuO-V2O5/TiO2catalyst for the selectibe catalytic reduction of NO with NH3[J]. Combustion Science and Technology, 2015,187(6):925-936.

[49] Nam K B, Lee S H, Hong S C. The role of copper in the enhanced performance of W/Ti catalysts for low-temperature selective catalytic reduction [J]. Applied Surface Science, 2021,544:148643.

[50] Liu T, Wei L, Yao Y, et al. La promoted CuO-MnOcatalysts for optimizing SCR performance of NO with CO [J]. Applied Surface Science, 2021,546:148971.

[51] Wang T, Li C, Zhao L, et al. The catalytic performance and characterization of ZrO2support modification on CuO-CeO2/TiO2catalyst for the simultaneous removal of Hg0and NO [J]. Applied Surface Science, 2017,400:227-237.

[52] Xiong Z, Wang W, Li J, et al. The synergistic promotional effect of W doping and sulfate modification on the NH3-SCR activity of CeO2catalyst [J]. Molecular Catalysis, 2022,522.

[53] Ye D, Wang X, Liu H, et al. Insights into the effects of sulfate species on CuO/TiO2catalysts for NH3-SCR reactions [J]. Molecular Catalysis, 2020,496.

[54] Kušar H M J, Ersson A G, Vosecký M, et al. Selective catalytic oxidation of NH3to N2for catalytic combustion of low heating value gas under lean/rich conditions [J]. Applied Catalysis B: Environmental, 2005,58(1/2):25-32.

[55] Poston J A, Siriwardane R V, Fisher E P, et al. Thermal decomposition of the rare earth sulfates of cerium(III), cerium(IV), lanthanum(III) and samarium(III) [J]. Applied Surface Science, 2003,214(1-4): 83-102.

[56] Ahmed M A K, Fjellvag H, Kiekshus A. Synthesis and characterization of zirconium and hafnium sulfates, hydroxide sulfates and oxide sulfates [J]. Acta Chemica Scandinavica, 1999,53:24-33.

[57] Xu L, Wang C, Chang H, et al. New insight into SO2poisoning and regeneration of CeO2-WO3/TiO2and V2O5-WO3/TiO2catalysts for low-temperature NH3-SCR [J]. Environmental Science & Technology, 2018,52(12):7064-7071.

Effect of additives and SO2on selective catalytic oxidation of NH3over CuO/TiO2catalysts.

CHEN Hao-hui1, WANG Ya-zhou2, YU Jie1, QIU Lei1, YIN Yi-meng1, WANG Chi-zhong1, CHANG Hua-zhen1 *

(1.School of Environment and Natural Resources, Renmin University of China, Beijing 100872, China；2.Beijing Municipal Research institute of Eco-Environmental Protection, Beijing 100037, China)., 2023,43(10)：5123～5130

A series of CuO-MO/TiO2(M=W, Zr, La) catalysts were prepared by impregnation method for the selective catalytic oxidation of NH3, and the effects of SO2poisoning on the oxidation of NH3over Cu/Ti-based catalysts were investigated. The results show that adding of transition metal oxides decreased the NH3conversion efficiency of Cu/Ti catalyst slightly, but significantly improved the N2selectivity. WO3was the best promoter among those additives, with an increase of N2selectivity by 36% at 300℃ in comparison to Cu/Ti catalyst. The H2-TPR and NH3-TPD results indicate that adding of WO3significantly increased the number of acid sites on the surface of Cu/Ti catalyst, and promoted the adsorption of NH3. But it affected the redox performance of the catalyst and inhibited the oxidation of NH3to NO. After SO2poisoning, the N2selectivity of CuO-MO/TiO2catalyst was further improved. The characterization results shows that the increase of acid sites and the reduction of redox performance are the key factors to improve the N2selectivity.

Cu/Ti-based catalysts；NH3selective catalytic oxidation；metal oxide adding；SO2poisoning

X511

A

1000-6923(2023)10-5123-08

2023-03-17

国家自然科学基金资助项目(22176217)

* 责任作者, 教授, chz@ruc.edu.cn

陈浩辉(1999-),男,河南驻马店人,中国人民大学硕士研究生,研究方向为大气污染控制.1020878834@qq.com.

陈浩辉,王亚洲,余 杰,等.助剂添加对CuO/TiO2催化剂NH3-SCO性能的影响研究 [J]. 中国环境科学, 2023,43(10):5123-5130.

Chen H H, Wang Y Z, Yu J, et al. Effect of additives and SO2on selective catalytic oxidation of NH3over CuO/TiO2catalysts [J]. China Environmental Science, 2023,43(10):5123-5130.