0 引 言

NOx与CO作为主要的大气污染物,严重威胁人类健康与自然和谐[1]。目前,NH3-SCR技术是工业上应用最广泛的脱硝技术,使用窗口温度为300～400 ℃的V2O5-WO3/TiO2催化剂[2],但对于低温烟气,需额外烟气升温步骤,增加运行成本,因此开发低温下具有优异活性的脱硝催化剂尤为重要。CO脱除常用催化氧化法和溶液吸收法,相较溶液吸收法,通过催化剂催化氧化CO,具有无污染、效率高等特点,被视为最有前景的CO脱除技术[3]。

目前研究的低温催化剂活性组分以过渡金属为主,主要包括Mn、Co、Ce、Fe、Cu等。Mn相较于其他金属,能形成多种稳定氧化物,如MnO、MnO2、Mn2O3等,这些多价态Mn之间的电子相互迁移,价态相互转换,可明显提高 NH3-SCR低温活性和CO氧化选择性,因此被广泛关注。同时基于现阶段NH3-SCR技术存在NH3逃逸及CO处理中化学能浪费等问题,研究者聚焦2类污染物低温协同处理,既可避免NH3-SCR技术中的缺陷,又能充分利用CO催化氧化产生的热量,使其成为烟气净化领域研究的热点。

笔者基于锰基催化剂的研究现状,阐述NH3-SCR、CO催化氧化、CO-SCR三个方面,介绍了锰基催化剂的复合调控对其性能的影响及锰基催化剂负载于不同载体上的众多研究工作,重点介绍了CO-SCR技术机理及O2在CO-SCR反应中的作用机制,以期为研究提供参考。

1 锰基催化剂用于NH3-SCR脱硝技术

1.1 金属修饰对催化剂性能的影响

由于单相锰及氧化物在制备过程中易团聚烧结,使反应活性和抗水抗硫性能下降[4]。研究发现[5],金属掺杂可改变离子间结合方式,形成复合金属氧化物,从而优化催化剂构造。

单一催化剂掺杂其他金属元素后,可明显提高催化性能。SUN等[6]通过Mo改性Mn/TiO2催化剂,发现Mo可有效提高Mn/TiO2的催化性能和抗硫性能,YANG等[7]通过制备Mo-MnOx/γ-Al2O3得到了相同结论,其共同特点是掺入适量Mo后促进Mn-O化合物在催化剂表面分散,降低活性成分结晶度,增加表面酸性位点,使表面吸附氧和Mn4 富集,增强催化剂还原性能。XIONG等[8]研究锰基催化剂掺杂Cu后发现,可显著提高催化剂比表面积、Mn4 含量和酸位数量,催化剂的温度窗口向低温活性拓宽,形成铜锰氧化物,可有效减少锰离子团聚,降低硫酸锰生成,进而提高催化剂的抗硫性能。GAO等[9]对比羟基锰、钴锰和镍锰催化剂活性时发现,掺杂Co、Ni后相比单相锰催化剂,对二氧化硫抗性均有所提高,但SO2与NH3在催化剂表面形成了硫酸铵盐难以分解,导致最终均被硫酸化[10-11]。LIU等[12]发现La-Cu-Mn-O复合催化剂可进一步提高催化剂的抗硫性,La与Cu、Mn发生强烈相互作用,使Cu、Mn氧化物表面形成高比例活性离子和大量表面氧缺陷,促进NO的解离和解离氧的转移,且La还可增加Cu和Mn的分散,避免催化剂的团聚烧结,增强催化活性和抗硫性。

1.2 制备方法对催化剂性能的影响

目前,催化剂常用制备方法主要有浸渍法、共沉淀法、热分解法、热熔融法、溶胶凝胶法等。不同制备工艺对催化剂的结构、性能有较大影响。

黄海风等[13]通过对比浸渍法、沉积法和共沉淀法制备的Mn/TiO2催化剂活性,发现共沉淀法制备催化剂表现出最好的低温活性,原因在于共沉淀法制备的催化剂具有最大的孔隙结构和总酸量,利于NH3吸附,且Mn在载体表面高度分散,并与TiO2存在强相互作用。可溶性前驱体盐常用共沉淀法制备催化剂,其特点是各组分分散均匀,且活性中心分散度较好,但每个组分沉淀终点的pH不同,使沉淀终点不易掌握。YAO等[14]通过机械混合、浸渍、水热处理、共沉淀和溶胶凝胶法制备了一系列Mn-Ce催化剂,不同方法制备催化剂的活性顺序为:水热处理>溶胶凝胶>共沉淀>浸渍>机械混合,分析发现水热高温高压处理后不仅有利于催化剂活性成分分散,得到结晶良好的催化剂本体,避免焙烧过程中发生催化剂团聚现象,还可使更多的Mn掺杂到CeO2晶格,形成均匀的CeO2基固溶体(含有Mn-O结构),可明显增强Mn-Ce-O相互作用。然而,高尔豪等[15]在研究水热法、沉淀法和溶胶凝胶法制备的Mn-Cr催化剂催化活性时发现,溶胶凝胶法制备的催化剂表面Mn-Cr氧化物为较纯的尖晶石相,且其表面活性物种浓度较高,展现出最佳的脱硝性能。但其抗水抗硫性能较差,在通入SO2和H2O后,表面金属离子的硫酸盐化导致催化剂发生不可逆性失活。类似地,HUANG等[16]研究了浸渍法、共沉淀法、溶胶-凝胶法对Nd-Mn/TiO2催化剂活性的影响。发现共沉淀法和溶胶-凝胶法相比浸渍法制备的催化剂具有更大的BET表面积、更小的平均孔径、更分散的锰氧化物,从而催化活性更强。特别是溶胶凝胶法,可使各组分在分子水平上均匀混合,有利于金属间高度结合,形成共金属氧化物。但溶胶凝胶法也存在一些问题:首先是所使用的原料价格比较昂贵且部分原料对健康不利;其次,溶胶凝胶制备过程所需时间较长,不利于工业化生产。

综上可知,催化剂活性主要受催化剂表面物化性质、活性成分之间的相互作用影响。因此,通过调整催化剂制备工艺,改变表面形貌、增加表面氧空位和活性位数量、诱导增强金属离子间的协同作用,可增加其催化剂表面活性成分分散度,提升反应过程中电子相互迁移;同时,可明显提升催化剂催化性能。

1.3 载体对催化剂性能的影响

由于脱硝催化反应在催化剂表面进行,因此催化剂载体优良的表面结构直接影响催化剂脱硝性能。具有较大比表面积的催化剂载体可促使活性成分在载体表面均匀分散,并防止活性成分烧结,同时某些载体自身还存在一定催化活性,提升催化剂整体性能。

TiO2、Al2O3等金属氧化物具有丰富的孔隙,在其表面负载金属Mn后,与Mn形成强相互作用,进一步提高催化活性。JUN等[17]通过密度泛函理论(DFT)研究γ-Al2O3载体负载MnOx后的脱硝反应机理时发现,NO稳定地吸附在活性中心上并形成亚硝基或亚硝酸盐,当O2存在,NO以桥连硝酸盐的形式被吸附;NH3主要以配位形式吸附在Mn和Al原子的顶位上,γ-Al2O3载体与MnOx结合成稳定的共金属氧化物促使发生上述吸附过程。ZHENG等[18]通过试验和理论模拟相结合的方法,研究MnOx/TiO2脱硝反应机理。发现NH3在Mn的Lewis位点的吸附解离形成—NH2,NO气体自发与—NH2反应形成NH2NO,然后进一步分解为HNNOH,最后自发分解成N2和H2O。JIN等[19]进一步比较了Mn-Ce/TiO2和Mn-Ce/Al2O3,并进行低温活性测试(80～220 ℃)。发现在反应温度为80～150 ℃时,Mn-Ce/TiO2催化活性明显高于Mn-Ce/Al2O3,而反应温度高于150 ℃时,结果恰好相反,原因为TiO2载体可提供丰富的Lewis酸性位点用于NH3的吸附和还原,而在Al2O3载体表面,丰富的Brönsted酸性位点起主要作用,并推论Mn-Ce/TiO2催化剂遵循E-R机理,低温下反应可快速发生;当温度超过150 ℃时,反应主要遵循L-H机理,此时Brönsted酸性位起主要作用。

为充分发挥TiO2、Al2O3的优势,LI等[20]以Ti-Al-O复合材料载体浸渍制备的Mn-Ce催化剂,由于活性成分分散性较好,载体与活性组分相互作用强,导致催化剂表面锰和化学吸附氧的相对浓度更高、还原性更强,对NH3和NO的吸附能力更强,从而表现出更优异的催化活性和抗硫性。类似地,QU等[21]比较了以γ-Al2O3-SiO2、γ-Al2O3-TiO2和γ-Al2O3-ZrO2为载体、以Mn-Ce为活性成分的脱硝催化剂,结果表明,Mn-Ce/γ-Al2O3-ZrO2具有较大的比表面积和适宜孔径,非晶型Mn2O3高度分散、Ce4 /Ce3 比例合理,显示出优异的NO脱除效率,并减轻SO2和H2O引起的失活。

分子筛具有独特的骨架结构,表面酸性位丰富、孔容积和比表面积大,利于反应物吸附与脱除。不同的分子筛对活性影响也较大,如SAPO-n类的分子筛具有可调的变酸性和较好的热稳定性,ZSM-5分子筛具有良好的耐酸性和独特的孔隙结构。ZHAO等[22]比较了SAPO-34和ZSM-5负载Cu-Mn催化剂的结构,发现SAPO-34物理结构保持较好,其稳定性高于ZSM-5,且其Cu-Mn的离子浓度相对稳定,具有更强的氧化还原循环。进一步地,杨颖欣等[23]研究不同分子筛负载MnOx制备催化剂的催化活性,在Mn负载量15%,反应温度200 ℃时,其催化活性顺序为MnOx/SAPO-34>MnOx/SAPO-5>MnOx/SAPO-11, 如图1所示。

通过分析认为载体不同,其表面MnOx的浓度及其氧化态也明显不同,因SAPO-34具有较大的比表面积和总孔容,使负载的MnOx更多暴露在表面,Mn4 浓度和Lewis酸性位较高,与催化活性相对应。

综上,研究者通过改变活性组分、制备方法、载体等优化锰基低温NH3-SCR催化剂,并取得进展,表1总结了部分文献中锰基NH3-SCR催化剂性能。但由于各成分间相互作用较为复杂,需进一步明确其反应过程,开发性能优良的锰基脱硝催化剂。

2 锰基催化剂用于CO脱除过程

CO主要来自汽车尾气、电厂冶金焦化等行业烟气排放[35-38],近些年其排放控制被逐渐重视。目前,CO的脱除方法以催化氧化为主,金属Mn不仅低温活性优异,还存在高度选择性,成为制备CO脱除催化剂氧化行业重点研究的材料之一。

2.1 霍加拉特催化剂

霍加拉特催化剂是由CuO和MnO2两种组分制备成的颗粒状催化剂,Mn作为氧供体,Cu作为氧受体,MnOx的存在促进CuOx还原[39]。但该催化剂抗水性能较差,当湿度大于45%时,催化剂快速失效[40]。近年来,多数研究通过改性提高霍加拉特催化剂抗水性。掺杂SnO2后,催化剂颗粒内可形成大量介孔,增加活性氧空位,表面暴露更多Cu2 ,增加了CO吸附能力,显著抑制H2O分子在催化剂表面的吸附,提高了催化剂抗水性[41]。DEY等[42]发现Au掺杂后在催化剂表面引入新的活性位点,提高催化剂抗水性,增加了晶格氧的迁移运动,改善了CO氧化性能,Au负载量在0.75%时CuMnOx催化剂具有最佳的催化活性。SOLSONA等[43]得到了类似结果。

经前人不断改进,霍加拉特催化剂成分发生了很大改变,其活性和抗水性得到了显著提高,研究者通过不同的制备条件、不同的前驱体以及合适的金属掺杂优化霍加拉特催化剂,但其寿命及失活后再生未能得到根本解决[44]。因此未来研究重点应增加霍加拉特催化剂寿命及稳定性。

2.2 Mn-Ce基催化剂

研究表明[45-46]MnOx掺杂Ce后,不仅增加催化剂的活性氧数量,还可提高Mn的分散性。ZHAN等[47]采用水热法制备介孔Mn-Ce催化剂,发现该系列催化剂为高比表面积的花状微球,同时部分锰离子可掺杂到CeO2晶格。SAJED等[48]得到同样结论,进一步发现Mn/CeO2催化剂虽然比表面积较低,但催化活性最高;在此基础上,深入探究催化剂中配比与结构的关系,如图2所示,可知Mn质量分数为20%时催化剂分散度、还原性能以及活性中心浓度最佳。然而,含水条件下,催化剂易团聚,活性位点被覆盖,催化活性快速下降。针对这一问题,王献忠等[49]研究发现,通过向Mn-Ce/TiO2添加Sb,可增大比表面积,促进活性组分均匀分散,增加表面活性位点数量,提高催化剂的抗硫抗水性能。

Mn-Ce催化剂具有优异的CO催化氧化性能已被证实[50],但限制Mn-Ce催化剂应用的主要问题是抗水抗硫性能较差以及实际应用时无法达到实验室测试效果,因此还需要进一步研究催化机理,开发抗硫抗水性能较佳的催化剂。

2.3 其他锰基催化剂

除锰铜、锰铈催化剂外,过渡金属因其性能可调,也被学者们广泛研究,KUNKALEKAR等[51]制备了纳米Ag掺杂锰基催化剂,添加微量的Ag有助于CO分子吸附在催化剂表面,并增强低温催化氧化活性,同时促进H2O和CO反应生成CO2和H2,提高催化剂抗水性。进一步研究了Pd对锰基催化剂性能的影响[52],其作用机理与Ag类似,显示较高的CO氧化活性和抗水性。

此外,MI等[53]通过密度泛函理论揭示CO在Mn-Ti催化剂表面催化机理,催化剂表面形成的分子氧空位是吸附的活性中心,同时提出了4个反应循环并计算反应热,为锰钛催化剂CO催化氧化反应机理提供基础信息。ROBERTO等[54]进一步合成了纳米Au修饰的Mn/TiO2催化剂并比较其催化活性,引入Au后改善了Mn与锐钛矿型TiO2之间的作用,增加Mn3 /Mn4 对数量。同时,CO吸附和O2的活化增强促进CO催化氧化性能增强。

综上所述,锰氧化物以其性能优良、价格低廉被广泛应用于CO氧化催化剂,通过改性优化其催化氧化性能已接近贵金属催化剂,今后应重点解决催化剂抗水抗硫性能以及低温活性等问题。

3 CO脱硝技术

CO广泛存在于冶金、焦化等工业烟气,其作为还原剂脱除NOx可避免NH3-SCR脱硝技术中低温效率差、氨逃逸等问题[55-57],可在氧化过程中释放热量,节省烟气再加热成本,展现出良好应用前景。目前,文献报道CO-SCR催化剂主要分为贵金属催化剂和过渡金属催化剂[58],贵金属催化剂因其成本昂贵,难以大规模运用,因此当前研究热点主要集中在锰等廉价过渡金属催化剂。

3.1 CO脱硝反应机理

CO催化氧化NOx技术起源于汽车中的三元催化剂,文献[59]首次提出以Ir为催化剂在O2存在下CO催化NOx的可行性。大量学者开始研究廉价过渡金属,LI等[60]研究表明铜锰等廉价过渡金属有一定的催化协同效果。目前,CO脱硝催化机理未有定论,学者们较认可L-H理论[61],其反应过程如式(1)所示:

NO CO1/2N2 CO2,ΔH=-328 kJ/mol。

(1)

其反应步骤为(*为吸附态,g为气态)[61]:

① 吸附过程如式(2)、(3)所示:

CO(g)CO(*),

(2)

NO(g)NO(*)。

(3)

② 解离过程

NO(*)N(*) O(*)。

(4)

③ 表面活性物质的重组、产物分子的脱附:

2N(*)N2(*),

(5)

N(*) NO(*)N2O(g),

(6)

CO(*) O(*)CO2(g),

(7)

2NO(*)N2(g) 2O(*),

(8)

2NO(*)N2O(g) O(*)。

(9)

此外,还存在中间产物N2O的反应:

N2O(g)N2O(*),

(10)

N2O(*)N2(g) O(*)。

(11)

首先NO形成吸附态的NO(*)并解离为自由基,然后自由基结合生成CO2与N2,或与未解离的NO生成N2O(低温易产生)。SHI等[62]证明使用双金属Ni-Mn负载到MOF-74上作为低温CO脱硝反应催化剂的可行性,其在175 ℃时实现了NOx完全转化;进一步讨论Ni和Mn的协同效应,推测在Ni-Mn/MOF-74催化剂表面CO脱硝反应可能遵循L-H机理。然而,YAN等[63]通过密度泛函理论研究La-Mn催化剂催化还原机理时认为,N2O2(ads)是SCR反应的关键反应中间体,其进一步与CO(ads)反应生成CO2和N2O(ads)中间体,催化剂表面CO-SCR的反应路径包含3个步骤如式(12)～(14)所示:

2NO(*)N2O2(*),

(12)

N2O2(*) CO(*)N2O(*) CO2,

(13)

N2O(*) CO(*)N2 CO2(*)。

(14)

DING等[64]通过过渡金属原子掺杂CeO2(111)上NO-CO反应机理得到了类似结论,因反应(12)～(14)活化能垒较低,双分子机制通道在动力学和热力学上有利于N2形成,如图3(a)所示。

WU等[65]研究LaCoO3钙钛矿Co部分取代时提出反应遵循E-R催化机理,当温度低于150 ℃时,NO优先吸附并抑制CO吸附,CO与NO(*)发生反应,生成少量N2O、N2和CO2。当温度在150～350 ℃时,NO(*)发生解吸/转化/解离,形成大量N2O和N2,部分吸附态的NO、CO反应生成CO2。过量CO将Co3 和Cu2 还原为Co2 和Cu ,促进Co2 Cu2 Co3 Cu 。大量Cu 产生更多CO吸附位点,·O自由基与吸附在Cu 上的CO发生反应,形成CO2分子。当温度升至350 ℃以上,催化剂进一步将Cu 还原为Cu,产生更多Co2 、Cu和氧缺陷位点,促进N2O向N2转化以及CO和O自由基向CO2的重组,从而检测到有更多的N2和CO2,如图3(b)所示。

而ZHANG等[66]给出了双机理解释,其认为低温段符合E-R机制(气态CO与吸附的NO类物质发生反应生成CO2和N2),而高温段符合L-H反应途径(吸附的NO类物质与活性位点上吸附的CO类物质发生反应生成CO2和N2)。LIU等[67]制备的MFe2O4(M = Co、Ni、Cu)也给出相似解释,如图3(c)所示。

目前,对于CO脱硝反应机制还未统一意见,笔者认为CO NO反应在不同催化剂、不同反应条件下会存在多种反应路径,如何控制反应路径还需进一步探讨。

3.2 用于CO脱硝反应的Mn基催化剂

Mn作为常见过渡金属,掺杂到催化剂后可有效增强活性成分间的相互作用,提高催化性能。付国友等[68]通过对比Fe-Mn/ETS-10催化剂不同Fe/Mn物质的量之比的脱硝效率时发现,5% Fe-1% Mn/ETS-10催化剂具有最佳的脱硝活性,原因在于Fe与Mn的协同作用,促进Fe3 Mn3 ←→Fe2 Mn4 氧化还原平衡反应。SHI等[69]以KMn8O16/CuFe2O4为前驱体合成由γ-Fe2O3、CuFe2O4、CuO三种物质构成的脱硝催化剂,分析发现Mn可以多种离子形式高度分散在3种物质之间,并与Fe形成强相互作用,同时,Mn4 促使在催化剂三相界面形成更多的活性氧,促进NO解离和O2转移。另有研究发现,铜、锰的混合可促进电子转移和反应的氧化还原平衡,可有效降低温度窗口,刘凯杰等[55]比较铜锰和铜钴催化剂,在相同反应温度下,铜锰催化剂活性更高,原因在于铜锰催化剂活性位上的Mn主要以Mn3O4为主,而Mn3O4更易与Cu协同,从而提高催化剂低温活性。DENG等[70]将Mn掺杂CeO2/CuO(CuO=12%)催化剂后,也得到类似结论,掺杂Mn有利于CuO的分散,提高催化活性和热稳定性;特别是当CuO/Ce∶Mn=10∶1(物质的量之比)时,催化剂比表面积最大,结构最均匀,晶格膨胀最大,更有利于吸附在催化剂表面NO的解离、转化和解吸。LIU等[71]发现掺杂镧到铜锰催化剂后,减小了铜锰颗粒的尺寸,明显改善催化剂团聚现象,增强了Cu2 、Mn3 含量,丰富了表面氧缺陷,促进了NO解离和解离氧的转移,增强了催化剂催化性能,使NO在250 ℃左右即可实现完全转化。孔令朋等[72]通过分析CuMnCeLa-O/γ-Al2O3催化剂性能也得到类似结论。MATTHIAS等[73]进一步尝试将贵金属(Pd、Pt、Ru、Rh)引入La(Cu0.7Mn0.3)O3催化剂中,所有贵金属 (Pd、Pt、Ru、Rh)掺杂后相比原始钙钛矿均表现出更高催化活性,尤其是掺杂Pd后显示出H2还原的最高活性和最低起始温度(70 ℃)。贵金属能高度分散在钙钛矿表面,改善了氧空位活性并提供了新的NO吸附位点。

3.3 O2在CO-SCR中的作用机制

氧气广泛存在于各种工业烟气中,其浓度比NOx高几个数量级,且氧化性更强。早期研究发现高浓度氧存在时,会抑制CO还原NOx,当O2体积分数小于0.1%时,CO-SCR反应才能发生[74]。HE等[75]所制备的MCe0.75Zr0.25Oy (M = Cu、Mn、Fe)也表现出相同结果,只有O2被过量CO消耗完全,才能进行CO NO反应,如图4所示。

随研究者不断努力,在O2氛围下可进行CO催化还原NO的催化剂逐渐被开发。TANG等[76]通过DFT研究Fe掺杂双空位石墨烯的NO CO反应,发现O2/NO或O2/CO分子的共吸附比单一NO或CO更稳定,表明O2的存在促进反应物稳定。GHOLAMI等[77]研究了一系列的M@La-Fe/AC (M = Mn, Ce)催化剂,由于O2的存在可促进碳(氧)络合物生成,并改善金属部位活化,使Mn@La3-Fe1/AC催化剂在400 ℃加入10%氧气后,NO转化率由92.7%增至93.8%。同时,研究发现O2是锰基CO-SCR反应的必须中间产物,可促进反应进行。BONINGARI等[78]在O2过量的条件下评价了Mn/TiO2催化剂,并利用同位素标记法揭示O2参与反应的方式。质谱仪检测同位素信号显示,当18O2通过催化剂时,交叉标记(16O2—18O2)的浓度随时间而增加,这意味着过量的气相氧会填充催化剂表面的氧空位,且在NO存在下,CO与O2的反应被抑制,直接证明Mn/TiO2具有优异的活性和选择性。杨智程[79]制备了5Ni/MnOx(400)催化剂,在200 ℃反应温度下,NO的脱除率随氧气的增加而提高,当O2体积分数高于6%时,NO转化率接近100%,并达到稳定,证实了O2促进了CO-SCR反应。

对于O2氛围下的高效CO脱硝催化剂,目前数量较少,且效率不高。通过金属掺杂、优化制备方法等提高催化剂的选择性,使其优先发生CO NO反应仍是未来几年的研究重点。

4 结语与展望

燃煤电厂、工业炉窑以及发动机烟气含有大量的大气污染物,催化反应技术是有效限制并消除NOx及CO等污染物的主要技术之一,对建设环境友好型社会、推动我国节能减排事业具有重要意义。Mn及其氧化物因其多变的化学价态和高度选择性深受青睐。目前,锰基催化剂在NH3-SCR技术、CO氧化、CO脱硝技术以及VOCs降解方面均表现出优异性能,并已在催化剂活性相类型、载体种类、制备方法、催化机理等方面取得一定进展,其催化剂抗中毒能力和寿命也得以提高,但仍存在一些问题有待探索,未来锰基催化剂的研究发展方向应考虑以下几个方面:

1)通过引入金属,探索适宜负载量、活性相比例和制备方法,改善催化剂表面的酸量、酸强,提高活性成分分散性,通过更先进、更全面的表征手段研究其相互作用机理。

2)从催化剂的抑制机理出发,针对性地提高失活物质的抗性,并寻求其失活再生方案,提高催化剂的使用寿命。

3)锰基催化剂目前大多数停留于试验验证阶段,多为颗粒状进行测试,未来可从成型角度考虑,在仿照现有成熟技术的基础上进一步优化催化剂结构,以期取得更好的成型效果,实现工业应用。

4)着重发展CO-SCR技术,从微观层面解释催化剂的电子结构和反应机制间的关系,结合计算模拟更深入了解反应过程。

5)随工业烟气排放条件愈加严苛,同时处理多种污染物的多功能锰基催化剂,如脱硝、除一氧化碳、除挥发性有机污染物,将成为日后催化剂发展的重点。

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Review of manganese based catalysts for catalytic removal of NOx and CO at low temperature

XUAN Chengbo1,2,ZHANG Xingyu1,2,WANG Luyuan1,2,ZHAO Tiantian1,2,HAN Shiwang1,2,CHEN Zhengxin1,2,LIU Qianqian1,2,WANG Xuetao3

(1.School of Energy and Power Engineering,Qilu University of Technology,Jinan 250014,China;2.Energy Research Institute of Shandong Academy of Sciences,Shandong Academy of Sciences,Jinan 250353,China;3.Transportation Engineering School,Henan University of Science Technology,Luoyang 471003, China)

Abstract：NOx and CO are the key pollutants to be treated. With the further improvement of flue gas emission standards such as steel sintering, the traditional NH3-SCR (NH3 selective catalytic reduction of NOx) denitration technology has significant shortcomings, especially the sintering flue gas emission temperature is lower than the window temperature of vanadium based catalysts, causing that the activity of vanadium based denitration catalyst is insufficient and the generated ammonium sulfide blocks the catalyst surface, but there is still a lack of effective means for CO control. Therefore, the development of low-temperature catalyst has become the key factor for removing NOx and CO from low-temperature flue gas. The progress of Mn based catalyst in removing NOx and CO was discussed, the effects of active components, preparation methods and supports on the catalytic activity of Mn based low-temperature catalyst were compared, and the effects of Cu、Ce and other metals on the modification of Mn based catalyst were introduced in detail, and the relationship between element doping and catalytic performance was analyzed. On this basis, the latest research results of no reduction technology by CO in recent years were systematically combed and summarized, and the reaction mechanism and the action mechanism of O2 in the reaction were emphatically discussed. The results show that the rich extranuclear electron arrangement of Mn element is the fundamental reason for its excellent activity in removing NOx and CO, but most of the current research results are only in the laboratory theoretical stage and lack of large-scale verification in the actual flue gas. Finally, the future development direction of Mn based catalyst was prospected, and the catalyst deactivation mechanism and the scheme to improve the anti poisoning of catalyst were put forward.

Key words：manganese catalyst;low temperature SCR;carbon monoxide oxidation;CO-NO

中图分类号：X511

文献标志码：A

文章编号：1006-6772(2023)03-0122-11

收稿日期：2021-09-15;

责任编辑:张 鑫

DOI：10.13226/j.issn.1006-6772.21091501

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基金项目：国家自然科学基金资助项目(201900130);山东省自然科学基金资助项目(ZR2021QE066;ZR2019BEE053)

作者简介：玄承博(1996—),男,山东潍坊人,硕士研究生。E-mail:15512777092@163.com

通讯作者:王鲁元(1988—),男,山东德州人,助理研究员,硕士生导师,博士。E-mail:luyuanwang1988@126.com

引用格式：玄承博, 张兴宇, 王鲁元,等.锰基催化剂低温催化脱除NOx及CO研究进展[J].洁净煤技术,2023,29(3):122-132.

XUAN Chengbo,ZHANG Xingyu,WANG Luyuan,et al.Review of manganese based catalysts for catalytic removal of NOx and CO at low temperature[J].Clean Coal Technology,2023,29(3):122-132.