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刘璐, 张强, 郭丽丽. CO为还原剂的脱硝催化剂研究进展[J]. 工业催化, 2017,25(12): 1-9.
Liu Lu, Zhang Qiang, Guo Lili. Research progress of denitrification catalysts with CO as reducing agent[J]. Industrial Catalysis, 2017,25(12): 1-9.  
DOI:10.3969/j.issn.1008-1143.2017.12.001
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CO为还原剂的脱硝催化剂研究进展
刘璐, 张强*, 郭丽丽
中国石油大学(华东),山东 青岛 266580
通讯联系人:张强,副教授,研究方向为石油与天然气加工。

作者简介:刘璐,1992年生,女,黑龙江省齐齐哈尔市人,在读硕士研究生,研究方向为石油与天然气加工。

收稿日期: 2017-06-20
基金资助: 国家自然基金青年科学基金项目(21406270)
摘要

从活性组分、助剂和载体方面综述贵金属催化剂(Ir、Pd、Rh、Ru、Ag)及非贵金属催化剂的研究进展。比较不同催化剂脱硝活性,表明贵金属催化剂及部分非贵金属催化剂均具有一定的脱硝活性。对于贵金属催化剂,中低温活性较高,但热稳定性差,易烧结,且不经济。对于非贵金属催化剂,高温活性较高,稳定性较强。助剂的引入及载体性质对催化剂脱硝活性均有不同程度的影响。

关键词: 催化剂工程; 贵金属; 非贵金属; 脱硝催化剂; 助剂
中图分类号:TQ426.6;X701    文献标志码:A    文章编号:1008-1143(2017)12-0001-09
Research progress of denitrification catalysts with CO as reducing agent
Liu Lu, Zhang Qiang*, Guo Lili
China University of Petroleum,Qingdao 266580,Shandong,China
Abstract

Active species,additives and supporters of noble metal(iridium,palladium,rhodium,ruthenium,silver) and other non-noble metal denitrification catalysts are reviewed.It is found that noble metal catalysts and some non-noble metal catalysts all have denitrification activity.Compare with non-noble metal catalysts,noble metal catalysts have high catalytic activity at medium and low temperature.However,noble metal catalysts easily to be sintered have poor thermal stability,and it is expensive.Non-noble metal catalysts have high catalytic activity and stability at high temperature.At the same time,the introduction of additives and the nature of supporters have different effects on the denitration activity of the catalyst.

Keyword: catalyst engineering; noble metal; non-noble metal; denitration catalysts; additives

近年来, 随着工业发展, 工业废气的排放对环境影响很大, 其中, 氮氧化物是主要污染物。NO是无色无味气体, 难溶于水, 有毒, 易与氧气反应生成NO2。NOx主要为燃煤发电厂和己二酸(尼龙单体)制造厂等固定源及汽车、火车等移动源排放的废气[1]。主要采用氧化、分解、还原和络合等方法脱硝[2]。在NO催化还原中NH3和H2是有效还原剂, 但考虑投资成本、高操作费用及资源减少等问题, CO作为还原剂逐渐受到关注。CO是大气污染物及FCC烟气主要成分, 在反应过程中, 利用CO催化还原NO受到很多限制[3]。

本文从活性组分、助剂和载体方面综述贵金属催化剂(Ir、Pd、Rh、Ru、Ag)及非贵金属催化剂的研究进展。

1 贵金属催化剂

贵金属颗粒表面易吸附反应物, 强度适中, 利于形成中间“ 活性化合物” , 具有较高的催化活性, 是重要的催化剂材料。工业上用于催化转化的贵金属包括昂贵的Pt和Rh, 现在多用Pd和Ru代替。但贵金属催化剂抗烧结能力较差, 常用于中低温脱硝[4, 5]。

1.1 Pd

Pd催化剂是常见的脱硝催化剂[6, 7, 8, 9], 最早用于汽车尾气净化。利用单金属Pd在不同实验条件下研究Pd催化剂脱硝活性。Martinez-Arias A等[10]分析Pd/Al2O3催化剂在CO-O2[V(CO): V(O2)=1: 0.5]和CO-O2-NO[V(CO): V(O2): V(NO)=1: 0.45: 0.1]反应中的活性。研究表明, NO的存在导致CO-O2反应向高温移动, 由质量分数1%、0.5%和0.05%的Pd/Al2O3催化剂上CO转化率温度T20=82 K、23 K、46 K和T50=34 K、22 K、25 K可知, NO的存在对1%Pd/Al2O3催化剂影响最大, 在1%Pd/Al2O3催化剂表面, NO与CO反应优于O2与CO反应。XANES结果证实, 实验过程中催化剂由无活性PdO状态转化到有活性Pd状态, 同时, NO还原反应受CO吸附以及活性中心种类与数目的限制; 增加Pd负载量后, 金属Pd颗粒的相对大小有所改变, 且NO还原活性随着颗粒大小的增加而增加。从DRIFTS发现, 催化剂主要区别在于Pd羰基的存在, 这些羰基的形成主要是由于NO在Pd样品上的吸附, 因而产生Pdn+的化学吸附位, 在1%Pd/Al2O3催化剂上温度低至303 K时NO也可以吸附, 表现出较高活性。

1.2 Rh

通常金属Rh不会被氧化, 抗氧能力较强, 常用于富氧条件下的脱硝反应。研究金属Rh在脱硝反应中的活性及其抗氧特性[11, 12], Ravichandra S Mulukutla等[13]采用不同水热合成条件制备出Rh氧化物颗粒大小、结构及在MCM-41上分布位置不同的催化剂。在催化剂Rh-MCM-41-B(< 3 nm, 位于MCM-41孔道)上, 反应温度小于300 K时, 催化剂无活性(NO体积分数1.25%, CO体积分数1.25%), O2的加入对NO+CO反应有促进作用, 过量O2使NO转化率从0升至20%(NO体积分数1.25%, CO体积分数1.25%, O2体积分数3%)。而在Rh-MCM-41-A[(6~8) nm, 位于MCM-41表面]上, O2则表现出抑制作用。这可能与纳米尺度的Rh氧化物前驱体的分布位置有关, 表明Rh氧化物在MCM-41上的位置很重要。Paulo Araya等[14]研究表明, 在Rh/SiO2上低温反应形成N2O, 吸附的NO物种以NO— 存在。虽然Rh基催化剂在富氧条件下的脱硝反应中表现出相对其他催化剂高的活性, 但NO转化率较低。

1.3 Ir

You-Jung Song等[15, 16, 17]发现Ir的脱硝活性及在CO+NO和CO+O2中的竞争作用。在1 000× 10-6NO、6 000× 10-6CO、体积分数5%O2、体积分数6%H2O和He稀释气条件下, 评价负载质量分数5%的Pt/SiO2、Rh/SiO2、Pd/SiO2和Ir/SiO2催化剂的脱硝活性[18, 19], 评价前在10%H2-6%H2O/He(873 K)条件下预处理1 h, 结果发现均无活性。引入20× 10-6SO2, Pt/SiO2、Rh/SiO2和Pd/SiO2仍无脱硝活性, Ir/SiO2则表现出不同的催化活性, NO转化率达68%, 由此表明, 在O2和SO2同时存在下, Ir是惟一的高活性贵金属。但O2体积分数不能超过10%, 过多O2会降低NO转化率, 可能是因为多数Ir0被氧化成IrO2。比较Ir/SiO2和Ir/Al2O3的脱硝活性, 不通SO2时, Ir/Al2O3的脱硝活性较低; 通入SO2后, NO转化率最高可达16.9%。通过TEM分析得出, Ir以(10~20)nm颗粒大小分散于SiO2上, 在Al2O3上则是(2~3)nm的团聚物, 猜测是晶粒大小导致的活性差别。Masaaki Haneda等[20]讨论了Ir分散度对催化剂脱硝活性的影响, 通过改变焙烧温度控制Ir分散度, 在673 K还原后的催化剂上Ir分散度最高, 为86%, 此时NO最高转化率约4%。随着焙烧温度增加, Ir分散度逐渐下降, 但NO转化率增加。Ir分散度6.0%时, NO转化率可达40%。由TOF结果可知, 大晶体可以表现出高活性, Ir氧化态依赖晶体大小。由FT-IR结果可知, 在Ir分散度13%的Ir/SiO2催化剂上, 在2 073 cm-1处出现Ir0-CO峰, 表明在O2和SO2存在下, 大Ir晶体表面是稳定金属态, 即大晶体不容易被氧化, 容易被还原。

1.4 其他

Ru基催化剂在各种工业催化反应以及环境处理中受到关注。Goslar J等[21]采用浸渍法制备了Ru/MgF2催化剂, 利用FT-IR研究常温下Ru/MgF2催化剂上探针分子吸附, 结果表明, 通入NO和CO后, 产生Ru-CO2和Ru-N的CO吸附峰, 表明发生了NO+CO→ NCO+O反应。通过比较NO和CO预先处理的催化剂发现, 由于Ru-NO(CO)物种的存在, Ru-NO的吸附峰从1 893 cm-1迁移至1 850 cm-1。Guglielminotti E等[22]研究Ru/ZrO2催化剂时发现, 将催化剂预吸附CO后, NO在室温下即可快速分解生成N2O和CO2。Archana Patel等[23]在MCM-41上负载不同金属, 结果表明, 在低温下催化剂活性顺序为:Ru-MCM-41> Co-MCM-41> Ni-MCM-41≈ Fe-MCM-41≈ Cu-MCM-41, 高于650 K, Ru-MCM-41活性好, NO转化率可达100%。

Ag催化剂常用于催化氧化反应。Zhang Hongyan等[24]采用金属盐高温焙烧法、沉淀法和均匀沉淀法制备CeO2(1)、CeO2(2)和CeO2(3), 并制备Ag/CeO2和Ag-Co/CeO2催化剂, 研究表明, 在V(NO): V(CO): V(O2)=0.25: 1.25: 0.5条件下, Ag/CeO2(3)表现出相对高的催化活性, 623 K时, NO转化率为100%, 比Ag/CeO2(1)和Ag/CeO2(2)高41%。评价了Ag-Co/CeO2(3)催化剂的NO+CO和NO+CO+O2催化活性, 发现O2的存在降低了低温活性, NO转化率从98%降至68%, 但573 K时, NO转化率达100%。在稳定性评价中, Ag-Co/CeO2催化剂50 h不失活。Iliopoulou E F等[25]在Ag/Al2O3催化剂上, 比较C3H6、CH4和CO作为还原剂的脱硝活性, 发现CO作为还原剂时, NO几乎无活性, 但由于评价条件不同, 目前实验室在FCC再生环境中表现出高活性。

2 非贵金属催化剂

由于贵金属催化剂价格昂贵, 寻找非贵金属催化剂代替, 包括Cu、Fe、Ce和Co等催化剂[26, 27, 28]。在非贵金属催化剂中研究最多的是Cu基催化剂。任丽萍等[29]评价Cu/Al2O3在NO+CO中的活性, 温度513 K时, NO可以完全转化。研究CO含量时发现, CO含量过高会打破Cu2+=Cu0间的平衡, 催化剂迅速失活。Martinez-Arias A等[30]制备CuC(CuO/CeO2)催化剂, 研究NO对CO-O2反应的促进作用。结果表明, 从催化剂上CO-O2和CO-O2-NO反应的DRIFTS结果可以看出, 形成的Cu+羰基键有所不同, 在CO-O2反应中, 313 K出现键强度的最大值; 而在CO-O2-NO反应中, 在303 K和353 K处出现最大值, 第二个高强度Cu+羰基键与CO氧化和NO从亚硝酸基上脱附有关。因此, 在NO存在条件下产生更多Cu+, 即产生更多的表面活性位, 促进CO-O2反应。Gu Xianrui等[31]对CuO/CeO2催化剂进行CO预处理, 降低铜价态, 促进CO以及NO转化。Mohamed Kacimi等[32]采用阳离子交换方法制备Cu/AlPO4催化剂, 在V(CO): V(NO): V(O2)=1.5: 0.2: 0.65条件下评价。通过比较Cu/AlPO4、2.5Cu/AlPO4和5Cu/AlPO4发现, 低负载量催化剂上Cu2+与载体相互作用更强, 需在高温下才能还原, 而5Cu/AlPO4催化剂在TPR中的还原峰处于低温; 在化学计量组成条件下评价, 5Cu/AlPO4催化剂活性最高, NO在473 K时开始转化, 673 K时NO转化率达85%。在体积分数5%H2预处理后, 5Cu/AlPO4催化剂在523 K时NO转化率达50%, 相比未预处理催化剂多40%。薛君等[33]对SBA-15分子筛改性, 引入Cu、Fe和Cr金属, 催化活性顺序为:Cr/SBA-15> Cu/SBA-15> Fe/SBA-15。

贵金属以及稀土金属催化剂虽然具有较高的脱硝效率, 但价格昂贵, 使用过程中易“ 中毒” 。Fe基催化剂作为既廉价又高效的烟气脱硝催化剂应用前景广阔。Li Jun等[34]采用沉淀法制备Fe基催化剂, 研究发现, Fe质量分数为3%时, NO含量迅速降为0。与此同时, 高Fe含量的催化剂促进CO+O2和CO+NO反应, 高含量Fe提供了更多活性位, 从而消耗更多O2。V(O2): V(CO)> 0.4时, NO转化率迅速降为0, 表明过量O2对NO还原有抑制作用。苏亚欣等[35]对Fe及其化合物的脱硝作用进行研究, 采用不同尺寸的铁丝网对NO进行还原, 反应温度> 1 173 K时, 脱硝率达99%。引入O2和CO后, 1 173 K时脱硝率降为90%。由XRD结果可知, 反应后Fe网中含有少量FeO。对于Fe基催化剂面临的问题, 包括Fe在反应过程中的相态以及O2的解析步骤, 研究NO、CO和O2在Fe基催化剂表面的化学吸附尤为重要。

3 助 剂

对于单金属催化剂存在反应温度窗口窄、富氧活性较差和抗SO2中毒能力差等问题, 在单金属催化剂上引入不同助剂Co、Ce和La等, 以提高脱硝活性。

Tanikawa K等[36]制备Pd/Al2O3和Pd-Ba/Al2O3催化剂, 研究Ba的添加对Pd/Al2O3催化剂CO氧化和NO还原活性的影响。在体积分数2.2%CO+0.2%NO+1.0%O2下进行评价, 结果表明, 添加Ba后, CO和NO起始转化温度均从493 K分别降至452 K和458 K, 由此可见, Ba的添加促进了CO-O2反应, 且反应温度> 473 K时, 抑制N2O生成。在Pd/Al2O3催化剂上分别负载质量分数5%和15%的Ba, 结果发现, NO转化率为50%时的温度分别为459 K和458 K, 表明负载质量分数5%的Ba就可以达到最佳负载量。Miller D D等[37]研究Ag对Ba基催化剂的改性, 制备了质量分数5%Pd/Al2O3和5%Ag-Pd/Al2O3催化剂。将1 cm3的O2脉冲通入NO/CO/He中, 由IR得知, 在5%Pd/Al2O3催化剂上检测到Pd+-NO吸附峰, 但O2的加入使Pd+-NO吸附峰减少, 并形成了NO2, 由此推测发生了Pd+→ NO+Pd-O→ Pd+Pd++NO2。通入O2后, NO转化率增加了10%~18%, 生成了NO2, 表明吸附的氧不会占据NO吸附所需的Pd活性位。Ag加入后出现了Pd0-NO的峰, 由此猜测, Pd表面还原态的Ag受到破坏, 并且Ag的存在维持Pd的还原状态。由IR和MS结果得出, Ag的加入进一步促进NO氧化生成NO2, 减缓CO氧化, Ag被认为是NO氧化活性最高的活性位[38]。Sergiy O Soloviev等[39]在Al2O3· 2MgO· 5SiO2上负载金属Pd和Co, 并在体积分数0.2%CO+0.2%NO条件下对催化剂进行活性评价, 结果表明, 473 K时NO即可完全转化, Pd与Co3O4间的相互作用促进了催化剂活性。引入CeO2后形成大量氧空位, 催化活性得到进一步提高, 423 K时NO即可完全转化。Li Yile等[40]研究CeO2和La2O3对Pd基催化剂在脱硝反应中的影响, 制备了Pd-Ce-La/Al2O3催化剂, 由CO化学吸附发现, 加入CeO2或La2O3或其混合物促进了Pd分散, 其中, Pd-Ce-La/Al2O3的分散度最高。由NO-TPD结果得出, CeO2或La2O3的添加促进了NO在Pd基催化剂上的吸附, 提高了催化剂脱硝活性。Joseph H Holles等[41]发现, Pd-Ce/Al2O3比Rh-Ce/Al2O3活性高, 此外, Ce和La等金属的引入影响Rh和Pd的动力学参数。Takashi Hirano等[42]在Pd/SiO2上引入In、Pb和Ce, 在V(NO): V(CO)=1: 1条件下, 发现NO起始转化温度降低了200 K。在Pd-In/SiO2和Pd-Pb/SiO2上促进形成N2O, 而Ce的添加促进了金属间的相互作用。从而促进NO转化。Julia Marí a Dí az Có nsul等[43]在1 560× 10-6NO和1 450× 10-6CO条件下, 对Pd-Mo催化剂进行评价, 发现Mo的引入使NO转化率降低约10%, 但由于Pd-Mo的相互作用促进Pd在NO+CO中的活性, 提高了N2选择性[44]。Tou A等[45]研究发现, Pd/LaMnO3/Al2O3在NO+CO中表现出较高活性, 573 K时NO转化率达90%, 表明Pd和LaMnO3的相互作用促进了催化剂活性。Chen Hui 等[46]制备了以镁铝尖晶石为载体的Pd-K/MgAlO催化剂, 催化剂脱硝活性顺序为:Pd-K/MgAlO> Pd/MgAlO> K/MgAlO, 在尖晶石上引入Pd和K后, 773 K时NOx转化率可达70%。

Abri De Sarkar等[47]采用Pt对铑基催化剂进行改性, 发现O2的加入抑制Rh基催化剂上NO还原活性, 一般认为O2消耗了大量CO, 但Chinnakonda S Gopinath等[48]发现, O2的添加使CO中毒。Dimitris I Kondarides等[49]在质量分数0.5%Rh/TiO2催化剂上进行脱硝实验, 发现O2的加入很大程度上抑制NO还原, 转化率降低70%。由于富氧条件下催化剂脱硝活性降低, Salker A V等[50]制备了Rh掺杂Co2O3的催化剂, 并在体积分数5%NO+5%CO条件下进行活性评价, 金属掺杂促进了催化剂的吸附能力, 提高了催化剂活性, NO转化率相比在Co3O4上增加了60%。但是在引入体积分数5%O2后, NO转化率相比无O2条件减少10%, Federico J Williams等[51]在研究中也发现了类似现象, 认为是O2将NO氧化成NO2, 使NOx反应更难进行。王玉云等[52]制备了含有Co和Ni的Pd-Rh三效催化剂, 在体积分数0.7%CO+0.1%C3H8+0.1%NO+0.8%O2条件下评价, 结果表明, Pd-Rh-1.0%Co3O4-2.0%NiO催化剂的脱硝活性最高, 673 K时NO可以完全转化。

负载单金属Ir的催化剂抗SO2中毒能力较差, 且分散度不高。为了促进Ir基催化剂活性, 对Ir基催化剂进行改性。Tsukasa Tamai等[53]比较Ir/SiO2、Ir/Nb2O3、Ir/Nb2O5/SiO2和Nb2O5/Ir/SiO2催化剂催化活性。结果表明, 活性组分负载顺序影响脱硝活性, 其活性顺序为:Ir/SiO2< Ir/Nb2O3< Ir/Nb2O5/SiO2< Nb2O5/Ir/SiO2, Ir/10Nb2O5/SiO2催化剂上NO最高转化率约30%, 而10Nb2O5/Ir/SiO2催化剂上NO转化率最高为80%。XRD结果表明, Ir/10Nb2O5/SiO2还原后未发现Nb2O5, 表明Nb2O5高度分散, 而10Nb2O5/Ir/SiO2上则发现Nb2O5, 并且由于Nb2O5与Ir相互作用, Nb2O5的添加使Ir难氧化, 从而促进催化剂活性。Masaaki Haneda等[54]通过引入不同金属对Ir/SiO2催化剂改性, 研究表明, 碱土金属对Ir/SiO2催化剂活性有促进作用。n(Ba): n(Ir)=1: 10时, NO最高转化率约65%。由此得出, Ir0活性位的稳定性是影响催化剂活性的关键。XRD结果表明, Ba可以抑制Ir在反应过程中被氧化成IrO2, 与TPO结果一致。

楼莉萍等[55]研究了CuO/TiO2和CuO/CeO2-TiO2在V(NO): V(CO)=1: 1条件下的催化活性, 结果表明, CuO质量分数12.0%时, CuO/TiO2活性最高。引入CeO2后, 催化剂活性进一步提高, CuO质量分数≤ 3.0%时, CeO2的引入对活性影响更大, 在3Cu-5Ce/TiO2上NO转化率为72%, 在3Cu-10Ce/TiO2上NO转化率为95%。Lu Guanzhong等[56]比较了不同单组分以及双金属的脱硝活性, 研究发现, CuO的催化活性最高, 引入一定量Mn后, 催化剂活性进一步提高。而Ce的添加促进了2NO+CO→ N2O+CO2。Yao Xiaojiang等[57]在CuO/CeO2中引入MnO2, 发现MnO2负载量低于0.4 mmol-Mn4+· (100 m2CeO2)-1时, 催化剂活性增加, 但负载量过多, 活性降低, Cu+/Cu0起关键性作用[58]。Wan Haiqin等[59]在体积分数5%NO+10%CO+85%He条件下比较了Mn/Al和Cu/Mn-Al的活性, 研究发现, 在Mn/Al上, NO转化率均低于10%, 随着氧化锰负载量增加, N2选择性在523 K时增加了约45%, 温度对其影响可以忽略。但在Cu/Mn-Al上, 随着温度增加, NO增加。由此可见, 氧化锰促进了CuO还原能力, 并增强了CO吸附能力。发生了Cu2++Mn3+⇌Cu++Mn4+, 在Cu/Mn-Al上形成Cu+。

Ce有较高的储放氧能力, 为了促进Cu基催化剂的低温活性以及富氧条件下的脱硝活性, 在Cu基催化剂中引入Ce。Wen Bin等[60]通过比较Cu/Mg/Al/O(Cu-cat)、Ce/Mg/Al/O(Ce-cat)和Cu/Ce/Mg/Al/O(CuCe-cat)的脱硝活性发现, 不通O2时(600× 10-6NO, CO体积分数1.4%), 在低温区域(T< 573 K), CuCe-cat上NO转化率比Cu-cat约高20%, Ce-cat活性最差。通入O2后(600× 10-6NO, CO体积分数1.4%, O2体积分数0.5%), CuCe-cat上NO转化率增加10%, 而Cu-cat和Ce-cat活性均降低。通过IR分析发现, 通入O2后CO所吸附的Cu+波段减少, 但NO吸附的Cu2+波段增加, 由此可见, O2的引入增强了NO吸附能力。与此同时, H2O的加入使NO转化率增加了13%(T=573 K), SO2对NO转化率几乎无影响。XPS结果发现[61], 在焙烧过程中, 一些Ce4+被Cu+替代, 产生大量Cu+和氧空位, 促进NO和CO吸附。由此可见, Mn和Ce对于转变Cu在脱硝反应中的价态有重要作用。Yu Qiang等[62]研究ZrO2在CuO/Al2O3上的添加方法对NO+CO的影响, 结果表明, ZrO2的添加促进高分散的CuO与不定型ZrO2的相互作用。共沉淀-浸渍法促进了CuO分散以及表面ZrO2含量, 促进催化剂活性, 623 K时NO几乎完全转化。

4 载 体

Martinez-Arias A等[63]在CexZr1-xO2和Al2O3混合载体上负载Pd, 在V(NO): V(CO): V(O2)=0.1: 1: 0.45条件下, 分别采用质量分数33%和10%的CexZr1-xO2制备催化剂, 随着CexZr1-xO2含量增加, 催化剂活性增加, T< 475 K时, NO转化率增加约10%; T> 543 K时, 33%CexZr1-xO2催化剂上无N2O生成, 而在低CexZr1-xO2含量的催化剂上则或多或少有N2O生成。Chen L F等[64]制备了质量分数3%Pd/Ce0.6Zr0.4O2催化剂, 并在685× 10-6CO+230× 10-6NO+10.5%O2条件下对催化剂进行活性评价, 结果表明, 温度低于423 K时, N2选择性为100%; 大于473 K时, 有NO2生成。认为温度低于473 K时, NO抑制了CO-O2反应, 从而促进NO-CO反应; 大于473 K时, 则促进了CO-O2反应。Di Monte R等[65]发现Ce0.6Zr0.4O2添加在Pd/Al2O3上影响催化剂性质, 并影响Pd稳定的氧化状态。Konsolakis M等[66]将Pd负载在氧化钇和稳定的氧化锆上, 并对其进行碱改性, 发现碱化催化剂增加了N2选择性, 促进了反应物的吸附强度。

Tadao Nakatsuji等[67]通过改变载体性质增加脱硝活性, 制备了不同载体负载的Rh基催化剂, 在500× 10-6NOx(480× 10-6NO和20× 10-6NO2)、5 000× 10-6H2、体积分数9%O2、10%CO2、1.5%CO和6%H2O条件下, 对催化剂进行评价。研究发现, 以H-β 分子筛为载体, 负载质量分数2%Rh时活性最高。在分子筛中加入Na, 含SO2条件下, 质量分数1%Rh/Na-β 催化剂上NOx转化率相比无SO2存在增加。Feng-Yim Chang等[68]研究表明, SO2会使Rh/Al2O3催化剂中毒。认为Na的加入抑制了SOx的中毒效应, 从而增强NOx还原。溶胶-凝胶法制备的Al2O3-ZrO2强度高, 氧化环境中稳定性好[69, 70], Castillo S等[71]制备了Rh/Al2O3-ZrO2催化剂, 在体积分数1.5%CO+0.5%NO+1.5%O2条件下进行活性评价, 比较有无O2条件下的脱硝活性时发现, NO转化率几乎不变, 约为5%, 但是产物中N2选择性降低了7%。

Iliopoulou E F等[72]在体积分数1%CO+1 000× 10-6NO+(0~1%)O2条件下, 对Ir/CPBase- Al2O3催化剂进行活性评价。研究发现, 随着Ir负载量增加, 脱除NOx活性降低, CO-O2反应能力增加。在改变负载量的同时, 晶粒增大。TPR结果表明, Ir的添加使催化剂在低温消耗大量H2。Ir/CPBase-Al2O3的还原温度为535 K, 而Ir负载在尖晶石或高岭土上的还原温度为643 K和613 K。由此可见, 载体影响Ir的还原能力。

Archana Patel等[73]分别采用SBA-15、MCM-41、MCM-48和KIT-6为载体制备Cu基催化剂, 研究表明, CuO负载在MCM-41和SBA-15上表现出更高的催化活性。H2-TPD结果表明, 在SBA-15和MCM-41上存在大量还原态Cu, 从而促进NO转化率。Liu Lianjun等[74]研究CuO/CexZ r1-xO2催化活性时发现, Ce含量多时有助于促进Cu与Ce的协同作用, 促进Cu物种的还原以及NO转化率, NO转化率最高增加45%。

5 结 语

对于脱硝反应, 非贵金属催化剂相比贵金属(Pd、Rh、Ir、Ru、Ag等)催化剂表现出更高的活性与优势, 贵金属资源稀少, 价格昂贵, 高温易烧结。引入助剂后, 促进了活性组分分散, 影响活性价态变化, 从而影响脱硝活性。载体性质影响其与活性组分间的相互作用。应根据不同组分和载体性质找到更合适的催化剂体系, 并实施应用。

The authors have declared that no competing interests exist.

参考文献
[1] 杜琰, 谢鲜梅, 王志忠. 氮氧化物NOx的催化消除[J]. 太原理工大学学报, 2003, 34(5): 535-539.
Du Yan, Xie Xianmei, Wang Zhizhong. Catalytic removal of nitrogen oxides[J]. Journal of Taiyuan University of Technology, 2003, 34(5): 535-539. [本文引用:1]
[2] 陈霞, 张俊丰. CO低温催化还原氮氧化物的研究进展[J]. 工业催化, 2008, 16(11): 6-11.
Chen Xia, Zhang Junfeng. Research progress of catalytic reduction of nitrogen oxides by CO at low temperature[J]. Industrial Catalysis, 2008, 16(11): 6-11. [本文引用:1]
[3] 徐春明, 杨朝合. 石油炼制工程[M]. 北京: 石油工业出版社, 2009: 354-355. [本文引用:1]
[4] Vilas Ravat, Preeti Aghalayam. Effect of noble metals deposition on the catalytic activity of MAPO-5 catalysts for the reduction of NO by CO[J]. Applied Catalysis A: General, 2010, 389(1/2): 9-18. [本文引用:1]
[5] 卢雯婷, 陈敬超, 冯晶, 等. 贵金属催化剂的应用研究进展[J]. 稀有金属材料与工程, 2012, 41(1): 184-188.
Lu Wenting, Chen Jingchao, Feng Jing, et al. Advances in application of precious metal catalysts[J]. Rare Metal Materials and Engineering, 2012, 41(1): 184-188. [本文引用:1]
[6] Hyeon Ung Shin, Dinesh Lolla, Zhorro Nikolov, et al. Pd-Au nanoparticles supported by TiO2 fibers for catalytic NO decomposition by CO[J]. Journal of Industrial and Engineering Chemistry, 2016, 33: 91-98. [本文引用:1]
[7] Tomoki Uchiyama, Reiko Karitaa, Maiko Nishibori, et al. Preparation and characterization of Pd loaded Sr-deficient K2NiF4-type (La, Sr)2MnO4catalysts for NO-CO reaction[J]. Catalysis Today, 2015, 251: 7-13. [本文引用:1]
[8] Chen Fan, Xiao Wende. Origin of site preference of CO and NO adsorption on Pd(111) at different coverages: a density functional theory study[J]. Computational and Theoretical Chemistry, 2013, 1004: 22-30. [本文引用:1]
[9] Tinku Baidya, Parthasarathi Bera, Bhaskar Devu Mukri, et al. DRIFTS studies on CO and NO adsorption and NO+CO reaction over Pd2+-substituted CeO2 and Ce0. 75Sn0. 25O2 catalysts[J]. Journal of Catalysis, 2013, 303: 117-129. [本文引用:1]
[10] Martinez-Arias A, Hungría A B, Fernández-García M, et al. Light-off behaviour of PdO/γ-Al2O3 catalysts for stoichiometric CO-O2 and CO-O2-NO reactions: a combined catalytic activity-in situ DRIFTS study[J]. Journal of Catalysis, 2004, 221(1): 85-92. [本文引用:1]
[11] Li Min, Wu Xiaodong, Cao Yidan, et al. NO reduction by CO over Rh/Al2O3 and Rh/AlPO4 catalysts: metal-support interaction and thermal aging[J]. Journal of Colloid and Interface Science, 2013, 408: 157-163. [本文引用:1]
[12] Duangkamol Na-Ranong, Ratanaporn Yuangsawad, Prakob Kitchaiya, et al. Application of periodic operation to kinetic study of NO-CO reaction over Rh/Al2O3[J]. Chemical Engineering Journal, 2009, 146(1): 275-286. [本文引用:1]
[13] Ravichand ra S Mulukutla, Takafumi Shido, Kiyotaka Asakura, et al. Characterization of rhodium oxide nanoparticles in MCM-41 and their catalytic performances for NO-CO reactions in excess O2[J]. Applied Catalysis A: General, 2002, 228(1/2): 305-314. [本文引用:1]
[14] Paulo Araya, Francisco Gracia, Joaquín Cortés, et al. FTIR study of the reduction reaction of NO by CO over Rh/SiO2 catalysts with different crystallite[J]. Applied Catalysis B: Environmental, 2002, 38: 77-90. [本文引用:1]
[15] You-Jung Song, Yaritza M. López-De Jesús, Paul T Fanson, et al. Kinetic evaluation of direct NO decomposition and NO-CO reaction over dendrimer-derived bimetallic Ir-Au/Al2O3 catalysts[J]. Applied Catalysis B: Environmental, 2014, 154: 62-72. [本文引用:1]
[16] Wögerbauer C, Maciejewski M, Baiker A. Reduction of nitrogen oxides over unsupported iridium: effect of reducing agent[J]. Applied Catalysis B: Environmental, 2001, 34(1): 11-27. [本文引用:1]
[17] Mostafa Nawdali, Eduard Iojoiu, Patrick Gélin, et al. Influence of the pretreatment on the structure and reactivity of Ir/γ-Al2O3 catalysys in the selective reduction of nitric oxide by propene[J]. Applied Catalysis A: General, 2001, 220: 129-139. [本文引用:1]
[18] Masaaki Haneda, Pusparatu, Yoshiaki Kintaichi, et al. Promotional effect of SO2 on the activity of Ir/SiO2 for NO reduction with CO under oxygen-rich conditions[J]. Journal of Catalysis, 2005, 229(1): 197-205. [本文引用:1]
[19] Tomohiro Yoshinari, Kazuhito Sato, Masaaki Haneda, et al. Remarkable promoting effect of coexisting SO2 on the catalytic activity of Ir/SiO2 for NO reduction in the presence of oxygen[J]. Catalysis Communications, 2001, 2(5): 155-158. [本文引用:1]
[20] Masaaki Haneda, Tadahiro Fujitani, Hideaki Hamada. Effect of iridium dispersion on the catalytic activity of Ir/SiO2 for the selective reduction of NO with CO in the presence of O2 and SO2[J]. Journal of Molecular Catalysis A: Chemical, 2006, 256(1/2): 143-148. [本文引用:1]
[21] Goslar J, Wojciechowska M, Zieliński M. Characterisation of the Ru/MgF2 catalyst with adsorbed O2, NO, CO probe molecules by EPR and IR spectroscopy[J]. Journal of Physics and Chemistry of Solids, 2006, 67(7): 1387-1393. [本文引用:1]
[22] Guglielminotti E, Boccuzzi F, Manzoli M, et al. Ru/ZrO2 Catalysts Ⅰ. O2, CO, and NO adsorption and reactivity[J]. Journal of Catalysis, 2000, 192(1): 149-157. [本文引用:1]
[23] Archana Patel, Pradeep Shukla, Thomas E Rufford, et al. Selective catalytic reduction of NO with CO using different metal-oxides incorporated in MCM-41[J]. Chemical Engineering Journal, 2014, 255: 437-444. [本文引用:1]
[24] Zhang Hongyan, Zhu Aimin, Wang Xinkui, et al. Catalytic performance of Ag-Co/CeO2 catalyst in NO-CO and NO-CO-O2 system[J]. Catalysis Communications, 2007, 8(3): 612-618. [本文引用:1]
[25] Iliopoulou E F, Evdou A P, Lemonidou A A, et al. Ag/alumina catalysts for the selective catalytic reduction of NOx using various reductants[J]. Applied Catalysis A: General, 2004, 274(1/2): 179-189. [本文引用:1]
[26] Salker A V, Fal Desai M S. CO-NO/O2 redox reactions over Cu substituted cobalt oxide spinels[J]. Catalysis Communications, 2016, 87: 116-119. [本文引用:1]
[27] Zhu Lin, Zhong Zhaoping, Yang Han, et al. Comparison study of Cu-Fe-Ti and Co-Fe-Ti oxide catalysts for selective catalytic reduction of NO with NH3 at low temperature[J]. Journal of Colloid and Interface Science, 2016, 478: 11-21. [本文引用:1]
[28] Lu Qiu, Pang Dand an, Zhang Changliang, et al. In situ IR studies of Co and Ce doped Mn/TiO2catalyst forlow-temperature selective catalytic reduction of NO with NH3[J]. Applied Surface Science, 2015, 357: 189-196. [本文引用:1]
[29] 任丽萍, 滕加伟, 李斌, 等. CuO/Al2O3催化剂上CO还原NO反应条件的研究[J]. 工业催化, 2014, 22(9): 725-728.
Ren Liping, Teng Jiawei, Li Bin, et al. Study on the reaction conditions of NO reduction with CO over CuO/Al2O3 catalyst[J]. Industrial Catalysis, 2014, 22(9): 725-728. [本文引用:1]
[30] Martínez-Arias A, Hungría A B, Iglesias-Juez A, et al. Redox and catalytic properties of CuO/CeO2 under CO+O2+NO: promoting effect of NO on CO oxidation[J]. Catalysis Today, 2012, 180(1): 81-87. [本文引用:1]
[31] Gu Xianrui, Li Hao, Liu Lichen, et al. Promotional effect of CO pretreatment on CuO/CeO2 catalyst for catalytic reduction of NO by CO, Journal of Rare Earths, 2014, 32(2): 139-145. [本文引用:1]
[32] Mohamed Kacimi, Mahfoud Ziyad, Leonarda FLiotta. Cu on amorphous AlPO4: preparation, characterization and catalytic activity in NO reduction by CO in presence of oxygen[J]. Catalysis Today, 2015, 241: 151-158. [本文引用:1]
[33] 薛君, 申力涛. M/SBA-15(M=Cu、Fe、Cr)介孔分子筛的制备、表征及其催化NO+CO反应研究[J]. 工业催化, 2013, 21(8): 31-36.
Xun Jun, Shen Litao. Preparation and characterization of M/SBA-15(M=Cu, Fe, Cr) mesoporous molecular sieve and its catalysis for NO+CO reaction[J]. Industrial Catalysis, 2013, 21(8): 31-36. [本文引用:1]
[34] Li Jun, Wang Shan, Zhou Li, et al. NO reduction by CO over a Fe-based catalyst in FCC regenerator conditions[J]. Chemical Engineering Journal, 2014, 255: 126-133. [本文引用:1]
[35] 苏亚欣, 苏阿龙, 任立铭. 铁基催化剂脱除NO气体的研究现状[J]. 化工进展, 2012, (S1): 154-157.
Su Yaxin, Su Along, Ren Liming. Research status of iron - based catalysts for NO gas removal[J]. Chemical Industry and Engineering Progress, 2012, (S1): 154-157. [本文引用:1]
[36] Tanikawa K, Egawa C. Effect of barium addition over palladium catalyst for CO-NO-O2 reaction[J]. Journal of Molecular Catalysis A: Chemical, 2011, 349(1/2): 94-99. [本文引用:1]
[37] Miller D D, Chuang S S C. The effect of O2 on the NO-CO reaction over Ag-Pd/Al2O3: an in situ infrared study[J]. Catalysis Communications, 2009, 10(9): 1313-1318. [本文引用:1]
[38] Gao Feng, Wang Yilin, Wayne Goodman D. CO/NO and CO/NO/O2 reactions over a Au-Pd single crystal catalyst[J]. Journal of Catalysis, 2009, 268(1): 115-121. [本文引用:1]
[39] Sergiy O Soloviev, Pavlo I Kyriienko, Nataliia O Popovych. Effect of CeO2 and Al2O3 on the activity of Pd/Co3O4/cordierite catalyst in the three-way catalysis reactions(CO/NO/CnHm)[J]. Journal of Environmental Sciences, 2012, 24(7): 1327-1333. [本文引用:1]
[40] Li Yile, Zhang Xiaoyu, Long Enyan, et al. Influence of CeO2 and La2O3 on properties of palladium catalysts used for emission control of natural gas vehicles[J]. Journal of Natural Gas Chemistry, 2009, 18: 415-420. [本文引用:1]
[41] Joseph H Holles, Matthew A Switzer, Robert J Davis. Influence of ceria and lanthana promoters on the kinetics of NO and N2O reduction by CO over alumina-supported palladium and rhodium[J]. Journal of Catalysis, 2000, 190: 247-260. [本文引用:1]
[42] Takashi Hirano, Yoshiyuki Ozawa, Takayuki Sekido, et al. Marked effect of In, Pb and Ce addition upon the reduction of NO by CO over SiO2 supported Pd catalysts[J]. Catalysis Communications, 2007, 8(8): 1249-1254. [本文引用:1]
[43] Julia María Díaz Cónsul, Ignacio Costilla, Carlos Eugenio Gigola, et al. NO reduction with CO on alumina-modified silica-supported palladium and molybdenum-palladium catalysts[J]. Applied Catalysis A: General, 2008, 339: 151-158. [本文引用:1]
[44] Schmal M, Baldanza MAS, Vannice MA, et al. Pd-xMo/Al2O3catalysts for NO reduction by CO[J]. Journal of Catalysis, 1999, 185: 138-151. [本文引用:1]
[45] Tou A, Einaga H, Teraoka Y. Preparation of alumina-supported Pd and LaMnO3 catalysts with the site-selective deposition and their catalytic activity for NO-CO reaction[J]. Catalysis Today, 2013, 201: 103-108. [本文引用:1]
[46] Chen Hui, Zhang Yexin, Xin Ying, et al. Enhanced NOx conversion by coupling NOx storage-reduction with CO adsorption-oxidation over the combined Pd-K/MgAlO and Pd/MgAlOcatalysts[J]. Catalysis Today, 2015, 258: 416-423. [本文引用:1]
[47] Abir De Sarkar, Badal C Khanra. Microkinetic model studies of impurity effects on CO+O2, CO+NO and CO+NO+O2 reactions over supported Pt-Rh nanocatalysts[J]. Chemical Physics Letters, 2004, 384(4/5/6): 339-343. [本文引用:1]
[48] Chinnakonda S Gopinath, Francisco Zaera. NO+CO+O2reaction kinetics on Rh(111): amolecular beam study[J]. Journal of Catalysis, 2001, 200(2): 270-287. [本文引用:1]
[49] Dimitris I Kondarides, Tarik Chafik, Xenophon E Verykios. Catalytic reduction of NO by CO over rhodium catalysts[J]. Journal of Catalysis, 2000, 191: 147-164. [本文引用:1]
[50] Salker A V, Fal Desai M S. Catalytic activity and mechanistic approach of NO reduction by CO over M0. 05Co2. 95O4(M=Rh, Pd & Ru) spinel system[J]. Applied Surface Science, 2016, 389: 344-353. [本文引用:1]
[51] Federico J Williams, Norman Macleod, Mintcho S Tikhov, et al. Electrochemical promotion of rhodium-catalyzed NO reduction by CO and by propene in the presence of oxygen[J]. The Journal of Chemical Physics, 2001, 105: 2800-2808. [本文引用:1]
[52] 王玉云, 沈岳松, 纵宇浩, 等. Co、Ni掺入对Pd-Rh型催化剂三效净化C3H8、CO、NO的影响[J]. 环境工程, 2015, (2): 62-68.
Wang Yuyun, Shen Yuesong, Zong Yuhao, et al. Effect of Co and Ni addition on the purification of C3H8, CO and NO by Pd-Rh catalyst[J]. Environmental Engineering, 2015, (2): 62-68. [本文引用:1]
[53] Tsukasa Tamai, Masaaki Haneda, Tadahiro Fujitani, et al. Promotive effect of Nb2O5 on the catalytic activity of Ir/SiO2 for NO reduction with CO under oxygen-rich conditions[J]. Catalysis Communications, 2007, 8(6): 885-888. [本文引用:1]
[54] Masaaki Haneda, Haruko Kudo, Yukinori Nagao, et al. Enhanced activity of Ba-doped Ir/SiO2 catalyst for NO reduction with CO in the presence of O2 and SO2[J]. Catalysis Communications, 2006, 7(7): 423-426. [本文引用:1]
[55] 楼莉萍, 陈英旭, 蒋晓原, 等. CuO负载在TiO2和CeO2-TiO2上对NO+CO反应的催化作用[J]. 环境科学学报, 2003, (3): 301-305.
Lou Liping, Chen Yingxu, Jiang Xiaoyuan, et al. Catalytic performance of CuO supported on TiO2 and CeO2-TiO2 for NO+CO reaction[J]. Chinese Journal of Environmental Science, 2003, (30): 301-305. [本文引用:1]
[56] Lu Guanzhong, Wang Ren. Roles of ceria on base metal oxide catalystsNO+CO reaction[J]. Journal of Rare Earths, 1992, 10(2): 102-107. [本文引用:1]
[57] Yao Xiaojiang, Xiong Yan, Sun Jingfang, et al. Influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 for NO reduction by CO[J]. Journal of Rare Earths, 2014, 32(2): 131-138. [本文引用:1]
[58] Deng Changshun, Huang Qingqing, Zhu Xiying, et al. The influence of Mn-doped CeO2 on the activity of CuO/CeO2 in CO oxidation and NO+CO model reaction[J]. Applied Surface Science, 2016, 389: 1033-1049. [本文引用:1]
[59] Wan Haiqin, Li Dan, Dai Yue, et al. Catalytic behaviors of CuO supported on Mn2O3 modified γ-Al2O3 for NO reduction by CO[J]. Journal of Molecular Catalysis A: Chemical, 2010, 332: 32-44. [本文引用:1]
[60] Wen Bin, He Mingyuan, Ethan Schrum, et al. NO reduction and CO oxidation over Cu/Ce/Mg/Al mixed oxide catalyst in FCC operation[J]. Journal of Molecular Catalysis A: Chemical, 2002, 180(1/2): 187-192. [本文引用:1]
[61] Wen Bin, He Mingyuan. Study of the Cu-Ce synergism for NO reduction with CO in the presence of O2, H2O and SO2 in FCC operation[J]. Applied Catalysis B: Environmental, 2002, 37(1): 75-82. [本文引用:1]
[62] Yu Qiang, Yao Xiaojiang, Zhang Hongliang, et al. Effect of ZrO2 addition method on the activity of Al2O3-supported CuO for NO reduction with CO: impregnation vs. coprecipitation[J]. Applied Catalysis A: General, 2012, 423-424: 42-51. [本文引用:1]
[63] Martínez-Arias A, Fernández-García M, Iglesias-Juez A, et al. New Pd/CexZr1-xO2/Al2O3 three-way catalysts prepared by microemulsionⅡ. In situ analysis of CO oxidation and NO reduction under stoichiometric CO+NO+O2[J]. Applied Catalysis B: Environmental, 2001, 31(1): 51-60. [本文引用:1]
[64] Chen L F, González G, Wang J A, et al. Surfactant-controlled synthesis of Pd/Ce0. 6Zr0. 4O2 catalyst for NO reduction by CO with excess oxygen[J]. Applied Surface Science, 2005, 243: 319-328. [本文引用:1]
[65] Di Monte R, Kaspar J, Fornasiero P, et al. NO reduction by CO over Pd/Ce0. 6Zr0. 4O2-Al2O3 catalysts: in situ FT-IR studies of NO and CO adsorption[J]. Inorganica Chimica Acta, 2002, 334: 318-326. [本文引用:1]
[66] Konsolakis M, Yentekakis I V. NO reduction by propene or CO over alkali-promoted Pd/YSZ catalysts[J]. Journal of Hazardous Materials, 2007, 149(3): 619-624. [本文引用:1]
[67] Tadao Nakatsuji, Takumi Yamaguchi, Naohiro Sato, et al. A selective NOx reduction on Rh-based catalysts in lean conditions using CO as a main reductant[J]. Applied Catalysis B: Environmental, 2008, 85(1/2): 61-70. [本文引用:1]
[68] Feng-Yim Chang, Ming-Yen Wey, Jyh-Cherng Chen. Effects of sodium modification, different reductants and SO2 on NO reduction bu Rh/Al2O3 catalysts at excess O2 conditions[J]. Journal of Hazardous Materials, 2008, 156: 348-355. [本文引用:1]
[69] Beitollahi A, Hosseini-Bay H, Sarpoolaki H. Synthesis and characterization of Al2O3-ZrO2 nanocomposite powder by sucrose process[J]. Journal of Materials Science: Materials in Electronics, 2010, 21(2): 130-136. [本文引用:1]
[70] Mari Lou Balmer, Fred F Lange, Vikram Jayaram, et al. Development of nano-composite microstructures in ZrO2-Al2O3 via the solution precursor method[J]. Journal of the American Ceramic Society, 1995, 78(6): 1489-1494. [本文引用:1]
[71] Castillo S, Morán-Pineda M, Gómez R. Reduction of NO by CO under oxidizing conditions over Pt and Rh supported on Al2O3-ZrO2 binary oxides[J]. Catalysis Communications, 2001, 2(10): 295-300. [本文引用:1]
[72] Iliopoulou E F, Efthimiadis EA, Nalband ian L, et al. Ir-based additives for NO reduction and CO oxidation in the FCC regenerator: evaluation, characterization and mechanistic studies[J]. Applied Catalysis B: Environmental, 2005, 60(3/4): 277-288. [本文引用:1]
[73] Archana Patel, Pradeep Shukla, Thomas Rufford, et al. Catalytic reduction of NO by CO over copper-oxide supported mesoporous silica[J]. Applied Catalysis A: General, 2011, 409-410: 55-65. [本文引用:1]
[74] Liu Lianjun, Yao Zhijian, Liu Bin, et al. Correlation of structural characteristics with catalytic performance of CuO/CexZr1-xO2 catalysts for NO reduction by CO[J]. Journal of Catalysis, 2010, 275: 45-60. [本文引用:1]