溫度對(duì)Mn-Ce/γ-Al2O3催化氧化柴油機(jī)尾氣NO性能的影響

王 攀，殷俊晨，羅 鵬，雷利利，宋金甌

?

溫度對(duì)Mn-Ce/-Al2O3催化氧化柴油機(jī)尾氣NO性能的影響

王 攀1，殷俊晨1，羅 鵬1，雷利利1，宋金甌2

（1. 江蘇大學(xué)汽車(chē)與交通工程學(xué)院，鎮(zhèn)江 212013；2. 天津大學(xué)內(nèi)燃機(jī)燃燒學(xué)國(guó)家重點(diǎn)實(shí)驗(yàn)室，天津 300072）

通過(guò)溶膠-凝膠法制備了MnCe/-Al2O3（∶為摩爾比，=4，6，8，10；=10）催化劑。利用X射線(xiàn)衍射（X-ray diffraction，XRD）和X射線(xiàn)光電子能譜（X-ray photoelectron spectroscopy，XPS）對(duì)催化劑的理化性能進(jìn)行了表征，并在管式固定床反應(yīng)器中考察了在不同溫度下催化劑對(duì)NO的催化氧化活性影響規(guī)律。結(jié)果表明，NO轉(zhuǎn)化率隨著溫度的升高而增加，在300 ℃時(shí)達(dá)到峰值，隨后受熱力學(xué)控制，NO轉(zhuǎn)化率隨溫度的升高有所降低。在250～350 ℃溫度區(qū)間，Mn10Ce/-Al2O3（≥6）催化劑都表現(xiàn)出較好的NO催化氧化活性。其中，6Mn10Ce/-Al2O3催化劑的低溫催化活性較好，在200 ℃時(shí)對(duì)NO的轉(zhuǎn)化率達(dá)44.8%，300 ℃時(shí)高達(dá)83.6%。Mn-Ce/-Al2O3催化劑的NO氧化性能由強(qiáng)到弱為：6Mn10Ce/-Al2O3> 8Mn10Ce/-Al2O3>10Mn10Ce/-Al2O3>4Mn10Ce/-Al2O3。

柴油機(jī)；排放控制；一氧化氮；催化氧化

0 引 言

柴油機(jī)的氮氧化物（NOx）排放是大氣污染物之一，同時(shí)也是酸雨和光化學(xué)煙霧的重要前驅(qū)體[1]，對(duì)大氣環(huán)境和人體健康會(huì)造成嚴(yán)重危害，因此需要對(duì)其進(jìn)行有效控制。目前，柴油機(jī)NOx后處理技術(shù)中主要有選擇性催化還原（selective catalytic reduction，SCR）和NOx存儲(chǔ)還原（NOxstorage and reduction，NSR）[2-3]。與SCR技術(shù)相比，NSR技術(shù)具有脫硝效率高、活性溫度區(qū)間較寬、還原劑用量較少等優(yōu)點(diǎn)[4]，被認(rèn)為是一種具有應(yīng)用前景的NOx控制技術(shù)，該技術(shù)的關(guān)鍵是優(yōu)化調(diào)節(jié)NO/NO2比率，以提高NOx脫除效率。與NO相比，NO2由于N-O鍵能較低，更容易被NSR催化劑存儲(chǔ)還原，但柴油機(jī)NOx排放中NO占90%左右。因此，將柴油機(jī)排氣中的NO氧化成NO2將有利于NOx排放的催化脫除。

與傳統(tǒng)催化劑相比，貴金屬催化劑（如鉑Pt）具有較高的NO氧化性能，但其成本較高，且容易受硫毒化，這也限制了其在催化領(lǐng)域的廣泛應(yīng)用[5-6]。研究發(fā)現(xiàn)，過(guò)渡金屬M(fèi)n在催化氧化反應(yīng)中有較好的催化活性[7-9]。Wu等[10]在對(duì)MnOx/TiO2催化劑氧化NO的研究中發(fā)現(xiàn)，催化劑在反應(yīng)溫度高于250 ℃時(shí)，有較好的催化氧化NO活性，但其在低溫時(shí)活性不高。稀土金屬Ce是優(yōu)良的催化劑助劑，CeO2具有較好的儲(chǔ)放氧能力和氧化還原性質(zhì)[11-14]，采用摻雜Ce的方式可以改善Mn基催化劑的低溫催化氧化活性[15-18]。李小海等[19]研究了摻雜Ce對(duì)Mn/TiO2催化劑性能的影響，發(fā)現(xiàn)摻雜Ce可以增大催化劑的比表面積以及提高催化劑對(duì)氧的吸附能力，從而提高了催化劑的氧化活性。Li等[20]對(duì)Mn-Ce-Ox催化劑氧化NO開(kāi)展了研究，發(fā)現(xiàn)Ce的加入可以增強(qiáng)催化劑低溫氧化NO的活性，在250 ℃時(shí)NO轉(zhuǎn)化率提高了37%。綜上分析可知，Mn-Ce催化劑具有良好的催化氧化NO活性。為了研究不同Mn/Ce比催化劑在不同溫度下的NO氧化機(jī)理，本文通過(guò)溶膠-凝膠法制備了MnCe/-Al2O3（∶為摩爾比，=4，6，8，10；=10）催化劑，并對(duì)其理化性能進(jìn)行表征，通過(guò)在管式固定床反應(yīng)器上進(jìn)行的模擬試驗(yàn)，深入分析了不同Mn/Ce比對(duì)Mn-Ce/-Al2O3催化氧化NO性能的影響。

1 試驗(yàn)部分

1.1 催化劑的制備

本文采用溶膠-凝膠法制備了一系列的MnCe/-Al2O3催化劑。首先，將適量-Al2O3粉末溶于適量的蒸餾水中，攪拌直至形成乳白色懸濁液；按照不同Mn/Ce摩爾比稱(chēng)取一定量的Ce(NO3)3·6H2O、C4H6MnO4·4H2O，分別溶于適量的去離子水中制成溶液，然后加入-Al2O3懸濁液中；加入Ce3+和Mn2+摩爾總量2倍的檸檬酸，和10%檸檬酸質(zhì)量的聚乙二醇，80 ℃磁力攪拌，直至形成透明凝膠，110 ℃干燥24 h，自然冷卻，再研磨成粉末，在馬弗爐中300 ℃焙燒1 h，然后升溫至500 ℃焙燒5 h，冷卻后壓片、破碎、篩選出40～60目的顆粒備用。

1.2 催化劑的評(píng)價(jià)

催化劑活性測(cè)試在管式固定床反應(yīng)器上進(jìn)行，測(cè)試示意圖如圖1所示。將催化劑（0.3 mL）置于石英反應(yīng)管中部，然后通入混合氣體，進(jìn)行程序升溫測(cè)試活性。反應(yīng)測(cè)試的混合氣體組成為：500×10-6體積分?jǐn)?shù)的NO，10%體積分?jǐn)?shù)的O2，以N2為平衡氣，空速為55 000 h-1。出口氣體中NO和NO2的濃度通過(guò)美國(guó)Thermo 42iHL NOx分析儀測(cè)量。催化劑活性測(cè)試中NO轉(zhuǎn)化率（NO）按下式計(jì)算

式中NO2 out表示反應(yīng)器出口處NO2的體積分?jǐn)?shù)，NOin表示反應(yīng)器入口處NO體積分?jǐn)?shù)。

圖1 催化劑活性測(cè)試示意圖

Fig.1 Schematic diagram of catalyst activity test

1.3 催化劑的表征

XRD在德國(guó)Bruker/D8 ADVANCE型射線(xiàn)衍射儀上進(jìn)行測(cè)試，輻射源采用CuKα（＝0.154 068 nm），掃描角速度為7(°)/min，20°～80°掃描，晶粒大小根據(jù)Scherrer公式進(jìn)行計(jì)算

/(cos)

式中為Scherrer常數(shù)；為晶粒尺寸，nm；為實(shí)測(cè)樣品衍射峰半高寬度，rad；為衍射角；為X射線(xiàn)波長(zhǎng)。

XPS在美國(guó)Thermo Fisher Scientific 生產(chǎn)的ESCALAB250Xi型儀器上進(jìn)行，該儀器采用Al K（= 1 486.6 eV）作為X射線(xiàn)源，分辨率為0.43 eV，分析范圍為0～5 000 eV，所測(cè)元素的結(jié)合能以表面污染碳（結(jié)合能=284.6 eV）為標(biāo)準(zhǔn)進(jìn)行校正。

2 結(jié)果與討論

2.1 催化劑XRD表征

Mn10Ce/-Al2O3（=4，6，8，10）催化劑的XRD譜圖如圖2所示。由圖2可見(jiàn)，在2為25.74°、5.32°、37.93°、43.53°、53.72°、57.65°、66.68°和68.36°出現(xiàn)了典型的-Al2O3特征衍射峰（PDF No. 48-0366）。CeO2的特征衍射峰與純CeO2（JCPDS:PDF 34-0394）較為接近，但存在向高角度偏移現(xiàn)象。催化劑在2為28.74°出現(xiàn)了一個(gè)較寬的衍射峰，說(shuō)明有無(wú)定形Ce結(jié)構(gòu)存在[21-22]。MnO2的特征峰與純MnO2的特征衍射峰（JCPDS:PDF 65-7467）重合度比較高，且在2為27.32°，57.10°出現(xiàn)了MnO2與CeO2重疊的特征衍射峰。此外，在2為31.84°處出現(xiàn)了Mn2O3特征衍射峰，與文獻(xiàn)[23-24]相一致。隨著值增加，2為31.84°處的Mn2O3特征衍射峰強(qiáng)度先變強(qiáng)后變?nèi)?，說(shuō)明隨著的增加，催化劑制取過(guò)程中Mn2O3的生成量先增多后減少，在=6時(shí)，有較多Mn2O3晶體出現(xiàn)。通過(guò)Scherrer方程可以估算CeO2晶粒尺寸為26 nm。CeO2衍射峰向高角度偏移，主要是因?yàn)镃eO2中半徑較大的Ce4+被半徑較小的Mn4+和Mn3+所取代，引起的晶胞收縮所致[25]，這有助于提高氧空位濃度，從而增加催化劑的活性。

2.2 催化劑的評(píng)價(jià)

在150～400 ℃溫度范圍內(nèi)，6Mn10Ce/-Al2O3催化劑作用下，NO2濃度隨時(shí)間變化曲線(xiàn)如圖3所示。由圖3可以看出，在250 ℃以下，NO2濃度到達(dá)穩(wěn)定的時(shí)間在900 s以上，在300 ℃時(shí)，穩(wěn)定時(shí)間迅速降低為570 s；之后，隨著溫度的升高穩(wěn)定時(shí)間緩慢降低。

表1為不同Mn/Ce摩爾比催化劑在不同溫度下的NO轉(zhuǎn)化率。由表1可見(jiàn)，不同Mn/Ce摩爾比的NO轉(zhuǎn)化率呈現(xiàn)先增加后降低的變化規(guī)律。溫度為300 ℃時(shí)，NO轉(zhuǎn)化率最高，之后受熱力學(xué)控制，NO2會(huì)發(fā)生熱分解現(xiàn)象，從而使得NO轉(zhuǎn)化率隨溫度升高有所降低。

在400～450 ℃時(shí)，受熱力學(xué)影響，所有催化劑的NO轉(zhuǎn)化率幾乎相同。在250～350 ℃溫度區(qū)間內(nèi)時(shí)，4Mn10Ce/-Al2O3催化劑的NO催化氧化活性最差，其他催化劑性能較為接近；低于200 ℃時(shí)，6Mn10Ce/-Al2O3催化劑表現(xiàn)出最好的低溫催化活性，在200 ℃時(shí)催化氧化NO的轉(zhuǎn)化率已達(dá)44.8%。所測(cè)樣品的NO氧化性能由強(qiáng)到弱的順序?yàn)椋?Mn10Ce/-Al2O3>8Mn10Ce/-Al2O3> 10Mn10Ce/-Al2O3>4Mn10Ce/-Al2O3。

表1 不同Mn/Ce摩爾比催化劑在不同溫度下的NO轉(zhuǎn)化率

2.3 XPS表征分析

6Mn10Ce/-Al2O3和8Mn10Ce/-Al2O3催化劑的Ce 3d XPS結(jié)合能譜圖如圖4a所示。從圖4a中可以看出譜圖中含有6個(gè)顯著的特征峰，Ce 3d3/2的主峰和兩個(gè)激峰位于900.9，908.2和917.0 eV，而位于882.4，889.1和898.8 eV峰位屬于Ce 3d5/2的主峰和兩個(gè)激峰。以上6個(gè)峰位對(duì)應(yīng)CeO2(Ce4+)的最終價(jià)態(tài)。Ce3+的特征峰峰位（885.1～885.8 eV，903.5～904.2 eV）沒(méi)有被檢測(cè)，說(shuō)明Ce元素在催化劑中以4價(jià)態(tài)存在。

6Mn10Ce/-Al2O3和8Mn10Ce/-Al2O3催化劑Mn 2p的XPS的結(jié)合能譜圖如圖4b所示。由圖4b可見(jiàn)，Mn 2p譜圖含有兩個(gè)特征峰，即自旋軌道雙峰Mn 2p1/2以及Mn 2p3/2。642 eV處的峰位屬于Mn 2p3/2，與純MnO2（614.7～642.4 eV）中的Mn 2p3/2結(jié)合能較為接近。結(jié)合XRD分析結(jié)果，可確定催化劑中存在MnO2。653.6 eV 處的Mn 2p1/2峰位，對(duì)應(yīng)Mn3+（653.57～653.61 eV）價(jià)態(tài)。Mn 2p3/2的XPS峰形的不對(duì)稱(chēng)也進(jìn)一步證實(shí)Mn3+和Mn4+同時(shí)存在，這表明催化劑中活性組分Mn以Mn4+和Mn3+混合價(jià)態(tài)的形式存在。

6Mn10Ce/-Al2O3和8Mn10Ce/-Al2O3催化劑O 1s 的XPS譜圖如圖4c所示。由圖4c可見(jiàn)，催化劑的O 1s峰均包含兩個(gè)對(duì)稱(chēng)峰，這表明催化劑含有兩種類(lèi)型的氧物種。其中，較低結(jié)合能（529.0～529.1 eV）處的峰為金屬氧化晶格氧O2-（定義為O）特征峰，較高結(jié)合能（531.1～531.2 eV）處的峰則認(rèn)為是表面化學(xué)吸附氧（定義為O）。此外，2種催化劑的晶格氧含量不同，其主要原因是它們的活性組分配比不同。NO氧化過(guò)程主要是：MnO2將氣相氧活化，活性氧氧化吸附在催化劑表面的NO，生成NO3-，MnO2被還原為MnO；NO3-受熱分解成NO2，MnO最終被CeO2釋放的晶格氧氧化為MnO2。因此，較高含量的O更有利于將NO轉(zhuǎn)化成NO2。

a. Ce 3db. Mn 2pc.O 1s

3 結(jié) 論

1）Ce主要以無(wú)定形結(jié)構(gòu)存在于Mn10Ce/-Al2O3（=4，6，8，10）催化劑中；而Mn在催化劑中主要以MnO2形式出現(xiàn)，當(dāng)=6時(shí)，有較多Mn2O3晶體出現(xiàn)。

2）CeO2中半徑較大的Ce4+被半徑較小的Mn4+和Mn3+所取代，有助于催化劑氧空位的形成，提高催化劑的催化氧化NO的性能。

3）隨溫度升高，催化劑的NO轉(zhuǎn)化率呈現(xiàn)先增加后降低的變化規(guī)律，在300℃時(shí)，NO轉(zhuǎn)化率達(dá)到峰值83.6%。其中，NO氧化性能由強(qiáng)到弱的順序?yàn)椋?Mn10Ce/-Al2O3>8Mn10Ce/-Al2O3>10Mn10Ce/-Al2O3>4Mn10Ce/-Al2O3。

[1] 王歡，呂麗，王東輝，等. 銅錳復(fù)合氧化物室溫催化氧化NO的研究[J]. 北京化工大學(xué)學(xué)報(bào)：自然科學(xué)版，2010，37(4)：24－28.

Wang Huan, Lü Li, Wang Donghui, et al. NO catalytic oxidation over copper manganese oxide at room temperature[J]. Journal of Beijing University of Chemical Technology: Natural Science, 2010, 37(4): 24－28. (in Chinese with English abstract)

[2] Maria P R, Isabella N, Enrico T. Experimental study of the NO oxidation to NO2over metal promoted zeolites aimed at the identification of the standard SCR rate determining step[J]. Top Catal, 2013, 56: 109－113.

[3] Visconti C G, Lietti L, Manenti F, et al. Spectrokinetic analysis of the NOxstorage over a Pt-Ba/Al2O3lean NOxtrap catalyst[J]. Topics in Catalysis, 2013, 56(1): 311－316.

[4] 孫英，黃妍，趙威，等. 負(fù)載型鈣鈦礦催化氧化NO及抗SO2性能研究[J]. 燃料化學(xué)學(xué)報(bào)，2014，42(10)：1246－1252.

Sun Ying, Huang Yan, Zhao Wei, et al. Research on catalytic performance of supported perovskite catalyst for NO oxidation and resistance to SO2poisoning[J]. Journal of Fuel Chemistry and Technology, 2014, 42(10): 1246－1252. (in Chinese with English abstract)

[5] Li J, Kumar A, Kamasamudram K, et al. Time- dependent hysteresis in the NO oxidation to NO2on Pt-based catalysts[J]. Catalysis Today, 2015, 258(4): 169－174.

[6] Shang D, Zhong Q, Cai W. High performance of NO oxidation over Ce-Co-Ti catalyst: The interaction between Ce and Co[J]. Applied Surface Science, 2015, 325(6): 211－216.

[7] Shen M Q, Zhao Z, Chen J H, et al. Effects of calcium substitute in LaMnO3perovskites for NO catalytic oxidation[J]. Journal of Rare Earths, 2013, 31(2): 119－123.

[8] 唐曉龍，李華，易紅宏，等. 過(guò)渡金屬氧化物催化氧化NO實(shí)驗(yàn)研究[J]. 環(huán)境工程學(xué)報(bào)，2010，4(3)：629－643.

Tang Xiaolong, Li Hua, Yi Honghong, et al. Transition metal oxides catalysts for oxidation of nitric oxide[J]. Chinese Journal of Environmental Engineering, 2010, 4(3): 629－643. (in Chinese with English abstract)

[9] Zhao B H, Rui R, Wu X D, et al. Comparative study of Mn/TiO2and Mn/ZrO2catalysts for NO oxidation[J]. Catalysis Communications, 2014, 56(41): 36－40.

[10] Wu Z B, Tang N, Xiao L. MnOx/TiO2composite nanoxides synthesized by deposition precipitation method as a superior catalyst for NO oxidation[J]. Journal of Colloid and Interface Science, 2010, 352(1): 143－148.

[11] Muhammad S M, Anil K P, Heon P H. Novel sulfation effect on low-temperature activity enhancement of CeO2-added Sb-V2O5/TiO2catalyst for NH3-SCR[J]. Applied Catalysis B Environmental, 2014, 152/153(25): 28－37.

[12] Lin F, Wu X D, Weng D. Effect of barium loading on CuOx-CeO2catalysts: NOxstorage capacity, NO oxidation ability and soot oxidation activity[J]. Catalysis Today, 2011, 175(1): 124－132.

[13] Ming C, Ye D Q, Liang H, et al. Catalytic combustion performance of soot over cerium-based transition metal composite oxide catalysts[J]. Acta Scientiae Circumtantiae, 2010, 30(1): 158－164.

[14] Wang S J, Zou G C, Xu Y, et al. Ce-based catalysts for simultaneous removal of both diesel soot and NOx[J]. Journal of Molecular Catalysis(China), 2015, 29(1): 60－67.

[15] Qi G S, Li W. NO oxidation to NO2over manganese-cerium mixed oxides[J]. Catalysis Today, 2015, 258(3): 205－213.

[16] Dimitrios D, Theophilos I. VOC oxidation over MnOx-CeO2catalysts prepared by a combustion method[J]. Applied Catalysis B: Environmental, 2008, 84(1/2): 303－312.

[17] Li K, Tang X L, Yi H H, et al. Low-temperature catalytic oxidation of NO over Mn-Co-Ce-Oxcatalyst[J]. Chemical Engineering Journal, 2012, 192(2): 99－104.

[18] Li H, Tang X L, Yi H H, et al. Low-temperature catalytic oxidation of NO over Mn-Ce-Oxcatalyst[J]. Journal of Rare Earth, 2010, 28(1): 64－68.

[19] 李小海，張舒樂(lè)，鐘秦. 鈰摻雜Mn/TiO2催化氧化NO的性能[J]. 化工進(jìn)展，2011，30(7)：1503－1508.

Li Xiaohai, Zhang Shule, Zhong Qin. Catalytic oxidation of NO over Ce-doped Mn/TiO2[J]. Chemical Industry and Engineering Progress, 2011, 30(7): 1503－1508. (in Chinese with English abstract)

[20] Li X H, Zhang S L, Jia Y, et al. Selective catalytic oxidation of NO with O2over Ce-doped MnOx/TiO2catalysts[J]. Journal of Natural Gas and Chemistry, 2012, 21(1): 17－24.

[21] Zou Z Q, Meng M, Guo L H, et al. Synthesis and characterization of CuO/Ce1-XTiXO2catalysts used for low-temperature CO oxidation[J]. J Hazard Mater, 2009, 163(2/3): 835－842.

[22] 王攀，谷文業(yè)，雷利利，等. 催化劑存儲(chǔ)還原柴油機(jī)NOX排放的試驗(yàn)[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2015，31(9)：230－234.

Wang Pan, Gu Wenye, Lei Lili, et al. Experiment of NOXstorage and reduction from diesel engine with NSR catalysts[J]. Transactions of the Chinese Society of Agricultural Engineering, (Transactions of the CSAE), 2015, 31(9): 230－234. (in Chinese with English abstract)

[23] Liu S, Wu X D, Weng D, et al. Combined promoting effects of platinum and MnOX–CeO2supported on alumina on NOX-assisted soot oxidation: Thermal stability and sulfur resistance[J]. Chemical Engineering Journal, 2012, 203(6): 25－35.

[24] Wu X D, Lee H R, Liu S, et al. Regeneration of sulfated MnOX-CeO2-Al2O3soot oxidation catalyst by reduction with hydrogen[J]. Industrial & Engineering Chemistry Research, 2013, 52(2): 716－721.

[25] 晏冬霞，王華，李孔齋，等. 鈰鐵鋯三元復(fù)合氧化物上碳煙的催化燃燒[J]. 燃料化學(xué)學(xué)報(bào)，2011，39(3)：229－235.

Yan Dongxia, Wang Hua, Li Kongzhai, et al. Catalytic combustion of soot on Ce-Fe-Zr-O ternary mixed oxide catalysts[J]. Journal of Fuel Chemistry and Technology, 2011, 39(3): 229－235. (in Chinese with English abstract)

Effects of temperature on oxidation characteristics of NO catalyzed by Mn-Ce/-Al2O3from diesel engine exhaust

Wang Pan1, Yin Junchen1, Luo Peng1, Lei Lili1, Song Jinou2

(1.,,212013,; 2.,,300072,)

With the aim of studying the effect of Mn-Ce catalysts on the NO oxidation activity, a series ofMnyCe/-Al2O3(:is mole ratio,=4, 6, 8, 10;=10) catalysts were synthesized by a sol-gel method. The samples were dried at 110 ℃ for 24 h , calcined in air for 1 h at 300℃and then for 5 h at 500 ℃to obtain the required 40-60 mesh powder.The effect of metallic Mn and Ce on their microstructure and catalytic properties were investigated by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) analysis. According to the results of analysis, the diffraction peaks of Mn2O3became stronger and then shifted to weaker with the value ofincreasing from 4 to 10, while Mn2O3reached up to its peak value whenwas 6. The grain size of cerium in the form of CeO2was 26 nm as indicated by Scherrer equation. CeO2diffraction peak shifted to a higher angle, due to the cell shrinkage caused by the fact that a part of Ce4+ions were replaced by Mn4+and Mn3+, which improved the oxygen vacancy concentration and increased the activity of catalyst. The dissymmetric peak of Mn 2p3/2observed in XPS spectra proved that Mn3+and Mn4+were both present in theMn10Ce/-Al2O3catalyst. MnO2could be reducted to MnO while MnO would be oxidated to MnO2by the lattice oxygen generated by CeO2. And the peak of O 1s indicated that the content of lattice oxygen of 6Mn10Ce/-Al2O3and 8Mn10Ce/-Al2O3was different, which was mainly because of the different Mn/Ce ratio. The higher level of O was more favorable to the oxidative of NO. Furthermore, the effects of temperature on the catalytic oxidation activity of NO were investigated based upon a tubular fixed bed reactor in the range of 150-450 ℃ with an inside diameter of 10 mm and plugged between two silica wool layers to prevent the sample being blew away. The gases used in test were 500 ppm NO, 10% O2, with N2in balance and a space velocity of 55 000/h. Results show that NO2concentration over 6Mn10Ce/-Al2O3catalysts reached stable after 900 s under 250℃, while the stable time reduced to 570 s at 300 ℃ and slowed down with the rising of temperature. NO conversion rate under different Mn/Ce ratios first increased and then decreased with the rise of temperature and reached up to the peak value at 300℃. It should be noticed that NO conversion rate would decrease as the further increase of temperature because of NO generated by the thermodynamics of NO2. In addition, NO conversions of all the catalysts kept almost the same in the temperature range from 400 to 450 ℃, due to the accelerated thermal decomposition of NO2under the influence of high temperature. TheMn10Ce/-Al2O3(≥6) catalysts showed better NO catalytic oxidation activity, over the temperature range from 250℃ to 350℃. Among all the catalysts, 6Mn10Ce/-Al2O3catalyst showed the highest catalytic activity at low temperature, and NO conversion rate reached up to 44.8% at 200 ℃ and 83.6% at 300 ℃，respectively. The reason was that the properties of the catalysts depended mainly on the active components, especially the Mn/Ce ratio. The results also indicated that MnOxwas the main contributor for NO oxidation, and the catalysts showed better oxidation capacity with the increase of MnOx. The NO oxidation activity followed the trend 6Mn10Ce/-Al2O3> 8Mn10Ce/-Al2O3>10Mn10Ce/-Al2O3>4Mn10Ce/-Al2O3.

diesel engines; emission control; nitric oxide; catalytic oxidation

10.11975/j.issn.1002-6819.2016.24.010

TK421+.5

A

1002-6819(2016)-24-0077-05

2016-04-20

2016-10-13

國(guó)家自然科學(xué)青年基金（51206068）；江蘇省自然科學(xué)青年基金（BK2015040369）；天津大學(xué)內(nèi)燃機(jī)國(guó)家重點(diǎn)實(shí)驗(yàn)室開(kāi)放基金（K15-07）

王 攀，男，副教授；研究方向：發(fā)動(dòng)機(jī)排放控制。鎮(zhèn)江 江蘇大學(xué)，212013。Email：wangpan@ujs.edu.cn