CeO2-doped WO3 composite catalyst based on acid site enhancement for diesel exhaust gas denitration
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摘要: 采用先电沉积后水热的方法将WO3负载于钛网上,后续采用电沉积负载CeO2制备CeO2-WO3/Ti催化剂用于柴油车尾气选择性催化还原(NH3-SCR)脱硝。通过固定床反应装置检测催化剂脱硝性能,考察了电沉积CeO2时间对催化剂脱硝性能的影响,结合SEM、XRD、XPS、H2-TPR、NH3-TPD和原位红外光谱等表征手段分析反应机制。结果表明,在WO3表面进行20 min电沉积CeO2的双组分催化剂NOx转化率提升最明显,在200 ℃时已达到91.89%,250−350 ℃均为100%。双组分催化剂表面负载了WO3纳米棒以及高度分散的CeO2,CeO2的负载引入Ce3+并提高了催化剂化学吸附氧所占比例,但样品对应氧化还原能力没有明显提升。中温段(250−350 ℃)脱硝性能提高的主要原因是复合后CeO2的引入有效增加了弱酸以及中强酸位点数量。Abstract: Based on the complicated preparation of current diesel vehicle exhaust gas denitration catalysts, an in-situ deposited composite oxide catalyst, CeO2-WO3 mixed oxide catalyst, was prepared by electrodeposition and hydrothermal methods, which was loaded on the titanium mesh and applied to the selective catalytic reduction denitration of diesel vehicle exhaust. Denitration performance of the catalysts was tested by a fixed bed reactor, and the influence of different electrodeposition time of CeO2 was investigated. The results demonstrate that 20 min is the best electrodeposition time of CeO2 (100% NOx conversion at 250−350 ℃). The high dispersion of active CeO2 on WO3 promotes the synergistic effects among different components. The as-prepared catalysts were characterized by SEM, XRD, XPS, H2-TPR, NH3-TPD and in-situ DRIFTS. It is evident that Ce3+ is successfully introduced by loading CeO2, which enhances the chemisorption of oxygen. Meanwhile, the increased acidity including both weak acid and medium-strong acid sites of CeO2-WO3 composite catalyst is observed, which improves the co-adsorption of NH3 on Lewis acid and Brønsted acid simultaneously and facilitates the denitration process. Through the characterization by in-situ DRIFTS, it is elucidated that the NH3-SCR reactions are mainly carried out following the Eley-Rideal (E-R) pathway in a medium-temperature range (250−350 ℃).
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Key words:
- titanium mesh /
- electrodeposition /
- composite oxide /
- acid sites
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表 1 单组分及双组分催化剂表面原子浓度
Table 1 Surface atomic concentration of catalysts
Sample Ce3+/ (Ce3++Ce4+) Oα/(Oα +Oβ) DCe(20)-W 31.72% 21.83% W-DS − 10.24% -
[1] GAO X, ZHANG S, DU W X, GONG X C, NGUYEN T T, GUO M H, ZHANG Z P. Wood-inspired high-performing hierarchical porous Ce0.7Zr0.3O2 catalyst for low-temperature selective catalytic reduction of NOx by NH3[J]. Ceram Int,2021,47:29149−29161. doi: 10.1016/j.ceramint.2021.07.078 [2] KANG H, WANG J J, JIAN Z, WEI C, TANG C J, JI J W, RUI R, WU M X, JING F L. Solvent-free elaboration of Ni-doped MnOx catalysts with high performance for NH3-SCR in low and medium temperature zones[J]. Mol Catal,2021,501:111376. doi: 10.1016/j.mcat.2020.111376 [3] LIANG Q, LI J, YUE T. Promotional effect of CeO2 on low-temperature selectivecatalytic reduction of NO by NH3 over V2O5-WO3/TiO2 catalysts[J]. Environ Technol Innov,2020,21(3):101209. [4] 胡晨晖, 刘春红, 胡达清, 蒋楠, 卓佐西, 范海东. 国六标准下柴油车尾气处理应对及分子筛 SCR脱硝技术进展[J]. 现代化工,2020,40(6):24−28.HU Chen-hui, LIU Chun-hong, HU Da-qing, JIANG Nan, ZHUO Zuo-xi, FAN Hai-dong. Progress in treatment measurement for diesel vehicle exhaust gas and molecular sieve SCR denitrification technology under China's national Ⅵ discharge standard[J]. Mod Chem Ind,2020,40(6):24−28. [5] BUSCA G, LIETTI L, RAMIS G, BERTI F. Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review[J]. Appl Catal B: Environ,1998,18:1−36. doi: 10.1016/S0926-3373(98)00040-X [6] 刘志远. 整体式分子筛基脱硝催化剂的研制及其应用性能[D]. 青岛: 中国石油大学(华东), 2018.LIU Zhi-yuan. The preparation and application of monolithic molecular sieve catalyst for De-NOx[D]. Qingdao: China University of Petroleum (East China), 2018. [7] 喻乐蒙 . 柴油机(车)尾气SCR脱硝催化剂的制备及性能研究[D]. 南京: 南京理工大学, 2016.YU Le-meng. Study on preparation and performance of SCR denitration catalysts for diesel vehicle exhaust[D]. Nanjing: Nanjing University of Science & Technology, 2016. [8] ZHAO W, DOU S P, ZHANG K, WU L C, WANG Q. Promotion effect of S and N co-addition on the catalytic performance of V2O5/TiO2 for NH3-SCR of NOx[J]. Chem Eng J,2019,364:401−409. doi: 10.1016/j.cej.2019.01.166 [9] LIU X S, CHEN H F, WU X D, CAO L, JIANG P, YU Q, MA Y. Effects of SiO2 modification on the hydrothermal stability of the V2O5/WO3-TiO2 NH3-SCR catalyst[J]. Catal Sci Technol,2019,9:3711−3720. doi: 10.1039/C9CY00385A [10] LIU X S, IANG P, CHEN Y, WANG Y G, DING Q L, SUI Z M, CHEN H F, SHEN Z Y, WU X D. A basic comprehensive study on synergetic effects among the metal oxides in CeO2-WO3/TiO2 NH3-SCR catalyst[J]. Chem Eng J,2021,421(2):127833. [11] GRANGER P, SIAKA H W, UMBARKAR S B. What news in the surface chemistry of bulk and supported vanadia based SCR-Catalysts: Improvements in their resistance to poisoning and thermal sintering[J]. Chemilal Record,2018,18:1−17. doi: 10.1002/tcr.201880101 [12] 潘龙君. 柴油车尾气 SCR 脱硝催化剂的研究[D]. 青岛: 中国石油大学(华东), 2017.PAN Long-jun. Study on SCR catalysts for the De-NOx of diesel exhaust[D]. Qingdao: China University of Petroleum (East China), 2017. [13] PU Y J, WANG P C, JIANG W J, DAI Z D, YANG L, JIANG X, JIANG Z C, YAO L. A novel CNTs functionalized CeO2/CNTs-GAC catalyst with high NO conversion and SO2 tolerance for low temperature selective catalytic reduction of NO by NH3[J]. Chemosphere,2021,284:131377. doi: 10.1016/j.chemosphere.2021.131377 [14] WANG C Z, TANG X L, YI H H, GAO F Y, NI S Q, ZHANG R C, SHI Y R. MnCo nanoarray in-situ grown on 3D flexible nitrogen-doped carbon foams as catalyst for high-performance denitration[J]. Colloids Surf A,2021,612:126007. doi: 10.1016/j.colsurfa.2020.126007 [15] CHEN Q Z, WANG D, GAO C, WANG B, NIU S L, ZHAO G J, PENG Y, LI J H, LU C M, CRITTENDEN J. Cerium-tungsten oxides supported on activated red mud for the selective catalytic reduction of NOx[EB/OL]. http://creativecommons.org/licenses/by-nc-nd/4.0/, 2021-1-7/2021-3-14. [16] ZHAN S H, ZHANG H, ZHANG Y, SHI Q, LI Y, LI X J. Efficient NH3-SCR removal of NOx with highly ordered mesoporous WO3(χ)-CeO2 at low temperatures[J]. Appl Catal B: Environ,2017,203:199−209. doi: 10.1016/j.apcatb.2016.10.010 [17] ZHAO G Y, LI M M, WANG L Y, WANG D Z, LIANG J S, XUE G. Environmentally-friendly tourmaline modified CeMnFeOx catalysts for low-temperature selective catalytic reduction of NOx with NH3[J]. Catal Today,2020,355:385−396. doi: 10.1016/j.cattod.2019.08.018 [18] LIU S S, WANG H, WEI Y, ZHANG R D. Core-shell structure effect on CeO2 and TiO2 supported WO3 for the NH3-SCR process[J]. Mol Catal,2020,485:110822. doi: 10.1016/j.mcat.2020.110822 [19] 李永龙. 三维有序大孔复合金属氧化物催化剂的制备及用于船舶尾气脱硝性能研究[D]. 南昌: 南昌大学, 2020.LI Yong-long. Synthesis and application of three-dimensionally ordered macroporous mixed metal oxide catalysts for removing NOx from marine diesel engine exhaust[D]. Nanchang: Nanchang university, 2020. [20] LI X, LI J H, PENG Y, CHANG H Z, ZHANG T, ZHAO S, SI W Z, HAO J M. Mechanism of arsenic poisoning on SCR catalyst of CeW/Ti and its novel efficient regeneration method with hydrogen[J]. Appl Catal B: Environ,2016,284:246−257. [21] SHAN W P, LIU F D, HE H, SHI X Y, ZHANG C B. A superior Ce-W-Ti mixed oxide catalyst for the selective catalytic reduction of NOx with NH3[J]. Appl Catal B: Environ,2012,115–116:100−106. [22] SHAN W P, LIU F D, HE H, SHI X Y, ZHANG C B. Novel cerium-tungsten mixed oxide catalyst for the selective catalytic reduction of NOx with NH3[J]. Chem Commun,2011,47:8046−8048. doi: 10.1039/c1cc12168e [23] LIAN Z H, LIU F D, SHAN W P, HE H. Improvement of Nb doping on SO2 resistance of VOx/CeO2 catalyst for the selective catalytic reduction of NOx with NH3[J]. J Phy Chem,2020,40(6):24−28. [24] YANG G S, TAKEI T, YANAGIDA S, KUMADA N. Hexagonal tungsten oxide-polyaniline hybrid electrodes for high-performance energy storage[J]. Appl Surf Sci,2019,498:14387. [25] CHAVHAN M P, LU C H, SOM S. Urea and surfactant assisted hydrothermal growth of ceria nanoparticles[J]. Colloids Surf A,2020,601:124944. doi: 10.1016/j.colsurfa.2020.124944 [26] 孙红. 蜂窝状金属丝网催化剂的制备及其贫燃条件下选择催化还原的研究[D]. 大连: 大连理工大学, 2007.SUN hong. Preparation of wire-mesh honeycomb catalysts and selective catalytic reduction of NOx with propene under lean-burn conditions[D]. Dalian: Dalian university of Technology, 2007. [27] OSTACHAVICIUTE S, ŠULCIUTE A, VALATKA E. The morphology and electrochemical properties of WO3 and Se-WO3 films modified with cobalt-based oxygen evolution catalyst[J]. Mater Sci Eng B,2020,260:11463. [28] DRONOVA M, LAIR V, VERMAUT P, RINGUEDE A, AN V. Study of ceria thin films prepared via electrochemical deposition: Role of selected electrochemical parameters on growth kinetics[J]. Thin Solid Films,2019,693:137674. [29] WADHENE R, LAMOUCHI A, ASSAKERI B, NACEUR J B, MARTINEZ-HUERTA M V, CHTOUROU R. Electrodeposition of Cu2ZnSnS4 thin films onto TiO2 Nanorods for photocatalytic application: Effect of deposition time[J]. Inorg Chem Commun,2020,122(4):108298. [30] 赵一铭. WO3/贵金属复合薄膜的光电性能研究[D]. 长春: 长春理工大学, 2020.ZHAO Yi-ming. The photoelectric properties of WO3/noble metal composite films[D]. Changchun: Changchun University of Science and Technology, 2020. [31] WAHLBERG A, PETTERSSON L J, KARIN B. Preparation, evaluation and characterization of copper catalysts for ethanol fuelled diesel engines[J]. Appl Catal B: Environ,1999,23(4):271−281. doi: 10.1016/S0926-3373(99)00083-1 [32] MA Z, WENG D, WU X D, FENG Y, SI Z C, WENG D. Effects of WOx modification on the activity, adsorption and redox properties of CeO2 catalyst for NOx reduction with ammonia[J]. J Environ Sci,2012,24(7):1305−1316. doi: 10.1016/S1001-0742(11)60925-X [33] SUN W B, LI X Y, ZHAO Q D, MU J C, CHEN J H. Fe-Mn mixed oxide catalysts synthesized by one-step urea precipitation method for the selective catalytic reduction of NOx with NH3 at low temperatures[J]. Catal Lett,2018,148:227−234. doi: 10.1007/s10562-017-2209-z [34] CAMACHO-RIOS M L, CRISTOBAL-GARCI J D, GUTIERREZ D L, ESTRADA-GUEL I, HERRERA-PEREZD G, PINON-ESPITIA M, MARTINEZ-SANCHEZ R. The influence of chelating agents on cerium oxide decorated on graphite synthesized by the hydrothermal route[J]. Ceram Int,2020,46(11):18791−18799. doi: 10.1016/j.ceramint.2020.04.197 [35] LI C X, SHEN M Q, WANG J Q, WANG J, ZHAI Y P. New insights into the role of WO3 in improved activity and ammonium bisulfate resistance for NO reduction with NH3 over V-W/Ce/Ti catalyst[J]. Ind Eng Chem Res,2020,40(6):24−28. [36] LIU C X, CHEN L, LI J H, MA L, ARANDIYAN H, DU Y, XU J Y, HAO J M. Enhancement of Activity and Sulfur Resistance of CeO2 Supported on TiO2-SiO2 for the selective catalytic reduction of NO by NH3[J]. Environ Sci Technol,2012,46:6182−6189. doi: 10.1021/es3001773 [37] KWON D W, HONG S C. Promotional effect of tungsten-doped CeO2/TiO2 for selective catalytic reduction of NOx with ammonia[J]. Appl Surf Sci,2015,356:181−190. doi: 10.1016/j.apsusc.2015.08.073 [38] XIE W W, ZHANG G D, MU B, TANG Z C, ZHANG J Y. The promoting effect of palygorskite on CeO2-WO3-TiO2 catalyst for the selective catalytic reduction of NOx with NH3[J]. Appl Clay Sci,2020,192:10564. [39] 刘一军, 黄剑锋, 王秀峰, 朱辉. 沉积时间对电沉积ZnS薄膜的影响[J]. 人工晶体学报,2010,39:69−72.LIU Yi-jun, HUANG Jian-feng, WANG Xiu-feng, ZHU Hui. Effect of deposition time on electrodeposited ZnS thin films[J]. J Synthetic Crystals,2010,39:69−72. [40] 张道军, 马子然, 孙琦, 徐文强, 李永龙, 竹涛, 王宝冬. 选择催化还原(SCR)反应机理研究进展[J]. 化工进展,2019,38(4):1611−1623.ZHANG Dao-jun, MA Zi-ran, SUN Qi, XU Wen-qiang, LI Yong-long, ZHU Tao, WANG Bao-dong. Progress in the mechanism of selective catalytic reduction (SCR) reaction[J]. Chem Ind Eng Prog,2019,38(4):1611−1623. [41] YANG S J, WANG C Z, MA L, PENG Y, QU Z, YAN N Q, CHEN J H, CHANG H Z, LI J H. Substitution of WO3 in V2O5/WO3-TiO2 by Fe2O3 for selective catalytic reduction of NO with NH3[EB/OL]. http://dx. doi.org/10.1039/c2cy20383a,2012-6-6/2012-8-31. [42] NAM K B, KWON D W, HONG S C. DRIFT study on promotion effects of tungsten-modified Mn/Ce/Ti catalysts for the SCR reaction at low-temperature[J]. Appl Catal A: Gen,2017,542:55−62. doi: 10.1016/j.apcata.2017.05.017 [43] WU Z B, JIANG B Q, LIU Y, WANG H Q, JIN R B. DRIFT study of manganese/titania-based catalysts for low-temperature selective catalytic reduction of NO with NH3[J]. Environ Sci Tech,2007,41:5812−5817. doi: 10.1021/es0700350 [44] PENG Y, LI J H, CHEN L, CHEN J H, HAN J, HANG H, HAN W. Alkali metal poisoning of a CeO2-WO3 catalyst used in the selective catalytic reduction of NOx with NH3: An experimental and theoretical study[J]. Environ Sci Technol,2012,46:2864−286. doi: 10.1021/es203619w