-
挥发性有机化合物(volatile organic compounds,VOCs)是一类重要大气污染物,与大气颗粒物、SO2、NOx同样为研究热点。世界卫生组织将饱和蒸汽压超过133.32 Pa、常压沸点为50~260 ℃的有机物定义为VOCs[1-2]。目前,VOCs处理技术包括吸附[3]、冷凝、热焚烧、催化燃烧、光催化[4]、等离子体催化降解技术[5]等。催化燃烧技术具有处理效率高、能耗低、无二次污染、适用范围广等优点,在VOCs治理领域具有广阔应用前景[6-10]。
研制高效稳定的催化剂是催化燃烧技术发展的核心[11-12]。常见的催化剂有贵金属和非贵金属氧化物催化剂[13-14]。常见的负载制备贵金属催化剂,一般以Pd、Pt、Rh、Pb等为活性组分,对于多种VOCs的催化燃烧具有较高活性[15-16]。钌(Ru) 作为铂系金属元素中最后被发现的金属元素,其活性较高,化学稳定性较强,低温催化效果较好,且Ru的价格相较于其他贵金属更为低廉。Ru与Au、Pt、Pd的催化活性差别不大,且在对乙酸乙酯、丁烷、丙烯等VOCs的催化活性较强,产物基本为CO2和H2O[17-18]。由于贵金属本身价格较昂贵、易挥发且高温下容易烧结,工业上常用比表面积高的载体来提高贵金属催化剂活性组分与反应物分子的接触面积,从而提高催化剂的活性及稳定性[19]。而沸石分子筛是一类具有孔道结构的优良材料,具有丰富的微孔、较大的比表面积、优异的热稳定性和较多的酸位点,可为活性组分提供有效表面和适宜孔结构,以降低活性组分的团聚,并增强催化剂的机械强度,为适宜的催化剂载体材料[20-23]。CeO2具有立方萤石结构[24],Ce3+和Ce4+间转换表现出独特的储氧能力和表面还原性,能有效提高负载型贵金属催化剂的催化活性及稳定性[25-27]。金属相互作用对催化剂活性具有促进作用[28-29]。王玉亭等[30]用Ce改性V2O5/TiO2催化剂发现投加浓度质量分数为10%的Ce可令催化剂在低浓度邻二甲苯的条件下有较好的氧化效率,T90%为380 ℃;SCIRÈ等[31]发现,Au/CeO2催化剂催化燃烧甲苯比CeO2催化剂具有更好的催化活性,由于Au的存在能减弱催化剂表面的Ce—O键强度,提高了催化剂表面晶格氧的流动性和活性,促进了催化剂在VOCs燃烧的活性。因此,以氧化铈与贵金属作为活性组分的催化剂,因其优异的氧转移机制及金属相互作用而备受研究者青睐。
本研究选取贵金属Ru和稀土金属Ce作为活性组分,将其负载到分子筛上制备成RuCe/ZSM-5催化剂,考察钌铈催化剂催化燃烧甲苯的性能,并通过改变Ru的负载量,调整实验条件及工况,得到活性优、选择性好、稳定性高的钌铈双金属催化剂,以期为贵金属催化技术在VOCs治理领域的应用提供参考。
负载型钌铈催化剂的甲苯催化氧化性能
Catalytic oxidation of toluene by supported ruthenium-cerium catalyst
-
摘要: 以ZSM-5分子筛为载体,采用浸渍法制备了RuCe/ZSM-5催化剂,研究了催化剂在不同Ru负载量、空速、反应温度、甲苯浓度下对甲苯的催化氧化性能,并探讨了催化剂的CO2选择性及稳定性。结果表明:Ru的负载可提升CeO2(20)/ZSM-5催化剂催化甲苯使其降解成高浓度CO2的能力;Ru(1.0)/CZ催化剂表现出优异的低温催化性能、CO2选择性及稳定性,在210 ℃条件时即可转化90%的甲苯,且CO2选择性达到90%以上。本研究制备的催化剂在较大空速及甲苯浓度范围内对甲苯具有优越的低温催化性能,未来可应用于VOC的工业化处理应用中。
-
关键词:
- RuCe/ZSM-5 /
- 挥发性有机物 /
- 甲苯 /
- 催化氧化
Abstract: RuCe/ZSM-5 catalysts were prepared by impregnation method with ZSM-5 molecular sieve as support. The catalytic oxidation performances of the catalyst of toluene were studied under different Ru loadings, space velocities, reaction temperatures, toluene concentrations. The CO2 selectivity and stability were also discussed. It was indicated that Ru doping could improve the catalytic ability of CeO2(20)/ZSM-5 for toluene degradation into high concentration of CO2. The Ru(1.0)/CZ catalyst exhibited excellent low-temperature catalytic performance, CO2 selectivity and stability. 90% toluence can be converted at 210℃, and the CO2 selectivity reached more than 90%. The catalyst prepared in this study showed superior catalytic oxidation performance to toluene at low temperature in a large space velocity and and toluene concentration range, and can be potentially used in processing VOC industrial applications.-
Key words:
- RuCe/ZSM-5 /
- volatile organic compounds /
- toluene /
- catalytic oxidation
-
表 1 ZSM-5分子筛、CeO2(20)/ZSM-5和Ru/CZ系列催化剂的物理结构参数
Table 1. Physical structure parameters of ZSM-5 , CeO2(20)/ZSM-5, Ru(0.5)/CZ, Ru(1.0)/CZ, Ru(1.5)/CZ
样品名称 比表面积/(m2·g−1) 孔体积/(cm3·g−1) 平均孔径/nm ZSM-5 409.578 0.061 1 3.226 5 CeO2(20)/ZSM-5 404.820 0.051 8 3.165 5 Ru(0.5)/CZ 339.733 0.098 2 4.506 5 Ru(1.0)/CZ 326.942 0.103 0 5.175 2 Ru(1.5)/CZ 332.675 0.088 6 4.621 5 表 2 不同催化剂催化燃烧甲苯的T50%和T90%
Table 2. The T50% and T90% of toluene by catalytic combustion of different catalysts
催化剂名称 T50%/℃ T90%/℃ ZSM-5 — — CeO2(20)/ZSM-5 136 - Ru(0.5)/CZ 225 260 Ru(1.0)/CZ 210 240 Ru(1.5)/CZ 245 283 注:T50%、T90%分别代表甲苯转化率为50%、90%时的温度。 表 3 不同甲苯浓度下Ru(1.0)/CZ催化剂催化燃烧甲苯的T50%和T90%
Table 3. The T50% and T90% of toluene by catalytic combustion of Ru(1.0)/CZ catalyst with different toluene concentrations
甲苯浓度/(mg·m−3) T50%/℃ T90%/℃ 205.5 125 210 411 210 240 822 250 280 1 233 252 281 -
[1] GUO Y, WEN M, LI G, et al. Recent advances in VOC elimination by catalytic oxidation technology onto various nanoparticles catalysts: A critical review[J]. Applied Catalysis B:Environmental, 2021, 281: 119447. doi: 10.1016/j.apcatb.2020.119447 [2] YANG C, MIAO G, PI Y, et al. Abatement of various types of VOCs by adsorption/catalytic oxidation: A review[J]. Chemical Engineering Journal, 2019, 370: 1128-1153. doi: 10.1016/j.cej.2019.03.232 [3] ZHANG X, GAO B, CREAMER A E, et al. Adsorption of VOCs onto engineered carbon materials: A review[J]. Journal of Hazardous Materials, 2017, 338: 102-123. doi: 10.1016/j.jhazmat.2017.05.013 [4] LI J, YU E, CAI S, et al. Noble metal free, CeO2/LaMnO3 hybrid achieving efficient photo-thermal catalytic decomposition of volatile organic compounds under IR light[J]. Applied Catalysis B:Environmental, 2019, 240: 141-152. doi: 10.1016/j.apcatb.2018.08.069 [5] WANG H, CHEN S, WANG Z, et al. A novel hybrid Bi2MoO6-MnO2 catalysts with the superior plasma induced pseudo photocatalytic-catalytic performance for ethyl acetate degradation[J]. Applied Catalysis B:Environmental, 2019, 254: 339-350. doi: 10.1016/j.apcatb.2019.05.018 [6] WANG F, DAI H, DENG J, et al. Manganese Oxides with rod-, wire-, tube-, and flower-Like Morphologies: Highly effective catalysts for the removal of Toluene[J]. Environmental Science & Technology, 2012, 46(7): 4034-4041. [7] IKHLAQ A, KASPRZYK-HORDERN B. Catalytic ozonation of chlorinated VOCs on ZSM-5 zeolites and alumina: Formation of chlorides[J]. Applied Catalysis B:Environmental, 2017, 200: 274-282. doi: 10.1016/j.apcatb.2016.07.019 [8] LUO S, GAO L, WEI Z, et al. Kinetic and mechanistic aspects of hydroxyl radical-mediated degradation of naproxen and reaction intermediates[J]. Water Research, 2018, 137: 233-241. doi: 10.1016/j.watres.2018.03.002 [9] LUO S, WEI Z, SPINNEY R, et al. UV direct photolysis of sulfamethoxazole and ibuprofen: An experimental and modelling study[J]. Journal of Hazardous Materials, 2018, 343: 132-139. doi: 10.1016/j.jhazmat.2017.09.019 [10] LIU L, LI J, ZHANG H, et al. In situ fabrication of highly active γ-MnO2/SmMnO3 catalyst for deep catalytic oxidation of gaseous benzene, ethylbenzene, toluene, and o-xylene[J]. Journal of Hazardous Materials, 2019, 362: 178-186. doi: 10.1016/j.jhazmat.2018.09.012 [11] FENG S, LIU J, GAO B. Synergistic mechanism of Cu-Mn-Ce oxides in mesoporous ceramic base catalyst for VOCs microwave catalytic combustion[J]. Chemical Engineering Journal, 2022, 429: 132302. doi: 10.1016/j.cej.2021.132302 [12] ALI S, WU X, ZUHRA Z, et al. Cu-Mn-Ce mixed oxides catalysts for soot oxidation and their mechanistic chemistry[J]. Applied Surface Science, 2020, 512: 145602. doi: 10.1016/j.apsusc.2020.145602 [13] JIANG Y, GAO J, ZHANG Q, et al. Enhanced oxygen vacancies to improve ethyl acetate oxidation over MnOx-CeO2 catalyst derived from MOF template[J]. Chemical Engineering Journal, 2019, 371: 78-87. doi: 10.1016/j.cej.2019.03.233 [14] LU H, KONG X, HUANG H, et al. Cu-Mn-Ce ternary mixed-oxide catalysts for catalytic combustion of toluene[J]. Journal of Environmental Sciences, 2015, 32: 102-107. doi: 10.1016/j.jes.2014.11.015 [15] GAO P, WANG A, WANG X, et al. Synthesis of highly ordered Ir-containing mesoporous carbon materials by organic-organic self-assembly[J]. Chemistry of Materials, 2008, 20(5): 1881-1888. doi: 10.1021/cm702815e [16] GUO J, LIN C, JIANG C, et al. Review on noble metal-based catalysts for formaldehyde oxidation at room temperature[J]. Applied Surface Science, 2019, 475: 237-255. doi: 10.1016/j.apsusc.2018.12.238 [17] OKAL J, ZAWADZKI M. Catalytic combustion of butane on Ru/γ-Al2O3 catalysts[J]. Applied Catalysis B:Environmental, 2009, 89(1-2): 22-32. doi: 10.1016/j.apcatb.2008.11.024 [18] DAI Q, BAI S, WANG J, et al. The effect of TiO2 doping on catalytic performances of Ru/CeO2 catalysts during catalytic combustion of chlorobenzene[J]. Applied Catalysis B:Environmental, 2013, 142-143: 222-233. doi: 10.1016/j.apcatb.2013.05.026 [19] SANTOS V P, CARABINEIRO S A C, TAVARES P B, et al. Oxidation of CO, ethanol and toluene over TiO2 supported noble metal catalysts[J]. Applied Catalysis B:Environmental, 2010, 99(1-2): 198-205. doi: 10.1016/j.apcatb.2010.06.020 [20] CARRETTIN S, CONCEPCIÓN P, CORMA A, et al. Nanocrystalline CeO2 Increases the Activity of Au for CO Oxidation by Two Orders of Magnitude[J]. Angewandte Chemie International Edition, 2004, 43(19): 2538-2540. doi: 10.1002/anie.200353570 [21] GÓMEZ D M, GALVITA V V, GATICA J M, et al. TAP study of toluene total oxidation over a Co3O4/La-CeO2 catalyst with an application as a washcoat of cordierite honeycomb monoliths[J]. Physical chemistry chemical physics:PCCP, 2014, 16(23): 11447-11455. doi: 10.1039/C4CP00886C [22] 杨卜源, 佟丽华, 左树锋, 等. 添加铈对锰基催化剂的织构-结构及其氧化还原性能的影响[J]. 中国稀土学报. 2011, 29(4): 433-438. [23] DAI Q, WANG W, WANG X, et al. Sandwich-structured CeO2@ZSM-5 hybrid composites for catalytic oxidation of 1, 2-dichloroethane: An integrated solution to coking and chlorine poisoning deactivation[J]. Applied Catalysis B:Environmental, 2017, 203: 31-42. doi: 10.1016/j.apcatb.2016.10.009 [24] KHAN M E, KHAN M M, CHO M H. Ce3+-ion, surface oxygen vacancy, and visible light-induced photocatalytic dye degradation and photocapacitive performance of CeO2-Graphene nanostructures[J]. Scientific Reports, 2017, 7(1) [25] LIU X, ZENG J, WANG J, et al. Catalytic oxidation of methyl bromide using ruthenium-based catalysts[J]. Catalysis Science & Technology[J], 2016, 6(12): 4337-4344. [26] ZHAO J, XI W, TU C, et al. Catalytic oxidation of chlorinated VOCs over Ru/TixSn1-x catalysts[J]. Applied Catalysis B:Environmental, 2020, 263: 118237. doi: 10.1016/j.apcatb.2019.118237 [27] AOUAD S, ABI-AAD E, ABOUKAÏS A. Simultaneous oxidation of carbon black and volatile organic compounds over Ru/CeO2 catalysts[J]. Applied Catalysis B:Environmental, 2009, 88(3/4): 249-256. doi: 10.1016/j.apcatb.2008.10.002 [28] LIU C, XIAN H, JIANG Z, et al. Insight into the improvement effect of the Ce doping into the SnO2 catalyst for the catalytic combustion of methane[J]. Applied Catalysis B:Environmental, 2015, 176-177: 542-552. doi: 10.1016/j.apcatb.2015.04.042 [29] WANG J, ZHAO H, LIU X, et al. Study on the Catalytic Properties of Ru/TiO2 Catalysts for the Catalytic Oxidation of (Chloro)-Aromatics[J]. Catalysis Letters, 2019, 149(7): 2004-2014. doi: 10.1007/s10562-019-02802-x [30] PENG R, SUN X, LI S, et al. Shape effect of Pt/CeO2 catalysts on the catalytic oxidation of toluene[J]. Chemical Engineering Journal, 2016, 306: 1234-1246. doi: 10.1016/j.cej.2016.08.056 [31] SCIRÈ S, MINICÒ S, CRISAFULLI C, et al. Catalytic combustion of volatile organic compounds on gold/cerium oxide catalysts[J]. Applied Catalysis B:Environmental, 2003, 40(1): 43-49. doi: 10.1016/S0926-3373(02)00127-3