Effect of nano-coating on the catalytic combustion performance of perovskite-based monolithic catalysts for VOCs
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摘要: 以堇青石蜂窝陶瓷为基体,纳米氧化物(CeO2、γ-Al2O3、SiO2)为涂层载体,通过悬浮涂渍法和溶胶-凝胶法两步制得LaCoO3/CeO2/堇青石、LaCoO3/γ-Al2O3/堇青石、LaCoO3/SiO2/堇青石三种整体式催化剂。通过XRD、SEM、XPS、H2-TPR、UT和N2 吸附-脱附等技术,对样品的物相、微观形貌、元素成分、氧化还原性、黏附强度、质构性能进行了表征分析。通过催化燃烧VOCs实验评价了整体式催化剂的催化活性、高温稳定性、停机/重启循环稳定性和水汽稳定性。实验结果表明,三种催化剂均显示出良好的催化活性和稳定性,涂层类型会造成催化性能的差异。其中,LaCoO3/CeO2/堇青石催化剂表现出最优的性能。当甲苯体积分数为0.1%、空速为18000 mL/(g·h)时,其达到50%和90%转化率时温度分别为158和214 ℃;在转化率为90%的温度下经历72 h的稳定性测试(高温、停启循环、水汽)后,甲苯转换率仅降低7%。表征结果显示,CeO2纳米涂层有助于形成多孔蓬松结构的催化层, 同时催化剂具有较高的吸附氧比例、较强的低温还原性以及良好的黏附性。Abstract: The LaCoO3/CeO2/cordierite, LaCoO3/γ-Al2O3/cordierite, LaCoO3/SiO2/cordierite monolithic catalysts were synthesized by the suspension coating method and sol-gel method in two steps using cordierite honeycomb ceramic as the substrate and nano-oxides (CeO2, γ-Al2O3, SiO2) as the coating carrier. The phase, microscopic morphology, element composition, redox property, adhesion strength, and texture properties of the samples were characterized and analyzed by XRD, SEM, XPS, H2-TPR, UT and N2 adsorption-desorption techniques. The catalytic activity, high-temperature stability, shutdown/restart cycle stability, and water vapor stability of the monolithic catalyst were evaluated through the catalytic combustion performance of VOCs. Experimental results show that three catalysts exhibit good catalytic activity and stability, and the type of coating can cause a difference in catalytic performance. Among three cattalysts, the LaCoO3/CeO2/cordierite catalyst has the best performance. When the volume fraction of toluene is 0.1% and the space velocity is 18000 mL/(g·h), the tempereratures for the conversion rates of 50% and 90% are 158 and 214 ℃, respectively. The toluene conversion rate is only reduced by 7% after 72 h of stability testing (high temperature, stop/restart cycle, water vapor). Characterization results show that the CeO2 nano-coating helps to form a catalytic layer with a porous and fluffy structure, which makes the catalyst have a higher ratio of adsorbed oxygen, strong low-temperature reducibility and good adhesion.
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Key words:
- coating /
- monolithic catalyst /
- catalytic combustion /
- perovskite /
- VOCs
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表 1 样品的质构性质
Table 1 Textural properties of the samples
Sample $S_{{\rm{BET}}}^{\rm{a}} $/(m2·g−1) $v_{ {\rm{p} } }^{\rm{b} }$/(cm3·g−1) $D_{{\rm{p}}}^{\rm{c}} $/nm Cordierite 1.2 0.013 7.2 Al2O3 138.1 0.771 11.1 γ-Al2O3/cordierite 11.7 0.068 13.9 LaCoO3/γ-Al2O3/cordierite 6.9 0.042 16.9 CeO2 48.7 0.198 81.3 CeO2/cordierite 3.3 0.016 10.0 LaCoO3/CeO2/cordierite 2.3 0.016 13.4 SiO2 187.0 0.060 50.0 SiO2/cordierite 11.9 0.080 21.5 LaCoO3/SiO2/cordierite 5.7 0.032 16.0 a: surface area, calculated by BET method, b: total pore volume, determined from the amount adsorbed at p/p0 = 0.99, c: average pore diameter, determined by BJH method of the desorption branch 表 2 XPS表征参数
Table 2 XPS characterization parameters
Sample Binding energy/eV Co/La Oads/Ototal La 3d5/2 La 3d3/2 Co 2p3/2 Co 2p1/2 Oads 1s Olatt 1s Ce 3d/Al 2p/Si 2p LaCoO3/γ-Al2O3 834.4/838 851.2/854.9 780.3 795.6 529.3 531.4 74.3 0.41 0.54 LaCoO3/CeO2 834.3/837.8 850.9/854.8 780.2 795.4 529.3 531.4 882.5 0.52 0.64 LaCoO3/SiO2 834.5/837.9 851.1/854.9 780.2 795.4 529.5 531.0 103.2 0.38 0.24 LaCoO3 833.7/837.5 850.6/854.4 779.9 795.2 529.0 531.1 − 0.55 0.651 表 3 本研究与其他文献中催化剂的甲苯催化燃烧性能比较
Table 3 Catalysts comparison of toluene catalytic combustion performance in this work and other literature
Catalyst Toluene GHSV T50/℃ T90/℃ Reference LaCoO3/CeO2/cordierite 0.1% 18000 mL/(g·h) 158 214 this work LaCoO3/γ-Al2O3/cordierite 180 219 LaCoO3/SiO2/cordierite 176 230 LaMnO3/TiO2 0.1% 18000 mL/(g·h) 278 303 [20] LaMnO3/YSZ 235 247 Co/La-CeO2/cordierite 0.1% 12000 mL/(g·h) 253 286 [38] Co/La-CeO2 229 258 0.05La-Co 0.1% 20000 mL/(g·h) 218 224 [39] LaMnO3-PL-2 0.1% 20000 mL/(g·h) 226 249 [40] 3DOM-La0.8Ce0.2MnO3/cordierite (600 ℃) 0.05% 6000 h−1 147 217 [19] 3DOM-La0.8Ce0.2MnO3/cordierite (700 ℃) 162 249 3DOM-La0.8Ce0.2MnO3/cordierite (800 ℃) 190 320 La0.75Sr0.25CoO3 0.05% 30000 h−1 212 228 [41] LaZn0.3Fe0.7O3 0.2% 15000 h−1 222 310 NiMnO3/Ce0.75Zr0.25O2/cordierit 500 mg/m3 15000 h−1 209 235 [42] 20%La0.8Ce0.2MnO3/ZSM-5 3 mg/L 20000 h−1 206 285 [43] -
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