Effect of preparation methods on the structure and catalytic performance of CeO2 for toluene combustion
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摘要: 采用溶胶-凝胶-超临界干燥法、水热法及共沉淀法分别合成了氧化铈气凝胶(CeO2-A)、纳米棒(CeO2-R)和纳米片(CeO2-F)。考察了不同形貌氧化铈的催化燃烧甲苯性能,通过多种方法分析表征了氧化铈样品的微观结构,讨论了不同方法制得的CeO2形貌结构对催化性能的影响。结果表明,CeO2-R和CeO2-F比表面积较低,并且仅暴露(111)晶面,催化燃烧甲苯活性较低。CeO2-A具有高比表面积和丰富的孔道结构,有利于反应物分子的吸附,而且同时暴露(100)和(111)两种活性晶面,增加了氧空位浓度(Osur/Olatt = 0.25)。此外,CeO2-A由于表面晶格氧移动性较强,有利于Ce3+/Ce4+氧化还原的循环,加快甲苯深度氧化反应的进行。因此,CeO2-A具有更加优异的催化燃烧甲苯活性,t50和t90分别为223 和239 ℃,这主要归因于其大比表面积、高暴露活性晶面以及强晶格氧迁移性。Abstract: CeO2 aerogel (CeO2-A), nanorod (CeO2-R) and nanoflake (CeO2-F) were prepared via sol-gel, hydrothermal and coprecipitation methods, respectively. The effect of morphology and structure of CeO2 on the catalytic performance in toluene combustion reaction was investigated based on structure analysis provided by characterization. The results revealed that the activity of both CeO2-R and CeO2-F was inferior to that of CeO2-A, due to CeO2-R and CeO2-F smaller specific surface area only exposed (111) crystal plane dominantly detected from their TEM images. While, the CeO2-A had a larger specific surface area and more exposed (111) and (100) facet, which contributed to exposure and formation of more oxygen vacancies and further to the adsorption of more gaseous oxygen. In addition, highly mobile lattice oxygen was another critical factor for influencing the catalytic performance of CeO2, which was beneficial to the redox cycle of Ce3+/Ce4+ and could further accelerate the toluene combustion. As a result, the CeO2-A catalyst exhibited the superior performance in toluene catalytic combustion with t50 of 223℃ and t90 of 239℃, respectively, owing to the larger specific surface area, higher exposure of reactive crystal plane and stronger mobility of lattice oxygen.
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Key words:
- ceria morphology /
- catalytic combustion /
- preparation method /
- crystal face /
- oxygen vacancy
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表 1 不同形貌氧化铈催化剂的织构性质
Table 1 Structural properties of CeO2 catalysts with different morphologies
Catalyst SBETa/
(m2·g−1)vtotalb/
(cm3·g−1)Average pore
diameterc d/nmCrystallite
sizesd d/nmCeO2-A 144.0 0.60 15.6 10.6 CeO2-R 99.7 0.20 5.3 16.7 CeO2-F 18.4 0.03 6.0 15.5 a: specific surface area was calculated using Brumauer-Emmett-Teller (BET) modelling;
b: total pore volume was measured by single point adsorption at p/p0 = 0.99;
c: most probable apertures calculated by BJH method;
d: calculated by the Scherrer equation applied to the CeO2 (111) peak表 2 不同形貌的氧化铈催化剂TPR表征
Table 2 TPR results of CeO2 catalysts with different morphologies
Catalyst Started reduction
temperature t/℃H2 consumption
below 600 ℃CeO2-A 281 5020 CeO2-R 313 4292 CeO2-F 328 3100 表 3 不同形貌氧化铈催化剂的表面元素分析
Table 3 Surface element analysis of CeO2 catalysts with different morphologies
Catalyst Ce3+/Ce4+ Osur/Olatt Ce3+/Ce CeO2-A 0.25 0.25 0.20 CeO2-R 0.23 0.22 0.19 CeO2-F 0.16 0.20 0.14 表 4 不同形貌氧化铈催化剂对甲苯燃烧的活性评价
Table 4 Catalytic activity of different morphologies CeO2 catalysts for oxidation of toluene
Sample Preparation method Toluene
concentration/
(g·L−1)WHSV/
(mL·g−1·h−1)t50/
℃t90/
℃CeO2-A sol-gel 1 78000 223 239 CeO2-R hydrothermal 1 78000 233 250 CeO2-F precipitation 1 78000 236 259 -
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