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基金项目：国家高技术研究发展计划项目(No.2013AA065005);国家自然科学基金(No.50978103,51108187);中央高校基金科研业务费专项资金(No.2012ZM0041)

叶代启
1. 华南理工大学环境与能源学院, 广州 510006;2. 广东省大气环境与污染控制重点实验室, 广州 510006;3. 大气污染控制广东高校工程技术研究中心, 广州 510006

摘要：采用氧化还原共沉淀法制备了一系列不同Mn/Ce摩尔比的MnO_x-CeO₂复合氧化物,并考察其对甲苯的催化活性.结果表明,MnO_x-CeO₂复合氧化物的催化活性优于单一CeO₂,MnO_x(0.5)-CeO₂的催化活性最高,T₉₀=190 ℃.同时,借助BET、XRD、H₂-TPR、Raman和XPS等技术对催化剂的结构及表面活性物种等进行了表征.结果显示,Mn进入CeO₂的立方萤石结构后形成固溶体结构,使得MnO_x-CeO₂复合氧化物的比表面积增大,氧空位和晶格氧含量增多,表面氧流动性增强.最后,对MnO_x(0.5)-CeO₂进行XPS和不同激发波长的Raman测试.结果显示,Mn主要分布在催化剂表面,且主要以Mn⁴⁺形式存在,Ce主要分布在催化剂体相.研究表明,高度分散在催化剂表面的Mn⁴⁺在甲苯氧化中起主要作用,Ce⁴⁺并未直接参与反应,而是起到了电子传递的作用.

Abstract：A series of MnO_x-CeO₂ mixed oxide catalysts with various Mn/(Mn+Ce) mole ratios were prepared by redox-precipitation method and were tested for the catalytic oxidation of toluene. The results indicated that MnO_x-CeO₂ mixed oxide presented superior catalytic performance to pure CeO₂, and MnO_x(0.5)-CeO₂ exhibited the highest catalytic activity with T₉₀=190 ℃. The structure properties and surface reactive species of the catalysts were characterized by BET,XRD,H₂-TPR,XPS and Raman techniques. The characterization demonstrated that the MnO_x-CeO₂ catalysts have larger surface area, more oxygen vacancies and lattice oxygen species, as well as stronger surface oxygen mobilities after the introduction of manganese, which may be due to manganese entering CeO₂ lattice to form a solid solution with fluorite structure. In addition, the results of XPS and Raman with different excitation wavelength measurement of MnO_x(0.5)-CeO₂ indicated that manganese was mainly in the form of Mn⁴⁺ and distributed on the surface of the catalyst, and Ce was enriched in the bulk of the catalyst. The highly dispersion of surface Mn⁴⁺ was believed to play a crucial role in toluene oxidation. Ce⁴⁺was not involved in the reaction directly,but functioned as the electron transfer regent.