摘要
用浸渍法制备了A l2O3,S iO2和MgO等不同性质载体负载的锰氧化物催化剂,考察了其对CO氧化反应的性能,并用XRD、XPS、TPR和XAFS等方法对催化剂进行了详细表征.活性测试结果表明,不同载体负载的样品的活性次序为:MnOx/A l2O3>MnOx/MgO>MnOx/S iO2.XRD结果表明,在S iO2和A l2O3上,负载量为15%的催化剂中没有检测到Mn氧化物的衍射峰,说明Mn物种在载体表面分散性很好,而在MgO上检测到Mg6MnO8物种.XAFS等表征结果表明,A l2O3和S iO2负载的样品中Mn主要以高分散的Mn2O3形式存在,MgO负载的样品中Mn的分散性相对较差,且与载体发生强相互作用.结合XPS和TPR结果,Mn氧化物与载体相互作用强弱的顺序为:MnOx/MgO>MnOx/A l2O3>MnOx/S iO2.负载Mn氧化物催化剂的活性与分散度没有直接对应关系,而是显示了明显的载体效应.
The catalysts of manganese oxides supported on Al2O3, SiO2 and MgO were prepared by impregnation method. Their catalytic behavior for CO oxidation was evaluated. The techniques of XRD, XPS, TPR and XAFS （XANES and EXAFS） were employed for catalyst characterization. The results of activity measurement indicate that for CO oxidation, the activity sequence is MnOx/Al2O3 〉 MnOx/MgO 〉 MnOx/SiO2. The XRD results show that the manganese oxide species are highly dispersed on Al2O3 and SiO2 supports, no any peaks of Mn species were detected, even though the loading of Mn reaches 15%. While on MgO support, a stable complex oxide phase, namely Mg6MnOs, was detected by XRD. The results of XAFS analysis suggest that on Al2O3 and SiO2 supports manganese exists mainly in the form of highly dispersed Mn2O3. The dispersion of manganese oxide on MgO is not as good as those on Al2O3 and SiO2. Combining the results of XPS and TPR, the extent for the metal-support interaction on different supports follows the sequence： MnOx/MgO 〉 MnOx/Al2O3 〉 MnOx/SiO2, which is different from their activity sequence. Therefore, it is concluded that the oxidation activity of the supported manganese catalysts does not depend on the dispersion of Mn species, and that a typical support effect for manganese oxide catalysts is exhibited.
出处
《分子催化》
EI
CAS
CSCD
北大核心
2006年第4期300-305,共6页
Journal of Molecular Catalysis(China)
基金
国家博士点专项基金(20040056028)
天津市自然科学基金(05YFJMJC09700)
天津大学"985教育振兴行动计划"资助项目
关键词
锰氧化物催化剂
XAFS
CO氧化
结构表征
载体效应
Manganese oxide catalysts
XAFS
CO oxidation
Structural characterization
Support effect
