Evolution of Defects in the Bulk Structure of MoO3 during Catalytic Oxidation of Propene
Evolution of Defects in the Bulk Structure of MoO3 during Catalytic Oxidation of Propene
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丙烯催化氧化过程中MoO3本体结构缺陷的演变
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
F. Girgsdies
中科院分区：
文献类型：
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作者：
T. Ressler;J. Wienold;R. Jentoft;F. Girgsdies
利用原位x射线吸收光谱和x射线衍射研究了丙烯氧化条件下MoO3体结构中特征缺陷的演变。在273 K ~ 773 K，丙烯与氧的比例为1:1 ~ 1:5的条件下，XRD检测到的结晶相只有正交MoO3。MoO3存在时丙烯与氧反应的起始温度与MoO3在He、H2和丙烯中开始还原的温度一致（≈620 K）。在720 K以下的温度下，与所用的气氛无关，观察到MoO3的部分还原导致α-MoO3层结构中形成“Mo18O52”型缺陷。在720 K以上的温度下，在氧气或氧化气氛下，“Mo18O52”型缺陷被再氧化为MoO3。显然，在720 K以下的部分氧化条件下，具有催化活性的氧化钼相并不具有正交α-MoO3的理想层状结构。结果清楚地表明，在所使用的反应条件下，对非均相催化剂进行体结构研究的必要性和潜力。整体结构，特别是材料中缺陷的类型和数量（“真实”结构）对催化性能有很大影响。因此，为了合理设计最具活性的多相催化剂，既需要详细了解表面的结构和反应，也需要仔细考虑体的结构、缺陷和反应。（©Wiley-VCH Verlag GmbH & Co. KGaA，德国Weinheim 69451, 2003）
The evolution of characteristic defects in the bulk structure of MoO3 under propene oxidation conditions was investigated by in situ X-ray absorption spectroscopy and X-ray diffraction. Under the reaction conditions employed (273 K to 773 K, and propene to oxygen ratios from 1:1 to 1:5), orthorhombic MoO3 remains the only crystalline phase detected by XRD. The starting temperature for the reaction of propene and oxygen in the presence of MoO3 coincides with the temperature at which reduction of MoO3 begins in He, H2 and propene (≈ 620 K). At temperatures below 720 K, and independent of the atmosphere used, partial reduction of MoO3 is observed resulting in the formation of “Mo18O52” type defects in the layer structure of α-MoO3. At temperatures above 720 K, and under oxygen or in an oxidizing atmosphere, the “Mo18O52” type defects are reoxidized to MoO3. Evidently, the catalytically active molybdenum oxide phase develops under partial oxidation conditions at temperatures below 720 K, and does not possess the undisturbed ideal layer structure of orthorhombic α-MoO3. The results presented clearly show the necessity and the potential for bulk structural investigations of heterogeneous catalysts under the reaction conditions used. The bulk structure, and particularly the type and number of defects in the material (“real” structure) considerably affect the catalytic properties. Hence, in order to rationally design a most active heterogeneous catalyst, both the structure and reactions of the surface, and the structure, defects, and reactions of the bulk need to be known in detail, and carefully considered. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)