Structural analysis of manganese oxides supported on SiO2 for benzene oxidation with ozone
Structural analysis of manganese oxides supported on SiO2 for benzene oxidation with ozone
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DOI：
10.1016/j.cattod.2014.05.018
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发表时间：
2015-03
期刊：
影响因子：
5.3
通讯作者：
H. Einaga;Shintaro Yamamoto;Nanako Maeda;Y. Teraoka
中科院分区：
文献类型：
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作者：
H. Einaga;Shintaro Yamamoto;Nanako Maeda;Y. Teraoka
采用硝酸锰和乙酸锰两种锰前驱体浸渍法制备了负载二氧化锰的锰氧化物（Mn/SiO2），并对苯进行了臭氧催化氧化。通过x射线衍射和x射线吸收测试对锰氧化物的结构进行了表征，并研究了锰氧化物的结构对其催化性能的影响。EXAFS研究表明，在催化剂制备中使用硝酸锰前驱体可以形成聚集的锰氧化物mn2o3，而使用醋酸锰前驱体可以形成高度分散的锰氧化物。在这两种情况下，结构不受锰负载水平的强烈影响。通过改变两种催化剂的锰负载，XANES区域吸收边估计的平均氧化态也几乎没有变化。在任意锰负载水平下，以乙酸锰为前驱体制备的Mn/SiO2催化剂在343 K下对臭氧氧化苯的催化活性均高于以硝酸锰为前驱体制备的催化剂，表明在SiO2上高度分散的锰氧化物比在SiO2上聚集的锰氧化物具有更高的活性。氧化锰结构对产物分布和臭氧利用效率影响不大。
Catalytic oxidation of benzene with ozone was carried out over SiO2-supported manganese oxides (Mn/SiO2) prepared by impregnation methods using two kinds of manganese precursors, manganese nitrate and acetate. The structure of manganese oxides were characterized by X-ray diffraction and X-ray absorption measurements and effects of the manganese oxide structures on their catalytic properties were investigated. EXAFS studies revealed that by using manganese nitrate precursor in catalyst preparation, aggregated manganese oxides Mn2O3were formed, whereas highly dispersed manganese oxides were formed when manganese acetate precursor was used. In both cases, the structures were not strongly affected by the manganese loading levels. The average oxidation state estimated form the absorption edge in the XANES region was also almost unchanged by changing the manganese loading for both catalysts. The catalytic activities of Mn/SiO2for benzene oxidation with ozone at 343 K were much higher for the catalysts prepared from manganese acetate precursors than those prepared from manganese nitrate precursor at any given manganese loading levels, indicating that highly dispersed manganese oxides on SiO2exhibited much higher activities for the reaction than the aggregated manganese oxides on SiO2. The product distribution and the efficiency for ozone utilization were not so much affected by the manganese oxide structures.