Oxidation state of Ce and ethanol-oxygen reaction of mesoporous titania-supported cerium oxide
Oxidation state of Ce and ethanol-oxygen reaction of mesoporous titania-supported cerium oxide
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DOI：
10.1016/j.micromeso.2008.03.009
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发表时间：
2008-12
影响因子：
5.2
通讯作者：
Y. Eguchi;Daiki Abe;H. Yoshitake
中科院分区：
文献类型：
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作者：
Y. Eguchi;Daiki Abe;H. Yoshitake
以Ce（NH 4）2（NO3）6和Ti（OiC 3 H7）4为前驱体，正十二胺为结构导向剂，采用共缩聚法制备了Ce-meso TiO 2。所得催化剂具有类似于介孔二氧化钛的高比表面积和窄孔径分布。通过XANES光谱研究了这些催化剂中Ce（III）的分布。虽然前驱体是四价的，但在以Ti/Ce=20和50的前驱体混合比制备的Ce-meso TiO 2催化剂中，Ce（III）的浓度分别接近100%和80%。在Ti/Ce=100的条件下制备的Ce-meso TiO 2，在473 ~ 673 K的温度范围内煅烧后，Ce-meso TiO 2的浓度从39%提高到69%。在不含正十二烷基胺的情况下制备的催化剂中，浓度仅为30%，这与P-25负载的Ce催化剂获得的值几乎相同。这些结果表明，低价变得稳定的介孔二氧化钛框架的存在下。在Ce/P-25催化剂上，乙醇-氧气反应生成了乙烯和二氧化碳。催化剂的活性和选择性对焙烧温度的依赖性很小，这与Ce（III）浓度恒定一致。Ce-meso TiO 2催化剂上的主要产物为乙醛和乙酸。乙酸的选择性随催化剂焙烧温度的升高而增加。三价铈的浓度与乙酸的生成有关。此外，利用拉曼光谱研究了Ce-meso TiO 2催化剂中Ti的局域结构。载体骨架的结构对乙醇-氧气反应的影响不大。
Cerium-incorporated mesoporous titania, Ce-meso TiO2, was prepared by the co-condensation method using Ce(NH4)2(NO3)6and Ti(OiC3H7)4as precursors and n-dodecylamine as a structural directing agent. The catalysts obtained had high surface area and narrow pore size distribution similar to mesoporous titania. The population of Ce(III) in these catalysts was investigated by XANES spectroscopy. Although the precursor was tetravalent, the concentration of Ce(III) was nearly 100% and 80% in Ce-meso TiO2catalysts prepared with the precursor mixing ratios of Ti/Ce=20 and 50, respectively. In Ce-meso TiO2prepared with Ti/Ce=100, the concentration increased from 39% to 69% after the calcination from 473K to 673K. In the catalyst prepared without n-dodecylamine, the concentration was only 30%, which is almost the same as the value obtained for P-25 supported Ce catalyst. These results imply that the lower valence becomes stable by the presence of mesoporous titania framework. In the ethanol–oxygen reaction, ethylene and carbon dioxide were formed on the Ce/P-25 catalyst. The activity and selectivity depended little on the calcination temperature of the catalyst, which concurs with the constant concentration of Ce(III). On the other hand, the main products on the Ce-meso TiO2catalyst were acetaldehyde and acetic acid. The selectivity for acetic acid increased with the calcination temperature of the catalyst. The concentration of trivalent Ce was correlated with the formation of acetic acid. Additionally, the local structure of Ti in the Ce-meso TiO2catalyst was investigated by Raman spectroscopy. The structure of the support framework had little influence on the ethanol–oxygen reaction.