N2O decomposition over iron-containing zeolites prepared by different methods: a comparison of the reaction mechanism
N2O decomposition over iron-containing zeolites prepared by different methods: a comparison of the reaction mechanism
复制标题
DOI：
10.1016/j.jcat.2004.03.031
复制
发表时间：
2004-06
影响因子：
7.3
通讯作者：
G. Pirngruber;M. Luechinger;P. Roy;A. Cecchetto;P. Smirniotis
中科院分区：
文献类型：
--
作者：
G. Pirngruber;M. Luechinger;P. Roy;A. Cecchetto;P. Smirniotis
采用水相离子交换法、FeCl3升华法和水热合成法制备了含铁沸石，并在873 K下进行了水蒸汽改性。这些样品含有不同种类的铁物质，从孤立的铁原子到含有几个原子和稍大的低聚物的小簇。然而，所有样品在N2O分解的动力学行为是定性相似的。脉冲实验表明，存在一个缓慢和快速的O2生成途径，这是反应的限速步骤。两者都对整个活动做出了贡献。快速途径占主导地位的孤立的铁网站，而缓慢的途径的贡献增加与高铁负载量的催化剂。蒸汽导致团聚的铁簇，并增加了活动（有一个例外）。蒸汽样品有一个特殊的时间上流的行为。它们表现出非常高的初始活性，然后缓慢衰减到稳定状态。这表明，蒸汽并不只是团聚的铁簇，但定性地改变了活性位点的性质。
Iron-containing zeolites were prepared by aqueous ion exchange, sublimation of FeCl3, or hydrothermal synthesis and were modified by steaming at 873 K. The samples contained different kinds of iron species ranging from isolated iron atoms to small clusters that contain a few atoms and somewhat larger oligomers. Yet, the dynamic behavior of all samples in N2O decomposition was qualitatively similar. Pulse experiments showed that a slow and fast pathway of O2formation, which is the rate-limiting step of the reaction, exists. Both contributed to the overall activity. The fast pathway dominated on isolated iron sites, whereas the contribution of the slow pathway increased on catalysts with high iron loadings. Steaming led to an agglomeration of the iron clusters and increased the activity (with one exception). The steamed samples had a peculiar time-on-stream behavior. They exhibited a very high initial activity and then slowly decayed to steady state. This indicates that steaming did not merely agglomerate the iron clusters, but qualitatively changed the nature of the active sites.