Origin and dynamics of oxygen storage/release in a Pt/ordered CeO2-ZrO2 catalyst studied by time-resolved XAFS analysis.
Origin and dynamics of oxygen storage/release in a Pt/ordered CeO2-ZrO2 catalyst studied by time-resolved XAFS analysis.
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DOI：
10.1002/anie.200703085
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发表时间：
2007-12
影响因子：
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通讯作者：
Takashi Yamamoto;A. Suzuki;Y. Nagai;Toshitaka Tanabe;Fei Dong;Y. Inada;M. Nomura;Mizuki Tada;Y. Iwasawa
中科院分区：
文献类型：
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作者：
Takashi Yamamoto;A. Suzuki;Y. Nagai;Toshitaka Tanabe;Fei Dong;Y. Inada;M. Nomura;Mizuki Tada;Y. Iwasawa
CeO2和铈基材料可以在缺氧条件下储存氧气，在缺氧条件下释放氧气，由于具有较高的氧储存/释放能力（OSC），被广泛用作汽车三元催化剂的促进剂。[1-8]丰田研究小组发现，在CeO2中加入锆阳离子可以显著提高盐含量和热稳定性。[9-11]最有效的CeO2-ZrO2 （CZ）材料是CeO2-ZrO2固溶体，其原子均匀有序的Ce和Zr离子排列在k-Ce2Zr2O8萤石相（见支持信息），[12]和盐含量随着阳离子排列均匀性的增加而增加。[7,13] pt促进的k-Ce2Zr2O8中89%的Ce离子在氧储存/释放过程中是有效的，而纯CeO2的OSC值较低（2%）。[7,12]在工作状态下，pt促进的k-Ce2Zr2O8在还原条件下转变为焦绿盐Ce2Zr2O7（见配套资料）。Ce2Zr2O7。Ce2Zr2O7在室温下长时间暴露于空气中会形成中间相，但没有关于Ce2Zr2O7形成的信息。5 .工作条件下的氧气储存/释放过程。通过Pt/CZ产物的时间分析、[15]时间分辨XRD、[16]和Pt/k-Ce2Zr2O8.[17]的氧释放热重分析等方法表征了CZ样品的氧储存/释放过程采用x射线吸收精细结构（XAFS）分析表征了Ce2Zr2O8相和k-Ce2Zr2O8相的OSC效率（52%），远低于k-Ce2Zr2O8相（89%）。[13,18]然而，以往的研究并没有关注CZ样品的实时动态，这可能是与盐含量功能最相关的。k-Ce2Zr2O8中Zr和Ce离子均处于+ 4氧化态和八坐标。[19]在焦绿石Ce2Zr2O7中，Ce离子的氧化态为+ 3，配位为8倍，Zr离子的氧化态为+ 4，配位为6倍。[19-21]在k-Ce2Zr2O8和Ce2Zr2O7之间的转化过程中，Zr位点改变了配位氧原子的数目而没有改变价，而Ce位点改变了配位氧原子的价而没有改变配位数。
CeO2 and cerium-based materials can store oxygen under excess-oxygen conditions and release it under oxygen-deficient conditions, and owing to the high oxygen storage/release capacity (OSC) they are widely used as promoters of automobile three-way catalysts.[1–8] Toyota research groups found that addition of zirconium cations to CeO2 dramatically improved the OSC and thermal stability.[9–11] The most efficient CeO2–ZrO2 (CZ) material is a CeO2–ZrO2 solid solution which has an atomically homogeneous, ordered arrangement of Ce and Zr ions assigned to the k-Ce2Zr2O8 fluorite phase (see the Supporting Information),[12] and the OSC increases with increasing homogeneity of the cation arrangement.[7, 13] 89% of the Ce ions in the Pt-promoted k-Ce2Zr2O8 are effective in the oxygen storage/release process, in contrast to the low OSC value of pure CeO2 (2%).[7, 12] The Pt-promoted k-Ce2Zr2O8 transforms into pyrochlore Ce2Zr2O7 under the reducing conditions in the working state (see the Supporting Information). A Ce2Zr2O7. 5 intermediate phase forms on prolonged exposure of Ce2Zr2O7 to air at room temperature,[14] but there is no information on the formation of Ce2Zr2O7. 5 during the oxygen storage/release process under working conditions. Oxygen storage/release processes on CZ samples have been characterized by various methods such as temporal analysis of products for Pt/CZ,[15] time-resolved XRD,[16] and thermogravimetric analysis for oxygen release from Pt/k-Ce2Zr2O8.[17] A tetragonal Ce2Zr2O8 phase with much lower OSC efficiency (52%) than the present k-Ce2Zr2O8 phase (89%) was also characterized by X-ray absorption fine structure (XAFS) analysis.[13, 18] Nevertheless, the previous studies did not focus on the real-time dynamics of CZ samples, which may be most relevant to theOSC function. Both Zr and Ce ions in k-Ce2Zr2O8 are in oxidation state+ 4 and eight-coordinate.[19] In pyrochlore Ce2Zr2O7, Ce ions have oxidation state+ 3 and eightfold coordination, while Zr ions have oxidation state+ 4 and are sixfold coordinated.[19–21] In the transformation between k-Ce2Zr2O8 and Ce2Zr2O7, Zr sites change the number of coordinated oxygen atoms without any change in valence, whereas Ce sites change their valence without changing their coordination number.