Formation of Ce1-xPdxO2-δ solid solution in combustion-synthesized Pd/CeO2 catalyst:: XRD, XPS, and EXAFS investigation
Formation of Ce1-xPdxO2-δ solid solution in combustion-synthesized Pd/CeO2 catalyst:: XRD, XPS, and EXAFS investigation
复制标题
DOI：
10.1021/cm0103895
复制
发表时间：
2002-05-01
影响因子：
8.6
通讯作者：
Lalla, NP
中科院分区：
文献类型：
--
作者：
Priolkar, KR;Bera, P;Lalla, NP
Pd/CeO2 （1 at）溶液燃烧法制备的钯金属、PdO和分散在CeO2上的钯具有更高的CO氧化和NO还原活性。为了了解更高的催化性能，1 at的结构。采用x射线衍射（XRD）、x射线光电子能谱（XPS）和扩展x射线吸收精细结构（EXAFS）对% Pd/CeO2催化剂材料进行了研究。在1 at的高分辨率XRD图中没有观察到Pd或PdO对应的衍射线。% Pd / CeO2。1 at的结构。% Pd/CeO2可精炼为ce0.99 - pd0.010 - o1.90，具有5%的氧化物离子空位的萤石结构。Pd（3d）在XPS中达到峰值。% Pd/CeO2移动了3ev，表明Pd处于高离子+2态。EXAFS研究表明，1 at的第一壳层中Pd2+离子周围的平均配位数为3。% Pd/CeO2的距离为2.02埃，而不是PdO中的4埃。第二个壳层在2.72埃处是由于Pd-Pd相关，PdO中的Pd-Pd相关大于2.69埃。在金属钯和PdO中均不存在具有7配位的3.31埃的第三壳层，这可归因于- pd2 +- ce4 +-相关。因此，1 at。% Pd/CeO2形成具有- pd2 +- o -2- ce4 +-键的ce1 - xpdxo2 - δ型固溶体。
Pd/CeO2 (1 at. %) prepared by the solution-combustion method shows a higher catalytic activity for CO oxidation and NO reduction than Pd metal, PdO, and Pd dispersed over CeO2 by the conventional method. To understand the higher catalytic properties, the structure of 1 at. % Pd/CeO2 catalyst material has been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The diffraction lines corresponding to Pd or PdO are not observed in the high-resolution XRD pattern of 1 at. % Pd/CeO2. The structure of 1 at. % Pd/CeO2 could be refined for the composition of Ce0.99Pd0.01O1.90 in the fluorite structure with 5% oxide ion vacancy. Pd(3d) peaks in the XPS in I at. % Pd/CeO2 are shifted by 3 eV indicating that Pd is in a highly ionic +2 state. EXAFS studies show the average coordination number of 3 around Pd2+ ion in the first shell of 1 at. % Pd/CeO2 at a distance of 2.02 Angstrom, instead of 4 as in PdO. The second shell at 2.72 Angstrom is due to Pd-Pd correlation which is larger than 2.69 Angstrom in PdO. The third shell at 3.31 Angstrom having 7 coordination is absent either in Pd metal or PdO, which can be attributed to -Pd2+-Ce4+- correlation. Thus, 1 at. % Pd/CeO2 forms the Ce1-xPdxO2-delta type of solid solution having -Pd2+-O-2-Ce4+- kinds of linkages.