Structure evolution of nanocrystalline Ce_{1鈭?span style='font-style: italic'>x}Pd_xO_{2鈭?span style='font-style: italic'>y} mixed oxide in oxidizing and reducing atmosphere: Reduction-induced activity in low-temperature CO o

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• 作者：M. Kurnatowska ; L. Kepinski ; ^{L.Kepinski@int.pan.wroc.pl} ; W. Mista
• 关键词：CePdO mixed oxide ; Nanocrystalline Pd doped ceria ; CO oxidation ; Reducibility ; TEM
• 刊名：Applied Catalysis B ; Environmental
• 出版年：2012
• 期刊代码：4_09263373
• 类别：ce
• 出版时间：18 May, 2012
• 卷：117-118
• 期：Complete
• 页码：135-147
• 文件大小：2210 K

摘要

Nanocrystalline (4-8 nm) Ce_1鈭?em>xPd_xO_2鈭?em>y mixed oxide (0 < x < 0.3), active in low temperature CO oxidation, has been prepared by microemulsion method. Thorough XRD, TEM, SEM-EDS, BET and FT Raman studies revealed that the oxide with x < 0.2 is a homogeneous solid solution structurally stable up to 800 掳C in oxidizing atmosphere. In hydrogen, already at 500 掳C segregation of Pd particles occurs, which exhibit preferential Pd (1 1 1)鈭eO₂ (1 1 1) orientation, preserved even after reduction at 800 掳C. Ce_0.89Pd_0.11O_2鈭?em>y oxide showed reversible extraction-dissolution of Pd upon successive reduction-oxidation cycles at 500 掳C, which is an example of 鈥渟elf-regenerative鈥?property important for potential catalytic applications. Doping with Pd strongly hinders the sintering of ceria at high temperatures and enhances its reducibility at low temperatures (below 500 掳C).

鈥淎s prepared鈥? oxidized Ce_0.89Pd_0.11O_2鈭?em>y sample demonstrates moderate activity in CO oxidation (reaching 85%conversion at 鈭?50 掳C) similar to that of 3%Pd/CeO₂ prepared by impregnation. The activity improves dramatically (measurable CO conversion below room temperature and 100%conversion at 鈭?20 掳C) after pre-reduction at 400 掳C in H₂. It appears that partially reduced Pd species, or extremely small particles (<1 nm) at the surface of ceria are responsible for the low temperature activity in CO oxidation. Such Pd species could be strongly bonded to the surface, e.g., exhibiting a special epitaxial orientation observed for larger Pd crystallites (鈭? nm) formed during reduction at higher temperatures.