Structural, physical and chemical properties of nanostructured nickel-substituted ceria oxides under reducing and oxidizing conditions
Structural, physical and chemical properties of nanostructured nickel-substituted ceria oxides under reducing and oxidizing conditions
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还原和氧化条件下纳米结构镍取代二氧化铈氧化物的结构、物理和化学性质
DOI：
10.1039/c6ra14853k
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
F. Figueiredo
中科院分区：
文献类型：
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作者：
R. O. Fuentes;L. M. Acuña;C. Albornoz;A. Leyva;N. Sousa;F. Figueiredo
本文报道了用阳离子络合法制备Ce1−xNixO2−δ （x = 0.05, 0.1, 0.15和0.2）纳米氧化物的合成，主要目的是利用电子显微镜、同步辐射x射线衍射（SR-XRD）和x射线吸收近边光谱（XANES）研究其氧化还原性能。Ce1−xNixO2−δ系列纳米粉体保持了纯二氧化铈的立方晶体结构（Fm3m空间群），XRD和透射电镜显示其平均晶粒尺寸为5 ~ 7nm。在500℃的还原气氛（5% H2/He, 5% CO/He）和氧化气氛（21% O2/N2）下进行的原位SR-XRD和XANES显示，室温下Ni在空气中的溶解度极限接近15 at%，在500℃的5% H2/He气氛中暴露后降至10 at%左右。在室温空气中，Ni对Ce1−xNixO2−δ晶格参数的影响可以忽略不计，而在500℃还原条件下，可以观察到晶格的明显膨胀。XANES显示，这与高达25%的Ce4+阳离子还原为更大的Ce3+有关，可能伴随着氧空位的形成。纳米晶ni取代的铈中Ce4+/Ce3+对的氧化还原能力与纯铈相比大大增强，或者通过使用其他掺杂剂（例如Gd， Tb或Pr）来实现，其中Ce阳离子的氧化还原能力限制在5%以下。
This work reports the synthesis of nanostructured Ce1−xNixO2−δ (x = 0.05, 0.1, 0.15 and 0.2) oxides prepared by a cation complexation route and with the main objective of studying their redox properties using a combination of electron microscopy, synchrotron radiation X-ray diffraction (SR-XRD) and X-ray absorption near-edge spectroscopy (XANES). The Ce1−xNixO2−δ series of nanopowders maintain the cubic crystal structure (Fm3m space group) of pure ceria, with an average crystallite size of 5–7 nm indicated by XRD patterns and confirmed by transmission electron microscopy. In situ SR-XRD and XANES carried out under reducing (5% H2/He; 5% CO/He) and oxidizing (21% O2/N2) atmospheres at temperatures up to 500 °C show a Ni solubility limit close to 15 at% in air at room temperature, decreasing to about 10 at% after exposure to 5% H2/He atmosphere at 500 °C. At room temperature in air, the effect of Ni on the lattice parameter of Ce1−xNixO2−δ is negligible, whereas a marked expansion of the lattice is observed at 500 °C in reducing conditions. This is shown by XANES to be correlated with the reduction of up to 25% of Ce4+ cations to the much larger Ce3+, possibly accompanied by the formation of oxygen vacancies. The redox ability of the Ce4+/Ce3+ couple in nanocrystalline Ni-substituted ceria is greatly enhanced in comparison to pure ceria or achieved by using other dopants (e.g. Gd, Tb or Pr), where it is limited to less than 5% of Ce cations.