Institute of Physical Chemistry, University of Innsbruck, Innrain 52c, A-6020 Innsbruck, Austria.
Phys Chem Chem Phys. 2018 Aug 29;20(34):22099-22113. doi: 10.1039/c8cp04350g.
The effect of Gd- and Sm-doping on pure CeO2 with respect to crystal structure, oxygen nonstoichiometry, hydrogen solubility and hydroxyl chemistry in a hydrogen atmosphere at elevated temperatures was studied using a combination of powder X-ray diffraction (XRD), temperature-programmed methods (such as reduction, desorption and oxidation), and Fourier-Transform Infrared Spectroscopy (FT-IR). In particular, Gd0.1Ce0.9O2-δ (GDC10) and Sm0.15Ce0.85O2-δ (SDC15) were compared to pure CeO2. After H2 reduction of GDC10/SDC15/CeO2 at 900 °C, two distinct phases form, which differ from each other in terms of oxygen nonstoichiometry. One phase is only slightly reduced and maintains a cubic fluorite unit cell. The other phase is strongly oxygen depleted and changes its lattice to triclinic. Enrichment or depletion of the dopants in the two phases upon reduction was not observed. No evidence for a long-range ordered cerium hydride could be found, despite the fact that all samples clearly incorporate hydrogen during the reduction procedure. Generally, the treatment of all three samples with flowing H2 at 700 °C, 800 °C and 900 °C causes the oxygen deficiency and the amount of bound hydrogen to increase with reduction temperature. Acceptor doping, thus, promotes hydrogen incorporation, but it at the same time decreases the amount of reactive oxygen. In conclusion, the study of hydroxyl chemistry shows that doping CeO2 with Gd or Sm creates binding sites for reactive hydroxyl groups that are not observed for pure CeO2. The distinct infrared absorption peak at ca. 2127 cm-1 - which originates from an electronic transition of Ce3+ (2F5/2 → 2F7/2) - is a viable indicator for the reduction degree of all three specimens.
采用粉末 X 射线衍射（XRD）、程序升温法（如还原、脱附和氧化）和傅里叶变换红外光谱（FT-IR）相结合的方法，研究了 Gd 和 Sm 掺杂对纯 CeO2 的晶体结构、氧非化学计量、高温氢气气氛中氢溶解度和羟基化学的影响。特别是，将 Gd0.1Ce0.9O2-δ（GDC10）和 Sm0.15Ce0.85O2-δ（SDC15）与纯 CeO2 进行了比较。在 900°C 下对 GDC10/SDC15/CeO2 进行 H2 还原后，形成了两种不同的相，它们在氧非化学计量方面存在差异。一个相仅略有还原，保持立方萤石单元晶格。另一个相则强烈缺氧，并使其晶格变为三斜晶系。在还原过程中，两种相中没有观察到掺杂剂的富集或耗尽。尽管所有样品在还原过程中都明显吸收了氢，但没有发现长程有序的氢化铈的证据。一般来说，在 700°C、800°C 和 900°C 的流动 H2 处理下，所有三种样品的氧缺陷和结合氢的量都会随着还原温度的升高而增加。因此，受主掺杂促进了氢的掺入，但同时减少了反应性氧的数量。总之，羟基化学的研究表明，在 CeO2 中掺杂 Gd 或 Sm 会产生与纯 CeO2 中观察到的不同的反应性羟基结合位点。在 2127 cm-1 左右的明显红外吸收峰-源自 Ce3+（2F5/2 → 2F7/2）的电子跃迁-是所有三种样品还原程度的可行指标。
