Ce_(1-x)Tb_xO_(2-δ)复合氧化物氧缺位的拉曼光谱研究

Raman Spectroscopic Study of Oxygen Vacancies in Ce_(1-x)Tb_xO_(2-δ) Mixed Oxides

采用溶胶-凝胶法制备了Ce1-xTbxO2-δ复合氧化物,利用不同Raman激发波长(514和785 nm),结合X射线衍射(XRD)、氢气-程序升温还原(H2-TPR)和氧气-程序升温脱附(O2-TPD)表征,考察了Ce1-xTbxO2-δ复合氧化物在O2,He和H2气氛下氧缺位的原位变化情况和CeO2的F2g特征Raman峰位的偏移.实验结果表明,随着Tb掺杂量的提高,由于晶胞收缩使得CeO2的F2g特征Raman振动峰发生蓝移.514nm Raman激发波长反映了催化剂的表面信息,而785 nm激发波长反映了整体信息.正是由于表面和整体变化的不一致,造成原位Raman实验过程中氧缺位浓度变化趋势的不同.在He和H2气氛下,由于温度升高时伴随着Ce1-xTbxO2-δ中O2气的脱出,使复合氧化物的微观结构发生改变,以致Ce0.9Tb0.1O2-δ中的氧缺位浓度(A587/A465)在785 nm激发波长下出现先升高后下降的现象.

A series of Ce1-xTbxO2-δ mixed oxides were prepared by a sol-gel method. In situ Raman spectroscopy combined with X-ray diffraction （XRD）, H2-temperature programmed reduction （H2-TPR） and O2-temperature programmed desorption（O2-TPD） were used to analyze oxygen vacancies in the mixed oxides under different atmospheres（ O2, He, and H2 ） with 514 and 785 nm excitation laser lines and the blue shift of the F2g vibration mode of CeO2. The results show that increasing Tb content in the sample result in the blue shift of F2g vibration mode of CeO2 because of dominant effect of the shrinking of the crystal. Furthermore, the difference in the changing trend of oxygen vacancies is due to the different Raman excitation laser lines. 514 nm excitation laser line can provide the surface information, while 785 nm excitation laser line can get the whole information of the sample. The Asa7/A465 ratio reflecting the oxygen vacancies shows an inflexion under He and H2 atmospheres could be explained by the change in microstructure of the sample along with the release of O2 during the heating process.