Wang Lian, Yu Yunbo, He Hong, Zhang Yan, Qin Xiubo, Wang Baoyi
State key Joint Laboratory of Environmental Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China.
Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China.
Sci Rep. 2017 Oct 9;7(1):12845. doi: 10.1038/s41598-017-13178-6.
Catalytic oxidation of o-xylene was investigated on CeO nanocubes calcined at 350, 450, 550, and 650 °C, among which the samples calcined at 550 °C exhibited the highest activity and long durability. Positron annihilation spectroscopy measurements revealed that the size and distribution of oxygen vacancies for CeO nanocubes could be tuned by carefully controlling the calcination temperature. An excellent linear correlation between a factor related to size and density of oxygen vacancy clusters and reaction rate of o-xylene oxidation was revealed on ceria nanocubes. This means that oxygen vacancy clusters with suitable size and distribution are responsible for catalytic reaction via simultaneous adsorption and activation of oxygen and o-xylene. Electron spin resonance spectra revealed that over the CeO cubes, water vapor significantly promoted the formation of ∙OH radicals with a sharp decrease in the signals relating to oxygen vacancies, accelerating the transformation of o-xylene to the intermediate benzoate species, resulting in an enhancement of catalytic activity. Water thus serves as a "smart" molecule; its introduction into the feed mixture further confirmed the key role of oxygen vacancies in the catalytic performance of CeO nanocubes. A possible mechanism of oxygen vacancy formation during the calcination process was also proposed.
研究了在350、450、550和650℃煅烧的CeO纳米立方体上邻二甲苯的催化氧化，其中在550℃煅烧的样品表现出最高的活性和长期耐久性。正电子湮没光谱测量表明，通过仔细控制煅烧温度，可以调节CeO纳米立方体的氧空位的尺寸和分布。在二氧化铈纳米立方体上，揭示了与氧空位簇的尺寸和密度相关的一个因子与邻二甲苯氧化反应速率之间存在良好的线性相关性。这意味着具有合适尺寸和分布的氧空位簇通过同时吸附和活化氧及邻二甲苯来负责催化反应。电子自旋共振光谱表明，在CeO立方体上，水蒸气显著促进了∙OH自由基的形成，与氧空位相关的信号急剧下降，加速了邻二甲苯向中间产物苯甲酸酯物种的转化，从而提高了催化活性。因此，水作为一种“智能”分子；将其引入进料混合物进一步证实了氧空位在CeO纳米立方体催化性能中的关键作用。还提出了煅烧过程中氧空位形成的可能机制。
