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Temperature-Dependent Formation of Redox Sites in Molybdenum Trioxide Studied by Electron Paramagnetic Resonance Spectroscopy
Tian Tan1,2,3, Ming Chen1,2,3, Ji-Hu Su*1,2,3, Jiang-Feng Du*1,2,3
1.Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China;2.Chinese Academy of Sciences Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China, Hefei 230026, China;3.Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
Abstract:
The formation and qualification of redox sites in transition metal oxides are always the active fields related to electronics, catalysis, sensors, and energy-storage units. In the present study, the temperature dependence of thermal reduction of MoO3 was surveyed at the range of 350 °C to 750 °C. Upon reduction, the formed redox species characterized by EPR spectroscopy are the MoV ion and superoxide anion radical (O2-) when the reduction was induced at the optimal temperature of 300-350 °C. When heating-up from 350 °C, the EPR signals started to decline in amplitude. The signals in the range of 400-450 °C decreased to half of that at 350 °C, and then to zero at ∽600 °C. Further treatment at even higher temperature or prolonged heating time at 500 °C caused more reduction and more free electrons were released to the MoO3 bulk, which results in a delocalized means similar to the antiferromagnetic coupling. These data herein are helpful to prepare and study the metal-oxide catalysts.
Key words:  MoO3, Thermal reduction, MoV, Superoxide anion radical, Electron paramagnetic resonance spectroscopy
FundProject:
利用EPR研究三氧化钼中氧还活性位点形成的温度依赖性
谭 天1,2,3, 陈 明1,2,3, 苏吉虎*1,2,3, 杜江峰1,2,3
1.中国科学技术大学近代物理系,合肥微尺度物质科学国家研究中心,合肥 230026;2.中国科学技术大学,中国科学院微观磁共振重点实验室,合肥 230026;3.中国科学技术大学,量子信息与量子科技前沿协同创新中心,合肥 230026
摘要:
本文利用热处理还原法,利用三氧化钼诱导形成具有氧化还原活性的中间产物及其温度相关特性. 电子顺磁共振波谱(EPR)实验结果表明,热处理后在MoVI离子被还原成MoV离子并形成了超氧阴离子自由基O2-. 这两种活性中心的最佳热还原温度约300∽350 °C. 自350 °逐渐升温,两种EPR信号强度迅速下降,下降∽50%所对应的温度是400∽450 °C;当温度升至600 °C或更高时,EPR信号降至0. 结果表明,较高温处理或持续长时间处理都使热还原更容易发生,积累了越来越多的电子,在基底中形成类似于反铁磁耦合的电子离域. 随着离域程度增大,EPR信号强度开始下降并直至消失.
关键词:  三氧化钼,热还原,MoV离子,超氧阴离子自由基,电子顺磁共振波谱
DOI:10.1063/1674-0068/cjcp1905097
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