在超临界水中,同质氧化催化剂Mn (II) (Br) (-1) (x) 的结构:X射线吸收细结构研究
Yongsheng Chen1, John L Fulton, Walter Partenheimer
1Chemical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
Journal of the American Chemical Society
|October 6, 2005
概括
在超临界水中, (II) 催化剂从八面体结构转变为四面体结构,形成Mn-Br接触离子对,这对甲酸合成至关重要.
科学领域:
- 无机化学 无机化学
- 材料科学 材料科学 材料科学
- 催化剂是一种催化剂.
背景情况:
- 在超临界水中的二化物 (MnBr2) 有效地催化了二甲酸的有氧氧化合成.
- 了解 (II) 和 (-1) 离子的协调结构是解释这种催化活性的关键.
研究的目的:
- 为了阐明超临界水中 (II) 和 (-1) 离子的第一层协调结构.
- 为了澄清MnBr2在甲基色化合物氧化中的催化作用的结构基础.
主要方法:
- 使用了扩展的X射线吸收细结构 (EXAFS) 和X射线吸收近边缘结构 (XANES) 谱镜.
- 在阿贡国家实验室的先进光子源收集了Mn和BrK边缘光谱.
主要成果:
- Mn(II) 协调从八面体 (环境) 转变为四面体 (超临界条件).
- 在超临界水中,Mn-OH2和Mn-Br的键距离分别为2.14 Å和2.46 Å.
- 溶解的MnBr2从[Mn(II) ((H2O) 6+2转化为[Mn(II) ((H2O) 2 ((Br-1)) 2),形成Mn-Br接触离子对.
结论:
- 超临界水中的活性MnBr2催化剂具有四面体结构,有两个Mn-Br接触离子对.
- 过多的化物离子增加了化物协调,减少了水联体.
- 乙酸离子通过形成不溶性氧化 (MnO) 来禁用催化剂.
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