机制,选择性促进,以及在Ag催化异质环氧化中新的超选择性途径
Federico J Williams1, Daniel P C Bird, Alejandra Palermo
1Chemistry Department, Cambridge University, Cambridge CB2 1EW, England.
Journal of the American Chemical Society
|July 9, 2004
概括
选择性烯氧化成环氧化物需要特定的表面条件. 氧原子和吸附基是关键的,通过电荷密度影响选择性. 一个新的途径涉及从酸直接转移氧气.
科学领域:
- 表面化学 表面化学
- 不同质的催化剂.
- 氧化反应 氧化反应
背景情况:
- styrene氧化对于生产有价值的环氧化物至关重要.
- 了解银的表面相互作用对于催化剂设计至关重要.
- 之前的研究缺乏选择性环氧化的确切条件.
研究的目的:
- 为了阐明选择性 styrene 环氧化在 Ag 100 上的精确表面条件.
- 为了研究氧气原子,吸附式烯和修饰剂的作用.
- 确定用于增强环氧化选择性的新型催化途径.
主要方法:
- 利用同步子快速X射线光电子光谱 (XPS) 进行表面分析.
- 采用温度编程反应光谱学来监测反应动力学.
- 研究了表面物种对干净和修改的Ag100) 表面的时间依赖性.
主要成果:
- 确立了氧气原子和pi-adsorbed styrene对于环氧化物形成至关重要.
- 证明增加的氧气覆盖和协同吸收的显著改变了环氧化选择性.
- 确定了一种新的低温途径,使用现场生成的酸,促进超选择性环氧化.
结论:
- 表面氧的值电荷密度对于环氧化选择性至关重要.
- 修饰和氧气覆盖极大地影响了反应结果.
- 酸通过来自氧离子的直接氧气转移促进了一种新的环氧化机制.
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