外层球表面酸度在烯环氧化中所扮演的角色,烯环氧化由素-Ti (IV) 复合物催化
Justin M Notestein1, Andrew Solovyov, Leandro R Andrini
1Department of Chemical Engineering, University of California at Berkeley, Berkeley, California 94720, USA.
Journal of the American Chemical Society
|November 23, 2007
概括
表面酸度和 (Ti) 易斯酸部位协同控制环氧化催化. SiO2通过平衡氧化物结合和氧气转移来支持增强速率,突出了Ti催化剂中的外部球相互作用.
科学领域:
- 不同质的催化剂.
- 表面化学 表面化学
- 有机金属化学 有机金属化学
背景情况:
- 氧化催化对于合成有价值的化学物质至关重要.
- 调整催化剂特性,如表面酸度和金属位点,是提高反应效率的关键.
- 了解支材料和活性位点之间的相互作用对于催化剂设计至关重要.
研究的目的:
- 在环氧化催化中,研究布伦斯特德酸性位点在氧化物表面和易斯酸性卡利沙-Ti(IV) 复合物的合作作用.
- 阐明支材料 (SiO2,Al2O3,TiO2) 和表面酸度在调节催化活性中的作用.
- 确定在环氧化反应中氧化物激活和氧气转移的机制.
主要方法:
- 在各种氧化物支 (SiO2,Al2O3,TiO2) 上合成移植的卡利沙-Ti(IV) 复合物.
- 使用紫外线可见光谱和Ti K边缘X射线吸收近边缘结构 (XANES) 光谱进行了表征.
- 使用 tert-butyl 氧化物在环烯环氧化过程中催化性能的评估.
- 分析表面特性,包括布伦斯特德酸度 (pKa) 和H-结合相互作用.
主要成果:
- 材料在不同的支物和卡力沙林替代物中表现出类似的Ti协调环境.
- 与同质系统相比,SiO2上的每一个Ti位点的氧化率增加了20倍.
- 较低的Al2O3和TiO2表面酸度支持相对于SiO2.2的50倍减少的催化速率.
- 催化剂性能对支持氧化物高度敏感,独立于Ti协调.
结论:
- SiO2通过优化氧化物结合和通过外部球H结合相互作用转移氧气来支持增强环氧化率.
- 支的Bronsted酸度起着至关重要的作用,较强的酸度 (较低的pKa) 会降低催化速率.
- 这些发现强调了支效应和外层相互作用在设计高效的基环氧化催化剂中的重要性.
相关概念视频
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