UV-assisted removal of inactive peroxide species for sustained epoxidation of cyclooctene on anatase TiO2.
UV-assisted removal of inactive peroxide species for sustained epoxidation of cyclooctene on anatase TiO2.
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DOI：
10.1002/chem.201400258
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发表时间：
2014-05
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影响因子：
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通讯作者：
Changjun Yang;Xianjun Lang;Wanhong Ma;Chuncheng Chen;Hongwei Ji;Jincai Zhao
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作者：
Changjun Yang;Xianjun Lang;Wanhong Ma;Chuncheng Chen;Hongwei Ji;Jincai Zhao
烯烃的过氧化氢环氧化反应是有机合成中最重要的反应之一。结果表明，TiO_2在室温下可以作为环辛烯环氧化反应的良好催化剂。然而，在过量H_2O_2存在下，催化剂很快失活，这是由于在TiO_2表面上形成了不活泼的侧位Ti-η（2）-过氧化物物种，其存在通过同位素标记的共振紫外拉曼光谱和动力学研究证实。有趣的是，在λ≥350 nm的紫外光照射下，环氧化反应可以显著加速。这一现象归因于光辅助去除了过氧化氢的活性物种，使TiO 2表面的活性中心得以再生，从而恢复了环辛烯与H2 O2的催化环氧化反应。这一发现为在室温下在TiO 2上进行持续的环氧化反应提供了一种替代方案。此外，它也有重要的意义上的失活途径和可能的解决方案，在钛基多相催化或催化剂。
Epoxidation of olefins with H2O2 is one of the most important reactions in organic synthesis. We found that anatase TiO2 can be a good catalyst for the epoxidation of cyclooctene with H2O2 at room temperature. However, the catalyst deactivated quickly in the presence of excess amount of H2O2 because of the formation of inactive side-on Ti-η(2)-peroxide species on the surface of TiO2, the presence of which was confirmed by isotope-labelled resonance UV Raman spectroscopy and kinetics studies. Interestingly, the epoxidation reaction could be dramatically accelerated under irradiation of UV light with λ≥350 nm. This phenomenon is attributed to the photo-assisted removal of the inactive peroxide species, through which the active sites on the surface of anatase TiO2 are regenerated and the catalytic epoxidation of cyclooctene with H2O2 is resumed. This finding provides an alternative for sustained epoxidation reactions on TiO2 at room temperature. Moreover, it also has significant implications on the deactivation pathway and possible solutions in Ti-based heterogeneous catalysis or photocatalysis.