Li Wei, He Da, Hu Guoxiang, Li Xiang, Banerjee Gourab, Li Jingyi, Lee Shin Hee, Dong Qi, Gao Tianyue, Brudvig Gary W, Waegele Matthias M, Jiang De-En, Wang Dunwei
Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, United States.
Department of Chemistry, University of California, Riverside, California 92521, United States.
ACS Cent Sci. 2018 May 23;4(5):631-637. doi: 10.1021/acscentsci.8b00130. Epub 2018 Apr 23.
The inertness of the C-H bond in CH poses significant challenges to selective CH oxidation, which often proceeds all the way to CO once activated. Selective oxidation of CH to high-value industrial chemicals such as CO or CHOH remains a challenge. Presently, the main methods to activate CH oxidation include thermochemical, electrochemical, and photocatalytic reactions. Of them, photocatalytic reactions hold great promise for practical applications but have been poorly studied. Existing demonstrations of photocatalytic CH oxidation exhibit limited control over the product selectivity, with CO as the most common product. The yield of CO or other hydrocarbons is too low to be of any practical value. In this work, we show that highly selective production of CO by CH oxidation can be achieved by a photoelectrochemical (PEC) approach. Under our experimental conditions, the highest yield for CO production was 81.9%. The substrate we used was TiO grown by atomic layer deposition (ALD), which features high concentrations of Ti species. The selectivity toward CO was found to be highly sensitive to the substrate types, with significantly lower yield on P25 or commercial anatase TiO substrates. Moreover, our results revealed that the selectivity toward CO also depends on the applied potentials. Based on the experimental results, we proposed a reaction mechanism that involves synergistic effects by adjacent Ti sites on TiO. Spectroscopic characterization and computational studies provide critical evidence to support the mechanism. Furthermore, the synergistic effect was found to parallel heterogeneous CO reduction mechanisms. Our results not only present a new route to selective CH oxidation, but also highlight the importance of mechanistic understandings in advancing heterogeneous catalysis.
CH 中 C-H 键的惰性给选择性 CH 氧化带来了重大挑战，一旦被激活，CH 氧化通常会一路进行到生成 CO。将 CH 选择性氧化为高价值工业化学品（如 CO 或 CHOH）仍然是一个挑战。目前，激活 CH 氧化的主要方法包括热化学、电化学和光催化反应。其中，光催化反应在实际应用中具有很大潜力，但研究较少。现有的光催化 CH 氧化演示对产物选择性的控制有限，CO 是最常见的产物。CO 或其他碳氢化合物的产率过低，没有任何实际价值。在这项工作中，我们表明通过光电化学（PEC）方法可以实现 CH 氧化高选择性地生成 CO。在我们的实验条件下，CO 生成的最高产率为 81.9%。我们使用的底物是通过原子层沉积（ALD）生长的 TiO，其具有高浓度的 Ti 物种。发现对 CO 的选择性对底物类型高度敏感，在 P25 或商业锐钛矿 TiO 底物上产率显著较低。此外，我们的结果表明对 CO 的选择性还取决于施加的电势。基于实验结果，我们提出了一种反应机理，该机理涉及 TiO 上相邻 Ti 位点的协同效应。光谱表征和计算研究为支持该机理提供了关键证据。此外，发现这种协同效应与多相 CO 还原机理相似。我们的结果不仅提供了一条选择性 CH 氧化的新途径，还突出了机理理解在推进多相催化中的重要性。
