School of Petroleum and Chemical Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Panjin 124221, China.
Environ Sci Technol. 2020 Jul 21;54(14):8601-8611. doi: 10.1021/acs.est.0c03427. Epub 2020 Jun 27.
Oxygen vacancies can capture and activate gaseous oxygen, forming surface chemisorbed oxygen, which plays an important role in the Hg oxidation process. Fine control of oxygen vacancies is necessary and a major challenge in this field. A novel method for facet control combined with morphology control was used to synthesize CoO nanosheets preferentially growing (220) facet to give more oxygen vacancies. X-ray photoelectron spectroscopy (XPS) results show that the (220) facet has a higher Co/Co ratio, leading to more oxygen vacancies via the Co reduction process. Density functional theory (DFT) calculations confirm that the (220) facet has a lower oxygen vacancy formation energy. Furthermore, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results suggest that CoO nanosheets yield more defects during the synthesis process. These results are the reasons for the greater number of oxygen vacancies in CoO nanosheets, which is confirmed by electron energy loss spectroscopy (EELS), Raman spectroscopy, and photoluminescence (PL) spectroscopy. Therefore, CoO nanosheets show excellent Hg removal efficiency over a wide temperature range of 100-350 °C at a high gas hourly space velocity (GHSV) of 180 000 h. Additionally, the catalytic efficiency of CoO nanosheets is still greater than 83%, even after 80 h of testing, and it recovers to its original level after 2 h of in situ thermal treatment at 500 °C.
氧空位可以捕获和激活气态氧，形成表面化学吸附氧，在汞氧化过程中起着重要作用。精细控制氧空位是必要的，也是该领域的主要挑战。本文采用了一种新的晶面控制和形貌控制相结合的方法，来合成优先生长（220）晶面的 CoO 纳米片，以提供更多的氧空位。X 射线光电子能谱（XPS）结果表明，（220）晶面具有更高的 Co/Co 比，通过 Co 还原过程产生更多的氧空位。密度泛函理论（DFT）计算证实，（220）晶面具有更低的氧空位形成能。此外，扫描电子显微镜（SEM）和透射电子显微镜（TEM）结果表明，CoO 纳米片在合成过程中产生更多的缺陷。这些结果是 CoO 纳米片中氧空位数量较多的原因，这通过电子能量损失谱（EELS）、拉曼光谱和光致发光（PL）光谱得到了证实。因此，CoO 纳米片在 100-350°C 的较宽温度范围内，在 180000 h-1 的高气速（GHSV）下，具有优异的汞去除效率。此外，即使经过 80 小时的测试，CoO 纳米片的催化效率仍大于 83%，并在 500°C 下原位热处理 2 小时后恢复到原来的水平。
