Enhancing nitrobenzene reduction to azoxybenzene by regulating the O-vacancy defects over rationally tailored CeO2 nanocrystals
Enhancing nitrobenzene reduction to azoxybenzene by regulating the O-vacancy defects over rationally tailored CeO2 nanocrystals
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DOI：
10.1016/j.apsusc.2021.151343
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发表时间：
2021-10-04
影响因子：
6.7
通讯作者：
Gao, Xiang
中科院分区：
文献类型：
--
作者：
Zhou, Xueke;Yang, Yang;Gao, Xiang
硝基苯还原反应中中间体选择性的精确控制是一个历史悠久的挑战。在这里，我们报告了一个监管的方法，用于提高氧化偶氮苯的选择性，使用四个合理定制的CeO 2催化剂，其暴露的平面，酸碱化学，并在Ce 3+阳离子和O-空位方面的缺陷性质进行了优化。在这四种催化剂中，纺锤形结构的CeO 2，其中具有最大浓度的Ce 3+阳离子和O-空位缺陷表现出最高的硝基苯转化率。然而，它表现出较低的氧化偶氮苯的选择性（70.5%）比棒CeO 2（90.4%）。基于半定量表征结果和速率决定步骤的初始速率，证明CeO 2催化剂的缺陷密度对应于其催化选择性。密度泛函理论（DFT）计算和原位盖帽实验进一步揭示了O空位缺陷的母体Ce ~（3+）阳离子是硝基苯硝基的吸附活化位。氧空位缺陷是氧化偶氮苯的主要活性中心，对氧化偶氮苯的过度还原起着重要作用，要提高氧化偶氮苯的选择性，必须抑制氧化偶氮苯的过度还原。因此，调节O-空位缺陷在中等浓度是负责令人满意的氧化偶氮苯产率为90.4%的棒状CeO 2纳米晶体所表现出的。
The precise control of the selectivity of intermediates in nitrobenzene reduction is a time-honored challenge. Herein, we report a regulatory method for improving the selectivity of azoxybenzene using four rationally tailored CeO2 catalysts, whose exposed planes, acid-base chemistries, and defect properties in terms of Ce3+ cations and O-vacancies are optimized. Among the four catalysts, Spindle-structured CeO2, which has the largest concentration of Ce3+ cations and O-vacancy defects exhibits the highest nitrobenzene conversion rate. However, it exhibits a lower azoxybenzene selectivity (70.5%) than Rod-CeO2 (90.4%). Based on the semi-quantitative characterization results and the initial rates of the rate-determining step, the defect densities of the CeO2 catalysts are demonstrated to correspond to their catalytic selectivity. Density functional theory (DFT) calculations and in situ capping tests further reveal that the parent Ce3+ cations of O-vacancy defects serve as adsorptionactivation sites for nitro groups of nitrobenzene. Moreover, the O-vacancy defects serve as the main active sites and conduce the over-reduction of azoxybenzene, which should be inhibited to improve the azoxybenzene selectivity. Therefore, regulating the O-vacancy defects at the moderate concentration is responsible for the satisfactory azoxybenzene yield of 90.4% exhibited by Rod-CeO2 nanocrystals.