Discriminating Catalytically Active FeNx Species of Atomically Dispersed Fe-N-C Catalyst for Selective Oxidation of the C-H Bond
Discriminating Catalytically Active FeNx Species of Atomically Dispersed Fe-N-C Catalyst for Selective Oxidation of the C-H Bond
复制标题
区分原子分散 Fe-N-C 催化剂的催化活性 FeNx 种类，用于 C-H 键的选择性氧化
DOI：
10.1021/jacs.7b05130
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发表时间：
2017-08-09
影响因子：
15
通讯作者：
Zhang, Tao
中科院分区：
文献类型：
--
作者：
Liu, Wengang;Zhang, Leilei;Zhang, Tao
纳米结构的Fe-N-C材料代表了一种新型的“类铂”非贵金属催化剂，用于各种电化学反应和有机转化。然而，由于Fe-N-C催化剂的颗粒尺寸和组成的不均匀性，在Fe-N-C催化剂的活性中心上没有达成共识。在本论文中，我们成功地制备了原子分散的Fe-N-C催化剂，该催化剂对C-H键的选择性氧化具有高活性和良好的重复使用性。在室温下，该催化剂可催化芳香族、杂环族和脂肪族烷烃等多种底物的氧化，产物的选择性高达99%。通过使用亚埃分辨率HAADF-STEM结合XPS，XAS，ESR和穆斯堡尔谱，我们已经提供了坚实的证据表明，Fe是唯一的，分散作为单个原子通过形成FeNx（x = 4-6），每个FeNx物种的相对浓度是严重依赖于热解温度。其中，中自旋（FeN 5）-N-III提供最高的转换频率（6455 h（-1）），其活性比高自旋和低自旋（FeN 6）-N-III结构高至少1个数量级，比（FeN 4）-N-II结构高3倍，尽管其在催化剂中的相对浓度远低于（FeN 6）-N-III结构。
Nanostructured Fe-N-C materials represent a new type of "platinum-like" non-noble-metal catalyst for various electrochemical reactions and organic transformations. However, no consensus has been reached on the active sites of the Fe-N-C catalysts because of their heterogeneity in particle size and composition. In this contribution, we have successfully prepared atomically dispersed Fe-N-C catalyst, which exhibited high activity and excellent reusability for the selective oxidation of the C-H bond. A wide scope of substrates, including aromatic, heterocyclic, and aliphatic alkanes, were smoothly oxidized at room temperature, and the selectivity of corresponding products reached as high as 99%. By using sub-angstrom-resolution HAADF-STEM in combination with XPS, XAS, ESR, and Mossbauer spectroscopy, we have provided solid evidence that Fe is exclusively, dispersed as single atoms via forming FeNx (x = 4-6) and that the, relative concentration of each FeNx species is critically dependent on the pyrolysis temperature. Among them, the medium-spin (FeN5)-N-III affords the highest turnover frequency (6455 h(-1)), which is at least 1 order of magnitude more active than the high-spin and low-spin (FeN6)-N-III structures and 3 times More active than the (FeN4)-N-II structure, although its relative concentration in the catalysts is much lower than that of the (FeN6)-N-III structures.