Yang Hongling, Zhang Xun, Yu Yi, Chen Zheng, Liu Qinggang, Li Yang, Cheong Weng-Chon, Qi Dongdong, Zhuang Zewen, Peng Qing, Chen Xin, Xiao Hai, Chen Chen, Li Yadong
Department of Chemistry, Tsinghua University Beijing 100084 China
School of Physical Science and Technology, Shanghai Tech University Shanghai 201210 China.
Chem Sci. 2021 Mar 16;12(17):6099-6106. doi: 10.1039/d1sc00700a.
Single-atom catalysts provide a pathway to elucidate the nature of catalytically active sites. However, keeping them stabilized during operation proves to be challenging. Herein, we employ cryptomelane-type octahedral molecular sieve nanorods featuring abundant manganese vacancy defects as a support, to periodically anchor single-atom Ag. The doped Ag atoms with tetrahedral coordination are found to locate at cation substitution sites rather than being supported on the catalyst surface, thus effectively tuning the electronic structure of adjacent manganese atoms. The resulting unique Ag-O-MnO unit functions as the active site. Its turnover frequency reaches 1038 h, one order of magnitude higher than for previously reported catalysts, with 90% selectivity for anti-Markovnikov phenylacetaldehyde. Mechanistic studies reveal that the activation of styrene on the ensemble site of Ag-O-MnO is significantly promoted, which can accelerate the oxidation of styrene and, in particular, the rate-determining step of forming the epoxide intermediate. Such an extraordinary electronic promotion can be extended to other single-atom catalysts and paves the way for their practical applications.
单原子催化剂为阐明催化活性位点的本质提供了一条途径。然而，在操作过程中保持它们的稳定性被证明具有挑战性。在此，我们采用具有丰富锰空位缺陷的隐钾锰矿型八面体分子筛纳米棒作为载体，来周期性地锚定单原子银。发现具有四面体配位的掺杂银原子位于阳离子取代位点，而不是负载在催化剂表面，从而有效地调节了相邻锰原子的电子结构。由此产生的独特的Ag-O-MnO单元充当活性位点。其周转频率达到1038 h-1，比先前报道的催化剂高一个数量级，对反马氏规则的苯乙醛的选择性为90%。机理研究表明，苯乙烯在Ag-O-MnO的整体位点上的活化得到显著促进，这可以加速苯乙烯的氧化，特别是形成环氧化物中间体的速率决定步骤。这种非凡的电子促进作用可以扩展到其他单原子催化剂，并为它们的实际应用铺平道路。
