Gao Jiayi, Huang Zhiwei, Chen Yaxin, Wan Jing, Gu Xiao, Ma Zhen, Chen Jianmin, Tang Xingfu
Institute of Atmospheric Sciences, Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Department of Environmental Science & Engineering, Fudan University, 200433, Shanghai, P.R. China.
Department of Applied Physics, Chongqing University, 400044, Chongqing, P.R. China.
Chemistry. 2018 Jan 12;24(3):681-689. doi: 10.1002/chem.201704398. Epub 2017 Dec 13.
Alkali-metal ions often act as promoters rather than active components due to their stable outermost electronic configurations and their inert properties in heterogeneous catalysis. Herein, inert alkali-metal ions, such as K and Rb , are activated by electron transfer from a Hollandite-type manganese oxide (HMO) support for HCHO oxidation. Results from synchrotron X-ray diffraction, absorption, and photoelectron spectroscopies demonstrate that the electronic density of states of single alkali-metal adatoms is much higher than that of K or Rb , because electrons transfer from manganese to the alkali-metal adatoms through bridging lattice oxygen atoms. Electron transfer originates from the interactions of alkali metal d-sp frontier orbitals with lattice oxygen sp orbitals occupied by lone-pair electrons. Reaction kinetics data of HCHO oxidation reveal that the high electronic density of states of single alkali-metal adatoms is favorable for the activation of molecular oxygen. Mn L -edge and O K-edge soft-X-ray absorption spectra demonstrate that lattice oxygen partially gains electrons from the Mn e orbitals, which leads to the upshift in energy of lattice oxygen orbitals. Therefore, the facile activation of molecular oxygen by the electron-abundant alkali-metal adatoms and active lattice oxygen are responsible for the high catalytic activity in complete oxidation of HCHO. This work could assist the design of efficient and cheap catalysts by tuning the electronic states of active components.
由于碱金属离子具有稳定的最外层电子构型以及在多相催化中的惰性，它们通常作为促进剂而非活性组分。在此，诸如K和Rb等惰性碱金属离子通过从钙钛矿型氧化锰（HMO）载体进行电子转移而被激活，用于HCHO氧化。同步辐射X射线衍射、吸收和光电子能谱的结果表明，单个碱金属吸附原子的态电子密度远高于K或Rb，这是因为电子通过桥连晶格氧原子从锰转移到碱金属吸附原子。电子转移源于碱金属d-sp前沿轨道与被孤对电子占据的晶格氧sp轨道之间的相互作用。HCHO氧化的反应动力学数据表明，单个碱金属吸附原子的高态电子密度有利于分子氧的活化。Mn L边和O K边软X射线吸收光谱表明，晶格氧部分从Mn e轨道获得电子，这导致晶格氧轨道能量上移。因此，富电子的碱金属吸附原子和活性晶格氧对分子氧的 facile活化是HCHO完全氧化中高催化活性的原因。这项工作可以通过调节活性组分的电子态来辅助设计高效且廉价的催化剂。
