Xiong Hao, Liu Zhiqiang, Chen Xiao, Wang Huiqiu, Qian Weizhong, Zhang Chenxi, Zheng Anmin, Wei Fei
Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China.
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China.
Science. 2022 Apr 29;376(6592):491-496. doi: 10.1126/science.abn7667. Epub 2022 Apr 28.
The crystallographic pore sizes of zeolites are substantially smaller than those inferred from catalytic transformation and molecular sieving capabilities, which reflects flexible variation in zeolite opening pores. Using in situ electron microscopy, we imaged the straight channels of ZSM-5 zeolite with benzene as a probe molecule and observed subcell flexibility of the framework. The opening pores stretched along the longest direction of confined benzene molecules with a maximum aspect change of 15%, and the space group symmetry of the MFI framework caused adjacent channels to deform. This compensation maintained the stability and rigidity of the overall unit cell within 0.5% deformation. The subcell flexibility originates mainly from the topologically soft silicon-oxygen-silicon hinges between rigid tetrahedral SiO units, with inner angles varying from 135° to 153°, as confirmed by ab initio molecular dynamics simulations.
沸石的晶体学孔径比催化转化和分子筛能力所推断的孔径小得多，这反映了沸石开孔的灵活变化。我们使用原位电子显微镜，以苯为探针分子对ZSM-5沸石的直通道进行成像，观察到骨架的亚晶胞灵活性。开孔沿受限苯分子的最长方向伸展，最大长宽比变化为15%，MFI骨架的空间群对称性导致相邻通道变形。这种补偿使整个晶胞在0.5%的变形范围内保持稳定和刚性。从头算分子动力学模拟证实，亚晶胞的灵活性主要源于刚性四面体SiO单元之间拓扑结构较软的硅-氧-硅铰链，其内角在135°至153°之间变化。
