Possible Misidentification of Heteroatom Species in Scanning Transmission Electron Microscopy Imaging of Zeolites

Dong Liu, Lingmei Liu, Kepeng Wu, Jinfei Zhou, Qingpeng Cheng, Jia Lv, Tong Cao, Daliang Zhang, Fang Lin, Yu Han

Research output: Contribution to journalArticlepeer-review

Abstract

Atomic-resolution scanning transmission electron microscopy (STEM) can be used to determine the location and state of heteroatom species in zeolites, which is essential for understanding their catalytic behavior. However, because of the complexity of zeolite structures and low heteroatom content, STEM images must be carefully interpreted to avoid misidentification. In this work, Fe-doped silicalite-1 was used as an example to illustrate this problem by combining STEM image simulation and experiments. Simulation results indicated that, unless the specimen has only one unit cell thickness, it is impossible to reliably identify Fe atoms in a zeolite framework using high-angle annular dark-field STEM (HAADF-STEM). Experimental HAADF-STEM images could not distinguish Fe-doped silicalite-1 and Fe-free silicalite-1 samples, thus confirming the infeasibility of using HAADF-STEM to determine the preferential occupancy of Fe between different crystallographic sites. It was also found that integrated differential phase contrast STEM (iDPC-STEM) could detect extraframework Fe species located in microporous channels only when the physically adsorbed volatile organic compounds were properly removed before imaging. The findings of this investigation provide important precautions and guidance for related research work.
Original languageEnglish (US)
JournalThe Journal of Physical Chemistry C
DOIs
StatePublished - Aug 24 2021

ASJC Scopus subject areas

  • Surfaces, Coatings and Films
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials

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