TY - JOUR
T1 - Possible Misidentification of Heteroatom Species in Scanning Transmission Electron Microscopy Imaging of Zeolites
AU - Liu, Dong
AU - Liu, Lingmei
AU - Wu, Kepeng
AU - Zhou, Jinfei
AU - Cheng, Qingpeng
AU - Lv, Jia
AU - Cao, Tong
AU - Zhang, Daliang
AU - Lin, Fang
AU - Han, Yu
N1 - KAUST Repository Item: Exported on 2021-08-31
Acknowledged KAUST grant number(s): FCC/1/1972-43-01
Acknowledgements: This research is supported by the AMPM CCF fund (FCC/1/1972-43-01) to Y.H. from King Abdullah University of Science and Technology and the research grant to F.L. from the National Natural Science Foundation of China (No. 61971201).
PY - 2021/8/24
Y1 - 2021/8/24
N2 - 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.
AB - 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.
UR - http://hdl.handle.net/10754/670759
UR - https://pubs.acs.org/doi/10.1021/acs.jpcc.1c05516
U2 - 10.1021/acs.jpcc.1c05516
DO - 10.1021/acs.jpcc.1c05516
M3 - Article
SN - 1932-7447
JO - The Journal of Physical Chemistry C
JF - The Journal of Physical Chemistry C
ER -