the C 6 plane of benzene molecules, and com-
pressed alongDmin(8.31 ± 0.12 Å), with an
aspect ratio of 1.176 (Fig. 1F). The difference
of theDmaxandDminreached 15%. The maxi-
mum pore diameter marked by Si atoms was
increased by 0.6 Å from the [010] projection
to match the critical dimension (6.702 Å) of
benzene molecules, determined from the
smallest cross section. This conclusion was
further confirmed in the iDPC imaging results
with different scan rotation angles (figs. S7
and S8), which indicates that the effect of scan
distortion could be neglected.
This geometrical match further reduced the
freedom of molecular translation and rotation
and constrained confined benzene molecules
to adopt nearly identical configurations, where
the C 6 planes were parallel toDmax.Thislocal
deformation of zeolite opening pores suggested
that the zeolite framework would change as
needed to adapt to the entrance or exit of guest
molecules, which is the core of the diffusion or
formation of larger guest molecules breaking
through the crystallographic pore size limit.
Despite such severe local deformation, the
overall crystal structure of ZSM-5 zeolite re-
mained intact, and the unit cell parameters
were almost unchanged, mainly due to the sym-
metry of the MFI framework (see below).
We achieved better imaging of O atoms in
the zeolite framework during benzene adsorp-
tion. Given the 40-nm thickness of the speci-
men, thermal diffusion and multiple electron
scattering could not be ignored and inevitably
hampered the imaging resolution ( 43 , 44 ).
Thus, we could only observe Si atoms on the
zeolite framework before benzene adsorption,
and the O atoms were blurred by nearby Si
atoms (Fig. 1H). However, after benzene ad-
sorption, we observed framework O atoms
(Fig. 1I). The observed O atoms are highlighted
with orange circles in the corresponding crystal
structure schematic (Fig. 1J); Fig. 1, H and I, was
cropped from fig. S9. We speculated that this
difference in O imaging occurred for two rea-
sons. When interacting with confined benzene
molecules, the flexible framework was tight-
ened, and the vibration of O atoms in the
zeolite framework was restrained, especially
in the Si 10 rings. Moreover, the straight chan-nels were stretched alongDmaxand com-
pressed alongDmin, which brought an increased
distance between adjacent Si-O-Si from the
[010] projection.Dynamic imaging of the benzene
desorption process
To further elucidate the host-guest interaction
between guest molecules and the zeolite frame-
work, we performed an in situ desorption ex-
periment to investigate the dynamic evolution
process of zeolite channels. Real-time iDPC-
STEM imaging results at different stages are
shown in Fig. 2. Before benzene adsorption,
the specimen was also degassed as described
above. The holder temperature was decreased
to 473 K and stabilized for 30 min. We then
introduced the gas mixture (10% benzene
and 90% N 2 , 450 torr). After 1 min, which was
shorter than the time required to obtain a
single iDPC-STEM image, the zeolite frame-
work was almost completely filled with ben-
zene (fig. S10). Thus, it was difficult to observe
the dynamic details of the adsorption process.
In contrast, the desorption of benzene moleculesSCIENCEscience.org 29 APRIL 2022¥VOL 376 ISSUE 6592 493
0 20 40 60 80 1000.20.30.40.50.60.70.80.91.01.11.001.051.101.151.20Aspect Ratio
Aspect Ratio(^) d
ez
il
a
mr
o
N
kr
o
we
ma
rF
/e
ne
zn
eB
Time (min)
Intensity
G
H
0 min
18 min
73 min Empty
Channel
A B15 min
CD
EF
41 min
30 40 50 60 70
0
50
100
0 min
0
50
100
Counts
0
50
100
18 min
15 min
Angle (°)
I Oriented Aromatic Column
θ
Fig. 2. Dynamic evolution of zeolite channels and corresponding
host-guest interactions in benzene desorption.(AtoF) iDPC-STEM
snapshots of a benzene@MFI specimen along the [010] projection at different
stages during the cyclic benzene desorption process. Benzene was taken
up at 473 K and 450 torr (10% benzene and 90% N 2 ) and released under
vacuum; the saturated state is denoted as 0 min. After ~80 min, the
temperature was increased to 923 K to release the remaining benzene
molecules. (G) Magnified iDPC-STEM images of straight channels extracted
from (A) to (F) (marked by the corresponding colored boxes), indicating the
changes in benzene contrast and channel geometry at different stages.
(H) Evolution of the normalized benzene/zeolite framework contrast ratio
and corresponding aspect ratios of Si 10 opening pores during the in situ
benzene uptake and release process. The pink stars indicate points where
the aspect ratios of Si 10 rings are correlated with the imaging contrast
of confined benzene molecules, which reached 1.15 in the saturated state.
Fifty opening pores were measured to obtain the error bars at each point.
(I) Statistical distribution of benzene orientations at different stages of
benzene desorption. Scale bars, 2 nm [(A) to (F)], 500 pm (G).
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