Science - USA (2021-07-16)

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without the aid of a template or binder (Fig.
1A and fig. S1). Neither high-temperature
calcination nor other posttreatment was re-
quired, circumventing the calcination-related
energy consumption and releases of waste
gases such as CO 2 and NOx. A larger-scale syn-
thesis created a large monolith (fig. S1F), illus-
trating the scalability of this synthesis. No
shrinkage was observable during the drying
process. The pressure needed to crush these
materials ranged from 24 to 38 MPa, illus-
trating their considerable mechanical stability
(table S1), which was far superior to previous
directly synthesized zeolite monoliths and
some traditional postmolded ones using bind-
ers ( 13 , 20 – 22 ).
Scanning electron microscopy (SEM) images
(Fig. 2, A to C, and fig. S2) demonstrated that
these monoliths were composed of an aggrega-
tion of prismatic crystals. They had abundant
macropores with diameters of several micro-
meters, and their Fe content increased along
with the initial Fe/Si molar ratio (fig. S3 and
table S1). Uniform distribution of Fe species


was observable in the high-angle annular
dark-field scanning transmission electron
microscopy (HAADF-STEM) images and the
corresponding energy-dispersive x-ray spectral
images(Fig.2,DtoG),aswellastheSEMele-
mental mapping images (fig. S4). Their crystal
MORtopology was supported by the x-ray dif-
fraction (XRD) patterns (fig. S5), transmission
electron microscopy (TEM) images, and the
related selected area electron diffraction pat-
terns (Fig. 2, H and I), as well as the^29 Si and

(^27) Al magic-angle spinning (MAS) nuclear mag-
netic resonance spectroscopy (NMR) spectra
(figs. S6 and S7) ( 26 – 29 ). The zeolite framework
was highly thermally stable, as demonstrated by
the thermogravimetric analysis (fig. S8) ( 26 , 27 )
and the well-preserved XRD patterns of Fe-
MOR(n)-C (C, calcined) obtained by treating
Fe-MOR(n) at 823 K for 5 hours (fig. S5B).
Fe K-edge x-ray absorption fine structure
(XAFS) analyses of Fe-MOR(0.1 to 1.0) were
performed (Fig. 3, A to C, and figs. S9 to S14).
X-ray absorption near-edge structure (Fig. 3A)
indicated that the iron status in Fe-MOR (0.1 to
1.0) is of Fe3+with a similar dominant tetrahe-
dral coordination environment, as demonstra-
ted by the sharp pre-edge peak ( 30 – 32 ). X-
ray photoelectron spectroscopy of Fe-MOR
(0.25) also confirmed the existence of Fe3+
species (fig. S15) ( 29 , 33 ). Only one prominent
peak at ~1.4 Å, mainly arising from the Fe–
O contribution, appeared in the Fourier-
transformedk^3 -weighted extended x-ray ab-
sorption fine structure (EXAFS) spectra (Fig.
3B). No signal attributable to the Fe–Fe or Fe–
O–Fe scattering was identified, excluding the
presence of aggregated ferric oxide clusters
( 30 – 32 ). The Fe-O coordination numbers of
Fe-MOR(0.1 to 1.0) were 3.6 to 3.9 and the Fe-
O bond length was 1.85 Å (Fig. 3C and table
S2), consistent with tetrahedral Fe3+species
coordinated to four O atoms. Aggregated
ferric species were further excluded by the
ultraviolet-visible (UV-vis) and electron spin
resonance (ESR) spectra (figs. S16 and S17).
The ESR signal atg=4.3wasassignedto
tetrahedral site Fe3+ions in rhombic distor-
tion (replacing zeolite framework T atoms)
SCIENCEsciencemag.org 16 JULY 2021•VOL 373 ISSUE 6552 317
Fig. 3. Fe species and pore information.(AandB) X-ray absorption
near-edge structure (A) andk^3 -weighted Fourier transform spectra (B)
derived from EXAFS of Fe K-edge for Fe-MOR(n) with the reference materials
Fe foil and Fe 2 O 3 .(C) Fourier-transformed EXAFS curves for the experimental
data and the fit for Fe-MOR(0.25). (DtoG) 3D framework structure (D) of
tetrahedral Fe species inside the 12-MR microchannels (blue is Si or Al,
red is O, and light brown is Fe) from combined Rietveld refinement on the
basis of powder XRD patterns [blue is the observed profile, red is the
calculated profile, gray is the difference profile, and green is the reflection
position (E)] and powder neutron diffraction patterns [90°-bank_2 and
168°-bank_1 for (F) and (G), respectively] of Fe-MOR(0.25). The inset
intensities in (E) are scaled by a factor of five.
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