Science - USA (2021-07-16)

the larger sizes of transition metal ions rela-
tive to those of Si and Al. TheMORzeolites
have parallel 12-membered ring (MR) one-
dimensional (1D) channels (6.5 Å by 7.0 Å) along
thec-axis direction (Cmcmspace group) ( 26 ).
We incorporated Fe ions into aMORframe-
work to prepare Fe-MOR through an unusual
“acid co-hydrolysis route”(Fig. 1A), enabling
slow co-condensation of Fe and Si/Al precur-

sors in the initial gelation stage for the fine

control of Fe doping. The strategy led to the

partial occupation of the microchannels by

tetrahedral Fe species, resulting in precisely

narrowed microchannels (Fig. 1, B and C) that

allowed exclusive molecular sieving abilities.

From a process operation point of view, the

present synthesis not only avoided the dis-

advantages of postmolding mentioned above

but also simplified the operation procedures

and made the preparation cost and energy

efficient and environmentally benign.

Structure characterization

During hydrothermal synthesis of Fe-MOR(n)

using the acid co-hydrolysis route (Fig. 1) ( 25 , 27 ),

monolithic macromorphology of cylindrical

shapes on the centimeter level autoformed

316 16 JULY 2021•VOL 373 ISSUE 6552 sciencemag.org SCIENCE

Fig. 1. Self-assembly of Fe-MOR monoliths.Shown are schematic illustrations of the synthetic procedure (A) and a side view (B) and top view (C) of precisely
narrowed microchannels (kinetic diameter: 3.3 to 3.4 Å) by occupying isolated tetrahedral Fe species inside the 12-MR MOR microchannel. Blue indicates Si or Al,
red is O, light brown is Fe, and gray is C.

Fig. 2. SEM and TEM images.Shown are SEM images (AtoC) and HAADF-STEM image (D) of Fe-MOR(0.25) and the corresponding energy-dispersive x-ray mapping
images for Al (E), Si (F), and Fe (G) elements. (HandI) TEM (H) and recorded (I) selected area electron diffraction pattern images of Fe-MOR(0.25).

RESEARCH | RESEARCH ARTICLES