Science - USA (2020-02-07)

leading to much faster transport of water mole-
cules through the zeolitic nanochannel.
To better understand the potential gating
effect of Na+,weperformeddensityfunctional
theory (DFT) simulations to mimic the process

of molecules passing the 8-oxygen ring aperture

(Fig. 2B). We consider the passage of a mole-

cule through the 8-oxygen ring as a three-step

process with four defined states of a molecule

(Fig. 2B): (i) approaching the surface of the

8-oxygen ring; (ii) entering the ring, referred

to as admission of a molecule to the ring; and

(iii) moving out of the ring and entering the

a-cage of the NaA zeolite. Our result suggests

that the most stable Na+location in NaA zeolite

Liet al.,Science 367 , 667–671 (2020) 7 February 2020 3of5

Fig. 2. DFT simulation of
the passage of molecules
through NaA zeolitic
channels.(A) Top view of
the structural framework of
NaA zeolite with three Na+
sites in the dehydrated crystal
structure. (B) The passage
of molecules through the zeolitic
channels of NaA. In state 1, the
gas molecule is away from
the 8-oxygen ring. In state 2,
the gas molecule is adsorbed
onto the ring. In state 3, the gas
molecule is in the ring. In
state 4, the gas molecule is in
thea-cage of the NaA zeolite. Numbers are energy levels calculated by DFT for three molecules moving into thea-cageofNaAzeolitethroughthe8-oxygenring.

Fig. 3. Schematics of the membrane reactor (MR) concept and catalytic
performance of the MR.(A) Schematics of WCM-incorporated dehydration
MR for high-purity methanol direct synthesis from renewable resources.
(B) Catalytic CO 2 conversion (points) and methanol yield (columns) obtained in
the traditional reactor (TR; orange) and in the MR (purple) as a function of
temperature at 35 bar and feed (CO 2 /H 2 = 1/3) gas hourly space velocity

(GHSV) of 5100 ml gcat–^1 hour–^1. Membrane length is 45 mm. Error bars denote

SD. (C) Catalytic performance of methanol synthesis from CO 2 hydrogenation

over 100 hours in the MR at 220°C and 35 bar. The feed (CO 2 /H 2 =1/3)GHSV

is 4200 ml gcat–^1 hour–^1 ; membrane length is 45 mm. (D) Demonstration

of high-purity methanol direct synthesis in the MR at different feed GHSVs at

220°C and 35 bar with three hollow-fiber WCMs 210 mm in length.

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