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ACKNOWLEDGMENTS
The authors thank all the developers of the GTAP Data Base,
E. Hansis for making contributions to the development of the
BLUE model, and J.E.M.S. Nabel for performing initial BLUE
simulations.Funding:C.H. acknowledges support from the
Scientific Research Start-up Funds (QD2021030C) from Tsinghua
Shenzhen International Graduate School. J.A.B., F.C.M., and
S.J.D. were supported by the US National Science Foundation
and US Department of Agriculture (INFEWS grant EAR 1639318),
and S.J.D. also acknowledges a grant from the ClimateWorks

Foundation (22-2100 / 2202-802317943). Q.Z. was supported by

the National Natural Science Foundation of China (41921005). H.Z.

was supported by the National Natural Science Foundation

of China (71904097). Y.L. was supported by the National Natural

Science Foundation of China (72125010 and 71974186). R.B.J.

acknowledges support from the Gordon and Betty Moore

Foundation (Grant GBMF5439,“Advancing Understanding of the

Global Methane Cycle”).Author contributions:C.H. and S.J.D.

conceived the study. C.H., H.Z., and Y.Q. performed the analyses,

with support from Q.Z., J.P., K.H., and Y.L. on datasets, and from

S.J.D., Q.Z., J.A.B., J.P., F.C.M., and R.B.J. on analytical

approaches. C.H. and S.J.D. led the writing with input from all

coauthors. All coauthors reviewed and commented on the

manuscript.Competing interests:The authors declare no

competing interests.Data and materials availability:Production-

based estimates of land-use emissions are available at https://

sustsys.ess.uci.edu/CALUE.html. Statistics on agricultural

production and land area as well as the agricultural emissions

are curated by the FAO and freely available at http://www.fao.org/

faostat/en/. The GTAP Data Base is available at https://www.gtap.

agecon.purdue.edu/databases/. The supplementary materials

contain our results. All data central to the main claims are available

in the main text or the supplementary materials.

SUPPLEMENTARY MATERIALS

science.org/doi/10.1126/science.abj1572

Materials and Methods

Figs. S1 to S17

Tables S1 to S3

References ( 53 – 69 )

Data S1 to S5

Submitted 23 April 2021; resubmitted 26 January 2022

Accepted 31 March 2022

10.1126/science.abj1572

CATALYSIS

The state of zinc in methanol synthesis over a

Zn/ZnO/Cu(211) model catalyst

Peter Amann^1 †, Bernhard Klötzer^2 , David Degerman^1 , Norbert Köpfle^2 ‡, Thomas Götsch^3 ,

Patrick Lömker4,1, Christoph Rameshan^5 , Kevin Ploner^2 , Djuro Bikaljevic^2 , Hsin-Yi Wang^1 ,

Markus Soldemo^1 §, Mikhail Shipilin^1 , Christopher M. Goodwin^1 , Jörgen Gladh^1 §,

Joakim Halldin Stenlid^1 ¶, Mia Börner^1 , Christoph Schlueter^4 , Anders Nilsson^1 *

The active chemical state of zinc (Zn) in a zinc-copper (Zn-Cu) catalyst during carbon dioxide/carbon

monoxide (CO 2 /CO) hydrogenation has been debated to be Zn oxide (ZnO) nanoparticles, metallic Zn,

or a Zn-Cu surface alloy. We used x-ray photoelectron spectroscopy at 180 to 500 millibar to probe

the nature of Zn and reaction intermediates during CO 2 /CO hydrogenation over Zn/ZnO/Cu(211),

where the temperature is sufficiently high for the reaction to rapidly turn over, thus creating an almost

adsorbate-free surface. Tuning of the grazing incidence angle makes it possible to achieve either

surface or bulk sensitivity. Hydrogenation of CO 2 gives preference to ZnO in the form of clusters or

nanoparticles, whereas in pure CO a surface Zn-Cu alloy becomes more prominent. The results reveal

a specific role of CO in the formation of the Zn-Cu surface alloy as an active phase that facilitates

efficient CO 2 methanol synthesis.

M

ethanol receives much interest as an

industrial chemical as well as for its

potential as an energy carrier ( 1 ). Its

gravimetric energy density is compa-

rable to that of liquid ammonia and

can easily be distributed and stored with es-

tablished technologies. To date, the leading

industrial catalyst for the CO/CO 2 hydrogena-

tion toward methanol consists of a mixture of

Cu, ZnO, and Al 2 O 3 ( 2 ). Methanol synthesis is

carried out between 150° and 300°C at pres-

sures of 50 to 100 bar but can also occur at sub-

stantially lower pressures of a few millibar ( 3 ).

Although this catalytic process is a century

old, years of intense research have aimed to

determine the mechanism and active sites.

The catalytic nature of the Zn in the catalyst

is still highly debated ( 2 ), and the mechanism

is not yet fully experimentally verified. The

addition of ZnO/Zn goes beyond the role of a

mere particle dispenser and acts as a chemi-

cally active promoter of the reaction (the ZnCu

synergistic effect). There are a number of hy-

potheses about the chemical state of Zn—more

specifically, whether it is in a metallic state

as a surface alloy ( 4 ) or a bulk alloy ( 5 ), and

whether small ZnO islands are present on the

surface ( 6 , 7 )orinbulkforms( 8 , 9 ). There is

also a proposal that mixed phases could co-

exist, either in the bulk or on the surface ( 10 ).

Additionally, Zn diffusion and Zn spillover on

SCIENCEscience.org 6 MAY 2022•VOL 376 ISSUE 6593 603

(^1) Department of Physics, Stockholm University, AlbaNova
University Center, 10691 Stockholm, Sweden.^2 Institute of
Physical Chemistry, University of Innsbruck, Innrain 52c,
6020 Innsbruck, Austria.^3 Department of Inorganic
Chemistry, Fritz Haber Institute of the Max-Planck Society,
Faradayweg 4-6, 14195 Berlin, Germany.^4 Photon Science,
Deutsches Elektronen-Synchrotron DESY, Notkestr. 85,
22607 Hamburg, Germany.^5 Institute of Materials Chemistry,
Technische Universität Wien, Getreidemarkt 9/BC/01, 1060
Vienna, Austria.
*Corresponding author. Email: [email protected]
†Present address: Scienta Omicron AB, Danmarksgatan 22, 75323
Uppsala, Sweden.
‡Present address: Plansee SE, Metallwerk-Planseestraße 71, 6600
Reutte, Austria.
§Present address: PULSE Institute, SLAC National Accelerator
Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
¶Present address: SUNCAT Center for Interface Science and
Catalysis, SLAC National Accelerator Laboratory, 2575 Sand Hill
Road, Menlo Park, CA 94025, USA.
RESEARCH | RESEARCH ARTICLES