CATALYSIS

Atomic-layered Au clusters on a-MoCas catalysts for the low-temperaturewater-gas shift reactionSiyu Yao,1* Xiao Zhang,2* Wu Zhou,3,4* Rui Gao,5,6 Wenqian Xu,7 Yifan Ye,8 Lili Lin,1

Xiaodong Wen,5,6 Ping Liu,7 Bingbing Chen,2 Ethan Crumlin,8 Jinghua Guo,8

Zhijun Zuo,9 Weizhen Li,1 Jinglin Xie,1 Li Lu,10 Christopher J. Kiely,10 Lin Gu,11

Chuan Shi,2† José A. Rodriguez,7† Ding Ma1†

The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogenand carbon dioxide) is an essential process for hydrogen generation and carbon monoxideremoval in various energy-related chemical operations. This equilibrium-limited reaction isfavored at a low working temperature. Potential application in fuel cells also requires aWGS catalyst to be highly active, stable, and energy-efficient and to match the workingtemperature of on-site hydrogen generation and consumption units. We synthesizedlayered gold (Au) clusters on a molybdenum carbide (a-MoC) substrate to create aninterfacial catalyst system for the ultralow-temperature WGS reaction.Water was activatedover a-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au siteswas apt to react with surface hydroxyl groups formed from water splitting, leading to ahigh WGS activity at low temperatures.

Efficient low-temperature catalysts for thewater-gas shift (WGS) reaction, especiallythose operating under 423 K (1–7), are ofinterest for applications in fuel cells, espe-cially those using H2 generated by hydro-

carbon reforming processes that are contaminatedwith CO, which deactivates the catalysts. For het-erogeneous catalysis, in addition to Cu-basedcatalysts, which display low activity at low tem-perature (8, 9), Pt-group noble metals and Au sup-ported on reducible metal oxides, such as ceria (1)or FeOx (10), which contain oxygen vacancies,are commonly used. Flytzani-Stephanopoulosand co-workers demonstrated that noble metalcatalysts dispersed on alkali-promoted inert sup-ports can also be active for the WGS reaction,making a reducible oxide support no longer arequirement (4, 6). The alkali ion–associated

surface OH groups are reactive toward CO in thepresence of atomically dispersed platinum or gold,giving the catalyst superior metal atom efficiencyin the WGS reaction. Metal carbide (e.g., hexag-onal closest packing b-Mo2C)–supported noblemetal catalysts provide similar functionalities andare more active for the reaction at low tempera-ture (7, 11, 12). However, none of these systems dis-plays an activity higher than 0.1 moles of CO permole of metal per second (molCO molmetal

–1 s–1)between 393 and 423 K (Table 1).To achieve high WGS activity at low temper-

ature, we searched for catalysts that could disso-ciate water efficiently and reform the generatedoxygen-containing species (reaction of surfaceoxygen or hydroxyl with CO*) at low temperature.We report that Au confined over face-centeredcubic–structured a-MoC is at least one order ofmagnitude more active than previous findingsfor the WGS reaction below 423 K. The a-MoCsubstrate facilitates epitaxially grown atomic Aulayers with altered electronic structure for favorablebonding with CO. The synergy of atomic-layeredAu clusters with adjacent Mo sites in a-MoC caneffectively activate water at low temperature.Catalysts made from Au supported by pure-

phase a-MoC [2 weight % (wt %) Au/a-MoC] weresynthesized by a precipitation method followedby sequential temperature-programmed ammo-nization and carburization. For comparative pur-poses, a-MoC, 2 wt % Au/b-Mo2C (13, 14), 2 wt %Au/SiO2 (15), and 2 wt % Au/CeO2 (1) catalystswere also prepared. The high dispersion of Auin the 2 wt % Au/a-MoC [hereafter, (2%)Au/a-MoC] catalyst was evidenced by the lack ofx-ray diffraction (XRD) peaks associated with Aucrystallites. Operando XRD studies (1% CO/3%H2O in He; 10 ml min–1) revealed that the bulkstructure of the (2%)Au/a-MoC catalyst remained

intact up to 523 K, beyond which the a-MoC wasgradually oxidized by water (Fig. 1A). Ex situ XRDexperiments [10.5% CO/21% H2O/20% N2 in Ar;gas hourly space velocity (GHSV) = 180,000 hour–1)confirmed that at higher water partial pressure,the bulk structure of catalysts is stable up to 473 K.Neither the oxidation of a-MoC nor the aggre-gation of Au was observed at temperatures up to473 K (fig. S1).The WGS activity was evaluated under product-

free (10.5% CO/21% H2O/20% N2 in Ar) and fullreformate (11% CO/26% H2O/26% H2/7% CO2 inN2) gas feeds. In the product-free gas (GHSV =180,000 hour−1), a-MoC showed very low CO con-version (3.4%) at 393 K (Fig. 1B), and none ofthe reference catalysts achieved >5% CO con-version below 423 K. However, for the (2%)Au/a-MoC catalyst, CO conversion was >95% at 393 Kand reached 98% at only 423 K. For reactiontemperatures 523 K and above, CO conversiondropped, which may result from the thermody-namic limitation, as well as the gradual trans-formation of a-MoC to molybdenum oxide, asconfirmed by the operando XRD results (Fig. 1Aand fig. S2). The Au-normalized activity of the(2%)Au/a-MoC catalyst in product-free gas was0.012, 0.13, 1.05, 1.66, and 3.19 molCO molAu

–1 s–1

at 313, 353, 393, 423, and 473 K, respectively; thishigh activity at low temperatures compares fa-vorably with other reported WGS catalysts (Table1 and fig. S3; CO conversion below 15%). Becauseof the limitation of the water saturation vaporpressure, at low temperature, the composition ofreactant gas was adjusted. We determined that2 wt % is the optimal Au loading for the Au/a-MoC catalyst (fig. S4).In full reformate gas feed under similar space

velocity, the activity dropped slightly (62% ac-tivity at 393 K) because of product (H2 and CO2)inhibition (Fig. 1D). However, the activity of the(2%)Au/a-MoC catalyst remained as high as 0.62and 2.02 molCO molAu

–1 s−1 at 393 and 473 K, re-spectively. The apparent barrier energy (Eapp) ofa-MoC itself is low (58 ± 10 kJ mol–1), and Eappis even lower for the (2%)Au/a-MoC catalyst (22 ±1 kJ mol–1). Thus, the addition of Au greatly en-hanced the low-temperature reactivity of a goodWGS catalyst (Fig. 1E). Its exceptional activityand high equilibrium CO conversion at low tem-perature can be exploited simultaneously (fig. S5),and the catalyst shows an excellent total turnovernumber, reaching up to 385,400 molCO molAu

–1 ina single-run reaction (fig. S6 and table S1).We designed a two-step temperature-programmed

surface reaction (TPSR) experiment to explore thereaction route. After preactivation of the catalysts,2%H2OinAr (100mlmin–1, 10min)was introducedinto the reactor at 303 K. Production of H2 wasimmediately observed on both (2%)Au/a-MoCand a-MoC catalysts, indicating the presenceof a low-temperature water dissociation centeron a-MoC that led to the formation of H2 andsurface OH species (Fig. 2, A and B, and figs. S7and S8). In contrast, no H2 production was ob-served on (2%)Au/SiO2 or (2%)Au/b-Mo2C cat-alysts (Fig. 2C and fig. S9). After purging withAr (100 ml min–1), the system was switched to

RESEARCH

Yao et al., Science 357, 389–393 (2017) 28 July 2017 1 of 5

1College of Chemistry and Molecular Engineering and Collegeof Engineering, Peking University, Beijing 100871, China.2State Key Laboratory of Fine Chemicals, College ofChemistry, Dalian University of Technology, Dalian 116024,China. 3School of Physical Sciences, CAS (Chinese Academyof Sciences) Key Laboratory of Vacuum Sciences, Universityof Chinese Academy of Sciences, Beijing 100049, China.4Materials Science and Technology Division, Oak RidgeNational Laboratory, Oak Ridge, TN 37831, USA. 5State KeyLaboratory of Coal Conversion, Institute of Coal Chemistry,Chinese Academy of Sciences, Post Office Box 165, Taiyuan,Shanxi 030001, China. 6Synfuels China, Beijing 100195,China. 7Chemistry Division, Building 555, BrookhavenNational Laboratory, Post Office Box 5000, Upton, NY 11973-5000, USA. 8Advanced Light Source, Lawrence BerkeleyNational Laboratory, Berkeley, CA 94720, USA. 9KeyLaboratory of Coal Science and Technology of Ministry ofEducation and Shanxi Province, Taiyuan University ofTechnology, Taiyuan 030024, Shanxi, China. 10Department ofMaterials Science and Engineering, Lehigh University,Bethlehem, PA 18015-3195, USA. 11Institute of Physics,Chinese Academy of Sciences, Beijing 100190, China.*These authors contributed equally to this work.†Corresponding author. Email: chuanshi@dlut.edu.cn (C.S.);rodrigez@bnl.gov (J.A.R.); dma@pku.edu.cn (D.M.)

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2% CO in Ar (100 ml min–1) at 303 K, kept at thattemperature for 10 min, and then increased to523 K at 5 K min–1. For the (2%)Au/SiO2 cat-alyst, only water desorption was observed at~403 K. In sharp contrast, CO2 and H2 were de-tected simultaneously on the (2%)Au/a-MoC cat-alyst at around 308 K, and their intensitiesreached the maxima at 367 K. Thus, the reactionof CO with surface OH could occur at very lowtemperature (308 K) to form CO2 and additionalH2. The reforming reaction could also happenon the a-MoC catalyst, but initiating at a muchhigher temperature (347 K).The coexistence of a low-temperature water disso-

ciation center on a-MoC and the low-temperaturereforming center on the (2%)Au/a-MoC catalystis the key to the exceptional activity of this cat-alyst. The Au L3-edge extended x-ray absorptionfine structure (EXAFS) fitting (table S2 and fig.S10) shows a low Au-Au first shell coordinationnumber (CN) of 6.9, indicating that the averagesize of Au species is ~1.5 nm for a hemisphericalmorphology (16). The Au-Mo CN of 1.6 is striking,considering that Au nanoparticles (NPs) tend toundergo sintering because of the low Tammanntemperature (668 K) of bulk Au. (17, 18) Giventhat this sample was activated at 973 K for morethan 2 hours, a strong metal-support interactionmust exist between Au and a-MoC. X-ray photo-electron spectroscopy (XPS) (fig. S11) revealedthat the Au 4f binding energy shifted 0.6 eV tohigher energy with respect to bulk gold (19), in-dicating that the electronic structure of the Auspecies is perturbed by the substrate. The reac-tion order of CO of –0.16 (Fig. 1D) also indicatedthat CO was already relatively strongly adsorbedon the electronically modified Au surface.Aberration-corrected scanning transmission elec-

tron microscopy (STEM) analysis on the (2%)Au/a-MoC catalyst showed that the catalyst supportswere porous assemblies of small a-MoC NPs (3 to20 nm in diameter; fig. S12). High-resolution STEMZ-contrast imaging (Fig. 2, D and E) revealed twotypes of Au species on the surface of a-MoC:(i) small layered Au clusters epitaxially grown onthe a-MoC support and (ii) atomically dispersedAu. The epitaxial Au clusters had an average di-ameter of 1 to 2 nm and thickness of 2 to 4 atomiclayers (<1 nm), as measured from edge-on clus-ters occasionally found in profile view (Fig. 2Eand fig. S13). Detailed crystal structure analysis(fig. S12, C and D) also showed that these epi-taxial Au clusters strongly aligned with the (111)planes of the a-MoC support, with some exposed(200) facets. There were no larger Au NPs presentin this sample (fig. S14). No obvious structuraldifference was observed between the fresh andused catalyst samples (Fig. 2F), and both types ofAu species were retained in the tested sample,which is also consistent with the relatively goodstability of the catalyst noted in the catalyticreaction.We used NaCN solution to selectively leach

the layered Au clusters from the (2%)Au/a-MoCcatalyst (1, 20). The Au loading decreased toaround 0.9 wt %, leaving predominantly theatomically dispersed Au atoms, as confirmed by

Yao et al., Science 357, 389–393 (2017) 28 July 2017 2 of 5

Eapp

Eapp

Eapp

Eapp

623 K

573 K

523 K

473 K

423 K

A

Fig. 1. Catalytic properties and structural characterization of the (2%)Au/a-MoC catalyst.(A) In situ XRD (wavelength, 0.3196 Å) of the (2%)Au/a-MoC catalyst under WGS reaction conditions atvarious temperatures. The y axes in the top and bottom panels are in arbitrary units. The rainbow colorscheme in the middle panel spans from no signal (blue) to high-intensity diffraction peaks (red). MoO2 anda-MoC are shown on the right as ball-and-stick diagrams (red, O; purple, Mo; black, C). (B) CO conversionon different catalysts at various temperatures (10.5%CO/21%H2O/20%N2 in Ar; GHSV, 180,000 hour−1).(0.9%)Au/a-MoCwasproducedbyNaCN leachingof (2%)Au/a-MoC. (C) The activityof different catalysts(moles of CO per moles of metal per second), measured at CO conversion below 15% in 11% CO/26%H2O/26% H2/7% CO2/30% N2. (D) Kinetic orders (n) of the reactants and products. (E) Apparentactivation energy Eapp of various catalysts in 10.5% CO/21% H2O/20% N2-Ar balance.

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both STEM and XAFS results (Fig. 2G; fig. S12,E to G; and table S2). The Au-normalized WGSactivities of (0.9%)Au/a-MoC (leached by NaCN)at 393 and 423 K decreased to around 1/11thand 1/6th of their original values, respectively,but were still higher than those of NaCN-leacheda-MoC catalyst (with Eapp similar to that of fresha-MoC; Fig. 1E). This result indicated that atom-ically dispersed Au species were indeed catalyt-ically active (1), but the catalytic efficacy of thelayered Au clusters on the a-MoC support for low-temperature WGS was even higher than that ofthe atomically dispersed Au. Furthermore, theEapp increased to 41 kJ mol–1 after NaCN leaching(Fig. 1E), suggesting some degree of blocking ofthe low-temperature reaction route after the re-moval of layered Au clusters. Thus, we attribute thelow-temperature WGS activity mainly to the epi-taxial Au clusters decorating the a-MoC support.We carried out density functional theory (DFT)

calculations to investigate the WGS reaction pathon the Au/a-MoC catalyst. Three catalyst models(fig. S15) of Au(111), monolayer Au/a-MoC(111),and cluster Au15/a-MoC(111) were constructedto represent the different sites on Au/a-MoC, inwhich Au(111) and monolayer Au/a-MoC(111) sim-ulate large Au NPs and electronic property–modified Au NPs, respectively. Au15/a-MoC(111)represents the interface model of our atomic-layered Au cluster over a-MoC(111). Similar toexperimental observations, the Au cluster inAu15/a-MoC has a layered structure, with (111)and (200) exposed facets.As shown in fig. S16, H2O is thermodynami-

cally and kinetically hard to dissociate on Au(111)and monolayer Au/a-MoC(111), with barriers of 1.91and 1.66 eV, and the reactions are endothermicby 1.57 and 1.15 eV, respectively. In contrast, whenwe investigated the first step of the WGS reaction

Yao et al., Science 357, 389–393 (2017) 28 July 2017 3 of 5

Fig. 2. Mechanism study andelectron microscopy charac-terization.Water adsorption(at 303 K) followed by CO TPSR,using (A) (2%)Au/a-MoC,(B) a-MoC, and (C) (2%)Au/SiO2.Signals of H2 [mass/charge(m/z) = 2], H2O (m/z = 18), CO(m/z = 28), and CO2 (m/z = 44)were detected. (D and E) High-resolution high-angle annulardark-field (HAADF)–STEM imagesof fresh (2%)Au/a-MoC, withsingle atoms of Au marked in bluecircles and layered Au structureshighlighted in yellow. The Auclusters were further identified byelemental analysis (figs. S18 andS19). (F) HAADF-STEM image ofthe (2%)Au/a-MoC catalyst afterreaction, in which the samplestill contains both single-atomAu and layered Au clusters.(G) HAADF-STEM image of the(2%)Au/a-MoC catalyst afterNaCN leaching, showing predominantly single atoms of Au, most of which overlap with Mo sites in the support lattice. The very bright features in thisimage are caused by overlapping MoC particles, as confirmed by elemental mapping (figs. S18 and S19).

A

B

C

D E

F GIn

tens

ityIn

tens

ityIn

tens

ity

Inte

nsity

Inte

nsity

Inte

nsity

Time (min) Temperature (K)

3.0

2.5

2.0

1.5

1.0

0.5

0.0CO+H2O+3O

CO+2OH+2O13CO+2OH

12CO+CO2+H2O

(0.22)(0.52)

(0.27)TS3*

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

-3.0

-3.5

-4.0

-4.5

-5.0

CO

(g) +2H

2 O(g)

(-1.42)

(-0.65)

(-1.83)

TS1(-1.26)

TS2

(-2.48) (-2.41)

COb (-2.26)

COt2(-1.76)

TS3 (-2.06)(-2.21)

(-1.41)

(-0.74)

(-2.86)

CO+2H2O

CO+H2O+OH+H

COt1+2OH+2H

CO+H2O+O+2H

CO2+H2O+2HH2O+2H

H2O

Au15/MoC(111)

H2O(g)

eV

eV

Fig. 3. The reaction paths for the WGS reaction on Au15/a-MoC(111). (A) H2O dissociation and COreforming at lower coverage, (B) O-assisted H2O dissociation on the boundary oxidized by three Oatoms, and (C) CO reforming at high coverage.The energies of gaseous molecules include the zero-pointenergy and entropy correction at 423 K. Au, Mo, C, O, and H atoms are shown in gold, cyan, gray,red, and white, respectively; to distinguish the C atom in CO, it is represented in black.The subscripts(g), b, and t denote gas phase, bridge site, and top site, respectively. TS, transition state.

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(namely, water dissociation) on Au15/a-MoC(111),we found that at lower coverage (Fig. 3A), twoH2O molecules could be easily dissociated andform two H atoms and two OH species with theeffective barrier of 0.77 eV (CO + 2H2O → CO +2OH + 2H), and the two OH species could imme-diately react (and without a barrier), forming asurface O atom (CO + 2OH + 2H→ CO +H2O +O + 2H; exothermic by 0.38 eV). These results in-dicate that some surface domains of a-MoC couldbe oxidized by water during the reaction, whichhas been confirmed by XPS and 18O nuclear mag-

netic resonance (NMR) experiments (figs. S7 andS8). After the surface was partially decoratedwith oxygen (Fig. 3B), the calculations showedthat surface O atoms could further promote waterdissociation. The successive O-assisted water dis-sociation (CO + 3O + H2O→ CO + 2O + 2OH) onthe boundary of Au15 and a-MoC(111) had a muchlower barrier of 0.22 eV, indicating that the firstO–H bond of water could be easily broken at lowtemperature by this bifunctional catalyst.The surface OH species formed on the Mo site

were apt to react with CO adsorbed on the adja-

cent Au surface, which has the right geometry(triangular) to enable a low reaction barrier. In-deed, at low CO coverage (Fig. 3A), the effectivebarrier for the reforming of CO on Au and OHon a-MoC(111) was 0.72 eV, including a migra-tion barrier of 0.22 eV and reaction barrier of0.50 eV. At high CO coverage (Fig. 3C), the reform-ing barrier was even lower—0.52 eV—demonstrat-ing that the reaction between adsorbed CO andsurface OH species on the peripheral interfaceof Au and a-MoC (CO + OH = CO2 + ½H2) wasapt to proceed. Although the reforming process

Yao et al., Science 357, 389–393 (2017) 28 July 2017 4 of 5

Table 1. Comparison of the activities of the representative catalytic systems for the low-temperature WGS reaction. The operating pressure of the

reactions was 1 bar.

Temperature

(kelvin)

Gas feed

composition

Mass-specific

activity (micromoles

of CO per grams

of catalyst

per second)

Metal-normalized

activity (moles

of CO per

moles of metal

per second)

Apparent

activation

energy

(kilojoules

per mole)

Reference

Reducible oxide supports.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Au/CeO2 523 11% CO/26% H2O/26% H2/7% CO2 in He 4.8 0.13 37 (1).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Pt/CeO2 523 11% CO/26% H2O/26% H2/7% CO2 in He 22 0.17 75 (1).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Ir1/FeOx 573 2% CO/10% H2O in He 1.2 2.32 50 (21).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Au/FeOx 598 11% CO/26% H2O/26% H2/7% CO2 in He 11 0.31 49 (22).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Alkali-promoted inert supports.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Au-Na/MCM41 423 11% CO/26% H2O/26% H2/7% CO2 in He 0.8 0.067 44 (5).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Pt-Na/SiO2 523 11% CO/26% H2O/26% H2/7% CO2 in He 12 0.24 70 (4).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Pt-Na/CNT 473 2% CO/10% H2O in He 1.25 0.024 70 (23).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Molybdenum carbide supports (b-Mo2C).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Pt/Mo2C 513 11% CO/ 21% H2O/43% H2/6% CO2 in N2 221 1.42 53 (11).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Pt/Mo2C 393 7% CO/22% H2O/37% H2/8.5% CO2 in Ar 1.8 0.023 48 (12).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Au/Mo2C 393 7% CO/22% H2O/37% H2/8.5% CO2 in Ar 1.6 0.021 44 (12).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Homogeneous catalysts.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Ru3(CO)12 373 1 bar CO, NaOH solution 0.12 2.6 × 10–5 no data (24).. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

Our results.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

(2%)Au/a-MoC

313 3% CO/6% H2O/ 20% N2 in Ar 1.22 0.012.. ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ...

3335% CO/10% H2O/20% N2 in Ar

5.91 0.06.. ... .. ... .. ... ... .. ... ... .. .

353 13.06 0.13–.. ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .

393

10.5% CO/21% H2O/20% N2 in Ar

103 1.05.. ... .. ... .. ... ... .. ... ... .. .

423 167 1.66 22*.. ... .. ... .. ... ... .. ... ... .. .

473 325 3.19.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

(2%)Au/a-MoC

3335% CO/10% H2O/10% H2/3% CO2 in N2

2.39 0.02

–

.. ... .. ... .. ... ... .. ... ... .. .

353 9.20 0.09.. ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .

393

11% CO/26% H2O/26% H2/7% CO2 in N2

53 0.62.. ... .. ... .. ... ... .. ... ... .. .

423 106 1.05 27.. ... .. ... .. ... ... .. ... ... .. .

473 213 2.02.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

(0.9%)Au/a-MoC

(leached by NaCN)

393

10.5% CO/21% H2O/20% N2 in Ar

9.07 0.09

–.. ... .. ... .. ... ... .. ... ... .. .

423 26.6 0.26 41.. ... .. ... .. ... ... .. ... ... .. .

473 73.1 0.72.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

(2%)Au/b-Mo2C

393

11% CO/26% H2O/26% H2/7% CO2 in N2

2.06 0.02

–.. ... .. ... .. ... ... .. ... ... .. .

423 4.29 0.04 38.. ... .. ... .. ... ... .. ... ... .. .

473 14.4 0.14.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

a-MoC

393

11% CO/26% H2O/26% H2/7% CO2 in N2

2.05

–.. ... .. ... .. ... ... .. ... ... .. .

423 8.57 64.. ... .. ... .. ... ... .. ... ... .. .

473 56.7.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

(2%)Au/SiO2 673 10.5% CO/21% H2O/20% N2 in Ar 0.24 2.4 × 10–3 –.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

(2%)Au/CeO2 423 11% CO/26% H2O/26% H2/7% CO2 in N2 1.1 0.01 –.. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .

*The activation energy was also determined by another method (fig. S17).

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was facile, it still had a higher barrier than thefirst step of the WGS reaction (water dissociationon partially oxidized a-MoC). Thus, the rate-determining step of the WGS reaction on Au15/a-MoC is the reforming process, which is in goodagreement with our TPSR observations (Fig. 2).The interfacial nature and optimum bonding ofthis a-MoC–confined Au nanostructure confersthe catalyst with outstanding WGS reactivity atlow temperature.

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ACKNOWLEDGMENTS

This work received financial support from the 973 Project (grants2017YFB0602200, 2013CB933100, and 2011CB201402), the CASPioneer Hundred Talents Program, and the Natural ScienceFoundation of China (grants 91645115, 21473003, 21222306,21373037, 21577013, and 91545121). The electron microscopywork was also supported in part by the U.S. Department of Energy(DOE), Office of Science, Office of Basic Energy Sciences, MaterialsSciences and Engineering Division (to W.Z.), and through a userproject at Oak Ridge National Laboratory's Center for NanophaseMaterials Sciences, which is a DOE Office of Science User Facility.The x-ray absorption spectroscopy experiments were conductedat the Shanghai Synchrotron Radiation Facility and the BeijingSynchrotron Radiation Facility. We also acknowledge the NationalThousand Young Talents Program of China, the Shanxi HundredTalents Program, and the Fundamental Research Funds for

the Central Universities (grants DUT15TD49 and DUT16ZD224). Theresearch done at Brookhaven National Laboratory (BNL) was financedunder contract no. DE-SC0012704 with the DOE. Some of thetheoretical calculations were done at the Center for FunctionalNanomaterials on the BNL campus. The Advanced Light Source issupported by the Director, Office of Science, Office of Basic EnergySciences, of the DOE under contract no. DE-AC02-05CH11231.Y.Y. acknowledges the support of the Advanced Light SourceDoctoral Fellowship. C.J.K. gratefully acknowledges funding from theU.S. National Science Foundation Major Research Instrumentationprogram (grant MRI/DMR-1040229). D.M. thanks L. Peng andM. Wang for help with 17O NMR experiments. All data are reportedin the main text and supplementary materials. C.S. and X.Z. areinventors on a patent application (ZL 2015 1 0253637.6) held byDalian University of Technology that covers the preparation ofAu/a-MoC. D.M., C.S., and J.A.R. designed the study. X.Z. and S.Y.performed most of the reactions. W.Z., L.Lu, C.J.K., and L.G.performed the electron microscopy study. R.G., X.W., P.L., and Z.Z.finished the DFT calculations. S.Y., W.X., and W.L. performed thex-ray structure characterization and analysis. S.Y., D.M., W.Z.,and J.A.R. wrote the paper. Other authors provided reagents,performed certain experiments, and revised the paper.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/357/6349/389/suppl/DC1Materials and MethodsSupplementary TextFigs. S1 to S32Tables S1 and S5References (25–38)

26 June 2016; resubmitted 12 April 2017Accepted 9 June 2017Published online 22 June 201710.1126/science.aah4321

Yao et al., Science 357, 389–393 (2017) 28 July 2017 5 of 5

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reaction-MoC as catalysts for the low-temperature water-gas shiftαAtomic-layered Au clusters on

and Ding MaCrumlin, Jinghua Guo, Zhijun Zuo, Weizhen Li, Jinglin Xie, Li Lu, Christopher J. Kiely, Lin Gu, Chuan Shi, José A. Rodriguez Siyu Yao, Xiao Zhang, Wu Zhou, Rui Gao, Wenqian Xu, Yifan Ye, Lili Lin, Xiaodong Wen, Ping Liu, Bingbing Chen, Ethan

originally published online June 22, 2017DOI: 10.1126/science.aah4321 (6349), 389-393.357Science 

, this issue p. 389ScienceMoC to form surface hydroxyl groups, which then reacted with CO adsorbed on the gold clusters.

at temperatures as low as 150°C. Water was activated on2 and CO2convert CO through its reaction with water into H developed a catalyst composed of layered gold clusters on molybdenum carbide (MoC) nanoparticles toet al.site. Yao

generated from hydrocarbons on2Carbon monoxide deactivates fuel cell catalysts, so it must be removed from HLow-temperature CO removal

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