Direct conversion of CO 2 into liquid fuels with high

Direct conversion of CO2 into liquid fuels with highselectivity over a bifunctional catalystPeng Gao1, Shenggang Li1,2, Xianni Bu1, Shanshan Dang1,3, Ziyu Liu1, Hui Wang1, Liangshu Zhong1*,Minghuang Qiu1, Chengguang Yang1, Jun Cai2,4, Wei Wei1,2 and Yuhan Sun1,2*

Although considerable progress has been made in carbon dioxide (CO2) hydrogenation to various C1 chemicals, it is still agreat challenge to synthesize value-added products with two or more carbons, such as gasoline, directly from CO2 becauseof the extreme inertness of CO2 and a high C–C coupling barrier. Here we present a bifunctional catalyst composed ofreducible indium oxides (In2O3) and zeolites that yields a high selectivity to gasoline-range hydrocarbons (78.6%) with avery low methane selectivity (1%). The oxygen vacancies on the In2O3 surfaces activate CO2 and hydrogen to formmethanol, and C−C coupling subsequently occurs inside zeolite pores to produce gasoline-range hydrocarbons with a highoctane number. The proximity of these two components plays a crucial role in suppressing the undesired reverse water gasshift reaction and giving a high selectivity for gasoline-range hydrocarbons. Moreover, the pellet catalyst exhibits a muchbetter performance during an industry-relevant test, which suggests promising prospects for industrial applications.

Owing to the growing energy demand, dwindling fossil fuelreserves and increasing atmospheric CO2 concentration,renewable energy sources, such as solar, wind and biomass,

foresee increasing usage. However, the widespread utilization ofrenewable energy sources is currently limited by their intermittentand fluctuating nature. In this context, the chemical conversion ofcarbon dioxide (CO2) into value-added products with the assistanceof hydrogen (H2) would represent a promising solution to thestorage of renewable energy1–3.

Thus, much attention has been paid to CO2 hydrogenation tovarious C1 feedstocks (for example, methane (CH4), methanol(CH3OH), carbon monoxide (CO) and formic acid) and considerableprogress has been achieved4–11. However, the extreme inertness of CO2

and the high kinetic barriers for the formation of C–Cbonds12,13meanit is still a great challenge to synthesize C2+ (hydrocarbons with two ormore carbons) products directly from CO2, such as gasoline (C5–C11

hydrocarbons), which is a very important transportation fuel widelyused around theworld. CO2 is well-known to be a very stable molecule(ΔfG

o= –396 kJ mol–1), the end product of any combustion process,either biological or chemical, alongwith water14,15. Another key bottle-neck problem is the assembly of the atoms and formation of chemicalbonds to convert the relatively simple CO2 molecules into the muchmore complex and energetic C5–C11 hydrocarbons. Obviously, signifi-cant catalytic advances are required for the large-scale production ofliquid fuels directly from CO2 hydrogenation. Currently, theFischer–Tropsch synthesis (FTS) route using modified Fe-basedcatalysts can be utilized to produce hydrocarbons directly from CO2.However, the maximum C5–C11 hydrocarbon fraction was limitedby the Anderson–Schulz–Flory distribution to ∼48%with an undesir-ableCH4 fraction of∼6%(refs 16,17). Furthermore, the heat of adsorp-tion of CO2 is lower than that of CO because of the thermodynamicstability of CO2, which leads to a much lower coverage of CO2 overthe catalyst, and thus a low CO2 reactivity and high CH4 selectivity.

In the present work, a bifunctional catalyst that contains partiallyreducible metal oxides (In2O3) and H-form Zeolite Socony Mobil-5

(HZSM-5) zeolites exhibits an excellent performance for the directproduction of gasoline-range hydrocarbons from CO2 hydrogen-ation with a high selectivity. The C5+ selectivity in hydrocarbon dis-tribution reached up to 78.6% with only 1% for CH4 selectivity at aCO2 conversion of 13.1% (Fig. 1a). There was no obvious catalystdeactivation over 150 hours, and a much better performance forCO2 hydrogenation to C5+ hydrocarbons was observed using apellet catalyst with internal gas recycling. Such results thus suggesta promising potential for its industrial application.

Results and discussionsThe bifunctional catalyst consists of a metal oxide (In2O3) with asmall particle size of about 10 nm (Fig. 1b and Supplementary Figs1 and 2) and a high specific surface area of 120 m2 g–1

(Supplementary Table 1), and a HZSM-5 zeolite with a hierarchicalmicro/mesoporous structure with a mesopore diameter of 4 nm(Fig. 1c and Supplementary Fig. 3a). The catalytic performanceand structure information of the sole In2O3 component wereinvestigated first.With In2O3 as the sole catalyst under the same reac-tion conditions, CO and CH3OH were the major products. Thehydrocarbon selectivity was rather low (2.4%) and no C5+ hydrocar-bons were detected (Fig. 1a). Density functional theory (DFT) calcu-lations (Supplementary Fig. 4) revealed that In2O3 is reducible, whichresults in a surface rich in oxygen vacancies. The oxygen vacancy onthe In2O3 surface benefits CO2 activation and hydrogenation, andcan also be generated through thermal desorption18,19. After pre-treatment of In2O3 in argon (Ar) at 400 °C for one hour, the amountof surface oxygen defects detected from oxygen atoms adjacent to thedefects by in situ near-ambient pressure X-ray photoelectron spec-troscopy (NAP–XPS, O 1s at 531.7 eV (Supplementary Fig. 5a andSupplementary Table 2)) increased to 24.8%. However, the changesin the particle sizes calculated from in situX-ray diffraction (XRD) pat-terns (Supplementary Fig. 1) and specific surface areas(Supplementary Table 1) were negligible during the pre-treatmentprocess. The CO2 and H2 adsorption properties of the In2O3

1CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai201210, China. 2School of Physical Science and Technology, ShanghaiTech University, Shanghai 201203, China. 3University of the Chinese Academy ofSciences, Beijing 100049, China. 4State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and InformationTechnology, Chinese Academy of Sciences, Shanghai 200050, China. *e-mail: [email protected]; [email protected]

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surface were investigated further by CO2 and H2 temperature-programmed desorption (TPD), respectively. As illustrated inSupplementary Fig. 6a, the observed peak at approximately 417 °Coriginated from the desorption of CO2 that interacted strongly withthe surface. The dissociative adsorption of H2 was detected at 114 °C,which formed atomic hydrogen on the In2O3 surface capable ofparticipating in hydrogenation reactions (Supplementary Fig. 6b).

The sole HZSM-5 zeolite used in the bifunctional catalyst wasalso tested for CH3OH conversion and exhibited a typical catalyticperformance of CH3OH to gasoline with a complete CH3OHconversion (100%) and a high C5+ selectivity of 71.4% (Fig. 1a)20,21.We therefore conclude that CO2 was first hydrogenated toCH3OH on the In2O3 surface, and CH3OH was then transformed

into hydrocarbons inside the HZSM-5. DFT calculations werecarried out to predict the catalytic cycle of CO2 hydrogenation toCH3OH at the oxygen-vacancy site of In2O3, and the potentialenergy surface is shown in Fig. 2a,c. CO2 first chemisorbed atthe oxygen-vacancy site, and the chemisorbed CO2* species(* represents the surface-adsorbed species) then underwent stepwisehydrogenation to give formate (bi-HCO2*), dioxymethylene(bi-H2CO2*), methoxy (mono-H3CO*) and finally CH3OH. Theoxygen vacancy was filled during the above process, and was regen-erated by subsequent hydrogenation. CH3OH formed over thesurface of In2O3 passed further through the HZSM-5 zeolite,where it was transformed into various hydrocarbons at the acidicsite of the zeolite via the hydrocarbon-pool mechanism, as shown

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Figure 1 | Catalytic performance over various catalysts and the morphology of the In2O3/HZSM-5 bifunctional catalyst. a, CO2 hydrogenation over variousbifunctional catalysts that contained Cu-based catalysts or In2O3 and HZSM-5 with different mass ratios, as shown in the parentheses, and the stand-aloneIn2O3 catalyst (reaction conditions, 340 °C, 3.0 MPa, 9,000 ml h–1 gcat

–1, H2/CO2/N2 = 73/24/3), as well as the conversion (conv.) of CH3OH over HZSM-5(reaction conditions, 340 °C, Ar 3.0 MPa, 9,000 ml h–1 gcat

–1; liquid CH3OH 0.855 ml h–1 gcat–1). Compared with Cu-based catalysts combined with HZSM-5,

the In2O3/HZSM-5 catalysts show much lower selectivities (sel.) of CO and CH4. The sole In2O3 metal oxide and HZSM-5 zeolite exhibit a typical catalyticperformance of CO2 hydrogenation into CH3OH, and CH3OH into gasoline, respectively. C5+, red; C2–4, blue; CH4, grey. b, HRTEM image of In2O3 with anexposed facet of (222) after the thermal treatment in Ar at 400 °C for 1 h. c, HRTEM image of HZSM-5 with a lattice spacing of 1.0 nm assigned to the(200) lattice plane of the ZSM-5 crystals.

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in Fig. 2b,d22–24. Moreover, it was also found that the C5–C11 iso-paraffins were mainly obtained from CO2 hydrogenation over theIn2O3/HZSM-5 composite catalyst, and the ratio of isoparaffins ton-paraffins was 16.8 (Supplementary Table 3 and SupplementaryFig. 7). This was very different from that of CO2-based FTS, inwhich normal paraffins and olefins were the main products, andnearly no isoparaffins with a high octane number were formed25–27.

CH3OH synthesis from CO2 hydrogenation is usuallyaccompanied by undesirable CO formation via the reverse watergas shift (RWGS) reaction, which is further enhanced by increasingthe reaction temperature because of the endothermicity of the RWGSreaction. According to the equilibrium calculations (SupplementaryFig. 8), the equilibrium selectivity of CO increases significantly withincreasing temperature, and reaches 97.1% at 340 °C. When thetypical Cu–ZnO–Al2O3 industrial catalyst28 for the synthesis ofCH3OH from syngas and the highly efficient Cu–ZnO–Al2O3–ZrO2 catalyst29 for CO2 hydrogenation to give CH3OH wereemployed for this reaction instead of In2O3, the main product wasCO with a much higher CH4 selectivity in the hydrocarbon distri-bution under the same reaction conditions (Fig. 1a). Similar resultswere found for other conventional CH3OH synthesis catalysts, suchas Cu–ZnO, Cu–ZnO–ZrO2 and Cu–ZnO–Cr2O3 combined withvarious zeolites30–33. Recent DFT calculations demonstrated thatthe key intermediates involved in CH3OH synthesis were morestable on the defective In2O3 surface than those on the Cu surface,which strongly suppressed the formation of CO (ref. 18). TheCH3OH selectivity over In2O3 can be tuned up to 100% when thespace velocity is above 16,000 h−1, even at the high reaction tempera-ture of 300 °C, whereas much higher space velocities are required forCu-based catalysts19,34. Consequently, CO selectivity over In2O3

integrated with the zeolite (<45%) was much lower than that overtraditional Cu-based catalysts (>90%) at 340 °C. Furthermore,compared with other reducible metal oxides, such as Ga2O3,Fe2O3, ZnO–Cr2O3 and ZnO–ZrO2 combined with HZSM-5, theIn2O3/HZSM-5 composite catalyst exhibited amuch better perform-ance for CO2 hydrogenation with a higher activity and a higherselectivity to C5+ hydrocarbons (Supplementary Table 4).

The hydrocarbon selectivity and distribution were also affectedmarkedly by the integration manner of the active components35,36.Using a dual-bed configuration with the HZSM-5 packed abovethe In2O3 and separated by a layer of inert quartz sand (Fig. 3a),the CH4 selectivity was very high (66.3%), whereas the selectivityto C5+ hydrocarbons was only 26.7% and a large amount ofCH3OH (31.8%) was detected. When HZSM-5 particles wereloaded below the oxides (Fig. 3b), the formed CH3OH can becompletely converted into hydrocarbons, and the C5+ selectivityincreased to 70.4%, whereas the CH4 selectivity dropped to 4.5%.Furthermore, by moving the two components into a closerproximity (from Fig. 3b to Fig. 3d), the CO selectivity decreasedsignificantly, because of the suppression of the undesired RWGSreaction, the C5+ selectivity enhanced and the CH4 selectivityreduced, although the CO2 conversion only changed slightly. Weobserved an even higher C5+ selectivity of 78.6% and a very lowCH4 selectivity of 1% over the composite catalyst without quartzsand (Fig. 3d). The effect of the relative amounts of each componentof In2O3/HZSM-5 on the catalytic performance was alsoinvestigated. With a decreasing relative amount of In2O3, bothCO2 conversion and CO selectivity decreased. The hydrocarbondistribution changed slightly when the oxide/zeolite mass ratiodecreased from 2:1 to 1:2, whereas the C5+ selectivity dropped and

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Figure 2 | Molecular-level mechanism for CO2 hydrogenation into hydrocarbons. a, Energy profile from DFT calculations for CO2 hydrogenation to CH3OHon the In2O3(110) surface (D and P stand for defective and perfect surfaces with and without the oxygen vacancy, respectively). b, Schematic of thehydrocarbon-pool mechanism for CH3OH conversion into hydrocarbons inside HZSM-5. c, Schematic for the formation of CH3OH from CO2 at the oxygen-vacancy site on the In2O3 catalyst surface, which involve four major steps: (1) CO2 adsorption at the oxygen-vacancy site, (2) sequential hydrogenation ofthe adsorbed CO2 species to CH3OH, (3) CH3OH desorption, which leads to the surface without the oxygen vacancy, and (4) hydrogenation of the surfaceto regenerate the oxygen-vacancy site. d, Schematic for hydrocarbon formation from CH3OH at the acidic site inside the pores of the HZSM-5 catalyst viathe hydrocarbon-pool mechanism.

NATURE CHEMISTRY DOI: 10.1038/NCHEM.2794 ARTICLES





CH3OH was detected with a selectivity of 2.5% when the weightratio increased from 2:1 to 4:1. In addition, an increase in thespace velocity can also greatly decrease the CO selectivity andenhance the C5+ selectivity (Fig. 4a, 80.3% at 11,250 ml h–1 gcat

–1).Therefore, any measure that improves the transport of the reactionintermediates in the gas phase should favour the shift of the reactionequilibrium for the selective formation of C5+ hydrocarbons.

The sample illustrated in Fig. 3d was composed of well-mixedmicrometre-sized In2O3 and HZSM-5 particles (SupplementaryFig. 3b). We tried to shorten the distance between the twocomponents further by grinding a powder mixture of them bothin an agate mortar to investigate the effect of their intimatecontact (Fig. 3e). For the sample obtained from this integrationmanner, the much smaller In2O3 particles (around 10 nm) werein much closer contact with the HZSM-5 particles of 500–800 nmin size (Supplementary Fig. 2c–f ). However, CO2 was convertedmainly into CH4 (94.3% in hydrocarbon distribution) with arather low CO2 conversion (8%). In addition, the C5+ hydrocarbonselectivity was only 4.2% and the CH3OH selectivity reached 51.9%,which suggests a significant deactivation of HZSM-5. The very closecontact between In2O3 and the zeolite appeared to weaken thesynergistic effect. A similar phenomenon was also observed byde Jong and co-workers, who reported that the closest proximityof bifunctional active sites was detrimental to the selective hydrocrack-ing of hydrocarbons37. Similar textural and structural properties, aswell as surface acidity, were observed for the spent samples pre-sented in Fig. 3d,e, which indicates that the integration mannerhas no significant effect on these properties (SupplementaryFig. 3). However, the number of strongly acidic sites of the spentcatalyst presented in Fig. 3e decreased markedly (Supplementary

Fig. 3d). As a result, the number of active sites for the C–C couplingin the zeolite pore was significantly reduced, which leads to a severedeactivation with very low C5+ hydrocarbon selectivity.

We also investigated the stability of the composite catalystwith granule stacking (Fig. 4b). The CO2 conversion and theCO selectivity decreased, whereas the C5+ selectivity increasedsignificantly during the initial 40 hours. However, the CO2

conversion and C5+ selectivity remained stable at around 12 and80%, respectively, after a time-on-stream of 150 hours at 340 °C,3.0 MPa and 9,000 ml h–1 gcat

–1, which suggests a promising poten-tial for industrial applications. In situ XRD characterization revealedthat the crystal size of In2O3 increased substantially after theexposure to the H2 and CO2 mixture at 340 °C during the initialstage (four hours), whereas it remained almost unchanged in thesubsequent reaction period (Supplementary Fig. 1). In addition,the effects of pressure and the H2/CO2 ratio on the catalytic per-formance were also studied. A higher pressure and H2/CO2 ratiocan enhance CO2 conversion and decrease CO selectivity(Supplementary Fig. 9). Moreover, a higher reaction rate with alower contact time suggested a negative effect of the generatedwater (H2O) on the catalyst performance (SupplementaryFig. 10a). The increasing trend of CO2 conversion with decreasingQ

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Figure 3 | Influence of the integration manner of the active components(In2O3/HZSM-5 mass ratio = 2:1) on catalytic behaviours under the sameconditions. a, Dual-bed configuration with In2O3 packed below HZSM-5 andseparated by a layer of quartz sand. b, HZSM-5 packed below In2O3 andseparated by quartz sand. c, Stacking of granules with the In2O3, HZSM-5 andquartz sand particle sizes of 250–380 µm. d, In2O3 and HZSM-5 particleswell mixed without quartz sand. e, In2O3 and HZSM-5 mixed with an agatemortar. The catalytic performance is improved significantly by moving the twocomponents to a closer proximity, whereas the C5+ hydrocarbon selectivitydecreases remarkably with a further increase in the proximity by grinding thepowder mixture of the two active components in an agate mortar.


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Figure 4 | Catalytic performance of the composite catalyst presented inFig. 3d. a, CO2 conversion, CO selectivity and hydrocarbon distribution atdifferent space velocities. CO selectivity decreases and C5+ selectivityincreases significantly with increasing space velocities. b, Stability of thecomposite catalyst with granule stacking at 9,000 ml h–1 gcat

–1. Both CO2

conversion and product selectivity remain stable after the initial 40 h ofreaction. Reaction conditions, 340 °C, 3.0 MPa, H2/CO2/N2 = 73/24/3 andIn2O3/HZSM-5 mass ratio = 2:1.






space velocity should lead to an increase in the H2O partial pressureacross the catalyst bed, which would oxidize In2O3 vacancies (e.g.H2O + D → P + H2) (ref. 38) and lead to a lower catalytic activity.This was proved by the steady drop in the reaction rate when H2Owas co-fed during CO2 hydrogenation (Supplementary Fig. 10b).

To investigate further the prospect of the In2O3/HZSM-5 bifunc-tional catalyst in industrial applications, the catalytic performancefor CO2 hydrogenation to C5+ hydrocarbons was evaluated usinga pellet catalyst under industrially relevant conditions. The drycatalyst powders were compressed by a high-pressure agglomerationtechnique to obtain both In2O3 and HZSM-5 pellets in acylindrical shape with a diameter of 3.0 mm and a height of3.5 mm (Φ3.0 × 3.5 mm). The catalytic performance of thewell-mixed In2O3 and HZSM-5 pellets (In2O3/HZSM-5 massratio = 1:2) was examined with tail-gas recycling (SupplementaryFig. 11), commonly used in industry for a more efficient utilizationof the feed39,40. As shown in Fig. 5a, the pellet catalyst exhibited a

similar performance to that of the granule catalyst under the samereaction conditions. With an increasing recycle ratio, defined asthe flow rate of the recycled tail gas over that of the original feedgas, both CO2 conversion (from 8.7 to 18.2%) and C5+ hydrocarbonselectivity (from 78.0 to 84.1%) increased, whereas CO selectivitydecreased substantially from 44.5 to 30.0%. The CO concentrationin the feed gas would obviously grow with an increasing recycleratio as the recycled tail gas contained a large amount of CO. Tostudy the effect of CO on the performance of CO2 hydrogenation,CO was added into the feed gas of the CO2/H2 mixture with theCO/(CO2 + CO) ratio increased from 0 to 100%. Increasing theCO concentration was found to boost the activity of CO2 hydrogen-ation to C5+ hydrocarbons, as shown in Fig. 5b. According to ourDFT calculations, the formation of oxygen vacancies on theIn2O3(110) surface by CO reduction is energetically much morefavourable than H2 reduction (Supplementary Fig. 4b), which isconsistent with the experimental observations (SupplementaryFig. 6c and Supplementary Table 2). In addition, the adsorptionstrength followed the order CO2> H2≫ CO at a relatively lowoxygen-vacancy coverage (Supplementary Fig. 4c). Consequently,CO can increase the number of active sites (oxygen vacancies),and then promote the CO2 hydrogenation activity and counterba-lance the efficient annihilation of vacancies by CO2. However, wedid not detect any C5+ hydrocarbon at CO/(CO2 + CO) = 100%(CO/H2) within eight hours, because In2O3 was reduced to the met-allic phase in the absence of CO2 at 340 °C (Supplementary Fig. 6d),and this metallic phase was unable to catalyse CO2 hydrogenation19.

With the above oxide/zeolite bifunctional catalyst for CO2 hydro-genation to hydrocarbons, the hydrocarbon distribution can beeasily tuned through the shape selectivity of the zeolite. WhenSAPO-34 was chosen as the active phase for C−C coupling, theselectivity to lower olefins (C2

=−C4=, generally referring to ethylene,

propylene and butylene) reached 76.9% in hydrocarbons with only4.4% of CH4 at a CO2 conversion of 34.1% (Supplementary Fig. 12).In addition, the main hydrocarbon products became liquefied pet-roleum gas (C3

o−C4o, referring to C3 and C4 paraffins) when the

Beta zeolite was used in combination with In2O3. Additionally, thecatalytic activity depended on the amount of the active vacancies,which could be increased substantially by the introduction ofmodifiers and/or the use of a suitable support (such as ZrO2).

ConclusionsIn summary, we discovered a bifunctional catalyst composed of par-tially reduced In2O3 and HZSM-5 that could convert CO2 directlyinto liquid fuels with an excellent selectivity for value-added pro-ducts. The C5+ selectivity reached 78.6% with only 1% CH4 at aCO2 conversion of 13.1%. We demonstrated that the CO2 conver-sion could be manipulated by controlling the surface structure ofthe oxide and the mass ratio of the oxides/zeolite. The proximity ofthe two components played a crucial role to suppress the undesiredRWGS reaction and obtain a high C5+ selectivity. Industry-relevanttests using the pellet catalyst were carried out to show that tail-gasrecycling could improve further the catalytic performance for CO2

hydrogenation to C5+ hydrocarbons, which suggests a promisingprospect for industrial applications.

MethodsCatalyst preparation. Various oxides were prepared by a co-precipitation method.HZSM-5 zeolites were prepared by the hydrothermal route with ethylamine as thetemplate. For the preparation of the composite catalyst presented in Fig. 2d, the In2O3

andHZSM-5were pressed, crushed and sieved to granules in the range of 40–60mesh(granule sizes of 250–400 µm). Then, the granules of the two samples were mixedtogether by shaking in a vessel. For the preparation of the composite catalyst presentedin Fig. 2e, the In2O3 andHZSM-5weremixed in an agatemortar for 20 min. Then, themixed samplewas pressed, crushed and sieved to particles in the range of 40–60mesh.

Catalyst characterization. Catalysts were characterized by in situ XRD, nitrogenphysisorption, X-ray fluorescence spectroscopy, scanning electron microscopy, TEM

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Figure 5 | Catalytic performance with tail-gas recycling and as a functionof CO concentration in the feed. a, Catalytic results over a technicalcatalyst composed of In2O3 and HZSM-5 pellets (size in cylindrical shape ofΦ3.0 × 3.5 mm, In2O3/HZSM-5 mass ratio = 1:2) with internal gas recyclingas functions of the recycle ratio. The recycle ratio represents the flow rate ofthe recycled tail gas over that of the original feed gas. With increasingrecycle ratio, the catalytic performance becomes much better over thewell-mixed In2O3 and HZSM-5 pellet catalyst under industrially relevantconditions. b, CO2 conversion and yield of C5+ hydrocarbons over aIn2O3/HZSM-5 composite catalyst (particle size, 250–380 µm) as afunction of CO concentration in the feed at H2/(CO2 + CO)/N2 = 73/24/3.The CO concentration in the feed gas will grow with increasing recycle ratio,and therefore CO was added into the feed gas to investigate the effect ofCO on the performance without internal gas recycling. The C5+ yieldincreases substantially with an increasing CO/(CO2 + CO) ratio. Reactionconditions, 340 °C, 3.0 MPa, space velocity of the original feed gas9,000 ml h–1 gcat

–1 and In2O3/HZSM-5 mass ratio = 1:2.

NATURE CHEMISTRY DOI: 10.1038/NCHEM.2794 ARTICLES





and high-resolution TEM (HRTEM), H2, CO2 and ammonia TPD, as well as H2 andCO temperature-programmed reduction techniques. In situ NAP–XPS wasperformed on a SPECS Surface Nano Analysis. The facility is composed of twochambers, an analysis chamber and a quick ample load–lock chamber. The analysischamber is equipped with a PHOIBOS NAP hemispherical electron energy analyser,a microfocus monochromatized Al-Kα X-ray source with a beam size of 300 µm, aSPECS IQE-11A ion gun and an infrared laser heater.

Catalytic evaluation. Activity measurements in the hydrogenation of CO2 werecarried out in a continuous-flow, high-pressure, fixed-bed reactor (internal diameterof 12 mm). Prior to the reaction, the catalyst was pre-treated in situ at 400 °C for 1 h inpure Ar (150 ml min−1). After the reactor was cooled down to 340 °C, the reactant gasmixture with a H2/CO2/N2 ratio of 73/24/3 and a pressure of 3.0 MPawas introducedinto the reactor. The catalytic reaction for CH3OH conversion was performed in thesame reactor. For the experiments with tail-gas recycling, the catalytic performance ofthe pellet catalyst (15 g) was investigated in our pilot-scale fixed-bed reactor (internaldiameter 19 mm, length 1,180 mm (Supplementary Fig. 11)), whichwas equipped foroperation at industrial working conditions with a recycled tail gas. The effluents wereanalysed quantitatively online with a Shimadzu GC-2010C gas chromatographequipped with thermal conductivity and flame-ionization detectors. The CO2

conversion was calculated by an internal normalization method. The hydrocarbondistribution presented in this work was calculated on a molar carbon basis.

DFT calculations. Periodic DFT calculations were carried out with the Vienna abinitio simulation package using the Perdew–Burke–Ernzerhof exchange-correlationfunctional and projector augmented wave potentials.

Data availability. All the data that support the findings of this study are availablewithin the paper and its Supplementary Information files, or from the correspondingauthor on reasonable request.

Received 23 January 2017; accepted 5 May 2017;published online 12 June 2017

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AcknowledgementsThis work was supported by the National Natural Science Foundation of China (21503260,21573271, 91545112 and 11227902), the Shanghai Municipal Science and TechnologyCommission, China (14DZ1207602, 16DZ1206900 and 15DZ1170500), the Ministry ofScience andTechnologyof China (2016YFA0202802) and theChinese Academyof Sciences(QYZDB-SSW-SLH035). We thank Z. Liu and Y. Han for the assistance with in situNAP–XPS, located at the State Key Laboratory of Functional Materials for Informatics, ShanghaiInstitute of Microsystem and Information Technology, Chinese Academy of Sciences.

Author contributionsP.G., L.Z. and Y.S. conceived the project, analysed the data and wrote the paper. P.G., S.L.andW.W. drafted the manuscript. P.G. and S.D. prepared the samples. S.L. performed DFTcalculations. Z.L. and H.W. studied the effect of the integration manner. X.B., M.Q. and C.Y.performed the catalytic evaluation. S.D., Z.L., X.B. and J.C. characterized the samples. Allthe authors discussed the results and commented on the manuscript.

Additional informationSupplementary information is available in the online version of the paper. Reprints andpermissions information is available online at www.nature.com/reprints. Publisher’s note:Springer Nature remains neutral with regard to jurisdictional claims in published mapsand institutional affiliations. Correspondence and requests for materials should be addressed toL.Z. and Y.S.

Competing financial interestsThe authors declare no competing financial interests.





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Direct conversion of CO 2 into liquid fuels with high