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Na promoter synergistic tuning Co-Fe alloy-carbide dual sites: Directing syngas conversion to C2+ alcohols
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Hengxuan ZHANG1, 2, Yan SUN2, *, Qiwen SUN2, *, Jianmin WU2
Journal of Fuel Chemistry and Technology | 2026, 54(7) : 20250381-1262 - 20250381-1272
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Journal of Fuel Chemistry and Technology | 2026, 54(7): 20250381-1262-20250381-1272
• RESEARCH PAPER •
Na promoter synergistic tuning Co-Fe alloy-carbide dual sites: Directing syngas conversion to C2+ alcohols
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Hengxuan ZHANG1, 2, Yan SUN2, *, Qiwen SUN2, *, Jianmin WU2
Affiliations
  • 1College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
  • 2State Key Laboratory of Coal Liquefaction, Gasification and Utilization with High Efficiency and Low-Carbon Technology, Shanghai Yankuang Energy R&D Co., Ltd., Shanghai 201203, China
Published: 2026-07-10 doi: 10.1016/S1872-5813(26)60670-6
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Designing highly efficient catalysts for the direct conversion of syngas to C2+ alcohols is crucial for the effective utilization of coal-based resources and the enhancement of national energy security. In this study, a series of Na-modified CoFe/Al2O3 catalysts were synthesized via the impregnation method, and their catalytic performance in syngas-to-alcohol reactions was systematically evaluated. Multiple characterization techniques, including XRD, N2 adsorption-desorption, H2-TPR, XPS, DRIFTS, in situ Raman and Mössbauer spectroscopy, were employed to elucidate the synergistic effects of Na and Fe promoters on the catalyst structure and catalytic behavior. The results demonstrate that Na facilitates the formation of Co-Fe alloy sites during the reaction. Simultaneously, Fe modifies the electronic state of Co species and promotes the transformation of lattice oxygen into adsorbed oxygen, thereby increasing the concentration of surface oxygen vacancies. The synergistic interaction between the alloy and carbide sites enhances the CO insertion capability of olefin intermediates, leading to a significantly improved selectivity towards C2+ alcohols. Under the conditions of 260 °C and 2 MPa, the Co1Fe1Na1 catalyst exhibited optimal performance, achieving a total alcohol selectivity of 45%, with C2+ alcohols accounting for 94.1%. This study provides novel insights into the rational design of Co-based catalysts for the efficient conversion of syngas to C2+ alcohols.

CO hydrogenation  /  ethanol  /  C2+ alcohols  /  Co-based catalysts  /  CO加氢  /  乙醇  /  C2+碳醇  /  钴基催化剂
张衡璇, 孙燕, 孙启文, 吴建民. Na助剂协同调控Co-Fe合金-碳化物双位点：合成气定向转化制C2+醇. 燃料化学学报（中英文）, 2026 , 54 (7) : 20250381-1262 -20250381-1272 . DOI: 10.1016/S1872-5813(26)60670-6
Hengxuan ZHANG, Yan SUN, Qiwen SUN, Jianmin WU. Na promoter synergistic tuning Co-Fe alloy-carbide dual sites: Directing syngas conversion to C2+ alcohols[J]. Journal of Fuel Chemistry and Technology, 2026 , 54 (7) : 20250381-1262 -20250381-1272 . DOI: 10.1016/S1872-5813(26)60670-6
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With the continuous growth of global energy demand and the increasing awareness of environmental protection, the development of non-petroleum-based energy technologies has become a major focus of scientific and technological advancement worldwide. China’s resource endowment, characterized as “rich in coal, poor in oil, and scarce in natural gas,” determines that coal will continue to play a dominant role in the national energy structure for a prolonged period[1−3]. Therefore, to realize the clean and efficient utilization of coal via developing coal-derived syngas conversion routes toward value-added chemicals is of great strategic significance. Higher alcohols (C2+ alcohols, HAs), defined as alcohols containing two or more carbon atoms, can serve not only as clean fuels and fuel additives but also as important chemical intermediates. It is widely used in the production of plasticizers, detergents and other high-value chemicals[4−6]. Consequently, the direct catalytic conversion of syngas into higher alcohols has attracted increasing research interests[7−8].
The direct synthesis of higher alcohols from syngas is a highly complex process involving both dissociative and non-dissociative CO activation steps. From the catalyst design, it is necessary to precisely regulate the synergistic interplay between C–C coupling and C–O insertion, making it particularly challenging to balance alcohol formation with carbon-chain growth[9−10]. Co-based catalysts have received considerable attention due to their strong chain-growth capability and relatively low cost. However, metallic Co0 sites exhibit negligible C–O insertion activity, and therefore require the introduction of additional C–O insertion sites to enable efficient higher-alcohol synthesis[11].
To address this challenge, previous studies have mainly focused on constructing two types of active sites. One strategy is introducing the second metal to form alloy structure. Su et al.[12] compared monometallic Co and bimetallic CoCu/SiO2 catalysts and found that the promotional role of Cu manifests in two key aspects: weakening CO/HCO dissociation to suppress the formation of CHx species, at the same time as controlling the size of surface Co species while inhibiting CHx insertion, thereby steering the reaction pathway toward alcohol formation. Cao et al.[13], combining density functional theory and microkinetic modeling, further elucidated the reaction mechanisms of higher-alcohol synthesis over CuCo alloy catalysts and revealed facet-dependent differences in methanol and ethanol formation. However, the susceptibility of active metals to sintering and the coverage of active sites by cobalt carbides during prolonged operation collectively will lead to the phenomenon of catalysts deactivation and a shift of products toward lower carbon numbers over time[14].
In addition to alloy-based strategies, constructing Co0/Co2C dual active sites represents another effective approach. Li et al.[15] investigated the role of Co0/Co2C dual sites in syngas-to-higher-alcohol synthesis, demonstrating that modulating the Na promoter content to control the Co0/Co2C ratio is crucial. They found that only within an optimal range can strong synergistic effects be realized, allowing the CO insertion rate to be well balanced with hydrogenation and chain-growth rates—a condition most favorable for oxygenate formation. Promoters also play a pivotal role in facilitating Co2C formation. Du et al.[16] reported that CaO promotes the formation of hexagonal close-packed (hcp) metallic Co, which is more prone to transformation into Co2C under reaction conditions. Zhao et al.[17] synthesized core-shell Co@Co2C catalysts and found that Mn enhances surface CO dissociation and disproportionation while partially suppressing H2 adsorption. It creates a carbon-rich and hydrogen-deficient surface environment, which promotes the transformation of metallic Co into Co2C and consequently favors the synthesis of higher alcohols and lower olefins. An et al.[18] further reported that Ga promoters simultaneously enhance both dissociative and non-dissociative CO adsorption, enabling the cooperative regulation of CO insertion and carbon-chain growth. Despite considerable progress in constructing bifunctional active sites, the fundamental nature of the active centers and their dynamic evolution are still not fully understood. This gap in knowledge hinders the rational engineering of catalytic sites for precise product selectivity and raises downstream separation costs.
In this study, we focus on regulating the synergistic interplay between CO insertion and chain growth. A series of Al2O3-supported CoFeNa catalysts were prepared via impregnation method. By optimizing the Co-Fe-Al ratios, the surface electronic properties of the catalysts were effectively tuned. A combination of XRD, H2-TPR, in situ infrared spectroscopy, in situ Raman spectroscopy and Mössbauer spectroscopy was employed to systematically elucidate the roles of Na and Fe promoters in tuning catalyst structure and enhancing catalytic performance. The high selectivity toward ethanol and propanol is attributed to precise control over the transformation pathways of key reaction intermediates.
1　Experimental
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1.1　Materials and reagents
Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), iron nitrate nonahydrate (Fe(NO3)3·9H2O), sodium nitrate (NaNO3), and pseudoboehmite were purchased from Sinopharm Chemical Reagent Co., Ltd. and used as received without further purification. All chemicals were of analytical grade. Hydrogen (H2), carbon monoxide (CO) and argon (Ar) with a purity of 99.99% were supplied by Air Liquide (Shanghai). Deionized water was produced in the laboratory and used throughout the experiments.
1.2　Catalyst preparation
The Al2O3 support was obtained by calcining pseudoboehmite in air at 500 °C for 2 h. All CoFeNa/Al2O3 catalysts were prepared by an impregnation method and denoted as CoxFeyNaz, where x, y and z represent the molar ratios of Co, Fe and Na, respectively. Taking the Co1Fe1Na1 catalyst as an example, 7.13 g of cobalt nitrate hexahydrate, 9.86 g of iron nitrate nonahydrate, and 2.07 g of sodium nitrate were dissolved in deionized water to prepare a metal precursor solution with n(Co)∶n(Fe) ∶n(Na) = 1.0∶1.0∶1.0.
Subsequently, 10 g of the Al2O3 support was added to a 100 mL round-bottom flask, followed by the addition of the above metal solution. The mixture was dried under vacuum using a rotary evaporator until complete solvent removal. The dried sample was then calcined in a muffle furnace at 400 °C for 6 h to obtain the Co1Fe1Na1 catalyst. Using the same procedure, Co1Fe2Na1 and Co2Fe1Na1 catalysts with different n(Co) : n(Fe) : n(Na) molar ratios, as well as the Fe-free Co1Na1 catalyst, were prepared.
1.3　Catalyst characterization
N2 adsorption-desorption measurements were carried out using a Micromeritics ASAP 2460 automated adsorption analyzer. Prior to measurement, samples were evacuated at 300 °C for 2 h. After degassing, the samples were backfilled with N2 to atmospheric pressure, removed, and accurately weighed before analysis. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method, and the pore size distribution was determined by the Barrett-Joyner-Halenda (BJH) method.
X-ray diffraction (XRD) patterns were collected on a Bruker D8 Advance powder diffractometer using Cu Kα radiation (λ = 0.154 nm), operated at 40 kV and 40 mA. Data were recorded over a 2θ range of 10°–80° at a scanning rate of 10(°)/min.
X-ray photoelectron spectroscopy (XPS) measurements were performed on a Shimadzu Axis Supra+ spectrometer using Al Kα radiation (hν = 1486.6 eV) as the X-ray source, with an operating voltage of 15 kV and a current of 10 mA. The C 1s peak at 284.8 eV was used as the binding energy reference.
H2 temperature-programmed reduction (H2-TPR) experiments were conducted on a Micromeritics AutoChem II 2920 system. First, 50 mg of catalyst was loaded and heated to 150 °C, followed by purging with helium for 1 h to remove moisture. After pretreatment, the temperature was lowered to 50 °C, and the gas flow was switched to a reducing mixture of 10% H2/90% Ar. The sample was then heated to 800 °C at a rate of 10 °C/min, while hydrogen consumption was monitored using a thermal conductivity detector (TCD).
In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was performed on a Thermo Fisher Nicolet iS50 FT-IR spectrometer. Under a H2 atmosphere, the pressure in the reaction cell was first increased to 0.2 MPa and the temperature raised to 420 °C for reduction. After reduction, the temperature was lowered to 260 °C, and the pressure was gradually increased to 2 MPa. Once the pressure reached 2 MPa, a background spectrum was recorded, after which the gas atmosphere was switched to a H2∶CO mixture (2∶1). Spectra were collected every 5 min.
In situ Raman spectroscopy was conducted using a Renishaw in via Raman spectrometer equipped with an in situ reaction cell. A 532 nm laser was used for excitation, and calibration was performed using a single-crystal silicon standard at 520 cm−1.
Mössbauer spectroscopy (MES) measurements were carried out on an LT-MS963rd Mössbauer spectrometer operating in constant-acceleration mode, using a 57Co(Rh) source. Spectral fitting and data analysis were performed using MossWinn 4.0 software.
1.4　Catalytic performance evaluation
The catalytic performance for syngas-to-alcohol synthesis was evaluated in a fixed-bed reactor. Typically, 4 g of catalyst (20–40 mesh) was thoroughly mixed with 4 g of quartz sand and loaded into the isothermal zone of the reactor, with quartz sand packed above and below the catalyst bed.
Prior to reaction, the catalyst was reduced at 420 °C and 0.2 MPa under a mixed H2/Ar atmosphere (φ(H2)∶φ(Ar) = 2∶1) at GHSV of 4500 mL/(g·h) for 20 h. After reduction, the reactor was cooled to 150 °C under pure Ar. Syngas with a composition of (φ(H2)∶φ(CO)∶φ(Ar)= 8∶4∶1, GHSV of 2000 mL/(g·h)) was then introduced, and the pressure was gradually increased to 2 MPa. Once the target pressure was reached, the temperature was increased to 260 °C at a rate of 0.5 °C/min.
Gaseous products were analyzed online using an Agilent 8890A gas chromatograph. The tail gas flow rate was quantified by the internal standard method using Ar as the internal standard. The concentrations of H2, CO and CO2 were determined by a thermal conductivity detector (TCD) equipped with a Hayesep Q packed column (6 ft × 1/8 in × 2 mm) and a molecular sieve packed column (8 ft × 1/8 in × 2 mm). Hydrocarbon products (C1–C4) were analyzed using a flame ionization detector (FID) with an Al2O3 capillary column (30 m × 0.53 mm × 15 μm).
Liquid products were collected using a cold-trap system and analyzed by gas chromatography-mass spectrometry (GC-MS). The injector temperature was set at 320 °C, with a split ratio of 50∶1 and an injection volume of 0.2 μL. An HT-PONA capillary column (50 m × 0.20 mm × 0.50 μm) was used with a constant column flow rate of 1.0 mL/min. The ion source temperature, interface temperature, and scan range were set to 230, 290 °C and 20–300 m/z, respectively. Qualitative analysis was performed using the mass spectrometer, while quantitative analysis of hydrocarbons and oxygenates in the oil phase was conducted using an FID detector with the external standard method.
The aqueous-phase products were analyzed by gas chromatography using an HT-FFAP capillary column (50 m × 0.32 mm × 0.50 μm). The injector temperature was set at 250 °C with a split ratio of 100∶1 and an injection volume of 0.2 μL. The oven temperature program was as follows: 60 °C for 4 min, then ramped to 200 °C at 5 °C/min. The FID detector temperature was 250 °C, with hydrogen and air flow rates of 30 and 400 mL/min, respectively. The compositions of oxygenates in the aqueous phase were quantified using the external standard method.
The calculation formulas for CO conversion, CO2 selectivity, and product selectivity are given in Eqs. (1)–(3), where $ {{x}}_{\text{CO}} $ represents the CO conversion (%), $ {{s}}_{{{\text{CO}}_{\text{2}}}} $ represents the CO2 selectivity (%), and $ {{s}}_{{i}} $ represents the selectivity of product i.
$ \begin{matrix}{{x}}_{\text{CO}}=\dfrac{{n}_{\text{CO}}^{\text{in}}{-n}_{\text{CO}}^{\text{out}}}{{n}_{\text{CO}}^{\text{in}}}\times {100\% }\end{matrix} $
$ \begin{matrix}{{s}}_{{{\text{CO}}_{\text{2}}}}=\dfrac{{n}_{{\text{CO}}_{\text{2}}}^{\text{out}}}{{n}_{\text{CO}}^{\text{in}}{-n}_{\text{CO}}^{\text{out}}}\times {100\% }\end{matrix} $
$ \begin{matrix}{{s}}_{{i}}=\dfrac{{n}_{{i}}^{\text{out}}}{{n}_{\text{CO}}^{\text{in}}{-n}_{\text{CO}}^{\text{out}}{-n}_{{\text{CO}}_{\text{2}}}^{\text{out}}}\times {100\% } \end{matrix} $
2　Results and discussion
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2.1　Structural characterization of catalysts
The N2 adsorption-desorption results of the fresh catalysts (Table 1) show that, compared with the Fe-free catalyst, the introduction of Fe species increases the specific surface area and pore volume of the catalysts to varying extents, which is favorable for the improvement of the activity of the reaction. The XRD patterns (Figure 1(a)) indicate that, for the Co1Na1 catalyst, only characteristic diffraction peaks located at 36.8° and 65.2° corresponding to the Co3O4 phase (PDF#43-1003) are observed. After the introduction of Fe species, the intensities of Co3O4 diffraction peaks in Co1Fe1Na1 and Co2Fe1Na1 catalysts are significantly weakened, while characteristic diffraction peaks of α-Fe2O3 (PDF#33-0664) appear at 33.2°, 35.6° and 54.1°. For the Fe-rich Co1Fe2Na1 catalyst, only α-Fe2O3 diffraction peaks are detected.
In addition, diffraction peaks corresponding to CoAl2O4 (PDF#44-0160) are observed in Co1Fe1Na1 and Co2Fe1Na1 catalysts, indicating enhanced Co-Al interactions with increasing Fe content. However, no characteristic diffraction peaks corresponding to the CoFe2O4 spinel are observed in any of the catalysts, indicating that the CoFe2O4 spinel phase—which requires strong metal-metal interactions—is not readily formed through impregnation and calcination alone. H2 temperature-programmed reduction (H2-TPR) profiles (Figure 1(b)) show that the introduction of Fe species effectively lowers the reduction temperature of Co species. For the Co1Na1 sample, the three of H2 consumption peaks centered at approximately 347, 425 and 565 °C were observed, the first two being attributed to partial reduction of Co3O4 to Co2+ and further reduction of Co2+ to Co0, while the third peak centered at 565 °C was attributed to reduction of CoAl2O4[19−20]. As the Fe/Co ratio increases, the temperature required for complete reduction of Co species gradually decreases from 565 to 481 °C, which indicates that the addition of Fe promotes the reduction process.
The Co 2p XPS spectra (Figure 2(a)) exhibit two main peaks at approximately 780.0 and 795.5 eV across all catalysts, corresponding to Co 2p3/2 and Co 2p1/2, respectively. For the Fe-free Co1Na1 catalyst, the Co species are primarily present as Co2+ (782.2 eV, dark red line) and Co3+ (780.2 eV, blue line), along with well-defined satellite peaks[17,21−22]. The introduction of Fe species induces a noticeable shift of Co 2p binding energies toward lower values compared with Co1Na1 catalyst. This shift remains significant with increasing Fe content (from Co2Fe1Na1 to Co1Fe1Na1). Specifically, the Co 2p3/2 peak position of Co1Fe1Na1 is shifted by −0.4 eV relative to that of Co1Na1, which confirms electron transfer from Fe species to Co species. As a result, the electron density at Co sites increases, thereby favoring the optimization of CO adsorption.
The Fe 2p spectra (Figure 2(b)) display characteristic peaks attributed to Fe2+ (~710.5 eV) and Fe3+ (~712.5 eV). With increasing Fe content, the Fe 2p binding energies also similarly shift toward lower values, further confirming the electronic interaction between Co and Fe species, which is crucial for the formation of Co-Fe alloy sites during subsequent reactions. These results indicate electronic transfer and synergistic reduction effects at the Co-Fe interface. The Fe promoter modifies the surface chemical state of Co species via electron transfer, increasing the proportion of Co2+ while decreasing that of Co3+. Meanwhile, Co species are reduced earlier than Fe species and activate H2 to generate active H*, which subsequently promotes the reduction of Fe3+ to Fe2+. Furthermore, the electron-donating effect of the Na promoter stabilizes Co2+ and Fe2+ species.
As the Co/Fe molar ratio decreases, the density of Co-Fe interfacial sites increase, with Co1Fe1Na1 exhibiting the highest proportion of Co2+ species. This surface valence-state modulation establishes the foundation for generating Co-Fe alloy-carbide dual active sites and their subsequent synergistic catalysis. Quantitative fitting of the Co 2p3/2 peak areas (Table 2) further reveals that the introduction of Fe species significantly alters the surface valence distribution of Co species. Co1Fe1Na1 shows the lowest Co3+/Co2+ ratio (0.52), indicating a pronounced enrichment of Co2+ species on the surface. Combined with the binding energy shift (−0.4 eV), these electron-rich Co2+ sites are identified as key precursors for the in situ formation of Co2C active phases during reaction[15,17]. Their synergy with Fe carbide sites effectively enhances CO insertion into olefinic intermediates, thereby enabling high selectivity toward ethanol and propanol.
Notably, the O 1s spectra (Figures 2(c) and 2(d)) show that with the introduction and increasing of Fe species, the proportion of lattice oxygen (OL) decreases significantly, while the fraction of adsorbed oxygen (OA) increases dramatically from 42% for Co1Na1 to 73% for Co1Fe2Na1. This trend indicates that Fe species induces lattice distortion, promotes the transformation of lattice oxygen into adsorbed oxygen species, and generates abundant oxygen vacancies. These oxygen vacancies enhance the adsorption and activation of oxygenated intermediates, facilitate C–O insertion steps during reaction, and constitute a key factor underlying the high C2+ alcohol selectivity of Co1Fe1Na1[23−24].
2.2　Catalytic performance evaluation
The catalytic performance of different catalysts for syngas-to-alcohol conversion at 260 °C and 2 MPa (Figure 3) reveals that, compared to Co1Na1, the Fe-doped Co1Fe1Na1 catalyst exhibits an increase in CO conversion from 30% to approximately 45%, corresponding to a 50% enhancement in catalytic activity. A further increase in Fe content confers a subsequent boost in the catalytic activity of Co1Fe2Na1, with the CO conversion rising to approximately 63%. Conversely, increasing the Co content instead (Co2Fe1Na1) results in an even higher CO conversion of 76%, but this is accompanied by a pronounced increase in alkane selectivity.
Regarding alcohol selectivity, the incorporation of Fe into Co1Fe1Na1 has only a minor effect on the total alcohol selectivity but significantly alters the carbon number distribution of alcohol products, exhibiting excellent selectivity toward C2+ alcohols, especially ethanol and propanol. Catalysts with higher Co or Fe molar ratios show markedly different reaction behaviors, with both alcohol and olefin selectivity decreasing significantly. In particular, Co2Fe1Na1 likely possesses stronger chain-growth capability due to its higher Co content, displaying catalytic behavior more similar to low-temperature Co-based F-T synthesis catalysts, characterized by high activity and high alkane selectivity.
In addition, Figure 4 depicts the 300 h stability test of the representative Co1Fe1Na1 catalyst for syngas-to-alcohol reactions. The time-on-stream profiles illustrate the dynamic changes of CO conversion and product selectivity. Although CO conversion decreases during the first 100 h due to dynamic evolution of active sites, it stabilizes at approximately 45% during the subsequent steady-state period from 100 to 300 h. Meanwhile, the total alcohol selectivity remains consistently above 43% (right Y-axis), with no obvious deactivation observed. Quantitative analysis at four sampling points (bar charts) shows that the selectivity distributions of hydrocarbons and total alcohols (ROH) remain nearly unchanged during the steady-state period. These results demonstrate that Co-Fe alloy and carbide sites reach a favorable balance under syngas atmospheres, ensuring the long-term operational stability of the catalyst.
2.3　Structure–performance relationship and mechanistic insights
To elucidate the origins of the outstanding selectivity of the Co1Fe1Na1 catalyst toward ethanol and propanol, in situ Raman spectroscopy was performed.
For the fresh catalyst, an absorption band at 680 cm−1 assigned to α-Fe2O3 was observed (Figure 5(a))[25]. After switching the atmosphere to H2, a distinct Co3O4 band appeared at 480 cm−1[26]. As the reduction temperature increased, the intensities of the Raman bands at 680 and 584 cm−1 gradually diminished and nearly vanished at 400 °C, indicating that the surface Co and Fe oxides could be substantially reduced to the metallic state under the reduction temperature (420 °C) employed for catalytic evaluation.
After completion of the reduction, the atmosphere was switched to syngas (Figure 5(b)). The characteristic G and D bands at 1595 and 1350 cm−1, respectively, only began to emerge gradually after 60 min of reaction[27], while a vibrational band attributable to Fe–O bonds manifested at 584 cm−1[28]. Meanwhile, symmetric stretching vibrations of surface formate species (HCOO*) were detected at 1031 and 810 cm−1[29]. The D band corresponds to amorphous/defective carbon, whereas the G band is associated with graphitized carbon. The amorphous carbon formed at the early reaction stage is related to the generation of active carbide phases, whereas excessive graphitic carbon (strong G band) may cause pore blockage.
A direct comparison of the in situ Raman spectra recorded during reaction for Co1Fe1Na1 (Figure 5(b)) and Co1Fe2Na1 (Figure 6) reveals that the characteristic bands observed for Co1Fe1Na1—including the carbon species at 1595/1350 cm−1 and formate species at 1031 cm−1—exhibit significantly higher signal-to-noise ratios, sharper peak shapes, and superior spectral resolution. This observation indicates a more ordered evolution of surface active sites and a more homogeneous distribution of reaction intermediates over Co1Fe1Na1. In contrast, Co1Fe2Na1 shows a much noisier Raman background, likely due to excessive Fe content inducing aggregation of surface active species or structural disorder, thereby limiting effective contact between intermediates and active sites.
In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) of Co1Fe1Na1 (Figure 7(a)) reveals that, upon introduction of CO and H2, typical gas-phase CO vibration bands at 2178 and 2111 cm−1 appear only after 20 min of reaction. Concurrently, infrared absorption bands corresponding to CO2 (2362 and 2332 cm−1) and CH2CO* intermediates (1604 and 1345 cm−1) were detected[30]. As the reaction proceeded from 20 to 50 min, the intensities of CO2 and CH2CO* bands gradually increased, accompanied by the emergence of distinct bridged CO adsorption bands at 1872 and 1933 cm−1[31]. After 50 min, the intensity of CO2 band decreased, indicating that CO2 participated in subsequent reactions.
The in situ DRIFTS results suggest that olefinic intermediates are readily formed on Co1Fe1Na1 during reaction; however, these intermediates are relatively unstable and can undergo CO insertion via non-dissociative adsorption of CO species on metallic Co0 or Fe0 sites to form alkoxy intermediates, or react with surface oxygen species to generate CH=CH–O* species, which are further hydrogenated to ethanol. This reaction pathway effectively suppresses excessive hydrogenation of C–C bonds.
With increasing Fe content (Figure 7(b)), Co1Fe2Na1 exhibits significantly more intense CH2CO* adsorption bands at 1603 and 1353 cm−1, weaker CO adsorption bands, and the appearance of a methane-related band at 3014 cm−1[32].
These findings indicate that Co1Fe2Na1 possesses a weaker CO insertion capacity, favoring C–C coupling and chain growth, as well as excessive hydrogenation to form alkanes or direct desorption of olefins. This behavior is consistent with the higher C2–C4 alkane/olefin selectivity observed for Co1Fe2Na1 during catalytic performance evaluation. In contrast, the olefinic intermediates on Co1Fe1Na1 demonstrate higher reactivity toward oxygenate formation while suppressing excessive chain growth, resulting in superior selectivity toward ethanol and propanol.
XRD patterns of the spent Co1Fe1Na1 and Co1Fe2Na1 catalysts (Figure 8(a)) reveal distinct diffraction peaks corresponding to Co3Fe7 alloy (PDF#50-0795), as well as Fe3C (PDF#35-0772) and Co2C (PDF#05-0704). This indicates that the Na promoter effectively facilitates the formation of Co-Fe alloys during the reaction and induces the generation of Co and Fe carbide phases under syngas atmospheres. Notably, the characteristic diffraction peaks of composite (CoxFe1−x)5C2 carbides were successfully identified in Co1Fe1Na1, confirming that Fe incorporation not only modulates electronic properties but also promote the formation sof Co-Fe composite active centers under reaction conditions. These composite carbide sites, in intimate contact with alloy sites, synergistically enhance the CO insertion capability of olefinic intermediates[33].
In addition, diffraction peaks attributable to CoFe2O4 spinel were observed in the spent catalysts, although this phase was not detected in the fresh catalysts, indicating that reduction and reaction processes promote Co-Fe interactions. Such interactions are favorable for the formation of carbides and metallic Co-Fe alloys at active sites, thereby regulating CO adsorption/activation and the formation of key enol intermediates, ultimately optimizing C–C coupling. Raman spectra of the spent catalysts (Figure 8(b)) demonstrate that the Fe3O4-related band (678 cm−1) only on Co1Fe2Na1[34].
Correspondingly, XPS results of the spent catalysts (Figure 9) further elucidate the electronic evolution of active sites. Compared with Co1Na1, Fe-containing catalysts exhibit a distinct shift of Co 2p3/2 binding energy toward higher values (+0.4 to +0.7 eV), which is attributed to the formation of Co2C and the electron transfer from Co species to C species during reaction. Five peaks were identified in the Co 2p3/2 XPS spectrum, except for two satellite peaks at 789. 2 and 785. 0 eV, and the characteristic peak at 777.6 eV could be attributed to carbonic Co[35]. Meanwhile, the fitted XPS spectrum of Fe 2p3/2 also has Fe C characteristic peak at 706.7 eV[36]. Besides, the Fe 2p3/2 binding energy shifts toward lower values, confirming that Fe species maintains a relatively high electron density during reaction. This observation demonstrates dynamic electron transfer between Co species and Fe species, optimizing the balance between CO dissociation and insertion.
Mössbauer spectra of the spent Co1Fe1Na1 catalyst (Figure 10) show that iron carbide phases mainly consist of χ-Fe5C2 and Fe2C, accounting for approximately 58% of total Fe species (Table 3). Notably, no Fe3O4 phase is detected, which is consistent with Raman results. The high content of composite carbide phases provides abundant active sites. Unlike those in F-T synthesis, the (CoxFe1−x)5C2 composite carbides formed in syngas-to-alcohol systems are considered to possess Rh-like CO insertion capability[15], which effectively promotes non-dissociative CO adsorption and insertion. In synergy with alloy sites, these carbides enable highly selective formation of higher alcohols[33].
Based on comprehensive in situ characterizations and post-reaction structural analyses, the structure-performance relationship of CoFeNa/Al2O3 catalysts can be summarized as follows: the Na promoter facilitates the formation of Co-Fe alloy sites during reaction, which enhance CO adsorption and dissociation (producing C and O species) and concurrently regulate hydrogenation capability to suppress methane formation. Under syngas atmospheres, Co-Fe alloy sites partially transform into metallic carbide phases (e.g., Co2C, FeCx), which strengthen non-dissociative CO adsorption and insertion, promote CO2 activation to a certain degree, and inhibit the formation of long-chain hydrocarbon formation. The Al2O3 support stabilizes oxygenated intermediates via its intrinsic basic environment and modulates the oxidation states of metal sites through oxygen vacancies, thereby optimizing C–C coupling efficiency. Appropriate Co-Fe interactions on Co1Fe1Na1 significantly enhance the CO insertion capability of olefinic intermediates and prevent excessive chain growth, ultimately leading to superior selectivity toward ethanol and propanol.
3　Conclusion
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A series of CoFeNa/Al2O3 catalysts were prepared via an incipient wetness impregnation method. Notably, the Co1Fe1Na1 catalyst (n(Co)∶n(Fe)∶n(Na) = 1∶1∶1) exhibited superior catalytic performance in syngas-to-alcohol reactions at 260 °C and 2.0 MPa, with distinct selectivity toward ethanol and propanol. The total alcohol selectivity reached 45%, with C2+ alcohols accounted for as high as 94.1% of the total alcohol products. Structural characterizations revealed that Fe incorporation efficiently modulated the electronic structure of Co species, improved the reducibility of the catalyst, and promoted the transformation of surface lattice oxygen into adsorbed oxygen species, thereby boosting the reactivity of oxygen-containing intermediates. Meanwhile, the Na promoter facilitated the formation of Co-Fe alloy active sites during reaction and further induced the generation of carbide phases (e.g., Co2C, FeCx) under syngas atmospheres. Combined in situ spectroscopic investigations and post-reaction catalyst analyses confirmed that the synergistic interplay between alloy and carbide sites efficiently regulated the balance between CO dissociation and non-dissociative adsorption/insertion, promoted CO insertion into olefinic intermediates, and suppressed excessive hydrogenation and chain overgrowth, ultimately enabling the highly selective formation of ethanol and propanol. This study offers valuable theoretical insights and experimental guidance for the precision engineering of dual active-site architectures in Co-based catalysts via multi-promoter synergy, providing an effective strategy for the selective and efficient conversion of syngas to higher alcohols.
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Year 2026 volume 54 Issue 7
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doi: 10.1016/S1872-5813(26)60670-6
  • Receive Date：2025-11-25
  • Online Date：2026-09-23
  • Published：2026-07-10
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  • Received：2025-11-25
  • Revised：2025-12-24
  • Accepted：2026-01-06
Affiliations
    1College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
    2State Key Laboratory of Coal Liquefaction, Gasification and Utilization with High Efficiency and Low-Carbon Technology, Shanghai Yankuang Energy R&D Co., Ltd., Shanghai 201203, China

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表12种不同金属材料的力学参数
科
Family		 属数
Number of
genus		 种数
Number of
species		 占总种数比例
Percentage of
total species (%)		 属
Genus		 种数
Number of
species		 占总种数比例
Percentage of total
species (%)
鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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