The effect of iron additive incorporation mode on the Fischer–Tropsch Synthesis performance of alumina-supported cobalt catalysts

The effect of iron additive incorporation mode on the Fischer–Tropsch Synthesis performance of alumina-supported cobalt catalysts | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The effect of iron additive incorporation mode on the Fischer–Tropsch Synthesis performance of alumina-supported cobalt catalysts Yixuan Li, Yuanli Xiang, Xinyan Ai, Yuhua Zhang, Yanxi Zhao, Chengchao Liu, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7061461/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Co-Fe bimetallic catalysts have attracted increasing attention in the field of Fischer–Tropsch synthesis (FTS). In this study, cobalt was supplied in the form of Co 3 O 4 nanoparticles, and three different methods of iron (Fe) incorporation were employed: (1) Fe modification of the Al 2 O 3 support prior to Co 3 O 4 loading (Co/Fe-Al 2 O 3 ), (2) co-loading of Fe and Co 3 O 4 (CoFe/Al 2 O 3 ), and (3) Fe modification of Co 3 O 4 prior to loading (Co-Fe/Al 2 O 3 ). These model catalysts were used to investigate the interactions between Co, Fe and the support and their impact on the catalytic activity and product selectivity of FTS. The results showed that the addition of Fe promotes cobalt reduction, modifies H 2 and CO adsorption properties and regulates catalytic performance. Compared with Co/Al 2 O 3 , Co/Fe-Al 2 O 3 exhibited the best reducibility and significantly reduced CH 4 selectivity from 19.2–11.2%. However, its CO adsorption weakened, decreasing CO conversion from 25.3–21.4%. Co-Fe/Al 2 O 3 showed enhanced H 2 and CO adsorption, increasing CO conversion by 18.9%. These findings demonstrate that the location of Fe affects the metal-support interaction, reducibility and adsorption activation abilities of the Co catalyst, ultimately altering FTS activity and selectivity. Fischer-Tropsch synthesis Co-Based Catalysts Fe Introduction Methods bimetallic catalysts Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction The Fischer–Tropsch synthesis (FTS) process can convert carbon-containing resources such as coal, biomass, and natural gas into clean fuels and high-value chemicals via syngas (CO and H 2 ). 1 – 3 Among the various FTS catalysts, including Fe-based, 4 Co-based, 5 – 6 Ni-based, 7 Ru-based, 8 and Rh-based, 9 systems, Fe-and Co-based catalysts have been successfully applied in industrial settings. 10 Fe-based catalysts are inexpensive and exhibit high selectivity for light hydrocarbons (C 1 –C 4 ) at medium to high temperatures (320–360°C). However, they generally exhibit lower catalytic activity and high water-gas shift (WGS) activity. 11 – 14 By contrast, cobalt-based catalysts offer high catalytic activity and selectivity for heavy hydrocarbons, as well as low WGS activity and good resistance to carbon deposition during the reaction. However, the rising cost of cobalt has led to concerns about the economic viability of these catalysts, which are essential for many industrial processes. 15 – 19 To combine the advantages of both Co-based and Fe-based catalysts, many studies focused on developing develop bimetallic catalysts by integrating these two metals. It has been found that the Fischer–Tropsch synthesis (FTS) performance of Co–Fe bimetallic catalysts is not a simple summation of the individual catalytic behaviours of Co and Fe. Rather, it is affected by factors such as metal–metal interactions, the bimetallic structure, particle size, and phase composition. 20 – 22 Early studies showed that, increasing the Fe content within a certain Fe/Co molar ratio range led to higher catalytic activity and C₅ ⁺ selectivity. 23 – 24 However, other research has indicated a significant negative correlation between the catalyst activity and C 5+ selectivity with the extent of CoFe alloying and alloy content. 25 – 29 Ma et al. 30 constructed Fe 5 C 2 /Co heterostructured nanoparticles using a “secondary growth” strategy. They found that during the reaction, Co mainly facilitated CO dissociation while Fe 5 C 2 promoted chain growth. The synergistic effect of these two active sites significantly enhanced FTS performance, increasing CO conversionfrom about 5% for Fe 5 C 2 alone to approximately 25% for the 12Fe 5 C 2 /Co catalyst. De et al. 31 reported a colloidal chemistry method to synthesize CoFe alloy catalysts supported on carbon nanotubes. The strong synergy between the Co and Fe reduced surface reconstruction of the cobalt species, resulting in lower methane selectivity. Ahmad et al 32 prepared CoFe bimetallic catalysts with a 10wt% Co loading using a co-impregnation method. Their results confirmed the synergistic interaction between Co and Fe. The presence of Fe improved the dispersion of Co particles and enhanced their reduction to metallic Co⁰, while also suppressing excessive methane formation. Valeria et al 33 used TiO 2 as a support and prepared CoFe bimetallic catalysts with a total metal loading of 12 wt% via microwave co-precipitation. All of the catalysts produced significant amounts of methane CH 4 and C 2 –C 4 hydrocarbons at low temperatures, with selectivity towards long-chain hydrocarbons increasing with temperature. Jae et al. 34 developed CoFe bimetallic catalysts for the production of low-carbon hydrocarbons (C 2 –C 4 and CH 4 ). Althoughthe interactions between Co and Fe have been extensively researched, the interactions between the active metals and the support, and the nature of the metal phases, remain debated. Therefore, the synergistic effects of CoFe bimetallic catalysts, the role of Fe as a promoter, and the underlying mechanisms require further investigation. This study involved preparing a series of Fe-modified Co/Al 2 O 3 Fischer–Tropsch synthesis (FTS) model catalysts were prepared using preformed Co 3 O 4 nanoparticles as the cobalt source via an ultrasound-assisted impregnation method. Characterization techniques including XRD, XPS, H 2 -TPR, H 2 -TPD, and CO-TPD were employed to investigate the effects of Fe distribution on the catalytic performance by tuning metal–metal and metal–support interactions. The results revealed that the Fe incorporation method had a significant impact on the reducibility, adsorption capacity, and catalytic performance of the Co/Al 2 O 3 catalysts. For the Co/Fe-Al 2 O 3 catalyst, in which the Fe was primarily deposited on the Al 2 O 3 support first, the strong Fe–support interaction weakened the Co–support interaction, making Co easier to reduce. This catalyst exhibited strong weak-site H 2 adsorption and the lowest CH 4 selectivity (11.2%). However, due to its weak CO adsorption, its catalytic activity was lowest catalytic activity, with CO conversion 15.4% lower than that of the Co/Al 2 O 3 reference catalyst. The CoFe/Al 2 O 3 catalyst, which has Fe and Co 3 O 4 co-loaded onto the Al 2 O 3 to form an CoFe alloy-like structure, benefits from alloying effects that enhance reducibility and reduce H₂ adsorption. It exhibited moderate CH 4 selectivity (15.8%) and strong CO adsorption, leading to a CO conversion of 8.7% higher than that of the reference. The Co-Fe/Al 2 O 3 catalyst, with Fe was preferentially deposited on the Co 3 O 4 surface to form a Co–Fe interface, exhibited enhanced reducibility and strong adsorption for both H 2 and CO. This configuration achieved the best catalytic performance, with a CO conversion 18.9% higher than that of the Co/Al 2 O 3 reference catalyst. 2 Experimental 2.1 Catalyst preparation A total of 3.2145 g of cobalt acetate tetrahydrate (C 4 H 6 CoO 4 ·4H 2 O) was dissolved sequentially in 100 mL of benzyl alcohol and 25 mL of benzylamine solution. The mixture was stirred and heated in a 40°C water bath for 2 h. Then, 25 mL of ammonia solution was added dropwise at a constant rate, followed by stirring for another 30 min. The resulting mixture was transferred to an oil bath and refluxed at 165°C for 2 h. After cooling to room temperature, the product was dried at 150°C for 12 h to obtain Co 3 O 4 particles. To prepare the Co/Al 2 O 3 catalyst, the Co 3 O 4 particles and Al 2 O 3 support were ultrasonically dispersed and mixed in ethanol for 30 min. The mixture was then evaporated at 70°C under rotary conditions, dried at 120°C for 10 h, and calcined in air at 500°C for 3 h. The resulting catalyst was denoted as Co/Al 2 O 3 . To prepare the Co/Fe-Al 2 O 3 catalyst, 1.1659 g of FeCl 3 ·6H 2 O was dissolved in a mixture of 3 mL deionized water and 2 mL ethanol to form an FeCl 3 solution. This solution was impregnated onto 4.0596 g of Al 2 O 3 support. After rotary evaporation at 50°C, the sample was dried at 100°C for 6 h and then calcined in air at 950°C for 5 h to obtain the Fe-Al 2 O 3 support. The Fe-Al 2 O 3 and preformed Co 3 O 4 particles were ultrasonically dispersed in ethanol for 30 min. After rotary evaporation at 70°C, the sample was dried at 120°C for 10 h and calcined in air at 500°C for 3 h. The resulting catalyst was denoted as Co/Fe-Al 2 O 3 . To prepare the Co-Fe/Al 2 O 3 catalyst, 1.1647 g of FeCl 3 ·6H 2 O was dissolved in 200 mL of deionized water and added to preformed Co 3 O 4 particles. The mixture was stirred at 30°C for 12 h. Then, 4.0615 g of Al 2 O 3 was added and ultrasonically dispersed for 30 min. The mixture was evaporated at 70°C, dried at 120°C for 10 h, and calcined at 500°C for 3 h. The resulting catalyst was named Co-Fe/Al 2 O 3 . To prepare the CoFe/Al 2 O 3 catalyst, 3.2179 g of C 4 H 6 CoO 4 ·4H 2 O and 1.1653 g of FeCl 3 ·6H 2 O were dissolved in 100 mL benzyl alcohol and 25 mL benzylamine. The solution was stirred at 40°C for 2 h in a water bath, followed by the dropwise addition of 25 mL ammonia solution. After stirring for 30 min, the mixture was transferred to a 165°C oil bath for reflux for 2 h. It was then cooled to room temperature and stirred at 30°C for 12 h. After that, 4.0661 g of Al 2 O 3 was added and ultrasonically dispersed for 30 min. The resulting mixture was evaporated at 70°C, dried at 120°C for 10 h, and calcined at 500°C for 3 h. The resulting black powder was denoted as CoFe/Al 2 O 3 . 2.2 Catalyst characterization The physical structure of the catalysts, including specific surface area and pore structure parameters, was characterized using a Quantachrome Autosorb-1-C instrument. The pore size distribution was calculated based on N₂ desorption isotherm data using the Barrett-Joyner-Halenda (BJH) model. The phase structure of the catalysts was characterized using X-ray powder diffraction (XRD, Bruker D8 Advance) with Cu Kα radiation at 40 kV and 40 mA. The scanning range was set from 5° to 80° (2θ). X-ray photoelectron spectroscopy (XPS) was carried out on a VG Multilab 2000 spectrometer using an Al Kα source under ultra-high vacuum (2 × 10⁻⁶ Pa) to analyze the surface chemical states of the elements. The reduction behavior of the catalysts was investigated using H 2 temperature-programmed reduction (H 2 -TPR) on an AMI-300 multifunctional chemisorption analyzer. Typically, 0.05 g of catalyst was pretreated in an Ar flow (30 mL·min⁻¹) at 150°C for 30 min and then cooled to 50°C. Subsequently, 5% H 2 /Ar was introduced and the sample was heated to 800°C at 10°C·min⁻¹ and held for 30 min. H 2 consumption was monitored using a thermal conductivity detector (TCD). H 2 temperature-programmed desorption (H 2 -TPD) was conducted on a BELCAT-II chemisorption analyzer to determine H 2 desorption behavior. About 30 mg of catalyst was reduced in H 2 (30 mL·min⁻¹) at 450°C for 2 h. After purging with He and cooling to 50°C, the sample was heated to 800°C in Ar at 10°C·min⁻¹. The desorption was recorded using TCD. CO temperature-programmed desorption (CO-TPD) was also performed on the BELCAT-II system. The sample was first reduced in H 2 (30 mL·min⁻¹) at 450°C for 2 h, purged with He, and cooled to 50°C. Then, CO (30 mL·min⁻¹) was adsorbed for 30 min, followed by desorption in He while heating to 800°C at 10°C·min⁻¹. TCD was used to record the signal. 2.3 FTS catalytic reaction The Fischer–Tropsch synthesis (FTS) performance evaluation was carried out using a four-channel micro fixed-bed reactor system operated under a unified temperature control system. A total of 0.1 g of catalyst was mixed thoroughly with 0.2 g of quartz sand and loaded into the reactor tube. The catalyst was reduced under pure H₂ at a flow rate of 8 SL·g⁻¹·h⁻¹ at 450°C for 8 h, followed by cooling to 50°C. The gas was then switched to syngas (H 2 : CO : N 2 = 60% : 30% : 10%) at a flow rate of 6 SL·g⁻¹·h⁻¹ and a pressure of 1.0 MPa. The reaction temperature was raised to 250°C to initiate the FTS reaction. The outlet gas products (CO, H 2 , CH 4 , CO 2 , and C 2 –C 8 hydrocarbons) were analyzed online using an Agilent 7890B gas chromatograph, with quantitative analysis performed by the external standard method. 3 Results and discussion 3.1 Catalyst Characterization To analyze the specific surface area and pore structure of the catalysts, N 2 physisorption–desorption characterization was performed on the series of catalysts. The results are shown in Fig. 1(a) and (b). As observed in Fig. 1(a), all catalysts exhibit H1-type hysteresis loops, indicating the presence of mesoporous structures. Comparing the synthesized catalysts, slight differences in the shape of the hysteresis loops suggest structural reconstruction during the preparation process, resulting in variations in pore structure. The average pore size distribution calculated using the BJH model is shown in Fig. 1(b). Combined with Table 1, the pore sizes of the catalysts are mainly distributed in the range of 15–30 nm. Compared with the Co/Al 2 O 3 catalyst, the Co-Fe/Al 2 O 3 catalyst shows no significant changes in pore structure parameters, indicating that the method of introducing Fe after the synthesis of Co 3 O 4 nanoparticles does not affect the specific surface area or pore structure of the final catalyst. Table 1 Structural properties of the Co catalysts Catalysts Surface area (m 2 ·g − 1 ) Pore size (nm) Pore volume (cm 3 ·g − 1 ) Co/Fe-Al 2 O 3 93.1 20.1 0.58 CoFe/Al 2 O 3 113.1 18.6 0.52 Co-Fe/Al 2 O 3 128.9 17.1 0.79 Co/Al 2 O 3 126.4 15.1 0.77 The phase composition of the catalysts was analyzed by X-ray diffraction (XRD). As shown in the diffraction patterns in Fig. 2, the Co species in all catalysts exist in the Co 3 O 4 crystalline phase (JCPDS 74-2120), while the support is mainly in the γ-Al 2 O 3 phase (JCPDS 23-1009). In the Co/Fe-Al 2 O 3 catalyst, characteristic peaks of α-Al 2 O 3 (JCPDS 74-1081) are also observed, which is likely due to the partial phase transformation of γ-Al 2 O 3 to α-Al 2 O 3 after high-temperature calcination of Fe-Al 2 O 3 at 950°C. No characteristic diffraction peaks associated with Fe species were detected in any of the four catalysts, which may be attributed to the uniform dispersion of Fe on the catalyst surface. Overall, the XRD results indicate that although the location and distribution of Fe species vary among the catalysts, they do not significantly affect the phase composition. To analyze the surface elemental composition and chemical states of the catalysts, X-ray photoelectron spectroscopy (XPS) was conducted on the catalyst series, as shown in Fig. 3. Figure 3(a) displays the Co 2p XPS spectra. After peak deconvolution, two sets of peaks corresponding to Co 2p₃/₂ and Co 2p₁/₂ were observed. The binding energies at approximately 780.5 eV and 796.3 eV are attributed to Co³⁺, while those around 782.5 eV and 797.7 eV are assigned to Co²⁺. The Co²⁺/Co³⁺ ratios calculated from the peak areas are listed in Table 2. Among them, the Co²⁺/Co³⁺ ratio of the Co-Fe/Al 2 O 3 catalyst is 1.13, indicating a relatively high Co²⁺ content in the catalyst. 35 Additionally, all Co²⁺/Co³⁺ ratios are below 2, suggesting that the primary phase of the catalysts is Co₃O₄. 36 Table 2 also shows that, compared to the Co/Al 2 O 3 catalyst, all Fe-promoted catalysts exhibit a shift in Co binding energy toward higher values. The order of Co binding energy is: CoFe/Al 2 O 3 > Co/Fe-Al 2 O 3 > Co-Fe/Al 2 O 3 > Co/Al 2 O 3 , indicating electron transfer between Co and Fe species. Figure 3(b) shows the Fe 2p XPS spectra. After peak fitting, peaks at around 711.5 eV and 720.5 eV correspond to Fe²⁺, while those at around 714.2 eV and 725.2 eV are assigned to Fe³⁺. According to Table 2, the Fe²⁺/Fe³⁺ ratios are all greater than 1, indicating a high surface concentration of Fe²⁺ species. The CoFe/Al 2 O 3 catalyst has the lowest Fe²⁺/Fe³⁺ ratio, likely due to electron transfer from Fe to Co, resulting in increased Fe³⁺ content. This also confirms the presence of interactions between Co and Fe metals. The Co 2p binding energy of CoFe/Al 2 O 3 is higher than that of the other three catalysts, suggesting that the method of Fe incorporation influences the electronic environment of Co and Fe. Therefore, differences in Fe deposition locations can affect the metal–metal and metal–support interactions in the Fe-modified Co catalysts Table 2 The XPS peak results of Co catalysts The reduction behavior of the catalyst series was investigated using H 2 -temperature programmed reduction (H 2 -TPR), and the corresponding results are presented in Fig. 4. For the Co/Al 2 O 3 catalyst, a weak reduction peak is observed around 371°C, which can be attributed to the reduction of Co 3 O 4 to CoO and Fe 2 O 3 to Fe 3 O 4 . A second reduction peak appears at approximately 556°C, corresponding to the further reduction of CoO to metallic Co⁰ and Fe 3 O 4 to lower-valence iron species.The CoFe/Al 2 O 3 and Co-Fe/Al 2 O 3 catalysts exhibit similar two-step reduction processes. However, compared to Co/Al 2 O 3 , the preferential incorporation of Fe species onto the Co 3 O 4 particles promotes the second reduction step, thereby facilitating the formation of metallic Co⁰. In contrast, the Co/Fe-Al 2 O 3 catalyst displays three distinct reduction peaks within the examined temperature range. A broad peak centered around 327°C is ascribed to the reduction of Co 3 O 4 to CoO, while the peak at approximately 404°C is associated with the reduction of CoO to Co⁰. A high-temperature peak at 645°C is attributed to the strong interaction between the Fe species and the Al 2 O 3 support. This suggests that the Fe promoter is highly dispersed on the Al 2 O 3 surface, which weakens the interaction between the Co species and the support, thereby enhancing the reducibility of the catalyst. 3.2 H₂ and CO Desorption Properties of the Catalyst To investigate the H 2 chemisorption capacity of the catalysts, H 2 -temperature programmed desorption (H 2 -TPD) measurements were performed, and the results are presented in Fig. 5. All catalysts exhibit multiple H 2 desorption peaks. The CoFe/Al 2 O 3 and Co/Fe-Al 2 O 3 catalysts show low-temperature desorption peaks below 300°C, indicating a relatively strong capacity for weak H₂ adsorption compared to Co/Al 2 O 3 and Co-Fe/Al 2 O 3 . Additionally, both CoFe/Al 2 O 3 and Co/Fe- Al 2 O 3 display strong H 2 adsorptionat 450–650°C. Notably, the Co/Fe-Al 2 O 3 catalyst exhibits the highest H 2 adsorption capacity across both low- and high-temperature regions among the tested samples. In contrast, the Co/Al 2 O 3 and Co-Fe/Al 2 O 3 catalysts present only a weak desorption peak around 370°C and a single strong desorption peak near 550°C, suggesting a predominance of strong H₂ adsorption. Based on the overall desorption profiles, the H₂ adsorption capacity of the catalysts follows the order: Co/Fe-Al 2 O 3 > CoFe/Al 2 O 3 > Co-Fe/Al 2 O 3 > Co/Al 2 O 3 .According to previous studies 37 , an optimal (i.e., moderate) H₂ adsorption capacity is essential for achieving high catalytic activity. Excessive adsorption of H₂ on the surface of Co/Fe-Al 2 O 3 and CoFe/Al 2 O 3 may lead to high surface hydrogen coverage, which can promote the formation of undesired CH₄ during Fischer–Tropsch synthesis (FTS). As a result, these two catalysts exhibit inferior FTS performance compared to Co-Fe/Al 2 O 3 .The H 2 -TPD results also reveal that the spatial distribution of Fe species plays a significant role in influencing H 2 adsorption behavior. The preferential incorporation of Fe onto the surface of Co 3 O 4 particles enhances the weak H 2 adsorption capacity of catalyst at lower temperatures, which could be beneficial for tuning catalytic performance. The CO adsorption behavior of the catalysts was characterized by CO-temperature programmed desorption (CO-TPD), and the results are shown in Fig. 6. The CoFe/Al 2 O 3 and Co-Fe/Al 2 O 3 catalysts exhibit four distinct desorption peaks, indicating the presence of four types of adsorption sites on their surfaces. The Co/Fe-Al 2 O 3 catalyst displays a low-temperature desorption peak ( 500°C). The Co/ Al 2 O 3 catalyst shows a pronounced low-temperature desorption peak and a high-temperature peak around 600°C. Both the CoFe/Al 2 O 3 and Co-Fe/Al 2 O 3 catalysts exhibit significant medium-temperature desorption peaks (200–400°C), with the Co-Fe/Al 2 O 3 catalyst demonstrating the highest desorption temperature in this range—exceeding 400°C. Overall, catalysts in which Fe is deposited on the surface of Co exhibit stronger CO adsorption capacity. Enhanced CO adsorption is generally beneficial for catalytic activity, as it facilitates CO activation on the catalyst surface. In contrast, excessive H₂ adsorption may occupy a large number of active sites, thereby hindering CO adsorption and potentially reducing catalytic performance. The CO-TPD results suggest that the spatial distribution of Fe significantly influences the ability to adsorb and activate CO of catalyst. Preferential modification of Co surfaces with Fe species enhances CO adsorption capacity, particularly in the medium-temperature range. In combination with the H 2 -TPD results, it is evident that the Co-Fe/Al 2 O 3 catalyst exhibits relatively balanced adsorption capacities for both H₂ and CO, which may contribute to its superior catalytic activity. Table 3 The percentage about CO-TPD peak area of a series of Co catalysts Catalysts Peak-1 Peak-2 Peak-3 Peak-4 Co/Fe-Al 2 O 3 35.7 42.7 21.6 -- CoFeAl 2 O 3 9.0 21.3 32.0 37.6 Co-Fe/Al 2 O 3 18.0 41.5 14.2 26.3 Co/Al 2 O 3 34.4 29.5 36.1 -- 3.2 FTS catalytic performance The Fischer–Tropsch synthesis (FTS) performance of catalysts was evaluated under the reaction conditions of 250°C, 1.0 MPa pressure, a syngas H 2 /CO ratio of 2, and a gas hourly space velocity (GHSV) of 6 SL·g⁻¹·h⁻¹. stability tests for catalysts (Fig. 7) indicated that all catalysts exhibited good stability, with no deactivation observed within 100 h. This stability is attributed to the high dispersion of active metal particles in the catalysts prepared by the ultrasound-assisted impregnation method, which effectively suppresses aggregation and sintering that typically lead to deactivation. 38 As shown in Table 4, the CO conversion for Co-Fe/Al 2 O 3 , CoFe/Al 2 O 3 , Co/Al 2 O 3 , and Co/Fe-Al 2 O 3 catalysts were 30.1%, 27.5%, 25.3%, and 21.4%, respectively. Notably, the Co-Fe/Al 2 O 3 catalyst, prepared by preferentially introducing Fe species onto the surface of Co 3 O 4 particles, exhibited the highest CO conversion and selectivity toward light hydrocarbons, reaching 30.1% and 10.7%, respectively. These results suggest that the method of Fe incorporation significantly influences the catalytic activity of CoFe-based catalysts in Fischer–Tropsch synthesis. Table 4 Reaction performance of catalysts for CO hydrogenation Catalysts CO conversion (%) CO 2 selectivity (%) Hydrocarbon selectivity (%) O/P (C 2 -C 4 ) CH 4 C 2 -C 4 C 2 = -C 4 = C 5+ Co/Fe-Al 2 O 3 21.4 3.7 11.2 9.6 6.3 79.2 1.8 CoFe/Al 2 O 3 27.5 3.7 15.8 10.5 5.6 73.7 1.1 Co-Fe/Al 2 O 3 30.1 3.3 17.2 10.7 6.2 72.1 1.4 Co/Al 2 O 3 25.3 2.8 19.2 10.0 5.8 70.8 1.2 4 Conclusions This study examined the preparation of CoFe/Al 2 O 3 , Co-Fe/Al 2 O 3 and Co/Fe-Al 2 O 3 catalysts using pre-synthesised Co 3 O 4 nanoparticles as the cobalt source, with different methods of introducing Fe as a promoter. The catalysts were synthesised using an ultrasound-assisted impregnation method. For comparison, a Fe-free Co/Al 2 O 3 catalyst was also prepared. The results suggest that introducing Fe altered the reducibility and chemisorption properties of the catalysts. The Co/Fe-Al 2 O 3 catalyst showed improved H₂ adsorption but reduced CO adsorption, leading to lower catalytic activity than the Co/Al 2 O 3 catalyst. In contrast, the adsorption capacities of both CoFe/Al 2 O 3 and Co-Fe/Al 2 O 3 for H 2 and CO were improved, which may contribute to their higher catalytic activity. Among these catalysts, Co-Fe/Al 2 O 3 showed the best H 2 and CO adsorption performance, and exhibited the highest Fischer–Tropsch synthesis activity under reaction conditions at 230°C, 1 MPa, and 6 SL·g cat ⁻¹·h⁻¹. Its CO conversion was 18.9% higher than that of the Co/Al 2 O 3 reference catalyst. Declarations Acknowledgments This work was supported by the National Key Research and Devel opment Program of China (2022YFB4101201), National Natural Science Foundation of China (U22A20394, 21902187), the Key Research and Development Program of Hubei Province (2022BCA084), the Funda mental Research Funds for the Central Universities of South-Central Minzu University (CZY23016, CZZ24008), and the Fund for Academic Innovation Teams of South-Central Minzu University (PTZ24011). Conflict of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data Availability No data was used for the research described in the article. Author contributions Yixuan Li: Writing – review & editing, Writing – original draft, Methodology, Investigation, Conceptualization. Yuanli Xiang: Writing – review & editing, Resources, Conceptualization. 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Angew Chem Int Ed 54(15):4553–4556. https://doi.org/10.1002/anie.201411708 Cheng Q, Tian Y, Lyu S, et al. (2018) Confined small-sized cobalt catalysts stimulate carbon-chain growth reversely by modifying ASF law of Fischer–Tropsch synthesis. Nat Commun 9(1):3250. https://doi.org/10.1038/s41467-018-05755-8 Li J, He Y, Tan L, et al. (2018) Integrated tuneable synthesis of liquid fuels via Fischer–Tropsch technology. Nat Catal 1(10):787–793. https://doi.org/10.1038/s41929-018-0144-z Guczi L, Boskovic G, Kiss E (2010) Bimetallic cobalt-based catalysts. Catal Rev 52(2):133–203. https://doi.org/10.1080/01614941003720134 Trépanier M, Tavasoli A, Dalai AK, Adjaye J (2009) Fischer–Tropsch synthesis over carbon nanotubes supported cobalt catalysts in a fixed bed reactor: influence of acid treatment. Fuel Process Technol 90(3):367–374. https://doi.org/10.1016/j.fuproc.2008.10.012 Calderone VR, Shiju NR, Ferré DC, Rothenberg G (2011) Bimetallic catalysts for the Fischer–Tropsch reaction. Green Chem 13(8):1925–1933. https://doi.org/10.1039/C0GC00919A Ishihara T, Ebitani K, Arai H (1987) Hydrogenation of carbon monoxide over SiO 2 -supported Fe–Co, Co–Ni and Ni–Fe bimetallic catalysts. Appl Catal 30(1):225–238. https://doi.org/10.1016/S0166-9834(00)84115-9 Arai H, Miya K, Seiyama T (1984) TiO 2 -supported Fe–Co, Co–Ni, and Ni–Fe alloy catalysts for Fischer–Tropsch synthesis. Chem Lett 13:365–368. https://doi.org/10.1246/cl.1984.1291 Duvenhage DJ, Coville NJ (2005) Fe:Co/TiO 2 bimetallic catalysts for the Fischer–Tropsch reaction. Appl Catal A 289(2):231–239. https://doi.org/10.1016/S0926-860X(02)00118-7 Lögdberg S, Tristantini D, Borg Y, et al. (2009) Hydrocarbon production via Fischer–Tropsch synthesis from H₂-poor syngas over different Fe–Co/γ-Al 2 O 3 bimetallic catalysts. Appl Catal B 89(1–2):167–182. https://doi.org/10.1016/j.apcatb.2008.11.037 Duvenhage DJ (1997) Fe:Co/TiO 2 bimetallic catalysts for the Fischer–Tropsch reaction I. Characterization and reactor studies. Appl Catal A 153(1):43–67. https://doi.org/10.1016/j.apcata.2005.05.008 Cabet C, Kiennemann A, Läkamp S, Pourroy G (1998) Synthesis of new Fe–Co based metal/oxide composite materials: application to the Fischer–Tropsch synthesis. J Catal 173(1):64–73. https://doi.org/10.1006/jcat.1997.1885 Duvenhage DJ, Coville NJ (2005) Effect of K, Mn and Cr on the Fischer–Tropsch activity of Fe:Co/TiO 2 catalysts. Catal Lett 104(3–4):129–133. https://doi.org/10.1007/s10562-005-7941-0 Yang C, Zhao B, Gao R, et al. (2017) Construction of synergistic Fe 5 C 2 /Co heterostructured nanoparticles as an enhanced low-temperature Fischer–Tropsch synthesis catalyst. ACS Catal 7(9):5661–5667. https://doi.org/10.1021/acscatal.7b01142 Ismail ASM, Casavola M, Liu B, et al. (2019) Atomic-scale investigation of the structural and electronic properties of cobalt–iron bimetallic Fischer–Tropsch catalysts. ACS Catal 9(9):7998–8011. https://doi.org/10.1021/acscatal.8b04334 Díaz JA, Akhavan H, Romero A, et al. (2014) Cobalt and iron supported on carbon nanofibers as catalysts for Fischer–Tropsch synthesis. Fuel Process Technol 128:417–424. https://doi.org/10.1016/j.fuproc.2014.08.005 Russo M, La Parola V, Testa ML, et al. (2020) Structural insight in TiO 2 supported CoFe catalysts for Fischer–Tropsch synthesis at ambient pressure. Appl Catal A 600:117614. https://doi.org/10.1016/j.apcata.2020.117621 Jo SB, Kim TY, Lee CH, et al. (2019) Selective CO hydrogenation over bimetallic Co–Fe catalysts for the production of light paraffin hydrocarbons (C 2 –C 4 ): effect of space velocity, reaction pressure and temperature. Catalysts 9(9):727. https://doi.org/ 10.3390/catal9090779 Bonnelle JP, Grimblot J, D’huysser A (1975) Influence de la polarisation des liaisons sur les spectres ESCA des oxydes de cobalt. J Electron Spectrosc Relat Phenom 7(2):151–162. https://doi.org/10.1016/0368-2048(75)80047-8 Khodakov AY, Griboval-Constant A, Bechara R, et al. (2002) Pore size effects in Fischer–Tropsch synthesis over cobalt-supported mesoporous silicas. J Catal 206(2):230–241. https://doi.org/10.1006/jcat.2001.3496 Jacobs G, Das TK, Zhang Y, et al. (2002) Fischer–Tropsch synthesis: support, loading, and promoter effects on the reducibility of cobalt catalysts. Appl Catal A 233(1–2):263–281. https://doi.org/10.1016/S0926-860X(02)00195-3 Liu C, Hong J, Zhang Y, et al. (2016) Synthesis of γ-Al 2 O 3 nanofibers stabilized Co 3 O 4 nanoparticles as highly active and stable Fischer–Tropsch synthesis catalysts. Fuel 180:777–784. https://doi.org/10.1016/j.fuel.2016.04.006 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 22 Jul, 2025 Reviews received at journal 21 Jul, 2025 Reviews received at journal 20 Jul, 2025 Reviewers agreed at journal 13 Jul, 2025 Reviewers agreed at journal 08 Jul, 2025 Reviewers invited by journal 08 Jul, 2025 Editor assigned by journal 08 Jul, 2025 Submission checks completed at journal 08 Jul, 2025 First submitted to journal 07 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7061461","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":482631225,"identity":"05b96789-06ce-493b-bd3e-851efc317400","order_by":0,"name":"Yixuan Li","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"Yixuan","middleName":"","lastName":"Li","suffix":""},{"id":482631227,"identity":"bd3cee1e-2b0a-4e58-9f9a-a5dc31a14d60","order_by":1,"name":"Yuanli Xiang","email":"","orcid":"","institution":"Hubei Three Gorges Laboratory","correspondingAuthor":false,"prefix":"","firstName":"Yuanli","middleName":"","lastName":"Xiang","suffix":""},{"id":482631230,"identity":"04b6b047-ae75-4e92-8e87-f513ffd91702","order_by":2,"name":"Xinyan Ai","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"Xinyan","middleName":"","lastName":"Ai","suffix":""},{"id":482631232,"identity":"dbfc301d-6223-4adf-b468-5351a6fdc788","order_by":3,"name":"Yuhua Zhang","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"Yuhua","middleName":"","lastName":"Zhang","suffix":""},{"id":482631233,"identity":"2cdfb99f-93b8-4dfb-bc56-59a566f3bf41","order_by":4,"name":"Yanxi Zhao","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"Yanxi","middleName":"","lastName":"Zhao","suffix":""},{"id":482631234,"identity":"1689d880-5176-40f4-813a-98e6a553f72c","order_by":5,"name":"Chengchao Liu","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"Chengchao","middleName":"","lastName":"Liu","suffix":""},{"id":482631235,"identity":"1c9f6a94-3497-4e71-8216-28096c412a34","order_by":6,"name":"Jinlin Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwUlEQVRIiWNgGAWjYBACxmYGxgMJDBY8/AzMDQeI1cIA1CLBI9nASKQWEACqlGAwOMDYQJxy5nbeAwce7pCQMT5+sPEwb9sdBv727gQCDuNLOJB4RoLH7ExiA1DLMwaJM2c3ENDCY3AgsQ2o5QBYy2EGA4lcIrUY9z8kVYuBBMm2SNx42HBwzrnDPAT9Yth/xvDhzzYbe/7+5MMf3pQdluNv7yWgpQGJw8TDwMCDVzkIyKO48gdB9aNgFIyCUTASAQBi7ks3txS8UQAAAABJRU5ErkJggg==","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":true,"prefix":"","firstName":"Jinlin","middleName":"","lastName":"Li","suffix":""}],"badges":[],"createdAt":"2025-07-07 05:23:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7061461/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7061461/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86443660,"identity":"7e1bc606-c86a-4354-9699-a42ddbd6a207","added_by":"auto","created_at":"2025-07-10 17:12:03","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":169763,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isothermsand \u003cstrong\u003eb\u003c/strong\u003e pore size distribution of the catalysts\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/2dad0a4dd29e45bdb407a5b0.png"},{"id":86443659,"identity":"2fa45886-cd6b-40a9-a1b1-487ec0770784","added_by":"auto","created_at":"2025-07-10 17:12:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":129224,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of Co catalysts\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/1a0a71a97bfb22fc451b535a.png"},{"id":86443824,"identity":"7e50f0d6-eb8e-40ac-b763-4f72f48b816a","added_by":"auto","created_at":"2025-07-10 17:20:03","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":203829,"visible":true,"origin":"","legend":"\u003cp\u003eThe spectra of Co catalysts. \u003cstrong\u003ea\u003c/strong\u003e Co2p. \u003cstrong\u003eb\u003c/strong\u003e Fe2p\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/d8a1c6c7d852fe80a4461bb4.png"},{"id":86443666,"identity":"94de2caa-1b17-4907-b494-f67cc8edd3fb","added_by":"auto","created_at":"2025-07-10 17:12:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":98729,"visible":true,"origin":"","legend":"\u003cp\u003eThe H\u003csub\u003e2\u003c/sub\u003e-TPR profiles of Co catalysts\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/83dcdb9974ede14ad76e5ed5.png"},{"id":86444365,"identity":"b6b6d9a2-6570-4864-8cb3-36f29114fceb","added_by":"auto","created_at":"2025-07-10 17:28:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":136582,"visible":true,"origin":"","legend":"\u003cp\u003eH\u003csub\u003e2\u003c/sub\u003e-TPD profiles of Co catalysts\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/b9f89ff225a6c79dfe90eca4.png"},{"id":86443829,"identity":"f4ecb97b-dc47-4c98-b108-c3dfe1f15c6e","added_by":"auto","created_at":"2025-07-10 17:20:03","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":135271,"visible":true,"origin":"","legend":"\u003cp\u003eCO-TPD profiles of Co catalysts\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/e01a3f1201bce2aede48aad7.png"},{"id":86443826,"identity":"c69b66e8-4fc3-4ba6-bcae-07db6ce23da4","added_by":"auto","created_at":"2025-07-10 17:20:03","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":100109,"visible":true,"origin":"","legend":"\u003cp\u003eTime on stream test on Fe based catalysts at 230 °C, 1 MPa, and 6 SL·g\u003csup\u003e⁻\u003c/sup\u003e¹·h\u003csup\u003e⁻\u003c/sup\u003e¹\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/ab4afb55fdfa7c23b0e83971.png"},{"id":86444977,"identity":"b4652d59-eccb-42e4-8126-cb70f36ad691","added_by":"auto","created_at":"2025-07-10 17:36:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1835840,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7061461/v1/38885d1d-316e-4359-916d-ff6811c50ab5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The effect of iron additive incorporation mode on the Fischer–Tropsch Synthesis performance of alumina-supported cobalt catalysts","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe Fischer\u0026ndash;Tropsch synthesis (FTS) process can convert carbon-containing resources such as coal, biomass, and natural gas into clean fuels and high-value chemicals via syngas (CO and H\u003csub\u003e2\u003c/sub\u003e).\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e Among the various FTS catalysts, including Fe-based,\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Co-based,\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e Ni-based,\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e Ru-based,\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e and Rh-based,\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e systems, Fe-and Co-based catalysts have been successfully applied in industrial settings.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e Fe-based catalysts are inexpensive and exhibit high selectivity for light hydrocarbons (C\u003csub\u003e1\u003c/sub\u003e\u0026ndash;C\u003csub\u003e4\u003c/sub\u003e) at medium to high temperatures (320\u0026ndash;360\u0026deg;C). However, they generally exhibit lower catalytic activity and high water-gas shift (WGS) activity.\u003csup\u003e\u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e By contrast, cobalt-based catalysts offer high catalytic activity and selectivity for heavy hydrocarbons, as well as low WGS activity and good resistance to carbon deposition during the reaction. However, the rising cost of cobalt has led to concerns about the economic viability of these catalysts, which are essential for many industrial processes.\u003csup\u003e\u003cspan additionalcitationids=\"CR16 CR17 CR18\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eTo combine the advantages of both Co-based and Fe-based catalysts, many studies focused on developing develop bimetallic catalysts by integrating these two metals. It has been found that the Fischer\u0026ndash;Tropsch synthesis (FTS) performance of Co\u0026ndash;Fe bimetallic catalysts is not a simple summation of the individual catalytic behaviours of Co and Fe. Rather, it is affected by factors such as metal\u0026ndash;metal interactions, the bimetallic structure, particle size, and phase composition.\u003csup\u003e\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Early studies showed that, increasing the Fe content within a certain Fe/Co molar ratio range led to higher catalytic activity and C₅\u003csub\u003e⁺\u003c/sub\u003e selectivity.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e However, other research has indicated a significant negative correlation between the catalyst activity and C\u003csub\u003e5+\u003c/sub\u003e selectivity with the extent of CoFe alloying and alloy content.\u003csup\u003e\u003cspan additionalcitationids=\"CR26 CR27 CR28\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e Ma et al.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e constructed Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/Co heterostructured nanoparticles using a \u0026ldquo;secondary growth\u0026rdquo; strategy. They found that during the reaction, Co mainly facilitated CO dissociation while Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e promoted chain growth. The synergistic effect of these two active sites significantly enhanced FTS performance, increasing CO conversionfrom about 5% for Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e alone to approximately 25% for the 12Fe\u003csub\u003e5\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e/Co catalyst. De et al.\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e reported a colloidal chemistry method to synthesize CoFe alloy catalysts supported on carbon nanotubes. The strong synergy between the Co and Fe reduced surface reconstruction of the cobalt species, resulting in lower methane selectivity. Ahmad et al\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e prepared CoFe bimetallic catalysts with a 10wt% Co loading using a co-impregnation method. Their results confirmed the synergistic interaction between Co and Fe. The presence of Fe improved the dispersion of Co particles and enhanced their reduction to metallic Co⁰, while also suppressing excessive methane formation. Valeria et al\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e used TiO\u003csub\u003e2\u003c/sub\u003e as a support and prepared CoFe bimetallic catalysts with a total metal loading of 12 wt% via microwave co-precipitation. All of the catalysts produced significant amounts of methane CH\u003csub\u003e4\u003c/sub\u003e and C\u003csub\u003e2\u003c/sub\u003e\u0026ndash;C\u003csub\u003e4\u003c/sub\u003e hydrocarbons at low temperatures, with selectivity towards long-chain hydrocarbons increasing with temperature. Jae et al.\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e developed CoFe bimetallic catalysts for the production of low-carbon hydrocarbons (C\u003csub\u003e2\u003c/sub\u003e\u0026ndash;C\u003csub\u003e4\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e). Althoughthe interactions between Co and Fe have been extensively researched, the interactions between the active metals and the support, and the nature of the metal phases, remain debated. Therefore, the synergistic effects of CoFe bimetallic catalysts, the role of Fe as a promoter, and the underlying mechanisms require further investigation.\u003c/p\u003e\u003cp\u003eThis study involved preparing a series of Fe-modified Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e Fischer\u0026ndash;Tropsch synthesis (FTS) model catalysts were prepared using preformed Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles as the cobalt source via an ultrasound-assisted impregnation method. Characterization techniques including XRD, XPS, H\u003csub\u003e2\u003c/sub\u003e-TPR, H\u003csub\u003e2\u003c/sub\u003e-TPD, and CO-TPD were employed to investigate the effects of Fe distribution on the catalytic performance by tuning metal\u0026ndash;metal and metal\u0026ndash;support interactions. The results revealed that the Fe incorporation method had a significant impact on the reducibility, adsorption capacity, and catalytic performance of the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts.\u003c/p\u003e\u003cp\u003eFor the Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, in which the Fe was primarily deposited on the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e support first, the strong Fe\u0026ndash;support interaction weakened the Co\u0026ndash;support interaction, making Co easier to reduce. This catalyst exhibited strong weak-site H\u003csub\u003e2\u003c/sub\u003e adsorption and the lowest CH\u003csub\u003e4\u003c/sub\u003e selectivity (11.2%). However, due to its weak CO adsorption, its catalytic activity was lowest catalytic activity, with CO conversion 15.4% lower than that of the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e reference catalyst.\u003c/p\u003e\u003cp\u003eThe CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, which has Fe and Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e co-loaded onto the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e to form an CoFe alloy-like structure, benefits from alloying effects that enhance reducibility and reduce H₂ adsorption. It exhibited moderate CH\u003csub\u003e4\u003c/sub\u003e selectivity (15.8%) and strong CO adsorption, leading to a CO conversion of 8.7% higher than that of the reference.\u003c/p\u003e\u003cp\u003eThe Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, with Fe was preferentially deposited on the Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e surface to form a Co\u0026ndash;Fe interface, exhibited enhanced reducibility and strong adsorption for both H\u003csub\u003e2\u003c/sub\u003e and CO. This configuration achieved the best catalytic performance, with a CO conversion 18.9% higher than that of the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e reference catalyst.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Catalyst preparation\u003c/h2\u003e\u003cp\u003eA total of 3.2145 g of cobalt acetate tetrahydrate (C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eCoO\u003csub\u003e4\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO) was dissolved sequentially in 100 mL of benzyl alcohol and 25 mL of benzylamine solution. The mixture was stirred and heated in a 40\u0026deg;C water bath for 2 h. Then, 25 mL of ammonia solution was added dropwise at a constant rate, followed by stirring for another 30 min. The resulting mixture was transferred to an oil bath and refluxed at 165\u0026deg;C for 2 h. After cooling to room temperature, the product was dried at 150\u0026deg;C for 12 h to obtain Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles.\u003c/p\u003e\u003cp\u003eTo prepare the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, the Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e support were ultrasonically dispersed and mixed in ethanol for 30 min. The mixture was then evaporated at 70\u0026deg;C under rotary conditions, dried at 120\u0026deg;C for 10 h, and calcined in air at 500\u0026deg;C for 3 h. The resulting catalyst was denoted as Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eTo prepare the Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, 1.1659 g of FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO was dissolved in a mixture of 3 mL deionized water and 2 mL ethanol to form an FeCl\u003csub\u003e3\u003c/sub\u003e solution. This solution was impregnated onto 4.0596 g of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e support. After rotary evaporation at 50\u0026deg;C, the sample was dried at 100\u0026deg;C for 6 h and then calcined in air at 950\u0026deg;C for 5 h to obtain the Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e support. The Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and preformed Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles were ultrasonically dispersed in ethanol for 30 min. After rotary evaporation at 70\u0026deg;C, the sample was dried at 120\u0026deg;C for 10 h and calcined in air at 500\u0026deg;C for 3 h. The resulting catalyst was denoted as Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eTo prepare the Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, 1.1647 g of FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO was dissolved in 200 mL of deionized water and added to preformed Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles. The mixture was stirred at 30\u0026deg;C for 12 h. Then, 4.0615 g of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e was added and ultrasonically dispersed for 30 min. The mixture was evaporated at 70\u0026deg;C, dried at 120\u0026deg;C for 10 h, and calcined at 500\u0026deg;C for 3 h. The resulting catalyst was named Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eTo prepare the CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, 3.2179 g of C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eCoO\u003csub\u003e4\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO and 1.1653 g of FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO were dissolved in 100 mL benzyl alcohol and 25 mL benzylamine. The solution was stirred at 40\u0026deg;C for 2 h in a water bath, followed by the dropwise addition of 25 mL ammonia solution. After stirring for 30 min, the mixture was transferred to a 165\u0026deg;C oil bath for reflux for 2 h. It was then cooled to room temperature and stirred at 30\u0026deg;C for 12 h. After that, 4.0661 g of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e was added and ultrasonically dispersed for 30 min. The resulting mixture was evaporated at 70\u0026deg;C, dried at 120\u0026deg;C for 10 h, and calcined at 500\u0026deg;C for 3 h. The resulting black powder was denoted as CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Catalyst characterization\u003c/h2\u003e\u003cp\u003eThe physical structure of the catalysts, including specific surface area and pore structure parameters, was characterized using a Quantachrome Autosorb-1-C instrument. The pore size distribution was calculated based on N₂ desorption isotherm data using the Barrett-Joyner-Halenda (BJH) model.\u003c/p\u003e\u003cp\u003eThe phase structure of the catalysts was characterized using X-ray powder diffraction (XRD, Bruker D8 Advance) with Cu Kα radiation at 40 kV and 40 mA. The scanning range was set from 5\u0026deg; to 80\u0026deg; (2θ).\u003c/p\u003e\u003cp\u003eX-ray photoelectron spectroscopy (XPS) was carried out on a VG Multilab 2000 spectrometer using an Al Kα source under ultra-high vacuum (2 \u0026times; 10⁻⁶ Pa) to analyze the surface chemical states of the elements.\u003c/p\u003e\u003cp\u003eThe reduction behavior of the catalysts was investigated using H\u003csub\u003e2\u003c/sub\u003e temperature-programmed reduction (H\u003csub\u003e2\u003c/sub\u003e-TPR) on an AMI-300 multifunctional chemisorption analyzer. Typically, 0.05 g of catalyst was pretreated in an Ar flow (30 mL\u0026middot;min⁻\u0026sup1;) at 150\u0026deg;C for 30 min and then cooled to 50\u0026deg;C. Subsequently, 5% H\u003csub\u003e2\u003c/sub\u003e/Ar was introduced and the sample was heated to 800\u0026deg;C at 10\u0026deg;C\u0026middot;min⁻\u0026sup1; and held for 30 min. H\u003csub\u003e2\u003c/sub\u003e consumption was monitored using a thermal conductivity detector (TCD).\u003c/p\u003e\u003cp\u003eH\u003csub\u003e2\u003c/sub\u003e temperature-programmed desorption (H\u003csub\u003e2\u003c/sub\u003e-TPD) was conducted on a BELCAT-II chemisorption analyzer to determine H\u003csub\u003e2\u003c/sub\u003e desorption behavior. About 30 mg of catalyst was reduced in H\u003csub\u003e2\u003c/sub\u003e (30 mL\u0026middot;min⁻\u0026sup1;) at 450\u0026deg;C for 2 h. After purging with He and cooling to 50\u0026deg;C, the sample was heated to 800\u0026deg;C in Ar at 10\u0026deg;C\u0026middot;min⁻\u0026sup1;. The desorption was recorded using TCD.\u003c/p\u003e\u003cp\u003eCO temperature-programmed desorption (CO-TPD) was also performed on the BELCAT-II system. The sample was first reduced in H\u003csub\u003e2\u003c/sub\u003e (30 mL\u0026middot;min⁻\u0026sup1;) at 450\u0026deg;C for 2 h, purged with He, and cooled to 50\u0026deg;C. Then, CO (30 mL\u0026middot;min⁻\u0026sup1;) was adsorbed for 30 min, followed by desorption in He while heating to 800\u0026deg;C at 10\u0026deg;C\u0026middot;min⁻\u0026sup1;. TCD was used to record the signal.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 FTS catalytic reaction\u003c/h2\u003e\u003cp\u003eThe Fischer\u0026ndash;Tropsch synthesis (FTS) performance evaluation was carried out using a four-channel micro fixed-bed reactor system operated under a unified temperature control system. A total of 0.1 g of catalyst was mixed thoroughly with 0.2 g of quartz sand and loaded into the reactor tube. The catalyst was reduced under pure H₂ at a flow rate of 8 SL\u0026middot;g⁻\u0026sup1;\u0026middot;h⁻\u0026sup1; at 450\u0026deg;C for 8 h, followed by cooling to 50\u0026deg;C. The gas was then switched to syngas (H\u003csub\u003e2\u003c/sub\u003e : CO : N\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;60% : 30% : 10%) at a flow rate of 6 SL\u0026middot;g⁻\u0026sup1;\u0026middot;h⁻\u0026sup1; and a pressure of 1.0 MPa. The reaction temperature was raised to 250\u0026deg;C to initiate the FTS reaction. The outlet gas products (CO, H\u003csub\u003e2\u003c/sub\u003e, CH\u003csub\u003e4\u003c/sub\u003e, CO\u003csub\u003e2\u003c/sub\u003e, and C\u003csub\u003e2\u003c/sub\u003e\u0026ndash;C\u003csub\u003e8\u003c/sub\u003e hydrocarbons) were analyzed online using an Agilent 7890B gas chromatograph, with quantitative analysis performed by the external standard method.\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec7\"\u003e\n \u003ch2\u003e3.1 Catalyst Characterization\u003c/h2\u003e\n \u003cp\u003eTo analyze the specific surface area and pore structure of the catalysts, N\u003csub\u003e2\u003c/sub\u003e physisorption\u0026ndash;desorption characterization was performed on the series of catalysts. The results are shown in Fig.\u0026nbsp;1(a) and (b). As observed in Fig.\u0026nbsp;1(a), all catalysts exhibit H1-type hysteresis loops, indicating the presence of mesoporous structures. Comparing the synthesized catalysts, slight differences in the shape of the hysteresis loops suggest structural reconstruction during the preparation process, resulting in variations in pore structure. The average pore size distribution calculated using the BJH model is shown in Fig.\u0026nbsp;1(b). Combined with Table\u0026nbsp;1, the pore sizes of the catalysts are mainly distributed in the range of 15\u0026ndash;30 nm. Compared with the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, the Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst shows no significant changes in pore structure parameters, indicating that the method of introducing Fe after the synthesis of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles does not affect the specific surface area or pore structure of the final catalyst.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eStructural properties of the Co catalysts\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCatalysts\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSurface area (m\u003csup\u003e2\u003c/sup\u003e\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePore size\u003c/p\u003e\n \u003cp\u003e(nm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePore volume\u003c/p\u003e\n \u003cp\u003e(cm\u003csup\u003e3\u003c/sup\u003e\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e93.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e113.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e128.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e126.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.77\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe phase composition of the catalysts was analyzed by X-ray diffraction (XRD). As shown in the diffraction patterns in Fig.\u0026nbsp;2, the Co species in all catalysts exist in the Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e crystalline phase (JCPDS 74-2120), while the support is mainly in the \u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e phase (JCPDS 23-1009). In the Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, characteristic peaks of \u0026alpha;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (JCPDS 74-1081) are also observed, which is likely due to the partial phase transformation of \u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e to \u0026alpha;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e after high-temperature calcination of Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e at 950\u0026deg;C. No characteristic diffraction peaks associated with Fe species were detected in any of the four catalysts, which may be attributed to the uniform dispersion of Fe on the catalyst surface. Overall, the XRD results indicate that although the location and distribution of Fe species vary among the catalysts, they do not significantly affect the phase composition.\u003c/p\u003e\n \u003cp\u003eTo analyze the surface elemental composition and chemical states of the catalysts, X-ray photoelectron spectroscopy (XPS) was conducted on the catalyst series, as shown in Fig.\u0026nbsp;3. Figure\u0026nbsp;3(a) displays the Co 2p XPS spectra. After peak deconvolution, two sets of peaks corresponding to Co 2p₃/₂ and Co 2p₁/₂ were observed. The binding energies at approximately 780.5 eV and 796.3 eV are attributed to Co\u0026sup3;⁺, while those around 782.5 eV and 797.7 eV are assigned to Co\u0026sup2;⁺. The Co\u0026sup2;⁺/Co\u0026sup3;⁺ ratios calculated from the peak areas are listed in Table\u0026nbsp;2. Among them, the Co\u0026sup2;⁺/Co\u0026sup3;⁺ ratio of the Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst is 1.13, indicating a relatively high Co\u0026sup2;⁺ content in the catalyst.\u003csup\u003e35\u003c/sup\u003e Additionally, all Co\u0026sup2;⁺/Co\u0026sup3;⁺ ratios are below 2, suggesting that the primary phase of the catalysts is Co₃O₄.\u003csup\u003e36\u003c/sup\u003eTable 2 also shows that, compared to the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, all Fe-promoted catalysts exhibit a shift in Co binding energy toward higher values. The order of Co binding energy is: CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, indicating electron transfer between Co and Fe species.\u003c/p\u003e\n \u003cp\u003eFigure 3(b) shows the Fe 2p XPS spectra. After peak fitting, peaks at around 711.5 eV and 720.5 eV correspond to Fe\u0026sup2;⁺, while those at around 714.2 eV and 725.2 eV are assigned to Fe\u0026sup3;⁺. According to Table\u0026nbsp;2, the Fe\u0026sup2;⁺/Fe\u0026sup3;⁺ ratios are all greater than 1, indicating a high surface concentration of Fe\u0026sup2;⁺ species. The CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst has the lowest Fe\u0026sup2;⁺/Fe\u0026sup3;⁺ ratio, likely due to electron transfer from Fe to Co, resulting in increased Fe\u0026sup3;⁺ content. This also confirms the presence of interactions between Co and Fe metals. The Co 2p binding energy of CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e is higher than that of the other three catalysts, suggesting that the method of Fe incorporation influences the electronic environment of Co and Fe. Therefore, differences in Fe deposition locations can affect the metal\u0026ndash;metal and metal\u0026ndash;support interactions in the Fe-modified Co catalysts\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e2\u003c/strong\u003e The XPS peak results of Co catalysts\u003c/p\u003e\n \u003cp\u003e\u003cimg 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\"\u003e\u003c/p\u003e\n \u003cdiv\u003eThe reduction behavior of the catalyst series was investigated using H\u003csub\u003e2\u003c/sub\u003e-temperature programmed reduction (H\u003csub\u003e2\u003c/sub\u003e-TPR), and the corresponding results are presented in Fig. 4. For the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, a weak reduction peak is observed around 371\u0026deg;C, which can be attributed to the reduction of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e to CoO and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e to Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. A second reduction peak appears at approximately 556\u0026deg;C, corresponding to the further reduction of CoO to metallic Co⁰ and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e to lower-valence iron species.The CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts exhibit similar two-step reduction processes. However, compared to Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, the preferential incorporation of Fe species onto the Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles promotes the second reduction step, thereby facilitating the formation of metallic Co⁰. In contrast, the Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst displays three distinct reduction peaks within the examined temperature range. A broad peak centered around 327\u0026deg;C is ascribed to the reduction of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e to CoO, while the peak at approximately 404\u0026deg;C is associated with the reduction of CoO to Co⁰. A high-temperature peak at 645\u0026deg;C is attributed to the strong interaction between the Fe species and the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e support. This suggests that the Fe promoter is highly dispersed on the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e surface, which weakens the interaction between the Co species and the support, thereby enhancing the reducibility of the catalyst.\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\"\u003e\n \u003ch2\u003e3.2 H₂ and CO Desorption Properties of the Catalyst\u003c/h2\u003e\n \u003cp\u003eTo investigate the H\u003csub\u003e2\u003c/sub\u003e chemisorption capacity of the catalysts, H\u003csub\u003e2\u003c/sub\u003e-temperature programmed desorption (H\u003csub\u003e2\u003c/sub\u003e-TPD) measurements were performed, and the results are presented in Fig.\u0026nbsp;5. All catalysts exhibit multiple H\u003csub\u003e2\u003c/sub\u003e desorption peaks. The CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts show low-temperature desorption peaks below 300\u0026deg;C, indicating a relatively strong capacity for weak H₂ adsorption compared to Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. Additionally, both CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co/Fe- Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e display strong H\u003csub\u003e2\u003c/sub\u003e adsorptionat 450\u0026ndash;650\u0026deg;C. Notably, the Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst exhibits the highest H\u003csub\u003e2\u003c/sub\u003e adsorption capacity across both low- and high-temperature regions among the tested samples. In contrast, the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts present only a weak desorption peak around 370\u0026deg;C and a single strong desorption peak near 550\u0026deg;C, suggesting a predominance of strong H₂ adsorption. Based on the overall desorption profiles, the H₂ adsorption capacity of the catalysts follows the order: Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.According to previous studies\u003csup\u003e37\u003c/sup\u003e, an optimal (i.e., moderate) H₂ adsorption capacity is essential for achieving high catalytic activity. Excessive adsorption of H₂ on the surface of Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003eand CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e may lead to high surface hydrogen coverage, which can promote the formation of undesired CH₄ during Fischer\u0026ndash;Tropsch synthesis (FTS). As a result, these two catalysts exhibit inferior FTS performance compared to Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.The H\u003csub\u003e2\u003c/sub\u003e-TPD results also reveal that the spatial distribution of Fe species plays a significant role in influencing H\u003csub\u003e2\u003c/sub\u003e adsorption behavior. The preferential incorporation of Fe onto the surface of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles enhances the weak H\u003csub\u003e2\u003c/sub\u003e adsorption capacity of catalyst at lower temperatures, which could be beneficial for tuning catalytic performance.\u003c/p\u003e\n \u003cp\u003eThe CO adsorption behavior of the catalysts was characterized by CO-temperature programmed desorption (CO-TPD), and the results are shown in Fig.\u0026nbsp;6. The CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts exhibit four distinct desorption peaks, indicating the presence of four types of adsorption sites on their surfaces. The Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst displays a low-temperature desorption peak (\u0026lt;\u0026thinsp;200\u0026deg;C) formed by the overlap of two peaks, and a high-temperature desorption peak (\u0026gt;\u0026thinsp;500\u0026deg;C). The Co/ Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst shows a pronounced low-temperature desorption peak and a high-temperature peak around 600\u0026deg;C. Both the CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts exhibit significant medium-temperature desorption peaks (200\u0026ndash;400\u0026deg;C), with the Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst demonstrating the highest desorption temperature in this range\u0026mdash;exceeding 400\u0026deg;C. Overall, catalysts in which Fe is deposited on the surface of Co exhibit stronger CO adsorption capacity. Enhanced CO adsorption is generally beneficial for catalytic activity, as it facilitates CO activation on the catalyst surface. In contrast, excessive H₂ adsorption may occupy a large number of active sites, thereby hindering CO adsorption and potentially reducing catalytic performance. The CO-TPD results suggest that the spatial distribution of Fe significantly influences the ability to adsorb and activate CO of catalyst. Preferential modification of Co surfaces with Fe species enhances CO adsorption capacity, particularly in the medium-temperature range. In combination with the H\u003csub\u003e2\u003c/sub\u003e-TPD results, it is evident that the Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003ecatalyst exhibits relatively balanced adsorption capacities for both H₂ and CO, which may contribute to its superior catalytic activity.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eThe percentage about CO-TPD peak area of a series of Co catalysts\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCatalysts\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePeak-1\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePeak-2\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePeak-3\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePeak-4\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCoFeAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\"\u003e\n \u003ch2\u003e3.2 FTS catalytic performance\u003c/h2\u003e\n \u003cp\u003eThe Fischer\u0026ndash;Tropsch synthesis (FTS) performance of catalysts was evaluated under the reaction conditions of 250\u0026deg;C, 1.0 MPa pressure, a syngas H\u003csub\u003e2\u003c/sub\u003e/CO ratio of 2, and a gas hourly space velocity (GHSV) of 6 SL\u0026middot;g⁻\u0026sup1;\u0026middot;h⁻\u0026sup1;. stability tests for catalysts (Fig.\u0026nbsp;7) indicated that all catalysts exhibited good stability, with no deactivation observed within 100 h. This stability is attributed to the high dispersion of active metal particles in the catalysts prepared by the ultrasound-assisted impregnation method, which effectively suppresses aggregation and sintering that typically lead to deactivation.\u003csup\u003e38\u003c/sup\u003e As shown in Table\u0026nbsp;4, the CO conversion for Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts were 30.1%, 27.5%, 25.3%, and 21.4%, respectively. Notably, the Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst, prepared by preferentially introducing Fe species onto the surface of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles, exhibited the highest CO conversion and selectivity toward light hydrocarbons, reaching 30.1% and 10.7%, respectively. These results suggest that the method of Fe incorporation significantly influences the catalytic activity of CoFe-based catalysts in Fischer\u0026ndash;Tropsch synthesis.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 4\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eReaction performance of catalysts for CO hydrogenation\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eCatalysts\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eCO conversion (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e selectivity (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eHydrocarbon selectivity (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eO/P (C\u003csub\u003e2\u003c/sub\u003e-C\u003csub\u003e4\u003c/sub\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCH\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003e2\u003c/sub\u003e-C\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e=\u003c/sup\u003e-C\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e=\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003e5+\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e73.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCo/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThis study examined the preparation of CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts using pre-synthesised Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles as the cobalt source, with different methods of introducing Fe as a promoter. The catalysts were synthesised using an ultrasound-assisted impregnation method. For comparison, a Fe-free Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst was also prepared. The results suggest that introducing Fe altered the reducibility and chemisorption properties of the catalysts. The Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst showed improved H₂ adsorption but reduced CO adsorption, leading to lower catalytic activity than the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst. In contrast, the adsorption capacities of both CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e for H\u003csub\u003e2\u003c/sub\u003e and CO were improved, which may contribute to their higher catalytic activity. Among these catalysts, Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e showed the best H\u003csub\u003e2\u003c/sub\u003e and CO adsorption performance, and exhibited the highest Fischer\u0026ndash;Tropsch synthesis activity under reaction conditions at 230\u0026deg;C, 1 MPa, and 6 SL\u0026middot;g\u003csub\u003ecat\u003c/sub\u003e⁻\u0026sup1;\u0026middot;h⁻\u0026sup1;. Its CO conversion was 18.9% higher than that of the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e reference catalyst.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e This work was supported by the National Key Research and Devel opment Program of China (2022YFB4101201), National Natural Science Foundation of China (U22A20394, 21902187), the Key Research and Development Program of Hubei Province (2022BCA084), the Funda mental Research Funds for the Central Universities of South-Central Minzu University (CZY23016, CZZ24008), and the Fund for Academic Innovation Teams of South-Central Minzu University (PTZ24011).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e No data was used for the research described in the article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e Yixuan Li: Writing \u0026ndash; review \u0026amp; editing, Writing \u0026ndash; original draft, Methodology, Investigation, Conceptualization. Yuanli Xiang: Writing \u0026ndash; review \u0026amp; editing, Resources, Conceptualization. Xinyan Ai: Writing \u0026ndash; review \u0026amp; editing, Methodology, Formal analysis, Conceptualization. Yuhua Zhang: Writing \u0026ndash; review \u0026amp; editing, Supervision, Formal analysis. Yanxi Zhao: Funding acquisition, Writing \u0026ndash; review \u0026amp; editing. Chengchao Liu: Writing \u0026ndash; review \u0026amp; editing, Supervision, Funding acquisition. Jinlin Li: Writing \u0026ndash; review \u0026amp; editing, Supervision, Funding acquisition.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKhodakov AY, Chu W, Fongarland P (2007) Advances in the development of novel cobalt Fischer\u0026ndash;Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels. Chem Rev 107:1692\u0026ndash;1744. https://doi.org/10.1021/cr050972v\u003c/li\u003e\n\u003cli\u003eJiao F, Li J, Pan X, Bao X, et al. 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(2016) Synthesis of \u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e nanofibers stabilized Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles as highly active and stable Fischer\u0026ndash;Tropsch synthesis catalysts. Fuel 180:777\u0026ndash;784. https://doi.org/10.1016/j.fuel.2016.04.006\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"catalysis-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Catalysis Letters](https://link.springer.com/journal/10562)","snPcode":"10562","submissionUrl":"https://submission.springernature.com/new-submission/10562/3","title":"Catalysis Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Fischer-Tropsch synthesis, Co-Based Catalysts, Fe Introduction Methods, bimetallic catalysts","lastPublishedDoi":"10.21203/rs.3.rs-7061461/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7061461/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCo-Fe bimetallic catalysts have attracted increasing attention in the field of Fischer\u0026ndash;Tropsch synthesis (FTS). In this study, cobalt was supplied in the form of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles, and three different methods of iron (Fe) incorporation were employed: (1) Fe modification of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e support prior to Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e loading (Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), (2) co-loading of Fe and Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (CoFe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), and (3) Fe modification of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e prior to loading (Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e). These model catalysts were used to investigate the interactions between Co, Fe and the support and their impact on the catalytic activity and product selectivity of FTS. The results showed that the addition of Fe promotes cobalt reduction, modifies H\u003csub\u003e2\u003c/sub\u003e and CO adsorption properties and regulates catalytic performance. Compared with Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Co/Fe-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e exhibited the best reducibility and significantly reduced CH\u003csub\u003e4\u003c/sub\u003e selectivity from 19.2\u0026ndash;11.2%. However, its CO adsorption weakened, decreasing CO conversion from 25.3\u0026ndash;21.4%. Co-Fe/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e showed enhanced H\u003csub\u003e2\u003c/sub\u003e and CO adsorption, increasing CO conversion by 18.9%. These findings demonstrate that the location of Fe affects the metal-support interaction, reducibility and adsorption activation abilities of the Co catalyst, ultimately altering FTS activity and selectivity.\u003c/p\u003e","manuscriptTitle":"The effect of iron additive incorporation mode on the Fischer–Tropsch Synthesis performance of alumina-supported cobalt catalysts","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-10 17:11:58","doi":"10.21203/rs.3.rs-7061461/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-22T10:37:06+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-22T02:36:51+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-20T10:48:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"151880182343963712263170722432711944062","date":"2025-07-13T10:02:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"268991347642724617516718515573269227991","date":"2025-07-09T00:56:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-08T17:08:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-08T04:06:44+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-08T04:06:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Catalysis Letters","date":"2025-07-07T05:20:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"catalysis-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Catalysis Letters](https://link.springer.com/journal/10562)","snPcode":"10562","submissionUrl":"https://submission.springernature.com/new-submission/10562/3","title":"Catalysis Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f69ba2bd-47b5-47cb-bcbe-72cd3de0d017","owner":[],"postedDate":"July 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-08-14T08:24:47+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-10 17:11:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7061461","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7061461","identity":"rs-7061461","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}