Fe-modified Co-C monolithic catalyst, preparation method thereof and application of Fe-modified Co-C monolithic catalyst in CO2 methanation

Abstract

The invention provides a Fe-modified Co-C monolithic catalyst and a preparation method and application thereof in CO2 methanation, and relates to the technical field of CO2 methanation catalyst.A cobalt source, an iron source and a carbon source are fully reacted through hydro-thermal treatment in advance, and a precursor catalyst with a carbon base as a carrier and Fe atoms evenly dispersed around Co active sites is formed; and printing the precursor catalyst into a monolithic catalyst precursor through 3D printing, and constructing a Co-Fe alloy phase or a Co-Fe interface structure through reduction to prepare the monolithic catalyst. On one hand, microcosmic high-activity sites of the monolithic catalyst are uniformly distributed, the monolithic catalyst has a hierarchical porous structure macroscopically, the contact area between the catalyst and reaction gas is increased, and CO2 and H2 can reach the active sites more efficiently; on the other hand, Fe atoms in the monolithic catalyst are uniformly dispersed around Co active sites, so that reaction products can be desorbed in time, and accumulation and blockage of the products at the active sites are avoided.

Description

Technical Field

[0001] This invention belongs to the field of CO2 methanation catalyst preparation technology, specifically relating to an Fe-modified Co@C monolithic catalyst, its preparation method, and its application in CO2 methanation. Background Technology

[0002] Converting CO2 into high-value-added methane (CH4, the main component of natural gas) through catalytic methanation not only enables the recycling of carbon resources but also alleviates the contradiction between energy supply and demand, making it one of the current research hotspots in the field of carbon capture, utilization and storage (CCUS).

[0003] However, existing CO2 methanation catalysts still face numerous technical bottlenecks, hindering their industrial application. Traditional Co-based and Ni-based catalysts typically require temperatures above 300 °C to effectively activate CO2 molecules; at low temperatures (<300 °C), CO2 conversion rates are low, making it difficult to meet the requirements of low-energy-consumption reaction processes. Most catalysts are prepared via impregnation or co-precipitation methods, resulting in the active components (such as Co and Fe) being prone to agglomeration, and their macroscopic structures are mostly particulate or blocky, leading to high mass transfer resistance and the formation of reaction intermediates (such as HCOO). - CO - The mismatch between the hydrogenation rate and the formation rate leads to a decrease in CH4 selectivity.

[0004] Existing monolithic catalysts (such as honeycomb and block catalysts) are mostly produced through extrusion molding or coating loading processes. These processes suffer from poor material compatibility (e.g., weak bonding between the active component and the support) and the tendency for post-processing (such as calcination and reduction) to lead to structural collapse or loss of active sites. Furthermore, the macroscopic hierarchical pore structure is difficult to precisely control, further limiting the improvement of catalytic performance. In addition, during the reaction, CO generated from CO2 activation easily polymerizes on the surface of active sites to form carbon deposits, covering the active centers and blocking the pores, leading to catalyst deactivation in a short time and shortening its service life.

[0005] Therefore, to address the above problems, it is necessary to develop an integral catalyst that combines high efficiency at low temperatures, excellent CH4 selectivity, strong resistance to carbon deposition, and the ability to achieve synergistic optimization of microscopic active sites and macroscopic structure, in order to overcome the technical bottleneck of CO2 methanation. Summary of the Invention

[0006] In view of this, the present invention provides an Fe-modified Co@C monolithic catalyst that combines high efficiency at low temperatures, excellent CH4 selectivity, strong resistance to carbon deposition, and the ability to achieve synergistic optimization of microscopic active sites and macroscopic structure.

[0007] A method for preparing Fe-modified Co@C monolithic catalyst is also provided.

[0008] It is also necessary to provide an application of Fe-modified Co@C monolithic catalyst in CO2 methanation.

[0009] The technical solution adopted by this invention to solve its technical problem is:

[0010] A method for preparing an Fe-modified Co@C monolithic catalyst involves first preparing a precursor catalyst in which Fe atoms are uniformly dispersed around the Co active sites, and then adjusting the macroscopic structure of the precursor catalyst to obtain a monolithic catalyst with hierarchical channels. The method specifically includes the following steps:

[0011] Preparation of precursor catalysts:

[0012] S1 dissolves a cobalt source, an iron source, and a carbon source in deionized water and stirs to form a homogeneous solution; wherein the cobalt source and the iron source are both soluble salts;

[0013] S2 involves a hydrothermal reaction of a homogeneous solution to generate a precipitate. The mixed solution from which the precipitate is generated is then post-treated to obtain a precursor catalyst with a carbon-based support and Fe atoms uniformly dispersed around the Co active sites.

[0014] Preparation of monolithic catalysts:

[0015] Step 1 involves mixing the precursor catalyst, photosensitive resin, and wetting and dispersing agent to obtain a slurry;

[0016] Step 2 involves printing the slurry into a catalyst model using a digital photopolymerization 3D printer to obtain an integral catalyst precursor that retains both the high density of active sites at the microscopic level and the multi-level pore structure at the macroscopic level.

[0017] Step 3 involves reducing the monolithic catalyst precursor to construct a Co-Fe alloy phase or Co-Fe interface structure to enhance the synergistic effect of Co and Fe, thereby obtaining the Fe-modified Co@C monolithic catalyst Co-Fe@C.

[0018] Preferably, in the precursor catalyst preparation S1, the molar ratio of cobalt in the cobalt source to carbon in the carbon source is 1:1-4, and the molar amount of iron in the iron source is 1%-5% of the molar amount of cobalt in the cobalt source.

[0019] Preferably, in the precursor catalyst preparation S1, the cobalt source is one or more of cobalt nitrate and cobalt acetate, the iron source is one or more of ferric nitrate and ferric chloride, and the carbon source is one or more of glucose, citric acid, and sucrose.

[0020] Preferably, in the precursor catalyst preparation S2, the hydrothermal reaction temperature is 150℃-185℃ and the reaction time is 10h-24h.

[0021] Preferably, in the precursor catalyst preparation S2, the post-treatment of the mixed solution from which the hydrothermal reaction produces a precipitate to obtain the precursor catalyst specifically involves: after the hydrothermal reaction is completed, filtering the mixed solution containing the precipitate after the reaction to obtain the precipitate, washing the precipitate and vacuum drying it to obtain the precursor catalyst.

[0022] Preferably, the washing of the precipitate requires a neutral solution.

[0023] Preferably, in step one of the preparation of the monolithic catalyst, the photosensitive resin is any one of Tough Resin Ultra, Tough Resin Ultra, Fast Resin, ABS-Like Resin, Water-Wash Resin, High Precision, and UV Curable Resin.

[0024] Preferably, in step one of the preparation of the monolithic catalyst, the mass ratio of the precursor catalyst to the photosensitive resin is 1-3:8-12.

[0025] A Fe-modified Co@C monolithic catalyst is prepared by the method described above for preparing the Fe-modified Co@C monolithic catalyst.

[0026] The catalyst prepared by the Fe-modified Co@C monolithic catalyst preparation method described above is used in the CO2 methanation process.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The method for preparing Fe-modified Co@C monolithic catalyst provided by this invention involves first dissolving a cobalt source, an iron source, and a carbon source in deionized water and stirring to form a homogeneous solution; subjecting the homogeneous solution to a hydrothermal reaction to generate a precipitate; and post-treating the mixed solution from which the precipitate is generated to obtain a precursor catalyst; mixing the precursor catalyst, photosensitive resin, and a wetting and dispersing agent to obtain a slurry; printing the slurry into a catalyst model using a digital photopolymerization 3D printer to obtain a monolithic catalyst precursor; and reducing the monolithic catalyst precursor to obtain the Fe-modified Co@C monolithic catalyst Co-xFe@C. Therefore, this invention pre-processes the cobalt source, iron source, and carbon source through hydrothermal treatment to fully react, forming a precursor catalyst with a carbon-based support and Fe atoms uniformly dispersed around the Co active sites; then, the precursor catalyst is printed into a monolithic catalyst precursor using 3D printing, and a multi-level porous monolithic catalyst is prepared by reducing and constructing a Co-Fe alloy phase or a Co-Fe interface structure. On the one hand, the monolithic catalyst exhibits a uniform distribution of highly active sites at the microscopic level and a hierarchical pore structure at the macroscopic level, increasing the contact area between the catalyst and the reactant gas and reducing the diffusion resistance of the reactant gas within the catalyst, allowing CO2 and H2 to reach the active sites more efficiently. On the other hand, because Fe atoms are uniformly dispersed around the Co active sites within the monolithic catalyst, reaction products (CH4, H2O) can be desorbed in a timely manner, preventing the accumulation and blockage of products at the active sites, thereby maintaining the long-term activity stability of the catalyst. Furthermore, the introduction of the carbon support not only provides a stable loading substrate for the Co and Fe active components but also further promotes the dispersion and electron transfer of the active components through its high specific surface area and electronic conductivity, while inhibiting the aggregation and carbon deposition of the active components during the reaction process. Attached Figure Description

[0029] Figure 1 This is a three-dimensional schematic diagram of the model constructed in Example 1-4.

[0030] Figure 2 This is a cross-sectional view of the model constructed in Example 1-4.

[0031] Figure 3 This is a top view of the model constructed in Example 1-4.

[0032] Figure 4 Scanning electron microscope image of the catalyst prepared for Example 3. Detailed Implementation

[0033] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] This application discloses a method for preparing an Fe-modified Co@C monolithic catalyst, which involves first preparing a precursor catalyst in which Fe atoms are uniformly dispersed around the Co active sites, and then adjusting the macroscopic structure of the precursor catalyst to obtain a multi-level porous monolithic catalyst. The method specifically includes the following steps:

[0035] Preparation of precursor catalysts:

[0036] S1 dissolves cobalt, iron, and carbon sources in deionized water and stirs to form a homogeneous solution; wherein the cobalt and iron sources are soluble salts; the carbon source serves as a carrier and performance regulator, and Co and Fe are the core active ingredients. Their d-orbital electrons can form chemical bonds with the reactants, reducing the activation energy of the reaction. Furthermore, cobalt exhibits higher activity at low temperatures, while iron is low in cost and resistant to high temperatures.

[0037] In one optional embodiment, to balance the concentration of active sites, performance adjustability, and reaction system stability, the molar ratio of cobalt in the cobalt source to carbon in the carbon source is 1:1-4, and the molar amount of iron in the iron source is 1%-5% of the cobalt in the cobalt source. For example, the molar ratio of cobalt in the cobalt source to carbon in the carbon source is 1:2, 1:2.5, or 1:3, and the molar amount of Fe is 1%, 2%, 3%, 4%, or 5% of Co.

[0038] In one optional embodiment, the cobalt source is one or more of cobalt nitrate and cobalt acetate, the iron source is one or more of ferric nitrate and ferric chloride, and the carbon source is one or more of glucose, citric acid, and sucrose. Cobalt nitrate or cobalt acetate, ferric nitrate or ferric chloride are readily soluble in water, thereby allowing Fe atoms to be uniformly dispersed around the Co active sites during the hydrothermal reaction.

[0039] S2 involves a hydrothermal reaction of a homogeneous solution to generate a precipitate. The mixed solution from which the precipitate is generated is then post-treated to obtain a precursor catalyst with a carbon-based support and Fe atoms uniformly dispersed around the Co active sites.

[0040] In one optional embodiment, the hydrothermal reaction temperature is 150℃-185℃ and the reaction time is 10h-24h. Preferably, in order to obtain a precursor catalyst with high purity and good dispersibility, the hydrothermal reaction temperature is 160℃-180℃ and the reaction time is 12h.

[0041] Specifically, the homogeneous solution can be poured into a stainless steel reactor lined with polytetrafluoroethylene (PTFE), placed in a drying oven at 160-180 °C, and the heating rate of the drying oven should be controlled. Hydrothermal treatment for 12 hours.

[0042] In one optional embodiment, the precursor catalyst is obtained by post-processing the mixed solution that produces a precipitate from the hydrothermal reaction: after the hydrothermal reaction is completed, the mixed solution containing the precipitate is filtered to obtain the precipitate, and the precipitate is washed and vacuum dried to obtain the precursor catalyst.

[0043] Furthermore, the washing of the precipitate must be done in a neutral state.

[0044] In one optional embodiment, the vacuum drying temperature is 70℃-90℃, and the drying time is more than 6 hours.

[0045] Specifically, after the hydrothermal reaction is completed, the mixed solution containing the precipitate in the stainless steel reactor is filtered to remove the filtrate and obtain the precipitate. The precipitate is then washed with deionized water until the washing solution is neutral, at which point the washing is finished. After washing, the precipitate is dried under vacuum for 12 hours to obtain the precursor catalyst.

[0046] Preparation of monolithic catalysts:

[0047] Step 1 involves mixing the precursor catalyst, photosensitive resin, and wetting and dispersing agent to obtain a slurry;

[0048] In one optional embodiment, the photosensitive resin is any one of Tough Resin Ultra, Tough Resin Ultra, Fast Resin, ABS-Like Resin, Water-Wash Resin, High Precision, and UV Curable Resin, and the wetting and dispersing agent is polyethylene glycol.

[0049] In one optional embodiment, in order to balance the basic catalytic activity, photocurability and component dispersion uniformity, the mass ratio of the precursor catalyst to the photosensitive resin is 1-3:8-12; for example, the ratio of the precursor catalyst to the photosensitive resin and the wetting dispersant is 8-12 g:50 g:(0.5-1) mL.

[0050] Step 2 involves printing the slurry into a catalyst model using a digital photopolymerization 3D printer to obtain a monolithic catalyst precursor. This monolithic catalyst has a uniform distribution of highly active sites on a microscopic scale and a multi-level pore structure on a macroscopic scale.

[0051] In one optional embodiment, an integral catalyst model is designed in 3ds Max software, wherein the integral catalyst model is a spiral hollow cylinder or a vertical hollow cylinder. A support model is designed in PiocreatBox software, with a contact shape diameter of 0.3 mm, a contact depth of 0.4 mm, an upper diameter of 0.3 mm, and a lower diameter of 0.8 mm. Then, the slurry is loaded into the material tank of a digital photopolymerization 3D printer for printing. After printing, the formed integral catalyst precursor model is removed, the surface residual slurry is rinsed with anhydrous ethanol, and dried to obtain the integral catalyst precursor.

[0052] Step 3 involves reducing the monolithic catalyst precursor to construct a Co-Fe alloy phase or Co-Fe interface structure to enhance the synergistic effect of Co and Fe, thereby obtaining the Fe-modified Co@C monolithic catalyst Co-Fe@C.

[0053] In one optional embodiment, the reduction temperature is 450℃-500℃ and the reduction time is 2.5-4h.

[0054] If the cobalt source, iron source, carbon source, photosensitive resin, and wetting dispersant are directly mixed for 3D printing, the resulting monolithic catalyst will have uneven internal distribution, leading to poor CO2 conversion and poor CH4 selectivity.

[0055] A Fe-modified Co@C monolithic catalyst is prepared by the method described above for preparing the Fe-modified Co@C monolithic catalyst.

[0056] The catalyst prepared by the Fe-modified Co@C monolithic catalyst preparation method described above is used in the CO2 methanation process.

[0057] In the application of the prepared monolithic catalyst for CO2 methanation: CO2 and H2 molecules preferentially adsorb onto the active sites of the monolithic catalyst (such as the metal surfaces of Co and Fe), forming stable adsorbed species; subsequently, the monolithic catalyst weakens the C≡O bond (or C=O bond) in CO / CO2 and the HH bond in H2 through its own electronic structure (such as the d orbitals of transition metals), thus "activating" these stable molecules into more reactive intermediates (such as adsorbed C, O, and H atoms); the activated intermediates undergo recombination on the surface of the monolithic catalyst, where C atoms gradually combine with H atoms to generate intermediate species such as CH, CH2, and CH3, eventually forming CH4 molecules; the generated CH4 molecules have a weaker binding force to the active sites of the monolithic catalyst and selectively desorb from the surface so that the active sites can be used for the next round of reaction, realizing the recycling of the monolithic catalyst.

[0058] The following specific examples illustrate a crystal pulling method for improving the production efficiency of lightly boron-doped perfect crystals.

[0059] Example 1:

[0060] Precursor catalyst preparation: S1: Weigh the raw materials according to the stoichiometric ratio: take 1 mmol Co(NO3)2·6H2O, 0.01 mmol Fe(NO3)3·9H2O and 2.5 mmol C6H 12 Add O6 to 60 mL of deionized water, place on a magnetic stirrer, and stir at 500 r / min for 30 min at room temperature until the solid is completely dissolved, forming a homogeneous, transparent pink solution.

[0061] S2: Slowly pour the homogeneous, transparent pink solution into a 100 mL stainless steel reactor lined with polytetrafluoroethylene (PTFE). Tighten the lid and place the reactor into a programmed temperature drying oven. Set the drying oven temperature program to 5 °C / min. -1 The temperature was increased to 160 °C at a rate of [missing information] and maintained at this temperature for 12 h for hydrothermal treatment. During the reaction, a brown precipitate gradually formed in the solution. After the hydrothermal treatment, the solution was allowed to cool naturally to room temperature. The reaction vessel was then opened, and the reaction mixture (precipitate + solution) was poured into a Buchner funnel. The precipitate was separated by vacuum filtration. The precipitate was repeatedly washed with deionized water, adding 20 mL of deionized water each time. The mixture was filtered until the filtrate was clear. The pH of the filtrate was checked with pH paper every 5 washes until the pH of the filtrate was 7 (neutral) to remove residual nitrates and other impurities from the surface of the precipitate.

[0062] The washed brown precipitate was transferred to a petri dish, placed in a vacuum drying oven, and dried overnight (about 12 h) at 80°C until the precipitate was completely dry, forming a loose brown powdery catalyst precursor catalyst, which was then sealed for later use.

[0063] Preparation of monolithic catalysts:

[0064] Step 1: Weigh 12 g of the obtained catalyst precursor and 50 g of photosensitive resin (ToughResinUltra (white)). Add 0.5 mL of wetting and dispersing agent (such as polyethylene glycol 400) and stir until the catalyst precursor is evenly dispersed in the photosensitive resin to form a uniform paste without obvious particle agglomeration.

[0065] Step 2: Design the catalyst model using 3ds Max software. The model structure is a spiral hollow cylinder with specific dimensions: diameter 10 mm, height 60 mm, and spiral hollow channel width 0.12 mm to ensure smooth gas flow in the reaction. Import the designed model file into PiocreatBox software, add support structures, and set the support parameters: contact shape diameter 0.3 mm, contact depth 0.4 mm, upper diameter 0.3 mm, and lower diameter 0.8 mm. Then, load the slurry into the material tank of the digital photopolymerization 3D printer and print according to the software settings (exposure time 10 s / layer, layer thickness 0.05 mm). After printing, remove the formed monolithic catalyst precursor model, rinse the surface with anhydrous ethanol to remove residual slurry, and let it dry for later use to obtain the monolithic catalyst precursor.

[0066] Step 3: Place the printed monolithic catalyst precursor in a tube furnace, and introduce a 10 vol.% H2 / Ar mixed gas into the tube furnace, controlling the gas flow rate to be 30 mL·min. -1 Purge for 30 minutes to remove air from the tubular furnace and prevent the active components from being oxidized during the reduction process.

[0067] Set the reduction program for the tubular furnace: at 2 °C·min -1 The temperature was increased to 500 °C at a certain rate, and the reduction was carried out at this temperature for 3 hours. After the reduction was completed, 10 vol.% H2 / Ar gas was kept flowing, and the temperature was naturally cooled to room temperature (about 4 hours) to obtain a black, structurally complete Co-1Fe@C monolithic catalyst.

[0068] Example 2:

[0069] The only difference from Example 1 is in the preparation of the precursor catalyst S1: 1 mmol Co(NO3)2·6H2O, 0.02 mmol Fe(NO3)3·9H2O, and 2.5 mmol C6H 12 O6 was added to 60 mL of deionized water and placed on a magnetic stirrer. The mixture was stirred at 500 r / min for 30 min at room temperature until the solid was completely dissolved, forming a homogeneous, transparent pink solution. The other steps were the same as in Example 1 to obtain the Co-2Fe@C monolithic catalyst.

[0070] Example 3:

[0071] The only difference from Example 1 is in the preparation of the precursor catalyst S1: 1 mmol Co(NO3)2·6H2O, 0.03 mmol Fe(NO3)3·9H2O, and 2.5 mmol C6H 12O6 was added to 60 mL of deionized water and placed on a magnetic stirrer. The mixture was stirred at 500 r / min for 30 min at room temperature until the solid was completely dissolved, forming a homogeneous, transparent pink solution. The other steps were the same as in Example 1 to obtain the Co-3Fe@C monolithic catalyst.

[0072] The monolithic catalyst model constructed in this example is as follows: Figure 1-3 As shown.

[0073] Scanning electron microscopy was used to examine the Co-3Fe@C monolithic catalyst, such as... Figure 4 As shown.

[0074] Example 4:

[0075] The only difference from Example 1 is in the preparation of the precursor catalyst S1: 1 mmol Co(NO3)2·6H2O, 0.04 mmol Fe(NO3)3·9H2O, and 2.5 mmol C6H 12 O6 was added to 60 mL of deionized water and placed on a magnetic stirrer. The mixture was stirred at 500 r / min for 30 min at room temperature until the solid was completely dissolved, forming a homogeneous, transparent pink solution. The other steps were the same as in Example 1 to obtain the Co-4Fe@C monolithic catalyst.

[0076] Comparative Example 1:

[0077] The only difference from Example 1 is in the preparation of the precursor catalyst S1: 1 mmol Co(NO3)2·6H2O and 2.5 mmol C6H 12 O6 was added to 60 mL of deionized water and placed on a magnetic stirrer. The mixture was stirred at 500 r / min for 30 min at room temperature until the solid was completely dissolved, forming a homogeneous and transparent pink solution, thus obtaining the Co@C monolithic catalyst.

[0078] Comparative Example 2

[0079] The monolithic catalyst prepared in Example 3 was ground into powder to obtain Co-3Fe@C-powder, and everything else was the same as in Example 3.

[0080] The catalysts prepared in Examples 1-4 and Comparative Examples 1-2 were evaluated in a micro-stationary reactor. The specific operating steps were as follows: 1.0 g of catalyst was weighed and placed in the isothermal zone of the reaction tube, with H2 / CO2 = 4 / 1, temperature 220 ℃, pressure 2 MPa, and space velocity (GHSV) 10000 ml / (g·h). After reaching a stable state, samples were taken for analysis at 3-hour intervals. Quantitative and qualitative analyses of the feed gas and products were performed using gas chromatography. The conversion rate and selectivity of each component were calculated using the methane correlation method in "Determination of H2, N2, CO, CO2 and C1-C8 hydrocarbons in coal-based Fischer-Tropsch synthesis tail gas by gas chromatography," and the specific results are shown in Table 1.

[0081] Table 1. Comparison of performance test results of Co-Fe@C catalysts prepared in Examples 1-4 and Comparative Examples 1-2 for carbon dioxide to methane reaction.

[0082]

[0083] Based on the performance test data of the Co-xFe@C series catalysts with different Fe contents prepared in Examples 1-4 and Comparative Example 1 in the CO2 methanation reaction (H2 / CO2=4 / 1, reaction temperature 220 ℃, pressure 2 MPa, space velocity 10000 mL / (g・h)), it can be seen that the Co@C catalyst without Fe addition (Comparative Example 1) exhibits the lowest CO2 conversion rate (23.4 %). As the Fe doping amount increases from 1 % (Example 1) to 3 % (Example 3), the CO2 conversion activity of the catalyst shows a significant upward trend. Among them, the CO2 conversion rate of the Co-3Fe@C catalyst reaches 79.9%, which is nearly 3.4 times higher than that of the Co@C catalyst (Comparative Example 1). This result fully confirms the promoting effect of Fe as a modifying component on the CO2 methanation activity of Co-based catalysts.

[0084] Furthermore, as can be seen from Examples 1-4, as the Fe doping amount increases from 1% (Example 1) to 4% (Example 4), the CO2 conversion rate shows a trend of first increasing and then decreasing. When the Fe doping amount is increased to 4% (Example 4), the CO2 conversion rate drops from 79.9% to 66.4%, indicating that the optimal Fe doping amount is 3% of cobalt. This is because when the Fe content is low (1%~3%), Fe atoms can be uniformly dispersed around the Co active sites, adjusting the electronic state density of Co through electron transfer, reducing the activation energy barrier of CO2 molecules, promoting the adsorption and dissociation of CO2 at the active sites, and improving the CO2 conversion rate. However, when the Fe content exceeds 3%, excess Fe easily forms an independent Fe-based oxide phase on the catalyst surface, which not only occupies part of the Co active sites but may also hinder reaction intermediates (such as HCOO). - CO -The migration and hydrogenation to the Co site lead to a decrease in catalytic activity.

[0085] From the perspective of CH4 selectivity, all tested Co-Fe@C series catalysts (Examples 1-4, Comparative Examples 1-2) exhibited extremely high CH4 selectivity (98.3%~98.7%). Furthermore, different Fe doping amounts and catalyst macroscopic morphologies (monolithic type (Example 3) vs. powdered type (Comparative Example 2)) had minimal impact on CH4 selectivity. This phenomenon indicates that Co, as the core active component in the CO2 methanation reaction, possesses a strong hydrogenation capacity for the C species generated from CO2 dissociation on its surface, efficiently promoting the stepwise hydrogenation of C species to CH4. The introduction of Fe enhances the CO2 activation rate without altering the selective adsorption and reaction characteristics of the Co sites for hydrogenation intermediates, thus maintaining consistently high CH4 selectivity. In addition, the presence of the carbon support (derived from carbon sources such as glucose) reduces carbon deposition by inhibiting the CO disproportionation reaction (2CO→C+CO2), and its high specific surface area and electronic conductivity further promote the dispersion and electron transfer of the active components, while simultaneously inhibiting the aggregation of active components during the reaction process, further ensuring the selectivity of CH4 formation.

[0086] By comparing Example 3 (monolithic Co-3Fe@C catalyst) and Comparative Example 2 (powdered Co-3Fe@C catalyst), it can be seen that although the two catalysts have the same Fe doping amount (3%) and active component composition, their CO2 conversion rates are significantly different: the CO2 conversion rate of the monolithic Co-3Fe@C catalyst (79.9%) is higher than that of the powdered Co-3Fe@C-powder catalyst (68.5%), with an increase of 16.6%. This result highlights the positive effect of the macroscopic spiral hollow structure constructed by 3D printing on the catalytic reaction. Designed using 3ds Max software and fabricated via digital photopolymerization 3D printing, this structure features regular spiral hollow channels (0.12 mm wide), effectively optimizing the mass transfer efficiency of the reaction system. On one hand, the hollow channels increase the contact area between the catalyst and the reactants, reducing diffusion resistance within the catalyst and allowing CO2 and H2 to reach the active sites more efficiently. On the other hand, the channel structure facilitates the timely desorption of reaction products (CH4, H2O), preventing product accumulation and blockage at active sites, thus maintaining the long-term activity stability of the catalyst. In contrast, powdered catalysts are prone to pore blockage due to particle accumulation during the reaction, which not only increases mass transfer resistance but may also cause localized overheating, affecting CO2 activation and intermediate hydrogenation efficiency. Therefore, their catalytic activity is lower than that of monolithic catalysts.

[0087] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for preparing Fe-modified Co@C monolithic catalyst, characterized in that, The precursor catalyst in which Fe atoms are uniformly dispersed around Co active sites is prepared in advance, and the macrostructure of the precursor catalyst is adjusted to obtain a monolithic catalyst with hierarchical pores, specifically including the following steps: Preparation of the precursor catalyst: S1: Dissolve the cobalt source, iron source and carbon source in deionized water and stir to form a uniform solution; wherein the cobalt source and iron source are both soluble salts; S2: Perform hydrothermal reaction on the uniform solution to generate a precipitate, and perform post-treatment on the mixed solution after the hydrothermal reaction to obtain a precursor catalyst with a carbon-based carrier and Fe atoms uniformly dispersed around Co active sites; Preparation of the monolithic catalyst: Step one: Mix the precursor catalyst, photosensitive resin and wet dispersant to obtain a slurry; Step two: Print the slurry into a catalyst model through a digital light curing 3D printer to obtain a monolithic catalyst precursor, which retains high active site density on the micro level and has a hierarchical pore structure on the macro level; Step three: Reduce the monolithic catalyst precursor to construct a Co-Fe alloy phase or Co-Fe interface structure to enhance the synergistic effect of Co and Fe, and obtain a Fe-modified Co@C monolithic catalyst Co-Fe@C.

2. The method of producing the Fe-modified Co@C monolithic catalyst according to claim 1, wherein In the preparation S1 of the precursor catalyst, the molar ratio of cobalt in the cobalt source to carbon in the carbon source is 1:1-4, and the molar amount of iron in the iron source is 1%-5% of the cobalt in the cobalt source.

3. The method of producing a Fe-modified Co@C monolithic catalyst according to claim 2, wherein In the preparation S1 of the precursor catalyst, the cobalt source is one or more of cobalt nitrate and cobalt acetate, the iron source is one or more of ferric nitrate and ferric chloride, and the carbon source is one or more of glucose, citric acid and sucrose.

4. The method of producing a Fe-modified Co@C monolithic catalyst according to claim 1, wherein In the preparation S2 of the precursor catalyst, the temperature of the hydrothermal reaction is 150℃-185℃, and the reaction time is 10h-24h.

5. The method of producing a Fe-modified Co@C monolithic catalyst according to claim 1, wherein In the preparation S2 of the precursor catalyst, the post-treatment of the mixed solution after the hydrothermal reaction to obtain the precursor catalyst specifically includes: after the hydrothermal reaction is completed, filtering the mixed solution containing the precipitate after the reaction to obtain the precipitate, washing and vacuum drying the precipitate to obtain the precursor catalyst.

6. The method of producing a Fe-modified Co@C monolithic catalyst according to claim 5, wherein The washing of the precipitate needs to be neutral.

7. The method of producing a Fe-modified Co@C monolithic catalyst according to claim 1, wherein In the preparation step one of the monolithic catalyst, the photosensitive resin is any one of Tough Resin Ultra, Tough Resin Ultra, FastResin, ABS-Like Resin, Water-Wash Resin, High Precision, and UV Curable Resin.

8. The method for preparing the Fe-modified Co@C monolithic catalyst as described in claim 1, characterized in that, In the preparation step one of the monolithic catalyst, the mass ratio of the precursor catalyst to the photosensitive resin is 1-3:8-12.

9. A Fe-modified Co@C monolithic catalyst, characterized in that, The Fe-modified Co@C monolithic catalyst is prepared by the method of any one of claims 1-8.

10. The application of the catalyst prepared by the method of any one of claims 1-8 in CO2 methanation.

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