Preparation method of MOFs derived C-coated CoFe alloy catalyst, catalyst and application thereof

Abstract

The application provides a preparation method of a MOFs derived C-coated CoFe alloy catalyst, and is characterized by comprising the following steps: S1: after mixing cobalt nitrate, iron nitrate, a ligand for forming a MOFs precursor and a solvent sufficiently, the mixture is subjected to a solvothermal reaction under heating at 150 DEG C to obtain a precursor CoxFe-MOF-74, wherein the doping molar ratio of the cobalt nitrate to the iron nitrate in the two raw materials is X, and X is (0.05-0.5); S2: after the precursor is discharged of air by using a hydrogen-argon mixed gas at room temperature, high-temperature pyrolysis reduction is further carried out under a hydrogen atmosphere to obtain a C-coated CoFe alloy catalyst; and the reduction temperature y is (500-575) DEG C. The prepared catalyst effectively improves the CO2 conversion rate. The catalyst is applied to photocatalytic reduction of CO2.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic reduction of CO2 technology, and particularly relates to a method for preparing an alloy catalyst derived from MOFs, the catalyst itself, and its application. Background Technology

[0002] With the continued growth of global energy demand and the increasingly severe environmental pollution problems, the development of clean and efficient renewable energy conversion and storage technologies, such as fuel cells, metal-air batteries, and water electrolysis for hydrogen production, has become a research hotspot. The core efficiency of these technologies largely depends on the electrocatalytic reactions that occur within them, especially the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the slow kinetics of these reactions severely restrict the energy conversion efficiency and commercialization process of related devices.

[0003] Currently, noble metal-based catalysts are the most effective catalysts for the aforementioned reactions. For example, platinum (Pt) and its alloys are considered the benchmark catalysts for ORR, while oxides of iridium (Ir) and ruthenium (Ru) are the benchmark catalysts for OER. However, noble metal catalysts suffer from high cost, poor stability, and limited catalytic function. To overcome the limitations of noble metal catalysts, researchers have turned their attention to non-noble metal-based catalysts. Among them, transition metals (such as Fe, Co, Ni, Mn, etc.) and their alloys, oxides, and nitrides have attracted much attention due to their wide availability, low cost, and potentially excellent catalytic activity. In particular, CoFe bimetallic alloys, due to the electronic synergistic effect between Fe and Co, can effectively regulate their d-band electronic structure and optimize the adsorption energy for reaction intermediates, thus enabling this alloy catalyst to exhibit activity superior to single metal catalysts. Non-noble metal catalysts, especially nanoscale CoFe alloys, still face challenges in preparation and application, such as easy particle agglomeration and poor chemical stability, posing a challenge to the application of these materials. To address the aforementioned issues, researchers developed a carbon encapsulation strategy, constructing a "core-shell" structure to encapsulate active metal nanoparticles within a graphitized carbon layer. This structure offers multiple advantages: the carbon shell acts as a physical barrier, effectively preventing the aggregation and leaching of the core nanoparticles during the reaction process, significantly enhancing catalyst stability; simultaneously, the graphitized carbon layer itself possesses excellent electronic conductivity, accelerating charge transport; furthermore, electronic interactions may exist between the carbon layer and the metal core, further modulating catalytic activity. Carbon encapsulation technology primarily involves coating the surface of active metal nanoparticles with one or more layers of carbon materials (such as graphitized carbon, amorphous carbon, carbon nanotubes, etc.) to form a physical barrier, particularly for the modification of non-noble metal (such as Fe, Co, Ni, Mn, etc.) catalysts. This technology is beneficial for improving stability, preventing aggregation or sintering; enhancing conductivity to promote charge transfer; and modulating interfacial properties to adjust the electronic structure of the active center. MOFs (Metal-Organic Elements) are a relatively new type of framework material. Due to their high specific surface area, tunable pore structure, and well-defined metal / carbon source composition, they are considered ideal precursors or self-templates for preparing carbon-encapsulated metal catalysts. Through high-temperature pyrolysis, organic ligands in MOFs can be transformed in situ into a graphitized carbon matrix, while metal ions are reduced and alloyed into nanoparticles, which are then naturally encapsulated by the carbon layer.

[0004] However, currently, due to the difficulty in controlling the uniformity of the carbon layer and the instability of interface engineering, different metal precursors exhibit significant differences in behavior during pyrolysis, easily leading to metal agglomeration or incomplete carbon layers. This is especially true for the Co-Fe bimetallic system, where differences exist in the reduction temperature, carbon affinity, and lattice matching degree between Fe and Co. Conventional methods (such as impregnation and co-precipitation) struggle to achieve uniform alloying and carbon encapsulation, easily resulting in phase separation or non-uniform alloying, thus affecting catalytic performance. For photothermal catalysis of CO2 using metals, current technologies often employ C, ZnO, SiO2, etc., as supports, loading metal materials onto these supports using methods such as the impregnation method described above to generate metal-carbon nanocomposites. However, the C in the samples obtained by this preparation method is mostly amorphous carbon, and the metals are often in a blended state or post-modified, resulting in uneven metal distribution, low effective active sites, and weak photocatalytic performance. Currently, commonly used MIL-53(Fe) type MOF materials use 2-aminoterephthalic acid (2-APDC) as the ligand. Pyrolysis requires two temperatures, with the highest being approximately 700℃. These high-temperature photothermal conditions easily cause the material's framework structure to collapse, disrupting the highly ordered pores and significantly reducing the specific surface area, leading to the burial of active sites and affecting catalytic performance. Summary of the Invention

[0005] Based on the aforementioned deficiencies in the existing technology, the purpose of this invention is to provide a method for preparing a MOF-derived C-encapsulated CoFe alloy catalyst. The catalyst prepared by this method exhibits excellent stability, high activity, and high selectivity in the photothermal catalytic reduction of carbon dioxide.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first objective of this invention is to provide a method for preparing a MOF-derived C-encapsulated CoFe alloy catalyst, comprising the following steps: S1: Cobalt nitrate and iron nitrate, the ligand forming the MOF precursor and the solvent are thoroughly mixed and the resulting mixture is subjected to a solvothermal reaction at 150°C to obtain the precursor CoxFe-MOF-74. In the two raw materials of cobalt nitrate and iron nitrate, the molar ratio of cobalt nitrate to iron nitrate metal element doping is denoted as X, and X is (0.05~0.5). S2: After the precursor is purged of air using a hydrogen-argon mixture at room temperature, it is then subjected to high-temperature pyrolysis reduction in a hydrogen atmosphere to obtain a CoFe alloy catalyst coated with a C layer; the reduction temperature y is (500-575)℃.

[0008] As a further improvement of the present invention: the ligand for forming the MOF precursor is 2,5-dihydroxyterephthalic acid (DTA). The solvent is N,N-dimethylformamide (DMF); wherein, for every 1616 mg Fe(NO3)3·9H2O, 724 mg DTA and 40 mg DMF are mixed.

[0009] As a further improvement of the present invention, in step S1, after the cobalt nitrate, iron nitrate and ligand are completely dissolved in the solvent, the temperature is raised from room temperature to 150°C in a closed hydrothermal reactor and kept at that temperature for 1200 min to obtain the MOF precursor CoxFe-MOF-74.

[0010] As a further improvement of the present invention, in step S1, the obtained MOF precursor CoxFe-MOF-74 needs to be washed three times each with ethanol and water, dried in a vacuum oven at 60°C, ground, and then sealed for storage.

[0011] As a further improvement of the present invention, in S2, the high-temperature pyrolysis reduction process is carried out in a tube furnace in an atmosphere of H2:Ar=1:9, and the gas flow rate is maintained at 20mL / min.

[0012] As a further improvement of the present invention, in S2, the time for venting air at room temperature is at least 0.5 h, then the temperature is heated to the reduction temperature at a rate of 5 °C / min and maintained at the reduction temperature for 2 h, wherein the reduction temperature y is 500-575 °C.

[0013] The second objective of this invention is to provide a catalyst prepared by the above-described method for preparing MOFs-derived C-encapsulated CoFe alloy catalysts: The catalyst is a CoFe alloy catalyst wrapped in a C layer, which is an alloy nanoparticle, and the nanostructure of the CoFe alloy is a grape-like morphology of ellipsoidal aggregation. In the CoFe alloy, the molar ratio of the two metallic elements Co to Fe in the product alloy is (0.106-0.465):1.

[0014] A third objective of this invention is to provide an application of the catalyst prepared by the above-described method for preparing MOFs-derived C-encapsulated CoFe alloy catalyst: the catalyst is used for photocatalytic reduction of CO2.

[0015] In a preferred embodiment of the present invention, in step S1, after the metal nitrate and ligand are completely dissolved in the solvent, the temperature is raised from room temperature to 150°C in a closed hydrothermal reactor and held for 1200 min to obtain the MOF precursor CoxFe-MOF-74. Compared to direct carbon adsorption, this method is equivalent to pyrolyzing the framework material outside the dispersed metal into carbon, resulting in a more uniform dispersion.

[0016] In a preferred embodiment of the present invention, the pyrolysis reduction requires first fully purging the air from the tubular furnace at room temperature. The purging time at room temperature is at least 0.5 hours. This is necessary to ensure more uniform dispersion, prevent oxidation under high-temperature conditions, and guarantee the safe use of hydrogen.

[0017] Compared with the prior art, the beneficial effects of the MOFs-derived alloy catalyst preparation method, the catalyst, and its application provided by this invention are as follows: 1. This invention involves directly mixing cobalt nitrate, iron nitrate, and ligands to prepare a precursor, followed by reduction. The resulting nanomaterial exhibits uniform Co and Fe doping, a uniform outer carbon coating, and abundant adsorption and reduction sites. In the CoFe alloy crystal structure, Co is completely integrated into the Fe lattice, and X-ray diffraction (XRD) shows almost complete overlap of the two metal peaks. Co atoms enter the Fe lattice, forming a uniform solid solution, while the outer layer is an ellipsoidal, grape-like carbon coating structure, possessing both high specific surface area and good conductivity. The core of this invention lies in the synergistic interface, uniform doping, and unique morphology of the CoFe alloy and carbon layer. The catalyst prepared by this method has advantages such as high absorbance, high metal loading, high dispersibility, and large specific surface area.

[0018] 2. The catalyst prepared by this invention exhibits excellent photothermal conversion and energy efficiency: This catalyst possesses broad-spectrum strong absorption characteristics from ultraviolet to near-infrared, resulting in high photothermal conversion efficiency. Utilizing solar energy as the sole energy input, the catalyst bed can rapidly rise to the required reaction temperature (200℃-400℃) through the photothermal effect, eliminating the need for external heating and significantly reducing process energy consumption. This highlights its significant advantages in solar energy utilization and energy conservation and emission reduction. This invention achieves ingenious synergy among multiple components through the alloying of Fe and Co and the encapsulation of the C layer. Fe acts as the main active center, driving the reverse water-gas shift and Fischer-Tropsch synthesis reactions. The incorporation of Co regulates the electronic structure of Fe, significantly enhancing the dissociation ability of H2. The porous structure of the carbon layer also facilitates reactant mass transfer. This synergistic effect is key to achieving high activity and high selectivity.

[0019] 3. Regarding the MOF precursor itself, existing technologies do not bind it to the ligand DTA, and MOF precursors are often used for photothermal catalysis of carbon dioxide hydrogenation in stationary phases. This invention precisely controls and selects the feed concentration, feed ratio, and pyrolysis temperature during solvothermal reaction. Taking full account of influencing factors, orthogonal experiments are used to determine the optimal doping ratio. Then, based on this doping ratio, variations in the pyrolysis temperature are explored to find the best synthesis conditions.

[0020] 4. This invention uses a specific CoxFe-MOF-74 as a precursor and achieves uniform C encapsulation of CoFe alloy nanoparticles by precisely controlling the Co doping molar ratio and pyrolysis conditions. This results in uniform dispersion of Co and Fe within the MOF framework, maintaining the alloy state after pyrolysis. Testing shows that the carbon-coated CoFe alloy nanoparticles provided by this invention, when used in the photothermal catalytic CO2 hydrogenation reduction reaction, achieve a performance of 3 W·cm⁻¹. -2 Under certain light intensity, for a CO:H2 mixture of 1:4, the CO yield is as high as 19.063 mmol·g. -1 ·h -1 It also has good photothermal conversion capability and can operate stably for 50 hours, indicating its good stability and lifespan in photothermal catalysis of CO2.

[0021] 5. The preparation method provided by this invention uses precursor MOFs as templates to prepare catalysts with high metal loading, high dispersion, and specific core-shell structures through a one-step pyrolysis method. This method uses readily available raw materials, has a simple process, mild reaction conditions, and requires no complex post-processing, providing a reliable route for the large-scale preparation of high-performance photothermal catalysts. Specifically, S1 obtains results directly in one step without adjusting pH, and S2 avoids multiple pyrolysis steps. Adjusting pH increases workload, and even small pH errors can have a significant impact, leading to quality control issues. Multiple pyrolysis steps also increase workload, and higher temperatures place higher demands on the strength of the synthesis equipment. Attached Figure Description

[0022] Figure 1 The figure shows the relationship between the feed ratio of the CoxFe-MOF-74 precursors prepared in Examples 1 and 3 and the molar ratio of Co to Fe measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the linear fitting graph.

[0023] Figure 2 The thermogravimetric analysis-differential thermogravimetric analysis (TG-DTG) curves of the Co0.1Fe-MOF-74 precursor prepared in Example 1 under Ar atmosphere.

[0024] Figure 3-1 The XRD patterns of the FeCo0.1@Cy catalysts prepared in Examples 1 and 2 are shown at pyrolysis temperatures y of 500, 525, 550, and 575 °C, respectively.

[0025] Figure 3-2 The XPS spectra of the FeCo0.1@Cy catalysts prepared in Examples 1 and 2 are shown at pyrolysis temperatures y of 500, 525, 550, and 575 °C, respectively.

[0026] Figure 3-3The UV-Vis-NIR absorption spectra of the FeCo0.1@Cy catalysts prepared in Examples 1 and 2 at pyrolysis temperatures y of 500, 525, 550, and 575 °C, respectively.

[0027] Figure 4 The images are: SEM and TEM images of the Co0.1Fe-MOF-74 precursor and Fe-MOF-74, and the pyrolysis products Fe@C-550 and FeCo0.1@C-550 prepared in Example 1, corresponding to (a)-(d) and (e)-(h), respectively.

[0028] Figure 5 The images are: HAADF images and line scan mappings of the Co0.1Fe-MOF-74 precursor prepared in Example 1.

[0029] Figure 6 The X-ray diffraction patterns of FeCox@C-550 prepared in Examples 1 and 3 are shown below, and compared with the diffraction cards of Fe element.

[0030] Figure 7 The conversion rate and selectivity of the main products generated by FeCox@C-550 prepared in Examples 1 and 3 when the doping rate x is 0, 0.05, 0.15, 0.2, 0.3, 0.4 and 0.5, respectively.

[0031] Figure 8 The conversion rate of the main product generated from FeCo0.1@Cy prepared in Examples 1 and 2 at pyrolysis temperatures y of 500, 525, 550, and 575℃, respectively.

[0032] Figure 9 The following is a performance curve of the FeCo0.1@C-550 prepared in Example 1 after 50 hours of stable operation:

[0033] Figure 10 The images show TEM images of the Fe / Co NPs control sample and the FeCo0.1-C impregnation control sample prepared in Comparative Examples 1 and 2.

[0034] Figure 11 The bar chart shows the comparison of the photothermal catalytic CO2 hydrogenation reduction reaction performance of the samples prepared in Example 1 and Comparative Examples 1 and 2.

[0035] Figure 12 The bar chart shows the performance of the CO2 hydrogenation reduction reaction of the sample prepared in Example 1 under photothermal conditions and the thermal control. Detailed Implementation

[0036] To further illustrate the present invention, detailed descriptions and examples are provided below. The experimental materials used in the following examples of the present invention are all commercially available products.

[0037] This invention provides a method for preparing a tunable MOF-derived C-encapsulated CoFe alloy catalyst by adjusting the Co concentration and reduction temperature. It is based on the existing Fe-MOF-74 precursor, which is modified by doping to obtain CoxFe-MOF-74. The Fe-MOF-74 precursor is a relatively mature three-dimensional porous crystal precursor type.

[0038] In this invention, the CoxFe-MOF-74 precursor has a grape-like morphology of ellipsoidal aggregates.

[0039] In this invention, among the two raw materials, cobalt nitrate and iron nitrate, the molar ratio of cobalt nitrate to iron nitrate metal element doping is denoted as x. Then, the precursor obtained by solvothermal reaction of Co(NO3)2·6H2O-doped DTA and Fe at 150℃ can be denoted as CoxFe-MOF-74, and the value of the subscript x is generally between 0.05 and 0.5.

[0040] In this invention, the preferred molar ratio of Co(NO3)2·6H2O to Fe(NO3)3·9H2O in the MOF-derived C-coated CoFe alloy catalyst is 0.1:1. Figure 7 This demonstrates that the highest CO2 conversion rate is achieved when the doping rate is 0.1, while also ensuring selectivity of over 90%.

[0041] In this invention, the temperature of pyrolysis reduction under hydrogen atmosphere is denoted as y, and the obtained MOFs derivative can be denoted as FeCo0.1@Cy. The value of the suffix y is generally between 500℃ and 575℃.

[0042] This invention provides a method for preparing a MOF-derived C-encapsulated CoFe alloy catalyst, comprising the following steps: A) 1616 mg Fe(NO3)3·9H2O, amg Co(NO3)2·6H2O and 724 mg 2,5-dihydroxyterephthalic acid were added sequentially to 40 mL of N,N-dimethylformamide and stirred for 10 min to completely dissolve the metal salt and ligand, resulting in a uniformly dispersed solution, where a = 1170x; B) The above solution was placed in a 100 mL high-pressure reactor lined with polytetrafluoroethylene, and the temperature was slowly increased from room temperature to 150 °C in an oven for crystallization reaction for 20 h. After that, it was naturally cooled to room temperature to obtain a brownish-black solid suspension or precipitate. C) The above product is washed three times with anhydrous ethanol and deionized water respectively, and then dried to obtain the CoxFe-MOF-74 precursor. This precursor needs to be stored in a sealed container to prevent oxidation. Co(NO3)2·6H2O is taken in amounts of 0 mg, 59 mg, 177 mg, 234 mg, 351 mg, 468 mg, and 585 mg to obtain CoxFe-MOF-74 with x values ​​of 0, 0.05, 0.15, 0.2, 0.3, 0.4, and 0.5. The drying is preferably vacuum drying, preferably at 60°C. D) Disperse 500 mg of the CoxFe-MOF-74 precursor prepared above uniformly in a ceramic boat, place the ceramic boat in the center of a tube furnace, and continuously introduce H2 / Ar mixed gas into the tube furnace at a flow rate of 20 mL min-1 for at least 0.5 h, wherein the volume fraction of H2 is 10%, to ensure that the air in the furnace is completely removed; E) At the same flow rate, at 5℃·min - The tubular furnace is heated to y℃ at a heating rate of ¹ and held at this temperature for 2 hours. After the tubular furnace cools naturally to room temperature, the target catalyst FeCox@Cy is obtained, where y can be between 500℃ and 575℃. In this invention, if the reduction temperature is too low, a large amount of high-melting-point Fe3O4 will exist in the phase, while if the temperature is too high, the FeCo alloy will further agglomerate, resulting in excessively large product particle size, which reduces the specific surface area and the number of active sites.

[0043] In this invention, the reduction serves to transform the organic complex framework into a C coating on the alloy surface, while simultaneously reducing the O that may be present in the solvothermal reaction.

[0044] In this invention, the photothermal catalytic performance of this catalyst for carbon dioxide hydrogenation was tested using mobile phase gas chromatography under a CO2 / H2 atmosphere. The specific method is as follows: After obtaining FeCox@Cy, it was loaded onto the surface of a substrate, and the gas chromatography was performed using a Shimadzu GC-2014. The following is the specific experimental procedure for testing the photothermal catalytic performance of carbon dioxide hydrogenation: In this invention, the substrate is preferably glass fiber or quartz glass, with glass fiber being the most preferred. After grinding the obtained MOF-derived C-coated CoFe alloy catalyst, a certain amount of catalyst is weighed and placed on a glass fiber filter membrane, ensuring uniform distribution. The catalyst mass is between 20 mg and 50 mg, and the distribution radius is preferably 0.7 cm to 0.8 cm. The filter membrane is then placed and fixed on a quartz support, and the reactor (a custom-made 50 mL batch reactor) is shut off.

[0045] In this invention, a light intensity meter needs to be fixed in advance at the location and height of the reactor, and the power and distance of the xenon lamp need to be adjusted to ensure consistent light intensity. The light intensity is 2.5 W·cm. -2 -3.2W·cm -2 3W·cm is preferred -2 .

[0046] In this invention, the specific steps for measuring the concentrations of CO and CH4, the products of photocatalytic reduction of carbon dioxide using the catalyst of this invention, are as follows: Connect the reactor inlet to a gas mixing device and the outlet to a gas chromatograph. Continuously introduce CO2 and H2 into the reactor at a 1:4 ratio to remove residual gas. After ensuring complete replacement of the air inside the reactor, adjust the gas flow rate to a lower value (preferably 5 mL / min-10 mL / min). Turn on the xenon lamp and run the mobile phase gas chromatography to calculate the rate of photothermal catalytic CO2 hydrogenation reduction reaction. The retention times of CO and CH4 are approximately 6.71 min-6.75 min and 5.95 min-6.00 min, respectively. The peaks corresponding to different retention times in the gas chromatography represent different products. By comparing with a fixed concentration-peak area standard curve for the gas chromatograph, the concentration can be calculated. Within the standard curve range, the peak area and concentration have a linear relationship. By directly dividing by the coefficient of this linear relationship, the yield of different products converted from CO2 can be further determined.

[0047] This invention provides carbon-coated CoFe alloy nanoparticles, prepared by reducing MOF precursors obtained through solvothermal processes using a metal source and ligands. The method provided by this invention utilizes readily available raw materials, is simple in process, employs mild reaction conditions, requires no complex post-processing, and is easily scaled up for production, thus offering a reliable pathway for the large-scale preparation of high-performance photothermal catalysts.

[0048] In the nanomaterials obtained by this invention, Co and Fe are uniformly mixed and exist in the form of an alloy, possessing abundant adsorption and reduction sites. Testing showed that the carbon-coated CoFe alloy nanoparticles provided by this invention, when used as a catalyst in the photothermal catalytic reduction of CO2, achieved a yield of 3 W·cm⁻¹. -2 Under certain light intensity, for a CO:H2 mixture of 1:4, the CO yield is as high as 19.063 mmol·g. -1 ·h -1 It also has strong broadband absorption characteristics and good photothermal conversion ability.

[0049] This invention achieves a clever synergy among multiple components through the alloying of Fe and Co and the encapsulation of a C layer. A comparison of the CO2 hydrogenation conversion rate of the control sample synthesized by a simple impregnation method shows that the three components are not simply superimposed, but rather a special coating structure combined with… Figure 10 , 11 The performance test and electron microscopy results show that, among them Figure 10 These are electron microscope images, showing the difference in morphology. It is evident that the CoFe alloy catalyst derived from MOFs and encapsulated with Co exhibits enhanced photothermal catalytic activity, with the undoped portion being the original Fe-MOF-74 precursor.

[0050] Figure 1 The graph shows the relationship between the feed ratio of the CoxFe-MOF-74 precursor prepared in Examples 1 and 3 and the molar ratio of Co to Fe measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), along with a linear fitting graph.

[0051] The horizontal axis represents the measured feed ratio, and the vertical axis represents the molar ratio. The linearity of the lines in the graph indicates that the atomic ratio of the product is almost directly proportional to the feed ratio, and the values ​​differ very little.

[0052] Figure 2 Thermogravimetric analysis-differential thermogravimetric analysis (TG-DTG) curves of the Co0.1Fe-MOF-74 precursor prepared in Example 1 under Ar atmosphere.

[0053] The orange line represents TG, and the green line represents DTG. As shown in the figure, the differential thermogravimetric curve shows two distinct characteristic peaks at 230℃ and 531℃, which correspond to the structural collapse of MOFs and the reduction of Fe2O3 to Fe, respectively.

[0054] Figure 3-1 The XRD patterns of the FeCo0.1@Cy catalysts prepared in Examples 1 and 2 are shown at pyrolysis temperatures y of 500, 525, 550, and 575 °C, respectively. The identical peak positions demonstrate structural similarity.

[0055] Figure 3-2 The XPS spectra of the FeCo0.1@Cy catalysts prepared in Examples 1 and 2 are shown at pyrolysis temperatures y of 500, 525, 550, and 575 °C, respectively. The consistent peak positions indicate consistent valence states.

[0056] Figure 3-3 The UV-Vis-NIR absorption spectra of the FeCo0.1@Cy catalysts prepared in Examples 1 and 2 at pyrolysis temperatures y of 500, 525, 550, and 575 °C, respectively, are shown. It can be seen that the materials at different pyrolysis temperatures exhibit similar color states, further illustrating the similarity in structure and valence state of this series of materials.

[0057] Figure 4The images show SEM and TEM images of the Co0.1Fe-MOF-74 precursor and Fe-MOF-74 precursor, and the pyrolysis products Fe@C-550 and FeCo0.1@C-550 prepared in Examples 1 and 3. image ad is a SEM image of the Co0.1Fe-MOF-74 precursor and Fe-MOF-74, and the pyrolysis products Fe@C-550 and FeCo0.1@C-550. image eh is a TEM image of the Co0.1Fe-MOF-74 precursor and Fe-MOF-74, and the pyrolysis products Fe@C-550 and FeCo0.1@C-550.

[0058] As can be seen from the figures, all the SEM and TEM morphologies are similar, proving that the catalyst prepared in this invention has the grape-like characteristics of ellipsoidal aggregation.

[0059] Figure 5 The images show high-angle annular dark-field (HAADF) images and line scan mappings of the Co0.1Fe-MOF-74 precursor prepared in Example 1. Images a, b, and c represent the distribution of C, Co, and Fe elements, while image d is a superimposed distribution of the three images, and image e is a high-angle annular dark-field (HAADF) image. The fluorescence color in each image represents the distribution of the corresponding element. The images show that the metal and C are uniformly dispersed in the ellipsoidal aggregates, demonstrating a uniform elemental distribution.

[0060] Figure 6 The X-ray diffraction patterns of FeCox@C-550 prepared in Examples 1 and 3 are shown, and compared with the diffraction cards of Fe element.

[0061] The positions of the peaks in the figure and their correspondence with the Fe standard diffraction card show that there are only peaks of Fe single metal, indicating that Co is incorporated into the Fe lattice to form an alloy structure under these conditions, even when the Co doping content is high.

[0062] Figure 7 The conversion rate and selectivity of the main products generated by FeCox@C-550 prepared in Examples 1 and 3 when the doping rate x is 0, 0.05, 0.15, 0.2, 0.3, 0.4 and 0.5, respectively.

[0063] As can be seen from the figure, the highest CO2 conversion rate is achieved when the doping rate is 0.1. The selectivity point corresponding to x=0.1 in the figure is above 90%, which means that selectivity of over 90% is guaranteed.

[0064] Figure 8 The conversion rates of the main products generated from FeCo0.1@Cy prepared in Examples 1 and 2 at pyrolysis temperatures y of 500, 525, 550, and 575 °C, respectively.

[0065] The bar chart with the highest product yield corresponding to pyrolysis at 550℃ shows that for samples with the same doping concentration, the pyrolysis temperature of 550℃ has the highest catalytic performance.

[0066] Figure 9 The performance curve of FeCo0.1@C-550 prepared in Example 1 after 50 hours of stable operation is shown.

[0067] The upper and lower curves in the figure represent the yields of CO and CH4, respectively, while the thicker curve in the middle represents the selectivity. Within 50 hours of stable operation, a selectivity of over 88% and a yield of 20 mmol·g⁻¹ can be maintained. -1 ·h -1 CO2 conversion rate.

[0068] Figure 10 TEM images of the Fe / Co NPs control sample and the FeCo0.1-C impregnation control sample prepared in Comparative Examples 1 and 2.

[0069] As can be seen from the figure, the control samples prepared by conventional methods have different morphologies. The Fe / Co NPs control sample prepared by conventional grinding method is a simple mixture of large agglomerates, while the impregnated control sample is attached to large amorphous graphite, which is different from the morphology of the product prepared in Example 1.

[0070] Figure 12 The bar chart shows the performance comparison of the CO2 hydrogenation reduction reaction of the sample prepared in Example 1 under photothermal conditions and the thermal control in step 3) of Example 1. The test method is the same as step 3) of Example 1. The thermal control is heated at the temperature corresponding to the light irradiation. The similar performance in the figure shows that the promotion of the reaction by the light conditions of the present invention is due to the photothermal effect.

[0071] The names, models, and manufacturers of the synthetic instruments and equipment used in this invention are listed in the table below:

[0072] The names, models, and manufacturers of the testing instruments and equipment are listed in the table below:

[0073] Example 1 1) The preparation steps of FeCo0.1@Cy are as follows: First, 1616 mg Fe(NO3)3·9H2O, 117 mg Co(NO3)2·6H2O, and 724 mg 2,5-dihydroxyterephthalic acid were sequentially added to 40 mL of N,N-dimethylformamide. The mixture was stirred for 10 min to completely dissolve Fe(NO3)3·9H2O, Co(NO3)2·6H2O, and the ligand, resulting in a uniformly dispersed solution. This solution was then placed in a 100 mL high-pressure reactor lined with polytetrafluoroethylene and placed in an oven. The temperature was slowly increased from room temperature to 150 °C and maintained at this temperature for 20 h for crystallization. Afterward, the mixture was allowed to cool naturally to room temperature. The mixture of the product and residual solvent was washed three times each with anhydrous ethanol and deionized water to remove the solvent and any unreacted raw materials. The mixture was then dried completely in a vacuum oven at 60 °C to obtain the Co0.1Fe-MOF-74 precursor, which must be stored in a sealed container. 500 mg of the Co0.1Fe-MOF-74 precursor prepared above was uniformly dispersed in a ceramic boat, and the ceramic boat was placed in the center of a tube furnace. A H2 / Ar (10% H2 volume fraction) mixture was continuously introduced into the tube furnace at a flow rate of 20 mL / min for at least 0.5 h to ensure air removal from the tube. Afterwards, the flow rate was increased to 5 °C / min. - The tube furnace was heated to 550°C at a heating rate of ¹ and held at that temperature for 2 hours. After natural cooling, the target catalyst FeCo0.1@C-550 was obtained.

[0074] 2) Performance test of photothermal catalytic CO2 hydrogenation reduction reaction: After grinding the obtained FeCo0.1@C-550, 30 mg of catalyst was weighed and placed on a glass fiber filter membrane, ensuring it was evenly distributed within a circle with a radius of 0.8 cm. The filter membrane was then fixed on a quartz support, the reactor was shut off, and the airtightness of the mobile phase device was checked. A 300 W xenon lamp was used as the light source, and the intensity was adjusted to 3 W·cm² using a photometer. -2 A CO2:H2 mixture of 1:4 was used as the feed gas. After ensuring complete replacement of the air inside the reactor, the gas flow rate was adjusted to 5 mL / min. The gas composition and content in the mobile phase were detected by online gas chromatography—the peak area corresponding to the retention time was displayed on the mobile phase, and the concentration was converted into the conversion rate using a standard curve. The sample concentration at 3 W·cm⁻¹ was measured. -2 The yields of CO and CH4 under the specified light intensity were 19.063 and 1.69 mmol·g, respectively. -1 ·h -1 .

[0075] from Figure 6The XRD pattern of FeCo0.1@C-550 shows that the product prepared in this embodiment has only a single peak at 2θ=44.672°. Since the peak positions of Co and Fe are very similar, it can be reasonably inferred that the crystal lattices of Co and Fe are mutually integrated and uniformly doped, rather than forming a separate powder mixture structure. Figure 6 The peak shape above and the position of the standard Fe peak below together provide evidence of the successful synthesis of the alloy structure. The XRD standard peak data for Fe are international standard data, as shown in the standard diffraction card.

[0076] 3) Photothermal temperature measurement of FeCo0.1@C-550 and thermocatalytic ability test at corresponding temperatures: Take 30 mg of FeCo0.1@C-550 catalyst and load it according to step 2) of this embodiment. The loading process is as described above: unscrew the hexagonal screws on the reactor cover, place the glass fiber carrying the catalyst inside, tighten the cover again, and check the airtightness before starting the reaction. After fixing the glass fiber carrying the sample onto the quartz stage, use an infrared thermal imager and thermocouples to control the catalyst temperature and maintain a temperature of 3 W·cm. -2 Under light intensity irradiation, the photothermal temperature of the sample surfaces was the same, both being 328℃. Figure 12 It is evident that the thermocatalytic performance is similar to the photothermal performance, further confirming the photothermal driving mechanism and indicating that the catalyst possesses excellent photothermal conversion capabilities. Combined with... Figure 12 The bar chart comparing the performance of the CO2 hydrogenation reduction reaction of the sample prepared in Example 1 under photothermal conditions and the thermal control is shown. During the test, the light irradiation was replaced with the photothermal temperature corresponding to the light irradiation. It can be seen that the light irradiation promoting the reaction in this invention is due to the photothermal effect.

[0077] Example 2 The specific process is the same as in Example 1, except that in step 2), the pyrolysis temperature is changed to 500, 525, and 575℃ respectively, to obtain FeCo0.1@Cy with y=500, 525, and 575℃. The remaining steps are the same. The activity of this catalyst group for photothermal catalytic CO2 hydrogenation was measured as follows: Figure 8 As shown, it can be seen that the highest CO2 conversion rate and selectivity are achieved when y=550. Combined with Example 1, it can be concluded that the optimal pyrolysis temperature is 550℃.

[0078] Example 3 The specific process is the same as in Example 1, except that in step 1), the mass of Co(NO3)2·6H2O is changed to 0 mg, 59 mg, 177 mg, 234 mg, 351 mg, 468 mg, and 585 mg, respectively, to obtain the precursor CoxFe-MOF-74 with x = 0, 0.05, 0.15, 0.2, 0.3, 0.4, and 0.5. Subsequent steps are the same, and after pyrolysis, FeCox@C-550 is obtained. The activity of this catalyst group for photothermal catalytic CO2 hydrogenation was measured as follows: Figure 7 As shown, the highest CO2 conversion rate and selectivity exceeding 90% are observed when x=0.1. Combined with Example 1, the optimal doping feed ratio is 0.1. Specifically, when x=0, there is a blank precursor Fe-MOF-74 and the corresponding pyrolysis product Fe@C-550.

[0079] Comparative Example 1 For Example 1, a control sample of Fe / Co NPs metal particle mixture was prepared using ball milling.

[0080] 1000 mg of commercial Fe powder (particle size <50 nm) and 73 mg of commercial Co powder (particle size <50 nm) were placed together in a ball mill jar. The jar was rotated forward at 1000 rpm for 15 minutes, stopped for 5 minutes, and then rotated in the reverse direction for 15 minutes to ensure uniform mixing. This yielded a control sample of uniformly mixed metal powder. Performance test results are as follows: Figure 11 As shown.

[0081] Comparative Example 2 For Example 1, a FeCo0.1-C control sample was prepared by impregnation. This control sample was a simple mixture of C and metal powder.

[0082] First, 100 mg of carbon black was dispersed in a mixed solution of 20 mL ethanol and 5 mL water, sonicated for 1-2 minutes, and then stirred for 1-2 minutes, repeating this process for a total of 30 minutes to ensure uniform dispersion. Next, 1808 mg of Fe(NO3)3·9H2O and 116 mg of Co(NO3)2·6H2O were weighed and stirred for 10 minutes to completely dissolve the metal salts. The suspension was then dried under heating conditions, preferably at 60-80°C. After complete evaporation, the resulting product was ground to obtain the precursor control sample. The precursor control sample was then subjected to pyrolysis reduction under the same conditions as described in this invention to obtain the FeCo0.1-C control sample.

[0083] Comparative Example 1 illustrates that the catalytic performance is not solely achieved through the mixing of metal powders themselves. Comparative Example 2, through... Figure 11This indicates that C and alloy particles are not simply supported materials; that is, C is not simply amorphous graphite supported on a substrate. A specific structure needs to be formed to achieve a good synergistic effect. The properties of the products prepared in Comparative Examples 1 and 2 are significantly lower than those of the product prepared in this invention, and this invention significantly increases the CO2 conversion rate. The difference between the materials in Comparative Example 1 and this invention lies in the C loading, demonstrating the synergistic effect of C and the metallic material. Figure 11 As shown, pure metal powder, corresponding to Comparative Example 1, and C simple adsorption + pyrolysis, corresponding to Comparative Example 2, did not have good performance. However, the pyrolysis of MOF precursors using the preparation method of the present invention showed high performance. Figure 11 The bar chart shows a comparison of the photothermal catalytic CO2 hydrogenation reduction reaction performance of the samples prepared in Example 1 and Comparative Examples 1 and 2 (the test method is directly the same as step 2 in Example 1). The chart shows that the performance of the catalyst prepared in this invention far exceeds that of Comparative Examples 1 and 2. This indicates that ① the C coating layer has a synergistic effect on the alloy; ② the C coating layer synthesized in this invention exhibits a significantly higher photocatalytic CO2 hydrogenation yield compared to conventional amorphous graphite as a support.

[0084] It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the invention. Furthermore, it should be understood that after reading the technical description of this invention, those skilled in the art can make various modifications, alterations, and / or variations to the invention, and all such equivalent forms also fall within the scope of protection defined by the appended claims. As is known from common technical knowledge, the invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the embodiments disclosed above are merely illustrative in all respects and are not exhaustive. All changes within the scope of this invention or equivalent to the scope of this invention are included in this invention.

Claims

1. A method for preparing a MOF-derived C-encapsulated CoFe alloy catalyst, characterized in that, Includes the following steps: S1: After thoroughly mixing cobalt nitrate, iron nitrate, ligands forming MOF precursors with solvent, the resulting mixture is subjected to a solvothermal reaction at 150°C to obtain the precursor CoxFe-MOF-74. In the two raw materials cobalt nitrate and iron nitrate, the molar ratio of cobalt nitrate to iron nitrate metal element doping is denoted as X, and X is (0.05~0.5). S2: After the precursor is purged of air using a hydrogen-argon mixture at room temperature, it is then subjected to high-temperature pyrolysis reduction in a hydrogen atmosphere to obtain a CoFe alloy catalyst coated with a C layer; the reduction temperature y is (500-575)℃.

2. The method for preparing MOFs-derived C-encapsulated CoFe alloy catalyst according to claim 1, characterized in that: The ligand that forms the MOF precursor is 2,5-dihydroxyterephthalic acid (DTA); The solvent is N,N-dimethylformamide (DMF); wherein, for every 1616 mg Fe(NO3)3·9H2O, 724 mg DTA and 40 mg DMF are mixed.

3. The method for preparing MOFs-derived C-encapsulated CoFe alloy catalyst according to claim 1, characterized in that: In step S1, after the cobalt nitrate, iron nitrate and ligand are completely dissolved in the solvent, the temperature is raised from room temperature to 150°C in a closed hydrothermal reactor and held for 1200 min to obtain the MOF precursor CoxFe-MOF-74.

4. The method for preparing MOFs-derived C-encapsulated CoFe alloy catalyst according to claim 1, characterized in that, In step S1, the obtained MOF precursor CoxFe-MOF-74 needs to be washed three times each with ethanol and water, dried in a vacuum oven at 60°C, ground, and then sealed for storage.

5. The method for preparing MOFs-derived C-encapsulated CoFe alloy catalyst according to claim 1, characterized in that, In S2, the high-temperature pyrolysis reduction process is carried out entirely in a tube furnace in an atmosphere of H2:Ar=1:9, with the gas flow rate maintained at 20mL / min.

6. The method for preparing MOFs-derived C-encapsulated CoFe alloy catalyst according to claim 1, characterized in that, In step S2, the time for venting air at room temperature is at least 0.5 hours, followed by heating to the reduction temperature at a rate of 5°C / min and maintaining it at the reduction temperature for 2 hours. The reduction temperature y is 500°C-575°C.

7. The catalyst prepared by the method for preparing MOFs-derived C-encapsulated CoFe alloy catalysts according to any one of claims 1-6, characterized in that: The catalyst is a CoFe alloy catalyst wrapped in a C layer, which is an alloy nanoparticle, and the nanostructure of the CoFe alloy is a grape-like morphology of ellipsoidal aggregation. In the CoFe alloy, the molar ratio of the two metallic elements Co to Fe in the product alloy is (0.106-0.465):

1.

8. The application of the catalyst prepared by the method for preparing MOFs-derived C-encapsulated CoFe alloy catalysts according to any one of claims 1-6, characterized in that: The catalyst is used for photocatalytic reduction of CO2.

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