Pyrolysis coordination polymer derived copper-rare earth diatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a pyrolytic coordination polymer derived copper-rare earth diatomic catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalytic materials. The preparation method comprises the following steps: firstly, constructing a formaldehyde-dicyandiamide-copper salt-rare earth salt quaternary coordination polymerization system, preparing a polymer precursor containing a metal-nitrogen coordination bond in situ, and realizing molecular-level uniform dispersion of copper and rare earth ions; and then coupling inert atmosphere pyrolysis and reducing atmosphere reduction processes, accurately constructing and stably anchoring copper-rare earth heteronuclear diatomic sites, and finally forming a target catalyst with the diatomic sites uniformly dispersed on the nitrogen-doped carbon carrier. When the material is used for a CO2 electrochemical reduction reaction, the methane Faraday efficiency reaches up to 78% under the current density of 400 mA cm <-2 >, and the stability is excellent; and in a wide current density interval of 200-600 mA cm <-2 >, the methane selectivity is stably maintained to be 60% or above. The process is simple and convenient, the cost is low, and an economic, reliable and large-scale technical scheme is provided for CO2 resource efficient conversion.

Description

Technical Field

[0001] This invention belongs to the field of catalytic material preparation and CO2 resource utilization technology, specifically relating to a copper-rare earth diatomic catalyst derived from pyrolysis coordination polymer and its preparation method, as well as the application of the catalyst in the electrochemical reduction of CO2 to methane. Background Technology

[0002] Electrocatalytic carbon dioxide (CO2) reduction technology can directionally convert greenhouse gas CO2 into high-value-added chemicals or fuels such as methane (CH4) and carbon monoxide, which has the dual value of environmental protection and energy supply. As a clean fuel, CH4 can be directly adapted to existing natural gas transmission and utilization infrastructure without additional modifications. Therefore, the reaction of CO2 electroreduction to CH4 has become a research hotspot in this field.

[0003] To improve the efficiency of electrocatalytic reactions, catalyst structural design is crucial. In recent years, single-atom catalysts have attracted widespread attention in the field of electrocatalysis due to their unique advantages such as maximized atom utilization and uniform active sites, providing new ideas for the efficient conduction of CO2 reduction reactions. However, single-atom catalysts have a single active site, while the reduction of CO2 to CH4 is a complex reaction involving multiple proton / electron transfers and the formation of multiple intermediates. A single active site can often only efficiently bind to one type of reaction intermediate, making it difficult to adapt to the adsorption and conversion requirements of intermediates throughout the entire reaction pathway. This results in limited catalytic activity and selectivity, failing to meet the requirements of industrial applications.

[0004] Against this backdrop, diatomic catalysts (DACs) have emerged. By constructing diatomic active sites composed of two different metal atoms on the surface of a support, they utilize the electronic synergistic effect between the two metals to optimize the adsorption strength of intermediates and regulate the reaction pathway, while retaining the advantage of high atom utilization. They have shown application potential far exceeding that of single-atom catalysts in electrocatalytic CO2 reduction reactions, becoming an important direction for breaking through existing technological bottlenecks.

[0005] However, the preparation of high-performance diatomic catalysts still faces many technical challenges that urgently need to be addressed: First, existing preparation methods mostly rely on precisely structured metal-organic frameworks (MOFs, such as the ZIF series) as precursors, which are then pyrolyzed at high temperatures to prepare the target catalyst. The synthesis of such precursors is cumbersome, the raw material costs are high, and the reaction conditions are harsh, making it difficult to achieve large-scale production. Second, there is an inherent contradiction between high metal loading and atomic dispersion. To improve catalytic activity, the metal loading needs to be increased, but excessive loading can easily lead to the migration and aggregation of metal atoms during pyrolysis, forming inactive nanoparticles, which significantly reduces the density of active sites and the atomic utilization rate. Currently, the metal loading of mainstream diatomic catalysts is generally low, which seriously limits the improvement of catalytic performance. Third, the metal combinations of existing diatomic catalysts are still significantly limited, mostly concentrated in homonuclear bimetallic or common 3d transition metal heteronuclear combinations (such as Fe-Co, Cu-Ni, etc.). There are few studies on introducing rare earth elements into diatomic catalyst systems and constructing rare earth-based heteronuclear diatomic sites. Rare earth elements, with their unique 4f orbital electronic structure, can optimize the electronic state of bimetallic active sites through electronic regulation, and precisely control the adsorption intensity and conversion pathway of reaction intermediates. Theoretically, they are ideal metal components for constructing highly efficient diatomic catalysts. In particular, the exploration of rare earth-based diatomic catalysts is even more lacking in the key area of ​​resource utilization, CO2 electroreduction, and there are obvious gaps in related technologies.

[0006] Chinese patent CN 117832524 A describes a nitrogen-doped porous carbon-supported rare earth-iron dual-single-atom catalyst constructed using rare earth elements. Although this technology introduces rare earth elements, its core is a "dual-single-atom" structure, meaning that the two metal single atoms exist independently without forming a synergistic dual-atom site. Furthermore, its precursor still relies on the ZIF metal-organic framework, failing to address the core pain points of complex preparation and high cost in existing technologies. In addition, the application scenario of this catalyst is the oxygen reduction (ORR) reaction, which is completely different from the reaction mechanism and catalytic requirements of the CO2 electroreduction reaction, and cannot provide effective technical inspiration for the research and development of rare earth-based dual-atom catalysts in the field of CO2 electroreduction.

[0007] In summary, existing diatomic catalysts generally suffer from the common problems of complex preparation processes, high costs, and difficulty in simultaneously achieving metal loading and atomic-level dispersion. Furthermore, the construction technology of rare-earth-based heteronuclear diatomic sites is still immature, and its application in the field of CO2 electroreduction is severely underdeveloped, making it difficult to meet the industrial requirements of CO2 electroreduction to CH4. Therefore, developing a simple, low-cost preparation technology that can achieve synergistic high metal loading and atomic-level dispersion, and accurately construct rare-earth-based heteronuclear diatomic sites, is of significant practical importance and application value in promoting the industrialization of CO2 resource utilization technologies. Summary of the Invention

[0008] This invention aims to address the problems existing in the prior art by innovatively proposing a copper-rare earth diatomic catalyst derived from pyrolysis coordination polymers, its preparation method, and its applications. This invention innovatively constructs a formaldehyde-dicyandiamide-copper salt-rare earth salt quaternary coordination polymerization system to prepare polymer precursors containing metal-nitrogen coordination bonds in situ, achieving molecular-level uniform dispersion of copper and rare earth ions. Furthermore, it couples a two-step synergistic process of "inert atmosphere pyrolysis - reducing atmosphere reduction" to precisely construct and stably anchor the copper-rare earth heteronuclear diatomic sites. This catalyst can be efficiently used in the electrochemical reduction of CO2 to CH4, realizing the directional conversion of CO2 to CH4 and providing an efficient, economical, reliable, and scalable technical route for the resource utilization of CO2.

[0009] This invention is achieved as follows: a method for preparing a copper-rare earth diatomic catalyst derived from a pyrolysis coordination polymer, comprising the following steps: 1) Add formaldehyde solution, dicyandiamide, copper salt and rare earth salt to water, mix and coordinate to form a homogeneous and stable mixture; 2) Dry the mixture obtained in step 1) to obtain a solid coordination polymer precursor, and grind it into powder; 3) The coordination polymer precursor powder is pyrolyzed under an inert atmosphere; 4) After pyrolysis, the mixture is allowed to cool naturally to room temperature, then switched to a reducing atmosphere for reduction treatment. After reduction, the mixture is cooled to obtain a copper-rare earth diatomic catalyst.

[0010] The preparation principle of this diatomic catalyst is as follows: using nitrogen-doped carbon as a support platform, and leveraging the nitrogen-rich environment provided by formaldehyde and dicyandiamide in the coordination polymer precursor, strong coordination interactions are formed between copper and rare earth metal ions. Combined with a subsequent two-step thermal conversion process, the bimetallic compounds are stably anchored to the carbon support in an atomically dispersed form. The first stage, inert atmosphere pyrolysis, promotes the full carbonization of the coordination polymer, constructing a stable conductive carbon framework rich in nitrogen vacancies. The second stage, reducing atmosphere heat treatment, further precisely controls the local coordination environment of the metals, inducing the directional migration and site-specific anchoring of metal atoms. Since copper and rare earth ions have achieved molecular-level homogeneous mixing in the polymer precursor, and rare earth metals have a strong affinity for nitrogen species, rare earth atoms preferentially bind to and anchor to nitrogen-deficient sites in the carbon support during pyrolysis, forming a stable rare earth-N coordination structure. This structure, through steric hindrance and electronic interactions, restricts the migration and aggregation of copper atoms, effectively inhibiting copper atom aggregation, ultimately forming a well-defined copper-rare earth diatomic active site. This preparation strategy optimizes the adsorption behavior of key reaction intermediates in the CO2 reduction process through the synergistic effect of the bimetallic electronic structure and the nitrogen-coordinated microenvironment, thereby achieving highly selective conversion of CO2 to CH4.

[0011] Further, in step 1), the copper salt and rare earth salt used are both soluble salts, selected from at least one of nitrates, sulfates, acetates, acetylacetone salts and chlorides, preferably nitrates; the rare earth element is selected from any one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, preferably samarium.

[0012] Further, in step 1), the molar ratio of copper salt to rare earth salt is 1:0.2~5, the mass ratio of copper salt to dicyandiamide is 1:1~10, the mass ratio of copper salt to formaldehyde solution is 1:1~5, and the mass ratio of copper salt to water is 1:5~50.

[0013] Preferably, the molar ratio of copper salt to rare earth salt is 1:1, the mass ratio of copper salt to dicyandiamide is 1:4~6, and the mass ratio of copper salt to formaldehyde solution is 1:4~5.

[0014] Further, in step 2), the drying temperature is 90~150℃, preferably 110℃; the drying time is 8~24 h, preferably 12 h; the obtained solid coordination polymer precursor is ground to a standard sieve of 150~250 mesh, preferably 200 mesh, to obtain fine powder.

[0015] Further, in step 3), the inert atmosphere is a nitrogen or argon atmosphere, preferably a nitrogen atmosphere; the pyrolysis temperature is 300~600℃, preferably 400℃; and the pyrolysis time is 1~6 h, preferably 2 h.

[0016] Further, in step 4), the reducing atmosphere is a hydrogen / argon mixture, wherein the volume fraction of hydrogen is 5%~100%, preferably 5%; the reduction temperature is 300~600℃, preferably 400℃; and the reduction time is 1~6 h, preferably 2 h.

[0017] This application also seeks protection for a copper-rare earth diatomic catalyst derived from a pyrolysis coordination polymer prepared by the above method, the catalyst comprising a nitrogen-doped carbon support and copper-rare earth diatomic active sites supported on the nitrogen-doped carbon support; the copper atoms and rare earth atoms are uniformly atomically dispersed in the form of diatomic clusters, and respectively form Cu-N coordination structures and rare earth-N coordination structures with nitrogen atoms in the nitrogen-doped carbon support.

[0018] The aforementioned copper-rare earth diatomic catalyst can be applied in the electrochemical reduction of CO2 to methane. In an alkaline electrolyte and a three-electrode flow electrolysis cell system, when the current density is 400 mA cm⁻¹... -2 At that time, the Faraday efficiency of methane can reach 78%.

[0019] The pyrolysis coordination polymer-derived copper-rare earth biatom catalyst provided in this application exhibits highly efficient catalytic performance due to its unique active site structure and the electronic synergistic effect of the nitrogen-doped carbon support: the copper sites possess moderate adsorption strength, ensuring the accessibility of the reaction sites; adjacent rare earth metal sites, through their unique 4f electron orbitals, efficiently regulate the migration and transformation of intermediates between the two sites; the nitrogen-doped carbon support not only provides atomically dispersed anchoring sites for the bimetallic atoms, inhibiting the re-migration and aggregation of metal atoms during the reaction, but also induces electronic structure modulation of the copper sites through strong metal-nitrogen coordination interactions, precisely optimizing their adsorption strength for key carbon-containing intermediates. Furthermore, the rare earth metals promote charge redistribution at the reaction interface, forming a stable synergistic catalytic microenvironment of electron-deficient copper sites and electron-rich rare earth sites, ultimately driving the efficient and highly selective conversion of CO2 to CH4.

[0020] Beneficial effects: 1. This application innovatively constructs a formaldehyde-dicyandiamide-copper salt-rare earth salt quaternary coordination polymerization system to prepare precursors. A nitrogen-rich organic framework is formed in situ through the aldehyde-amine condensation reaction of formaldehyde and dicyandiamide. With the strong coordination between N atoms and metal ions in the framework, the molecular-level uniform dispersion of copper ions and rare earth ions is achieved. This suppresses the core problem of easy migration and aggregation of metal atoms in the preparation of bimetallic catalysts from the source, and lays a solid structural foundation for the precise construction of subsequent biatomic active sites. 2. This application employs a two-step synergistic process of "inert atmosphere pyrolysis - reducing atmosphere reduction" to prepare the catalyst: the inert atmosphere pyrolysis stage can simultaneously achieve in-situ carbonization and nitrogen doping of coordination polymers, efficiently constructing a stable nitrogen-doped carbon support rich in nitrogen defects; the reduction stage can precisely control the metal valence state and local coordination environment, inducing directional anchoring of metal atoms; the entire process is simple, key parameters are easy to control, and it does not require harsh reaction conditions such as high temperature and high pressure, precious metal additives, or complex equipment, thus possessing the potential for large-scale industrial production; 3. The catalyst prepared in this application has a unique and efficient microstructure. Copper atoms and rare earth atoms are atomically dispersed on the surface of nitrogen-doped carbon support in the form of diatomic clusters, forming stable Cu-N and rare earth-N coordination structures, respectively. Rare earth atoms can continuously suppress the aggregation of copper atoms through the dual regulation of steric hindrance effect and electronic interaction. At the same time, the synergistic effect of the electronic structure of copper and rare earth and the unique 4f orbital regulation of rare earth can accurately optimize the adsorption intensity and conversion path of key nitrogen / carbon intermediates in the CO2 reduction process, breaking the technical bottleneck of poor adaptability of adsorption intensity of single metal sites to CO2 reduction intermediates. 4. The copper-rare earth diatomic catalyst prepared in this application exhibits excellent methanogenic performance in the electrochemical reduction reaction of CO2, at 400 mA cm⁻¹. -2At industrial-grade current densities, methane achieves a Faraday efficiency of up to 78%, and this efficiency is maintained in the range of 200–600 mAcm⁻¹. -2 Within a wide current density range, the methane selectivity remains stable at over 60%, and its overall performance is significantly better than that of existing copper-based single-atom catalysts and bimetallic nanoparticle catalysts in terms of methane selectivity and current density adaptability. 5. The copper-rare earth diatomic catalyst prepared in this application can withstand temperatures up to 400 mA cm⁻¹. -2 After 17 hours of continuous operation at high current density, the methane Faraday efficiency remained above 60%, with small fluctuations in electrode potential, demonstrating excellent structural and electrochemical stability. This is attributed to the strong anchoring effect of the nitrogen-doped carbon support and the stable coordination structure of the two atomic sites, which avoids the migration, aggregation, or oxidative deactivation of metal atoms during the reaction process, thus solving the problem that existing CO2 reduction catalysts cannot simultaneously achieve high activity and high stability. Attached Figure Description

[0021] Figure 1 The image shows a scanning electron microscope (SEM) image of the copper samarium diatomic catalyst prepared in Example 1. Figure 2 Aberration-corrected transmission electron microscope (AC-TEM) image of the copper samarium diatomic catalyst prepared in Example 1; Figure 3 The elemental distribution surface scan of the copper-samarium diatomic catalyst prepared in Example 1; Figure 4 The X-ray absorption near-edge structure (XANES) spectrum of copper element in the copper-samarium diatomic catalyst prepared in Example 1; Figure 5 The Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum of copper element for the copper-samarium diatomic catalyst prepared in Example 1; Figure 6 X-ray photoelectron spectroscopy (XPS) Cu LMM Auger spectra of copper in the copper samarium diatomic catalyst prepared in Example 1, the copper gadolinium diatomic catalyst prepared in Example 2, and the copper single-atom catalyst prepared in Comparative Example 1. Figure 7 The image shows the samarium element X-ray absorption near-edge structure (XANES) spectrum of the copper samarium diatomic catalyst prepared in Example 1. Figure 8 The Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum of the copper samarium diatomic catalyst prepared in Example 1; Figure 9 The copper samarium diatomic catalyst prepared in Example 1 was used at 50–600 mA cm⁻¹ -2The graph shows the test results of the product Faraday efficiency distribution during the electrochemical reduction of CO2 within the current density range. Figure 10 The copper-rare earth diatomic catalysts prepared in Examples 1-7 and the copper single-atom catalyst prepared in Comparative Example 1 were tested at 400 mA cm⁻¹. -2 Comparison of the Faraday efficiency performance of methane electrochemical reduction of CO2 at different current densities; Figure 11 The copper samarium diatomic catalyst prepared in Example 1 was tested at 400 mA cm⁻¹. -2 Figure showing the stability test results under current density. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0023] Example 1

[0024] This embodiment discloses a copper-samarium diatomic catalyst, the specific preparation process of which is as follows:

[0025] (1) Add 4.4 mL of formaldehyde solution (37 wt%, 4.75 g) and 5.0 g of dicyandiamide to 25 mL of deionized water, stir magnetically for 30 min until the dicyandiamide is completely dissolved, then add 1.01 g of copper nitrate trihydrate (4.2 mmol) and 1.87 g of samarium nitrate hexahydrate (4.2 mmol), and continue stirring for 60 min to form a homogeneous and stable mixture;

[0026] (2) Place the mixture obtained in step (1) in an oven at 110°C and dry it at a constant temperature for 12 h. After the water is completely evaporated, a solid coordination polymer precursor is obtained. Grind it to a standard sieve of 200 mesh to obtain a uniform fine powder for later use.

[0027] (3) Place the precursor powder in a quartz boat, put it in a tube furnace, heat it to 400°C at a rate of 5°C / min under N2 atmosphere, keep it at the temperature for 2 h, and let it cool naturally to room temperature after the reaction is finished.

[0028] (4) Switch to 5% H2 / Ar mixed gas to purge for 20 min, replace N2 in the furnace, heat to 400℃ at a rate of 5℃ / min, keep at a constant temperature for 2 h, after reduction, maintain 5% H2 / Ar gas flow until the tubular furnace cools naturally to room temperature (avoid air entering and causing catalyst oxidation), and finally obtain copper samarium diatomic catalyst.

[0029] The copper-samarium diatomic catalyst prepared in this embodiment exhibits a rough, aggregate-like macroscopic morphology. Figure 1This structure facilitates the exposure of more active sites and optimizes the mass transfer efficiency of reactants / products. To accurately characterize its microstructure, the catalyst was observed at atomic resolution using aberration-corrected projection electron microscopy, with results as follows: Figure 2 As shown, Cu atoms and Sm atoms do not form obvious nanoparticles or large-sized aggregates, but are uniformly dispersed on the surface of nitrogen-doped carbon support in the form of isolated atoms or diatomic clusters. Moreover, there is a clear close-range coordination between Cu atoms and Sm atoms, which confirms the successful construction of copper samarium diatomic active sites.

[0030] Figure 3 The image shows a transmission electron microscope (TEM) scan of the elemental distribution of the copper-samarium diatomic catalyst prepared in Example 1. The image clearly shows that both Cu and Sm elements were successfully loaded into the catalyst. At the observation scale of 50 nm, both Cu and Sm elements were uniformly dispersed with the N element of the support, without local enrichment or agglomeration, which confirms the high dispersion of Cu and Sm in the catalyst.

[0031] Figure 4 The absorption spectrum of Example 1 is shown to be between the 0-valent standard copper foil and the +1-valent standard cuprous oxide, which intuitively indicates that the Cu valence state in this catalyst is in the range of 0 and +1.

[0032] Figure 5 The Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum of the copper samarium diatomic catalyst prepared in this embodiment shows that the characteristic peaks of Example 1 are dominated by Cu-N coordination signals, accompanied only by weak Cu-O signals, and no obvious Cu-Cu coordination characteristic peaks are observed. This result directly confirms that Cu atoms exist in an atomically dispersed state on the support surface without metal agglomeration.

[0033] From X-ray photoelectron spectroscopy (XPS) Cu LMM Auger spectrum ( Figure 6 As you can see, the Cu Auger peak of the diatomic catalyst prepared in Example 1 is located at 916.3 eV, which is lower than that of Cu. 2+ The characteristic Auger peak position, with Cu + The standard Auger peak position is more consistent, and the Auger parameters calculated by combining the Cu2p photoelectron peak further verify that the Cu element in this catalyst mainly exists in the +1 valence form.

[0034] Figure 7 The image shows the X-ray absorption near-edge structure (XANES) spectrum of the copper-samarium diatomic catalyst prepared in Example 1. It can be seen that the position and shape of the characteristic absorption peak of Sm in this catalyst are basically consistent with the spectrum of standard samarium oxide (whose Sm valence state is +3). This directly indicates that the valence state of Sm in this copper-samarium diatomic catalyst is close to +3.

[0035] Figure 8 The image shows the Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum of the copper samarium diatomic catalyst prepared in this embodiment. The figure shows that the main characteristic peaks of the catalyst prepared in Example 1 correspond to Sm-N coordination signals, and there are no Sm-O coordination peaks present in standard samarium oxide, nor are there any Sm-Sm agglomeration characteristic peaks. Combined with the peak differences of the standard sample, it can be directly confirmed that Sm atoms exist in an atomically dispersed state on the surface of the catalyst support, without metal agglomeration, and are stably anchored mainly through coordination with N atoms.

[0036] Combining the macroscopic morphology and microstructure characterization results, it is shown that the efficient preparation of copper samarium diatomic catalysts was achieved through formaldehyde-dicyandiamide coordination polymerization and a two-step pyrolysis reduction process. Its atomic-level dispersion characteristics provide a structural basis for subsequent electrochemical catalytic performance.

[0037] Example 2

[0038] This embodiment is based on the technical solution of Example 1, except that the rare earth salt component is replaced and adjusted as a single variable: 1.87 g of samarium nitrate hexahydrate (4.2 mmol) in step (1) is replaced with an equimolar amount of gadolinium nitrate hexahydrate (4.2 mmol, 1.90 g); the remaining process steps and key parameters are completely consistent with Example 1, and the copper gadolinium diatomic catalyst is successfully prepared.

[0039] Example 3

[0040] This embodiment is based on the technical solution of Example 1, only the amount of copper salt and rare earth salt is replaced and adjusted: "1.01 g copper nitrate trihydrate (4.2 mmol) and 1.87 g samarium nitrate hexahydrate (4.2 mmol)" in step (1) is replaced with "1.35 g copper nitrate trihydrate (5.6 mmol) and 1.24 g samarium nitrate hexahydrate (2.8 mmol)"; the remaining process steps and key parameters are completely consistent with Example 1, and the copper samarium diatomic catalyst is successfully prepared.

[0041] Example 4

[0042] This embodiment is based on the technical solution of Example 1, except that the amounts of formaldehyde solution and dicyandiamide are replaced and adjusted: in step (1), “4.4 mL formaldehyde solution (37 wt%, 4.75 g) and 5.0 g dicyandiamide” is replaced with “2.2 mL formaldehyde solution (37 wt%, 2.38 g) and 7.5 g dicyandiamide”; the remaining process steps and key parameters are completely consistent with Example 1, and the copper samarium diatomic catalyst is successfully prepared.

[0043] Example 5

[0044] This embodiment is based on the technical solution of embodiment 1, and only the drying conditions in step (2) are adjusted: the original "drying at a constant temperature in an oven at 110℃ for 12 h" is replaced with "drying at a constant temperature in an oven at 150℃ for 10 h". The remaining process steps and key parameters are completely consistent with those of embodiment 1, and the copper samarium diatomic catalyst is successfully prepared.

[0045] Example 6

[0046] This embodiment is based on the technical solution of embodiment 1, and only the pyrolysis conditions of step (3) are adjusted: the original "heated to 400°C at a rate of 5°C / min under N2 atmosphere and held at the temperature for 2 h" is replaced with "heated to 500°C at a rate of 5°C / min under N2 atmosphere and held at the temperature for 4 h". The remaining process steps and key parameters are completely consistent with those of embodiment 1, and the copper samarium diatomic catalyst is successfully prepared.

[0047] Example 7

[0048] This embodiment is based on the technical solution of embodiment 1, and only the reduction conditions of step (4) are adjusted: the original "heat to 400°C at a rate of 5°C / min and hold for 2 h" is replaced with "heat to 300°C at a rate of 5°C / min and hold for 1 h". The remaining process steps and key parameters are completely consistent with those of embodiment 1, and the copper samarium diatomic catalyst is successfully prepared.

[0049] Comparative Example 1

[0050] The only difference between this comparative example and Example 1 is that 1.87 g of samarium nitrate hexahydrate (4.2 mmol) was not added as a raw material in step (1). All other process steps and key parameters are completely consistent with Example 1, and the copper single-atom catalyst was successfully prepared.

[0051] Application examples

[0052] The electrode materials prepared in Examples 1-7 and Comparative Example 1 were used as working electrodes in a three-electrode flow electrolysis cell system. Anion exchange membranes were used to separate the anode and cathode flow chambers of the electrolysis cell. The electrolytes for both the cathode and anode were 1.0 M KOH. The counter electrode was a foam electrode, and the reference electrode was a silver / silver chloride (Ag / AgCl) electrode. The CO2 flow rate was 20 mL / min.

[0053] Cyclic voltammetry (CV) activation: The electrode was activated using a Shanghai Chenhua CHI 760E electrochemical workstation with a CV program. The test potential range was -0.5 to -1.9 V (vs. RHE), and the scan rate was 50 mV s. -1 After 30 cyclic scans, the electrochemical performance of the electrode reached a stable state.

[0054] Faraday efficiency (FE) test: After activation, the program is switched to constant current-time mode. During the test, the concentration of gaseous products generated at the cathode is quantitatively analyzed online by a gas chromatograph (GC, Fuli 9790II) to accurately calculate the Faraday efficiency of each product.

[0055] Figure 9 The copper samarium diatomic catalyst prepared in Example 1 was used at 50–600 mA cm⁻¹ -2 The distribution of the Faradaic efficiency of CO2 electroreduction products within the current density range is shown in the figure. As can be seen from the figure, as the current increases from 50 mA cm⁻¹... -2 Gradually increase to 400mA cm -2 The Faraday efficiency of methane shows an increasing trend and reaches a peak of 78%; when the current density is further increased to 600 mAcm -2 At the same time, the Faraday efficiency of methane remained above 60%. Meanwhile, the Faraday efficiencies of byproducts such as hydrogen, carbon monoxide, and ethylene remained at relatively low levels, indicating that the catalyst has excellent selectivity for the electroreduction of CO2 to methane.

[0056] The catalysts prepared in Examples 1-7 and Comparative Example 1 were subjected to an induction reaction at 400 mA cm⁻¹. -2 A comparison of the performance of CO2 electroreduction for methanogenesis under different current densities was conducted (results are shown below). Figure 10 As shown in the figure): The methane Faraday efficiency of Comparative Example 1 is significantly lower than that of the other examples. This result indicates that the atomic-level spatial arrangement and synergistic effect of copper and rare earth bimetals are the core factors for improving methane selectivity.

[0057] The electrode material prepared in Example 1 was placed in a flowing electrolytic cell at 400 mA cm⁻¹. -2 Continuous stability testing was conducted at industrial-grade current densities, and the results are as follows: Figure 11 As shown, throughout the test, the working potential of the working electrode (blue curve) remained stable within the range of -1 to -2 V (vs RHE), with small potential fluctuations, demonstrating the good electrochemical stability of the electrode under high current density conditions. Simultaneously, the methane Faradaic efficiency (red curve) did not show significant decay throughout the test, consistently remaining above 60%, and the product selectivity remained stable. These results indicate that the copper-smarium diatomic catalyst prepared in Example 1 can achieve high electrochemical stability under high current density conditions. -2 It can achieve long-term continuous operation for 17 hours under high current density and can stably maintain high methane selectivity, which strongly verifies the feasibility of its large-scale industrial application in the field of CO2 electrochemical reduction to methane.

[0058] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the protection scope of the present invention.

Claims

1. A method for preparing a copper-rare earth diatomic catalyst derived from a pyrolysis coordination polymer, characterized in that, Includes the following steps: 1) Add formaldehyde solution, dicyandiamide, copper salt and rare earth salt to water to form a homogeneous and stable mixture; 2) Dry the mixture obtained in step 1) to obtain a solid coordination polymer precursor, and grind it into powder; 3) The coordination polymer precursor powder is pyrolyzed under an inert atmosphere; 4) After pyrolysis, the mixture is allowed to cool naturally to room temperature, then switched to a reducing atmosphere for reduction treatment. After reduction, the mixture is cooled to obtain a copper-rare earth diatomic catalyst.

2. The method for preparing the copper-rare earth diatomic catalyst derived from the pyrolysis coordination polymer as described in claim 1, characterized in that, In step 1), the copper salt and rare earth salt used are both soluble salts, selected from at least one of nitrates, sulfates, acetates, acetylacetones and chlorides; the rare earth element is selected from any one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

3. The method for preparing the copper-rare earth diatomic catalyst derived from the pyrolysis coordination polymer as described in claim 1, characterized in that, In step 1), the molar ratio of copper salt to rare earth salt is 1:0.2~5, the mass ratio of copper salt to dicyandiamide is 1:1~10, the mass ratio of copper salt to formaldehyde solution is 1:1~5, and the mass ratio of copper salt to water is 1:5~50.

4. The method for preparing the copper-rare earth diatomic catalyst derived from the pyrolysis coordination polymer as described in claim 1, characterized in that, In step 2), the drying temperature is 90~150℃ and the drying time is 8~24 h; the obtained solid coordination polymer precursor is ground to a standard sieve of 150~250 mesh to obtain fine powder.

5. The method for preparing the copper-rare earth diatomic catalyst derived from the pyrolysis coordination polymer as described in claim 1, characterized in that, In step 3), the inert atmosphere is a nitrogen or argon atmosphere; the pyrolysis temperature is 300~600℃ and the pyrolysis time is 1~6 h.

6. The method for preparing the copper-rare earth diatomic catalyst derived from the pyrolysis coordination polymer as described in claim 1, characterized in that, In step 4), the reducing atmosphere is a hydrogen / argon mixture, wherein the volume fraction of hydrogen is 5% to 100%; the reduction temperature is 300 to 600°C and the reduction time is 1 to 6 hours.

7. A copper-rare earth diatomic catalyst derived from a pyrolysis coordination polymer, characterized in that, The catalyst is prepared by any one of claims 1-6, and comprises a nitrogen-doped carbon support and copper-rare earth diatomic active sites supported on the nitrogen-doped carbon support; the copper atoms and rare earth atoms are atomically dispersed in the form of diatomic clusters, and respectively form Cu-N coordination structures and rare earth-N coordination structures with nitrogen atoms in the nitrogen-doped carbon support.

8. The application of the copper-rare earth diatomic catalyst as described in claim 7 in the electrochemical reduction of CO2 to methane.

9. The application as described in claim 8, characterized in that, In an alkaline electrolyte and a three-electrode flow electrolytic cell system, when the current density is 400 mA cm⁻¹ -2 At that time, the Faraday efficiency of methane reached 78%.

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