Cu / Zn bimetal organic framework catalyst and application thereof

Abstract

The invention provides a Cu / Zn bimetal organic framework catalyst and application thereof. The Cu-based MOF HKUST-1 and the Zn-based MOF ZIF-8 are compounded through a coprecipitation method to prepare the Cu / Zn bimetal organic framework catalyst, by regulating and controlling geometric isolation and electronic structures of active sites of Cu and Zn, wide-range adjustment of the H2 / CO proportion in CO2 reduction products is achieved, generation of by-products is inhibited, and the diversified requirements of the chemical industry for synthesis gas are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and in particular relates to a Cu / Zn bimetallic organic framework catalyst and applications thereof. Background Art

[0002] Electrocatalytic CO2 reduction (CO2RR) to produce synthesis gas (CO / H2) is a promising carbon-neutral technology that can convert CO2 into industrially valuable chemical feedstocks. Syngas is a key feedstock in important chemical processes such as Fischer-Tropsch synthesis and methanol synthesis, and its H2 / CO ratio directly influences the selectivity of downstream products. However, existing catalytic systems still face numerous challenges in terms of selectivity, product ratio control, and reaction efficiency.

[0003] Currently, the research on electrocatalytic CO2RR to produce syngas mainly focuses on metal-based catalysts and metal-organic framework (MOF) materials. Among metal-based catalysts, Cu-based materials can produce CO and H2 simultaneously due to their unique electronic structure, but they have the defect of poor selectivity and are prone to produce formic acid, methane and even C 2+ products (such as ethylene). Although Zn-based catalysts (such as ZnO) have high selectivity for CO, the competition with the hydrogen evolution reaction (HER) is serious, which makes it difficult to control the H2 / CO ratio. It is difficult for single-metal MOFs to simultaneously optimize CO2 activation and HER inhibition, resulting in an uncontrollable H2 / CO ratio. Bimetallic catalysts (such as Cu-Zn alloys) improve the product distribution to a certain extent through metal synergistic effects, but still cannot achieve a wide range of H2 / CO ratio regulation. Therefore, there is an urgent need to develop a catalyst with high CO2RR efficiency, low by-product generation rate, wide range of adjustable H2 / CO ratio, and high catalytic performance. Summary of the Invention

[0004] The object of the present invention is to provide a Cu / Zn bimetallic organic framework catalyst.

[0005] The purpose of the present invention is to provide a method for preparing a Cu / Zn bimetallic organic framework catalyst.

[0006] The present invention also aims to provide a Cu / Zn bimetallic organic framework catalyst for use in preparing electrocatalytic CO2 reduction to produce synthesis gas.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] Cu / Zn bimetallic organic framework catalyst, comprising a bimetallic organic framework structure of Cu-based HKUST-1 and Zn-based ZIF-8.

[0009] The preparation method of the catalyst comprises the following steps:

[0010] S11. Add Cu(NO3)2·3H2O and Zn(NO3)2·6H2O to 10 mL of methanol and stir to obtain a blue solution.

[0011] S12. To the blue solution of step S11, a methanol solution of 2-methylimidazole was added and stirred at room temperature for 10 min to obtain a uniform dark blue solution;

[0012] S13. A mixed solution of 1,3,5-trichemic acid, triethylamine and methanol was added to the dark blue solution obtained in step S12;

[0013] S14. The product of step 13 was stirred at room temperature for 3 hours, centrifuged at 8000 rpm, washed, and dried to obtain a catalyst Cu / Zn-MOF-I;

[0014] S15. The product of step 13 was stirred at room temperature for 4 hours, centrifuged at 8000 rpm, washed, and dried to obtain the catalyst Cu / Zn-MOF-II.

[0015] Preferably, the molar ratio of Cu(NO3)2·3H2O to Zn(NO3)2·6H2O in step S11 is 1:1.

[0016] The methanol solution of 2-methylimidazole in step S12 is prepared by dissolving 20.0 mmol of 2-methylimidazole in 5 mL of methanol.

[0017] Preferably, the mixed solution in step S13 is prepared by taking 700 mg of 1,3,5-trichemic acid, adding 5 mL of triethylamine, dissolving the mixture, and then adding 10 mL of methanol solution and mixing.

[0018] Preferably, at a potential of -1.2 V vs RHE, the CO Faradaic efficiency of the catalyst Cu / Zn-MOF-I reaches 82%.

[0019] Preferably, at a potential of -1.2 V vs RHE, the Cu / Zn-MOF-II catalyst has a H2 Faradaic efficiency of 78%.

[0020] A use of the catalyst in preparing synthesis gas by electrocatalytic reduction of CO2.

[0021] Preferably, the synthesis gas ratio can be controlled within the range of 0.25-3.39.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] First, the Cu / Zn bimetallic organic framework catalyst provided by the present invention has high catalytic efficiency. At a potential of -1.2 V vs RHE, the CO Faradaic efficiency of Cu / Zn-MOF-I reaches 82%, and the H2 Faradaic efficiency of Cu / Zn-MOF-II reaches 78%.

[0024] Second, by regulating the geometric isolation and electronic structure of the Cu and Zn active sites, the H2 / CO ratio in the CO2 reduction product can be precisely controlled in the range of 0.25-3.39, and the total Faradaic efficiency of the synthesis gas (H2 / CO) reaches more than 90%, without the generation of C2 products, meeting the chemical industry's diverse needs for synthesis gas.

[0025] Third, the present invention prepares a Cu / Zn-dual MOF catalyst through a co-precipitation method, in which the Zn-based MOF ZIF-8 isolates the Cu active sites and regulates the adsorption capacity for *H and *CO intermediates; some carboxyl groups in the Cu-based MOF HKUST-1 break, forming oxygen vacancies, stabilizing the *COOH intermediate and promoting CO generation; this method regulates the catalyst particle size by adjusting the synthesis time, affecting the electrochemical active area (ECSA) and charge transfer efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 Scanning electron microscopy images of catalysts Cu / Zn-MOF-I and Cu / Zn-MOF-II;

[0028] Figure 2 TEM images of catalysts Cu / Zn-MOF-I and Cu / Zn-MOF-II; (a, b) are TEM images of Cu / Zn-MOF-I, (c) is TEM image of Cu / Zn-MOF-II, (d, e) are HR-TEM images of Cu / Zn-MOF-I, and (f) is HR-TEM image of Cu / Zn-MOF-II;

[0029] Figure 3 Structural analysis diagrams of Cu / Zn-MOF-I, Cu / Zn-MOF-II, ZIF-8, and HKUST-1, where (a) is the XRD pattern and (b) is the Fourier transform infrared spectrum;

[0030] Figure 4 XPS spectra of catalysts Cu / Zn-MOF-I and Cu / Zn-MOF-II, where (a) is the XPS scan spectrum and (b) is C1s;

[0031] Figure 5 XPS spectra of Cu / Zn-MOF-I, Cu / Zn-MOF-II, ZIF-8 and HKUST-1 catalysts; (a) is Cu 2p and (b) is Zn 2p.

[0032] Figure 6 XPS O 1s spectra; (a) is Cu / Zn-MOF-I, (b) is Cu / Zn-MOF-II, and (c) is the relative content of different oxygen atoms in the catalyst.

[0033] Figure 7 LSV curves of the electrodes in 0.1 M KHCO3 saturated with Ar and CO2, where (a) is HKUST-1, (b) is ZIF-8, (c) is Cu / Zn-MOF-I, and (d) is Cu / Zn-MOF-II;

[0034] Figure 8 The Faraday efficiency diagram of CO2 reduction products of each catalyst, where (a) is ZIF-8, (b) is HKUST-1, (c) is Cu / Zn-MOF-I, and (d) is Cu / Zn-MOF-II;

[0035] Figure 9 The electrocatalytic CO2 reduction performance diagram of catalysts Cu / Zn-MOF-I, Cu / Zn-MOF-II, HKUST-1 and ZIF-8 at different potentials, where (a) is the total Faraday efficiency of H2 and CO, (b) is H2 / CO, and (c) is the range distribution of synthesis gas regulated by catalysts Cu / Zn-MOF-I and Cu / Zn-MOF-II;

[0036] Figure 10 Nyquist plots of different catalysts;

[0037] Figure 11 CV graphs and double-layer capacitance values of catalysts Cu / Zn-MOF-I and Cu / Zn-MOF-II at different scan rates;

[0038] Figure 12 CV scans of ZIF-8, Cu / Zn-MOF-I and Cu / Zn-MOF-II in CO2-saturated 0.1M KHCO3 electrolyte. DETAILED DESCRIPTION

[0039] The following specific descriptions are exemplary and are intended to provide further explanation of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solutions of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements shall fall within the scope of protection of the present invention.

[0040] Unless otherwise specified, the test methods used in the following experimental examples are conventional methods.

[0041] Example 1: Preparation and morphology analysis of Cu / Zn-bi-MOF catalyst

[0042] Cu(NO₃)₂·3H₂O (1.21 g, 5.0 mmol) and Zn(NO₃)₂·6H₂O (1.49 g, 5.0 mmol) were added to 10 mL of methanol and stirred to obtain a blue solution. 2-Methylimidazole (1.64 g, 20.0 mmol) was dissolved in 5 mL of methanol and added to the solution. Stirring was continued at room temperature for 10 minutes, resulting in a uniform dark blue solution. A 10 mL methanol solution containing 1,3,5-pyromellitic acid (H₃BTC, 700 mg, 3.33 mmol) and triethylamine (TEA, 5 mL) was then added to the solution with stirring. The reaction was stirred at room temperature for 3 hours. After completion of the reaction, the reaction was centrifuged at 8000 rpm, and the solid product was washed three times with methanol and dried in a vacuum oven at 80°C overnight to obtain the Cu / Zn-MOF-I catalyst.

[0043] The preparation method was the same as that of Cu / Zn-MOF-I. 10 mL of methanol solution containing H3BTC (700 mg, 3.33 mmol) and TEA (5 mL) was added to the dark blue solution under stirring, and the mixture was stirred at room temperature for 4 h. The solution was then centrifuged, washed, and dried to obtain the Cu / Zn-MOF-II catalyst.

[0044] The morphology of Cu / Zn-bi-MOF catalyst synthesized by co-precipitation method changes with the synthesis time. Figure 1 As shown in the figure, both catalysts are composed of irregular small particles of uneven size, accumulated into clusters; the particles of Cu / Zn-MOF-II are larger than those of Cu / Zn-MOF-I. The smaller the catalyst particles, the larger the electrochemical catalytic active area is likely to be. Energy dispersive X-ray (EDS) spectroscopy results show that the Cu, Zn, O, and N elements in Cu / Zn-MOF-I and Cu / Zn-MOF-II are uniformly distributed, indicating that the HKUST-1 and ZIF-8 components in the prepared dual MOF catalyst are uniformly dispersed.

[0045] The morphology, structure and Cu / Zn site distribution of Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts were further analyzed by TEM and HR-TEM characterization. Figure 2 As shown in Figure 2, the Cu / Zn dual MOF catalyst has a block-like stacking structure, and the structure of the Cu / Zn-MOF-I catalyst is slightly looser than that of the Cu / Zn-MOF-II catalyst, which is consistent with the SEM characterization results. Figure 2 As can be seen from (df), there are dispersed Cu and Zn metal particles and partial structures composed of non-metals in the sample, and the metal sites in Cu / Zn-MOF-I are denser than those in Cu / Zn-MOF-II, which further indicates that Cu / Zn-MOF-II has a relatively fluffy MOF combination structure, and the Cu-Zn bimetallic sites in Cu / Zn-MOF-I have a closer distance.

[0046] Example 2: Composition and structure analysis of Cu / Zn-bi-MOF catalyst

[0047] The crystal structures of Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts were characterized by X-ray diffraction spectroscopy (XRD). Figure 3 (a). It can be clearly observed from the figure that the ZIF-8 sample has three characteristic peaks at 7.2°, 10.2° and 12.5°, which are respectively attributed to the (011), (002) and (112) crystal planes of the ZIF-8 structure, indicating that high-purity ZIF-8 crystals were successfully synthesized; the HKUST-1 sample has typical characteristic peaks of (200), (220), (222) and (400) crystal planes at 6.6°, 9.4°, 11.5° and 13.4°, indicating that high-crystallinity HKUST-1 catalyst was successfully prepared. Compared with pure ZIF-8 and HKUST-1 catalysts, Zn / Cu-MOF-I and Zn / Cu-MOF-II show a characteristic peak distribution of the combination of the two, and the characteristic peaks attributed to the ZIF-8 structure are relatively stronger, while the peaks attributed to HKUST-1 are relatively weaker, which indicates that the content of ZIF-8 in the dual MOF structure is higher and the crystallinity of ZIF-8 is higher. To confirm the above results, the molecular structures of the above catalysts were further characterized using Fourier transform infrared (FT-IR) spectroscopy. Figure 3 As shown in (b), Cu / Zn-MOF-I and Cu / Zn-MOF-II have the highest peaks at 1620 cm -1 、1438cm -1 、1363cm -1 、1148cm -1 、1110cm -1 and 421cm-1 There is an obvious infrared absorption peak at 1620cm -1 、1438cm -1 and 1363cm -1 The absorption peak is attributed to the Cu 2+ -COO - The stretching vibration of the dual MOF catalyst is significantly weakened compared to HKUST-1. This test result shows that the BTC in the dual MOF catalyst is 3- -COO in the ligand - The chemical environment of the molecule changes or the molecule is partially broken. -1 The infrared absorption peak at 1148 cm corresponds to the stretching vibration of the CO bond in the MOF structure. -1 The absorption peak at 421 cm is attributed to the vibration absorption peak of the CN bond in ZIF-8. -1 The presence of these characteristic infrared spectroscopy peaks further confirms the formation of a Cu / Zn-bi-MOF structure. Notably, the infrared spectroscopy peaks attributable to ZIF-8 are more pronounced, while the peaks attributable to HKUST-1 are very weak, further demonstrating that the ZIF-8 structure in the bi-MOF catalyst prepared by co-precipitation is more stable, consistent with the XRD results.

[0048] The Cu and Zn metal content of the two dual-MOF catalysts was determined using inductively coupled plasma elemental analysis (ICP-OES). The test results show that while the Cu and Zn content of the Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts differ slightly, the Cu / Zn ratio is essentially the same (around 0.88), with the Zn content being higher than the Cu content, consistent with the XRD and FTIR results. This suggests that, although the catalyst particle size changes with increasing synthesis time, the Cu / Zn ratio remains essentially unchanged. This suggests that during the catalyst synthesis process, the reaction rates of the two MOFs are similar, and an increase in synthesis time does not result in differences in the relative content of the elements. Therefore, the differences in the electrocatalytic performance of the dual-MOF catalysts obtained with different synthesis times are unrelated to the Cu / Zn ratio of the catalysts.

[0049] XPS was further used to analyze the surface composition and chemical valence of ZIF-8, HKUST-1, Cu / Zn-MOF-I, and Cu / Zn-MOF-II catalysts. Figure 4As shown in the full spectrum of Cu / Zn-MOF-I and Cu / Zn-MOF-II dual MOF samples, there are five different binding energy signals: C 1s (284-291eV), O 1s (528-538eV), N 1s (398-402eV), Cu 2p (936-967eV) and Zn 2p (1020-1046eV), which are consistent with the constituent elements in the dual MOF structure. First, the spectra of all samples were calibrated with C (284.8eV) as the benchmark. By analyzing the C1s spectrum, it was found that compared with the pure HKUST-1 sample, the peak belonging to OC=O in the two dual MOF catalyst samples was weakened. The OC=O peak corresponds to the carboxyl carbon (-COO) of the ligand in HKUST-1. - ). This test result shows that the ligand in the Cu-MOF structure in the dual MOF catalyst may be from Cu 2+ There is a detachment on the node, resulting in Cu 2+ -COO - The bond is broken, which is consistent with the previous XRD and FT-IR test results.

[0050] The chemical state distribution of Cu and Zn elements was further analyzed. Figure 5 (a) The Cu 2p spectrum shows typical binding energy peaks at 934.4eV and 953.8eV, which are respectively attributed to Cu 2+ Cu 2p 3 / 2 and Cu 2p 1 / 2 characteristic peaks, and obvious satellite peaks. In addition, no other valence states (such as Cu + / Cu 0 ). Further comparison revealed that the Cu 2p spectra of Cu / Zn-MOF-I and Cu / Zn-MOF-II belong to Cu 2+ The satellite peaks of Cu / Zn-MOF-I and Cu / Zn-MOF-II are significantly weaker than those of HKUST-1. 3 / 2 Peaks and Cu 2p in HKUST-1 3 / 2 Compared with the peaks, the peaks all shifted toward lower binding energy, which indicates that the electron density around Cu has changed. Combined with the previous analysis results of XRD, FT-IR and XPSC1s spectra, it can be concluded that the partial detachment or breakage of HKUST-1 ligands leads to the change of Cu. 2+ The coordination environment of the metal site changes, which leads to a decrease in the Cu 2p binding energy. In addition, we also tested and analyzed the Zn 2p spectra of all Zn-containing catalysts. Figure 5As shown in (b), the Zn 2p spectra of all catalysts show a set of spin-orbit doublet peaks at 1021.8eV and 1044.7eV, corresponding to the Zn 2+ Zn 2p 3 / 2 and Zn 2p 1 / 2 Orbital. Zn 2p with pure ZIF-8 catalyst 3 / 2 The peak positions of Zn 2p in Cu / Zn-MOF-I and Cu / Zn-MOF-II are compared. 3 / 2 There is no obvious shift in the peak position, indicating that the electronic structure of Zn in the dual MOF catalyst has not changed significantly, the coordination environment of Zn itself remains stable, and the binding energy remains unchanged.

[0051] If the carboxyl group breaks or detaches in the dual MOF catalyst, it is often accompanied by the generation of oxygen defects, and the concentration of oxygen defects in the catalyst will also have a certain impact on the electrocatalytic properties of the catalyst. Therefore, the XPS O 1s spectra of the catalysts Cu / Zn-MOF-I and Cu / Zn-MOF-II were analyzed, as shown in the following figure: Figure 6 The O 1s spectrum consists of three different peaks, the oxygen peaks at 530.8eV, 531.6eV and 532.7eV, which correspond to the lattice oxygen (O L ), oxygen vacancies (Ov) and surface adsorbed oxygen molecules (O C ) (such as -OH, H2O). Perform semi-quantitative analysis on the peaks of different oxygen species in the O1s spectrum by fitting integration, such as Figure 6 (c) A comparison reveals that the concentration of oxygen vacancies in Cu / Zn-MOF-I is higher than that in Cu / Zn-MOF-II. Studies have shown that oxygen vacancies can act as Lewis acidic sites, preferentially stabilizing *COOH, a key intermediate in CO2 reduction, and promoting CO production through localized electron regulation.

[0052] Example 3: Electrocatalytic CO2 Reduction Performance of Cu / Zn-Dual MOF Catalyst

[0053] In an H-type electrolytic cell, a classic three-electrode system was used to conduct electrochemical tests on the CO2RR performance of various catalysts. First, the electrochemical activities of ZIF-8, HKUST-1, Cu / Zn-MOF-I and Cu / Zn-MOF-II in 0.1M KHCO3 electrolyte solution saturated with Ar and CO2 were evaluated by linear sweep voltammetry (LSV). Figure 7As shown, when tested in an Ar-saturated electrolyte solution, the current density is primarily due to the hydrogen evolution reaction (HER). However, when the electrolyte solution is CO2-saturated, a higher current density indicates CO2RR activity. HKUST-1 exhibits a higher current density in a CO2-saturated electrolyte solution, indicating superior CO2RR activity. However, in a CO2-saturated electrolyte, the current density of ZIF-8 is much lower than that of Cu / Zn-MOF-I, Cu / Zn-MOF-II, and HKUST-1, indicating that ZIF-8 is less active in electrocatalytic CO2RR. The Cu / Zn-MOF-I catalyst achieves a higher current density in a CO2-saturated electrolyte solution, indicating its higher CO2RR activity. In contrast, the Cu / Zn-MOF-II catalyst exhibits a higher current density in an Ar-saturated electrolyte solution, with its HER activity significantly higher than its CO2RR activity. This suggests that the final H2 content on this catalyst may be dominant.

[0054] The catalytic performance of ZIF-8, HKUST-1, Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts at different potentials was further systematically evaluated at high current density. Figure 8 As shown, both ZIF-8 and HKUST-1 generate multiple products, including H2, CO, and HCOOH. For the ZIF-8 catalyst, the H2 Faradaic efficiency decreases with increasing potential, while the total Faradaic efficiency of the generated C1 products (CO and HCOOH) increases, indicating that ZIF-8 exhibits superior CO2RR activity at high potentials. The H2 Faradaic efficiency of the HKUST-1 catalyst did not change significantly throughout the test range. At high potentials, C2H4 appears in the CO2 reduction products corresponding to HKUST-1, indicating that the pure HKUST-1 catalyst surface can undergo CC coupling to generate C2 products at high potentials. Notably, the products of both the ZIF-8 and HKUST-1 catalysts contain significant amounts of formic acid. In contrast, the electrocatalytic CO2 reduction products of Cu / Zn-MOF-I and Cu / Zn-MOF-II are primarily H2 and CO, with formic acid production suppressed. These results indicate that the composite of ZIF-8 and HKUST-1 catalysts changes the adsorption capacity of Cu at the key active site for the key intermediate of formic acid, resulting in a decrease in the Faradaic efficiency of formic acid in the dual-MOF catalyst product.

[0055] The product distribution of CO and H2 prepared by dual MOF catalysts was further analyzed. Figure 8As can be seen, at the same potential, the dual-MOF catalyst Cu / Zn-MOF-I has significantly better selectivity for CO than Cu / Zn-MOF-II, and the hydrogen evolution reaction is suppressed. This may be attributed to the Cu / Zn-MOF-I sample having closer Cu / Zn dual sites, which is conducive to CO2 activation and intermediate conversion. As the potential increases, the selectivity for CO increases linearly, while the selectivity for H2 gradually decreases. The Faraday efficiency of CO for the Cu / Zn-MOF-I sample reaches 80.2% at a potential of -1.2V vs RHE. In the Cu / Zn-MOF-II product, the selectivity for H2 is greater than the selectivity for CO, which is consistent with the result shown by LSV that the HER activity is significantly higher than the electrocatalytic CO2 reduction activity.

[0056] The total FE of the two syngas components, CO and H2, obtained by the dual MOF catalyst at different test potentials reached more than 90%, such as Figure 9 As shown in (a). As the potential increases, no C2 product is detected in the product, and the total FE is close to 100%, which indicates that the Cu / Zn dual MOF hinders the CC coupling pathway, thereby improving the purity of the synthesis gas. The H2 / CO ratio is further determined by calculating the H2 and CO contents and calculating their Faradaic efficiency (FE). The results are shown in Figure 9 (b). As the potential increases, the H2 / CO ratio of the product obtained by the electrocatalytic CO2 of catalyst HKUST-1 shows a trend of first decreasing and then increasing, with the ratio range of 2-3.03. Similarly, at the test potential, the H2 / CO ratio of the product obtained by the electrocatalytic CO2 of catalyst ZIF-8 shows a trend of first increasing and then decreasing, with the range of 0.7-2.64. The composition of the synthesis gas obtained by Cu / Zn dual MOF catalyst at different reaction times is shown in Figure 2. Figure 9 As shown in (c). The Faradaic efficiency of CO in the products of the Cu / Zn-MOF-I catalyst is consistently greater than that of H2, enabling low-range H2 / CO ratio regulation in the syngas range of 0.25-0.79. The Cu / Zn-MOF-II catalyst exhibits even higher selectivity for H2, achieving a Faradaic efficiency of 78% for H2 at a potential of -0.9 V vs RHE, enabling high-range H2 / CO ratio regulation in the syngas range of 1.37-3.39. Based on the experimental results for the Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts, it can be inferred that rationally designed Cu / Zn dual-MOF catalysts can not only produce relatively pure syngas product components at different test potentials, but also exhibit a wider H2 / CO ratio range, adjustable between 0.25-3.39. Compared with most electrocatalysts used for syngas production, the dual MOF catalyst exhibits superior performance and allows the H2 / CO ratio to be adjusted over a wide range, making it suitable for Fischer-Tropsch synthesis processes with different requirements.

[0057] Example 4 Comparison of catalysts Cu / Zn-MOF-I and Cu / Zn-MOF-II

[0058] By adjusting the reaction time of the synthesized catalysts, Cu / Zn dual MOF catalysts with varying catalytic performance were obtained. The combination of the two MOFs can improve the selectivity of syngas components in the electrocatalytic CO2 product, enabling the production of high-purity syngas at different potentials. Based on this, the authors explored the composite regulation mechanism of the dual MOF catalyst.

[0059] Firstly, the electrochemical impedance spectroscopy (EIS) of HKUST-1, ZIF-8, Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts was measured. Figure 10 . It can be observed from the figure that there are obvious differences in the radii of the curves. The difference in the radius of the curve reflects the difference in charge transfer resistance. The larger the diameter, the greater the charge transfer resistance. After comparison, it was found that the charge transfer resistance of pure ZIF-8 was significantly higher than that of HKUST-1, Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts, indicating that the Cu-MOF catalyst has better charge transfer ability among the dual MOF catalysts. The charge transfer ability of the dual MOF catalyst Cu / Zn-MOF-I, which is closer to Cu-Zn, is between the two, while Cu / Zn-MOF-II has better charge transfer ability.

[0060] Previous studies have shown that the ZIF-8 component of the dual-MOF catalyst maintains structural stability, primarily serving to geometrically isolate the Cu sites. The partial detachment or breakage of the carboxylic acid groups in the HKUST-1 component increases the electron cloud density around the Cu sites, resulting in changes in electron localization. This shift modulates the reaction activation energies of different pathways and influences the catalyst surface's ability to generate and stabilize key reaction intermediates for different products. Due to the suppression of the formic acid formation pathway and the CC coupling reaction, the catalyst produces only pure syngas (H2 and CO) during the electrocatalytic CO2 reduction process, effectively regulating the electrocatalytic CO2 product selectivity.

[0061] In addition, there are also performance differences between the two dual-MOF catalysts. The Cu / Zn-MOF-I catalyst's products are dominated by CO, enabling low-ratio regulation of the synthesis gas H2 / CO in the range of 0.25-0.79. The Cu / Zn-MOF-II catalyst, on the other hand, has a higher selectivity for H2, enabling high-ratio regulation of the synthesis gas H2 / CO in the range of 1.37-3.39. Further investigation was conducted to determine the reasons for the starkly different performances of the Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts.

[0062] From the previous characterization results, it can be seen that the Cu / Zn-MOF-I and Cu / Zn-MOF-II catalysts have the same Cu / Zn ratio and only differ in particle size. Therefore, it is speculated that the difference in their product selectivity may be due to the particle size. First, the electrochemical active area (ECSA) of the two catalysts was tested, and the results are shown in Figure 2. Figure 11 Cu / Zn-MOF-I has a higher ECSA value, and the higher catalytic surface area may expose more Cu 2+ 、Zn 2+ The dual metal sites enhance the CO pathway activation and improve CO selectivity, while the ECSA of Cu / Zn-MOF-II is relatively low.

[0063] The small particle size of the catalyst Cu / Zn-MOF-I gives it a higher ECSA, indicating that it exposes more active sites, which may further affect the reaction path. *H and *CO2·- are key intermediates in the CO2RR reaction. The adsorption strength of the catalyst on *CO2·- and *H directly affects the selectivity of H2 and CO in the final product. The adsorption strength of *H on the catalyst surface has a crucial influence on the formation of H2 and carbon-containing products. The dominant products in the two dual MOF catalysts are different, and the adsorption strength of *H on their catalytic sites must be different. In order to study the difference in *H adsorption on different catalysts, we tested the electrochemical cyclic voltammetry curves of ZIF-8, Cu / Zn-MOF-I and Cu / Zn-MOF-II in CO2-saturated 0.1M KHCO3. The results are shown in Figure 2. Figure 12As shown. The peaks at ~0.4V and 0.1-0.2V correspond to the desorption and adsorption peaks of *H. Analysis of the peak positions for each catalyst shows that a negative shift in the adsorption peak potential corresponding to the catalytic reaction indicates a weakened adsorption capacity of the catalyst surface for H, potentially reducing the *H coverage on the catalyst surface. The *H desorption and adsorption peaks for ZIF-8 are located at 0.56V and 0.03V, respectively, while those for Cu / Zn-MOF-I and Cu / Zn-MOF-II shift further to 0.59V / 0.01V and 0.67V / 0.05V. Compared to the difference between the hydrogen desorption and adsorption peaks of ZIF-8, the difference between the hydrogen desorption and adsorption peaks of Cu / Zn-MOF-I and Cu / Zn-MOF-II is larger, with higher peaks and broader peaks, indicating that Cu / Zn-MOF-I and Cu / Zn-MOF-II have stronger adsorption capacities for *H than ZIF-8. Furthermore, the Cu / Zn-MOF-II catalyst exhibits a stronger affinity for H than Cu / Zn-MOF-1, leading to higher H selectivity for electrocatalytic CO2 reduction using Cu / Zn-MOF-II than Cu / Zn-MOF-I. A larger difference between the adsorption and desorption peaks indicates a significant difference in the free energy changes between adsorption and desorption, likely due to strong *H adsorption or slow desorption kinetics. This may result in hydrogen atoms occupying active sites on the catalyst surface, inhibiting CO2 activation (competing with intermediates such as *COOH for adsorption sites), reducing the selectivity of CO2RR, and favoring H2 production. If the catalyst has a moderate adsorption capacity for H and a small peak position difference, the adsorption and desorption of H can be balanced.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Cu / Zn bimetallic organic framework catalyst, characterized by The catalyst comprises a bimetallic organic framework structure of Cu-based HKUST-1 and Zn-based ZIF-8.

2. The Cu / Zn bimetallic organic framework catalyst according to claim 1, characterized in that The preparation method of the catalyst comprises the following steps: S11. Add Cu(NO3)2·3H2O and Zn(NO3)2·6H2O to 10 mL of methanol and stir to obtain a blue solution. S12. To the blue solution of step S11, a methanol solution of 2-methylimidazole was added and stirred at room temperature for 10 min to obtain a uniform dark blue solution; S13. A mixed solution of 1,3,5-trichemic acid, triethylamine and methanol was added to the dark blue solution obtained in step S12; S14. The product of step S13 was stirred at room temperature for 3 hours, centrifuged at 8000 rpm, washed, and dried to obtain a catalyst Cu / Zn-MOF-I; S15. The product of step S13 was stirred at room temperature for 4 hours, centrifuged at 8000 rpm, washed, and dried to obtain the catalyst Cu / Zn-MOF-II.

3. The Cu / Zn bimetallic organic framework catalyst according to claim 2, characterized in that The molar ratio of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O in step S11 is 1:

1.

4. The Cu / Zn bimetallic organic framework catalyst according to claim 2, characterized in that The methanol solution of 2-methylimidazole in step S12 is prepared by dissolving 20.0 mmol of 2-methylimidazole in 5 mL of methanol.

5. The Cu / Zn bimetallic organic framework catalyst according to claim 2, characterized in that The mixed solution in step S13 is prepared by taking 700 mg of 1,3,5-trichemic acid, adding 5 mL of triethylamine, dissolving the mixture, and then adding 10 mL of methanol solution and mixing.

6. The Cu / Zn bimetallic organic framework catalyst according to claim 2, characterized in that The washing method in step S14 and step S15 is washing with methanol three times.

7. The Cu / Zn bimetallic organic framework catalyst according to claim 2, characterized in that At a potential of -1.2 V vs RHE, the CO Faradaic efficiency of the Cu / Zn-MOF-I catalyst reaches 82%.

8. The Cu / Zn bimetallic organic framework catalyst according to claim 2, characterized in that At a potential of -1.2 V vs RHE, the Cu / Zn-MOF-II catalyst has a H2 Faradaic efficiency of 78%.

9. Use of the catalyst according to claim 1 in preparing synthesis gas by electrocatalytic reduction of CO2.

10. Use of the catalyst according to claim 8 in preparing synthesis gas by electrocatalytic CO2 reduction, characterized in that: The synthesis gas ratio can be adjusted within the range of 0.25-3.39.

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