Catalyst for regulating nitrogen distribution in nitrogen-doped carbon based on copper as well as preparation method and application of catalyst

Abstract

The invention discloses a preparation method and application of a catalyst for regulating nitrogen distribution in nitrogen-doped carbon based on copper. The preparation process of the catalyst comprises the following steps: uniformly mixing a chelating agent and a copper salt aqueous solution to obtain a precursor solution; adjusting the pH value of the precursor solution to 10-12, then adding organic matters containing nitrogen and carbon, fully dispersing, and then sequentially drying, calcining, washing and carbonizing, so as to obtain the composite material. According to the catalyst, based on the synergistic effect between Cu and N, by controlling the introduction amount of the Cu element, regulation and control of the pore structure of the catalyst are achieved, regulation and control of nitrogen species are also achieved, then the activity of carbon dioxide reduction and hydrogen evolution reactions in electrochemistry are effectively balanced, and linear regulation and control of the two reactions can be achieved only through potential control. Tests show that the adjustment range of the Cu5 / N-COA10 catalyst on FECO and FEH is 10%-90% when the Cu5 / N-COA10 catalyst is in the potential range of-0.5 V to-1.3 V, the Cu5 / N-COA10 catalyst shows good linear characteristics, and the technical problem that the Faraday efficiencies of CO and H2 cannot be synchronously adjusted in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to a copper-based catalyst, in particular to a catalyst based on copper for regulating the distribution of nitrogen in nitrogen-doped carbon and a preparation method and application thereof, and belongs to the technical field of electrocatalytic synthesis gas. BACKGROUND

[0002] Synthesis gas is one of the key raw materials for various industrial processes such as Fischer-Tropsch synthesis and fermentation. The main methods for large-scale production of synthesis gas, such as water-gas shift reaction and steam reforming of natural gas, all face the problems of high energy consumption, complex parameters and the need for frequent adjustment and optimization of synthesis gas ratio. Through the two-electron (2e - ) pathway of the electrochemical CO2 reduction reaction (eCO2RR) coupled with the hydrogen evolution reaction (HER), synthesis gas can be directly synthesized, which is an environmentally friendly and flexible downstream industry solution, can reduce gas transportation and large-scale on-site storage requirements, and thus improve the safety of the production process.

[0003] Although there have been many studies on eCO2RR for CO or HER for H2, the technology is still limited by high thermodynamic barriers, slow electron transfer kinetics, and low activity and selectivity caused by competing reactions. In the prior art, catalysts mainly include noble metal catalysts, transition metal catalysts and non-metal catalysts. However, in specific industrial processes, there are still problems in adapting to different reaction processes and reactor parameters, so how to balance the activities of CO2 reduction reaction and hydrogen evolution reaction to achieve dynamic regulation of synthesis gas composition still faces major challenges.

[0004] Some research institutions in the prior art have reported catalysts with controllable CO / H2 ratio such as Ag-P@HCS (0.92-0.39) and Pd-SnO2 (3.6-0.24), but the above systems all rely on the selectivity of noble metal for eCO2RR to CO, and cannot achieve simultaneous adjustment of the Faraday efficiency of CO and H2. In addition, noble metal catalysts also face problems such as high cost and difficult maintenance, which further hinder the large-scale popularization and application of electrocatalytic synthesis gas. SUMMARY

[0005] In view of the problems in the prior art, the first object of the present application is to provide a catalyst based on copper for regulating the distribution of nitrogen in nitrogen-doped carbon. Based on the synergistic effect between Cu-N, by controlling the amount of Cu element introduced, the catalyst not only realizes the regulation of the pore structure of the catalyst, but also realizes the regulation of the nitrogen species, thereby effectively balancing the activities of eCO2RR and HER, and linear regulation of eCO2RR and HER reactions can be achieved by only controlling the potential.

[0006] A second object of the present application is to provide a preparation method of a catalyst for regulating the nitrogen distribution in nitrogen-doped carbon based on copper. The method uses a calcination-carbonization synergistic process to convert the Cu ion-chelating agent-protein network into an armored catalyst structure with reduced copper (Cu 0 / Cu + ) as the core and nitrogen-doped carbon as the outer coating. This not only effectively prevents metal particle agglomeration, improves catalytic activity and stability, but also ensures stronger adsorption of intermediates, thereby achieving a CO-dominant selectivity in the eCO2RR reaction and effectively avoiding side reactions.

[0007] A third object of the present application is to provide an application of a catalyst for regulating the nitrogen distribution in nitrogen-doped carbon based on copper, which is used in electrocatalytic synthesis gas reactions. Based on the characteristics of the above-mentioned catalyst, it is applied to electrocatalytic synthesis gas reactions, ensuring that the electronic efficiency of synthesis gas reaches 100%, and also achieving linear regulation of eCO2RR and HER reactions. Tests show that the Cu5 / N-COA 10 catalyst has a regulation range of FECO and FEH2 of 10%~90% and exhibits good linear characteristics in the working potential range of-0.5 V~ -1.3 V, solving the technical problem of the inability to simultaneously regulate the Faraday efficiencies of CO and H2 in the prior art.

[0008] To achieve the above technical objectives, the present application provides a preparation method of a catalyst for regulating the nitrogen distribution in nitrogen-doped carbon based on copper, which comprises: uniformly mixing a chelating agent with a copper salt aqueous solution to obtain a precursor solution; adjusting the pH of the precursor solution to 10~12 and then adding organic matter containing nitrogen and carbon, and then drying, calcining, washing, and carbonizing in sequence to obtain the catalyst.

[0009] The molar ratio of the chelating agent to copper ions in the copper salt aqueous solution is 1:0.8~1.2, and the molar mass ratio of copper ions to organic matter in the copper salt aqueous solution is 1:1~20 mol / kg.

[0010] In the technical solution provided by the present application, the key lies in the regulating effect of Cu on N elements in nitrogen-doped carbon. Therefore, if the amount of Cu added is too much, it is difficult to form an armored catalyst structure, which is not conducive to electrocatalytic reactions. On the contrary, if the amount of Cu added is too small, there are fewer Cu cores and weaker synergistic regulation of N, which cannot effectively achieve linear regulation of eCO2RR and HER reactions.

[0011] As a preferred scheme, the copper salt aqueous solution is at least one of copper nitrate, copper sulfate, and copper chloride.

[0012] ​As a preferred embodiment, the pH adjuster for the precursor solution is sodium hydroxide and / or potassium hydroxide.

[0013] As a preferred embodiment, the organic matter is plant protein and / or animal protein.

[0014] As a preferred embodiment, the plant protein is at least one of woody oilseed protein such as camellia oleifera, legume protein such as soybean, and nut protein such as walnut.

[0015] As a preferred embodiment, the animal protein is at least one of dairy products, meat products, and egg products.

[0016] As a preferred embodiment, when the organic matter is plant protein, the molar mass ratio of copper ions to plant protein in the copper salt aqueous solution is 1:1~10 mol / kg.

[0017] As a preferred embodiment, when the organic matter is animal protein, the molar mass ratio of copper ions to plant protein in the copper salt aqueous solution is 1:1~13 mol / kg.

[0018] In this invention, the raw material for nitrogen-doped carbon is primarily protein, more preferably plant protein. Plant proteins have lower sulfur and nitrogen content than animal proteins, but higher potassium, phosphorus, and oxygen content. During carbonization, they can better participate in pore formation, thereby creating a defect-rich carbon framework that facilitates the encapsulation and embedding of Cu. Furthermore, because plant proteins have a lower sulfur content, they have less "toxic" effect on Cu, making it easier to achieve the goal of controlling the type of N element through Cu to balance the carbon dioxide reduction reaction and the hydrogen evolution reaction, thus making the electrocatalytic syngas reaction more likely to produce linear characteristics.

[0019] As a preferred embodiment, the drying method is at least one of baking, freeze drying, and vacuum drying.

[0020] As a preferred embodiment, the calcination and carbonization are both carried out under a protective atmosphere, namely nitrogen and / or argon.

[0021] As a preferred embodiment, the calcination conditions are as follows: under a protective atmosphere, the temperature is raised from room temperature to 600~800℃, held for 3~5 hours, and then cooled to room temperature in the furnace; the carbonization conditions are as follows: under a protective atmosphere, the temperature is raised from room temperature to 800~1000℃, held for 1~3 hours.

[0022] As a preferred embodiment, the washing process is as follows: first, wash with 4-8M nitric acid 3-5 times, then wash with deionized water until the washing solution is neutral.

[0023] The present invention also provides a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon, obtained by any of the preparation methods described above.

[0024] The present invention also describes the application of a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon for electrocatalytic synthesis gas reaction. The process is as follows: using catalyst-modified carbon paper as the working electrode, and using a saturated CO2 or saturated N2 bicarbonate aqueous solution as the reaction liquid, CO2 electrocatalytic synthesis gas reaction is carried out.

[0025] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0026] 1) The catalyst provided by this invention is based on the synergistic effect between Cu and N. By controlling the amount of Cu introduced, not only is the pore structure of the catalyst regulated, but also the nitrogen species are regulated, thereby effectively balancing the activities of eCO2RR and HER. The linear regulation of the eCO2RR and HER reactions can be achieved by simply controlling the potential.

[0027] 2) The preparation method provided by this invention employs a calcination-carbonization synergistic process to transform the Cu ion-chelating agent-protein network into a reduced copper (Cu) network. 0 / Cu + A nitrogen-doped carbon-coated armored catalyst structure, with a core of [core material], generates electron-rich Cu sites while adjusting the proportion of nitrogen species in the catalyst. This not only prevents metal particle agglomeration and improves catalytic activity and stability, but also ensures [catalytic stability]. The adsorption of intermediates enables CO to selectively dominate the eCO2RR reaction, effectively avoiding side reactions.

[0028] 3) In the technical solution provided by this invention, based on the characteristics of the above-mentioned catalyst, it is applied to the electrocatalytic syngas reaction. While ensuring that the syngas electron efficiency reaches 100%, it can also achieve linear control of the eCO2RR and HER reactions. Testing shows that Cu5 / N-COA... 10 The catalyst exhibits good linearity with an adjustment range of 10% to 90% for FECO and FEH2 within the working potential range of -0.5V to -1.3V, solving the technical problem that the Faraday efficiency of CO and H2 cannot be adjusted synchronously in the existing technology. Attached Figure Description

[0029] Figure 1 Electron micrographs of Examples 1-3 and Comparative Examples 1 and 2;

[0030] in, Figure 1 (a) is N-COA 10 Scanning electron microscope image, Figure 1 (b) is Cu1 / N-COA10 Scanning electron microscope image, Figure 1 (c) is Cu5 / N-COA 10 Scanning electron microscope image, Figure 1 (d) is Cu 10 / N-COA 10 Scanning electron microscope image, Figure 1 (e) is Cu 20 / N-COA 10 Scanning electron microscope image, Figure 1 (f) is Cu5 / N-COA 10 High-resolution transmission electron microscopy image.

[0031] Figure 2 The electrocatalytic synthesis gas performance of Examples 1-3 and Comparative Example 2 is shown in the figure. The reaction solution is 0.5 MkHCO3 aqueous solution under saturated N2.

[0032] in, Figure 2 (a) is Cu1 / N-COA 10 , Figure 2 (b) is Cu5 / N-COA 10 , Figure 2 (c) is Cu 10 / N-COA 10 , Figure 2 (d) is Cu 20 / N-COA 10 .

[0033] Figure 3 The electrocatalytic synthesis gas performance of Examples 1-3 and Comparative Example 2 is shown in the figure. The reaction solution is 0.5 MkHCO3 aqueous solution under saturated CO2.

[0034] in, Figure 3 (a) is Cu1 / N-COA 10 , Figure 3 (b) is Cu5 / N-COA 10 , Figure 3 (c) is Cu 10 / N-COA 10 , Figure 3 (d) is Cu 20 / N-COA 10 . Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying tables. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] This embodiment provides a method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon. The specific process is as follows:

[0038] 1) Mix 5 mmol EDTA and 5 mL 1 mol / L copper nitrate solution evenly and then sonicate for 30 min to obtain the precursor solution;

[0039] 2) Add NaOH to the precursor solution to adjust the pH of the system to 11. After the solution is completely clear, add 10.0 g of camellia seed protein at a uniform rate while stirring for 30 min to obtain Cu-EDTA-protein solution.

[0040] 3) The Cu-EDTA-protein solution was dried in an oven at 60°C to constant weight, ground and crushed, and then placed in a muffle furnace. The temperature was raised from room temperature to 700°C under a nitrogen atmosphere and calcined for 4 h. Then the furnace was cooled to room temperature to obtain the calcined sample.

[0041] 4) The calcined sample was washed four times with 6M nitric acid, then rinsed with deionized water until the washing solution was neutral. After complete drying, it was placed back in a muffle furnace and carbonized at 900℃ under a nitrogen atmosphere for 2 hours, followed by furnace cooling to room temperature to obtain Cu5 / N-COA. 10 The catalyst, characterized by ICP, showed a Cu loading of 0.79 wt%.

[0042] Example 2

[0043] This embodiment is exactly the same as Example 1, except that: the amount of EDTA added is 1 mmol, the amount of copper nitrate solution added is 1 mL, and the resulting catalyst is denoted as Cu1 / N-COA. 10 ICP characterization showed that the Cu loading was 0.36 wt%.

[0044] Example 3

[0045] This embodiment is exactly the same as Example 1, except that: the amount of EDTA added is 10 mmol, the amount of copper nitrate solution added is 10 mL, and the resulting catalyst is denoted as Cu. 10 / N-COA 10ICP characterization showed that the Cu loading was 1.63 wt%.

[0046] Example 4

[0047] This embodiment is exactly the same as Example 1, except that: the amount of camellia seed meal protein added is 5.0 g, the resulting catalyst is denoted as Cu5 / N-COA5, and the Cu loading is 1.75 wt% as characterized by ICP.

[0048] Example 5

[0049] This embodiment is exactly the same as Example 1, except that: the camellia seed meal protein is replaced with egg white protein, and the resulting catalyst is denoted as Cu5 / N-EW. 10 ICP characterization showed that the Cu loading was 0.73 wt%.

[0050] Comparative Example 1

[0051] This comparative example is exactly the same as Example 1, except that copper nitrate solution is not added, and the resulting catalyst is denoted as N-COA. 10 .

[0052] Comparative Example 2

[0053] This comparative example is exactly the same as the example example, except that: the amount of EDTA added is 20 mmol, the amount of copper nitrate solution added is 20 ml, and the resulting catalyst is denoted as Cu. 20 / N-COA 10 ICP characterization showed that the Cu loading was 2.21 wt%.

[0054] The present invention also performed scanning electron microscopy tests on Examples 1-3 and Comparative Examples 1 and 2, and the results are as follows: Figure 1 As shown in the image, N-COA 10 The catalyst surface is smooth with irregular depressions. With the introduction of Cu, Cu5 / N-COA 10 Cu 10 / N-COA 10 The catalyst exhibits a rich porous network structure; however, with further increases in Cu content, the hollow structure in the catalyst gradually transforms into macropores, and the average pore size gradually increases. When the Cu content reaches 20 mmol, the obtained Cu... 20 / N-COA 10 The pore structure of the catalyst collapses. Furthermore, this invention also addresses Cu5 / N-COA. 10 The catalyst was subjected to high-resolution transmission electron microscopy (HRTEM) analysis, and the results showed Cu5 / N-COA 10The catalyst exhibits significant pore permeability, with an amorphous carbon phase present on the surface of the Cu particles, and no Cu lattice fringes observed. This indicates that the Cu particles are completely encapsulated by the armor structure of nitrogen-doped carbon. The introduction of Cu not only alters the pore structure of the catalyst but also directly affects the type of nitrogen in the nitrogen-doped carbon, promoting pyridine nitrogen (primarily affecting eCO2RR) and graphitic nitrogen (primarily affecting HER) to become reaction centers, thereby balancing the activities of eCO2RR and HER.

[0055] The present invention also tested the electrocatalytic synthesis gas performance of the catalysts obtained in Examples 1-4 and Comparative Examples 1 and 2 using linear sweep voltammetry. The catalyst-modified carbon paper was used as the working electrode, and 0.5M KHCO3 aqueous solution under saturated CO2 and saturated N2 was used as the reaction solution to carry out CO2 electrocatalytic synthesis gas reaction.

[0056] Among them, the test results using a 0.5 MkHCO3 aqueous solution under saturated N2 as the reaction solution are as follows: Figure 2 As shown in the figure, the catalysts obtained in Examples 1 to 4 all exhibit high current densities, indicating that they have excellent hydrogen evolution reaction (HER) activity.

[0057] Among them, the test results using 0.5 MkHCO3 aqueous solution under saturated CO2 as the reaction solution are as follows: Figure 3 As shown in the figure, its current density is higher than that of the corresponding saturated N2 aqueous solution, which indicates that the activity of CO2 reduction reaction (eCO2RR) in the electrochemical process is higher than that of HER.

[0058] However, it should be noted that, through Figure 2 and Figure 3 It can be seen that as the Cu content in the catalyst increases, the current density in the test results shows a trend of first increasing and then decreasing. This phenomenon occurs because at the stage of low Cu content, the introduction of electron-rich Cu sites and the improvement of graphite nitrogen strength can enhance the electrocatalytic activity and conductivity of the material. When the Cu content is too high, too many medium and large pores will be formed, causing the pore structure to collapse, which in turn affects the overall current density.

[0059] Furthermore, gas chromatography and nuclear magnetic resonance analysis of the products obtained from the above electrochemical reaction showed that the catalyst products contained only CO and H2, meeting the requirements for syngas. The introduction of Cu effectively inhibited HER activity and improved eCO2RR activity, and this activity could be linearly adjusted by potential. This is a key performance characteristic for controlling the CO / H2 competitive reaction and obtaining a controllable CO / H2 ratio syngas. (Using Cu5 / N-COA...) 10Taking the catalyst as an example, it can be seen that the maximum Faraday efficiency (FE) for CO reaches 92.4%, while the maximum and minimum selectivity for H2 are 94.0% and 9.18%, respectively. The FE for both CO and H2 can be linearly adjusted, completely covering the range of 10.0% to 90.0%. This invention also conducted a long-term durability test at a potential of −0.6 V. Within 50 hours, neither the current density nor the FE decreased, indicating that Cu5 / N-COA… 10 The catalyst exhibits excellent stability. This stability stems from the fact that the Cu particles are coated with nitrogen-doped porous carbon, which enhances the oxidation resistance of the copper sites and prevents the deactivation of active sites during the process.

Claims

1. A method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon, characterized in that, include: After the chelating agent is mixed evenly with the copper salt aqueous solution, the precursor solution is obtained. After adjusting the pH of the precursor solution to 10-12, add organic matter containing nitrogen and carbon, disperse it thoroughly, and then successively dry, calcine, wash and carbonize to obtain the product. The molar ratio of the chelating agent to copper ions in the copper salt aqueous solution is 1:0.8~1.2; the molar mass ratio of copper ions to organic matter in the copper salt aqueous solution is 1:1~20 mol / kg.

2. The method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon according to claim 1, characterized in that: The chelating agent is at least one of EDTA, DTPA, and EDDS; the copper salt aqueous solution is at least one of copper nitrate, copper sulfate, and copper chloride.

3. The method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon according to claim 1, characterized in that: The pH adjuster for the precursor solution is sodium hydroxide and / or potassium hydroxide; the organic matter is plant protein and / or animal protein; the plant protein is at least one of woody oilseed protein such as camellia oleifera, legume protein such as soybean, and nut protein such as walnut; the animal protein is at least one of dairy products, meat products, and egg products.

4. The method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon according to claim 3, characterized in that: When the organic matter is plant protein, the molar ratio of copper ions to plant protein in the copper salt aqueous solution is 1:1 to 10 mol / kg; when the organic matter is animal protein, the molar ratio of copper ions to plant protein in the copper salt aqueous solution is 1:1 to 13 mol / kg.

5. The method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon according to claim 1, characterized in that: The drying method is at least one of baking, freeze drying and vacuum drying; the calcination and carbonization are carried out under a protective atmosphere, which is nitrogen and / or argon.

6. The method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon according to claim 5, characterized in that: The calcination conditions are as follows: under a protective atmosphere, the temperature is raised from room temperature to 600~800℃ and held for 3~5 hours, then cooled to room temperature in the furnace; the carbonization conditions are as follows: under a protective atmosphere, the temperature is raised from room temperature to 800~1000℃ and held for 1~3 hours.

7. The method for preparing a catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon according to claim 1, characterized in that: The washing process is as follows: first, wash with 4-8M nitric acid 3-5 times, then wash with deionized water until the washing solution is neutral.

8. A catalyst based on copper-controlled nitrogen distribution in nitrogen-doped carbon, characterized in that: Obtained by the preparation method according to any one of claims 1 to 7.

9. The application of the catalyst according to claim 8, which is based on copper-controlled nitrogen distribution in nitrogen-doped carbon, characterized in that: The process for electrocatalytic synthesis gas reaction is as follows: using catalyst-modified carbon paper as the working electrode and a saturated CO2 or saturated N2 bicarbonate aqueous solution as the reaction liquid, the electrocatalytic synthesis gas reaction is carried out.

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