Modified iron monatomic catalyst based on biomass carbon base as well as preparation method and application of modified iron monatomic catalyst

Abstract

The invention relates to the technical field of electro-catalysis, in particular to a modified iron monatomic catalyst based on biomass carbon as well as a preparation method and application of the modified iron monatomic catalyst. The preparation method comprises the following steps: mixing and stirring chitosan, an acetic acid solution, thiourea and ferric chloride, adjusting the pH value to 7.5-8.5, and freeze-drying to obtain an aerogel precursor; pre-carbonizing the aerogel precursor to obtain a pre-carbonized product; mixing the pre-carbonized product with an alkali reagent, and calcining to obtain a metal nanoparticle doped monatomic catalyst; and carrying out ultrasonic treatment on the metal nanoparticle doped monatomic catalyst by using a mixed acid solution, washing to be neutral, and drying to obtain the modified iron monatomic catalyst. By adopting the modified iron monatomic catalyst provided by the invention, non-polar CO2 molecules and NO3 <-> are efficiently converted into urea under mild conditions, the yield of the urea is up to 2978.6 mu g h <-1 > mgcat <-1 >, and the maximum Faraday efficiency is up to 30.4%.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and particularly to a modified iron single-atom catalyst based on biomass carbon and its preparation method and application. Background Art

[0002] As the most widely used nitrogen fertilizer raw material globally, urea plays an irreplaceable role in promoting crop growth, increasing agricultural yields, and improving the physical and chemical properties of soil. However, the current industrial production of urea still relies on the energy-intensive Haber-Bosch process for ammonia synthesis, and then the Bosch-Meiser process with high carbon emissions is used to couple NH3 and CO2 to prepare urea under high temperature and high pressure (180 - 200 °C, 15 - 25 MPa) conditions.

[0003] Although noble metal-based catalysts exhibit excellent intrinsic activity, their high cost and scarcity limit their practical applications. In contrast, transition metal catalysts are more promising for industrialization due to their abundant resources and low cost. In this context, transition metal single-atom catalysts have become a research hotspot due to their maximized atomic utilization efficiency and adjustable electronic structure. The typical Fe-N4 configuration has a porphyrin-like structural feature, but the symmetric coordination environment leads to poor adsorption energy of intermediates, affecting the reaction kinetics. By constructing an asymmetric coordination structure (such as introducing heteroatoms like sulfur and phosphorus) to regulate the d-band electronic structure of the metal center, the charge distribution of the active site can be effectively optimized, reducing the C-N coupling energy barrier, and thus reducing the theoretical overpotential for urea synthesis. This atomically precise regulation strategy provides a new idea for the design of highly efficient electrocatalytic urea production. Therefore, the research and development of biomass carbon-based modified iron single-atom electrocatalytic materials not only helps to solve the bottlenecks of existing technologies but also brings new breakthroughs and progress in the fields of greenhouse gas and industrial wastewater treatment. Summary of the Invention

[0004] To solve the above problems, the present invention provides a modified iron single-atom catalyst based on biomass carbon and its preparation method and application. Using the modified iron single-atom catalyst provided by the present invention, non-polar CO2 molecules and NO3 - are efficiently converted into urea under mild conditions, with a urea yield as high as 2978.6 μg h -1 mg cat -1 , and the maximum Faraday efficiency reaches 30.4%.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a modified iron single-atom catalyst based on biomass carbon, comprising the following steps:

[0007] 1) Mix chitosan, acetic acid solution, thiourea and iron chloride, stir the mixture, adjust the pH value to 7.5 - 8.5, and then conduct freeze-drying to obtain an aerogel precursor;

[0008] 2) Pre-carbonize the aerogel precursor obtained in step 1) to obtain a pre-carbonized product;

[0009] 3) Mix the pre-carbonized product obtained in step 2) with an alkali reagent and then conduct calcination to obtain a single-atom catalyst doped with metal nanoparticles;

[0010] 4) Subject the single-atom catalyst doped with metal nanoparticles obtained in step 3) to ultrasonic treatment with a mixed acid solution, wash it until neutral, and dry it to obtain a modified iron single-atom catalyst.

[0011] Preferably, the mass ratio of chitosan, the volume of acetic acid solution, the mass of thiourea and the mass of iron chloride in step 1) is 1 g: 100 mL: 0.5 g: 0.05 - 0.15 g;

[0012] The mass percentage content of the acetic acid solution is 1%.

[0013] Preferably, the conditions for the mixing and stirring in step 1) include: temperature is 60 °C, time is 12 h, and rotation speed is 500 rpm;

[0014] The conditions for the freeze-drying include: temperature is -50 °C, and time is 48 h.

[0015] Preferably, the conditions for the pre-carbonization in step 2) include: pre-carbonize for 2 h in a nitrogen atmosphere at a temperature of 250 °C, and the heating rate is 5 °C / min.

[0016] Preferably, the mass ratio of the pre-carbonized product to the alkali reagent in step 3) is 2:1;

[0017] The alkali reagent includes potassium hydroxide;

[0018] The conditions for the calcination include: calcine for 1 h in a nitrogen atmosphere at a temperature of 800 °C, and the heating rate is 5 °C / min.

[0019] Preferably, in the mixed acid solution in step 4), the concentration of sulfuric acid is 0.5 mol / L, and the concentration of hydrogen chloride is 0.1 mol / L;

[0020] The time for the ultrasonic treatment is 6 h.

[0021] The present invention also provides a modified iron single-atom catalyst prepared by the preparation method described in the above technical solution.

[0022] The present invention also provides the application of the modified iron single-atom catalyst described in the above technical solution in the electrocatalytic preparation of urea.

[0023] Preferably, the application includes the following steps: using an H-shaped electrolytic cell as the reaction device, using the modified iron single-atom catalyst described in the above technical solution as the working electrode, using an Ag / AgCl electrode as the reference electrode, and a platinum sheet electrode as the counter electrode, continuously introducing CO2 into the electrolyte for electrocatalytic reaction to prepare urea.

[0024] Preferably, the electrolyte is a potassium nitrate solution;

[0025] The flow rate of the CO2 is 30 mL / min;

[0026] The diaphragm of the H-shaped electrolytic cell is a proton exchange membrane.

[0027] Advantages of the present invention:

[0028] 1. The present invention selects chitosan and transition metal salts with rich reserves and low cost as raw materials, reducing the production cost, and the obtained catalyst has higher use value and economic benefits.

[0029] 2. The process flow of the biochar-based modified iron single-atom catalyst synthesized by the present invention is simple, the conditions are mild, the preparation process is pollution-free and environmentally friendly, and it has the advantages of fast and efficient.

[0030] 3. The biochar-based modified iron single-atom catalyst synthesized by the present invention regulates the Fe-N4 symmetric local electric field through asymmetric sulfur atom doping, induces changes in the electronic structure of the active sites, improves the adsorption-desorption process of key intermediates, and realizes the efficient conversion of non-polar CO2 molecules and NO3 - into urea under mild conditions, with a urea yield as high as 2978.6 μg h - 1 mg cat -1 , and the maximum Faraday efficiency reaches 30.4%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments.

[0032] Figure 1 XRD patterns of different samples in Embodiments 1-3 of the present invention;

[0033] Figure 2 Raman test diagrams of different samples in Embodiments 1-3 of the present invention;

[0034] Figure 3 BET and BJH diagrams of different samples in Embodiments 1-3 of the present invention;

[0035] Figure 4 This is the aberration-corrected transmission electron microscopy image of Fe-S2NC in Example 2 of the present invention;

[0036] Figure 5 This is the near-edge spectrum and extended-edge spectrum of the K-edge of Fe element in the Fe-S2NC catalyst in Example 2 of the present invention;

[0037] Figure 6 This is the X-ray photoelectron spectroscopy image of Fe 2p in the Fe-S2NC catalyst in Example 2 of the present invention;

[0038] Figure 7 This is the X-ray photoelectron spectroscopy image of N1s in the Fe-S2NC catalyst in Example 2 of the present invention;

[0039] Figure 8 This is for Fe-S in Examples 4-6 of the present invention x NC(x = 1, 2, 3) as a single-atom catalyst applied to the experimental results of electrocatalytic preparation of urea; among them, a is Fe-S x The yield of electrocatalytic preparation of urea by NC(x = 1, 2, 3) under the condition of CO2-saturated 0.1 M potassium nitrate, and b is Fe-S x The Faraday efficiency of electrocatalytic preparation of urea by NC(x = 1, 2, 3) under the condition of CO2-saturated 0.1 M potassium nitrate. Detailed implementation manners

[0040] The present invention provides a preparation method of a modified iron single-atom catalyst based on biomass carbon-based, including the following steps:

[0041] 1) Mix chitosan, acetic acid solution, thiourea and ferric chloride and stir, adjust the pH value to 7.5 - 8.5, and then perform freeze-drying to obtain an aerogel precursor;

[0042] 2) Pre-carbonize the aerogel precursor obtained in step 1) to obtain a pre-carbonized product;

[0043] 3) Mix the pre-carbonized product obtained in step 2) with an alkali reagent and then perform calcination to obtain a single-atom catalyst doped with metal nanoparticles;

[0044] 4) Ultrasonically treat the single-atom catalyst doped with metal nanoparticles obtained in step 3) with a mixed acid solution, wash it to neutral, and dry it to obtain a modified iron single-atom catalyst.

[0045] The present invention mixes chitosan, acetic acid solution, thiourea and ferric chloride and stirs them, adjusts the pH value to 7.5 - 8.5, and then performs freeze-drying to obtain an aerogel precursor. In the present invention, the mass ratio of chitosan, the volume of acetic acid solution, the mass of thiourea and the mass of ferric chloride is preferably 1g:100mL:0.5g:0.05 - 0.15g. In the present invention, the mass percentage content of the acetic acid solution is preferably 1%. The present invention has no special limitation on the source of the chitosan, and conventional commercially available products can be used, such as brand: Macklin; manufacturer: Shandong Keyuan Biochemical Co., Ltd.; production place: Middle section of Nengyuan Avenue, Chemical Industry Park, Dongguantun Town, Juye County, Heze City, Shandong Province; product: chitosan, deacetylation degree ≥95%, molecular weight 50000 - 60000Da. In the present invention, the conditions for the mixing and stirring preferably include: temperature of 60°C, time of 12h, rotation speed of 500rpm. In the present invention, the conditions for the freeze-drying preferably include: after rapid freezing with liquid nitrogen, drying at a temperature of -50°C for 48h.

[0046] The present invention pre-carbons the obtained aerogel precursor to obtain a pre-carbonized product. In the present invention, the conditions for the pre-carbonization preferably include: pre-carbonizing for 2h in a nitrogen atmosphere at a temperature of 250°C, with a heating rate of 5°C / min.

[0047] The present invention mixes the obtained pre-carbonized product with an alkali reagent and then performs calcination to obtain a single-atom catalyst doped with metal nanoparticles. In the present invention, the mixing of the pre-carbonized product and the alkali reagent is preferably carried out by ball milling, and the present invention has no special limitation on the condition parameters of the ball milling. In the present invention, the mass ratio of the pre-carbonized product to the alkali reagent is preferably 2:1. In the present invention, the alkali reagent preferably includes potassium hydroxide. In the present invention, the conditions for the calcination preferably include: calcining for 1h in a nitrogen atmosphere at a temperature of 800°C, with a heating rate of 5°C / min.

[0048] The present invention ultrasonically treats the obtained single-atom catalyst doped with metal nanoparticles with a mixed acid solution, washes it to neutral, and dries it to obtain a modified iron single-atom catalyst. In the present invention, the concentration of sulfuric acid in the mixed acid solution is preferably 0.5mol / L, and the concentration of hydrogen chloride is preferably 0.1mol / L. In the present invention, the time for the ultrasonic treatment is preferably 6h, the ultrasonic frequency is 40KHz, and the power is 240W.

[0049] In order to further illustrate the present invention, the present invention will be described in detail below in conjunction with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0050] Example 1

[0051] A single-atom iron catalyst Fe-S1NC based on biomass carbon-based modification, and the preparation steps are as follows:

[0052] (1) Dissolve 1 g of chitosan in 100 mL of acetic acid solution with a mass percentage of 1%, and stir until completely dissolved. Add 0.5 g of thiourea and 0.05 g of FeCl3·6H2O, and stir at 60 °C for 12 hours. Adjust the pH to 8.0 with NH4OH. Rapidly freeze with liquid nitrogen and freeze-dry at -50 °C for 48 hours to obtain an aerogel precursor with porous structural characteristics.

[0053] (2) Calcinate the aerogel precursor in a tubular muffle furnace. In an N2 atmosphere, heat it to 250 °C at a rate of 5 °C / min and hold for 2 hours to obtain a pre-carbonized product. Mix the pre-carbonized product and KOH by ball milling at a mass ratio of 2:1. In an N2 atmosphere, heat it to 800 °C at a rate of 5 °C / min and hold for 1 hour to obtain a single-atom catalyst doped with metal nanoparticles.

[0054] Ball milling conditions: Ball mill type: planetary ball mill; Grinding ball material: zirconia ball; Ball-to-material ratio: 10:1; Rotation speed: 400 rpm; Ball milling time: 4 hours; Grinding medium: dry milling;

[0055] (3) Treat the single-atom catalyst doped with metal nanoparticles with a mixed acid of 0.5 M H2SO4 + 0.1 M HCl by ultrasonic treatment (ultrasonic frequency is 40 KHz, power is 240 W) for 6 hours, wash it with water until neutral, and dry it in vacuum (60 °C for 12 h) to obtain the single-atom iron catalyst Fe-S1NC.

[0056] Example 2

[0057] This example provides a single-atom iron catalyst Fe-S2NC based on biomass carbon-based modification. The preparation method is the same as that of Example 1, except that the addition amount of FeCl3·6H2O is adjusted to 0.1 g. The obtained catalyst is labeled as Fe-S2NC.

[0058] Example 3

[0059] This example provides a single-atom iron catalyst Fe-S3NC based on biomass carbon-based modification. The preparation method is the same as that of Example 1, except that the addition amount of FeCl3·6H2O is adjusted to 0.15 g. The obtained catalyst is labeled as Fe-S3NC.

[0060] Characterization results:

[0061] Perform X-ray diffraction (XRD) characterization on the single-atom catalysts Fe-S x NC (x = 1, 2, 3) obtained in Examples 1-3, as Figure 1As shown, all three samples exhibit typical diffraction peaks at 2θ = 26.0 ± 0.2° and 44.1 ± 0.2°, corresponding to the (002) crystal plane layered stacking structure and the (101) crystal plane in-plane ordered arrangement of graphite carbon, respectively.

[0062] For the Fe-S x NC(x = 1, 2, 3) single-atom catalysts obtained in Examples 1 - 3, Figure 2 it can be seen that more defect sites are formed in the graphite phase of the Fe-S2NC single-atom catalyst.

[0063] For the Fe-S x NC(x = 1, 2, 3) single-atom catalysts obtained in Examples 1 - 3, BET and BJH tests were carried out. Figure 3 It can be seen that the micropore diameter (0.7 - 1.2 nm) of Fe-S2NC is smaller than that of Fe-S1NC and Fe-S3NC (1.3 - 1.9 nm). The degree of structural refinement of Fe-S2NC increases, enhancing its ability to adsorb small molecules, thereby improving the electrocatalytic activity.

[0064] For the Fe-S x NC(x = 1, 2, 3) single-atom catalysts obtained in Examples 1 - 3, aberration-corrected electron microscopy characterization was carried out. Figure 4 It can be seen that isolated Fe atoms were observed through the aberration-corrected electron microscopy images, proving that the iron single-atom catalyst based on biomass carbon-based modification was successfully prepared in this invention, and all the reactions in the preparation process were successful.

[0065] For the Fe-S2NC single-atom catalyst obtained in Example 2, near-edge spectroscopy and extended-edge spectroscopy characterizations of the K-edge of the Fe element were carried out. Figure 5 It can be seen that Fe exists in the form of single atoms in the Fe-S2NC single-atom catalyst prepared in this invention, further proving that all the preparation steps were successful.

[0066] For the Fe-S x NC(x = 1, 2, 3) single-atom catalysts obtained in Examples 1 - 3, X-ray photoelectron spectroscopy characterization was carried out. Figure 6 It can be seen that Fe exists in an oxidized state rather than a metallic state and Fe-S2NC shows a stronger reduced state. Figure 7 It can be seen that the binding energy of N1s in Fe-S2NC shifts towards a lower binding energy, and electrons are migrating from sulfur atoms to nitrogen atoms, corroborating that sulfur atoms are doped in the non-second coordination layer, precisely regulating the d-band electronic structure of the metal center, indicating that the Fe-S2NC single-atom catalyst prepared in this invention exhibits the best reduction performance.

[0067] Example 4

[0068] This embodiment provides a method for electrocatalytic preparation of urea, which is carried out according to the following steps:

[0069] The electrochemical experiment was carried out on a CHI 760E electrochemical workstation (CH Instruments, Inc., Shanghai, China). The two electrode compartments of the electrolytic cell were separated by a Nafion 117 membrane. Before the experiment, the Nafion membrane was heated in an aqueous H2O2 solution with a mass percentage of 5% and 0.5 M H2SO4 at 80 °C for 1 hour, and then the Nafion membrane was soaked in ultrapure water at 80 °C for 0.5 hours for pretreatment. Before the electrochemical test, the cathode electrolyte was pre-purified with CO2 for 0.5 hours. A three-electrode system was adopted. The electrode clamp held the catalyst carbon paper prepared in Example 1, and the Ag / AgCl and platinum wire electrodes were used as the reference electrode and the counter electrode respectively. An H-type electrolytic cell was used as the reaction device. The cathode compartment was filled with 30 mL of a potassium nitrate solution saturated with 0.1 M CO2 as the electrolyte, and the anode compartment was filled with 30 mL of 0.1 M potassium nitrate solution as the electrolyte. During the electrolysis process, the cathode compartment was stirred at a speed of 500 rpm, and the purified CO2 was set to enter the electrolyte at a flow rate of 30 mL min -1 The product was detected by NMR, and the yield of urea was calculated to be 547.27 μg h -1 mg cat -1 , and the Faraday efficiency was 18.9% ( Figure 8 ).

[0070] The carbon paper is the catalyst carrier. The model of the carbon paper: TGP-H-090 hydrophilic; specification: 20*20 cm.

[0071] Preparation of the working electrode:

[0072] Generally, 4 mg of the catalyst, 2 mg of superconducting carbon black and 40 μL of Nafion (5 wt.%) solution were added to 760 μL of isopropanol. Then it was ultrasonicated for 1 h to form a homogeneous catalyst ink. 20 μL of the ink was dropped onto a commercial hydrophilic carbon paper (TGP-H-090) with an active area of 1*1 cm 2 to prepare the working electrode, and the catalyst dosage was 0.1 mg cm -2 . It should be noted that this catalyst loading remained the same in all measurements.

[0073] Example 5

[0074] This example provides a method for electrocatalytic preparation of urea. It is the same as Example 4, except that the Fe-S1NC single-atom catalyst in Example 1 is replaced with the Fe-S2NC single-atom catalyst in Example 2. The product was detected by NMR, and the urea yield was calculated to be 2978.6 μg h -1 mg cat -1 , and the Faraday efficiency was 30.4% ( Figure 8 ).

[0075] Example 6

[0076] This example provides a method for electrocatalytic preparation of urea. It is the same as Example 4, except that the Fe-S1NC single-atom catalyst in Example 1 is replaced with the Fe-S3NC single-atom catalyst in Example 3. The product was detected by NMR, and the urea yield was calculated to be 1958.88 μg h -1 mg cat -1 , and the Faraday efficiency was 27.1% ( Figure 8 ).

[0077] Urea yield formula:

[0078] R urea =(c urea ×V) / (t×m)

[0079] The Faraday efficiency of electrocatalytic preparation of urea is obtained through the following equation:

[0080] FE=(16F×c urea ×V) / (60.06×Q)

[0081] where c urea is the measured urea concentration (μg mL -1 ), V is the total volume of the electrolyte (mL), t is the electrocatalytic time (h), m is the catalyst loading (mg), F is the Faraday constant (96485.3 C mol -1 ), and Q is the total charge passed through the working electrode (C).

[0082] Although the above examples have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. People can also obtain other embodiments according to this example without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of a modified iron single-atom catalyst based on biomass carbon, characterized in that, It includes the following steps: 1) Mix and stir chitosan, acetic acid solution, thiourea and ferric chloride, adjust the pH value to 7.5 - 8.5, and then carry out freeze-drying to obtain an aerogel precursor; 2) Carry out pre-carbonization on the aerogel precursor obtained in step 1) to obtain a pre-carbonized product; 3) Mix the pre-carbonized product obtained in step 2) with an alkali reagent and then carry out calcination to obtain a single-atom catalyst doped with metal nanoparticles; 4) Subject the single-atom catalyst doped with metal nanoparticles obtained in step 3) to ultrasonic treatment with a mixed acid solution, wash it to neutrality, and dry it to obtain a modified iron single-atom catalyst.

2. The preparation method according to claim 1, wherein In step 1), the mass ratio of chitosan, the volume of acetic acid solution, the mass of thiourea and the mass of ferric chloride is 1g:100mL:0.5g:0.05 - 0.15g; The mass percentage content of the acetic acid solution is 1%.

3. The preparation method according to claim 1, characterized in that, The conditions for the mixing and stirring in step 1) include: temperature is 60°C, time is 12h, and rotation speed is 500rpm; The conditions for the freeze-drying include: temperature is -50°C, time is 48h.

4. The preparation method according to claim 1, characterized in that, The conditions for the pre-carbonization in step 2) include: pre-carbonize for 2h at 250°C in a nitrogen atmosphere, and the heating rate is 5°C / min.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the pre-carbonized product to the alkali reagent in step 3) is 2:1; The alkali reagent includes potassium hydroxide; The conditions for the calcination include: calcine for 1h at 800°C in a nitrogen atmosphere, and the heating rate is 5°C / min.

6. The preparation method according to claim 1, wherein In the mixed acid solution in step 4), the concentration of sulfuric acid is 0.5mol / L, and the concentration of hydrogen chloride is 0.1mol / L; The time for the ultrasonic treatment is 6h.

7. A modified iron single-atom catalyst prepared by the preparation method according to any one of claims 1 - 6.

8. Application of the modified iron single-atom catalyst according to claim 7 in the electrocatalytic preparation of urea.

9. The application according to claim 8, wherein The application includes the following steps: Using an H-type electrolytic cell as the reaction device, using the modified iron single-atom catalyst according to claim 7 as the working electrode, using an Ag / AgCl electrode as the reference electrode, and using a platinum plate electrode as the counter electrode, continuously introduce CO2 into the electrolyte for electrocatalytic reaction to prepare urea.

10. The application according to claim 9, wherein The electrolyte is a potassium nitrate solution; The flow rate of CO2 is 30mL / min; The diaphragm of the H-type electrolytic cell is a proton exchange membrane.

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