A Co@CeO2 / NC composite nanoparticle catalytic material, its preparation method and application

Abstract

This invention discloses a Co@CeO2 / NC composite nanoparticle catalytic material, its preparation method, and its applications, relating to the field of catalyst materials technology. The composite nanoparticle catalytic material comprises NC nanosheets and a Ce-O-Co coordination compound formed by cerium oxide and metallic cobalt and grown in situ on the NC nanosheets. This composite nanoparticle catalytic material not only effectively modulates the electronic structure of the 3d orbitals of Co atoms through the Ce-O-Co bond formed by the composite of cerium oxide and cobalt, achieving a synergistic effect between cerium oxide and cobalt, thereby optimizing the adsorption capacity of cobalt atoms for intermediates and greatly improving the reactivity of cobalt atoms; but also, by growing the Ce-O-Co coordination compound in situ on NC nanosheets, it significantly improves the contact area between cobalt atoms and catalytic reactants, the electron transfer rate, and the catalytic stability by utilizing the sufficient specific surface area provided by the nitrogen-carbon nanosheets and their excellent conductivity and structural stability.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials technology, mainly to the field of catalyst materials technology for nitrate reduction to ammonia synthesis, specifically to a Co@CeO2 / NC composite nanoparticle catalyst material, its preparation method and application. Background Technology

[0002] The nitrogen cycle in biology and the natural environment is closely related to the development and progress of modern society. It is noteworthy that among the many compounds involved in the nitrogen cycle, ammonia (NH3) is not only a key chemical in fertilizer synthesis but also an excellent green energy carrier, playing a significant role in promoting population growth and increasing energy storage. Electrocatalytic nitrate reduction (NO3)... - RR (Rapid Reduction) is a process for synthesizing ammonia (NH3) using renewable electricity and highly active catalysts. It not only effectively avoids the problems of high energy consumption and high emissions of polluting gases associated with industrial NH3 synthesis, but also improves the pollution problem of nitrates in the environment. It has the dual advantages of high environmental protection and high energy conversion, which is very much in line with the current green and sustainable development path and shows broad application prospects.

[0003] While nitrate reduction to ammonia synthesis is an effective way to convert waste nitrates into high-value ammonia and has significant application value, the industrial production process is affected by the Faraday efficiency (FE) at high current density and low potential, leading to NO3... - In the reaction kinetics of RR, charge is difficult to transfer efficiently to the nitrate π orbital, resulting in NO3... - The RR ammonia synthesis process often fails to meet expectations. Furthermore, nitrate reduction involves not only complex electron transfer steps but also faces strong competition from the hydrogen evolution reaction (HER) and a series of byproducts, making NO3... - The industrialization of RR ammonia synthesis is even more difficult. Therefore, high-performance catalysts are used to accelerate NO3 synthesis. - RR reaction rate is essential for achieving efficient ammonia synthesis, especially for NO3. - The industrialization of RR ammonia synthesis is of great significance.

[0004] With in-depth research into the synthesis of ammonia from nitrate reduction, catalytic materials with high catalytic activity and reaction efficiency are constantly being discovered, such as transition metal-based materials (e.g., iron, copper, cobalt and their oxides), noble metal-based materials (e.g., ruthenium, platinum, palladium), and composite catalysts. It is worth noting that although noble metal-based materials exhibit excellent catalytic performance, their high cost and scarcity limit their large-scale industrial application. In contrast, transition metal-based materials have received considerable attention and favor due to their low cost, environmental friendliness, and wide distribution. Among them, cobalt-based catalysts, with their high catalytic activity and selectivity, can significantly improve NO3-reduction reactions. - Reactive reaction kinetics (RR) suggests that cobalt-based catalysts are ideal catalyst materials. However, in practical applications, it has been found that existing cobalt-based catalysts still suffer from problems such as small contact area, low conductivity, and low reactivity, resulting in a significant gap between their catalytic performance and the requirements of practical applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of small contact area, low conductivity and low reactivity of existing cobalt-based catalysts, and to propose a Co@CeO2 / NC composite nanoparticle catalytic material, its preparation method and application.

[0006] To achieve the above objectives, the present invention provides a Co@CeO2 / NC composite nanoparticle catalytic material, wherein the composite nanoparticle catalytic material comprises NC nanosheets and a Ce-O-Co coordination compound formed by cerium oxide (CeO2) and metallic cobalt and grown in situ on the NC nanosheets.

[0007] This invention discloses a Co@CeO2 / NC composite nanoparticle catalytic material. It not only achieves a synergistic effect between cerium oxide and cobalt by effectively regulating the electronic structure of the 3d orbitals of Co atoms through the Ce-O-Co bond formed by the composite of cerium oxide and cobalt metal, thereby optimizing the adsorption capacity of cobalt atoms for intermediates and greatly improving the reactivity of cobalt atoms, thus significantly enhancing the performance of cobalt atoms in the reduction of nitrate to ammonia; but also significantly improves the contact area between cobalt atoms and catalytic reactants, electron transfer rate, and catalytic stability by in-situ growing Ce-O-Co coordination compounds on NC nanosheets. Utilizing the sufficient specific surface area, excellent conductivity, and structural stability provided by the nitrogen-carbon nanosheets, it further enhances the catalytic efficiency and stability for the reduction of nitrate to ammonia. This composite nanoparticle catalytic material exhibits excellent catalytic efficiency and stability for the reduction of nitrate to ammonia, making it suitable for large-scale industrial application in this process.

[0008] Preferably, in the composite nanoparticle catalytic material, the molar ratio of cerium oxide to cobalt is 1:2-3; more preferably, the molar ratio of cerium oxide to cobalt is 1:2.5. With the preferred molar ratio, the Ce-O-Co formation formed by cerium oxide and cobalt has better stability and higher catalytic activity.

[0009] Preferably, in the composite nanoparticle catalytic material, the molar ratio of metallic cobalt to NC nanosheets is 2-3:10; the preferred molar ratio results in a moderate density of cobalt atoms supported on the NC nanosheets, leading to higher catalytic efficiency and catalyst utilization for the reduction of nitrate to ammonia; more preferably, the molar ratio of metallic cobalt to NC nanosheets is 2.5:10.

[0010] To achieve the above objectives, the present invention further provides a method for preparing Co@CeO2 / NC composite nanoparticle catalytic materials, comprising the following steps: (1) Cobalt nitrate, cerium nitrate, melamine and sucrose are mixed and stirred in water to obtain a mixed solution; (2) The mixed solution was subjected to hydrothermal reaction at a temperature of 190~200℃ for 9-11 hours, and solid-liquid separation was performed to obtain precursor powder; (3) The precursor powder was calcined in a mixed atmosphere of argon and hydrogen to obtain Co@CeO2 / NC composite nanoparticle catalytic material.

[0011] This invention discloses a method for preparing Co@CeO2 / NC composite nanoparticle catalytic materials. The method utilizes a simple hydrothermal process and calcination, offering advantages such as low temperature, short preparation cycle, and ease of operation. Furthermore, it enables controllable synthesis and effective regulation of the nanoparticle morphology of the composite nanoparticle catalytic materials. It effectively transforms supramolecular structures into layered nitrogen-doped carbon nanosheets through π-π stacking effects, achieving efficient, stable, and controllable preparation of the composite nanoparticle catalytic materials. Simultaneously, the method utilizes inexpensive and readily available raw materials that do not contain precious metals, resulting in low production costs and suitability for large-scale, industrial production of Co@CeO2 / NC composite nanoparticle catalytic materials.

[0012] In step (1), preferably, the molar ratio of cobalt nitrate to cerium nitrate in the mixed solution is 2-3:1; the mass concentration ratio of melamine to sucrose is 1-2:1; the preferred concentration ratio results in better catalytic performance of the prepared composite nanoparticle catalytic material.

[0013] Preferably, in the mixed solution, the concentration of cobalt nitrate is 0.02~0.09 mol / L, the concentration of cerium nitrate is 0.01~0.03 mol / L, the concentration of melamine is 50~150 g / L, and the concentration of sucrose is 30-90 g / L; the preferred reactant concentrations result in good reaction controllability, regular nano-morphology of the product, and higher catalytic efficiency.

[0014] In step (3), preferably, the volume ratio of argon to hydrogen in the mixed atmosphere is 1:2-4; more preferably, the volume ratio is 1:3. The preferred volume ratio results in high calcination efficiency, good controllability, and better stability of the obtained composite nanoparticle catalytic material.

[0015] Preferably, the calcination treatment is carried out at a temperature of 800-900℃ for 2-3 hours; the preferred calcination conditions result in high calcination efficiency and better structural stability of the obtained composite nanoparticle catalytic material.

[0016] To further achieve the above objectives, this invention also provides an application of Co@CeO2 / NC composite nanoparticle catalytic material as a catalyst in the synthesis of ammonia by nitrate reduction. The composite nanoparticle catalytic material of this invention, when used for the catalysis of ammonia synthesis by nitrate reduction, has the advantages of high catalytic efficiency and good catalytic stability, which can greatly improve the ammonia yield and shorten the synthesis cycle.

[0017] Preferably, in the synthesis of ammonia by nitrate reduction, the amount of the composite nanoparticle catalyst used is 3-5 wt% of the total amount of raw materials.

[0018] The beneficial effects of this invention are: 1. The composite nanoparticle catalytic material of the present invention effectively regulates the electronic structure of the 3d orbital of Co atoms by combining cerium oxide and cobalt metal and utilizing the formed Ce-O-Co bond, thereby realizing the synergistic effect of cerium oxide and cobalt metal, thus optimizing the adsorption capacity of cobalt atoms for intermediates, greatly improving the reactivity of cobalt atoms, and significantly improving the performance of cobalt atoms in the reduction of nitrate to ammonia.

[0019] 2. The composite nanoparticle catalytic material of the present invention significantly improves the contact area between cobalt atoms and catalytic reactants, electron transfer rate and catalytic stability by growing Ce-O-Co coordination compounds in situ on NC nanosheets and utilizing the sufficient specific surface area provided by the nitrogen-carbon nanosheets as well as their excellent conductivity and structural stability.

[0020] 3. The preparation method of the composite nanoparticle catalytic material of the present invention is carried out by a simple hydrothermal method and calcination process, which has the advantages of low temperature, short preparation cycle and easy operation.

[0021] 4. The preparation method of the composite nanoparticle catalytic material of the present invention can realize the controllable synthesis and effective regulation of the nanomorphology of the composite nanoparticle catalytic material. It can effectively transform the supramolecular structure into layered nitrogen-doped carbon nanosheets through the π-π stacking effect, thereby achieving efficient, stable and controllable preparation of composite nanoparticle catalytic materials.

[0022] 5. The preparation method of the composite nanoparticle catalytic material of the present invention uses inexpensive and readily available raw materials that do not contain precious metals, resulting in low production costs. This method is suitable for the large-scale and industrial production of Co@CeO2 / NC composite nanoparticle catalytic materials. Attached Figure Description

[0023] Figure 1 The images show the XRD patterns of the composite nanoparticle catalytic materials prepared in Example 1 and Comparative Examples 1-2 of this invention.

[0024] Figure 2 This is a transmission electron microscope (TEM) image of the composite nanoparticle catalytic material prepared in Example 1 of this invention.

[0025] Figure 3 This is an elemental mapping diagram of the composite nanoparticle catalytic material prepared in Example 1 of the present invention.

[0026] Figure 4 Linear voltammetric scan curves of the composite nanoparticle catalytic materials prepared in Example 1 and Comparative Examples 1-2 of this invention.

[0027] Figure 5 The diagram shows the ammonia production Faraday efficiency of the composite nanoparticle catalytic materials prepared in Example 1 and Comparative Examples 1-2 of this invention.

[0028] Figure 6 The diagram shows the ammonia yield of the composite nanoparticle catalytic materials prepared in Example 1 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0030] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available products.

[0031] Example 1

[0032] A Co@CeO2 / NC composite nanoparticle catalytic material is prepared by the following steps: (1) Cobalt nitrate, cerium nitrate, melamine and sucrose are mixed and stirred in water to obtain a mixed solution; in the mixed solution, the concentration of cobalt nitrate is 0.05 mol / L, the concentration of cerium nitrate is 0.02 mol / L, the concentration of melamine is 75 g / L and the concentration of sucrose is 50 g / L. (2) The mixed solution was subjected to a hydrothermal reaction at 200°C for 10 h, filtered, and the solid was collected to obtain the precursor powder; (3) The precursor powder was calcined in a mixed atmosphere of argon and hydrogen (volume ratio of 1:3) (temperature of 800℃, time of 3h) to obtain Co@CeO2 / NC composite nanoparticle catalytic material.

[0033] Testing revealed that the Co@CeO2 / NC composite nanoparticle catalytic material comprises NC nanosheets and a Ce-O-Co coordination compound formed by cerium oxide (CeO2) and metallic cobalt grown in situ on the NC nanosheets; wherein the molar ratio of cerium oxide to metallic cobalt is 1:2.5; and the molar ratio of metallic cobalt to NC nanosheets is 2.5:10.

[0034] Comparative Example 1

[0035] A composite nanoparticle catalytic material is prepared using the following method: (1) Cobalt nitrate, melamine and sucrose are mixed and stirred in water to obtain a mixed solution; in the mixed solution, the concentration of cobalt nitrate is 0.05 mol / L, the concentration of melamine is 75 g / L and the concentration of sucrose is 50 g / L. (2) The mixed solution was subjected to a hydrothermal reaction at 200°C for 10 h, filtered, and the solid was collected to obtain the precursor powder; (3) The precursor powder was calcined in a mixed atmosphere of argon and hydrogen (volume ratio of 1:3) (temperature of 800℃, time of 3h) to obtain Co / NC composite nanoparticle catalytic material.

[0036] Testing revealed that the Co-NC composite nanoparticle catalytic material comprises NC nanosheets and Co metal grown in situ on the NC nanosheets; wherein the molar ratio of cobalt metal to NC nanosheets is 2.5:10.

[0037] Comparative Example 2

[0038] A composite nanoparticle catalytic material is prepared using the following method: (1) Cerium nitrate, melamine and sucrose are mixed and stirred in water to obtain a mixed solution; in the mixed solution, the concentration of cerium nitrate is 0.02 mol / L, the concentration of melamine is 75 g / L and the concentration of sucrose is 50 g / L; (2) The mixed solution was subjected to a hydrothermal reaction at 200°C for 10 h, filtered, and the solid was collected to obtain the precursor powder; (3) The precursor powder was calcined in a mixed atmosphere of argon and hydrogen (volume ratio of 1:3) (temperature of 800℃, time of 3h) to obtain CeO2 / NC composite nanoparticle catalytic material.

[0039] Testing revealed that the CeO2 / NC composite nanoparticle catalytic material comprises NC nanosheets and cerium oxide (CeO2) grown in situ on the NC nanosheets; wherein the molar ratio of cerium oxide to NC nanosheets is 1:10.

[0040] Experimental Example

[0041] (a) The Co@CeO2 / NC composite nanoparticle material prepared in Example 1 was subjected to performance testing.

[0042] (1) such as Figure 1 As shown, the XRD diffraction peaks of Example 1 and Comparative Examples 1-2 correspond to the standard PDF card, indicating that the synthesized Co@CeO2 / NC composite nanoparticle material was successfully prepared.

[0043] (2) For example Figure 2 As shown, it can be clearly seen that Co@CeO2 / NC composite nanoparticles grow on nitrogen-carbon nanosheets, which can provide sufficient specific surface area for the reduction of nitrates to synthesize ammonia.

[0044] (3) such as Figure 3 As shown, the elemental distribution of Co@CeO2 / NC composite nanoparticles grown on nitrogen-carbon nanosheets can be clearly seen, and Co is successfully combined with CeO2 to achieve a synergistic effect.

[0045] (4) such as Figure 4 The figure shows the linear voltammetric scan curves of Co@CeO2 / NC composite nanoparticles and Co / NC, CeO2 / NC catalysts, specifically in a 1M KOH + 0.1 M KNO3 solution, at a scan rate of 5 mV / s. -1 With IR compensation at 100%, and current density measured at a voltage of -0.8~0.1V vs. RHE, the results show that the Co@CeO2 / NC composite nanoparticle material exhibits the highest current density, indicating that the Co@CeO2 / NC composite nanoparticle material possesses the optimal NO3- content. - RR catalytic performance.

[0046] (5) such as Figure 5The figure shows the Faradaic efficiency of ammonia synthesis from Co@CeO2 / NC composite nanoparticles and Co / NC and CeO2 / NC catalysts at different potentials. Specifically, the ammonia synthesis was carried out in 1M KOH + 0.1 M KNO3 solution at potentials of 0 to -0.5V vs. RHE for 1 h. - The RHE test results showed that the Co@CeO2 / NC composite nanoparticles had better Faradaic efficiency than the Co / NC and CeO2 / NC catalysts at all potentials, and exhibited the best Faradaic efficiency (97.19%) at -0.1V vs. RHE, indicating that the Co@CeO2 / NC composite nanoparticle material has better efficiency in nitrate reduction to ammonia synthesis.

[0047] (6) For example Figure 6 The figure shows the ammonia yield of Co@CeO2 / NC composite nanoparticles and Co / NC, CeO2 / NC catalysts at different potentials. Specifically, the ammonia yield was determined by reacting NO3- in 1M KOH + 0.1 M KNO3 solution at potentials of 0 to -0.5 V vs. RHE for 1 h. - RR testing showed that the ammonia yield increased with increasing potential. Among them, the Co@CeO2 / NC composite nanoparticles exhibited a higher ammonia yield than the Co / NC and CeO2 / NC catalysts at all potentials, and achieved a yield as high as 0.278 mmol / h at -0.5 V vs. RHE. -1 cm -2 The increased ammonia yield further demonstrates that the Co@CeO2 / NC composite nanoparticle material exhibits better performance in nitrate reduction for ammonia synthesis.

[0048] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Co@CeO2 / NC composite nanoparticle catalytic material, characterized in that, The composite nanoparticle catalytic material includes NC nanosheets and Ce-O-Co coordination compounds formed by cerium oxide and metallic cobalt and grown in situ on the NC nanosheets. 2.The Co@CeO2 / NC composite nanoparticle catalytic material according to claim 1, characterized in that, In the composite nanoparticle catalytic material, the molar ratio of cerium oxide to cobalt is 1:2-3; preferably, the molar ratio of cerium oxide to cobalt is 1:2.

5. 3.The Co@CeO2 / NC composite nanoparticle catalytic material of claim 1, wherein, In the composite nanoparticle catalytic material, the molar ratio of cobalt metal to NC nanosheets is 2-3:10; preferably, the molar ratio of cobalt metal to NC nanosheets is 2.5:

10.

4. A method for preparing the Co@CeO2 / NC composite nanoparticle catalytic material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Cobalt nitrate, cerium nitrate, melamine and sucrose are mixed and stirred in water to obtain a mixed solution; (2) The mixed solution was subjected to hydrothermal reaction at a temperature of 190~200℃ for 9-11 hours, and solid-liquid separation was performed to obtain precursor powder; (3) The precursor powder was calcined in a mixed atmosphere of argon and hydrogen to obtain Co@CeO2 / NC composite nanoparticle catalytic material.

5. The preparation method according to claim 4, characterized in that, In step (1), the molar ratio of cobalt nitrate to cerium nitrate in the mixed solution is 2-3:1; the mass concentration ratio of melamine to sucrose is 1-2:

1.

6. The preparation method according to claim 5, characterized in that, In the mixed solution, the concentration of cobalt nitrate is 0.02~0.09 mol / L, the concentration of cerium nitrate is 0.01~0.03 mol / L, the concentration of melamine is 50~150 g / L, and the concentration of sucrose is 30~90 g / L.

7. The preparation method according to claim 4, characterized in that, In step (3), the volume ratio of argon to hydrogen in the mixed atmosphere is 1:2-4; preferably, the volume ratio of argon to hydrogen is 1:

3.

8. The preparation method according to claim 4, characterized in that, In step (3), the calcination treatment is carried out at a temperature of 800-900℃ for 2-3 hours.

9. The application of the Co@CeO2 / NC composite nanoparticle catalytic material according to any one of claims 1-3 as a catalyst in the synthesis of ammonia by nitrate reduction.

10. The application according to claim 9, characterized in that, The amount of the Co@CeO2 / NC composite nanoparticle catalytic material used is 3-5 wt% of the total raw material.

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