Preparation method of dendritic copper oxide catalyst and application thereof in electrocatalytic reduction of nitrate to ammonia

Abstract

This invention discloses a method for preparing a dendritic copper oxide catalyst and its application in the electrocatalytic reduction of nitrate to ammonia. The method includes the following steps: S1, preparing aqueous solutions of metaborate and copper source compound using metaborate and a copper source compound respectively, then adding the aqueous solution of metaborate to the aqueous solution of copper source compound, stirring and dispersing to obtain an emulsion; S2, placing the obtained emulsion in a hydrothermal reactor and carrying out a hydrothermal reaction at a certain temperature to obtain the dendritic copper oxide catalyst. This invention utilizes BO2... ‑ Adjusting the microstructure and electronic structure of Cu-based oxide catalysts significantly improved the electrocatalytic performance of copper catalysts for NO3-. ‑ The technical effects of conversion for ammonia production: The prepared dendritic copper oxide catalyst exhibited excellent ammonia product selectivity and NH3 yield in the electrocatalytic nitrate reduction reaction.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical catalytic synthesis technology, and specifically relates to a method for preparing a dendritic copper oxide catalyst and its application in the electrocatalytic reduction of nitrate to ammonia. Background Technology

[0002] Ammonia is an important chemical widely used in agriculture, medicine, and renewable energy. Currently, the main method for synthesizing ammonia is the Haber-Bosch process, but this process requires high temperature and pressure conditions, consuming approximately 2-5% of global energy demand and generating 1% of carbon dioxide, a greenhouse gas. NO3 - The accumulation of nitrates in water bodies leads to eutrophication and disruption of the nitrogen cycle. Meanwhile, excessively high nitrate concentrations in drinking water threaten human health, potentially causing methemoglobinemia and gastrointestinal cancers. Electrocatalytic reduction of nitrates to ammonia (NO3RR) is a highly efficient and green pathway that can convert nitrates into harmless or value-added products. However, the NO3RR reaction pathway is complex (8e...). - (Reaction pathway), leading to an increase in reaction byproducts and a decrease in selectivity.

[0003] Currently, existing Cu-based catalysts are favored due to their excellent ability to utilize NO3-. - Deoxygenation to NO2 - Cu-based catalysts are widely used in the electrocatalytic reduction of nitrate to ammonia. However, Cu-based catalysts have poor stability, and the reaction intermediate NO2... - Low conversion rate on the catalyst surface leads to a decrease in NH3 selectivity and ammonia production yield.

[0004] Therefore, this invention achieves the control of NO3 by adjusting the morphology of Cu-based catalysts and the electronic structure of Cu. - The improved conversion capacity provides a new approach to enhancing the electrocatalytic reduction of nitrate to ammonia using CuO catalysts. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a method for preparing a dendritic copper oxide catalyst and its application in the electrocatalytic reduction of nitrate to ammonia. This preparation method is simple, and the resulting dendritic copper oxide catalyst can efficiently catalyze the reduction of nitrate to ammonia, thereby improving the NO3- concentration. - Faraday efficiency and ammonia yield in reduction ammonia production.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a method for preparing a dendritic copper oxide catalyst, comprising the following steps:

[0008] S1. Prepare aqueous solutions of metaborate and copper source compound using metaborate and copper source compound respectively. Then add the aqueous solution of metaborate to the aqueous solution of copper source compound and stir to disperse to obtain an emulsion.

[0009] S2. The obtained emulsion is placed in a hydrothermal reactor and subjected to a hydrothermal reaction at a certain temperature to obtain a copper oxide catalyst.

[0010] Preferably, in step S1, the metaborate is NaBO2·xH2O or KBO2·xH2O; the copper source compound is CuSO4·5H2O or Cu(CH3COO)2·H2O.

[0011] Preferably, the metaborate reacts with BO2 in the copper source compound. - / Cu 2+ The molar ratio is 1.5~2.3:1.

[0012] Preferably, the aqueous solution of the metaborate has a mass-volume concentration of 0.05~0.10 g / ml; and the aqueous solution of the copper source compound has a mass-volume concentration of 0.01~0.08 g / ml.

[0013] Preferably, in step S2, the temperature of the hydrothermal reaction is 160~200℃, and the hydrothermal reaction time is 4~8h.

[0014] Preferably, in step S2, after the hydrothermal reaction is completed, a purification step is further included: the reaction product is sequentially filtered, washed until neutral, and dried.

[0015] A second aspect of the present invention provides a dendritic copper oxide catalyst prepared by the above-described preparation method.

[0016] A third aspect of the present invention provides the application of the above-described dendritic copper oxide catalyst in the electrocatalytic reduction of nitrate to ammonia.

[0017] The present invention has the following beneficial effects:

[0018] This invention prepares a dendritic copper oxide catalyst via a hydrothermal reaction using metaborate and a copper source compound as raw materials and water as a solvent. Metaborate is used in this invention because of the BO2 content in metaborate. - In the hydrothermal crystal growth process, it can play a role in morphology regulation. Test results show that CuO catalysts with different morphologies exhibit differences in the electronic structure of Cu after electrocatalytic reduction. Furthermore, experimental results indicate that when this dendritic copper oxide catalyst is applied to NO3… -During the reduction of ammonia, it exhibited excellent Faraday efficiency and NH3 yield. This means that the dendritic copper oxide catalyst prepared in this invention significantly improved the reduction of NO3 by adjusting the microstructure and electronic structure of the Cu-based catalyst. - The technical effects of ammonia production. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 XRD patterns of copper oxides (Cu-B2 and Cu-B4) prepared in Example 1 and Comparative Example 1;

[0021] Figure 2 SEM images of copper oxide prepared in Examples 1-2: (a) Cu-B 1.5 (b) Cu-B2;

[0022] Figure 3 SEM images of copper oxide prepared for comparative examples 1-3: (a) Cu-B4; (b) Cu-B3; (c) Cu-B6;

[0023] Figure 4 The copper oxide catalysts (Cu-B2 and Cu-B4) prepared for Example 1 and Comparative Example 1 were used in 1 M KOH (containing 0.05 M NO3) - Or does not contain 0.05 M NO3 - Electrochemical LSV curves;

[0024] Figure 5 The graph shows the results of the synthesis yield and Faradaic efficiency of NH3 from the copper oxide catalysts (Cu-B2 and Cu-B4) prepared in Example 1 and Comparative Example 1.

[0025] Figure 6 The results of the 12-hour iterative test and cycle stability test of the copper oxide catalyst (Cu-B2) prepared in Example 1 are shown in the figure.

[0026] Figure 7 SEM image of copper oxide (Cu-B2) after cyclic stability testing;

[0027] Figure 8 The graph shows the electrochemical active surface area test results of Cu-B2 and Cu-B4 prepared in Example 1 and Comparative Example 1.

[0028] Figure 9 XPS fine spectra of Cu 2p for the copper oxide catalysts (Cu-B2 and Cu-B4) prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0029] In the following description, specific details such as particular system structures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the art will understand that the present invention may also be implemented in other embodiments without these specific details. The present invention will now be described in detail with reference to embodiments.

[0030] Example 1

[0031] (1) Weigh 1.1g NaBO2·4H2O and 1.0g CuSO4·5H2O and add each to 30 mL of water to dissolve them completely, so as to obtain a NaBO2 solution with a mass-volume concentration of 0.037g / mL and a CuSO4 solution with a mass-volume concentration of 0.033g / mL;

[0032] (2) Add CuSO4 solution to NaBO2 solution while stirring rapidly and stir magnetically to obtain a uniform light blue emulsion.

[0033] (3) The light blue emulsion was placed in a 100 mL polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 180 °C for 5 h. After filtration, the emulsion was washed with water and ethanol until it was neutral. The emulsion was dried at 80 °C to obtain a copper oxide catalyst, denoted as Cu-B2.

[0034] Example 2

[0035] (1) Weigh 0.827 g NaBO2·4H2O and 1.0 g CuSO4·5H2O and add each to 30 mL of water to dissolve them completely, so as to obtain a NaBO2 solution with a mass-volume concentration of 0.027 g / mL and a CuSO4 solution with a mass-volume concentration of 0.033 g / mL;

[0036] (2) Add CuSO4 solution to NaBO2 solution while stirring rapidly and stir magnetically to obtain a uniform light blue emulsion.

[0037] (3) The pale blue emulsion was placed in a 100 mL polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 180 °C for 5 h. After filtration, the emulsion was washed with water and ethanol until it was neutral. The emulsion was then dried at 80 °C to obtain the copper oxide catalyst, denoted as Cu-B. 1.5 .

[0038] Example 3

[0039] (1) Weigh 1.267g NaBO2·4H2O and 1.0g CuSO4·5H2O and add each to 30 mL of water to dissolve them completely, so as to obtain a NaBO2 solution with a mass-volume concentration of 0.042 g / mL and a CuSO4 solution with a mass-volume concentration of 0.033 g / mL;

[0040] (2) Add CuSO4 solution to NaBO2 solution while stirring rapidly and stir magnetically to obtain a uniform light blue emulsion.

[0041] (3) The pale blue emulsion was placed in a 100 mL polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 180 °C for 5 h. After filtration, the emulsion was washed with water and ethanol until it was neutral. The emulsion was then dried at 80 °C to obtain the copper oxide catalyst, denoted as Cu-B. 2.3 .

[0042] Comparative Example 1

[0043] (1) Weigh 2.2g NaBO2·4H2O and 1.0g CuSO4·5H2O and add each to 30 mL of water to dissolve them completely, so as to obtain a NaBO2 solution with a mass-volume concentration of 0.073g / mL and a CuSO4 solution with a mass-volume concentration of 0.033g / mL;

[0044] (2) Add CuSO4 solution to NaBO2 solution while stirring rapidly and stir magnetically to obtain a uniform light blue emulsion.

[0045] (3) The light blue emulsion was placed in a 100 mL polytetrafluoroethylene liner and subjected to hydrothermal reaction at 180 °C for 5 h. After filtration, the emulsion was washed with water and ethanol until it was neutral. The emulsion was dried at 80 °C to obtain copper oxide catalyst, denoted as Cu-B4.

[0046] Comparative Example 2

[0047] (1) Weigh 1.65g NaBO2·4H2O and 1.0g CuSO4·5H2O and add each to 30 mL of water to dissolve them completely, so as to obtain a NaBO2 solution with a mass-volume concentration of 0.055 g / mL and a CuSO4 solution with a mass-volume concentration of 0.033 g / mL;

[0048] (2) Add CuSO4 solution to NaBO2 solution while stirring rapidly and stir magnetically to obtain a uniform light blue emulsion.

[0049] (3) The light blue emulsion was placed in a 100 mL polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 180°C for 5 h. After filtration, the emulsion was washed with water and ethanol until it was neutral. The emulsion was dried at 80°C to obtain copper oxide, denoted as Cu-B3.

[0050] Comparative Example 3

[0051] (1) Weigh 3.3g NaBO2·4H2O and 1.0g CuSO4·5H2O and add each to 30 mL of water to dissolve them completely, so as to obtain NaBO2 solutions with a mass-volume concentration of 0.110 g / mL, namely solution A and solution B;

[0052] (2) Add solution B to solution A while stirring rapidly and stir magnetically to obtain a uniform light blue emulsion;

[0053] (3) The light blue emulsion was placed in a 100 mL polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 180 °C for 5 h. After filtration, the emulsion was washed with water and ethanol until it was neutral. The emulsion was dried at 80 °C to obtain a copper oxide catalyst, denoted as Cu-B6.

[0054] (a) The copper oxides (i.e., Cu-B2 and Cu-B4) prepared in Example 1 and Comparative Example 1 were characterized by XRD and SEM, and the results are shown in the figure. Figure 1 .

[0055] Depend on Figure 1 The results show that Cu-B2 and Cu-B4 prepared in Example 1 and Comparative Example 1 of this invention both contain CuO phase.

[0056] Depend on Figure 2 Results (a)-(b) show that the copper oxides (Cu-B2 and Cu-B2) prepared in Examples 1-2... 1.5 The morphology of all of them is dendritic.

[0057] Depend on Figure 3 The results show that the copper oxides (Cu-B4, Cu-B3, Cu-B6) prepared in Comparative Examples 1-3 all have a leaf-like structure.

[0058] Analysis of the above XRD and SEM test results shows that BO2 in metaborate - Cu in copper source compounds 2+ The molar ratio is in the range of 1.5~2.3:1, and the Cu content varies with different molar ratios. 2+ And BO2 - Copper oxide catalysts with different dendritic morphologies can be prepared. When the molar ratio exceeds the above range, the morphology of the copper oxide obtained is a leaf-like structure.

[0059] (b) Study on catalyst activity

[0060] Specific steps: Cu-B2 and Cu-B4 prepared in Example 1 and Comparative Example 1 of this invention were respectively placed in a three-electrode system, with and without NO3. -Linear sweep voltammetry was performed in KOH solution, and the results are shown in [Figure number missing]. Figure 4 .

[0061] Depend on Figure 4 The results show that, compared with Cu-B4 prepared in Comparative Example 1, the current density response value of Cu-B2 prepared in Example 1 is much greater than that of Cu-B4, indicating that the dendritic Cu-B2 has superior catalytic properties for NO3. - The performance of ammonia production by reduction.

[0062] (c) The ammonia production yield and Faraday efficiency of Cu-B2 and Cu-B4 prepared in Example 1 and Comparative Example 1 were analyzed, and the results are shown in […]. Figure 5 .

[0063] Depend on Figure 5 The results showed that the ammonia production yield of dendritic Cu-B2 was as high as 14.6 mg h. -1 cm -2 The Faraday efficiency was 92%, significantly better than that of leaf-shaped Cu-B4 (yield of 10.4 mg / h). -1 cm -2 Faraday efficiency is 82%.

[0064] (d) The catalytic stability of Cu-B2 prepared in Example 1 was tested, and its morphology after 12 h of ionization (it) was characterized by SEM. The results are shown in the figure. Figure 6 and Figure 7 .

[0065] Depend on Figure 6 The results show that after 12 hours of IT testing, the current density decreased by only 8%, and after 5 cycles of stability testing, the Faraday efficiency changed by only 3%.

[0066] Depend on Figure 7 The results show that the dendritic morphology of Cu-B2 was basically maintained after 12 h of it test reaction.

[0067] The above tests show that the dendritic copper oxide prepared by this invention has excellent catalytic stability.

[0068] (e) The electrochemical active surface area of ​​Cu-B2 and Cu-B4 prepared in Example 1 and Comparative Example 1 was measured, and the results are shown in [Figure number missing]. Figure 8 .

[0069] Depend on Figure 8 The results show that the electrochemically active surface area of ​​Cu-B2 is 2.55 mF cm⁻¹. -2 Greater than Cu-B4 (1.10 mF cm) -2This indicates that the Cu-B2 prepared in Example 1 of this invention exposes more active sites. This electrochemical characterization demonstrates that the Cu-B2 catalyst has a larger electrochemical active surface area and exposes more catalytic active sites, thereby enhancing its catalytic activity.

[0070] (f) Fine Cu 2p spectra XPS analysis was performed on the copper oxide catalysts (Cu-B2 and Cu-B4) prepared in Example 1 and Comparative Example 1. The results are shown in [Figure number missing]. Figure 9 .

[0071] Depend on Figure 9 High-resolution Cu 2p XPS spectra show that the two characteristic peaks at 934.5 and 954.6 eV correspond to Cu. 2+ 2p 3 / 2 and Cu 2+ 2p 1 / 2 The satellite peaks in the XPS at 940-944 eV indicate the presence of Cu. 2+ The presence of the species; the characteristic peaks at 932.5 and 952.5 eV can be attributed to Cu, respectively. 0 2p 3 / 2 and Cu 0 2p 1 / 2 ; and Cu in Cu-B4 catalyst 0 The species exhibits a significant negative migration in binding energy compared to Cu-B2, indicating that Cu in Cu-B2 undergoes a negative migration. 0 The oxidation state of the substance is lower than that of Cu-B4. This low-oxidation-state catalyst favors the conversion of NO3-. - It provides electrons to carry out the reduction reaction.

[0072] This invention is not limited to the specific embodiments described above. Any modifications made by those skilled in the art based on the above concept without creative effort are within the scope of protection of this invention.

Claims

1. A method for preparing a dendritic copper oxide catalyst, characterized in that, Includes the following steps: S1. Prepare aqueous solutions of metaborate and copper source compound using metaborate and copper source compound respectively. Then add the aqueous solution of metaborate to the aqueous solution of copper source compound and stir to disperse to obtain an emulsion. S2. The obtained emulsion is placed in a hydrothermal reactor and subjected to a hydrothermal reaction at a certain temperature to obtain a copper oxide catalyst. In step S1, the metaborate is NaBO2·xH2O or KBO2·xH2O; the copper source compound is CuSO4·5H2O or Cu(CH3COO)2·H2O; the metaborate and the BO2 in the copper source compound... - and Cu 2+ The molar ratio is 1.5~2.3:1; In step S2, the temperature of the hydrothermal reaction is 160~200℃, and the hydrothermal reaction time is 5~8h.

2. The method for preparing the dendritic copper oxide catalyst according to claim 1, characterized in that, In step S1, the mass-volume concentration of the aqueous solution of the metaborate is 0.05~0.10 g / ml; the mass-volume concentration of the aqueous solution of the copper source compound is 0.01~0.08 g / ml.

3. The method for preparing the dendritic copper oxide catalyst according to claim 1, characterized in that, In step S2, after the hydrothermal reaction is completed, a purification step is also included: the reaction product is sequentially filtered, washed until neutral, and dried.

4. A dendritic copper oxide catalyst prepared by the preparation method according to any one of claims 1-3.

5. The application of the dendritic copper oxide catalyst as described in claim 4 in the electrocatalytic reduction of nitrate to ammonia.

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