A ternary metal catalyst, its preparation method and electrocatalytic applications thereof

Abstract

The application relates to a ternary metal nanocatalyst and a preparation method and application thereof, and relates to the field of catalytic chemistry. The specific steps of the method are as follows: soluble iron salt, soluble nickel salt and soluble aluminum salt are added into deionized water, and a carbon carrier is added as a substrate and is subjected to ultrasonic treatment. An alkaline solution containing sodium carbonate and sodium hydroxide is added dropwise into the prepared metal salt solution under vigorous stirring. The metal salt suspension is aged; the obtained solution is centrifuged, the solid is collected and vacuum dried and ground. The activated carbon loaded iron-nickel-aluminum ternary metal nanocatalyst can realize the complementary advantages among multiple components, and the synergistic mechanism makes the iron-nickel-aluminum catalyst exhibit better ammonia production rate and selectivity than single metal components in a neutral environment, and can be used for electrocatalytic nitrate reduction to prepare ammonia.

Description

Technical Field

[0001] This invention relates to the field of electrochemical catalysis, specifically to a ternary metal electrocatalyst and its application in the electrocatalytic reduction of nitrate to ammonia. Background Technology

[0002] The nitrogen cycle is a vital fundamental cycle in the biosphere. In recent years, human activities (including industrial wastewater discharge, fossil fuel combustion, the extensive use of chemical fertilizers in agriculture, and the indiscriminate discharge of domestic wastewater) have led to a dramatic increase in nitrate levels in groundwater and surface water. This severely disrupts the nitrogen cycle in ecosystems and may pose a serious threat to biological health. Among various nitrogenous pollutants, nitrates exhibit high mobility, high solubility, and stability in water. Common methods for removing nitrates from water include biological, physicochemical, and chemical methods. Electrocatalytic nitrate reduction reaction (eNO3RR) is a highly efficient and environmentally friendly removal technology that has emerged in recent years. It boasts advantages such as good environmental compatibility, no secondary pollution, low maintenance costs, ease of remote control and automation, the ability to convert renewable energy sources (such as solar, wind, and tidal energy) into electricity under normal temperature and pressure, and ease of scaling up from laboratory-scale to large-scale applications. It demonstrates significant advantages and application potential in purifying nitrate-contaminated water bodies and ensuring water safety.

[0003] Currently, compared to transition metals, noble metals are the preferred choice for catalyst design in nitrate reduction processes due to their high catalytic activity, high selectivity, and improved electron transfer kinetics. However, when using noble metals, the cost and complexity involved in catalyst synthesis must be considered. Furthermore, noble metals may be susceptible to poisoning from substances present in nitrate solutions (such as sulfur compounds) encountered in real-world water treatment scenarios. Therefore, developing high-abundance, low-cost non-transition metal alternative catalysts has become a research hotspot in this field. Achieving efficient eNO3RR requires a complex eight-electron transfer process. Traditional single-metal catalysts (such as single iron, cobalt, or nickel) have limited active sites, making it difficult to simultaneously achieve effective nitrate activation and sufficient hydrogen supply, resulting in slow reaction kinetics and ammonia production rates and selectivity that fail to meet practical requirements. Moreover, even if the introduction of binary metals improves reaction kinetics to some extent, their interfacial structures are often unstable and prone to reconstruction or deactivation at high current densities. In addition, traditional materials, without reasonable nanoscale structural design, are prone to particle aggregation and limited mass transfer. These multi-dimensional shortcomings ultimately make it difficult to further improve the ammonia yield and Faraday efficiency of the system. Summary of the Invention

[0004] To address the aforementioned technical challenges, the present invention aims to provide a stable, highly efficient, and cost-effective activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst for electrocatalytic nitrate-to-ammonia production. This nanocatalyst achieves complementary advantages among its multiple components: iron excels in adsorption and initial deoxygenation, nickel in proton donation and deep hydrogenation, and aluminum enhances the catalyst's robustness during the electrocatalytic process. This synergistic mechanism enables the iron-nickel-aluminum catalyst to exhibit significantly higher ammonia production yield and selectivity under neutral conditions compared to single-metal components.

[0005] To achieve this objective, the present invention adopts the following solution:

[0006] (1) Add soluble iron salt, soluble nickel salt and soluble aluminum salt to deionized water, and add carbon support as substrate, and sonicate.

[0007] (2) Under vigorous stirring, an alkaline solution containing sodium carbonate and sodium hydroxide is added dropwise to the prepared metal salt solution.

[0008] (3) Aging the metal salt suspension; centrifuging the resulting solution, collecting the solid and vacuum drying and grinding.

[0009] Preferably, in step (1), the molar ratio of iron to nickel in the iron salt and nickel salt is 1:3 to 3:1, the molar ratio of aluminum to nickel in the nickel salt and aluminum salt is 1:1, and the mass of the carbon support accounts for 5%-10% of the solid content of the metal salt solution.

[0010] Preferably, in step (1), the soluble iron salt can be one of ferrous nitrate, ferrous sulfate, or ferrous chloride; the soluble nickel salt can be one of nickel nitrate, nickel sulfate, or nickel chloride; and the soluble aluminum salt can be one of aluminum nitrate, aluminum sulfate, or aluminum chloride.

[0011] Preferably, in step (2), the pH value of the alkaline solution is 9-10.

[0012] Preferably, in step (3), the solution aging temperature is 60-90℃ and the time is 6-12 hours. The vacuum drying temperature is 50-60℃ and the time is 12-24 hours.

[0013] The catalyst prepared by this invention can be used in the electrocatalytic reduction of nitrate to ammonia.

[0014] Preferably, an electrochemical workstation is used to perform electrochemical measurements in a three-electrode H-type cell. CP, Ag / AgCl, and platinum electrodes modified with electrocatalysts are used as the working electrode, reference electrode, and counter electrode, respectively.

[0015] Preferably, a sodium sulfate and sodium phosphate buffer solution is used as the electrolyte solution to simulate an industrial wastewater environment. The catalytic reaction is carried out at room temperature and pressure.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This catalyst utilizes transition metals iron and nickel to construct active centers, aiming to leverage the nitrate-trapping capacity of iron sites and the efficient water dissociation characteristics of nickel sites under neutral conditions. Through intermetallic electronic synergy and active hydrogen spillover effects, a highly efficient relay catalytic system was successfully constructed, effectively addressing the problem of slow reaction kinetics under neutral conditions. Commercially available activated carbon, an economical and practical material, serves as the supporting framework. Its densely packed defects and functional groups provide ideal metal binding sites, effectively overcoming the problem of nanoparticle agglomeration during traditional reduction processes. This robust anchoring effect allows metal nanoparticles to be uniformly dispersed on the support surface at extremely small sizes, thereby significantly increasing the effective catalytic active sites of the system.

[0018] In nitrate reduction, the catalyst maintained a total Faradaic efficiency close to 100% across multiple cycles; the ammonia yield and Faradaic efficiency remained at 0.55 mol h⁻¹. -1 g -1 With an efficiency of 93% or higher, the catalyst exhibits good durability and catalytic performance. In simulations of actual industrial and commercial wastewater, the catalyst demonstrates high Faradaic efficiency and yield for the reduction of nitrate to ammonia, indicating the potential of the ternary catalyst to treat nitrate-contaminated water under various electrolyte conditions and in the presence of interfering ions. During long-term constant-potential electrolysis, the catalyst remains active after 38 hours of electrolysis, demonstrating excellent stability compared to traditional zero-valent iron materials that are prone to passivation and deactivation. Attached Figure Description

[0019] Figure 1 The LSV current is given by the ternary metal catalyst electrode and the carbon paper electrode in a phosphate solution with or without nitrate ions.

[0020] Figure 2 A comparison chart of the Faraday efficiencies of iron-aluminum hydroxy complex salt, nickel-aluminum hydroxy complex salt, and the ternary metal catalyst described in this invention for constant potential electrolysis of ammonia production.

[0021] Figure 3 A comparison chart of the Faraday efficiencies of iron-aluminum hydroxy complex salts, nickel-aluminum hydroxy complex salts, and the byproducts of constant-potential electrolysis using the ternary metal catalyst described in this invention.

[0022] Figure 4 The yield of ammonium and the Faraday efficiency of the three-way catalyst were tested by cyclic testing in sulfate solution.

[0023] Figure 5 The yield of byproducts and Faraday efficiency of the three-way catalyst were tested by cyclic analysis in sulfate solution.

[0024] Figure 6 The yield of ammonium and the Faraday efficiency of the three-way catalyst were tested by cyclic testing in phosphate solution.

[0025] Figure 7 The yield of byproducts and Faraday efficiency of the three-way catalyst were tested by cycling in phosphate solution.

[0026] Figure 8 The yield and Faraday efficiency of the three-way catalyst were tested in simulated commercial and industrial wastewater cycles.

[0027] Figure 9 This is a graph showing the results of long-term operation of the three-way catalyst. Specific implementation methods

[0028] The present invention will now be described in detail through specific embodiments.

[0029] Example 1

[0030] (1) Dissolve Fe(NO3)2·H2O (1.5 mmol), Al(NO3)3·9H2O (0.5 mmol), Ni(NO3)2·3H2O (0.5 mmol) and 50 mg of carbon powder in 10 mL of deionized water and then sonicate.

[0031] (2) While stirring, add an alkaline solution containing 0.05 M Na2CO3 and 0.2 M NaOH dropwise to the prepared metal salt solution, and use a pH meter to detect the pH value of the solution in real time until the pH of the solution reaches 10 (±0.1).

[0032] (3) The prepared metal salt suspension needs to be aged at 90°C for 6 hours.

[0033] (4) The mixture obtained by centrifugation was washed three times with deionized water and ethanol respectively, the solid was collected and dried under vacuum at 60°C for 24 hours. The dried solid was ground to obtain the catalyst.

[0034] (5) Add 2 mg of catalyst to 192 μL of ethanol and 8 μL of Nafion membrane solution and sonicate for 20 min. Take 20 μL and drop it onto a 1 cm membrane. 2 The carbon paper was vacuum dried on both sides for 20 minutes to obtain a catalyst-modified carbon paper electrode.

[0035] Example 2

[0036] Electrochemical measurements were performed in a three-electrode H-type cell using a 660E electrochemical workstation (CH Instrument). A carbon paper electrode modified with an electrocatalyst, an Ag / AgCl (3 M KCl) electrode, and a platinum electrode were used as the working electrode, reference electrode, and counter electrode, respectively. The electrolyte solution was neutral, with a KNO3 concentration of 50 mM. The electrolyte capacity in each chamber of the H-cell was 30 mL. Before the electrochemical experiments, the top space of the H-cell was purged with argon gas.

[0037] Linear sweep voltammetry (LSV) at 10 mV s -1 The scan rate is [specified]. The electrodes include a carbon paper (CP) electrode and a catalyst electrode. For example... Figure 1 As shown, the linear voltammetric curves (denoted as FeNiAlNO3) of the CP electrode in 0.5 M sodium phosphate buffer (CP), the catalyst electrode in 0.5 M sodium phosphate buffer (FeNiAl), and the catalyst electrode in 0.5 M sodium phosphate buffer containing 50 mM potassium nitrate were tested respectively. - This shows that the catalyst has good catalytic performance for nitrate reduction.

[0038] Example 3

[0039] The selectivity of nitrate reduction products was evaluated by constant-potential electrolysis of the ternary metal catalyst. The electrochemical testing environment was the same as in Example 2, using an H-type electrolytic cell. A silver / silver chloride electrode was used as the reference electrode, and a platinum electrode as the counter electrode. Each cell was filled with 30 ml of electrolyte. The electrolyte was a 0.5 M sodium phosphate buffer solution containing 50 mM potassium nitrate. Figure 2 and Figure 3 The catalysts tested included: iron-aluminum hydroxy complex salt (FeAl), nickel-aluminum hydroxy complex salt (NiAl), and the ternary metal catalyst described in this invention (FeNiAl). The electrolysis time was 30 min. The reduction products of nitrite and ammonia were quantified using a colorimetric method. It is evident that the ternary metal catalyst exhibits high selectivity for ammonia (e.g., ...). Figure 2 ), while exhibiting low selectivity for the byproduct nitrite (e.g. Figure 3 ).

[0040] Example 4

[0041] To evaluate the durability of the three-way catalyst, the Faradaic efficiency and yield of nitrate reduction were monitored for six cycles, each lasting 30 minutes, in 0.5 M sodium phosphate buffer containing 50 mM nitrate and 0.5 M sodium sulfate solution containing 50 mM potassium nitrate. Figure 4 , Figure 5The overall Faraday efficiency was close to 100% for all six cycles; the ammonia yield and Faraday efficiency remained at 0.55 mol / h. -1 g -1 The yields and faradaic efficiency of the byproduct nitrite were consistently below 0.1 mol / h. -1 g -1 and less than 5%. In sodium phosphate solution (e.g. Figure 6 , Figure 7 The overall Faradaic efficiency of the ternary metal catalyst for nitrate reduction remained above 90% for six consecutive cycles without decline. The ammonia yield and Faradaic efficiency remained at 0.4 mol / h. -1 g -1 The yields and faradaic efficiency of the byproduct nitrite were consistently below 0.006 mol / h. (Above and >90%) -1 g -1 And less than 0.3%.

[0042] Example 5

[0043] Based on literature reports, simulated actual industrial and commercial wastewater was prepared to study the role of catalysts in real commercial and industrial wastewater fluid environments. The proportions of nitrate and phosphate in industrial wastewater (1000 ppm nitrate and 21 ppm phosphate) were increased proportionally to raise the total concentration of nitrate and phosphate in the solution to 50 mM (3100 ppm); the proportions of nitrate and sulfate in commercial laundry water (8.37 ppm nitrate and 21.06 ppm sulfate) were also increased proportionally to raise the total concentration of nitrate and sulfate to 50 mM (3100 ppm); chloride ions were introduced to make the total electrolyte concentration 0.5 M. It is evident that the ternary metal catalyst exhibits high Faraday efficiency and yield (e.g., ...) in wastewater simulating both commercial and industrial wastewater with high phosphate and sulfate content. Figure 8 In commercial laundry water systems, its NH3 content is... 4+ The Faraday efficiency is as high as approximately 93%, corresponding to a yield of approximately 0.57 mol / h. -1 g -1 In industrial wastewater, the Faraday efficiency is approximately 89%, and the yield is approximately 0.48 mol / h. -1 g -1 This indicates that the three-way catalyst has the potential to treat nitrate-contaminated water under various electrolyte conditions and in the presence of interfering ions.

[0044] Example 6

[0045] To evaluate the durability of the ternary catalyst, it was continuously electrolyzed at a constant potential of -1.1 V for 38 h using a 0.5 M phosphate buffer solution containing 50 mM nitrate. The catalytic current remained relatively stable during the long-term electrolysis process, indicating that the catalyst can maintain its activity even under prolonged operation (e.g., ...). Figure 9 Compared to traditional zero-valent iron materials that are prone to passivation and deactivation, ternary metal catalysts exhibit good stability.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst, characterized in that: Step 1: Add soluble iron salt, soluble nickel salt and soluble aluminum salt to deionized water, add carbon support as substrate, and sonicate to obtain metal salt solution; Step 2: Under vigorous stirring, an alkaline solution containing sodium carbonate and sodium hydroxide is added dropwise to the prepared metal salt solution to obtain a metal salt suspension; Step 3: Aging the metal salt suspension; The resulting solution was centrifuged, the solid was collected, and then vacuum dried and ground to obtain the catalyst.

2. The method for preparing an activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst according to claim 1, characterized in that, In step 1, the molar ratio of iron to nickel in the iron salt and nickel salt is 1:3 to 3:1, the molar ratio of aluminum to nickel in the nickel salt and aluminum salt is 1:1, and the mass of the carbon support accounts for 5%-10% of the solid content of the metal salt solution.

3. The method for preparing an activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst according to claim 1, characterized in that, In step 1, the soluble iron salt may be one of ferrous nitrate, ferrous sulfate, or ferrous chloride; the soluble nickel salt may be one of nickel nitrate, nickel sulfate, or nickel chloride; and the soluble aluminum salt may be one of aluminum nitrate, aluminum sulfate, or aluminum chloride.

4. The method for preparing an activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst according to claim 1, characterized in that, In step (2), the pH value of the metal salt suspension is 9-10.

5. The method for preparing an activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst according to claim 1, characterized in that, In step 3, the solution aging temperature is 60-90℃ and the time is 6-12 hours; the vacuum drying temperature is 50-60℃ and the time is 12-24 hours.

6. An activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. The application of the activated carbon-supported iron-nickel-aluminum trimetallic nanocatalyst according to claim 6 in the electrocatalytic reduction of nitrate to ammonia.

8. The application according to claim 7, characterized in that: The electrolyte contains sulfates or phosphates.

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