Method for reducing nitrate in wastewater

Abstract

The invention relates to a method for reducing nitrate in waste water, and the method comprises the following steps: adding a first reducing agent into the waste water, and adjusting the pH value of the waste water to 6.5-7.5 to obtain waste water to be treated; carrying out contact catalytic reduction reaction on the wastewater to be treated and a catalyst; wherein the first reducing agent comprises oxysalt of sulfur; the catalyst comprises a carrier and an active component loaded on the carrier, the active component comprises an iron element and a noble metal element, and the noble metal element is one or more of ruthenium, palladium and tin. The method disclosed by the invention is simple and easy to implement, mild in operation condition, free of an oxygen-free environment and limitation of an over-high or over-low pH value, relatively high in tolerance to the content of organic matters in the wastewater and salinity, and high in removal rate of nitrate.

Description

Technical Field

[0001] This disclosure relates to the field of wastewater treatment technology, and more specifically, to a method for reducing nitrates in wastewater. Background Technology

[0002] Nitrate is a common water pollutant, mainly originating from industrial wastewater, agricultural drainage, and domestic sewage. High concentrations of nitrate can have adverse effects on the environment and human health, such as causing eutrophication, damaging aquatic ecosystems, producing carcinogens, and entering the human body through the food chain, posing potential health risks. Therefore, developing effective nitrate removal methods is of significant theoretical and practical importance.

[0003] Currently, the main methods for treating high-nitrate wastewater include biological, physical, and chemical methods. Biological methods primarily utilize the denitrification process of microorganisms to convert nitrates into nitrogen gas, thereby removing nitrates. Physical methods mainly include ion exchange, electrodialysis, and membrane separation, which primarily separate nitrates from wastewater through physical processes. Chemical methods mainly use chemical reactions to convert nitrates into other harmless substances, such as ammonia and nitrogen gas, with added reducing agents such as hydrogen, iron powder, and ferrous sulfate. In recent years, more research has focused on active metal reduction, electrochemical reduction, catalytic hydrogenation reduction, and photocatalytic reduction. However, existing nitrate removal methods all have some problems and drawbacks. For example, the treatment effect of biological methods is affected by various factors, such as the biodegradability of the wastewater, dissolved oxygen, pH value, and carbon source, and the treatment time is relatively long, making it unsuitable for treating nitrate wastewater with poor biodegradability. Physical methods only transfer nitrates from the aqueous phase to the adsorption phase, without truly solving the nitrate pollution problem, and may cause secondary pollution. Electrochemical and photocatalytic methods are energy-intensive, require strict operating conditions, have poor reaction selectivity, and may produce harmful byproducts. Catalytic hydrogenation reduction denitrification is highly efficient, but there are safety hazards in the transportation and storage of the reducing agent hydrogen, resulting in high risks in on-site applications.

[0004] CN108499567A discloses a treatment method for various industrial nitrate-containing wastewaters using nano-nickel as a catalyst for nitrate reduction reaction. This method has the ability to rapidly and efficiently degrade nitrates without causing secondary pollution. The reduction reaction is less affected by pH value. However, the reduction reaction needs to be carried out under anaerobic conditions, and the deoxygenation treatment is costly, which limits its application in wastewater treatment plants.

[0005] CN109622019A discloses a technology for the catalytic reduction of acid salts in wastewater under ultraviolet light irradiation. Nitrogen compounds in the water act as photocatalysts, possessing a relatively negative conduction band potential. The photogenerated electrons generated by photon excitation can directly reduce nitrates in the water. However, the reaction requires the addition of formic acid or EDTA-2Na as a hole scavenger, resulting in high energy consumption during the removal process. Furthermore, the addition of formic acid or EDTA-2Na increases the COD of the wastewater.

[0006] CN111533220A discloses a method for removing nitrates from wastewater by electrochemical catalytic reduction. Hydrogen is generated through a hydrogen evolution reaction at the cathode and directly used as a reducing agent for catalytic reduction of nitrates. By suspending the denitrification catalyst in the electrolyzer, the mass transfer between hydrogen and the catalyst is increased, enabling the denitrification system to perform both electrocatalytic hydrogen evolution and catalytic hydrogenation. However, using hydrogen as a reducing agent to remove nitrates easily produces the byproduct NH4. + This reduces the effectiveness of total nitrogen removal. Summary of the Invention

[0007] The purpose of this disclosure is to provide a method for reducing nitrates in wastewater. The method is simple and easy to implement, operates under mild conditions, does not require an anaerobic environment or excessively high or low pH values, has high tolerance for organic matter content and salt content in wastewater, and has a high nitrate removal rate.

[0008] To achieve the above objectives, this disclosure provides a method for reducing nitrates in wastewater, the method comprising: adding a first reducing agent to the wastewater and adjusting the pH of the wastewater to 6.5-7.5 to obtain wastewater to be treated; and contacting the wastewater to be treated with a catalyst to react. The first reducing agent comprises an oxyacid salt of sulfur; the catalyst comprises a support and an active component supported on the support, the active component comprising iron and a noble metal element, the noble metal element comprising one or more of ruthenium, palladium and tin.

[0009] Optionally, based on the weight of the catalyst, the iron element accounts for 1-8% by mass, and the precious metal element accounts for 0.07-0.3% by mass. The carrier includes one or more of activated carbon, activated coke, petroleum coke and alumina, preferably petroleum coke.

[0010] Optionally, the precious metal element is ruthenium and tin; based on the weight of the catalyst, the mass percentage of iron is 1-8%; the mass percentage of ruthenium is 0.02-0.1%; and the mass percentage of tin is 0.05-0.2%.

[0011] Optionally, the precious metal element is ruthenium and palladium; based on the weight of the catalyst, the mass percentage of iron is 1-8%; the mass percentage of ruthenium is 0.02-0.1%; and the mass percentage of palladium is 0.01-0.1%.

[0012] Optionally, the first reducing agent includes one or more of thiosulfate, sulfite and dithionite, preferably thiosulfate.

[0013] Optionally, the chemical oxygen demand (COD) of the wastewater is 0-1000 mg / L, preferably 1-700 mg / L; the NO3 in the wastewater... - The concentration is 10~400mg / L.

[0014] Optionally, the mass ratio of the first reducing agent to the nitrate in the wastewater is 1~8:1, preferably 1.5~5:1; the mass ratio of the catalyst to the nitrate in the wastewater is 5~25:1, preferably 15~20:1.

[0015] Optionally, the reaction conditions include: a reaction temperature of 10~40℃, preferably 20~35℃; and a reaction time of 10~120min, preferably 30~50min.

[0016] Optionally, the method for preparing the catalyst includes: impregnating the support with a salt solution containing the iron element and the noble metal element, and then calcining and activating the impregnated solid.

[0017] Optionally, the calcination conditions include: a temperature of 200~550℃, preferably 300~450℃; and a time of 1~6h, preferably 2~4h. The second reducing agent used in the activation treatment includes one or more of potassium borohydride and sodium borohydride, preferably potassium borohydride.

[0018] Through the above technical solution, this disclosure reduces nitrates in wastewater by adjusting the pH of the wastewater, using a precious metal supported catalyst, and using sulfur-containing oxyacid salts as a reducing agent. The method is simple and easy to implement, the operating conditions are mild, and there is no need for an anaerobic environment or excessively high or low pH value restrictions. It has a high tolerance for organic matter content and salt content in wastewater, is suitable for treating high nitrate wastewater of various sources and properties, and has a high nitrate removal rate.

[0019] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0020] The specific embodiments described below are detailed below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of this disclosure.

[0021] This disclosure provides a method for reducing nitrates in wastewater, the method comprising: adding a first reducing agent to the wastewater and adjusting the pH of the wastewater to 6.5-7.5 to obtain wastewater to be treated; and contacting the wastewater to be treated with a catalyst to react. The first reducing agent comprises an oxyacid salt of sulfur; the catalyst comprises a support and an active component supported on the support, the active component comprising iron and a noble metal element, the noble metal element comprising one or more of ruthenium, palladium and tin.

[0022] This disclosure describes a method for reducing nitrates in wastewater by adjusting the pH, using a precious metal-supported catalyst, and using a sulfur-containing oxyacid acid reducing agent. The method is simple and easy to implement, operates under mild conditions, does not require an anaerobic environment or excessively high or low pH values, has high tolerance for organic matter content and salt content in wastewater, is suitable for treating high nitrate wastewater of various sources and properties, and has a high nitrate removal rate.

[0023] The catalytic reduction of nitrate disclosed herein is accomplished through multiple steps, NO3 - NO2 is first generated under the action of a catalyst. - NO is then generated on the catalyst metal surface. x NO x It combines to form an N-N bond to generate N2, but if it encounters H, it will form an NH bond, and then generate NH4. + This disclosure uses thiosulfate as a reducing agent, avoiding the use of organic compounds such as sodium formate and hydrogen as reducing agents. This avoids the excessive COD introduced into the wastewater by organic compounds such as sodium formate, and also avoids the safety risks associated with using hydrogen. Furthermore, it avoids the adsorption of H and NO on the catalyst metal surface. x This combination produces a large amount of the byproduct NH4. + This affects the removal efficiency of total nitrogen in wastewater.

[0024] The active component of the catalyst disclosed herein includes iron and noble metal elements, wherein the noble metal elements are one or more of ruthenium, palladium and tin. The catalyst has good catalytic activity and stability, and can efficiently catalyze the reduction of nitrates in chemical reduction reactions. It has a good effect on removing nitrate nitrogen from wastewater at normal temperature and pressure, while avoiding the generation of byproduct ammonia nitrogen.

[0025] According to one embodiment of this disclosure, based on the weight of the catalyst, the iron element accounts for 1-8% by mass, and the precious metal element accounts for 0.07-0.3% by mass. This embodiment is beneficial for improving the activity of the catalyst.

[0026] According to one embodiment of this disclosure, the carrier is selected from one or more of activated carbon, activated coke, petroleum coke, and alumina, preferably petroleum coke. The above-mentioned preferred embodiment uses a suitable catalyst carrier, which provides stable loading of the active components. Furthermore, petroleum coke has a large specific surface area, requires a small amount, and can be reused, thus helping to reduce processing costs.

[0027] According to one embodiment of this disclosure, the precious metal elements are ruthenium and tin; based on the weight of the catalyst, the mass percentage of iron is 1-8%; the mass percentage of ruthenium is 0.02-0.1%; and the mass percentage of tin is 0.05-0.2%. This embodiment is beneficial for obtaining catalysts with higher catalytic activity and achieving better reduction of nitrates in wastewater.

[0028] According to one embodiment of this disclosure, the precious metal elements are ruthenium and palladium; based on the weight of the catalyst, the mass percentage of iron is 1-8%; the mass percentage of ruthenium is 0.02-0.1%; and the mass percentage of palladium is 0.01-0.1%. This embodiment is beneficial for obtaining catalysts with higher catalytic activity and achieving better reduction of nitrates in wastewater.

[0029] According to one embodiment of this disclosure, the first reducing agent includes one or more of thiosulfate, sulfite, and dithionite; the thiosulfate can be a conventional thiosulfate in the art, preferably sodium thiosulfate; the sulfite can be a conventional sulfite in the art, preferably sodium sulfite; and the dithionite can be a conventional dithionite in the art, preferably sodium dithionite. The above embodiment avoids the safety problems or COD pollution that may arise from using other reducing agents.

[0030] According to one embodiment of this disclosure, the chemical oxygen demand (COD) of the wastewater is 0-1000 mg / L, preferably 1-700 mg / L; the NO3 in the wastewater... - The concentration is 10~400mg / L.

[0031] According to one embodiment of this disclosure, the method includes: adjusting the pH of the wastewater to 7.0-7.5 after adding a first reducing agent. Adjusting pH is a conventional practice in the art, and this disclosure does not impose any specific limitations. For example, the adjusting agents that can be used include one or more of hydrochloric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0032] According to one embodiment of this disclosure, the mass ratio of the first reducing agent to nitrate in the wastewater is 1-8:1, preferably 1.5-5:1; the mass ratio of the catalyst to nitrate in the wastewater is 5-25:1, preferably 15-20:1. This embodiment is beneficial for improving the removal rate of nitrate nitrogen and avoiding the generation of the byproduct ammonia nitrogen.

[0033] According to one embodiment of this disclosure, the reaction conditions include: a reaction temperature of 10-40°C, preferably 20-35°C; and a reaction time of 10-120 min, preferably 30-50 min. The above embodiment is beneficial for improving the removal efficiency of nitrates from wastewater.

[0034] According to one embodiment of this disclosure, the method for preparing the catalyst includes: impregnating the support with a salt solution containing the iron element and the noble metal element, and calcining and activating the impregnated solid.

[0035] According to one embodiment of this disclosure, the calcination conditions include: a temperature of 200-550°C, preferably 300-450°C; a time of 1-6 hours, preferably 2-4 hours; and the second reducing agent used in the activation treatment is selected from one or more of potassium borohydride and sodium borohydride, preferably potassium borohydride. The above embodiments are beneficial for obtaining catalysts with good catalytic activity and stability.

[0036] According to one embodiment of this disclosure, the method for preparing the catalyst further includes: washing, centrifuging, and drying the activated product. The washing, centrifuging, and drying processes are all conventional operations in the art, and this disclosure does not impose any special limitations.

[0037] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this disclosure. Unless otherwise specified, all reagents used in this disclosure are commercially available.

[0038] In this disclosure, NO3 in the treated wastewater is determined according to HJ / T346-2007 "Determination of Nitrate Nitrogen - Ultraviolet Spectrophotometry". - The concentration of NH4 in the treated wastewater was determined according to HJ / 535-2009 "Determination of Ammonia Nitrogen - Nessler's Reagent Spectrophotometric Method". + The concentration.

[0039] Example 1 Example 1 uses wastewater from a chemical plant. The water quality is as follows: pH value 6.4, NO3- - The concentration was 394.3 mg / L, NH4 +The concentration was 1.2 mg / L, the conductivity was 1.32 ms / cm, and the COD was 216.8 mg / L; The catalyst used in Example 1 was S1 (iron-ruthenium-palladium), and the specific preparation method included: soaking the catalyst support petroleum coke in a solution containing Fe. 3+ 10% by mass, containing Ru 2+ Mass concentration 3000 mg / L, Pd 2+ The supported metal catalyst S1 (iron-ruthenium-palladium) was obtained by calcination, activation, washing, centrifugation, and drying in a salt solution with a mass concentration of 1500 mg / L. The calcination temperature was 380℃ for 2.5 h, the activation temperature was 40℃, and the activation time was 3 h. Potassium borohydride was used as the reducing agent for the activation treatment. Tests revealed that catalyst S1 comprises a petroleum coke support and iron, ruthenium, and palladium elements supported on the support; based on the weight of the catalyst, the mass percentage of iron is 2%, the mass percentage of ruthenium is 0.1%, and the mass percentage of palladium is 0.08%. Add 1500 mg / L sodium thiosulfate (the first reducing agent) to 200 mL of wastewater and adjust the pH to 7.0-7.5 to obtain the wastewater to be treated. Add 1.5 g of catalyst S1 to the wastewater and stir to ensure full contact between the wastewater and the catalyst for catalytic reduction reaction. The reaction temperature is 25℃ and the reaction time is 45 min. After the reaction, take samples to determine the nitrate and ammonia nitrogen in the wastewater, and measure NO3. - The concentration was 16.7 mg / L, NH4 + The concentration was 3.4 mg / L. In this embodiment, the mass ratio of the first reducing agent to nitrate in the wastewater was 3.80:1; the mass ratio of the catalyst to nitrate in the wastewater was 19.02:1.

[0040] Example 2 Example 2 uses petrochemical wastewater with the following water quality characteristics: pH 7.4, NO3- - The concentration was 142.8 mg / L, NH4 + The concentration was 2.1 mg / L, the conductivity was 0.46 ms / cm, and the COD was 663.6 mg / L; The catalyst used in Example 2 is the same as that in Example 1, namely S1 (iron-ruthenium-palladium). Add 600 mg / L sodium thiosulfate as the first reducing agent to 200 mL of wastewater and adjust the pH of the wastewater to 7.0-7.5. Then add 0.5 g of catalyst S1 and stir to ensure that the wastewater and catalyst are in full contact for catalytic reduction reaction. The reaction time is 45 min. After the reaction is completed, take a sample to measure NO3 in the wastewater. - The concentration was 11.8 mg / L, NH4+ The concentration is 2.5 mg / L. In this embodiment, the mass ratio of the first reducing agent to the nitrate in the wastewater to be treated is 4.2:1; the mass ratio of the catalyst to the nitrate in the wastewater to be treated is 17.6:1.

[0041] Example 3 The method and wastewater treatment in this embodiment are the same as in Example 2, the only difference being that the catalyst used is an S2 catalyst (iron-ruthenium-tin). The specific preparation method includes: immersing the catalyst support alumina in a solution containing Fe... 3+ 10% by mass, containing Ru 2+ Mass concentration 2500 mg / L, Sn 2+ The supported metal catalyst S2 (iron-ruthenium-tin) was obtained by calcining, activation, washing, centrifugation, and drying in a salt solution with a mass concentration of 1500 mg / L. The calcination conditions included a temperature of 380℃ and a time of 2.5 h. The activation agent used in the activation treatment was potassium borohydride, and the activation temperature was 40℃ for 2 h. Tests revealed that catalyst S2 comprises an alumina support and iron, ruthenium, and tin elements supported on the support; based on the weight of the catalyst, the mass percentage of iron is 2%, the mass percentage of ruthenium is 0.08%, and the mass percentage of tin is 0.1%. Add 600 mg / L sodium thiosulfate as a reducing agent to 200 mL of wastewater and adjust the pH of the wastewater to 7.0-7.5. Then add 0.5 g of catalyst S1 and stir to ensure that the wastewater and catalyst are in full contact for catalytic reduction reaction. The reaction time is 45 min. After the reaction is completed, take a sample to measure the NO3 in the wastewater. - The concentration was 13.5 mg / L, NH4 + The concentration was 2.8 mg / L. In this embodiment, the mass ratio of the reducing agent to nitrate in the wastewater was 4.2:1; the mass ratio of the catalyst to nitrate in the wastewater to be treated was 17.6:1.

[0042] Example 4 The wastewater treatment method in this embodiment is the same as in Example 2, except that in Example 4, the reducing agent added is 200 mg / L sodium thiosulfate, and the mass ratio of the reducing agent to nitrate in the wastewater is 1.4:1. After the reaction is complete, samples are taken to determine the NO3 in the wastewater. - The concentration was 42.6 mg / L, NH4 + The concentration was 7.2 mg / L.

[0043] Example 5 The wastewater used in this embodiment is the same as in Example 2, and the catalyst used is S3 (iron-ruthenium). The method is as follows: 600 mg / L of sodium thiosulfate is added to the wastewater and the pH value of the wastewater is adjusted to 7.0-7.5. Then, 0.5 g of catalyst S3 is added and stirred to ensure that the wastewater to be treated is in full contact with the catalyst for catalytic reduction reaction. The reaction temperature is 25°C and the reaction time is 45 min. After the reaction is completed, samples are taken to measure NO3 in the wastewater. - The concentration was 29.9 mg / L, NH4 + The concentration was 5.4 mg / L. In this embodiment, the mass ratio of the reducing agent to nitrate in the wastewater was 4.2:1; the mass ratio of the catalyst to nitrate in the wastewater was 17.6:1. The preparation method of catalyst S3 is the same as that of catalyst S1 in Example 1, except that palladium is not added during the preparation of catalyst S3, and the active metals are iron and ruthenium.

[0044] Comparative Example 1 The wastewater used in this comparative example is the same as in Example 2. The method is as follows: 600 mg / L of sodium thiosulfate, a reducing agent, is added to the wastewater, and the pH value of the wastewater is adjusted to 10.0. Then, 0.5 g of catalyst S1 is added, and the mixture is stirred to ensure that the wastewater to be treated is in full contact with the catalyst for catalytic reduction reaction. The reaction time is 45 min. After the reaction is completed, samples are taken to measure the NO3 in the wastewater. - The concentration was 50.1 mg / L, NH4 + The concentration was 13.3 mg / L.

[0045] Comparative Example 2 The wastewater used in this comparative example is the same as in Example 2. The method is as follows: 600 mg / L of sodium thiosulfate was added to the wastewater and the pH value of the wastewater was adjusted to 4.5. Then, 0.5 g of catalyst S1 was added and stirred to ensure that the wastewater to be treated is in full contact with the catalyst for catalytic reduction reaction. The reaction time was 45 min. After the reaction was completed, samples were taken to measure the NO3 in the wastewater. - The concentration was 58.8 mg / L, NH4 + The concentration was 18.8 mg / L.

[0046] Comparative Example 3 The wastewater used in this comparative example is the same as in Example 2, except that sodium thiosulfate is not added, and only 0.5g of catalyst is added. After the reaction is completed, samples are taken to measure NO3 in the wastewater. - The concentration was 134.5 mg / L, NH4 + The concentration was 3.2 mg / L.

[0047] The catalysts used in Examples 1-5 and Comparative Examples 1-3 and the test results are listed in Table 1.

[0048] Table 1

[0049] As shown in Table 1, this disclosure reduces nitrate nitrogen in water by using suitable catalysts and reducing agents, adjusting the pH of the wastewater to a specific value, thereby giving the catalyst high catalytic activity. This effectively removes nitrate nitrogen from the water while avoiding the generation of byproduct ammonia nitrogen and NO3. - Good removal effect, NO3 - High removal rate, NH4 + The growth rate is low.

[0050] A comparison of Examples 2 and 4 shows that, within the preferred mass ratio range of reducing agent to nitrate in wastewater disclosed in this invention, NO3... - It has a better removal effect.

[0051] A comparison between Examples 2 and 5 shows that, within the range of preferred catalyst active metals disclosed in this invention, NO3... - It has a better removal effect.

[0052] The preferred embodiments have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0053] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0054] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for reducing nitrates in wastewater, characterized in that, The method includes: adding a first reducing agent to wastewater and adjusting the pH of the wastewater to 6.5-7.5 to obtain wastewater to be treated; and bringing the wastewater to be treated into contact with a catalyst to react. The first reducing agent comprises an oxyacid salt of sulfur; the catalyst comprises a support and an active component supported on the support, the active component comprising iron and a noble metal element, the noble metal element comprising one or more of ruthenium, palladium and tin.

2. The method according to claim 1, wherein, Based on the weight of the catalyst, the iron element accounts for 1-8% of the total mass, and the precious metal element accounts for 0.07-0.3% of the total mass. The carrier includes one or more of activated carbon, activated coke, petroleum coke and alumina, preferably petroleum coke.

3. The method according to claim 1, wherein, The precious metal elements are ruthenium and tin; based on the weight of the catalyst, the mass percentage of iron is 1-8%; the mass percentage of ruthenium is 0.02-0.1%; and the mass percentage of tin is 0.05-0.2%.

4. The method according to claim 1, wherein, The precious metal elements are ruthenium and palladium; based on the weight of the catalyst, the mass percentage of iron is 1-8%; the mass percentage of ruthenium is 0.02-0.1%; and the mass percentage of palladium is 0.01-0.1%.

5. The method according to claim 1, wherein, The first reducing agent includes one or more of thiosulfate, sulfite and dithionite, preferably thiosulfate.

6. The method according to claim 1, wherein, The chemical oxygen demand (COD) of the wastewater is 0-1000 mg / L, preferably 1-700 mg / L; the NO3 in the wastewater... - The concentration is 10~400mg / L.

7. The method according to claim 1, wherein, The mass ratio of the first reducing agent to the nitrate in the wastewater is 1~8:1, preferably 1.5~5:1; the mass ratio of the catalyst to the nitrate in the wastewater is 5~25:1, preferably 15~20:

1.

8. The method according to claim 1, wherein, The reaction conditions include: a reaction temperature of 10~40℃, preferably 20~35℃; and a reaction time of 10~120min, preferably 30~50min.

9. The method according to claim 1, wherein, The method for preparing the catalyst includes: impregnating the support with a salt solution containing the iron element and the noble metal element, and then calcining and activating the impregnated solid.

10. The method according to claim 9, wherein, The calcination conditions include: a temperature of 200~550℃, preferably 300~450℃; and a time of 1~6h, preferably 2~4h. The second reducing agent used in the activation treatment includes one or more of potassium borohydride and sodium borohydride, preferably potassium borohydride.

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