A nitrogen-doped catalyst and method of making, and method of catalytic wet oxidation

Abstract

The present application provides a kind of nitrogen-doped catalyst and catalytic wet oxidation method, catalyst is carried out by the coprecipitation reaction of soluble salt of iron, lanthanum and copper, and in rotary evaporator device, aging, dry and then mixed with nitrogen-containing precursor grinding, calcination is obtained under inert atmosphere.The specific surface area of catalyst of the present application is 60-120cm 2 ·g ‑1 , the doping amount of nitrogen is 0.5-2.0wt%.For catalytic wet oxidation, due to the doping of copper in B site, it is anchored in the lanthanum ferrite framework, reducing the loss of metal copper, making the catalyst more stable, and improving the catalytic performance of lanthanum ferrite catalyst.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a nitrogen-doped catalyst and its application in wastewater treatment. Background Technology

[0002] Among advanced oxidation technologies, wet oxidation boasts advantages such as strong oxidation capacity and rapid mineralization rate, and is primarily used for treating high-concentration organic wastewater. However, for certain specific wastewaters, wet oxidation requires stringent operating conditions, such as high temperature and pressure, and long operating times. Catalytic wet oxidation technology, by introducing catalysts, can significantly mitigate the operating conditions of wet oxidation and significantly improve the degradation efficiency of organic matter. Perovskite catalysts, characterized by high catalytic activity, strong oxidation capacity, and long lifespan, have received increasing attention in recent years.

[0003] Patent CN112547087A discloses a method for preparing and applying a lanthanum iron manganese oxide catalyst. The catalyst, obtained through co-deposition and calcination, exhibits high stability, low cost, and high activity. It shows good results in the synergistic treatment of m-cresol model wastewater and biochemical effluent from explosives using ozone, peroxide, and hydrogen peroxide. However, this catalyst requires a long aging time, and the prepared catalyst has a relatively small specific surface area, only 5-40 cm². 2 ·g -1 This will significantly affect the reaction activity of the catalyst.

[0004] Patent CN111151264A discloses a catalytic wet oxidation catalyst comprising a zirconium-titanium oxide support and perovskite active centers, used for degrading high-salt, high-concentration organic wastewater, exhibiting stable and high-efficiency characteristics. However, the catalyst preparation process is relatively cumbersome, requiring multiple metal components, some of which contain expensive precious metals, resulting in high costs. Furthermore, it requires a long activation time (8-24 hours). Similarly, the prepared catalyst suffers from a small specific surface area, which affects its adsorption performance for oxygen and organic matter. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention relates to a nitrogen-doped catalyst. The catalyst is prepared by a co-precipitation reaction and a nitrogen-doping reaction, resulting in a nitrogen-metal co-doped catalyst. This catalyst is simple to prepare, low in cost, and has a large specific surface area, making it suitable for mass production. It can be used in wet oxidation processes, significantly improving the mineralization efficiency of organic matter and showing broad application prospects.

[0006] To achieve the above technical objectives, the technical solution of the present invention is as follows:

[0007] The first aspect of the technical objective of this invention is to provide a method for preparing a nitrogen-doped catalyst, comprising the following:

[0008] (1) Dissolve soluble salts of iron, lanthanum and copper in water, add low carbon alcohols to obtain solution I;

[0009] (2) Dissolve ammonia and / or ammonium carbonate and polyol in water to obtain solution II;

[0010] (3) When solution I is mixed with solution II, a co-precipitation reaction occurs between the two.

[0011] (4) The reaction solution was transferred to a rotary evaporator and aged; after filtration, washing and drying, a solid product was obtained.

[0012] (5) The solid product obtained in step (4) is mixed and ground with the nitrogen-containing precursor and calcined under an inert atmosphere to obtain a nitrogen-doped catalyst.

[0013] Furthermore, the soluble salts of iron, lanthanum, and copper are selected from at least one of their nitrates, sulfates, chlorides, and acetates.

[0014] Furthermore, in terms of the amount of substance, the ratio of lanthanum to the total of copper and iron is 1:1, and the molar ratio of iron to copper is (1-9):1.

[0015] Furthermore, the lower alcohol is selected from at least one of methanol, ethanol, and propanol.

[0016] Furthermore, the volume ratio of lower alcohol to water in solution I is 1:(1-6), preferably 1:(1-3).

[0017] Furthermore, the amount of ammonia and / or ammonium carbonate used is such that the ratio of the amount of ammonia and / or ammonium carbonate to the amount of total metal elements is (4-10):1.

[0018] Furthermore, the polyol is selected from at least one of polyethylene glycol, polypropylene glycol, and polybutanediol.

[0019] Furthermore, the polyol has a molecular weight of 5000-20000 and is added in an amount of 0.2-1.0 g / L.

[0020] Furthermore, solutions I and II are treated in any of the prior art methods that promote solution mixing before mixing, so as to obtain solutions I and II that are uniformly mixed, preferably by ultrasonic treatment.

[0021] Furthermore, in step (3), solution I is added to solution II by dropping. Specifically, solution I is added to solution II dropwise at a rate of 1-6 mL / min.

[0022] Furthermore, the coprecipitation reaction takes 1-4 hours, and preferably, the reaction is carried out under stirring conditions.

[0023] Furthermore, the aging time is 1-4 hours, preferably 1-2 hours. The reaction temperature of the solution in the rotary evaporator is 40-90℃, and the pressure is -0.2MPa-0MPa.

[0024] Furthermore, the drying temperature in step (4) is 80-120℃.

[0025] Furthermore, the nitrogen-containing precursor is selected from at least one of melamine, urea, and dicyandiamide.

[0026] Furthermore, the nitrogen-containing precursor is added at a mass ratio of 1:(4-10) to the solid obtained in step (4).

[0027] Furthermore, the roasting temperature in step (5) is 400-1200℃.

[0028] The technical objective of the second aspect of this invention is to provide a nitrogen-doped catalyst prepared by the above method.

[0029] The catalyst prepared by the method of the present invention, on the one hand, forms LaFe due to Cu doping at the B site in the perovskite structure compound. x Cu 1-x The O3 structure reduces copper loss and improves stability. Furthermore, the co-calcination process of the nitrogen-containing precursor and catalyst increases the specific surface area of ​​the catalyst, which is beneficial for improving reaction performance. The catalyst prepared in this invention has a specific surface area of ​​60-120 cm². 2 ·g -1 The nitrogen doping amount is 0.5-2.0 wt%.

[0030] The technical objective of a third aspect of this invention is to provide a method for catalytic wet oxidation, in which the aforementioned catalyst is reacted with wastewater containing organic matter. Under the catalysis of the catalyst of this invention, COD in the wastewater can be effectively removed.

[0031] Furthermore, the temperature of the catalytic wet oxidation reaction is 180-280℃, the reaction pressure is 2.8-8.0 MPa, and the concentration of the catalyst in the reaction is 0.5-3 g / L.

[0032] The present invention is characterized in that the catalyst can be used to catalyze wet oxidation processes.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The preparation method of the present invention is simple, can be mass-produced, has no noble metal doping, and has low preparation cost; and as verified by experiments, copper doping at the B site is anchored in the lanthanum ferrite framework, which reduces the loss of metallic copper, makes the catalyst more stable, and improves the catalytic performance of the lanthanum ferrite catalyst.

[0035] (2) Using negative pressure vacuum aging shortens the aging time and the resulting catalyst has better crystallinity;

[0036] (3) The co-calcination step of nitrogen-containing precursor and catalyst increases the specific surface area of ​​catalyst and the adsorption performance of catalyst for oxygen. Nitrogen doping improves the electron transport performance of catalyst and its ability to remove organic matter when used for wastewater treatment. Detailed Implementation

[0037] The method of the present invention will be further described in detail below through embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0039] In the examples, the specific surface area of ​​the catalyst was determined using a nitrogen physical adsorption analyzer; the total organic carbon in the wastewater was determined using a TOC analyzer; the copper ion leaching amount was determined using inductively coupled plasma chromatography; and the nitrogen doping amount was analyzed using X-ray fluorescence spectroscopy.

[0040] Example 1

[0041] (1) Weigh 0.1 mol of ferric sulfate, 0.1 mol of copper sulfate and 0.2 mol of lanthanum sulfate and add them to 100 mL of distilled water and 100 mL of ethanol. Mix them evenly by sonication to obtain solution I;

[0042] (2) Add 1.6 mol of ammonium carbonate and 0.4 g / L of polyethylene glycol with a molecular weight of 10000 to distilled water, and mix evenly by ultrasonication to obtain solution II;

[0043] (3) Coprecipitation reaction: Add solution I dropwise to solution II at a rate of 2 mL / min and continue stirring. The total time for the addition and reaction process is 2 hours.

[0044] (4) Aging: The mixture from step (3) was placed in a rotary evaporator and aged for 1 hour at a temperature of 60°C and a pressure of -0.1 MPa. After that, it was repeatedly filtered and washed 8 times and dried in an oven at 100°C to obtain a solid product.

[0045] (5) Nitrogen doping: 20g of the solid obtained in step (4) is mixed and ground with 4g of melamine and placed in a nitrogen atmosphere furnace for calcination at a temperature of 1000℃ to obtain nitrogen-doped powder LaFeCuO3, which is denoted as catalyst A1.

[0046] The specific surface area of ​​catalyst A1 is 96.5 cm². 2 ·g -1 The nitrogen doping content is 0.93 wt%.

[0047] Catalyst A1 was used in a catalytic wet oxidation process. The simulated wastewater was a 4000 mg / L ascorbic acid solution, and the catalyst was added at a rate of 1 g / L of wastewater. The reaction was carried out at a temperature of 260℃ and a pressure of 6.5 MPa for 2 hours, and the TOC removal rate was measured to be 92.6%.

[0048] Example 2

[0049] (1) Weigh 0.15 mol of ferric sulfate, 0.05 mol of copper sulfate and 0.2 mol of lanthanum sulfate and add them to 100 mL of distilled water and 100 mL of ethanol. Mix them evenly by sonication to obtain solution I.

[0050] (2)-(5) are performed in the same manner as in Example 1, and catalyst A2 is obtained.

[0051] The specific surface area of ​​catalyst A2 is 94.3 cm². 2 ·g -1 The nitrogen doping content is 0.89 wt%.

[0052] Catalyst A2 was used in a catalytic wet oxidation process. The simulated wastewater was a 4000 mg / L ascorbic acid solution, and the catalyst was added at a rate of 1 g / L of wastewater. The reaction was carried out at a temperature of 260℃ and a pressure of 6.5 MPa for 2 hours, and the TOC removal rate was measured to be 90.5%.

[0053] Example 3

[0054] Except for the polyethylene glycol concentration of 0.6 g / L in step (2), the rest is the same as in Example 1, and catalyst A3 is obtained.

[0055] The specific surface area of ​​catalyst A3 is 97.8 cm². 2 ·g -1 The nitrogen doping content is 0.97 wt%.

[0056] Catalyst A3 was used in a catalytic wet oxidation process. The simulated wastewater was a 4000 mg / L ascorbic acid solution, and the catalyst was added at a rate of 1 g / L of wastewater. The reaction was carried out at a temperature of 260℃ and a pressure of 6.5 MPa for 2 hours, and the TOC removal rate was measured to be 93.8%.

[0057] Example 4

[0058] Except for the aging temperature of 65℃, the pressure of -0.15Mpa, and the aging time of 2h in step (4), the rest is the same as in Example 1, and catalyst A4 is obtained.

[0059] The specific surface area of ​​catalyst A4 is 95.3 cm². 2 ·g -1 The nitrogen doping content is 1.02 wt%.

[0060] Catalyst A4 was used in a catalytic wet oxidation process. The simulated wastewater was a 4000 mg / L ascorbic acid solution, and the catalyst was added at a rate of 1 g / L of wastewater. The reaction was carried out at a temperature of 260℃ and a pressure of 6.5 MPa for 2 hours, and the TOC removal rate was measured to be 94.4%.

[0061] Example 5

[0062] Except for replacing 4g of melamine with 6g of melamine in step (5), the rest is the same as in Example 1, and catalyst A5 is obtained.

[0063] The specific surface area of ​​catalyst A5 is 110.3 cm². 2 ·g -1 The nitrogen doping content is 1.12 wt%.

[0064] Catalyst A5 was used in a catalytic wet oxidation process. The simulated wastewater was a 4000 mg / L ascorbic acid solution, and the catalyst was added at a rate of 1 g / L of wastewater. The reaction was carried out at a temperature of 260℃ and a pressure of 6.5 MPa for 2 hours, and the TOC removal rate was measured to be 96.2%.

[0065] Comparative Example 1

[0066] Except for step (1) where copper salt is not added and the amount of iron salt is changed to 0.2 mol, the other steps are the same as in Example 1. Catalyst C1 is obtained.

[0067] The specific surface area of ​​catalyst C1 is 90.8 cm². 2 ·g -1 .

[0068] Catalyst C1 was used in a catalytic wet oxidation process, and the reaction procedure was the same as in Example 1. The TOC removal rate was measured to be 73.9%, therefore, the copper-doped catalyst prepared in Example 1 showed superior performance.

[0069] Comparative Example 2

[0070] Except for omitting the grinding and mixing with the nitrogen-containing precursor in step (5), the other steps are the same as in Example 1. Catalyst C2 is obtained.

[0071] The specific surface area of ​​catalyst C2 is 42.3 cm². 2 ·g -1 .

[0072] Catalyst C2 was used in a catalytic wet oxidation process, following the same reaction procedure as in Example 1. The TOC removal rate was measured to be 56.2%. Therefore, compared to other methods, nitrogen doping can improve the specific surface area and catalytic performance of the catalyst.

[0073] Comparative Example 3

[0074] Except for step (5), where the mass of the nitrogen-containing precursor is 1.5 g, the other steps are the same as in Example 1. Catalyst C3 was obtained with a nitrogen doping content of 0.39%.

[0075] The specific surface area of ​​catalyst C3 is 61.6 cm². 2 ·g -1 .

[0076] Catalyst C3 was used in the catalytic wet oxidation process, and the reaction procedure was the same as in Example 1. The TOC removal rate was determined to be 73.5%.

[0077] Comparative Example 4

[0078] Except for step (4), which does not use a rotary evaporator but instead ages the coprecipitated reactants at 60°C for 1 hour in a conventional reaction vessel, the other steps are the same as in Example 1. Catalyst C4 is obtained.

[0079] The specific surface area of ​​catalyst C4 is 92.7 cm². 2 ·g -1 .

[0080] Catalyst C4 was used in the catalytic wet oxidation process, and the reaction procedure was the same as in Example 1. The TOC removal rate was determined to be 82.6%.

[0081] Compared with Example 1, the traditional aging method cannot achieve better copper metal B-site doping and crystallinity. In comparison, the catalyst prepared in Example 1 has better performance.

[0082] Comparative Example 5

[0083] (1) Weigh 0.1 mol of ferric sulfate and 0.2 mol of lanthanum sulfate and add them to 100 mL of distilled water and 100 mL of ethanol. Mix them evenly by sonication to obtain solution I;

[0084] (2) Add 1.6 mol of ammonium carbonate and 0.4 g / L of polyethylene glycol with a molecular weight of 10000 to distilled water, and mix evenly by ultrasonication to obtain solution II;

[0085] (3) Coprecipitation reaction: Add solution I dropwise to solution II at a rate of 2 mL / min and continue stirring. The total time for the addition and reaction process is 2 hours.

[0086] (4) Aging: Mix 0.1 mol of copper sulfate with the mixture in step (3), place it in a rotary evaporator, and age it for 1 hour at a temperature of 60°C and a pressure of -0.1 MPa; then filter and wash it repeatedly 8 times, and dry it in an oven at 100°C to obtain a solid product.

[0087] (5) Nitrogen doping: 20g of the solid obtained in step (4) is mixed and ground with 4g of melamine, and then placed in a nitrogen atmosphere furnace for calcination at a temperature of 1000℃ to obtain solid powder, which is catalyst C5.

[0088] Catalyst C5 was used in a catalytic wet oxidation process. The simulated wastewater was a 4000 mg / L ascorbic acid solution, and the catalyst was added at a rate of 1 g / L of wastewater. The reaction was carried out at a temperature of 260°C and a pressure of 6.5 MPa for 2 hours. The TOC removal rate was measured to be 88.6%, but the copper ion leaching amount reached 96.8 mg / L. This treatment effect mainly comes from the homogeneous catalytic effect of copper leaching, while the catalyst in Example 1 of this invention was only detected to leach 8.3 mg / L.

Claims

1. A method for preparing a nitrogen-doped catalyst for catalytic wet oxidation, comprising the following: (1) Dissolve soluble salts of iron, lanthanum and copper in water, add low carbon alcohols to obtain solution I; (2) Dissolve ammonia and / or ammonium carbonate and polyol in water to obtain solution II; (3) When solution I is mixed with solution II, a co-precipitation reaction occurs between the two. (4) The reaction solution was transferred to a rotary evaporator and aged; after filtration, washing and drying, a solid product was obtained. (5) The solid product obtained in step (4) is mixed and ground with the nitrogen-containing precursor. The nitrogen-containing precursor is added at a mass ratio of 1:4-10 with the solid obtained in step (4). The mixture is then calcined under an inert atmosphere to obtain a nitrogen-doped catalyst.

2. The preparation method according to claim 1, characterized in that, The soluble salts of iron, lanthanum, and copper are selected from at least one of their nitrates, sulfates, chlorides, and acetates.

3. The preparation method according to claim 1, characterized in that, In terms of the amount of substance, the ratio of lanthanum to the total of copper and iron is 1:1, and the molar ratio of iron to copper is 1-9:

1.

4. The preparation method according to claim 1, characterized in that, The lower alcohol is selected from at least one of methanol, ethanol and propanol.

5. The preparation method according to claim 1, characterized in that, The amount of ammonia and / or ammonium carbonate used is such that the ratio of the amount of ammonia and / or ammonium carbonate to the amount of total metal elements is 4-10:

1.

6. The preparation method according to claim 1, characterized in that, The polyol is selected from at least one of polyethylene glycol, polypropylene glycol, and polybutylene glycol.

7. The preparation method according to claim 1, characterized in that, The aging time is 1-4 hours.

8. The preparation method according to claim 7, characterized in that, The aging time is 1-2 hours.

9. The preparation method according to claim 1, characterized in that, The reaction temperature of the solution in the rotary evaporator is 40-90℃, and the pressure is -0.2MPa-0MPa.

10. The preparation method according to claim 1, characterized in that, The nitrogen-containing precursor is selected from at least one of melamine, urea, and dicyandiamide.

11. The nitrogen-doped catalyst prepared by the preparation method according to any one of claims 1-10.

12. A method for catalytic wet oxidation, wherein the nitrogen-doped catalyst of claim 11 is reacted with wastewater containing organic matter.

13. The method according to claim 12, characterized in that, The temperature for the catalytic wet oxidation reaction is 180-280℃, the reaction pressure is 2.8-8.0 MPa, and the concentration of the catalyst in the reaction is 0.5-3 g / L.