A modified LiMn2O4 catalyst for the preparation of N2O, its preparation method and application

Abstract

This invention provides a modified LiMn2O4 catalyst for N2O preparation, its preparation method, and its application. The preparation method includes: calcining LiMn2O4 material, or mixing and calcining LiMn2O4 material with an alkali metal compound for loading modification, or pre-calcining LiMn2O4 material and then mixing and sintering the pre-calcined LiMn2O4 material with an alkali metal compound to obtain the modified LiMn2O4 catalyst. This invention modifies the number of Mn metal exposed sites by calcining LiMn2O4 material, loading alkali metal oxide clusters onto LiMn2O4 material, or combining both methods. This allows for the control of the number of Mn metal exposed sites, resulting in a modified LiMn2O4 catalyst that significantly improves N2O yield under low-temperature conditions, making it suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials, specifically relating to a modified LiMn2O4 catalyst for preparing N2O, its preparation method, and its application. Background Technology

[0002] Nitrous oxide (N₂O) is a colorless gas with a sweet taste. Because it can induce laughter, it is also known as "laughing gas." N₂O is soluble in water, ethanol, ether, and concentrated sulfuric acid. It is an oxidizing agent and can support combustion under certain conditions, but it is stable at room temperature. N₂O has wide applications in related fields. For example, in dentistry, because N₂O does not undergo any biotransformation or degradation in the body, the vast majority is exhaled unchanged, with only a small amount evaporating through the skin, and it does not accumulate. Inhalation produces analgesia within 30-40 seconds, with a strong analgesic effect and a weak anesthetic effect. The patient remains conscious during procedures, avoiding complications associated with general anesthesia, and recovery is rapid, which greatly benefits dentists.

[0003] In the field of aerospace technology, N₂O has a wide range of applications. It can be used not only in solid-liquid engines, but also in cold gas propulsion, monopropellant propulsion, bipropellant propulsion, and electrothermal propulsion, with thrust ranging from millinewtons to Newtons and even kilonewtons. Since the decomposition products of N₂O are oxygen and nitrogen, the collected oxygen can be used by astronauts, thus serving as an oxygen source for spacecraft. Simultaneously, the conversion of liquid N₂O to gas absorbs a large amount of heat, which can also be used as a cooling source for spacecraft. Furthermore, nitrous oxide has high permeability and can replace helium for vacuum leak detection, protecting this precious and rare resource and reducing production costs.

[0004] In both laboratory and industrial settings, N2O is typically prepared by the thermal decomposition of ammonium nitrate. However, the thermal decomposition of ammonium nitrate is a highly exothermic reaction, and continued operation at high temperatures may result in an explosion. Furthermore, the reaction is generally difficult to operate, which increases production costs to some extent.

[0005] It has been found that in the field of NH3 selective catalytic reduction technology, using NH3 as a reducing agent and O2 and NO as raw material gases, NO can be converted into N2 and N2O through a selective catalytic reduction reaction process.

[0006] Therefore, designing a catalyst that can efficiently prepare N2O at low temperatures is a current research hotspot. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a modified LiMn2O4 catalyst for N2O preparation, its preparation method, and its applications. The present invention modifies LiMn2O4 material by calcining it, loading alkali metal oxide clusters onto it, or combining both methods. This allows for the control of the number of exposed Mn metal sites, resulting in a modified LiMn2O4 catalyst that significantly improves N2O yield under low-temperature conditions, making it suitable for industrial production.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising:

[0010] The LiMn2O4 material was calcined.

[0011] Alternatively, LiMn2O4 material can be mixed with alkali metal compounds and calcined for loading modification.

[0012] Alternatively, the LiMn2O4 material can be pre-calcined, and then the pre-calcined LiMn2O4 material can be mixed with an alkali metal compound and sintered to obtain the modified LiMn2O4 catalyst.

[0013] This invention modifies the LiMn2O4 material by calcining it, or by loading alkali metal oxide clusters onto it, or by combining the two. This allows for the control of the number of exposed Mn metal sites, resulting in a modified LiMn2O4 catalyst that can significantly improve the N2O yield at low temperatures, making it suitable for industrial production.

[0014] It should be noted that this invention does not specifically limit the source of the raw material LiMn2O4. Exemplarily, it can be synthesized by a simple method, such as preparing LiMn2O4 spinel material via the sol-gel method. The specific steps are as follows: Add manganese acetate tetrahydrate and lithium carbonate powder to a beaker, add it to deionized water and stir to dissolve. Add citric acid monohydrate to another beaker and dissolve it with an equal volume of deionized water. Then, add the mixed solution of Li and Mn sources dropwise to the citric acid aqueous solution, stirring until homogeneous. Heat to 70°C and stir until the water evaporates to form a sol. Dry the sol in an oven at 120°C for 8 hours, cool, grind into powder, and finally calcine in air at 500°C for 3 hours to obtain LiMn2O4 spinel material. The raw material LiMn2O4 catalyst can also be recovered from waste battery cathode materials. Optimizing the recovered material for N2O synthesis is also a good way to recycle resources and maximize their value.

[0015] As a preferred embodiment of the present invention, both the calcination treatment and the pre-calcination treatment are carried out in an air atmosphere.

[0016] Preferably, the calcination treatment and the pre-calcination treatment are independently 200-1000℃, for example, 200℃, 300℃, 400℃, 450℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, etc., preferably 400-800℃.

[0017] It should be noted that in this invention, "independently" means that the calcination treatment can be any value between 200-1000℃, and the pre-calcination treatment temperature can also be any value between 200-1000℃. The selection of the two does not interfere with each other and can be the same or different. The following "independently" is the same.

[0018] In this invention, if the calcination temperature is too low, the material will have poor crystallinity and it will be difficult to form the target phase, thus affecting the catalytic performance; if the calcination temperature is too high, the active sites will be reduced due to the excessively large crystal grains, resulting in the loss of catalytic activity.

[0019] Preferably, the holding time for the calcination treatment and the pre-calcination treatment is independently 1-5 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, preferably 2-4 hours.

[0020] Preferably, the heating rate of the calcination treatment and the pre-calcination treatment is independently 1-10℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc.

[0021] As a preferred embodiment of the present invention, the cation in the alkali metal compound includes any one or a combination of at least two of potassium ions, sodium ions, rubidium ions or cesium ions, preferably sodium ions and / or potassium ions.

[0022] Preferably, the anion of the alkali metal compound includes nitrate ions or carbonate ions.

[0023] As a preferred technical solution of the present invention, the roasting and sintering temperatures are independently 300-800℃, for example, 300℃, 400℃, 500℃, 600℃, 700℃ or 800℃, etc., preferably 500-600℃.

[0024] Preferably, the roasting and sintering time is independently 1-5h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, and preferably 2-4h.

[0025] Preferably, the heating rate of the calcination and sintering is independently 1-10℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc.

[0026] In a second aspect, the present invention provides a modified LiMn2O4 catalyst for preparing N2O, wherein the modified LiMn2O4 catalyst for preparing N2O is prepared by the preparation method described in the first aspect.

[0027] As a preferred embodiment of the present invention, the modified LiMn2O4 catalyst is supported on alkali metal oxide clusters.

[0028] In this invention, the modified LiMn2O4 catalyst is loaded with alkali metal oxide clusters, which is beneficial to improving the conversion rate of the product N2O.

[0029] As a preferred technical solution of the present invention, based on the mass of the modified LiMn2O4 catalyst, the mass percentage of the alkali metal oxide cluster is 0.1-10%, for example, it can be 0.1%, 0.5%, 1%, 3%, 5%, 7%, 9% or 10%, etc., preferably 0.5-1%.

[0030] In this invention, if the mass percentage of alkali metal oxide clusters is too low, the modification effect will be insignificant; if the mass percentage of alkali metal oxide clusters is too high, the catalytic activity will be sacrificed due to catalyst poisoning.

[0031] Thirdly, the present invention provides an application of the modified LiMn2O4 catalyst for the preparation of N2O as described in the second aspect, characterized in that the modified LiMn2O4 catalyst is used for the catalytic preparation of N2O.

[0032] As a preferred technical solution of the present invention, the specific steps of the application include:

[0033] The modified LiMn2O4 catalyst, reducing agent, and raw material gas are placed in a reaction vessel to carry out a catalytic reduction reaction to obtain N2O.

[0034] This invention provides a method for preparing N2O at low temperature and with high efficiency. This method is simple to operate, does not contain precious metals, is low in cost and energy consumption, and the modified LiMn2O4 catalyst used enables the method to obtain a high N2O yield at 200℃.

[0035] In a preferred embodiment of the present invention, the reducing agent comprises ammonia.

[0036] Preferably, the raw material gas includes oxygen, nitrogen oxides, and a balance gas.

[0037] Preferably, the balancing gas includes nitrogen.

[0038] The present invention does not specifically limit the composition of the nitrogen oxides, but for example, they may be nitric oxide and / or nitrogen dioxide.

[0039] Preferably, the content of the reducing agent is 0-5000ppm and is not 0, for example, it can be 10ppm, 100ppm, 200ppm, 500ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm or 5000ppm, etc., preferably 300-700ppm.

[0040] Preferably, the volume fraction of oxygen is 0-20%, and not 0, for example, it can be 2%, 5%, 10%, 15% or 20%, etc., preferably 5-10%.

[0041] It should be noted that the volume fraction of oxygen is based on the total volume of the raw material gas.

[0042] Preferably, the content of nitrogen oxides is 0-5000 ppm and is not 0, for example, it can be 10 ppm, 100 ppm, 200 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm or 5000 ppm, etc., preferably 300-700 ppm.

[0043] Preferably, the temperature of the catalytic reduction reaction is 50-200℃, for example, it can be 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ or 200℃.

[0044] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The present invention modifies the LiMn2O4 material by calcining LiMn2O4 material, or by loading alkali metal oxide clusters onto LiMn2O4 material, or by combining the two, thereby controlling the number of Mn metal exposure sites, so that the modified LiMn2O4 catalyst prepared can greatly improve the yield of N2O under low temperature conditions, and is suitable for industrial production.

[0047] (2) This invention provides a method for low-temperature and high-efficiency preparation of N2O. This method is simple to operate, does not contain precious metals, is low in cost, and has low energy consumption. The modified LiMn2O4 catalyst used enables the method to obtain a high N2O yield at 200℃, and has broad application prospects. In addition, the raw material LiMn2O4 used in this invention can be self-made or obtained by recycling waste battery cathode materials. Optimizing the recycled materials for use in the field of low-temperature N2O preparation is a good way to recycle resources and maximize their value. Attached Figure Description

[0048] Figure 1 The graph shows the trend of NO conversion rate with temperature during the N2O preparation process of the modified LiMn2O4 catalyst prepared in Example 1 of this invention.

[0049] Figure 2 The graph shows the trend of N2O selectivity as a function of temperature during the N2O preparation process of the modified LiMn2O4 catalyst prepared in Example 1 of this invention.

[0050] Figure 3 The graph shows the trend of NO conversion rate with temperature during the N2O preparation process of the modified LiMn2O4 catalyst prepared in Example 8 of this invention.

[0051] Figure 4 The graph shows the trend of N2O selectivity as a function of temperature during the N2O preparation process of the modified LiMn2O4 catalyst prepared in Example 8 of this invention. Detailed Implementation

[0052] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0053] Example 1

[0054] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0055] (1) Preparation of LiMn2O4 material: 4.91g of manganese acetate tetrahydrate and 0.37g of lithium carbonate were added to a beaker, and 30mL of deionized water was added and stirred to dissolve. 6.93g of citric acid monohydrate was added to another beaker and dissolved in 30mL of deionized water. The mixed solution of Li and Mn source was then added dropwise to the citric acid aqueous solution and stirred evenly. The solution was heated to 70℃ and stirred until the water evaporated to form a sol. The sol was then dried in an oven at 120℃ for 8h. After cooling, it was ground into powder and finally calcined in air at 500℃ for 3h to obtain LiMn2O4 material.

[0056] (2) Take 300 mg of LiMn2O4 material and place it in a muffle furnace and calcine it in an air atmosphere at 600 °C for 3 h to obtain the modified LiMn2O4 catalyst.

[0057] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0058] 250 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0059] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0060] Figure 1 and Figure 2 The figure shows the trend of NO conversion rate and N2O selectivity with temperature during the N2O preparation process of the modified LiMn2O4 catalyst prepared in this embodiment. As can be seen from the figure, both NO conversion rate and N2O selectivity increase with increasing temperature, and both reach about 90% after 150℃, showing a high N2O generation rate.

[0061] Example 2

[0062] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0063] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0064] (2) Take 300 mg of LiMn2O4 material and place it in a muffle furnace and calcine it in an air atmosphere at 700 °C for 3 h. The heating rate is 5 °C / min to obtain the modified LiMn2O4 catalyst.

[0065] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0066] 250 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0067] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0068] Example 3

[0069] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0070] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0071] (2) Take 300 mg of LiMn2O4 material and place it in a muffle furnace and calcine it in an air atmosphere at 800 °C for 3 h. The heating rate is 7 °C / min to obtain the modified LiMn2O4 catalyst.

[0072] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0073] 250 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0074] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0075] Example 4

[0076] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0077] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0078] (2) Take 300 mg of LiMn2O4 material and place it in a muffle furnace and calcine it in an air atmosphere at 900 °C for 3 h. The heating rate is 8 °C / min to obtain the modified LiMn2O4 catalyst.

[0079] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0080] 250 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0081] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0082] Example 5

[0083] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0084] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0085] (2) Take 300 mg of LiMn2O4 material and place it in a muffle furnace and calcine it in an air atmosphere at 1000 °C for 3 h. The heating rate is 10 °C / min to obtain the modified LiMn2O4 catalyst.

[0086] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0087] 250 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0088] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0089] Example 6

[0090] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0091] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0092] (2) Take 300 mg of LiMn2O4 material and place it in a muffle furnace and calcine it in an air atmosphere at 400 °C for 4 h. The heating rate is 3 °C / min to obtain the modified LiMn2O4 catalyst.

[0093] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0094] 250 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0095] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0096] Example 7

[0097] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0098] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0099] (2) Take 300 mg of LiMn2O4 material and place it in a muffle furnace and calcine it in an air atmosphere at 200 °C for 5 h. The heating rate is 1 °C / min to obtain the modified LiMn2O4 catalyst.

[0100] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0101] 250 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0102] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0103] Example 8

[0104] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0105] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0106] (2) Weigh 0.0068 g NaNO3 and dissolve it in 2 mL of deionized water. After it is completely dissolved, add 0.5 g LiMn2O4 material into a 20 mL bottle, let it stand for 12 h and then dry it at 80 °C. Then grind the dried material and calcine it in an air atmosphere at 500 °C for 3 h with a heating rate of 5 °C / min to obtain a modified LiMn2O4 catalyst supported on sodium oxide clusters.

[0107] Based on the mass of the modified LiMn2O4 catalyst, the mass percentage of sodium oxide clusters is 0.5%.

[0108] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0109] 100 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0110] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0111] Figure 3 and Figure 4 The figure shows the trend of NO conversion and N2O selectivity with temperature during the N2O preparation process of the modified LiMn2O4 catalyst prepared in this embodiment. As can be seen from the figure, both NO conversion and N2O selectivity increase with increasing temperature. At 200℃, the NO conversion is close to 100% and the N2O selectivity reaches 80%, which also shows a high N2O generation rate.

[0112] Example 9

[0113] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0114] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0115] (2) Weigh 0.014g NaNO3 and dissolve it in 2mL of deionized water. After it is completely dissolved, add 0.5g LiMn2O4 material into a 20mL bottle, let it stand for 12h and then dry it at 80℃. Then grind the dried material and calcine it in an air atmosphere at 500℃ for 3h with a heating rate of 5℃ / min to obtain the modified LiMn2O4 catalyst supported on sodium oxide clusters.

[0116] Based on the mass of the modified LiMn2O4 catalyst, the mass percentage of sodium oxide clusters is 1%.

[0117] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0118] 100 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0119] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0120] Example 10

[0121] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0122] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0123] (2) Weigh 0.0053g KNO3 and dissolve it in 2mL of deionized water. After it is completely dissolved, add 0.5g LiMn2O4 material into a 20mL bottle, let it stand for 12h and then dry it at 80℃. Then grind the dried material and calcine it in an air atmosphere at 500℃ for 3h with a heating rate of 5℃ / min to obtain modified LiMn2O4 catalyst supported on potassium oxide clusters.

[0124] Based on the mass of the modified LiMn2O4 catalyst, the mass percentage of potassium oxide clusters is 0.5%.

[0125] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0126] 100 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0127] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0128] Example 11

[0129] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0130] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0131] (2) Weigh 0.011g KNO3 and dissolve it in 2mL of deionized water. After it is completely dissolved, add 0.5g LiMn2O4 material into a 20mL bottle, let it stand for 12h and then dry it at 80℃. Then grind the dried material and calcine it in an air atmosphere at 500℃ for 3h with a heating rate of 5℃ / min to obtain modified LiMn2O4 catalyst supported on potassium oxide clusters.

[0132] Based on the mass of the modified LiMn2O4 catalyst, the mass percentage of potassium oxide clusters is 1%.

[0133] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0134] 100 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0135] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0136] Example 12

[0137] This embodiment provides a method for preparing a modified LiMn2O4 catalyst for preparing N2O, the method comprising the following steps:

[0138] (1) Preparation of LiMn2O4 material: Same as step (1) in Example 1;

[0139] (2) The LiMn2O4 material was placed in a muffle furnace and pre-calcined in an air atmosphere at 600°C for 3 hours with a heating rate of 5°C / min to obtain the pre-calcined product;

[0140] (3) Weigh 0.0068g NaNO3 and dissolve it in 2mL of deionized water. After complete dissolution, add 0.5g of pre-calcined product into a 20mL bottle, let it stand for 12h and then dry it at 80℃. Then grind the dried material and sinter it in an air atmosphere at 500℃ for 3h with a heating rate of 5℃ / min to obtain modified LiMn2O4 catalyst supported on sodium oxide clusters.

[0141] Based on the mass of the modified LiMn2O4 catalyst, the mass percentage of sodium oxide clusters is 0.5%.

[0142] This embodiment also provides application steps for the above-mentioned catalyst in the catalytic preparation of N2O, the application steps including:

[0143] 100 mg of the modified LiMn2O4 catalyst was loaded into a reactor, and then a reducing agent and raw material gas were introduced. The total gas flow rate was 10000 mL / min. Catalytic reduction reactions were carried out at 50℃, 75℃, 100℃, 125℃, 150℃, 175℃ and 200℃ respectively to obtain the N2O.

[0144] The reducing agent is ammonia with a content of 550 ppm, the raw material gas includes NO with a content of 550 ppm, oxygen with a volume fraction of 5%, and nitrogen as the balance gas.

[0145] Example 13

[0146] The difference between this embodiment and embodiment 1 is that the calcination temperature in step (2) is 100°C.

[0147] The remaining preparation methods and parameters are consistent with those in Example 1.

[0148] Example 14

[0149] The difference between this embodiment and embodiment 1 is that the calcination temperature in step (2) is 1200℃.

[0150] The remaining preparation methods and parameters are consistent with those in Example 1.

[0151] Example 15

[0152] The difference between this embodiment and embodiment 8 is that by adjusting the amount of NaNO3 added in step (2), the mass ratio of sodium oxide clusters in the prepared modified LiMn2O4 catalyst is 0.05%.

[0153] The remaining preparation methods and parameters are consistent with those in Example 8.

[0154] Example 16

[0155] The difference between this embodiment and embodiment 8 is that by adjusting the amount of NaNO3 added in step (2), the mass ratio of sodium oxide clusters in the prepared modified LiMn2O4 catalyst is 15%.

[0156] The remaining preparation methods and parameters are consistent with those in Example 8.

[0157] Comparative Example 1

[0158] The difference between this comparative example and Example 1 is that step (2) is omitted.

[0159] The remaining preparation methods and parameters are consistent with those in Example 1.

[0160] Performance testing

[0161] The catalysts provided in Examples 1-16 and Comparative Example 1 were used to catalyze the preparation of N2O at 200°C, and the conversion rate of NO and the yield of product N2O were detected.

[0162] The test results are shown in Table 1.

[0163] Table 1

[0164]

[0165] analyze:

[0166] As shown in the table above, the present invention modifies the LiMn2O4 material by calcining it, or by loading alkali metal oxide clusters onto the LiMn2O4 material for modification, or by combining the two, thereby controlling the number of exposed Mn metal sites. This allows the prepared modified LiMn2O4 catalyst to greatly improve the yield (i.e., selectivity) of N2O under low temperature conditions, making it suitable for industrial production.

[0167] As can be seen from the data results of Examples 1-7, the conversion rate of NO gradually decreases as the calcination temperature increases. This is because higher calcination temperatures lead to particle sintering, which affects the number of exposed active sites. At the same time, the yield of N2O gradually increases because greater crystallinity enhances redox ability, thereby generating more N2O.

[0168] The data from Examples 8-9 show that increasing the loading of alkali metal oxide clusters leads to a decrease in NO conversion rate. This is because the presence of alkali metals poisons the catalyst, preventing it from effectively adsorbing ammonia during the reaction and thus reducing its activity. At the same time, it leads to an increase in N2O yield, which is also due to the reduction in acidic sites.

[0169] The data from Examples 8 and 12 show that if the LiMn2O4 material is first calcined and then loaded with alkali metal oxide clusters, the two modification methods can work together to achieve an additive effect.

[0170] The data from Examples 1 and 13-14 show that if the calcination temperature is too low, the improvement effect will be minimal; if the calcination temperature is too high, the catalytic activity will be severely lost due to sintering.

[0171] The data results from Examples 8 and 15-16 show that if the mass percentage of alkali metal oxide clusters is too low, the improvement effect will be minimal; if the mass percentage of alkali metal oxide clusters is too high, it will lead to alkali metal poisoning.

[0172] The data from Example 1 and Comparative Example 1 show that modifying LiMn2O4 material can effectively improve the conversion rate of N2O.

[0173] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a modified LiMn204 catalyst for the production of N20, characterized in that, The preparation method comprises: the LiMn2O4 material is calcined, or the LiMn2O4 material is mixed with an alkali metal compound and calcined to perform load modification, or the LiMn2O4 material is first pre-fired, and then the pre-fired LiMn2O4 material is mixed with an alkali metal compound and sintered to obtain the modified LiMn2O4 catalyst; the calcination and pre-firing temperatures are independently 400-800℃; the calcination and pre-firing temperature rising rates are independently 5-10℃ / min; the calcination and pre-firing holding times are independently 1-5h; the calcination and sintering temperatures are independently 300-800℃; the calcination and sintering temperature rising rates are independently 5-10℃ / min; the reducing agent for preparing N2O comprises ammonia, and the raw gas comprises oxygen and nitrogen oxide.

2. The production method according to claim 1, characterized by, The calcination and pre-firing are both performed in an air atmosphere.

3. The preparation method according to claim 1, characterized in that, The cation in the alkali metal compound comprises any one or a combination of at least two of potassium ion, sodium ion, rubidium ion or cesium ion.

4. The production method according to claim 3, characterized by, The cation in the alkali metal compound is sodium ion and / or potassium ion.

5. The preparation method according to claim 3, characterized in that, The anion in the alkali metal compound comprises nitrate ion or carbonate ion.

6. The method of claim 1, wherein, The calcination and sintering temperatures are independently 500-600℃.

7. The preparation method according to claim 1, characterized in that, The calcination and sintering times are independently 1-5h.

8. A modified LiMn204 catalyst for the production of N20, characterized in that, The modified LiMn2O4 catalyst for preparing N2O is prepared by the preparation method according to any one of claims 1-7.

9. The modified LiMn204 catalyst for producing N20 according to claim 8, characterized in that, The modified LiMn2O4 catalyst is loaded with alkali metal oxide clusters.

10. The modified LiMn204 catalyst for producing N20 according to claim 9, characterized in that, The mass percentage of the alkali metal oxide clusters in the modified LiMn2O4 catalyst is 0.1-10% based on the mass of the modified LiMn2O4 catalyst.

11. The modified LiMn204 catalyst for producing N20 according to claim 9, characterized in that, The mass percentage of the alkali metal oxide clusters in the modified LiMn2O4 catalyst is 0.5-1% based on the mass of the modified LiMn2O4 catalyst.

12. Use of a modified LiMn204 catalyst according to any one of claims 8 to 11 for the production of N20, characterized in that, The modified LiMn2O4 catalyst is used for catalytic preparation of N2O.

13. Use according to claim 12, characterized in that, The specific steps of the application comprise: the modified LiMn2O4 catalyst, the reducing agent and the raw gas are placed in a reaction container to perform catalytic reduction to obtain N2O; the reducing agent comprises ammonia; the raw gas comprises oxygen, nitrogen oxide and balance gas.

14. Use according to claim 13, characterized in that, The content of the reducing agent is 0-5000ppm and not 0.

15. Use according to claim 14, characterized in that, The content of the reducing agent is 300-700ppm.

16. The use according to claim 13, characterized in that, The volume fraction of the oxygen is 0-20% and not 0.

17. Use according to claim 16, characterized in that The volume fraction of the oxygen is 5-10%.

18. The use according to claim 13, characterized in that, The content of the nitrogen oxide is 0-5000ppm and not 0.

19. Use according to claim 18, characterized in that, The content of the nitrogen oxide is 300-700ppm.

20. The use according to claim 13, characterized in that, The temperature of the catalytic reduction is 50-200℃.

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