Preparation method and application of a nickel-manganese solid solution and a composite oxide thereof

Abstract

The application provides a preparation method and application of a nickel-manganese solid solution and a composite oxide thereof, and belongs to the technical field of environmental protection. The state of reaction is controlled by adjusting the ratio of bivalent nickel and bivalent manganese, so that a nickel-manganese solid solution or a nickel-manganese composite oxide catalyst with different nickel-manganese contents is generated; the nickel-manganese solid solution and the oxide thereof prepared by the application can efficiently catalyze and decompose ozone under the conditions of high ozone concentration, high mass space velocity and a wide humidity range, while the preparation method is simple, the time is short, the cost is low, the environment is not polluted, and the ozone removal efficiency is excellent under the condition of high relative humidity, and the shortcoming that traditional catalysts are easily deactivated under humid conditions is overcome.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, and in particular relates to a method for preparing and applying a nickel-manganese solid solution and its composite oxide. Background Technology

[0002] Surface ozone is a secondary pollutant formed by the photochemical reaction of nitrogen oxides, carbon monoxide, and volatile organic compounds under sunlight. Even long-term exposure to low ozone levels can cause serious harm to human health, such as leading to nervous system weakness, respiratory damage, and decreased immune function. Furthermore, residual ozone indoors can react chemically with volatile organic compounds and particulate matter to produce secondary pollutants such as formaldehyde, organic aerosols, and ultrafine particulate matter, exacerbating the threat to human health. Therefore, developing effective methods and materials for ozone elimination to protect the environment and human health is imperative.

[0003] Catalytic decomposition methods are widely used for ozone removal due to their economic, efficient, and safe advantages. Among these, manganese-based catalysts, with their diverse valence states, controllable crystal phases, tunable morphology, abundant reserves, and excellent activity, have proven effective in catalytic ozone decomposition. Oxygen vacancies on the catalyst surface act as active sites, decomposing adsorbed ozone into oxygen and oxygen ions. Subsequently, ozone reacts with oxygen ions to generate oxygen and oxygen peroxide species. The desorption of oxygen peroxide species releases oxygen vacancies and oxygen again. Therefore, the quantity and properties of oxygen vacancies determine the catalyst's performance.

[0004] However, due to their similar chemical structures, water molecules compete with ozone molecules for adsorption at oxygen vacancies, occupying active sites. This makes manganese-based catalysts more sensitive to moisture, resulting in decreased activity or even gradual deactivation in high humidity environments. In practical applications, varying degrees of humidity are always present in the air, especially in industries such as wastewater treatment, where emissions are characterized by high ozone concentrations, low temperatures, and high humidity.

[0005] Therefore, promoting the generation of oxygen vacancies, improving the water resistance of oxygen vacancies, and developing catalysts that can stably catalyze the decomposition of ozone in the presence of water molecules, especially under high humidity, are of great significance in protecting people from ozone pollution in their daily lives and production and ensuring their health. Summary of the Invention

[0006] One of the technical problems that this invention aims to solve is that existing manganese-based catalysts have weak resistance to moisture and their activity decreases in high humidity environments, making it impossible to guarantee efficient decomposition of ozone.

[0007] To address the aforementioned technical problems, this embodiment provides a method for preparing a nickel-manganese solid solution, which includes the following steps:

[0008] S1. Dissolve the metal salts of divalent nickel and divalent manganese in water to obtain a first solution. Add permanganate to the first solution to obtain a second solution and stir until homogeneous. Dissolve a pH adjuster in water to obtain a third solution.

[0009] The stirring time is 0.1 to 1 hour.

[0010] S2. Add the third solution to the second solution and stir at room temperature to obtain a mixed solution;

[0011] In this process, a third solution is added dropwise to the second solution to control the pH value of the mixed solution.

[0012] S3. Transfer the mixed solution to the reaction vessel and place it in an oven for hydrothermal reaction to obtain the hydrothermal reaction product;

[0013] The hydrothermal reaction temperature is 90–160℃, and the time is 1–5 hours.

[0014] S4. Centrifuge the hydrothermal reaction product, wash with deionized water until the pH of the filtrate is neutral, collect the solid phase and dry it to obtain nickel-manganese solid solution.

[0015] In some embodiments, the aforementioned method for preparing a nickel-manganese solid solution includes, in S1, a metal salt comprising one or more of nitrates, chlorates and acetates, and the molar ratio of divalent nickel to divalent manganese in the metal salt being (1-8):(0-8).

[0016] In some embodiments, in the aforementioned method for preparing a nickel-manganese solid solution, the permanganate in S1 includes one or more of sodium permanganate, potassium permanganate, and lithium permanganate, the mass ratio of the metal salt to the permanganate is 3:(1-2), and the concentration of the permanganate is 0.03-0.15 mol / L.

[0017] In some embodiments, in the aforementioned method for preparing a nickel-manganese solid solution, the third solution in S1 is a KOH solution with a concentration of 1–6 mol / L.

[0018] In some embodiments, in the aforementioned method for preparing a nickel-manganese solid solution, the stirring reaction time at room temperature in S2 is 0.5 to 2 hours, and the pH value of the mixed solution is controlled at 8 to 13.

[0019] In some embodiments, in the aforementioned method for preparing a nickel-manganese solid solution, the number of times deionized water is washed in S4 is 3 to 10, the drying temperature is 70 to 100°C, and the time is 6 to 20 hours.

[0020] The second aspect of this application provides the application of the nickel-manganese solid solution obtained by the aforementioned preparation method in ozone.

[0021] The third aspect of this application provides a method for preparing a nickel-manganese composite oxide, which includes calcining the nickel-manganese solid solution obtained by the preparation method in an air atmosphere and collecting the solid phase to obtain the nickel-manganese composite oxide.

[0022] In some embodiments, the aforementioned method for preparing a nickel-manganese solid solution involves calcination at a temperature of 200–700°C for a time of 2–6 hours.

[0023] The fourth aspect of this application provides the application of the nickel-manganese composite oxide obtained by the aforementioned preparation method in ozone.

[0024] The present invention provides a method for preparing a nickel-manganese solid solution and its composite oxide, and its application, which have the following beneficial effects:

[0025] This invention utilizes the redox reaction between divalent nickel and divalent manganese with permanganate under alkaline conditions. By adjusting the ratio of divalent nickel to divalent manganese, the reaction state is controlled to generate nickel-manganese solid solutions or nickel-manganese composite oxide catalysts with different nickel-manganese contents. The nickel-manganese solid solutions and nickel-manganese composite oxide catalysts fully leverage the synergistic effect between nickel and manganese, promoting the formation of oxygen vacancies and significantly improving their hydrophobicity. Compared to pure manganese oxides, the nickel-manganese solid solutions contain more trivalent manganese and surface-adsorbed oxygen, indicating a richer oxygen vacancy content.

[0026] Secondly, the adsorption capacity of nickel-manganese solid solution catalysts for water molecules is much lower than that of pure manganese oxides, exhibiting stronger hydrophobicity. When a certain amount of ozone is introduced, the water absorption of nickel-manganese solid solution decreases significantly, while the water absorption of pure manganese oxides increases slightly. This indicates that nickel-manganese solid solution has a stronger affinity for ozone molecules than for water molecules, while pure manganese oxides tend to adsorb water molecules.

[0027] Therefore, the nickel-manganese solid solution and its oxide prepared in this invention can efficiently catalyze the decomposition of ozone under high ozone concentration, high mass hourly space velocity and wide humidity range as an ozone decomposition catalyst. At the same time, the preparation method is simple, quick, and low in cost, and will not cause environmental pollution. Furthermore, it has excellent ozone removal efficiency under extremely high relative humidity conditions, overcoming the shortcomings of traditional catalysts that are prone to deactivation under humid conditions. Attached Figure Description

[0028] Figure 1 A flowchart of a method for preparing a nickel-manganese solid solution provided by the present invention;

[0029] Figure 2 The XRD patterns of the nickel-manganese solid solutions and manganese oxides prepared in Examples 1 to 4 and Comparative Example 1 of this invention are shown below.

[0030] Figure 3The XRD patterns are of the nickel-manganese composite oxides prepared in Examples 11 and 12 of this invention.

[0031] Figure 4 This is an in-situ diffuse reflectance study of water adsorption in pure manganese oxide and nickel-manganese solid solution at 60% relative humidity. Detailed Implementation

[0032] The present invention will be further explained below through specific embodiments. The embodiments are only some examples of the present invention and do not limit the present invention in any way. That is, the present invention is not limited to the following steps. Equivalent substitution of raw materials or changes in the quality of raw materials are all within the protection scope of the present invention.

[0033] Example 1

[0034] like Figure 1 As shown, this embodiment provides a method for preparing a nickel-manganese solid solution, comprising the following steps:

[0035] S1. Dissolve 1.60g of nickel chloride hexahydrate and 1.65g of manganese acetate tetrahydrate in 60mL of deionized water to obtain the first solution; add 1.06g of potassium permanganate to the first solution and stir until homogeneous to obtain the second solution; dissolve 16.83g of potassium hydroxide in 100mL of deionized water to obtain the third solution.

[0036] S2. Add the third solution dropwise to the second solution, control the pH of the reaction solution to 12, and stir at room temperature for 0.5 h to obtain a mixed solution;

[0037] S3. Transfer the mixed solution to a reaction vessel and place it in an oven for hydrothermal reaction at a temperature of 120°C for 2 hours to obtain the hydrothermal reaction product.

[0038] S4. The hydrothermal reaction product was washed with deionized water until neutral, and then dried overnight in an oven at 85°C to obtain a nickel-manganese solid solution catalyst, denoted as Mn1Ni1.

[0039] Example 2

[0040] The difference between this embodiment and Example 1 is that S1 involves dissolving 0.53g of nickel chloride hexahydrate and 2.20g of manganese acetate tetrahydrate in 60mL of deionized water to obtain the first solution; other conditions are exactly the same as in Example 1; and the resulting nickel-manganese solid solution is denoted as Mn4Ni1.

[0041] Example 3

[0042] The difference between this embodiment and Example 1 is that in S1, 3.20g of nickel chloride hexahydrate and 0.83g of manganese acetate tetrahydrate are dissolved in 60mL of deionized water to obtain the first solution; other conditions are exactly the same as in Example 1; and the obtained nickel-manganese solid solution is denoted as Mn1Ni4.

[0043] Example 4

[0044] The difference between this embodiment and Embodiment 1 is that S1 involves dissolving 4.81g of nickel chloride hexahydrate in 60mL of deionized water to obtain the first solution; other conditions are exactly the same as in Embodiment 1; and the obtained nickel-manganese solid solution is denoted as Mn0Ni, where the volume of divalent manganese in this embodiment is 0, so the subscript of Mn in Mn0Ni is 0, and the manganese source in the nickel-manganese solid solution in this embodiment is manganese in potassium permanganate.

[0045] Comparative Example 1

[0046] In this comparative example, the amorphous manganese oxide was prepared using the following steps:

[0047] S1. Dissolve 2.48g of manganese acetate tetrahydrate in 60mL of deionized water to obtain the first solution; add 1.06g of potassium permanganate to the first solution and stir until homogeneous to obtain the second solution; dissolve 16.83g of potassium hydroxide in 100mL of deionized water to obtain the third solution.

[0048] S2. Add the third solution dropwise to the second solution, control the pH of the reaction solution to 12, and stir at room temperature for 0.5 h to obtain a mixed solution;

[0049] S3. Transfer the mixed solution to a reaction vessel and place it in an oven for hydrothermal reaction at a temperature of 120°C for 2 hours to obtain the hydrothermal reaction product.

[0050] S4. The hydrothermal reaction product was washed with deionized water until neutral, and then dried overnight in an oven at 85°C to obtain an amorphous manganese oxide catalyst, denoted as MnNi0.

[0051] Example 5

[0052] like Figure 1 As shown, this embodiment provides a method for preparing a nickel-manganese solid solution, comprising the following steps:

[0053] S1. Dissolve 0.48g of nickel chloride hexahydrate and 0.99g of manganese acetate tetrahydrate in 30mL of deionized water to obtain the first solution; add 0.53g of potassium permanganate to the first solution and stir until homogeneous to obtain the second solution; dissolve 16.83g of potassium hydroxide in 100mL of deionized water to obtain the third solution.

[0054] S2. Add the third solution dropwise to the second solution, control the pH of the reaction solution to 12, and stir at room temperature for 0.4 h to obtain a mixed solution;

[0055] S3. Transfer the mixed solution to a reaction vessel and place it in an oven for hydrothermal reaction at a temperature of 120°C for 2 hours to obtain the hydrothermal reaction product.

[0056] S4. The hydrothermal reaction product was washed with deionized water until neutral, and then dried overnight in an oven at 85°C to obtain a nickel-manganese solid solution catalyst, denoted as Mn2Ni1-0.5.

[0057] Example 6

[0058] The difference between this embodiment and embodiment 5 is that S1 is 1.20g of nickel chloride hexahydrate and 0.62g of manganese acetate tetrahydrate dissolved in 30mL of deionized water to obtain the first solution; other conditions are exactly the same as in embodiment 5; and the obtained nickel-manganese solid solution is denoted as Mn1Ni2-0.5.

[0059] Example 7

[0060] The difference between this embodiment and embodiment 5 is that S1 involves dissolving 0.80g of nickel chloride hexahydrate and 0.83g of manganese acetate tetrahydrate in 30mL of deionized water to obtain the first solution; other conditions are exactly the same as in embodiment 5; and the obtained nickel-manganese solid solution is denoted as Mn1Ni1-0.5.

[0061] Example 8

[0062] The difference between this embodiment and embodiment 5 is that in S1, 0.80g of nickel chloride hexahydrate and 0.67g of manganese chloride tetrahydrate are dissolved in 30mL of deionized water to obtain the first solution; other conditions are exactly the same as in embodiment 5; and the obtained nickel-manganese solid solution is denoted as Mn-Cl-Ni-Cl.

[0063] Example 9

[0064] The difference between this embodiment and embodiment 5 is that in S1, 0.84 g of nickel acetate tetrahydrate and 0.83 g of manganese acetate tetrahydrate are dissolved in 30 mL of deionized water to obtain the first solution; other conditions are exactly the same as in embodiment 5; and the obtained nickel-manganese solid solution is denoted as Mn-Ac-Ni-Ac.

[0065] Example 10

[0066] The difference between this embodiment and Example 5 is that S1 involves dissolving 0.98g of nickel nitrate hexahydrate and 0.83g of manganese acetate tetrahydrate in 30mL of deionized water to obtain the first solution; other conditions are exactly the same as in Example 5; and the obtained nickel-manganese solid solution is denoted as Mn-Ac-Ni-NO3.

[0067] Example 11

[0068] S1. Dissolve 5.03g of nickel acetate tetrahydrate in 60mL of deionized water to obtain the first solution; add 1.06g of potassium permanganate to the first solution and stir until homogeneous to obtain the second solution; dissolve 16.83g of potassium hydroxide in 100mL of deionized water to obtain the third solution.

[0069] S2. Add the third solution dropwise to the second solution, control the pH of the reaction solution to 12, and stir at room temperature for 1 hour to obtain a mixed solution;

[0070] S3. Transfer the mixed solution to a reaction vessel and place it in an oven for hydrothermal reaction at a temperature of 120°C for 2 hours to obtain the hydrothermal reaction product.

[0071] S4. The hydrothermal reaction product was washed with deionized water until neutral, and then dried overnight in an oven at 85°C to obtain the nickel-manganese composite oxide precursor.

[0072] S5. The nickel-manganese composite oxide precursor obtained in S4 is placed in a muffle furnace and calcined at 300°C for 2-4 hours in an air atmosphere to obtain the nickel-manganese composite oxide, denoted as NiMn-300.

[0073] Example 12

[0074] The difference between this embodiment and Embodiment 11 is that in S5, the nickel-manganese composite oxide precursor obtained in S4 is placed in a muffle furnace and calcined at 500°C for 2-4 hours in an air atmosphere; other conditions are exactly the same as in Embodiment 11; and the obtained nickel-manganese solid solution is denoted as NiMn-500.

[0075] Next, the performance of the catalysts described in Examples 1 to 12 and Comparative Example 1 in catalytic decomposition of ozone was tested. The test methods and conditions are as follows:

[0076] The specific conditions for the activity evaluation test were as follows: ozone concentration in the reaction gas was 45 ppm, temperature was 30℃, relative humidity was 80% and 60%, test space velocity was 600 L / g / h, and test time was 3.5h; the ozone conversion rate of each example was recorded and a comparison table was made as shown in Table 1.

[0077] Table 1: Comparison of Ozone Conversion Rates in Various Examples

[0078]

[0079] As can be seen from the table above, the nickel-manganese solid solution and its oxide catalyst of the present invention have a high ability to catalyze the decomposition of ozone. Under the conditions of 30°C, 80% relative humidity, and 600 L / g / h space velocity, the catalytic efficiency can reach over 99% after 3.5 hours of catalytic reaction. In Example 11, the oxide catalyst, under the conditions of 30°C, 80% relative humidity, and a high space velocity of 1200 L / g / h, still achieved a catalytic efficiency of 95.64% after 3.5 hours of catalytic reaction.

[0080] The XRD patterns of nickel-manganese solid solutions with different nickel-manganese molar ratios are shown below. Figure 2 As shown, the XRD patterns of nickel-manganese composite oxides with different crystallinities are as follows: Figure 3 As shown.

[0081] As can be seen from the comparison of Examples 1 to 4 and Comparative Example 1, the introduction of nickel significantly improves the performance of the catalyst in catalytically decomposing ozone compared to pure manganese oxide; furthermore... Figure 4 As shown, under a relative humidity of 60%, by Figure 4 (a) to Figure 4 (b) It can be seen that the nickel-manganese solid solution catalyst exhibits stronger hydrophobicity, due to Figure 4 (c) to Figure 4 (d) It can be seen that the nickel-manganese solid solution exhibits a stronger ozone affinity after the introduction of ozone. Comparing Examples 1-10, it can be seen that in the preparation process of the nickel-manganese solid solution catalyst of the present invention, the molar ratio of divalent nickel salt and divalent manganese salt and the type of precursor affect the catalytic performance of the ozone catalyst. When the molar ratio of divalent nickel salt and divalent manganese salt is controlled at 1:(0.5~2), the catalytic effect of the ozone decomposition catalyst is better. The molar ratio of divalent nickel salt and divalent manganese salt is obtained from the subscripts of the products obtained in different examples. That is, in Example 1, the nickel-manganese solid solution catalyst is denoted as Mn1Ni1, and the molar ratio of divalent nickel salt and divalent manganese salt is 1:1.

[0082] A comparison of Examples 11 and 12 shows that the calcination temperature affects the performance of the ozone decomposition catalyst during the preparation of the nickel-manganese composite oxide of the present invention. Controlling the calcination temperature at 300°C results in a better catalytic effect of the ozone decomposition catalyst. If the calcination temperature is too high, the catalyst's ability to decompose ozone will decrease significantly.

[0083] Next, the stability test of the catalyst: taking the catalysts in Example 1 and Example 11 as examples, the ozone conversion rate corresponding to the test time of 25h and 30h was recorded respectively. Other test conditions were the same as those in the activity evaluation test. In addition, taking Example 1 as an example, the ozone removal efficiency under extremely high humidity conditions (100%RH) was recorded, as shown in Table 2 below.

[0084] Table 2: Ozone conversion rates of the catalysts in Examples 1, 11, and Example 1 under special conditions.

[0085]

[0086] As can be seen from the stability test results of the catalyst in the table above, the nickel-manganese solid solution and nickel-manganese composite oxide catalysts of the present invention have high stability and can decompose ozone efficiently for a long time. They can be applied to the treatment of ozone and various ozone-containing gases with long-term and efficient decomposition.

[0087] In addition, the effect of humidity on catalyst performance: taking the catalysts in Example 1 and Example 11 as examples, the ozone conversion rates corresponding to relative humidity of 5%, 30%, 60% and 90% (other test conditions are the same as in the activity evaluation test) are recorded respectively, as shown in Table 3;

[0088] Table 3: Comparison of ozone conversion rates of catalysts in Examples 1 and 11 under different humidity conditions

[0089]

[0090] As can be seen from the table above, the catalyst of the present invention can achieve a conversion rate of over 99% for catalytic ozone decomposition under a wide relative humidity range of 5-80%, indicating that the nickel-manganese solid solution and its oxide catalyst described in the present invention can maintain a high ozone conversion efficiency under the entire relative humidity conditions.

[0091] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. Modifications of the present invention by those skilled in the art in various equivalent forms all fall within the scope defined by the appended claims.

Claims

1. A method for preparing a nickel-manganese composite oxide, characterized in that, Includes the following steps: S1. Dissolve 5.03g of nickel acetate tetrahydrate in 60mL of deionized water to obtain the first solution; add 1.06g of potassium permanganate to the first solution and stir until homogeneous to obtain the second solution; dissolve 16.83g of potassium hydroxide in 100mL of deionized water to obtain the third solution. S2. Add the third solution dropwise to the second solution, control the pH of the reaction solution to 12, and stir at room temperature for 1 hour to obtain a mixed solution; S3. Transfer the mixed solution to a reaction vessel and place it in an oven for hydrothermal reaction at a temperature of 120°C for 2 hours to obtain the hydrothermal reaction product. S4. The hydrothermal reaction product was washed with deionized water until neutral, and then dried overnight in an oven at 85°C to obtain the nickel-manganese composite oxide precursor. S5. Place the nickel-manganese composite oxide precursor obtained in S4 into a muffle furnace and calcine it at 300°C for 2-4 hours in an air atmosphere to obtain the nickel-manganese composite oxide.

2. The application of a nickel-manganese composite oxide obtained by the preparation method described in claim 1 in the decomposition of ozone.

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