Ni-mn bimetallic oxide catalyst, preparation method and application thereof

Abstract

The application discloses a Ni-Mn bimetallic oxide catalyst, a preparation method and application thereof, and the preparation method comprises the following steps: dissolving a nickel salt, then adding a manganese salt and hydrogen peroxide to obtain a Ni-Mn acidic solution; dissolving an alkali metal hydroxide, then adding an alkali metal carbonate to obtain an alkaline solution; mixing the Ni-Mn acidic solution and the alkaline solution, then heating and reacting, after the reaction is completed, performing solid-liquid separation, washing, drying and calcining to obtain the Ni-Mn bimetallic oxide; the catalyst is used for catalyzing CO2 methanation, and the catalyst is pretreated by H2 before catalysis. The catalyst has excellent stability and excellent CO2 conversion rate and CH4 selectivity.

Description

Technical Field

[0001] This invention relates to a Ni-Mn bimetallic oxide catalyst, its preparation method, and its application, belonging to the field of catalyst catalysis technology. Background Technology

[0002] As human society becomes increasingly industrialized, the consumption of fossil fuels and industrial production have led to a sharp increase in CO2 emissions, triggering global climate change and rising sea levels, posing a significant threat to the survival of humans and animals. Among these advancements, the production of sustainable fuels (methane) from carbon dioxide holds great promise. This technology not only serves as an effective means of mitigating the greenhouse effect but also enables resource recycling and provides crucial raw materials for the petrochemical industry, potentially playing a positive role in environmental control and energy structure adjustment.

[0003] Currently, key characteristics such as metal particle size, reducibility, and oxygen vacancies primarily determine the activity and stability of carbon dioxide methanation catalysts. Noble metal catalysts exhibit good stability and activity in CO2 conversion, but their high cost and low reserves hinder large-scale industrial production. Among non-noble metals, nickel-based catalysts have attracted widespread attention due to their low cost, wide distribution, and high activity. However, in the catalytic reduction of CO2, nickel particles are prone to aggregation and carbon deposition during the reaction, leading to deactivation and severely affecting the catalyst's activity and stability. Furthermore, the carbonyl groups and byproducts (such as CO and H2O) continuously formed during the catalytic reaction of Ni-based catalysts also affect catalyst stability and can even lead to deactivation. Therefore, the search for highly efficient and stable catalysts is of great significance in my country's environmental control and energy structure adjustment fields. Summary of the Invention

[0004] The purpose of this invention is to provide a Ni-Mn bimetallic oxide catalyst, its preparation method, and its application. This catalyst exhibits excellent stability, as well as excellent CO2 conversion rate and CH4 selectivity.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a Ni-Mn bimetallic oxide catalyst includes the following steps:

[0007] S1. Dissolve the nickel salt, then add the manganese salt and hydrogen peroxide and mix to obtain an acidic Ni-Mn solution;

[0008] S2. Dissolve the alkali metal hydroxide and then add the alkali metal carbonate to mix, thus obtaining an alkaline solution;

[0009] S3. Mix the acidic and alkaline solutions of Ni-Mn and heat them to react. After the reaction is completed, separate the solid and liquid components, wash, dry and calcine to obtain Ni-Mn bimetallic oxide.

[0010] Preferably, in step S1, the nickel salt is one or a mixture of nickel nitrate, nickel sulfate, and nickel chloride;

[0011] Manganese salts are one or more of manganese nitrate, manganese sulfate, and manganese chloride;

[0012] Furthermore, the molar ratio of nickel salt to manganese salt is (2-4):1;

[0013] In Ni-Mn acidic solutions, the concentration of nickel salt is 0.6-0.8 mol / L and the concentration of manganese salt is 0.2-0.3 mol / L.

[0014] Preferably, in step S2, the alkali metal hydroxide is sodium hydroxide and / or potassium hydroxide;

[0015] Alkali metal carbonates are sodium carbonate and / or potassium carbonate;

[0016] Furthermore, in the alkaline solution, the concentration of alkali metal hydroxides is 1.4-1.8 mol / L; and the concentration of alkali metal carbonates is 0.4-0.6 mol / L.

[0017] Preferably, in step S3, the Ni-Mn acidic solution and the alkaline solution are mixed in a volume ratio of 1:(1-3).

[0018] Preferably, in step S3, the reaction temperature is 70-90℃ and the reaction time is 4-6h.

[0019] Preferably, in step S3, the drying temperature is 70-90℃ and the drying time is 6-24h.

[0020] Preferably, in step S3, the calcination temperature is 450-550℃, the calcination time is 3-5h, and the heating rate during the calcination process is 3-5℃ / min.

[0021] A Ni-Mn bimetallic oxide catalyst is prepared by any of the methods described above.

[0022] The application of the aforementioned Ni-Mn bimetallic oxide catalyst in the catalytic methanation of CO2 specifically includes the following steps:

[0023] (1) Press, crush, and screen the catalyst into 40-60 mesh particles. Weigh 100 mg of the sample using an electronic balance and place it in the middle of the quartz tube of the CO2 catalytic reduction test equipment (fixed bed continuous flow reactor).

[0024] (2) After the gas components have stabilized through the bypass, the reaction gas passes through the quartz tube; at this time, the changes in CO2 concentration and the generation of CH4 can be observed through the instrument detection system. By processing and analyzing the data, the catalytic oxidation effect of the catalyst can be seen more intuitively.

[0025] (3) Detect the changes in concentration before and after the reaction. The CO2 concentration before the reaction is recorded as CO2in; under the above experimental conditions, the CO2 concentration after the reaction is CO2out; the CH4 generation concentration is represented as CH4out.

[0026] (4) Calculate the CO2 conversion rate and the catalyst selectivity for CH4 according to the following formula;

[0027] CO2 conversion rate:

[0028]

[0029] Methane selectivity:

[0030]

[0031] In the formula, CO2in is the initial concentration of CO2, in ppm.

[0032] CH4out----Concentration of CH4 after reaction, in ppm;

[0033] CO2out----The concentration of CO2 after the reaction, in ppm.

[0034] Preferably, a pretreatment step of the catalyst is performed before the catalyst catalyzes the methanation of CO2;

[0035] The specific method of the pretreatment is as follows: after the catalyst is placed in the middle of the quartz tube of the fixed bed continuous flow reactor, it is treated at 200-400℃ in an H2 atmosphere for 5-120 min, with an H2 flow rate of 20-100 ml / min.

[0036] The beneficial effects of this invention are as follows:

[0037] The co-precipitation method for preparing Ni-Mn bimetallic oxides is simple, and hydrogen pretreatment significantly enhances the catalyst's performance in catalyzing the methanation of CO2. After 24 hours of reaction, the catalyst achieves a CO2 conversion rate of 94% and a methane selectivity of 94%, exhibiting good time stability. Attached Figure Description

[0038] Figure 1 The X-ray diffraction patterns of Ni-Mn bimetallic oxide catalysts under different pretreatment conditions are shown.

[0039] Figure 2 These are scanning electron microscope images of the catalyst prepared in Example 1;

[0040] Figure 3 The graphs show the catalytic performance of the catalysts obtained in Examples 1, 2, and 3.

[0041] Figure 4 The graphs show the catalytic performance of the catalysts obtained in Examples 1, 4, and 5.

[0042] Figure 5 The graph shows the catalytic performance of the catalysts obtained in Example 1 and Comparative Example 1.

[0043] Figure 6 The image shows the stability test results of Example 1 after 24 hours of catalysis under the conditions of 300℃ and H2 pretreatment for 1 hour. Detailed Implementation

[0044] This invention provides a method for preparing a highly efficient CO2 methanation catalyst. The catalyst exhibits excellent CO2 conversion and CH4 selectivity. Through hydrogen modification of the catalyst, studies have shown that 100 mg of Ni-Mn bimetallic oxide catalyst exhibits the best catalytic effect under conditions of 300℃ and hydrogen pretreatment for 60 min. Furthermore, this catalyst demonstrates excellent CO2 methanation catalytic performance at a low temperature of 200℃: CO2 conversion reaches 95.39% and CH4 selectivity reaches 96.67%. Even after long-term reaction performance testing, it can still maintain a catalytic efficiency of over 94%. The catalyst preparation process of this invention is simple. Ni-Mn-type hydrotalcite is prepared by co-precipitation, followed by calcination and hydrogen modification, which greatly enhances the performance of CO2 methanation and has promising application prospects.

[0045] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0046] Example 1

[0047] A highly efficient CO2 methanation catalyst: a method for preparing Ni-Mn bimetallic oxide, comprising the following steps:

[0048] (1) Under room temperature conditions, weigh 3.94 g (15 mmol) of NiSO4·6H2O and dissolve it in 18 ml of deionized water. Add 1.175 ml (5 mmol) of Mn(NO3)2 solution and add 0.5 ml of hydrogen peroxide dropwise. Stir well to obtain Ni-Mn acidic solution A.

[0049] (2) At room temperature, weigh 1.28g of NaOH and dissolve it in 20ml of deionized water, then add 1.06g of Na2CO3 and use a magnetic stirrer to dissolve it completely to obtain alkaline solution B;

[0050] (3) Place the beaker containing 40ml of deionized water into the oil bath and heat it to 80℃ to ensure that the temperature of the deionized water is stable at 80℃.

[0051] (4) Add solutions A and B obtained in steps (1) and (2) evenly to the beaker in step (3) at a rate of 1-3 ml / min to allow them to react fully; after the addition is complete, seal the beaker and keep it in an oil bath for 5 hours.

[0052] (5) After cooling the solution obtained in step (4) to room temperature, filter it and wash it several times with deionized water until neutral; dry the obtained solid precipitate in an oven at 80°C overnight;

[0053] (6) The dried solid obtained in step (5) is transferred to a muffle furnace and heated to 500°C at a rate of 3°C / min and held for 4 hours for calcination to obtain Ni-Mn bimetallic oxide;

[0054] (7) The Ni-Mn bimetallic oxide obtained in step (6) was placed in a CO2 catalytic reduction test device for H2 (flow rate of 40 ml / min) pretreatment, and the conditions were 300℃ pretreatment for 1 hour.

[0055] (8) After cooling the catalyst pretreated in step (7), the performance was tested in the range of 200 to 350°C. The CO2 conversion rate and CH4 selectivity were obtained after data processing.

[0056] Example 2

[0057] It is basically the same as Example 1, except that in step (7), the H2 pretreatment conditions are: 200℃ pretreatment for 1 hour.

[0058] Example 3

[0059] It is basically the same as Example 1, except that in step (7), the H2 pretreatment conditions are: 400℃ pretreatment for 1 hour.

[0060] Example 4

[0061] It is basically the same as Example 1, except that in step (7), the H2 pretreatment conditions are: 300℃ pretreatment for 5 minutes.

[0062] Example 5

[0063] It is basically the same as Example 1, except that in step (7), the H2 pretreatment conditions are: 300℃ pretreatment for 2 hours, and other conditions are exactly the same as those in Example 1.

[0064] Comparative Example 1

[0065] The results are basically the same as in Example 1, except that step (7) is not performed in this comparative example. Instead, after obtaining the catalyst, the performance is directly tested in the range of 200-350°C after the catalyst is cooled. The CO2 conversion rate and CH4 selectivity are obtained after data processing.

[0066] Characterization analysis:

[0067] Figure 1 X-ray diffraction patterns of Ni-Mn bimetallic oxide catalysts under different pretreatment conditions are shown. The characteristic diffraction peaks of the active component NiO are mainly located at 2θ = 36.7°, 42.6°, 62.0°, and 74.3°, corresponding to its (111), (200), (220), and (311) crystal planes, respectively. The characteristic diffraction peaks of the active component metallic Ni are mainly located at 2θ = 44.5° and 51.8°, corresponding to its (111) and (200) crystal planes, respectively. Compared with Examples 2 and 4, Example 1 exhibits metallic Ni diffraction peaks, indicating that it has better reducibility; compared with Examples 3 and 5, Example 1 has better reaction conditions under the premise of better reducibility, which has the advantage of reducing energy consumption.

[0068] Figure 2 The image shows a scanning electron microscope (SEM) image of the Ni-Mn bimetallic oxide catalyst in Example 1. As shown, the catalyst nanosheets are smaller and their surfaces are rougher due to shrinkage during the thermal reduction process; Ni, Mn, and O species are also uniformly distributed in the catalyst.

[0069] Performance testing:

[0070] The CO2 methanation performance of the catalyst samples obtained in Examples 1, 2, and 3 was evaluated by simulating the actual CO2 concentration in flue gas. The test conditions were: total flow rate of 50 mL / min, CO2 content of 200,000 ppm, and reaction temperature of 200–350 °C, with tests conducted in 30 °C increments. The test results are as follows: Figure 3 As shown.

[0071] Figure 3 The catalytic effects of Ni-Mn bimetallic oxides pretreated with hydrogen for 1 hour at pretreatment temperatures of 200℃, 300℃, and 400℃ are shown in the figures. The results indicate that hydrogen pretreatment at 300℃ for 1 hour significantly improves the catalytic activity of the catalyst. The catalyst exhibits excellent CO2 conversion and CH4 selectivity at 200℃. Through repeated experiments, it was confirmed that the catalyst obtained under high temperature conditions of 300℃ and hydrogen pretreatment for 1 hour exhibits the best catalytic activity.

[0072] The CO2 methanation performance of the catalyst samples obtained in Examples 1, 4, and 5 was evaluated by simulating the actual CO2 concentration in flue gas. The test conditions were: total flow rate of 50 mL / min, CO2 content of 200,000 ppm, and reaction temperature within the range of 200–350 °C, with tests conducted in 30 °C increments. The test results are as follows: Figure 4 As shown.

[0073] Figure 4 The catalytic performance of Ni-Mn bimetallic oxide catalysts obtained at a temperature of 300℃ for pretreatment times of 5 min, 60 min, and 120 min is shown in the figure. The results indicate that hydrogen pretreatment at 300℃ for 60 min significantly improves the catalytic activity of the catalyst. The catalyst exhibits excellent CO2 conversion and CH4 selectivity at 200℃. Through repeated experiments, it was confirmed that the catalyst obtained at 300℃ with hydrogen pretreatment for 60 min exhibits the best catalytic activity.

[0074] The catalyst sample prepared in Example 1 underwent a long-term CO2 methanation performance evaluation. The test conditions were: total flow rate of 50 mL / min, CO2 content of 200,000 ppm, reaction temperature of 200 °C, and reaction time of 24 h. The test results are as follows: Figure 5 As shown.

[0075] Depend on Figure 5 It can be seen that the catalyst, after being pretreated with H2 at 300℃ for 1 hour, still maintained a CO2 conversion rate and CH4 selectivity of over 94% after a long-term stability test at 200℃ for 24 hours, indicating that the catalyst has a certain degree of stability.

[0076] The CO2 methanation performance of the catalyst samples from Example 1 and Comparative Example 1 was evaluated by simulating the actual CO2 concentration in flue gas. The test conditions were: total flow rate of 50 mL / min, CO2 content of 200,000 ppm, and reaction temperature of 200–350 °C, with tests conducted in 30 °C increments. The test results are as follows: Figure 6 As shown.

[0077] Depend on Figure 6 It can be seen that the catalyst pretreated with H2 at 300℃ for 1 hour exhibits superior CO2 conversion and CH4 selectivity at 200℃ compared to the catalyst without H2 pretreatment.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of a Ni-Mn bimetallic oxide catalyst in the catalytic methanation of CO2, characterized in that, The preparation method of Ni-Mn bimetallic oxide catalyst includes the following steps: S1. Dissolve the nickel salt and then add the manganese salt and hydrogen peroxide to mix, and obtain a Ni-Mn acidic solution, with the molar ratio of nickel in the nickel salt to manganese in the manganese salt being 3:1; S2. Dissolve the alkali metal hydroxide and then add the alkali metal carbonate to mix, thus obtaining an alkaline solution; S3. Mix the acidic Ni-Mn solution and the alkaline solution at a volume ratio of 1:(1-3) and react at 80℃ for 5h. After the reaction is completed, separate the solid and liquid, wash and dry, and then heat to 500℃ at a rate of 3℃ / min and calcine for 4h to obtain Ni-Mn bimetallic oxide. A pretreatment step for the catalyst was performed before the catalyst catalyzed the CO2 methanation; The specific method of pretreatment is as follows: treat at 300℃ in an H2 atmosphere for 60 min, with an H2 flow rate of 40 ml / min; The obtained catalyst achieved a CO2 conversion rate of 95.39% and a CH4 selectivity of 96.67% at a total CO2 and H2 flow rate of 50 mL / min, a CO2 content of 200,000 ppm, and a reaction temperature of 200 °C.

2. The application according to claim 1, characterized in that, In step S1, the nickel salt is one or a mixture of nickel nitrate, nickel sulfate, and nickel chloride; Manganese salts are one or more of manganese nitrate, manganese sulfate, and manganese chloride; In Ni-Mn acidic solutions, the concentration of nickel salt is 0.6-0.8 mol / L and the concentration of manganese salt is 0.2-0.3 mol / L.

3. The application according to claim 2, characterized in that, In step S2, the alkali metal hydroxide is sodium hydroxide and / or potassium hydroxide; Alkali metal carbonates are sodium carbonate and / or potassium carbonate; Furthermore, in the alkaline solution, the concentration of alkali metal hydroxides is 1.4-1.8 mol / L; and the concentration of alkali metal carbonates is 0.4-0.6 mol / L.

4. The application according to claim 1, characterized in that, In step S3, the drying temperature is 70-90℃ and the drying time is 6-24h.

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