A nickel-based carbon dioxide methanation catalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of CO2 methanation catalysts, and particularly relates to a nickel-based carbon dioxide methanation catalyst, a preparation method thereof and application thereof. The method obtains a precursor by ion exchange of Ni ions to exchange part of Mg ions in a hydroxide gel, and obtains a nickel-based CO2 methanation catalyst with a whole wrapping structure of a magnesium oxide carrier wrapping Ni metal nanoparticles after calcination. The degree of wrapping is affected by calcination in other atmospheres before hydrogen section, so as to control the catalytic activity, and the catalytic activity is close to that of complete hydrogen calcination at a catalytic temperature of 300-500 DEG C, so as to reduce the use of hydrogen. The obtained catalyst has good low-temperature catalytic performance, and has the advantages of oxidation resistance and anti-coking. The preparation method of the catalyst is simple, and is very suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of CO2 methanation catalyst technology. More specifically, it relates to a nickel-based carbon dioxide methanation catalyst, its preparation method, and its application. Background Technology

[0002] The massive combustion of fossil fuels globally has led to a surge in atmospheric CO2 concentrations, exacerbating the greenhouse effect and impacting the Earth's ecological balance. Technologies for reducing CO2 emissions primarily rely on (I) carbon capture and storage (CCS) and (II) CO2 capture and utilization (CCU). While CCS is a viable strategy for reducing CO2 emissions, it requires CO2 storage near emission sources or transporting the captured CO2 to storage sites, which is extremely time-consuming and labor-intensive. In comparison, CCU is considered a feasible alternative to CCS, as it can convert carbon dioxide into commercially valuable products through electrochemical, thermocatalytic, photochemical, and biochemical methods.

[0003] Carbon dioxide methanation is a CCU (Carbon Dioxide Reforming) technology that uses a specific catalyst to hydrogenate CO2 into methane. Theoretically, CO2 can be completely converted to methane through this technology, thus effectively utilizing CO2 and achieving its conversion to methane. Nickel-based catalysts are a key focus of CH4-CO2 reforming research; however, they are prone to carbon deposition and sintering / coking. The catalyst is crucial for the methane and carbon dioxide reforming reaction. Besides the catalyst's composition, the preparation method and conditions affect its structure. Furthermore, the structure, dispersion, and reducibility of the active components significantly impact the reforming activity and resistance to coking. Therefore, the catalyst preparation method directly influences its activity, selectivity, and resistance to coking.

[0004] Chinese patent application CN107321354A discloses a method for preparing a magnesium-aluminum spinel support using hydrothermal synthesis, then uniformly loading nickel-containing components onto the support using nickel nitrate as an impregnation solution, and finally acid-washing the impregnated catalyst precursor to obtain a nickel-based carbon dioxide methanation catalyst. This nickel-based catalyst is still prepared using an impregnation method. Although it has a high CO2 conversion rate, it requires catalysis at 600℃, which is extremely high and consumes a lot of energy. Similarly, Chinese patent application CN114870846A discloses a carbon dioxide methanation catalyst. Although the resulting catalyst can exert its catalytic effect at 250℃, it requires the addition of biomass tar, utilizing the phenolic organic compounds in the biomass tar as a dispersion medium. Biomass tar, as a mixture, contains many components, including some carcinogenic ones, and is difficult to completely burn, leaving residues that can easily harm human health and the environment.

[0005] Therefore, there is an urgent need to develop a green, mild, efficient, low-temperature active, and coking-resistant CO2 methanation catalyst. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings and deficiencies of existing nickel-based CO2 methanation catalysts, which exhibit poor low-temperature catalytic activity, require higher temperatures (>500℃) to exert their catalytic effect, or necessitate modification with organic compounds that can easily cause human health or environmental pollution. Based on the above technical problems, the primary objective of this invention is to provide a green, mild, efficient, low-temperature catalytically active, and coking-resistant method for preparing a nickel-based CO2 methanation catalyst.

[0007] A secondary objective of this invention is to provide a nickel-based CO2 methanation catalyst prepared by the aforementioned preparation method.

[0008] Another object of the present invention is to provide the application of the CO2 methanation catalyst.

[0009] The above-mentioned objectives of the present invention are achieved through the following technical solutions:

[0010] This invention protects a method for preparing a nickel-based carbon dioxide methanation catalyst, comprising the following steps: dispersing magnesium hydroxide gel in water to obtain a suspension, then mixing it thoroughly with a solution containing nickel salt, allowing the reaction to proceed completely, and obtaining a magnesium-nickel catalyst precursor;

[0011] The magnesium-nickel catalyst precursor is obtained by calcining it in a hydrogen atmosphere for 1-3 hours.

[0012] Alternatively, the magnesium-nickel catalyst precursor can be fully calcined at 500–800°C for 0.5–1 h in a non-reducing gas atmosphere, followed by calcination for another 1–2 h in a hydrogen atmosphere to obtain the catalyst.

[0013] The nickel-based carbon dioxide methanation catalyst contains 14-20% nickel by mass.

[0014] This method creatively employs a simple ion exchange method, redispersing the self-made magnesium hydroxide gel and then adding a nickel-containing salt solution. This allows some of the Mg ions in the magnesium hydroxide gel to be exchanged for Ni ions. During the exchange reaction, Ni ions are gradually encapsulated by the magnesium hydroxide gel, forming a stable precursor of Ni encapsulated in magnesium hydroxide gel. During the calcination of the catalyst precursor, the magnesium hydroxide gel transforms into a magnesium oxide support with a stable structure, while the Ni metal nanoparticles are gradually anchored and transformed into stable Ni metal nanoparticles.

[0015] The method described above, which forms a stable magnesium oxide support encapsulation structure, can rapidly encapsulate Ni metal nanoparticles, thereby limiting the size and composition of the active metal component. Simultaneously, the encapsulation structure can disperse the Ni metal nanoparticles, thus achieving multi-site catalytic properties. The outer magnesium oxide support encapsulation structure can also effectively protect the Ni metal nanoparticles from carbon dioxide oxidation, ensuring the catalytic stability of the catalyst. Therefore, in the catalyst obtained using the method of this application, the Ni metal nanoparticles anchored by the magnesium oxide support exhibit an encapsulated and dispersed structure, enabling faster and more efficient low-temperature catalysis while also possessing good stability, oxidation resistance, and anti-coking ability. In contrast, in catalysts obtained directly by impregnation of magnesium oxide and nickel salts, Ni metal nanoparticles tend to agglomerate, resulting in poor catalytic activity.

[0016] In addition, calcining with a non-reducing gas for a period of time before using hydrogen for reduction calcination can have a certain impact on the degree of encapsulation, thereby controlling its catalytic activity. At a catalytic temperature of 300-500℃, the catalytic activity can be achieved that is close to that of calcination in a hydrogen atmosphere. This can shorten the hydrogen reduction time, reduce the use of hydrogen, and save energy and protect the environment.

[0017] Preferably, the preparation method of the nickel-based carbon dioxide methanation catalyst includes the following steps: dispersing magnesium hydroxide gel with water to obtain a suspension, then mixing it thoroughly with a solution containing nickel salt, and after the reaction is complete, obtaining a magnesium-nickel catalyst precursor, and calcining the magnesium-nickel catalyst precursor at 500-700°C for 1-2 hours in a hydrogen atmosphere to obtain the catalyst.

[0018] Preferably, the magnesium-nickel catalyst precursor is fully calcined at 500–700°C for 1 hour in a non-reducing gas atmosphere, and then calcined again in a hydrogen atmosphere for 1–2 hours to obtain the catalyst.

[0019] Preferably, the nickel content in the nickel-based carbon dioxide methanation catalyst is 15-20% by mass, more preferably 15-18%, and most preferably 15%.

[0020] Specifically, the mass of the nickel-based carbon dioxide methanation catalyst refers to the total mass of MgO and Ni.

[0021] Furthermore, the non-reducing gas is any one of nitrogen, carbon dioxide, or air.

[0022] Preferably, the nickel salt is nickel nitrate, nickel sulfate, nickel chloride, or a hydrate of any of the above nickel salts.

[0023] Furthermore, the magnesium hydroxide gel is obtained by fully reacting a magnesium salt-containing solution with an alkaline solution. Further, the magnesium salt-containing solution is fully reacted with the alkaline solution by adding the magnesium salt-containing solution dropwise into the alkaline solution to obtain the magnesium hydroxide gel.

[0024] Preferably, the molar ratio of magnesium ions in the magnesium salt to nickel ions in the nickel salt is 5 to 10:1.

[0025] More preferably, the molar ratio of magnesium ions in the magnesium salt to nickel ions in the nickel salt is 6.8 to 9.4.

[0026] Preferably, the suspension and the nickel-containing salt solution are thoroughly mixed by adding the nickel-containing salt solution dropwise into the suspension to ensure thorough mixing of the two solutes.

[0027] Furthermore, the process before calcination includes pre-calcination, the purpose of which is to raise the temperature to the target temperature (calcination temperature). This can be carried out under a protective gas atmosphere, and the heating rate of the pre-calcination is 6-10℃ / min.

[0028] Furthermore, the protective gas used for pre-calcination is any one of nitrogen, argon, neon, or helium.

[0029] Preferably, the solute in the alkaline solution is sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, or potassium bicarbonate.

[0030] Preferably, the solute in the alkaline solution is sodium hydroxide or potassium hydroxide.

[0031] Preferably, the temperature at which the reaction is completed is 20–40°C.

[0032] Preferably, the reaction takes 30 to 60 minutes to complete.

[0033] Preferably, the reaction is carried out while stirring, and the stirring speed is 600-1000 r / min.

[0034] Furthermore, the preparation method of the nickel-based carbon dioxide methanation catalyst also includes post-treatment after the reaction is complete.

[0035] Furthermore, the post-processing includes filtration, washing, and drying.

[0036] Furthermore, the filtration process involves adding water in stages.

[0037] Furthermore, the drying conditions are as follows: drying at 65–105°C for 6–12 hours.

[0038] Preferably, the drying method is to dry at 105°C for 12 hours.

[0039] Preferably, the drying equipment is a blower drying oven.

[0040] This invention protects a nickel-based carbon dioxide methanation catalyst, which is prepared by the above-described preparation method.

[0041] This invention protects the application of the nickel-based carbon dioxide catalyst in the catalytic conversion of CO2 to CH4.

[0042] Furthermore, the present invention also claims protection for a method for converting CO2 into methane, the method comprising: passing a mixed gas containing H2 and CO2 into a catalyst bed containing a nickel-based carbon dioxide methanation catalyst, and heating the mixture to generate methane gas.

[0043] Preferably, the volume ratio of H2 to CO2 is 2 to 4:1.

[0044] Furthermore, the nickel-based carbon dioxide catalyst is used in the heating reaction at a temperature of 200–500°C to catalyze the conversion of CO2 into CH4.

[0045] Preferably, the temperature of the heating reaction is 250–400°C.

[0046] Preferably, the temperature of the heating reaction is 300–400°C.

[0047] More preferably, the space velocity of the heating reaction is 15,000 to 150,000 mL·g. -1 ·h -1 .

[0048] Furthermore, the space velocity is the amount of gas processed per unit time per unit mass of catalyst.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] This invention obtains a precursor through ion exchange, in which Ni ions exchange some Mg ions from a hydroxide gel. After calcination, a nickel-based CO2 methanation catalyst with a magnesium oxide support encapsulating Ni metal nanoparticles forms an integral encapsulated structure. Calcination under different atmospheres before hydrogen calcination affects the degree of encapsulation, thus controlling the catalytic activity. At a catalytic temperature of 300–500°C, the catalyst achieves catalytic activity close to that of calcination using only hydrogen, reducing hydrogen consumption. Furthermore, the resulting catalyst exhibits good low-temperature catalytic performance and possesses advantages such as oxidation resistance and coking resistance. Moreover, the preparation method of this catalyst is simple and highly suitable for large-scale production. Attached Figure Description

[0051] Figure 1 This is a statistical chart of ICP elemental analysis data for the CO2 methanation catalysts obtained in Examples 1, 5, and Comparative Examples 1-3.

[0052] Figure 2 Statistical data to characterize the antioxidant properties of the CO2 methanation catalysts obtained in Example 1 and Comparative Example 1.

[0053] Figure 3 EDS energy spectrum to characterize the dispersion characteristics of the CO2 methanation catalyst obtained in Example 1.

[0054] Figure 4 The EDS spectrum is used to characterize the encapsulated structure of the CO2 methanation catalyst obtained in Example 1.

[0055] Figure 5 The images show TEM images (top) of the CO2 methanation catalysts obtained in Examples 1-3 and the average particle size distribution of Ni metal nanoparticles in the corresponding catalysts (bottom).

[0056] Figure 6 The images show TEM images (top) of the CO2 methanation catalysts obtained in Examples 4-5 and Comparative Example 1, and the particle size distribution of the Ni metal nanoparticles in the corresponding catalysts (bottom).

[0057] Figure 7 The above are statistical diagrams of X-ray diffraction data of the CO2 methanation catalysts obtained in Examples 1-4 and Comparative Example 1.

[0058] Figure 8 The chart shows the statistical data of CO2-TPD and CO2 adsorption content analysis of the CO2 methanation catalysts obtained in Examples 1-4 and Comparative Example 1. Detailed Implementation

[0059] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0060] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0061] Example 1: Preparation of CO2 methanation catalyst

[0062] 0.112 mol of sodium hydroxide (4.48 g) was added to 100 ml of water and stirred for 10 min to obtain solution A. 0.056 mol of magnesium nitrate hexahydrate (14.36 g) was added to 50 ml of deionized water and stirred for 10 min to obtain solution B. Solution B was first added dropwise to solution A (to obtain magnesium hydroxide gel), and stirred for 30 min to obtain suspension C. Suspension C was then filtered, with 600 ml of deionized water added three times during filtration to remove sodium nitrate produced in the suspension. After filtration, the precipitate was returned to a beaker, 100 ml of water was added, and the mixture was stirred for 30 min until the precipitate was homogeneous. After uniform dispersion, suspension D was obtained. 0.006 mol of nickel nitrate hexahydrate (1.748 g) was added to 50 ml of deionized water and stirred for 10 min to obtain solution E. Solution E was added dropwise to suspension D and stirred for 30 min to obtain suspension F. Suspension F was filtered by suction, and 600 ml of deionized water was added three times to wash the solution during the filtration. After the filtration was completed, the precipitate obtained by suction was placed in a 105℃ forced-air drying oven and dried for 12 h. After drying, the temperature was raised to 600℃ at a rate of 10℃ / min in an atmosphere furnace, and calcined at 600℃ in a hydrogen atmosphere for 2 h to obtain CO2 methanation catalyst.

[0063] like Figure 1 As shown, ICP elemental analysis revealed that the mass percentage of Ni in the obtained CO2 methanation catalyst was 15%, and the mass percentage of Ni in the CO2 methanation catalysts obtained in Examples 2-4 was basically the same as that in Example 1.

[0064] Example 2: Preparation of CO2 methanation catalyst

[0065] The difference from Example 1 is that the calcination atmosphere in Example 2 is nitrogen and hydrogen. Specifically, after drying, the catalyst is heated to 600°C in a nitrogen atmosphere at a rate of 10°C / min in an atmosphere furnace, and then calcined at 600°C in a nitrogen atmosphere for 1 hour and calcined at 600°C in a hydrogen atmosphere for 1 hour to obtain the CO2 methanation catalyst.

[0066] The other steps and parameters are the same as in Example 1.

[0067] Example 3: Preparation of CO2 methanation catalyst

[0068] The difference from Example 1 is that the calcination atmosphere in Example 3 is carbon dioxide gas and hydrogen gas. Specifically, after drying, the catalyst is heated to 600°C in a nitrogen atmosphere at a rate of 10°C / min in an atmosphere furnace, and then calcined at 600°C in a pure carbon dioxide atmosphere for 1 hour and in a hydrogen atmosphere for 1 hour to obtain the CO2 methanation catalyst.

[0069] The other steps and parameters are the same as in Example 1.

[0070] Example 4: Preparation of CO2 methanation catalyst

[0071] The difference from Example 1 is that the calcination atmosphere in Example 4 is air and hydrogen. Specifically, after drying, the catalyst is heated to 600°C in a nitrogen atmosphere at a rate of 10°C / min in an atmosphere furnace, and then calcined at 600°C in an air atmosphere for 1 hour and calcined at 600°C in a hydrogen atmosphere for 1 hour to obtain the CO2 methanation catalyst.

[0072] The other steps and parameters are the same as in Example 1.

[0073] Example 5: Preparation of CO2 methanation catalyst

[0074] The difference from Example 1 is that Ni accounts for 20% of the total mass in Example 5.

[0075] Specifically, the preparation of the CO2 methanation catalyst includes the following steps:

[0076] 0.117 mol of sodium hydroxide (4.68 g) was added to 100 ml of water and stirred for 10 min to obtain solution A. 0.0585 mol of magnesium nitrate hexahydrate (15 g) was added to 50 ml of deionized water and stirred for 10 min to obtain solution B. Solution B was first added dropwise to solution A (to obtain magnesium hydroxide gel), and stirred for 30 min to obtain suspension C. Suspension C was then filtered, with 600 ml of deionized water added three times during filtration to remove sodium nitrate produced in the suspension. After filtration, the precipitate was returned to a beaker, 100 ml of water was added, and the mixture was stirred for 30 min until the precipitate was homogeneous. After uniform dispersion, suspension D was obtained. 0.0085 mol of nickel nitrate hexahydrate (2.477 g) was added to 50 ml of deionized water and stirred for 10 min to obtain solution E. Solution E was added dropwise to suspension D and stirred for 30 min to obtain suspension F. Suspension F was filtered by suction, and 600 ml of deionized water was added three times during the filtration. After the filtration was completed, the obtained precipitate was placed in a 105℃ forced-air drying oven and dried for 12 h. After drying, it was heated to 600℃ in an atmosphere furnace at a rate of 10℃ / min under nitrogen atmosphere and calcined at 600℃ under hydrogen atmosphere for 2 h to obtain CO2 methanation catalyst.

[0077] Among them, such asFigure 1 As shown, ICP elemental analysis revealed that the Ni mass percentage in the CO2 methanation catalyst obtained in Example 5 was 20%.

[0078] Example 6: Preparation of CO2 methanation catalyst

[0079] The difference from Example 1 is that the calcination temperature of Example 6 is 500°C.

[0080] The other steps and parameters are the same as in Example 1.

[0081] Example 7 Preparation of CO2 methanation catalyst

[0082] The difference from Example 1 is that the calcination temperature of Example 7 is 800°C.

[0083] The other steps and parameters are the same as in Example 1.

[0084] Comparative Example 1: Preparation of Conventional Nickel-Based Catalysts

[0085] The preparation of conventional nickel-based catalysts includes the following steps:

[0086] 0.2 mol magnesium oxide powder and 0.048 mol sodium hydroxide were dissolved in 200 ml of water and stirred for 30 min to obtain suspension A. 0.02 mol nickel nitrate hexahydrate was dissolved in 50 ml of water and stirred for 10 min to obtain solution B. The two solutions were then mixed to obtain suspension C (mainly to obtain nickel hydroxide gel). Suspension C was filtered, and during filtration, 600 ml of deionized water was added three times to wash the suspension to remove the sodium nitrate produced. After filtration, the precipitate was placed in a 105℃ forced-air drying oven and dried for 12 h. After drying, the temperature was increased to 600℃ at a rate of 10℃ / min in an atmosphere furnace, and then calcined at 600℃ in a hydrogen atmosphere for 2 h to obtain a conventional nickel-based catalyst.

[0087] like Figure 1 As shown, ICP elemental analysis revealed that the Ni mass percentage in the conventional nickel-based catalyst obtained in Comparative Example 1 was 14%.

[0088] Preparation of comparative 2CO2 methanation catalyst

[0089] The difference from Example 1 is that Ni accounts for 5% of the total mass in Comparative Example 2.

[0090] Specifically, the preparation of the CO2 methanation catalyst includes the following steps:

[0091] 0.10358 mol of sodium hydroxide (4.14 g) was added to 100 ml of water and stirred for 10 min to obtain solution A. 0.05179 mol of magnesium nitrate hexahydrate (13.27 g) was added to 50 ml of deionized water and stirred for 10 min to obtain solution B. Solution B was first added dropwise to solution A (to obtain magnesium hydroxide gel), and stirred for 30 min to obtain suspension C. Suspension C was then filtered, with 600 ml of deionized water added three times during filtration to remove sodium nitrate produced in the suspension. After filtration, the resulting precipitate was returned to a beaker, 100 ml of water was added, and stirred for 30 min until the precipitate was evenly dispersed. To obtain suspension D, take 0.00179 mol of nickel nitrate hexahydrate (0.5215 g) and add it to 50 ml of deionized water. Stir for 10 min to obtain solution E. Add solution E dropwise to solution D and stir for 30 min to obtain suspension F. Filter suspension F. During filtration, add 600 ml of deionized water three times to wash the suspension to remove sodium nitrate generated in the suspension. After filtration, place the obtained precipitate in a 105℃ forced-air drying oven and dry for 12 h. After drying, heat it to 600℃ in an atmosphere furnace at a rate of 10℃ / min under nitrogen atmosphere, and calcine it at 600℃ under hydrogen atmosphere for 2 h to obtain CO2 methanation catalyst.

[0092] Among them, such as Figure 1 As shown, ICP elemental analysis revealed that the Ni mass percentage in the CO2 methanation catalyst obtained in Comparative Example 2 was 5%.

[0093] Preparation of comparative 3CO2 methanation catalyst

[0094] The difference from Example 1 is that Ni accounts for 10% of the total mass of the catalyst in Comparative Example 3.

[0095] Specifically, the preparation of the CO2 methanation catalyst includes the following steps:

[0096] 0.10756 mol of sodium hydroxide (4.296 g) was added to 100 ml of water and stirred for 10 min to obtain solution A. 0.05378 mol of magnesium nitrate hexahydrate (13.76 g) was added to 50 ml of deionized water and stirred for 10 min to obtain solution B. Solution B was first added dropwise to solution A (to obtain magnesium hydroxide gel), and stirred for 30 min to obtain suspension C. Suspension C was then filtered, with 600 ml of deionized water added three times during filtration to remove sodium nitrate produced in the solution. After filtration, the precipitate was returned to a beaker, 100 ml of water was added, and the mixture was stirred for 30 min. After the precipitate is evenly dispersed, suspension D is obtained. 0.00378 mol of nickel nitrate hexahydrate (1.1 g) is added to 50 ml of deionized water and stirred for 10 min to obtain solution E. Solution E is added dropwise to suspension D and stirred for 30 min to obtain suspension F. Suspension F is filtered by suction, and 600 ml of deionized water is added three times to wash the solution during the filtration. After the filtration is completed, the obtained precipitate is placed in a 105℃ forced-air drying oven and dried for 12 h. After drying, it is heated to 600℃ in an atmosphere furnace at a rate of 10℃ / min under nitrogen atmosphere and calcined at 600℃ under hydrogen atmosphere for 2 h to obtain CO2 methanation catalyst.

[0097] Among them, such as Figure 1 As shown, ICP elemental analysis revealed that the Ni mass percentage in the CO2 methanation catalyst obtained in Comparative Example 3 was 10%.

[0098] Experimental Performance Testing

[0099] (1) Determination of CO2 conversion rate

[0100] 1. Experimental Method:

[0101] 0.1 g of the CO2 methanation catalysts prepared in Examples 1-5 and the Ni-based catalysts prepared in Comparative Examples 1-3 were respectively loaded into a fixed-bed reactor. One end of the fixed bed was connected to an inlet, and the gas inlet pipe was connected to a mixed gas with an H2 / CO2 ratio of 4. The reaction temperature was 200-500 °C, and the reaction space velocity was 15000 mL·g. -1 ·h -1 The gaseous products after the reaction were tested using an Agilent 6820 catalytic converter, with the CO2 conversion rate in the gas being the indicator; the higher the conversion rate, the better the catalytic performance.

[0102] 2. Experimental Results

[0103] The experimental results are shown in Table 1: The CO2 methanation catalysts obtained in Examples 1-5 exhibit good low-temperature catalytic activity, with a CO2 conversion rate >55% at a catalytic temperature of 300℃. In particular, the catalyst obtained in Example 1 achieves a CO2 conversion rate of 68.71% at a catalytic temperature of 250℃. The catalysts obtained in Examples 6 and 7 have essentially the same conversion rates as those in the examples.

[0104] Table 1 CO2 Conversion Rate

[0105]

[0106] (2) Determination of antioxidant properties

[0107] 1. Experimental Methods

[0108] The difference from the above-mentioned method for determining CO2 conversion rate is that the catalysts obtained in Example 1 and Comparative Example 1 are used as the test objects, and the reaction conditions are 350°C and 60,000 mL·g. -1 h-1, with other conditions and parameters remaining unchanged.

[0109] 2. Experimental Results

[0110] The measurement results are as follows Figure 2 As shown, the catalyst prepared in Example 1 maintained a conversion rate of approximately 80% after 50 hours of continuous catalysis, indicating that it possesses good antioxidant and anti-coking properties. In contrast, the conversion rate of the catalyst obtained in Comparative Example 1 began to decrease with prolonged catalysis time, suggesting that the nickel in the catalyst of Comparative Example 1 was oxidized during long-term use, leading to a decline in catalytic activity. The catalysts obtained in Examples 2-7 exhibited essentially the same antioxidant and anti-coking properties as the catalyst obtained in Example 1, and their catalytic activity remained unchanged after prolonged use.

[0111] (3) Morphological determination

[0112] The CO2 methanation catalysts obtained in Example 1 and Comparative Example 1 were analyzed using TEM field-emitting transmission electron microscopy combined with energy dispersive spectroscopy. The results are as follows: Figure 3 As shown, the catalyst obtained in Example 1 contains Ni, Mg, and O elements. Ni is distributed in the catalyst in particulate form, and these Ni particles are uniformly distributed within the MgO support, demonstrating the characteristic of uniform catalyst dispersion. Figure 4 As shown, the catalyst prepared in Example 1 has the structural characteristic of nickel being integrally encapsulated by the magnesium oxide support. The catalysts obtained in Examples 2-7 have essentially the same structural characteristics as those in Example 1.

[0113] (4) Particle size distribution determination

[0114] Depend on Figures 5-6TEM and particle size distribution maps show that the catalysts obtained in Examples 1-5 have good dispersibility, with Ni metal nanoparticles (black particles) uniformly distributed on the magnesium oxide support. The particle size distribution of Ni metal nanoparticles varies in catalysts calcined under different atmospheres; the smaller the particle size, the better the catalytic activity. The catalyst obtained in Example 1, which was directly calcined in a hydrogen atmosphere after reaching the target temperature, has the smallest particle size and exhibits the best low-temperature catalytic activity, achieving a CO2 conversion rate of 39.28% at 220°C and 68.71% at 250°C. The catalyst obtained by first performing non-reducing calcination for a period of time and then reducing and activating it with hydrogen showed an increase in the particle size of Ni metal nanoparticles (Examples 2-4), but still exhibited a relatively small particle size (<20nm). At a catalytic temperature of 300℃, it achieved a catalytic activity similar to that of Example 1 (>60%), thus shortening the hydrogen reduction time, reducing hydrogen consumption, and saving energy and protecting the environment. When the Ni content was further increased compared to Example 1, the particle size of the Ni metal nanoparticles in the resulting catalyst also further increased (Example 5), but this catalyst still exhibited good catalytic activity (>55%) at a catalytic temperature of 300℃. Comparative Example 1 (…) Figure 6 The catalyst shown in the far right figure was obtained by conventional impregnation method. The Ni metal nanoparticles in it are prone to agglomeration, have poor dispersibility, and have a large particle size, which is much larger than the particle size of the Ni metal nanoparticles in the catalysts obtained in Examples 1 to 5.

[0115] (4) X-ray diffraction

[0116] The X-ray diffraction results of Examples 1-4 and Comparative Example 1 are as follows: Figure 7 As shown in the figure, the catalysts obtained by calcination in each embodiment contain MgO and Ni.

[0117] (5) CO2-TPD analysis

[0118] The adsorption capacity of CO2 by the catalysts obtained in Examples 1-4 and Comparative Example 1 was determined using a CO2-TPD analyzer. A stronger peak intensity indicates stronger CO2 adsorption. The results are as follows: Figure 8 As shown, the catalysts of Examples 1-4 exhibit strong CO2 adsorption, especially the catalyst of Example 1, which shows the strongest CO2 adsorption, while the CO2 adsorption peak of Comparative Example 1 is the weakest. This is consistent with the catalytic activity results of the aforementioned catalysts.

[0119] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. The application of a nickel-based carbon dioxide methanation catalyst in the catalytic conversion of CO2 to CH4, characterized in that, The nickel-based carbon dioxide methanation catalyst is prepared by the following steps: Magnesium hydroxide gel was dispersed in water to obtain a suspension, which was then thoroughly mixed with a solution containing nickel salt. After the reaction was complete, a magnesium-nickel catalyst precursor was obtained. The magnesium-nickel catalyst precursor was calcined at 500-700 °C for 1-2 h in a hydrogen atmosphere to obtain the catalyst. The nickel-based carbon dioxide methanation catalyst contains 15% to 18% nickel by mass. The magnesium hydroxide gel is obtained by fully reacting a magnesium salt solution with an alkaline solution. The nickel-based carbon dioxide methanation catalyst is used in the heating reaction at a temperature of 200~350 °C to catalyze the conversion of CO2 to CH4.

2. The application according to claim 1, characterized in that, The nickel salt is nickel nitrate, nickel sulfate, nickel chloride, or a hydrate of any of the above nickel salts.

3. The application according to claim 1, characterized in that, The magnesium salt is magnesium nitrate, magnesium sulfate, magnesium chloride, or a hydrate of any of the above magnesium salts.

4. The application according to claim 3, characterized in that, The molar ratio of magnesium ions in the magnesium salt to nickel ions in the nickel salt is 5~10:1.

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