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

Abstract

This invention belongs to the field of carbon dioxide methanation technology, and particularly relates to a carbon dioxide methanation catalyst, its preparation method, and its application. The method includes: dissolving a metal salt in deionized water to obtain a first solution; mixing an alkali metal hydroxide solution with the first solution and reacting to obtain a high-entropy hydroxide; calcining the high-entropy hydroxide to obtain a catalyst precursor, and then reducing it to obtain the carbon dioxide methanation catalyst; the metal in the metal salt includes one from Group II, one from Group III, and at least three from transition metals, with nickel being one of the transition metals. This invention can produce a multi-component oxide material with a uniform crystal structure, high catalytic activity, and structural stability. By inducing the precipitation of active metals through catalyst reduction, ultra-high density oxygen vacancies can be dynamically constructed in the catalyst, thereby achieving excellent carbon dioxide conversion and methane selectivity under mild conditions, and improving catalyst lifetime.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide methanation technology, and particularly relates to a carbon dioxide methanation catalyst, its preparation method, and its application. Background Technology

[0002] The technology converts carbon dioxide (CO2) into high-value chemicals such as methane (CH4), methanol (CH3OH), formic acid (HCOOH), and carbon monoxide (CO) to achieve resource recycling. Among these, methane has advantages such as high ignition energy, narrow explosion limits, and mild liquefaction conditions, making CO2 methanation considered the most ideal carbon dioxide conversion product.

[0003] The high conversion rate of carbon dioxide methanation reduces product purification costs, making it both economical and convenient. CO2 methanation is a strongly exothermic reaction (∆H = -165 kJ / mol), and low temperatures favor methane formation. However, this reaction involves an eight-electron transfer process, which is kinetically limited. While high temperatures can alleviate kinetic limitations and accelerate the reaction rate, the strongly exothermic nature of the reaction promotes the reverse equilibrium, leading to decreased methane selectivity. Furthermore, high temperatures can easily cause catalyst carbon deposition and sintering of active components, and the high-temperature process consumes more energy.

[0004] In existing technologies, even at low temperatures, the CO2 conversion rate of products obtained by conventional carbon dioxide methanation techniques is still below 90%. For example, the Ni / ZrO2 catalyst developed by Ye et al. achieves 98.6% methane selectivity at 230℃, but its carbon dioxide conversion rate is only 84.0% [Ye, R. et al. Angew. Chem. Int. Ed., 2024, 63, 1433-7851.] for low-temperature carbon dioxide methanation. The Ru / TiO2 noble metal catalyst prepared by Zhou et al. can achieve 100% methane selectivity at a low temperature of 300℃, but the carbon dioxide conversion rate is 89.2%, and the 2-5% ruthenium loading significantly increases the catalyst cost [Zhou et al, Nature Communications, 2022, 13: 327]. The Co / CeO2 catalyst developed by Struijs et al. using a strong electrostatic adsorption-wet impregnation method has improved anti-carbon deposition performance and low carbon dioxide partial pressure (0.4). High activity was observed at low temperatures (mbar) and low temperatures (175℃), with methane selectivity exceeding 95%, but the carbon dioxide conversion rate was less than 30%. The complex preparation process further hindered its industrial scale-up [Struijs et al, Angew Chem Int Ed, 2023, 62: 1521-3773]. Therefore, developing highly active low-temperature CO2 methanation catalysts is crucial for achieving CO2 methanation. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a carbon dioxide methanation catalyst, its preparation method, and its application, which can achieve carbon dioxide methanation with high selectivity and high conversion rate.

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

[0007] In a first aspect, this application provides a method for preparing a carbon dioxide methanation catalyst, comprising the following steps:

[0008] The metal salt was dissolved in deionized water to obtain the first solution;

[0009] The alkali metal hydroxide solution was mixed with the first solution and reacted to obtain a high-entropy hydroxide.

[0010] The catalyst precursor was obtained by calcining the high-entropy hydroxide.

[0011] The catalyst precursor was reduced to obtain the carbon dioxide methanation catalyst;

[0012] The metal salt contains one of Group II metals, one of Group III metals, and at least three of transition metals.

[0013] Optionally, the molar ratio of the second group metal, the third group metal and any transition metal is 1:1:(0.5 to 3).

[0014] Optionally, the second group metal is selected from magnesium, calcium, and barium, the third group metal is selected from boron, aluminum, and gallium, and the transition metal includes nickel and two of cobalt, manganese, iron, molybdenum, and zirconium.

[0015] Optionally, the second main group metal is calcium or magnesium, and the transition metals are four types: nickel, cobalt, manganese, and iron.

[0016] Optionally, the reaction conditions for the alkali metal hydroxide solution and the first solution are: stirring at a speed of 300 to 12000 rpm and reacting at 60 to 90°C for 1 to 24 hours.

[0017] Optionally, the molar ratio of the total amount of metal cations in the first solution to deionized water is 1:(50-60); and / or, the metal salt is selected from one of nitrates, sulfates, chlorides, carbonates, and citrates.

[0018] Optionally, the concentration of the alkali metal hydroxide solution is 0.1–10 mol / L; and / or, the alkali metal is selected from sodium, potassium, and cesium.

[0019] Optionally, the calcination conditions are: calcination at 300–1200°C for 1–48 h; and / or, the reduction conditions are: reducing the catalyst precursor at 300–500°C for 40–150 min.

[0020] Secondly, this application also provides a carbon dioxide methanation catalyst, which is prepared by the method described in the first aspect.

[0021] Thirdly, this application also provides the application of the carbon dioxide methanation catalyst described in the second aspect in carbon dioxide methanation.

[0022] Optionally, the process includes: performing carbon dioxide methanation on the feed gas under the action of the carbon dioxide methanation catalyst at a temperature of 200–300°C and a pressure of 2–4 MPa, wherein the flow rate of the feed gas relative to the catalyst is 150–300 mL / min / g catalyst; and the volume ratio of carbon dioxide to hydrogen in the feed gas is 1:4.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] The carbon dioxide methanation catalyst prepared in this invention is a high-entropy oxide with a single-phase solid solution structure, composed of at least three of a Group II metal, a Group III metal, and a transition metal, along with oxygen. It possesses a uniform crystal structure and exhibits both high catalytic activity and structural stability as a multi-component oxide material. By inducing the precipitation of active metals through catalyst reduction, ultra-high density oxygen vacancies can be dynamically constructed within the catalyst, thereby achieving excellent carbon dioxide conversion and methane selectivity under mild conditions. Furthermore, the unique lattice distortion effect and configurational entropy stability of the high-entropy oxide ensure that the carbon dioxide conversion and methane selectivity show no significant decline in stability testing over 800 hours, demonstrating significantly improved long-term catalytic stability. In addition, compared to the traditional Ni / Al₂O₃ catalyst, the reaction temperature of this method is reduced by approximately 100°C. Attached Figure Description

[0025] Figure 1 These are X-ray diffraction patterns of the dried high-entropy hydroxides in different embodiments;

[0026] Figure 2 X-ray diffraction patterns of the catalysts after the carbon dioxide methanation reaction in different embodiments;

[0027] Figure 3 This is a transmission electron microscope image of the catalyst precursor in Example 1;

[0028] Figure 4 The energy dispersive X-ray spectrum of the catalyst precursor in Example 1;

[0029] Figure 5 This is an XPS image of the carbon dioxide methanation catalyst in Example 1. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings:

[0031] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0032] All reagents and materials used in this example can be purchased routinely. The quantitative experiments involved in the examples were all repeated at least three times, and the results were averaged.

[0033] Example 1:

[0034] A carbon dioxide methanation catalyst is prepared by the following method:

[0035] First, add 5 mmol of calcium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of ferric nitrate, and 5 mmol of cobalt nitrate to 30 mL of deionized water to obtain the first solution. Prepare a 1 mol / L sodium hydroxide solution, which is the alkali metal hydroxide solution. Take 50 mL of deionized water and heat it to 80°C in a beaker. Add the first solution and the alkali metal hydroxide solution to the beaker in parallel flow using a peristaltic pump. Control the beaker temperature at 80°C and the pH value at 10.5 throughout the process, and stir and age the solution at 800 rpm for 8 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, dry it in an oven (its X-ray diffraction pattern is shown in the figure). Figure 1 (As shown), and then calcined at 600℃ for 6 h to obtain the catalyst precursor; then the catalyst precursor was placed in an N2 atmosphere containing 20% ​​(volume content) H2 and reduced at 450℃ for 90 min (XPS test was performed) to obtain the carbon dioxide methanation catalyst, the transmission electron microscope (TEM) image and energy dispersive X-ray spectroscopy (EDS) image of which are shown in the figure. Figure 3 and Figure 4 The uniform dispersion of each metal component indicates that the prepared catalyst has formed a solid solution structure.

[0036] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment. The flow rate of the feed gas relative to the catalyst is 200 mL / min per gram of catalyst, i.e., the mass hourly space velocity is 200 mL / (g·min).

[0037] Figure 2XRD results showed characteristic diffraction peaks of metallic nickel after the carbon dioxide methanation reaction, indicating that metallic nickel was precipitated in situ within the solid solution structure of the catalyst; combined with Figure 5 XPS characterization results showed the presence of oxygen-rich vacancies, further demonstrating that the in-situ precipitation of metallic nickel is accompanied by the generation of a large number of oxygen vacancies. These oxygen vacancies can both stabilize the precipitated nickel species and effectively reduce the activation energy of carbon dioxide.

[0038] Example 2:

[0039] A carbon dioxide methanation catalyst is prepared by the following method:

[0040] First, 5 mmol of calcium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of ferric nitrate, and 5 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 5 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH value at 11 throughout the process. The reaction was stirred and aged at 12000 rpm for 10 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was then reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0041] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment. The flow rate of the feed gas relative to the catalyst is 200 mL / min per gram of catalyst, i.e., the mass hourly space velocity is 200 mL / (g·min).

[0042] Example 3:

[0043] A carbon dioxide methanation catalyst is prepared by the following method:

[0044] First, 5 mmol of barium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of ferric nitrate, and 5 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 1 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH value at 10.5 throughout the process. The mixture was stirred and aged at 800 rpm for 8 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was then reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0045] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment. The flow rate of the feed gas relative to the catalyst is 200 mL / min per gram of catalyst, i.e., the mass hourly space velocity is 200 mL / (g·min).

[0046] Example 4:

[0047] A carbon dioxide methanation catalyst is prepared by the following method:

[0048] First, 5 mmol of magnesium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of ferric nitrate, and 5 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 1 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH value at 10.5 throughout the process. The mixture was stirred and aged at 800 rpm for 8 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and then calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was then reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0049] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment. The flow rate of the feed gas relative to the catalyst is 200 mL / min per gram of catalyst, i.e., the mass hourly space velocity is 200 mL / (g·min).

[0050] Example 5:

[0051] A carbon dioxide methanation catalyst is prepared by the following method:

[0052] First, 6 mmol of calcium nitrate, 6 mmol of manganese nitrate, 3 mmol of aluminum nitrate, 6 mmol of nickel nitrate, 3 mmol of ferric nitrate, and 6 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 2 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH value at 11 throughout the process. The mixture was stirred and aged at 800 rpm for 10 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and then calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0053] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0054] Example 6:

[0055] A carbon dioxide methanation catalyst is prepared by the following method:

[0056] First, 5 mmol of calcium nitrate, 2.5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 10 mmol of nickel nitrate, 5 mmol of ferric nitrate, and 1.5 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 2 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80 °C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80 °C and the pH value at 10 throughout the process. The mixture was stirred and aged at 800 rpm for 8 h to obtain a high-entropy hydroxide. The high-entropy hydroxide was filtered, washed, dried in an oven, and then calcined at 600 °C for 6 h to obtain the catalyst precursor. The catalyst precursor was reduced at 450 °C for 90 min to obtain the carbon dioxide methanation catalyst.

[0057] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0058] Example 7:

[0059] A carbon dioxide methanation catalyst is prepared by the following method:

[0060] First, 6 mmol of barium nitrate, 6 mmol of manganese nitrate, 3 mmol of aluminum nitrate, 6 mmol of nickel nitrate, 3 mmol of ferric nitrate, and 6 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 2 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH value at 10.5 throughout the process. The mixture was stirred and aged at 800 rpm for 8 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and then calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0061] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0062] Example 8:

[0063] A carbon dioxide methanation catalyst is prepared by the following method:

[0064] First, 5 mmol of calcium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, and 5 mmol of ferric nitrate were added to 30 mL of deionized water to obtain the first solution. A 2 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH at 10.5 throughout the process, and the mixture was stirred at 800 rpm for 8 h to obtain a high-entropy hydroxide. The high-entropy hydroxide was filtered, washed, dried in an oven, and then calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0065] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0066] Example 9:

[0067] A carbon dioxide methanation catalyst is prepared by the following method:

[0068] First, 5 mmol of calcium nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of ferric nitrate, and 5 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 1 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH at 10.5 throughout the process. The mixture was stirred and aged at 800 rpm for 8 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and then calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0069] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this embodiment, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0070] The X-ray diffraction patterns of the catalyst precursors in Examples 1, 3, and 4 before calcination are shown below. Figure 1 As shown, the XRD patterns of the catalyst precursors prepared in this invention before calcination all conform to the characteristic XRD patterns of high-entropy hydroxides; the X-ray diffraction patterns of the catalysts after carbon dioxide methanation are shown below. Figure 2 As shown, the catalyst prepared in this invention conforms to the XRD characteristic spectrum of a high-entropy oxide single-phase solid solution. (And...) Figure 1 In contrast, only nickel precipitated as zero-valent nickel after the reaction, while other metal elements remained as a single spinel solid solution, indicating that nickel precipitated in situ in the high-entropy oxide.

[0071] Comparative Example 1:

[0072] A carbon dioxide methanation catalyst is prepared by the following method:

[0073] First, 5 mmol of calcium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of ferric nitrate, and 5 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 1 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH at 10.5 throughout the process. The mixture was stirred and aged at 800 rpm for 8 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0074] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this comparative example, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0075] Comparative Example 2:

[0076] A carbon dioxide methanation catalyst is prepared by the following method:

[0077] First, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of ferric nitrate, and 5 mmol of cobalt nitrate were added to 30 mL of deionized water to obtain the first solution. A 1 mol / L sodium hydroxide solution was prepared, which is the alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker. The first solution and the alkali metal hydroxide solution were added to the beaker in parallel flow using a peristaltic pump. The beaker temperature was maintained at 80°C and the pH at 10.5 throughout the process. The mixture was stirred and aged at 800 rpm for 8 h to obtain a high-entropy hydroxide. After filtering and washing the high-entropy hydroxide, it was dried in an oven and then calcined at 600°C for 6 h to obtain the catalyst precursor. The catalyst precursor was reduced at 450°C for 90 min to obtain the carbon dioxide methanation catalyst.

[0078] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this comparative example, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0079] Comparative Example 3:

[0080] The difference between this comparative example and Example 8 is that manganese nitrate is replaced with ferric nitrate and nickel nitrate. Specifically, 5 mmol of calcium nitrate, 5 mmol of aluminum nitrate, 7.5 mmol of nickel nitrate, and 7.5 mmol of ferric nitrate are added to 30 mL of deionized water to obtain the first solution.

[0081] Comparative Example 4:

[0082] The difference between this comparative example and Example 8 is that ferric nitrate is replaced with manganese nitrate and nickel nitrate. Specifically, 5 mmol of calcium nitrate, 5 mmol of aluminum nitrate, 7.5 mmol of nickel nitrate, and 7.5 mmol of manganese nitrate are added to 30 mL of deionized water to obtain the first solution.

[0083] Comparative Example 5:

[0084] Following the method described in the literature [Song, C et al, Nat Chem Eng, 2024, 1, 638-649.], nickel nitrate hexahydrate was dissolved in 50 mL of ethanol. Then, a 0.5 mol / L oxalic acid-ethanol solution was added to the vigorously stirred mixture. The resulting NiC₂O₄ solid was dispersed in ethanol by centrifugation (denoted as solution A). Zirconium nitrate pentahydrate, cerium nitrate hexahydrate, and oxalic acid-ethanol solution were simultaneously added dropwise to solution A. After reacting for 3 h, the resulting solid was centrifuged and dried at 60 °C for 12 h. The dried powder was then calcined in a muffle furnace at 400 °C for 3 h to obtain the catalyst precursor. The catalyst precursor was then reduced at 450 °C for 180 min to obtain the carbon dioxide methanation catalyst.

[0085] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 280°C, 0.1 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this comparative example, wherein the flow rate of the feed gas relative to the catalyst is 15,000 ml / min / gram of catalyst.

[0086] Comparative Example 6:

[0087] Following the method described in the literature [Ye, R. et al. Angew. Chem. Int. Ed., 2024, 63, 1433-7851.], 5.681 g of nickel nitrate hexahydrate and 3.230 g of zirconium nitrate were dissolved in 25 mL of deionized water; simultaneously, 6.195 g of citric acid was dissolved in 25 mL of deionized water, and the mixture was poured into the above metal salt solution and stirred for 1 h. The mixture was heated to 80 °C to evaporate the water until a gel was formed. The resulting gel was dried at 85 °C for 8 h, dried at 150 °C for 4 h, and then calcined at 300 °C for 2 h and 450 °C for 2 h to obtain the catalyst precursor; the catalyst precursor was then reduced at 450 °C for 180 min to obtain the carbon dioxide methanation catalyst.

[0088] The process of producing methane by carbon dioxide hydrogenation includes the following steps: carbon dioxide methanation is carried out at 280°C, 0.1 MPa, with a carbon dioxide to hydrogen volume ratio of 1:4 in the feed gas, and under the action of the carbon dioxide methanation catalyst prepared in this comparative example, wherein the flow rate of the feed gas relative to the catalyst is 12000 ml / min / gram of catalyst.

[0089] The test results of the catalysts in the carbon dioxide to methane reaction in different embodiments and comparative examples are shown in Table 1.

[0090] Testing equipment and experimental conditions

[0091] Product analysis equipment: Online gas chromatograph (Agilent GC-8860), equipped with thermal conductivity detector (TCD) and flame ionization detector (FID), for analyzing the composition of reactor outlet gas.

[0092] Calculation of CO2 conversion rate and product selectivity:

[0093] CO2 conversion was calculated using Ar as an internal standard; the selectivity of the product was calculated by correlating TCD and FID components using CH4; the formulas for product selectivity and conversion are as follows:

[0094] ;

[0095] ;

[0096] in CO2 conversion rate, This represents the peak area of ​​CO2. This represents the peak area of ​​the argon gas. R represents the peak area of ​​methane in the reaction gas, and R is the reaction gas used (here, the reaction gas is CO2:H2:Ar:CH4 = 1:4:0.1:0.026, that is, the CO2 and argon gas emitted by the chromatogram when only the reaction gas is passed through without adding a catalyst). ） The peak area ratio of CO2 to argon in chromatography;

[0097] For the selectivity of product i, Let be the peak area of ​​product i. The relative molar correction factor for product i (where =1, =0.76), This represents the peak area of ​​each product. represents the relative molar correction factor for each product.

[0098] Table 1: Carbon dioxide conversion rate and methane selectivity in the carbon dioxide to methane reaction with different catalysts

[0099]

Claims

1. A method for preparing a carbon dioxide methanation catalyst, characterized in that, Includes the following steps: The metal salt was dissolved in deionized water to obtain the first solution; The alkali metal hydroxide solution was mixed with the first solution and reacted to obtain a high-entropy hydroxide. The catalyst precursor was obtained by calcining the high-entropy hydroxide. The catalyst precursor was reduced to obtain the carbon dioxide methanation catalyst; The metal salt contains one of Group II metals, one of Group III metals, and at least three of transition metals. The conditions for the reaction of the alkali metal hydroxide solution with the first solution are as follows: the two solutions are added in parallel flow, and the pH value is kept constant at 10, 10.5 or 11 during the mixing process, and the reaction is carried out at 60 to 90°C. The carbon dioxide methanation catalyst exhibits in-situ nickel precipitation and oxygen vacancy generation. The molar ratio of the second group metal, the third group metal, and any transition metal is 1:1:(0.5~3). The second group metal is selected from magnesium, calcium and barium, the third group metal is selected from aluminum and gallium, and the transition metal includes nickel and two of cobalt, manganese and iron.

2. The method for preparing the carbon dioxide methanation catalyst according to claim 1, characterized in that, The reaction conditions for the alkali metal hydroxide solution and the first solution are: a stirring speed of 300-12000 rpm for 1-24 hours.

3. The method for preparing the carbon dioxide methanation catalyst according to claim 1, characterized in that, The molar ratio of the total amount of metal cations in the first solution to that of deionized water is 1:(50-60). And / or, the metal salt is selected from one of nitrates, sulfates, chlorides, carbonates, and citrates; And / or, the second group metal is calcium or magnesium.

4. The method for preparing the carbon dioxide methanation catalyst according to claim 1, characterized in that, The concentration of the alkali metal hydroxide solution is 0.1–10 mol / L; and / or, the alkali metal is selected from sodium and potassium.

5. The method for preparing the carbon dioxide methanation catalyst according to claim 1, characterized in that, The calcination conditions are: calcination at 300–1200℃ for 1–48 h; And / or, the reduction conditions are: reducing the catalyst precursor at 300-500°C for 40-150 min.

6. A carbon dioxide methanation catalyst, characterized in that, It is prepared by the method described in any one of claims 1 to 5.

7. The use of the carbon dioxide methanation catalyst according to claim 6 in carbon dioxide methanation.

8. The application of the carbon dioxide methanation catalyst according to claim 7 in carbon dioxide methanation, characterized in that, include: At a temperature of 200–300℃ and a pressure of 2–4 MPa, the feed gas undergoes carbon dioxide methanation under the action of the carbon dioxide methanation catalyst, wherein the flow rate of the feed gas relative to the catalyst is 150–300 mL / min / g catalyst; and the volume ratio of carbon dioxide to hydrogen in the feed gas is 1:4.

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