Carbon dioxide methanation catalyst, preparation method and application

Abstract

The invention belongs to the technical field of carbon dioxide methanation, and particularly relates to a carbon dioxide methanation catalyst, a preparation method and application. The method comprises the following steps: dissolving metal salt in deionized water to obtain a first solution; mixing and reacting the alkali metal hydroxide solution with the first solution to obtain high-entropy hydroxide; calcining the high-entropy hydroxide to obtain a catalyst precursor, and reducing to obtain the carbon dioxide methanation catalyst; the metals in the metal salt comprise one of the metals of the second main group, one of the metals of the third main group and at least three of transition metals, and the transition metals comprise nickel. The method provided by the invention can be used for preparing the multi-element oxide material with a uniform crystal structure and high catalytic activity and structural stability. The catalyst is reduced to induce active metal to separate out, and ultrahigh-density oxygen vacancies can be dynamically constructed in the catalyst, so that excellent carbon dioxide conversion rate and methane selectivity are realized under mild conditions, and the service life of the catalyst is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon dioxide methanation, and particularly relates to a carbon dioxide methanation catalyst, a preparation method and application. BACKGROUND

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

[0003] High conversion rate of carbon dioxide methanation reaction can reduce the cost of product purification, and has economic and convenient. CO2 methanation reaction is a strong exothermic reaction (∆H=-165 kJ / mol), and low temperature is beneficial to the generation of methane. However, the reaction involves an eight-electron transfer process, which is significantly limited in kinetics. Although high temperature can alleviate the kinetic limitation and accelerate the reaction rate, the strong exothermic reaction of the reaction will promote the reverse progress of the reaction equilibrium, resulting in the decrease of methane selectivity; at the same time, high temperature is easy to cause carbon deposition and sintering of active components of the catalyst, and the energy consumption of high temperature process is high.

[0004] In the prior art, even under low temperature conditions, the CO2 conversion rate of the product obtained by the conventional carbon dioxide methanation technology is still less than 90%. For example, the Ni / ZrO2 catalyst developed by Ye et al. achieves 98.6% methane selectivity at 230℃, but the carbon dioxide conversion rate is only 84.0% [Ye, R. et al. Angew. Chem. Int. Ed., 2024, 63, 1433-7851.]; The methane selectivity of the Ru / TiO2 noble metal catalyst prepared by Zhou et al. can reach 100% at a low temperature of 300℃, but the carbon dioxide conversion rate is 89.2%, and the ruthenium loading of 2-5% significantly increases the cost of the catalyst [Zhou et al, Nature Communications, 2022, 13: 327]; The Co / CeO2 catalyst prepared by Struijs et al. using the strong electrostatic adsorption-wet impregnation method has improved carbon deposition resistance and low carbon dioxide partial pressure (0.4 mbar) and low temperature (175℃), and shows high activity, with methane selectivity exceeding 95%, but the carbon dioxide conversion rate is less than 30%, and the complex preparation process further restricts its industrialization [Struijs et al, Angew Chem Int Ed, 2023, 62: 1521-3773]. Therefore, developing a low-temperature CO2 methanation catalyst with high activity is the key to realizing CO2 methanation. SUMMARY

[0005] In order to solve the above problems in the prior art, the present application provides a carbon dioxide methanation catalyst, a preparation method and an application, which can realize carbon dioxide methanation with high selectivity and high conversion rate.

[0006] To achieve the above object, the technical scheme provided by the present application is as follows: In a first aspect, the present application provides a preparation method of a carbon dioxide methanation catalyst, comprising the following steps: dissolving a metal salt in deionized water to obtain a first solution; mixing and reacting an alkali metal hydroxide solution with the first solution to obtain a high-entropy hydroxide; calcining the high-entropy hydroxide to obtain a catalyst precursor; reducing the catalyst precursor to obtain the carbon dioxide methanation catalyst; wherein the metal in the metal salt comprises one of the second main group metals, one of the third main group metals and at least three of the transition metals.

[0007] Optionally, the molar ratio of the second main group metal, the third main group metal and any transition metal is 1:1:(0.5-3).

[0008] Optionally, the second main group metal is selected from one of magnesium, calcium and barium, the third main group metal is selected from one of boron, aluminum and gallium, and the transition metal comprises nickel and two of cobalt, manganese, iron, molybdenum and zirconium.

[0009] Optionally, the second main group metal is calcium or magnesium, and the transition metal is four, which are nickel, cobalt, manganese and iron, respectively.

[0010] Optionally, the mixing and reacting of the alkali metal hydroxide solution with the first solution is carried out at a stirring speed of 300-12000 rpm and a reaction temperature of 60-90°C for 1-24 h.

[0011] 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 nitrate, sulfate, chloride, carbonate and citrate.

[0012] Optionally, the concentration of the alkali metal hydroxide solution is 0.1-10 mol / L; and / or, the alkali metal is selected from one of sodium, potassium and cesium.

[0013] Optionally, the calcination is carried out at 300-1200°C for 1-48 h; and / or, the reduction is carried out at 300-500°C for 40-150 min.

[0014] In a second aspect, the application also provides a carbon dioxide methanation catalyst prepared by the method of the first aspect.

[0015] In a third aspect, the application also provides use of the carbon dioxide methanation catalyst of the second aspect in carbon dioxide methanation.

[0016] Optionally, the method comprises: under a temperature of 200-300 DEG C and a pressure of 2-4 MPa, the raw gas is subjected to carbon dioxide methanation under the action of the carbon dioxide methanation catalyst, wherein the flow rate of the raw gas relative to the catalyst is 150-300 mL / min / g of catalyst; and the volume ratio of carbon dioxide to hydrogen in the raw gas is 1:4.

[0017] Compared with the prior art, the application has at least the following beneficial effects: The carbon dioxide methanation catalyst prepared by the application is a high-entropy oxide with a single-phase solid solution structure, which is composed of one of the second main group metals, one of the third main group metals, and at least three kinds of transition metals and oxygen. The high-entropy oxide material has a uniform crystal structure and high catalytic activity and structural stability. By reducing the catalyst to induce the precipitation of active metals, an ultra-high density of oxygen vacancies can be dynamically constructed in the catalyst, thereby achieving excellent carbon dioxide conversion rate and methane selectivity under mild conditions. In addition, the unique lattice distortion effect and configuration entropy stability of the high-entropy oxide also make the catalyst have no significant decay in carbon dioxide conversion rate and methane selectivity in the stability test of 800 h, which exhibits significantly improved long-term catalytic stability. In addition, compared with the traditional catalyst Ni / Al2O3, the reaction temperature of the present application is reduced by about 100 DEG C. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 X-ray diffraction spectra of the high-entropy hydroxides after drying in different embodiments; Figure 2 X-ray diffraction spectra of the catalysts after carbon dioxide methanation reaction in different embodiments; Figure 3 Transmission electron microscope image of the catalyst precursor in Example 1; Figure 4 Energy dispersive X-ray spectrogram of the catalyst precursor in Example 1; Figure 5 XPS graph of the carbon dioxide methanation catalyst in Example 1. DETAILED DESCRIPTION

[0019] The application will be further described in detail below with reference to the accompanying drawings: The experimental methods used in the embodiments of the present application are all conventional methods unless otherwise specified.

[0020] The reagent materials used in the present example can be purchased conventionally, and the quantitative experiments involved in the embodiments are all set up with at least three repeated experiments, and the results are averaged.

[0021] Example 1:

[0022] A carbon dioxide methanation catalyst is prepared by the following method: First, 5 mmol of calcium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of iron nitrate, and 5 mmol of cobalt nitrate are added to 30 mL of deionized water to obtain a first solution; a 1 mol / L sodium hydroxide solution is prepared, which is an alkali metal hydroxide solution. 50 mL of deionized water is heated to 80℃ in a beaker, and the first solution and the alkali metal hydroxide solution are added to the beaker by a peristaltic pump, the temperature of the beaker is controlled at 80℃, the pH value is 10.5, and the stirring speed is 800 rpm for 8 h of aging, to obtain a high-entropy hydroxide; the high-entropy hydroxide is filtered and washed, then placed in an oven for drying (its X-ray diffraction spectrum is shown in Figure 1 ), and then calcined at 600℃ for 6 h to obtain a catalyst precursor; the catalyst precursor is then reduced in a N2 atmosphere containing 20% (volume content) H2 at a temperature of 450℃ for 90 min (XPS test is performed), to obtain a carbon dioxide methanation catalyst, the transmission electron microscope (TEM) image and the energy dispersive X-ray spectroscopy (EDS) image of which are shown in Figure 3 and Figure 4 , respectively, and the metal components are uniformly dispersed, indicating that the prepared catalyst forms a solid solution structure.

[0023] Carbon dioxide hydrogenation to methane includes the following steps: carbon dioxide methanation is carried out at 250℃, 3 MPa, a carbon dioxide to hydrogen volume ratio of 1:4, and the carbon dioxide methanation catalyst prepared in the present embodiment, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst, i.e. the mass space velocity is 200 mL / (g·min).

[0024] Figure 2 The XRD results show that the catalyst appears a characteristic diffraction peak of metallic nickel after carbon dioxide methanation reaction, which indicates that the metallic nickel realizes in-situ precipitation in the solid solution structure of the catalyst; combined with Figure 5 the XPS characterization results, wherein the characteristic of oxygen vacancy enrichment appears, further proving that the in-situ precipitation process of metallic nickel is accompanied by the generation of a large number of oxygen vacancies, which can not only stabilize the precipitated nickel species, but also effectively reduce the activation energy of carbon dioxide.

[0025] Example 2

[0026] A carbon dioxide methanation catalyst is prepared by the following method: First, 5 mmol of calcium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of iron nitrate, and 5 mmol of cobalt nitrate are added to 30 mL of deionized water to obtain a first solution; a 5 mol / L sodium hydroxide solution is prepared, which is an alkali metal hydroxide solution. 50 mL of deionized water is heated to 80°C in a beaker, and the first solution and the alkali metal hydroxide solution are added to the beaker by a peristaltic pump in a parallel flow, the temperature of the beaker is controlled at 80°C, the pH value is 11, and the aging reaction is stirred at a speed of 12000 rpm for 10 hours to obtain a high-entropy hydroxide; the high-entropy hydroxide is filtered and washed, then placed in an oven for drying, calcined at 600°C for 6 hours to obtain a catalyst precursor; and the catalyst precursor is reduced at a temperature of 450°C for 90 minutes to obtain a carbon dioxide methanation catalyst.

[0027] Carbon dioxide hydrogenation to produce methane includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, a volume ratio of carbon dioxide to hydrogen in the raw material gas is 1:4, and a carbon dioxide methanation catalyst prepared in this embodiment is used, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst, that is, the mass space velocity is 200 mL / (g·min).

[0028] Example 3

[0029] A carbon dioxide methanation catalyst is prepared by the following method: First, 5 mmol of barium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of iron nitrate, and 5 mmol of cobalt nitrate are added to 30 mL of deionized water to obtain a first solution; a 1 mol / L sodium hydroxide solution is prepared, which is an alkali metal hydroxide solution. 50 mL of deionized water is heated to 80°C in a beaker, and the first solution and the alkali metal hydroxide solution are added to the beaker by a peristaltic pump in a parallel flow, the temperature of the beaker is controlled at 80°C, the pH value is 10.5, and the aging reaction is stirred at a speed of 800 rpm for 8 hours to obtain a high-entropy hydroxide; the high-entropy hydroxide is filtered and washed, then placed in an oven for drying, calcined at 600°C for 6 hours to obtain a catalyst precursor; and the catalyst precursor is reduced at a temperature of 450°C for 90 minutes to obtain a carbon dioxide methanation catalyst.

[0030] Carbon dioxide hydrogenation to methane, comprising the following steps: carbon dioxide methanation is carried out at 250℃, 3 MPa, the volume ratio of carbon dioxide to hydrogen in the raw material gas is 1:4, and the carbon dioxide methanation catalyst prepared in this embodiment is used, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst, that is, the mass space velocity is 200 mL / (g·min).

[0031] Example 4:

[0032] A carbon dioxide methanation catalyst is prepared by the following method: First, 5 mmol of magnesium nitrate, 5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 5 mmol of nickel nitrate, 5 mmol of iron nitrate, and 5 mmol of cobalt nitrate are added to 30 mL of deionized water to obtain a first solution; a 1 mol / L sodium hydroxide solution is prepared, which is an alkali metal hydroxide solution. Take 50 mL of deionized water in a beaker and heat it to 80℃, then add the first solution and the alkali metal hydroxide solution to the beaker through a peristaltic pump, control the temperature of the beaker to be 80℃ and the pH value to be 10.5 during the whole process, and stir and age at a speed of 800 rpm for 8 h to obtain a high-entropy hydroxide; the high-entropy hydroxide is filtered and washed, then placed in an oven for drying, and then calcined at 600℃ for 6 h to obtain a catalyst precursor; then the catalyst precursor is reduced at a temperature of 450℃ for 90 min to obtain a carbon dioxide methanation catalyst.

[0033] Carbon dioxide hydrogenation to methane, comprising the following steps: carbon dioxide methanation is carried out at 250℃, 3 MPa, the volume ratio of carbon dioxide to hydrogen in the raw material gas is 1:4, and the carbon dioxide methanation catalyst prepared in this embodiment is used, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst, that is, the mass space velocity is 200 mL / (g·min).

[0034] Example 5:

[0035] A carbon dioxide methanation catalyst is prepared by the following method: Firstly, 6 mmol of calcium nitrate, 6 mmol of manganese nitrate, 3 mmol of aluminum nitrate, 6 mmol of nickel nitrate, 3 mmol of iron nitrate, and 6 mmol of cobalt nitrate were added into 30 mL of deionized water to obtain a first solution; a 2 mol / L sodium hydroxide solution was prepared, which was an alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker, and the first solution and the alkali metal hydroxide solution were added into the beaker by a peristaltic pump in a parallel flow, the temperature of the beaker was controlled to be 80°C, the pH value was controlled to be 11, and the aging was performed for 10 h under stirring at a speed of 800 rpm, to obtain a high-entropy hydroxide; the high-entropy hydroxide was filtered and washed, and then was placed into an oven for drying, and then was calcined at 600°C for 6 h to obtain a catalyst precursor; the catalyst precursor was reduced at a temperature of 450°C for 90 min to obtain a carbon dioxide methanation catalyst.

[0036] The carbon dioxide hydrogenation to produce methane includes the following steps: carbon dioxide methanation is performed at 250°C, 3 MPa, a volume ratio of carbon dioxide to hydrogen in a raw material gas of 1:4, and the carbon dioxide methanation catalyst prepared in the embodiment, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst.

[0037] Example 6:

[0038] A carbon dioxide methanation catalyst is prepared by the following method: Firstly, 5 mmol of calcium nitrate, 2.5 mmol of manganese nitrate, 5 mmol of aluminum nitrate, 10 mmol of nickel nitrate, 5 mmol of iron nitrate, and 1.5 mmol of cobalt nitrate were added into 30 mL of deionized water to obtain a first solution; a 2 mol / L sodium hydroxide solution was prepared, which was an alkali metal hydroxide solution. 50 mL of deionized water was heated to 80°C in a beaker, and the first solution and the alkali metal hydroxide solution were added into the beaker by a peristaltic pump in a parallel flow, the temperature of the beaker was controlled to be 80°C, the pH value was controlled to be 10, and the aging was performed for 8 h under stirring at a speed of 800 rpm, to obtain a high-entropy hydroxide; the high-entropy hydroxide was filtered and washed, and then was placed into an oven for drying, and then was calcined at 600°C for 6 h to obtain a catalyst precursor; the catalyst precursor was reduced at a temperature of 450°C for 90 min to obtain a carbon dioxide methanation catalyst.

[0039] The carbon dioxide hydrogenation to produce methane includes the following steps: carbon dioxide methanation is performed at 250°C, 3 MPa, a volume ratio of carbon dioxide to hydrogen in a raw material gas of 1:4, and the carbon dioxide methanation catalyst prepared in the embodiment, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst.

[0040] Example 7:

[0041] A carbon dioxide methanation catalyst is prepared by the following method: First, 6 mmol of barium nitrate, 6 mmol of manganese nitrate, 3 mmol of aluminum nitrate, 6 mmol of nickel nitrate, 3 mmol of iron nitrate, and 6 mmol of cobalt nitrate are added to 30 mL of deionized water to obtain a first solution; a 2 mol / L sodium hydroxide solution is prepared, which is an alkali metal hydroxide solution. 50 mL of deionized water is heated to 80°C in a beaker, and the first solution and the alkali metal hydroxide solution are added to the beaker by a peristaltic pump, the temperature of the beaker is controlled at 80°C, the pH value is 10.5, and the stirring speed is 800 rpm for 8 h of aging to obtain a high-entropy hydroxide; the high-entropy hydroxide is filtered and washed, then dried in an oven, and calcined at 600°C for 6 h to obtain a catalyst precursor; the catalyst precursor is reduced at a temperature of 450°C for 90 min to obtain a carbon dioxide methanation catalyst.

[0042] Carbon dioxide hydrogenation to produce methane includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, a volume ratio of carbon dioxide to hydrogen in the raw material gas is 1:4, and the carbon dioxide methanation catalyst prepared in this embodiment is used, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst.

[0043] Example 8:

[0044] A carbon dioxide methanation catalyst is prepared by the following method: 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 iron nitrate are added to 30 mL of deionized water to obtain a first solution; a 2 mol / L sodium hydroxide solution is prepared, which is an alkali metal hydroxide solution. 50 mL of deionized water is heated to 80°C in a beaker, and the first solution and the alkali metal hydroxide solution are added to the beaker by a peristaltic pump, the temperature of the beaker is controlled at 80°C, the pH value is 10.5, and the stirring speed is 800 rpm for 8 h of aging to obtain a high-entropy hydroxide; the high-entropy hydroxide is filtered and washed, then dried in an oven, and calcined at 600°C for 6 h to obtain a catalyst precursor; the catalyst precursor is reduced at a temperature of 450°C for 90 min to obtain a carbon dioxide methanation catalyst.

[0045] Carbon dioxide hydrogenation to produce methane includes the following steps: carbon dioxide methanation is carried out at 250°C, 3 MPa, a volume ratio of carbon dioxide to hydrogen in the raw material gas is 1:4, and the carbon dioxide methanation catalyst prepared in this embodiment is used, wherein the flow rate of the raw material gas relative to the catalyst is 200 milliliters per minute per gram of catalyst.

[0046] Example 9:

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

[0048] 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.

[0049] 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.

[0050] Comparative Example 1: A carbon dioxide methanation catalyst is prepared by the following method: 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.

[0051] 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.

[0052] Comparative Example 2: A carbon dioxide methanation catalyst is prepared by the following method: 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.

[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 comparative example, wherein the flow rate of the feed gas relative to the catalyst is 200 ml / min / g catalyst.

[0054] Comparative Example 3: 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.

[0055] Comparative Example 4: 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.

[0056] Comparative Example 5: 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.

[0057] 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.

[0058] Comparative Example 6: 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.

[0059] 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.

[0060] The test results of the catalysts in the carbon dioxide to methane reaction in different embodiments and comparative examples are shown in Table 1.

[0061] Testing equipment and experimental conditions 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.

[0062] Calculation of CO2 conversion rate and product selectivity: 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: ;

[0063] ;

[0064] 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; 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.

[0065] Table 1: Carbon dioxide conversion rate and methane selectivity in the carbon dioxide to methane reaction with different catalysts

Claims

1. A method for preparing a carbon dioxide methanation catalyst, characterized by, The method comprises the following steps: dissolving a metal salt in deionized water to obtain a first solution; mixing and reacting an alkali hydroxide solution with the first solution to obtain a high-entropy hydroxide; calcining the high-entropy hydroxide to obtain a catalyst precursor; reducing the catalyst precursor to obtain the carbon dioxide methanation catalyst; wherein the metal in the metal salt comprises one of the second main group metals, one of the third main group metals, and at least three of the transition metals.

2. The method of making a carbon dioxide methanation catalyst according to claim 1, wherein, The molar ratio of the second main group metal, the third main group metal, and any transition metal is 1:1:(0.5-3).

3. The method of making a carbon dioxide methanation catalyst according to claim 2, wherein, The second main group metal is selected from one of magnesium, calcium, and barium, the third main group metal is selected from one of boron, aluminum, and gallium, and the transition metal comprises nickel and two of cobalt, manganese, iron, molybdenum, and zirconium.

4. The method of making a carbon dioxide methanation catalyst according to claim 1, wherein, The mixing and reacting of the alkali hydroxide solution with the first solution is carried out at a stirring speed of 300-12000 rpm and a temperature of 60-90℃ for 1-24 h.

5. The method of making a carbon dioxide methanation catalyst according to claim 1, wherein, 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 nitrate, sulfate, chloride, carbonate, and citrate. And / or, the second main group metal is calcium or magnesium, and the transition metal is four, namely nickel, cobalt, manganese, and iron.

6. The method of making a carbon dioxide methanation catalyst according to claim 1, wherein, The concentration of the alkali hydroxide solution is 0.1-10 mol / L; and / or, the alkali metal is selected from one of sodium, potassium, and cesium.

7. The method of making a carbon dioxide methanation catalyst according to claim 1, wherein, The calcination is carried out at a temperature of 300-1200℃ for 1-48 h. And / or, the reduction is carried out at a temperature of 300-500℃ for 40-150 min.

8. A carbon dioxide methanation catalyst characterized by, The carbon dioxide methanation catalyst is prepared by the method of any one of claims 1-7.

9. Use of the carbon dioxide methanation catalyst of claim 8 in carbon dioxide methanation.

10. Use of a carbon dioxide methanation catalyst according to claim 9 for carbon dioxide methanation, characterized in that, The method comprises: carrying out carbon dioxide methanation of a raw material gas on the carbon dioxide methanation catalyst at a temperature of 200-300℃ and a pressure of 2-4 MPa, wherein the flow rate of the raw material gas relative to the catalyst is 150-300 milliliters per minute per gram of catalyst, and the volume ratio of carbon dioxide to hydrogen in the raw material gas is 1:4.

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