A method for preparing a modified Ni / CeO2 catalyst and its application

Abstract

The present invention aims to provide a method for preparing a modified Ni / CeO2 catalyst and its application, belonging to the field of CO2 methanation catalyst technology. This invention uses ammonia solutions in different solvents as precipitants, adding the precipitants dropwise to a cerium salt solution and stirring to obtain a flocculent mixture. After filtration, washing, drying, and calcination, a CeO2 support modified with ammonia solutions in different solvents is obtained. The modified Ni / CeO2 catalyst precursor is prepared using a volumetric impregnation method. By modifying the CeO2 support with ammonia solutions in different solvents, the synthesized Ni / CeO2 catalyst precursor is treated with a reducing atmosphere, and the aggregation of Ni nanoparticles is effectively suppressed by optimizing the Ni-CeO2 interaction structure. The Ni / CeO2 catalyst prepared by this invention using ammonia solutions with water as the solvent exhibits excellent low-temperature methanation activity, with a CH4 selectivity approaching 100%, and stable catalytic performance.

Description

Technical Field

[0001] This invention belongs to the field of CO2 methanation catalyst technology, specifically relating to a method for preparing a modified Ni / CeO2 catalyst and its application. Background Technology

[0002] In recent years, the overuse of fossil fuels such as coal and oil has led to the emission of large amounts of carbon dioxide (CO2) into the atmosphere, causing severe damage to the ecology and environment. Against the backdrop of "carbon peaking" and "carbon neutrality," the hydrogenation of CO2 to synthesize high-value-added fuels and chemicals is of great significance for energy conservation, emission reduction, and the recycling of carbon resources. Under specific reaction conditions and with the aid of catalysts, CO2 hydrogenation can synthesize specific target products, such as methane (CH4), methanol, carbon monoxide, formic acid, ethanol, and alkanes. Among these, the synthesis of CH4 from CO2 hydrogenation has become a focus of research in both academia and industry due to its advantages such as low operating costs, mild reaction conditions, high methane demand, high synthesis yield, and high production efficiency.

[0003] CO2 methanation, the core of natural gas power generation (PtG) technology, utilizes green hydrogen (H2) produced by the electrolysis of H2O from intermittent, low-density renewable energy sources (wind, solar, etc.) and CO2 captured from flue gas in power plants and coking plants. Under the action of a catalyst, H2 and CO2 are synthesized into high-energy-density CH4. PtG technology synthesizes natural gas through a coupling of electrochemical decomposition and chemical synthesis, and it is likely one of the most convenient ways to store large amounts of surplus electrical energy over the long term. It holds promise for reducing CO2 emissions on a large scale while simultaneously reducing dependence on traditional fossil fuels. Therefore, CO2 methanation is a highly promising low-carbon and clean route.

[0004] CO2 methanation catalysts are generally composed of group 8, 9, 10, and 11 transition metals. Nickel-based and ruthenium-based catalysts produce almost exclusively CH4, while less active metal components (Pd, Pt, Rh, Mo, Re, and Au) simultaneously catalyze the production of CH4, CH3OH, and CO. Among numerous catalytic systems, nickel (Ni)-based catalysts have become important candidate catalysts for CO2 methanation due to their strong H2 dissociation ability, excellent CH4 selectivity, and low cost. CO2 methanation is a strongly exothermic reaction, and Ni-based catalysts are prone to sintering under high-temperature reaction conditions. Therefore, improving the atomic utilization of active Ni and suppressing Ni particle agglomeration are key to achieving high performance and long lifespan in low-temperature methanation catalysts.

[0005] Chinese patent CN 116809110 A discloses a high specific surface area nickel-based methanation catalyst using mesoporous material TUD-1 as a support. Although it exhibits high CO2 conversion at low temperatures, its preparation process is complex, requiring a high active metal loading. The optimal reaction conditions are a reaction pressure of 2.0-2.5 MPa for catalyst performance evaluation, resulting in significant energy consumption. Chinese patent application CN103143364A discloses a nanocomposite catalyst with high active metal dispersion. While it also demonstrates high CO2 conversion, the catalytic reaction requires high temperatures of 700-1000℃, leading to extremely high energy consumption. Chinese patent CN 104923225 A discloses a noble metal-supported CO2 methanation catalyst. Although this catalyst exhibits excellent methanation performance at low temperatures, the high cost of noble metals and the high calcination temperature required to synthesize the catalyst support hinder large-scale industrial production. Chinese patent CN114870846A discloses a methanation catalyst with uniform nickel-zirconium distribution and porous structure, which exhibits excellent catalytic activity under low conditions. However, the catalyst uses a large amount of biomass tar in its synthesis process and utilizes phenols and phenolic compounds in the tar as a dispersion medium, which seriously harms the environment and human health during the preparation process.

[0006] Therefore, there is an urgent need to develop low-temperature CO2 methanation catalysts that are highly active, have stable catalytic performance, are inexpensive, and are environmentally friendly. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a modified Ni / CeO2 catalyst and its application. This method produces a green, environmentally friendly, low-cost, low-temperature, high-efficiency CO2 methanation catalyst with a long catalytic lifetime. This invention utilizes a strategy of obtaining a modified CeO2 support by changing the solvent type of the ammonia solution and regulating the interaction between the active metal Ni and the CeO2 support by modifying the surface properties of the support.

[0008] The present invention adopts the following technical solution: A method for preparing a modified Ni / CeO2 catalyst includes the following steps: S1. Prepare a cerium salt solution and an excess of ammonia solutions in different solvents; under stirring conditions, mix the cerium salt solution with ammonia solutions in different solvents respectively, and continue stirring for 20-240 minutes to obtain a mixed suspension; S2. The mixed suspension was filtered and washed with a mixed solution of deionized water and anhydrous ethanol in a volume ratio of 1:1 until neutral, and then dried at 120°C for 12 hours to obtain a solid powder. S3. The solid powder was calcined in a muffle furnace at 250-700℃ for 1-48h to obtain CeO2 supports modified with ammonia aqueous solution in different solvents. S4. Prepare a nickel salt solution of a certain concentration in advance, pour CeO2 support into the nickel salt solution and stir overnight, then heat and evaporate the solution to a paste, dry at 80-180℃ for 4-18h to obtain the catalyst precursor, then grind and sieve the obtained catalyst precursor to 20-40 mesh to obtain the shaped catalyst precursor. S5. The formed catalyst precursor is activated in a reducing atmosphere at 350-550℃ for 0.5-10 h to finally obtain the target catalyst.

[0009] Further, in S1, the cerium salt includes any one of cerium nitrate, cerium nitrate hydrate, cerium carbonate, cerium carbonate hydrate, cerium chloride, cerium chloride hydrate, cerium acetate, and cerium acetate hydrate.

[0010] Furthermore, in S1, the solvent for the ammonia solution includes any one of deionized water, ethanol, and methanol, the volume ratio of ammonia to solvent is 1:1 to 8:1, and the mass concentration of ammonia is 28%.

[0011] Further, in S4, the nickel salt includes any one of nickel nitrate, nickel nitrate hydrate, nickel carbonate, nickel carbonate hydrate, nickel acetate, and nickel acetate hydrate.

[0012] Furthermore, in S4, the nickel accounts for 3-15% of the mass fraction of the catalyst.

[0013] A modified Ni / CeO2 catalyst is used for gas-solid phase CO2 methanation reaction in a fixed bed at atmospheric or near atmospheric pressure, with a reaction temperature of 200-500℃.

[0014] The beneficial effects of this invention are as follows: 1. This invention modulates the surface of CeO2 by controlling the solvent of ammonia solution, thereby controlling the Ni-CeO2 interaction structure. The strong metal-support interaction of the Ni / CeO2-W catalyst promotes the dispersion of Ni particles and effectively inhibits the agglomeration of the active component Ni particles, giving the catalyst a longer service life in the CO2 methanation reaction. The efficient interfacial sites in the Ni / CeO2-W catalyst promote the adsorption and activation of CO2, giving Ni / CeO2-W a high CO2 conversion rate and excellent CH4 selectivity.

[0015] 2. The modified Ni / CeO2 catalyst prepared in this invention has a simple preparation process, low cost, and is environmentally friendly. Compared with catalysts containing precious metals, it has higher economic value and market application prospects, and is suitable for large-scale industrial application. Attached Figure Description

[0016] Figure 1SEM images of CeO2 supports modified with ammonia solutions in different solvents: (a) CeO2-W, (b) CeO2-E, and (c) commercial CeO2 supports, CeO2-C; Figure 2 (a) XRD patterns of CeO2 supports modified with ammonia solutions in different solvents and commercial CeO2 supports; (b) XRD patterns of Ni-supported CeO2 supports modified with ammonia solutions in different solvents and commercial CeO2 supports; (c) Partial magnified XRD patterns of Ni-supported CeO2 supports modified with ammonia solutions in different solvents and commercial CeO2 supports. Figure 3 (a) H2 pulse diagrams of Ni-supported CeO2 modified with ammonia solutions in different solvents and commercial CeO2 support; (b) CO2-TPD diagrams of Ni-supported CeO2 modified with ammonia solutions in different solvents and commercial CeO2 support. Figure 4 Performance evaluation diagrams of Ni / CeO2 catalysts modified with ammonia aqueous solution in different solvents: (a) CO2 conversion rate, (b) product (CH4 / CO) selectivity; Figure 5 The graph shows the CO2 methanation performance of the Ni / CeO2-W catalyst at different space velocities at a reaction temperature of 573 K. Figure 6 The results represent the long-term stability evaluation of the NiCeO2-W catalyst for CO2 methanation at a reaction temperature of 573 K. Detailed Implementation

[0017] The present invention will be described below with reference to specific embodiments and accompanying drawings, but the embodiments are not intended to limit the present invention in any way. Unless otherwise specified, the equipment, materials, reagents, etc. used in the present invention are all commercially available; the specific experimental steps are conventional experimental methods in this technical field.

[0018] Examples 1-3 illustrate the preparation of Ni / CeO2 catalysts modified with ammonia aqueous solutions in different solvents. Example 1 10.1 g of cerium nitrate hexahydrate was dissolved in 50 mL of deionized water, while 9 mL of ammonia (28% wt.) was dissolved in 9 mL of deionized water to prepare an alkaline solution. The alkaline solution was slowly added dropwise to the cerium nitrate solution while stirring, followed by uniform stirring for 120 minutes to obtain a mixed suspension. The mixed suspension was then filtered and washed until neutral with a 1:1 mixture of deionized water and anhydrous ethanol, dried at 120 °C for 12 hours, and calcined at 500 °C for 4 hours to obtain the modified CeO2 support, which was labeled CeO2-W.

[0019] The Ni / CeO2 catalyst (5 wt%) was prepared by an impregnation-reduction method. Specifically, 3 g of CeO2 support was added to an ethanol solution of 0.7822 g of nickel nitrate, and the mixture was stirred uniformly for 8 hours for impregnation. The mixture was then evaporated to a paste state at 85 °C while stirring. The paste was dried at 120 °C for 12 hours to obtain the catalyst precursor. The catalyst precursor was sieved to 20-40 mesh and then reduced at 450 °C in an H2 atmosphere for 1 hour to obtain the modified catalyst Ni / CeO2-W.

[0020] Example 2 Except for dissolving 10.1 g of cerium nitrate hexahydrate in 50 mL of anhydrous ethanol and dissolving 9 mL of ammonia (28% wt.) in 9 mL of anhydrous ethanol to prepare an alkaline solution, the rest of the preparation method was exactly the same as in Example 1, and the modified catalyst Ni / CeO2-E was obtained.

[0021] Example 3 Commercial CeO2 was selected as the support, and the catalyst preparation method was exactly the same as in Example 1, resulting in the catalyst Ni / CeO2-C.

[0022] Examples 4-8 illustrate the preparation of Ni / CeO2-W catalysts with different nickel loadings. Example 4 A method for preparing CeO2 support modified with ammonia solution using deionized water as solvent (ammonia to deionized water volume ratio 1:1): 10.1 g of cerium nitrate hexahydrate was dissolved in 50 mL of deionized water, and simultaneously 9 mL of ammonia (28% wt.) was dissolved in 9 mL of deionized water to prepare an alkaline solution. The alkaline solution was slowly added dropwise to the cerium salt solution while stirring. After the addition was complete, the mixture was stirred uniformly for 120 minutes to obtain a mixed suspension. The mixed suspension was then filtered and washed until neutral with a mixed solution of deionized water and anhydrous ethanol (volume ratio 1:1). It was then dried at 120 °C for 12 hours and calcined at 500 °C for 4 hours to obtain the CeO2 support modified with ammonia solution using deionized water as solvent, labeled CeO2-W.

[0023] The Ni / CeO2-W catalyst (5 wt% Ni loading) was prepared by an impregnation-reduction method. Specifically, 3 g of modified CeO2 support was added to a pre-prepared 0.7822 g nickel nitrate ethanol solution, and the mixture was stirred uniformly for 8 hours for impregnation. The mixture was then evaporated to a paste state at 80 °C while stirring. The paste was dried at 120 °C for 12 hours to obtain the catalyst precursor, which was then sieved to 20-40 mesh. The precursor was then reduced with H2 at 450 °C for 1 hour to obtain a 5% Ni-loaded catalyst, labeled as 5Ni / CeO2-W.

[0024] Example 5 The Ni / CeO2-W catalyst (3wt% Ni loading) was prepared in the same manner as in Example 4, except that a pre-prepared 0.469g nickel nitrate ethanol solution was used. The resulting catalyst was labeled as 3Ni / CeO2-W with a loading of 3%.

[0025] Example 6 The Ni / CeO2-W catalyst (7wt% Ni loading) was prepared using the same method as in Example 4, except for the pre-prepared 1.095g ethanol solution of nickel nitrate. The resulting catalyst had a loading of 7% and was labeled as 7Ni / CeO2-W.

[0026] Example 7 The Ni / CeO2-W catalyst (10wt% Ni loading) was prepared using the same method as in Example 4, except for the pre-prepared 1.564g ethanol solution of nickel nitrate. The resulting catalyst had a loading of 10% and was labeled as 10Ni / CeO2-W.

[0027] Example 8 The Ni / CeO2-W catalyst (15wt% Ni loading) was prepared using the same method as in Example 4, except for the pre-prepared 1.564g ethanol solution of nickel nitrate. The resulting target catalyst with a loading of 15% was denoted as 15Ni / CeO2-W.

[0028] Examples 9-12 are Ni / CeO2-W catalysts modified with alkaline solutions of different ammonia to deionized water volume ratios. Example 9 Ni / CeO2 catalysts were modified with ammonia solutions of varying ammonia-to-deionized water volume ratios (1:1). 10.1 g of cerium nitrate hexahydrate was dissolved in 50 mL of deionized water, while 9 mL of ammonia (28% wt.) was dissolved in 9 mL of deionized water to prepare an alkaline solution. The alkaline solution was slowly added dropwise to the cerium salt solution while stirring. After the addition was complete, the mixture was stirred uniformly for 120 minutes to obtain a mixed suspension. The suspension was then filtered and washed until neutral with a 1:1 mixture of ethanol and water, dried at 120 °C for 12 hours, and calcined at 500 °C for 4 hours to obtain an alkaline solution-modified CeO2 support with an ammonia-to-deionized water volume ratio of 1, labeled CeO2-W-1.

[0029] The Ni / CeO2-W catalyst (5 wt% Ni loading) was prepared by an impregnation-reduction method. Specifically, 3 g of modified CeO2 support was added to a pre-prepared 0.7822 g nickel nitrate ethanol solution, and the mixture was stirred uniformly for 8 hours (80 rpm) for impregnation. The mixture was then evaporated to a paste state at 80 °C while stirring. The paste was dried at 120 °C for 12 hours to obtain the catalyst precursor, which was then sieved to 20-40 mesh. The precursor was then reduced with H2 at 450 °C for 1 hour to obtain a 5% Ni-loaded catalyst, labeled 5Ni / CeO2-W-1.

[0030] Example 10 Ni / CeO2 catalyst was modified with alkaline solutions of different ammonia-to-deionized water volume ratios (ammonia-to-deionized water volume ratio of 0.5:1). 10.1 g of cerium nitrate hexahydrate was dissolved in 50 mL of deionized water, while 4.5 mL of ammonia (28% wt.) was dissolved in 9 mL of deionized water to prepare an alkaline solution. The remaining preparation methods were exactly the same as in Example 9, yielding 5Ni / CeO2-W-0.5.

[0031] Example 11 Ni / CeO2 catalysts were modified with alkaline solutions of different ammonia-to-deionized water volume ratios (ammonia-to-deionized water volume ratio of 2:1). 10.1 g of cerium nitrate hexahydrate was dissolved in 50 mL of deionized water, while 18 mL of ammonia (28% wt.) was dissolved in 9 mL of deionized water to prepare an alkaline solution. The remaining preparation methods were exactly the same as in Example 9, yielding 5Ni / CeO2-W-2.

[0032] Example 12 Ni / CeO2 catalysts were modified with alkaline solutions of different ammonia-to-deionized water volume ratios (ammonia-to-deionized water volume ratio 3:1). 10.1 g of cerium nitrate hexahydrate was dissolved in 50 mL of deionized water, while 27 mL of ammonia (28% wt.) was dissolved in 9 mL of deionized water to prepare an alkaline solution. The remaining preparation methods were exactly the same as in Example 9, yielding 5Ni / CeO2-W-3.

[0033] SEM images of the modified supports obtained in Comparative Examples 1-3 ( Figure 1 It can be clearly seen that commercial CeO2 is composed of blocky and non-uniform particles, while the CeO2 support synthesized by precipitation method is composed of a large number of small and uniform nanoparticles, indicating that the modified CeO2 support has a larger specific surface area than CeO2-C.

[0034] XRD patterns of the support and catalyst obtained in Comparative Examples 1-3 ( Figure 2It can be seen that all samples exhibit characteristic diffraction peaks at 2θ of 28.6, 33.1, 47.5, and 56.4°, belonging to the CeO2 (111), (200), (220), and (311) crystal planes, indicating that both the support and the catalyst possess a typical cubic fluorite structure of CeO2. The reduced catalyst ( Figure 2 (b) No obvious Ni was found. 0 The characteristic peaks indicate that Ni 0 The nanoparticles are highly dispersed on the surface of the carrier. Figure 2 (c) It can be seen that for the Ni / CeO2-C catalyst, metallic Ni 0 Nanoparticles exist in a highly dispersed form in the modified Ni / CeO2 catalyst.

[0035] H2 pulse diagrams of the catalysts obtained in Comparative Examples 1-3 ( Figure 3 (a) shows that, compared to the Ni / CeO2-C catalyst, the modified Ni / CeO2-W and Ni / CeO2-E catalysts adsorb more H2, and the adsorption capacity of Ni / CeO2-W for H2 is greater than that of Ni / CeO2-E. This indicates that the active metal Ni in the modified Ni / CeO2-W is highly dispersed and a large amount of metal Ni is exposed. 0 The site effectively promotes the activation of H2.

[0036] Comparative Examples 1-3 showed higher CO2-TPD ( Figure 3 (b) shows that, compared to the adsorption capacity of Ni / CeO2-C catalyst at weakly basic and moderately basic sites, the modified Ni / CeO2-W and Ni / CeO2-E catalysts have a large number of weakly and moderately basic sites on their surfaces, which can effectively promote the adsorption of CO2 on the catalyst surface. Specifically, the Ni / CeO2-W catalyst surface has a large number of weakly basic sites and a small number of moderately basic sites, while the Ni / CeO2-E catalyst surface has both weakly basic and moderately basic sites. These weakly basic and moderately basic sites can promote the adsorption and activation of CO2, improving the low-temperature methanation performance of the catalyst.

[0037] The catalysts prepared in Examples 1-12 were used for CO2 methanation reaction performance evaluation and performance comparison. The steps for evaluating the CO2 methanation performance of the catalysts are as follows: Step 1: Loading the catalyst precursor. Mix 0.1g of 20-40 mesh catalyst precursor with 0.4g of 40-60 mesh quartz sand evenly and load the mixture into a quartz tube fixed-bed reactor.

[0038] Step 2: Catalyst precursor activation treatment. H2 (purity greater than 99.999%) is introduced into the fixed-bed reactor at a flow rate of 10 mL / min. The fixed-bed heater is heated from room temperature to the reduction temperature (350-550℃) for 30-180 min.

[0039] Step 3: Catalyst performance testing. A certain proportion of CO2 and H2 gas is introduced into a mixing tank through a flow meter, mixed evenly, and then fed into a fixed-bed reactor. The molar ratio of CO2 to H2 is 1:0.25-1:5, the mass hourly space velocity is 20-90 L / (g·h), the reaction temperature is 200-450℃, and the reaction pressure is atmospheric or near-atmospheric pressure.

[0040] The resulting tail gas mixture was cold-trapped and then analyzed by an Agilent 4890D gas chromatograph using a thermal conductivity detector (TCD), with H2 as the carrier gas and a TDX-01 packed column. N2 was used as the internal standard. The CO2 conversion and CH4 selectivity were calculated using the correction factor obtained from the internal standard curve. Long-term stability evaluation: The stability of the Ni / CeO2-W catalyst was tested for 50 hours at a reaction temperature of 300℃ and a mass hourly space velocity of 60 L / (g·h).

[0041] The test results are attached. Figure 4 Appendix Figure 5 and attached Figure 6 .

[0042] The CO2 methanation performance of Ni / CeO2 catalysts modified with ammonia solutions in different solvents is as follows: Figure 4 As shown. Under normal pressure, a CO2:H2 molar ratio of 1:4, a reaction temperature of 473-723 K, and a mass hourly space velocity of 60 L / (g·h), the CO2 conversion rate of the catalyst is as follows: Figure 4 As shown in (a), the methanation activity of the catalysts increases with increasing reaction temperature. Among them, the Ni / CeO2-W catalyst exhibits the highest CO2 methanation activity. At a reaction temperature of 573 K, the CO2 conversion rates of Ni / CeO2-W and Ni / CeO2-E are 57.0% and 46.2%, respectively, which are 25.3% and 14.5% higher than the activity of the commercial Ni / CeO2-C catalyst (31.7%). This indicates that the modified Ni / CeO2 utilizes the metal-support interaction to promote the methanation of metallic Ni. 0 The high dispersion and the formation of a large number of weakly and moderately basic sites promote the adsorption and activation of H2 and CO2, resulting in the modified catalyst exhibiting excellent CO2 methanation performance. In particular, the Ni / CeO2-W catalyst modified with deionized water as solvent has suitable metal-support interaction. Figure 4(b) is a distribution of the selectivity of the catalyst for CO2 methanation. Within the test temperature range, the selectivity of the catalyst for CH4 is close to 100%, which almost completely suppresses the occurrence of the reverse water gas shift (RWGS) side reaction.

[0043] To investigate the catalyst's ability to process feed gas, the CO2 methanation performance of Ni / CeO2-W at different space velocities was examined. The test results are as follows: Figure 5 As shown, as the mass hourly space velocity (MHV) increases from 45 L / (g·h) to 90 L / (g·h), the CO2 conversion of Ni / CeO2-W decreases from 54.0% to 41.2%, and the CH4 selectivity decreases from 98.7% to 98.0%, with the selectivity remaining almost unchanged. This indicates that even under high MHV conditions, Ni / CeO2-W still exhibits excellent methane selectivity.

[0044] The stability of the modified Ni / CeO2-W catalyst was analyzed, and the test results are as follows: Figure 6 As shown, a 50-hour long-term stability test of CO2 methanation was conducted under the conditions of 573 K, an H2 / CO2 molar ratio of 4, and a space velocity of 60 L / (g·h). During the entire stability test, the CO2 conversion rate decreased slightly (3.8%) from the initial 60.5% to 56.7%, while the CH4 selectivity remained close to 100%. This indicates that the suitable metal-support interaction structure in the modified Ni / CeO2-W catalyst effectively inhibits the aggregation of Ni nanoparticles, exhibiting excellent long-term stability.

[0045] Unless otherwise specified, the pharmaceuticals, gases, and equipment used in this invention are all commonly used pharmaceuticals, gases, and equipment in the field; and the methods used in this invention are all conventional methods in the field unless otherwise specified.

[0046] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the present invention in any way. Any simple modifications, alterations, or equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a modified Ni / CeO2 catalyst, characterized in that: Includes the following steps: S1. Prepare a cerium salt solution and an excess of ammonia solutions in different solvents; under stirring conditions, mix the cerium salt solution with ammonia solutions in different solvents respectively, and continue stirring for 20-240 minutes to obtain a mixed suspension; S2. The mixed suspension was filtered and washed with a mixed solution of deionized water and anhydrous ethanol in a volume ratio of 1:1 until neutral, and then dried at 120°C for 12 h to obtain a solid powder. S3. The solid powder was calcined in a muffle furnace at 250-700℃ for 1-48 h to obtain CeO2 supports modified with ammonia aqueous solution in different solvents. S4. Prepare a nickel salt solution of a certain concentration in advance, pour CeO2 support into the nickel salt solution and stir overnight, then heat and evaporate the solution to a paste, dry at 80-180℃ for 4-18h to obtain the catalyst precursor, then grind and sieve the obtained catalyst precursor to 20-40 mesh to obtain the shaped catalyst precursor. S5. The formed catalyst precursor is activated in a reducing atmosphere at 350-550℃ for 0.5-10 h to finally obtain the target catalyst.

2. The method for preparing a modified Ni / CeO2 catalyst according to claim 1, characterized in that: In S1, the cerium salt includes any one of cerium nitrate, cerium nitrate hydrate, cerium carbonate, cerium carbonate hydrate, cerium chloride, cerium chloride hydrate, cerium acetate, and cerium acetate hydrate.

3. The method for preparing a modified Ni / CeO2 catalyst according to claim 1, characterized in that: In S1, the solvent for the ammonia solution includes any one of deionized water, ethanol, and methanol, and the volume ratio of ammonia to solvent is 1:1 to 8:1, with a mass concentration of 28%.

4. The method for preparing a modified Ni / CeO2 catalyst according to claim 1, characterized in that: In S4, the nickel salt includes any one of nickel nitrate, nickel nitrate hydrate, nickel carbonate, nickel carbonate hydrate, nickel acetate, and nickel acetate hydrate.

5. The method for preparing a modified Ni / CeO2 catalyst according to claim 1, characterized in that: In S4, the nickel accounts for 3-15% of the mass fraction of the catalyst.

6. A modified Ni / CeO2 catalyst prepared by the method described in claim 1 is used for a fixed-bed gas-solid phase CO2 methanation reaction at atmospheric or near-ambient pressure, with a reaction temperature of 200-500℃.

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