A catalyst for low-temperature methanation of CO2, its preparation method and application

Abstract

The application provides a catalyst for CO2 low-temperature methanation and a preparation method and application thereof, and belongs to the technical field of catalysts. The preparation method of the catalyst comprises the following steps: grinding CeO2, ZnCo2O4, yttrium nitrate and a particle size regulator after mixing, and then sequentially performing drying and calcination to obtain ZnCo2O4-Y2O3-CeO2; reducing the ZnCo2O4-Y2O3-CeO2 in a hydrogen atmosphere to obtain the catalyst. The catalyst has the advantages that on the one hand, the catalyst catalyzes the CO2 hydrogenation methanation reaction at a low temperature, and carbon deposition, sintering and agglomeration of the catalyst are avoided; on the other hand, the catalyst has a CO2 conversion rate not inferior to that of a traditional nickel-based catalyst and excellent methane selectivity. Therefore, the invention and implementation of the catalyst can realize the resource utilization of CO2 by coupling the capture of CO2 emitted by a traditional chemical enterprise with green hydrogen.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a catalyst for low-temperature methanation of CO2, its preparation method, and its application. Background Technology

[0002] The combustion of fossil fuels is the dominant factor causing a sharp increase in greenhouse gas emissions, with CO2 accounting for nearly three-quarters of total emissions. Large-scale CO2 emissions have triggered a series of chain reactions, resulting in numerous negative ecological and environmental effects such as global warming and ocean acidification. Furthermore, the current energy supply and demand imbalance is prominent, and energy and ecological problems are intertwined, creating an extremely serious situation. CO2 possesses characteristics such as wide availability, low cost, high renewability, and non-toxicity. Based on these properties, it is considered an ideal C1 feedstock in the field of chemical synthesis, suitable for the preparation of high-value-added chemicals such as methane.

[0003] The stable thermodynamic properties and significant kinetic inertness of CO2 are key obstacles to its direct conversion into methane. As a typical linear symmetrical triatomic molecule, it contains 16 valence electrons, with each atom having ns and np orbitals. The central carbon atom bonds to the oxygen atom via sp hybrid orbitals. In this configuration, the CO2 molecule harbors multiple activation sites: the carbon atom exhibits Lewis acidity and can act as an electrophilic center, while the oxygen atom exhibits Lewis baseity and can act as a nucleophilic center. Compared to isoelectronic molecules, CO2's first ionization energy of 13.79 eV makes its conversion into methane difficult. + And the low-energy empty orbit (2π) u Its 38 eV electron affinity also makes it readily convertible to CO2. - Therefore, by introducing electrons in an appropriate manner or by taking electrons from other molecules during the reaction, the inertia of CO2 can be overcome, thereby achieving its activation and transformation.

[0004] Catalysts play a crucial role in the CO2 hydrogenation to methane reaction. Common catalysts used in this reaction include oxide catalysts, bimetallic catalysts, and noble metal catalysts. Among these catalysts, due to their inherent structural characteristics, the reaction requires relatively high reaction temperatures, making them prone to active component migration and sintering, as well as Ostwald ripening, leading to catalyst deactivation. Furthermore, higher reaction temperatures result in more severe carbon deposition during the reaction process. To address these challenges, strategies such as adding noble metal promoters, carefully constructing confined structures, and enhancing the interaction between the metal and the support are typically employed to lower the reaction temperature or suppress catalyst sintering and deactivation. In addition, limited by thermodynamic factors and the intrinsic activity of existing catalyst active centers, the current CO2 hydrogenation reaction temperature remains relatively high. Therefore, developing catalysts for low-temperature CO2 methanation is crucial for advancing the industrial application of CO2 hydrogenation to methane. Summary of the Invention

[0005] Based on the above, the purpose of this invention is to provide a catalyst for low-temperature methanation of CO2, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of this invention is a method for preparing a catalyst for low-temperature methanation of CO2, comprising the following steps:

[0008] CeO2, ZnCo2O4, yttrium nitrate and particle size modifier were mixed and ground, and then dried and calcined in sequence to obtain ZnCo2O4-Y2O3-CeO2;

[0009] The catalyst was obtained by reducing the ZnCo2O4-Y2O3-CeO2 under a hydrogen atmosphere.

[0010] The second technical solution of the present invention is a catalyst for low-temperature methanation of CO2 prepared by the above preparation method.

[0011] The third technical solution of the present invention is the application of the above-mentioned catalyst in the catalytic hydrogenation of CO2 to methane.

[0012] The present invention discloses the following technical effects:

[0013] (1) This invention utilizes ultrasound-assisted preparation of CeO2, which significantly shortens the precipitation reaction time. Compared with the traditional precipitation method, the reaction time can be reduced by 30%-50%, greatly improving production efficiency. The prepared CeO2 particles exhibit uniform nanoscale size with an average particle size between 10-30 nm, narrow particle size distribution, and good particle dispersion. This is attributed to the dispersion and regulation effect of ultrasound, which gives the material a larger specific surface area and more active sites, thus demonstrating excellent performance in catalysis, photocatalysis, and other applications.

[0014] (2) This invention utilizes microwave radiation to prepare ZnCo2O4, which significantly shortens the reaction time. Compared with the traditional hydrothermal method, the reaction time can be shortened by 1 / 2 to 2 / 3, greatly improving production efficiency. The prepared ZnCo2O4 particles exhibit uniform nanoscale size, narrow particle size distribution, and an average particle size between 20-50 nm, effectively avoiding agglomeration. This is due to the precise nucleation and growth control under microwave assistance, which increases the specific surface area of ​​the material and significantly improves its electrochemical and catalytic performance.

[0015] (3) The catalyst of this invention has the advantages of low temperature for the hydrogenation and methanation of CO2, thus avoiding carbon deposition, sintering and agglomeration of the catalyst. On the other hand, the catalyst has a CO2 conversion rate and excellent methane selectivity that are comparable to traditional nickel-based catalysts. Therefore, the invention and implementation of this catalyst can capture CO2 emitted by traditional chemical enterprises and couple it with green hydrogen to realize the resource utilization of CO2, which has high environmental and economic benefits.

[0016] (4) The catalyst of the present invention has a low temperature for catalytic CO2 methanation reaction, which avoids carbon deposition, sintering and agglomeration of the catalyst. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The XRD characterization results are those of the catalyst obtained in Example 1;

[0019] Figure 2 This is a scanning electron microscope image of the catalyst sample obtained in Example 1. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0021] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0022] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0023] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0024] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0025] The first aspect of this invention provides a method for preparing a catalyst for low-temperature methanation of CO2, comprising the following steps:

[0026] CeO2, ZnCo2O4, yttrium nitrate and particle size modifier were mixed and ground, and then dried and calcined in sequence to obtain ZnCo2O4-Y2O3-CeO2;

[0027] The catalyst was obtained by reducing the ZnCo2O4-Y2O3-CeO2 under a hydrogen atmosphere.

[0028] In a preferred embodiment of the present invention, the method for preparing CeO2 is as follows: a precipitant solution is added to a cerium nitrate solution to carry out a precipitation reaction, the precipitate is collected, and then the precipitate is washed, dried, and calcined in sequence to obtain CeO2.

[0029] In this invention, the specific steps for adding a precipitant solution to a cerium nitrate solution to carry out a precipitation reaction are as follows: under ultrasonic conditions, ammonium carbonate solution is added dropwise to the cerium nitrate solution. After the addition is complete, ultrasonic treatment is continued for 15-30 minutes to ensure that the precipitation reaction is complete. The frequency of the ultrasonic treatment is 20-50 kHz and the power is 100-300 W. The dropwise addition rate is 1-3 mL / min.

[0030] In a preferred embodiment of the present invention, the precipitant solvent is an ammonium carbonate solution; the concentration of the ammonium carbonate solution is 0.5-1.5 mol / L; the concentration of the cerium nitrate solution is 0.2-0.6 mol / L; the calcination heating rate is 0.2-2℃ / min, the temperature is 400-600℃, and the time is 2-4 h. The present invention does not impose a special limitation on the amount of ammonium carbonate solution used; any amount well-known to those skilled in the art that allows the cerium nitrate solution to fully undergo the precipitation reaction can be selected.

[0031] In a preferred embodiment of the present invention, the method for preparing ZnCo2O4 includes the following steps:

[0032] Zinc salt, cobalt salt and precipitant are reacted in water to produce a precursor suspension;

[0033] The precursor suspension was subjected to a microwave hydrothermal reaction. After the reaction, the precipitate was collected and then washed, dried, and calcined in sequence.

[0034] In a preferred embodiment of the present invention, the zinc salt is zinc nitrate, zinc chloride, or zinc sulfate, the cobalt salt is cobalt nitrate, cobalt chloride, or cobalt sulfate, and the precipitant is NaOH; the molar ratio of Zn in the zinc salt to Co in the cobalt salt is 1:2; the parameters of the microwave hydrothermal reaction are: microwave power 300-600W, temperature 120-180℃, time 30-90min; the heating rate of the calcination is 0.2-2℃, the temperature is 500-750℃, and the time is 2-4h. The present invention does not impose any special limitation on the amount of sodium hydroxide used; any amount well-known to those skilled in the art that allows the zinc salt and cobalt salt to fully undergo the precipitation reaction can be selected.

[0035] In this invention, the specific steps for precipitating zinc salt, cobalt salt, and a precipitant in water to obtain a precursor suspension are as follows:

[0036] Zinc salt and cobalt salt are dissolved in water to obtain a mixed salt solution;

[0037] After the mixed salt solution is added dropwise to the aqueous solution of sodium hydroxide under stirring conditions, stirring is continued for 15-30 minutes after the addition is complete to ensure that the solution is fully mixed and homogeneous, forming a precursor suspension.

[0038] In a preferred embodiment of the present invention, the particle size regulator is a mixture of citric acid and ethylenediamine in a mass ratio of 1-5:1; the mass ratio of the particle size regulator to ZnCo2O4 is 0.5-1:1; and the mass ratio of ZnCo2O4, Y2O3 and CeO2 in ZnCo2O4-Y2O3-CeO2 is 50-100:1-10:100.

[0039] The mixture of citric acid and ethylenediamine, as a particle size modifier, possesses a unique combination of chemical structures and properties. Their interaction allows for precise adsorption onto the surface of target particles. Through various mechanisms such as steric hindrance and charge interaction, it effectively prevents excessive particle aggregation and growth, thereby achieving fine control over particle size. This ensures that the product's particle size distribution remains within a narrow, desirable range, which is crucial for the preparation of high-end materials requiring extremely high particle size precision.

[0040] In this invention, CeO2, ZnCo2O4, yttrium nitrate, and a particle size modifier are mixed and then ground. The specific steps are as follows:

[0041] Yttrium nitrate was dissolved in water to prepare a 0.1-0.3 mol / L yttrium nitrate solution, which was then mixed with CeO2, ZnCo2O4 and a particle size modifier before grinding. The grinding media used in the grinding process were zirconia balls.

[0042] In a preferred embodiment of the present invention, the calcination heating rate is 0.2-2℃, the temperature is 300-500℃, and the time is 3-6h; the conditions for reducing ZnCo2O4-Y2O3-CeO2 in a hydrogen atmosphere are: H2 atmosphere, pressure 0.1-2MPa, temperature 330-400℃, and space velocity 400-2000h. -1 .

[0043] A second aspect of the present invention provides a catalyst for low-temperature methanation of CO2 prepared by the above-described preparation method.

[0044] A third aspect of the present invention provides the application of the above-mentioned catalyst in the catalytic hydrogenation of CO2 to methane.

[0045] In a preferred embodiment of the present invention, the catalyst is used in the catalytic hydrogenation of CO2 to methane under the following reaction conditions: an H2 / CO2 volume flow rate ratio of 3.0-4.5, a reactant gas pressure of 0.1-2 MPa, a reaction temperature of 200-300°C, and a space velocity of 5000-20000 h⁻¹. -1 .

[0046] In this invention, the ZnCo2O4 dispersed on CeO2 in the catalyst is partially reduced during the reduction process, yielding the main active component, a CoZn alloy species. The CoZn alloy precipitates uniformly from the ZnCo2O4 and forms close contact with CeO2, thereby enhancing the Co-CeO2 interaction within the catalyst. Furthermore, this invention allows for the adjustment of the reduction degree of ZnCo2O4 by controlling the reduction temperature, thereby regulating the Co content in the main active component, the Co species. 2+ With Co 0 The ratio of Co in the catalyst is thus adjusted to achieve the desired concentration. 2+ Precise control of the ratio can alter the adsorption strength of the intermediate product CO*, preventing the formation of byproducts and achieving high methane selectivity. Furthermore, by controlling the reduction conditions, the contact mode between the main active component CoZn species and CeO2 (Co-Zn-O-Ce) can be regulated, thereby controlling surface oxygen vacancies and thus regulating the adsorption state of the intermediate product to enhance CO2 activation.

[0047] In the catalyst system of this invention, CeO2 possesses a certain degree of reducibility, enabling it to synergistically interact with the supported active component, Co species. This regulates the electronic structure and dispersion state of the active component, facilitating its adsorption and activation of reactants and enhancing the performance of the low-temperature methanation reaction of CO2. Regarding the physical properties of the modified Co-based catalyst, doping with an appropriate amount of CeO2 increases oxygen vacancies, enhancing the Co-CeO2 interaction within the catalyst by anchoring Co species. This prevents sintering and agglomeration of active sites under reaction conditions, improving catalyst stability and meeting the requirements for long-term industrial applications. Simultaneously, the abundant oxygen vacancies within CeO2 itself also promote CO2 adsorption and activation.

[0048] The acidity or basicity of a catalyst affects the adsorption and reaction behavior of reactants and active components on its surface. In the catalyst system of this invention, basic Y₂O₃ acts as a promoter, which is beneficial for the adsorption and activation of CO₂, thereby promoting the low-temperature methanation reaction. Simultaneously, it exhibits good anti-carbon deposition performance in the low-temperature methanation reaction of CO₂. The synergistic effect among the three oxides significantly improves the catalytic activity of the catalyst, enabling efficient catalytic conversion of CO₂ at low temperatures without the addition of precious metals. It possesses excellent high selectivity, low-temperature catalytic activity, and long service life.

[0049] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0050] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0051] Example 1

[0052] Preparation of CeO2: Cerium nitrate (Ce(NO3)2·6H2O) was dissolved in deionized water to prepare a 0.2 mol / L cerium nitrate solution (100 mL); ammonium carbonate ((NH4)2CO3) was dissolved in deionized water to prepare a 0.5 mol / L ammonium carbonate solution (100 mL); the prepared cerium nitrate solution was placed in the reaction vessel of an ultrasonic generator, the ultrasonic frequency was turned on, and the power was set to 20 kHz and 100 W; under the action of ultrasound, the ammonium carbonate solution was added dropwise at a rate of 1 mL / min to ensure thorough mixing and precipitation. Precipitation reaction was initiated; after the addition was complete, ultrasonic treatment was continued for 15 minutes to ensure complete precipitation; after the precipitation reaction was completed, ultrasonication was stopped, and the reaction mixture was filtered through a vacuum filter to collect the precipitate; the precipitate was washed with deionized water until the conductivity of the filtrate was below 5 μS / cm to remove impurity ions and ensure product purity; the washed precipitate was placed in a vacuum drying oven and dried at 60℃ for 24 hours to obtain dried precursor powder; the precursor powder was transferred to a muffle furnace for calcination at 400℃ for 4 hours, with the heating rate controlled at 0.2℃ / min. During this process, the precursor underwent thermal decomposition, transforming into high-purity, highly active CeO2;

[0053] Preparation of ZnCo2O4: Zinc nitrate (NO3)2·6H2O and cobalt nitrate (Co(NO3)2·6H2O) were weighed and dissolved in deionized water according to a precise Zn:Co molar ratio of 1:2 to prepare a mixed metal salt solution with a concentration controlled at 0.1 mol / L (100 mL). Sodium hydroxide (NaOH) was weighed as a precipitant and dissolved in deionized water to prepare a 1 mol / L alkaline solution (100 mL). The mixed metal salt solution was added dropwise to the alkaline solution with continuous magnetic stirring during the addition. After the addition was complete, stirring was continued for 15 min to ensure thorough mixing and the formation of a precursor suspension. The precursor was then... The suspension was transferred to a microwave-assisted hydrothermal reactor, with the reactor filling rate controlled at 60%. The microwave power was set to 300W, the reaction temperature to 120℃, and the reaction time to 30min. Under these conditions, the microwave-assisted hydrothermal reaction was carried out. After the microwave-assisted hydrothermal reaction was completed, the reactor was naturally cooled to room temperature. The product in the reactor was washed three times alternately with deionized water and anhydrous ethanol, and the precipitate was collected by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 60℃ for 24h to obtain ZnCo2O4 precursor powder. The precursor powder was transferred to a muffle furnace for calcination at 500℃ for 4h, with the heating rate controlled at 0.2℃ / min.

[0054] Preparation of ZnCo2O4-Y2O3-CeO2:

[0055] The ZnCo2O4 and CeO2 obtained in the above steps were placed in an agate mortar and ground for 30 minutes to refine and evenly disperse the particles. The particles were then passed through a 300-mesh sieve to obtain the processed ZnCo2O4 powder and CeO2 powder. According to the mass ratio of ZnCo2O4, Y2O3, and CeO2 in ZnCo2O4-Y2O3-CeO2 = 50.5:1:100, 5.05 g of ZnCo2O4 powder, 10.0 g of CeO2 powder, 0.339 g of yttrium nitrate hexahydrate, and citric acid-ethylenediamine (the mass ratio of citric acid to ethylenediamine...) were weighed. 2.7 g of a 1:1 mixture was placed in the grinding jar of a planetary ball mill, with zirconia balls added as the grinding medium at a ball-to-material ratio of 20:1. The ball mill was set to 300 rpm and milled for 4 hours to obtain a mixed slurry. The slurry was then transferred to a vacuum drying oven and dried at 60°C and 0.05 MPa for 24 hours to remove moisture, yielding a dried mixed powder. The dried powder was then placed in a tube furnace and calcined at 300°C at a heating rate of 0.2°C / min for 6 hours under inert gas protection to promote the oxidation of Y... 3+ It undergoes a solid-state reaction with ZnCo₂O₄ and CeO₂ to yield ZnCo₂O₄-Y₂O₃-CeO₂. (The rest of the text appears to be a continuation of the previous sentence and can be left as is.) Figure 2 It can be seen that the average particle size of ZnCo2O4-Y2O3-CeO2 particles is 30 nm, and the specific surface area is 110 m². 2 / g.

[0056] ZnCo2O4-Y2O3-CeO2 was reduced in a H2 atmosphere under the following conditions: H2 atmosphere, pressure 0.1 MPa, temperature 330℃, and space velocity 400 h⁻¹. -1 The final catalyst was obtained.

[0057] The catalyst prepared above was subjected to performance testing in a fixed-bed reactor under the following reaction conditions: H2 / CO2 volumetric flow rate ratio of 3.0, reactant gas pressure of 0.1 MPa, reaction temperature of 220 °C, and space velocity of 10000 h⁻¹. -1 Under these reaction conditions, the CO2 conversion rate was 75.2%, and the CH4 selectivity was 98.3%.

[0058] Example 2

[0059] CeO2 preparation: Cerium nitrate was dissolved in deionized water to prepare a 0.4 mol / L cerium nitrate solution (100 mL); ammonium carbonate was dissolved in deionized water to prepare a 1.0 mol / L ammonium carbonate solution (100 mL); the prepared cerium nitrate solution was placed in the reaction vessel of an ultrasonic generator, the ultrasonic frequency was turned on, and the power was set to 30 kHz and 200 W; under ultrasonic action, ammonium carbonate solution was added dropwise at a rate controlled at 2 mL / min to ensure thorough mixing and precipitation; after the addition was complete... Continue ultrasonic treatment for 20 minutes to ensure complete precipitation reaction. After precipitation reaction, stop ultrasonication and filter the reaction mixture through a vacuum filter to collect the precipitate. Wash the precipitate with deionized water until the conductivity of the filtrate is below 5 μS / cm to remove impurity ions and ensure product purity. Place the washed precipitate in a vacuum drying oven and dry at 70℃ for 18 hours to obtain dried precursor powder. Transfer the precursor powder to a muffle furnace for calcination at 500℃ for 3 hours, with a heating rate controlled at 1℃ / min. During this process, the precursor undergoes thermal decomposition, transforming into high-purity, highly active CeO2.

[0060] Preparation of ZnCo2O4: Zinc nitrate and cobalt nitrate were weighed and dissolved in deionized water at a precise Zn:Co molar ratio of 1:2 to prepare a mixed metal salt solution with a concentration controlled at 0.3 mol / L (100 mL). Sodium hydroxide was weighed as a precipitant and dissolved in deionized water to prepare a 2 mol / L alkaline solution (100 mL). The mixed metal salt solution was added dropwise to the alkaline solution with continuous magnetic stirring during the addition. After the addition was complete, stirring was continued for 20 min to ensure thorough mixing and the formation of a precursor suspension. The precursor suspension was then transferred to a microwave hydrothermal reactor. The reactor was filled to 70% capacity. The microwave power was set to 500W, the reaction temperature to 160℃, and the reaction time to 60min. Under these conditions, a microwave-assisted hydrothermal reaction was carried out. After the microwave hydrothermal reaction was completed, the reactor was naturally cooled to room temperature. The product in the reactor was washed four times alternately with deionized water and anhydrous ethanol. The precipitate was collected by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 70℃ for 18h to obtain ZnCo2O4 precursor powder. The precursor powder was transferred to a muffle furnace for calcination at 650℃ for 3h, with a heating rate controlled at 1℃ / min.

[0061] Preparation of ZnCo2O4-Y2O3-CeO2:

[0062] The ZnCo2O4 and CeO2 obtained in the above steps were placed in an agate mortar and ground for 45 minutes to refine and evenly disperse the particles. The particles were then passed through a 200-mesh sieve to obtain the treated ZnCo2O4 powder and CeO2 powder. According to the mass ratio of ZnCo2O4, Y2O3, and CeO2 in ZnCo2O4-Y2O3-CeO2 = 75:5:100, 7.5g of ZnCo2O4 powder, 10.0g of CeO2 powder, 1.696g of yttrium nitrate, and citric acid-ethylenediamine (citric acid to ethylenediamine mass ratio) were weighed. 7.5 g of a 3:1 mixture was placed in the grinding jar of a planetary ball mill, with zirconia balls added as the grinding medium at a ball-to-material ratio of 25:1. The ball mill was set to 400 rpm and milled for 3 hours to obtain a mixed slurry. The slurry was then transferred to a vacuum drying oven and dried at 70°C and 0.08 MPa for 18 hours to remove moisture, yielding a dried mixed powder. The dried powder was then placed in a tube furnace and calcined at 400°C at a heating rate of 1°C / min for 5 hours under inert gas protection to promote the oxidation of Y... 3+ A solid-state reaction was conducted with ZnCo₂O₄ and CeO₂ to yield ZnCo₂O₄-Y₂O₃-CeO₂. The average particle size of ZnCo₂O₄-Y₂O₃-CeO₂ particles was 18.2 nm, and the specific surface area was 130 m². 2 / g.

[0063] ZnCo2O4-Y2O3-CeO2 was reduced in an H2 atmosphere under the following conditions: H2 atmosphere, pressure 1 MPa, temperature 360℃, and space velocity 1000 h⁻¹. -1 The final catalyst was obtained.

[0064] The catalyst prepared above was subjected to performance testing in a fixed-bed reactor. The reaction conditions were: H2 / CO2 ratio of 4.0, reactant gas pressure of 1 MPa, reaction temperature of 250 °C, and space velocity of 15000 h⁻¹. -1 Under these reaction conditions, the CO2 conversion rate was 81.5%, and the CH4 selectivity was 98.2%.

[0065] Example 3

[0066] CeO2 Preparation: Cerium nitrate was dissolved in deionized water to prepare a 0.6 mol / L cerium nitrate solution (100 mL); ammonium carbonate was dissolved in deionized water to prepare a 1.5 mol / L ammonium carbonate solution (100 mL); the prepared cerium nitrate solution was placed in the reaction vessel of an ultrasonic generator, the ultrasonic frequency was turned on, and the power was set to 50 kHz and 300 W; under ultrasonic action, ammonium carbonate solution was added dropwise at a rate controlled at 3 mL / min to ensure thorough mixing and precipitation; after the addition was complete... Continue ultrasonic treatment for 30 minutes to ensure complete precipitation reaction. After precipitation reaction, stop ultrasonication and filter the reaction mixture through a vacuum filter to collect the precipitate. Wash the precipitate with deionized water until the conductivity of the filtrate is below 5 μS / cm to remove impurity ions and ensure product purity. Place the washed precipitate in a vacuum drying oven and dry at 80℃ for 124 hours to obtain dried precursor powder. Transfer the precursor powder to a muffle furnace for calcination at 600℃ for 4 hours, with a heating rate controlled at 2℃ / min. During this process, the precursor undergoes thermal decomposition, transforming into high-purity, highly active CeO2.

[0067] Preparation of ZnCo₂O₄: Zinc nitrate and cobalt nitrate were weighed and dissolved in deionized water at a precise Zn:Co molar ratio of 1:2 to prepare a mixed metal salt solution with a concentration controlled at 0.5 mol / L (100 mL). Sodium hydroxide was weighed as a precipitant and dissolved in deionized water to prepare a 3 mol / L alkaline solution (100 mL). The mixed metal salt solution was added dropwise to the alkaline solution with continuous magnetic stirring during the addition. After the addition was complete, stirring was continued for 30 min to ensure thorough mixing and the formation of a precursor suspension. The precursor suspension was then transferred to a microwave hydrothermal reactor. The reactor was filled to 80% capacity. The microwave power was set to 600W, the reaction temperature to 180℃, and the reaction time to 30min. Under these conditions, a microwave-assisted hydrothermal reaction was carried out. After the microwave hydrothermal reaction was completed, the reactor was naturally cooled to room temperature. The product in the reactor was washed five times alternately with deionized water and anhydrous ethanol. The precipitate was collected by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 80℃ for 12h to obtain ZnCo2O4 precursor powder. The precursor powder was transferred to a muffle furnace for calcination at 750℃ for 2h, with a heating rate controlled at 2℃ / min.

[0068] Preparation of ZnCo2O4-Y2O3-CeO2:

[0069] The ZnCo2O4 and CeO2 obtained in the above steps were placed in an agate mortar and ground for 60 minutes to refine and evenly disperse the particles. The particles were then passed through a 120-mesh sieve to obtain the processed ZnCo2O4 powder and CeO2 powder. According to the mass ratio of ZnCo2O4, Y2O3, and CeO2 in ZnCo2O4-Y2O3-CeO2 = 99:10:100, 9.9 g of ZnCo2O4 powder, 10.0 g of CeO2 powder, 3.392 g of yttrium nitrate, and citric acid-ethylenediamine (the mass ratio of citric acid to ethylenediamine...) were weighed. 9.9 g of a mixture (5:1 ratio) was placed in the grinding jar of a planetary ball mill, with zirconia balls added as grinding media at a ball-to-material ratio of 30:1. The ball mill was set to 500 rpm and milled for 2 hours to obtain a mixed slurry. The slurry was then transferred to a vacuum drying oven and dried at 70°C and 0.05 MPa for 12 hours to remove moisture, yielding a dried mixed powder. The dried powder was then placed in a tube furnace and calcined at 500°C at a heating rate of 2°C / min for 3 hours under inert gas protection to promote the oxidation of Y... 3+ A solid-state reaction was conducted with ZnCo₂O₄ and CeO₂ to yield ZnCo₂O₄-Y₂O₃-CeO₂. The average particle size of ZnCo₂O₄-Y₂O₃-CeO₂ particles was 22 nm, and the specific surface area was 117 m². 2 / g.

[0070] ZnCo2O4-Y2O3-CeO2 was reduced in an H2 atmosphere under the following conditions: H2 atmosphere, pressure 2 MPa, temperature 400℃, and space velocity 2000 h⁻¹. -1 .

[0071] The catalyst prepared above was subjected to performance testing in a fixed-bed reactor. The reaction conditions were: H2 / CO2 ratio of 4.5, reactant gas pressure of 2 MPa, reaction temperature of 250 °C, and space velocity of 15000 h⁻¹. -1 Under these reaction conditions, the CO2 conversion rate was 89.3%, and the CH4 selectivity was 98.8%.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst for low-temperature methanation of CO2, characterized in that, Includes the following steps: CeO2, ZnCo2O4, yttrium nitrate and particle size modifier were mixed and ground, and then dried and calcined in sequence to obtain ZnCo2O4-Y2O3-CeO2; The catalyst was obtained by reducing the ZnCo2O4-Y2O3-CeO2 under a hydrogen atmosphere. The particle size regulator is a mixture of citric acid and ethylenediamine in a mass ratio of 1-5:1; the mass ratio of the particle size regulator to ZnCo2O4 is 0.5-1:1; the mass ratio of ZnCo2O4, Y2O3 and CeO2 in ZnCo2O4-Y2O3-CeO2 is 50~100:1~10:

100.

2. The preparation method according to claim 1, characterized in that, The method for preparing CeO2 is as follows: a precipitant solution is added to a cerium nitrate solution to carry out a precipitation reaction, the precipitate is collected, and then the precipitate is washed, dried and calcined in sequence to obtain CeO2.

3. The preparation method according to claim 2, characterized in that, The precipitant solvent is an ammonium carbonate solution; the concentration of the ammonium carbonate solution is 0.5-1.5 mol / L; the concentration of the cerium nitrate solution is 0.2-0.6 mol / L; the calcination heating rate is 0.2-2℃ / min, the temperature is 400-600℃, and the time is 2-4h.

4. The preparation method according to claim 1, characterized in that, The preparation method of ZnCo2O4 includes the following steps: Zinc salt, cobalt salt and precipitant are reacted in water to produce a precursor suspension; The precursor suspension was subjected to a microwave hydrothermal reaction. After the reaction, the precipitate was collected and then washed, dried, and calcined in sequence.

5. The preparation method according to claim 4, characterized in that, The zinc salt is zinc nitrate, zinc chloride, or zinc sulfate; the cobalt salt is cobalt nitrate, cobalt chloride, or cobalt sulfate; and the precipitant is NaOH. The molar ratio of Zn in the zinc salt to Co in the cobalt salt is 1:

2. The parameters of the microwave hydrothermal reaction are: microwave power 300-600W, temperature 120-180℃, and time 30-90min. The heating rate of the calcination is 0.2-2℃, the temperature is 500-750℃, and the time is 2-4h.

6. The preparation method according to claim 1, characterized in that, The calcination process involves a heating rate of 0.2-2℃, a temperature of 300-500℃, and a time of 3-6 hours. The conditions for reducing ZnCo2O4-Y2O3-CeO2 under a hydrogen atmosphere are: H2 atmosphere, pressure 0.1-2 MPa, temperature 330-400℃, and space velocity 400-2000 h⁻¹. -1 .

7. A catalyst for low-temperature methanation of CO2 prepared by the preparation method according to any one of claims 1 to 6.

8. The use of the catalyst of claim 7 in the catalytic hydrogenation of CO2 to methane.

9. The application according to claim 8, characterized in that, In the catalytic hydrogenation of CO2 to methane, the catalyst is used under the following reaction conditions: an H2 / CO2 volume flow rate ratio of 3.0-5.0, a reactant gas pressure of 0.1-2 MPa, a reaction temperature of 200-300℃, and a space velocity of 5000-20000 h⁻¹. -1 .

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