Catalyst for low-temperature methanation of CO2 as well as preparation method and application of catalyst

Abstract

The invention provides a catalyst for low-temperature methanation of CO2 as well as a preparation method and application of the catalyst, and belongs to the technical field of catalysts. The preparation method of the catalyst comprises the following steps: mixing CeO2, ZnCo2O4, yttrium nitrate and a particle size regulator, grinding, and sequentially drying and calcining to obtain ZnCo2O4-Y2O3-CeO2; and the ZnCo2O4-Y2O3-CeO2 is subjected to reduction in a hydrogen atmosphere, such that the catalyst is obtained. On one hand, the catalyst disclosed by the invention is low in reaction temperature for catalyzing CO2 hydrogenation methanation, so that carbon deposition, sintering and agglomeration of the catalyst are avoided; on the other hand, the catalyst has CO2 conversion rate which is not inferior to that of a traditional nickel-based catalyst and excellent methane selectivity. Therefore, CO2 discharged by traditional chemical enterprises can be captured and subjected to a green hydrogen coupling reaction through the invention, implementation and utilization of the catalyst, and resource utilization of CO2 is achieved.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and in particular to a catalyst for low-temperature methanation of CO2, a preparation method thereof, and an application thereof. Background Art

[0002] The combustion of fossil fuels is the dominant factor driving the dramatic increase in greenhouse gas emissions, with CO₂ accounting for nearly three-quarters of total greenhouse gas emissions. This massive CO₂ emission has triggered a series of chain reactions, resulting in global warming, ocean acidification, and numerous negative ecological and environmental impacts. Furthermore, the current energy supply and demand imbalance is prominent, and energy and ecological issues are intertwined, creating an extremely serious situation. CO₂'s widespread availability, low cost, strong renewability, and non-toxicity make it an ideal carbon-based feedstock for chemical synthesis, suitable for the production of high-value-added chemicals such as methane.

[0003] The stable thermodynamic properties and significant kinetic inertness of CO2 are the key obstacles to its direct conversion to methane. As a typical linear symmetrical triatomic molecule, it contains 16 valence electrons, each atom has ns and np orbitals, and the central C atom forms a bond with the O atom via an sp hybrid orbital. Under this configuration, the CO2 molecule has multiple potential activation sites. The C atom has Lewis acid properties and can act as an electrophilic center, and the O atom has Lewis base properties and can act as a nucleophilic center. Compared with molecules with isoelectronic configurations, the first ionization energy of CO2 of 13.79eV makes it difficult to convert to CO2 + , and the low-energy empty orbital (2π u ) and 38eV electron affinity can make it easy to form CO2 - Therefore, by inputting electrons in an appropriate manner or seizing electrons from other molecules during the reaction, it is possible to overcome the inertness of CO2 and achieve its activation and conversion.

[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 precious metal catalysts. Due to their structural characteristics, these catalysts require relatively high reaction temperatures to proceed, making them susceptible to active component migration, sintering, and Ostwald ripening, which can lead to catalyst inactivity. Furthermore, the higher the reaction temperature, the more severe the carbon deposition during the reaction. To address these challenges, strategies such as adding precious metal additives, carefully constructing confined structures, and strengthening the interaction between the metal and the support are often required to lower the reaction temperature or suppress catalyst sintering and deactivation. Furthermore, due to thermodynamic factors and the intrinsic activity of the active centers of existing catalysts, the CO2 hydrogenation reaction temperature of current catalysts remains relatively high. Therefore, the development of catalysts for low-temperature CO2 methanation is crucial to promoting the industrialization of the CO2 hydrogenation to methane reaction. Summary of the Invention

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

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

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

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

[0009] The ZnCo2O4-Y2O3-CeO2 is reduced under a hydrogen atmosphere to obtain the catalyst.

[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 an application of the above catalyst in catalytic CO2 hydrogenation to methane.

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

[0013] (1) The present invention utilizes ultrasound to assist in the preparation of CeO2, significantly shortening 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 10-30nm, a narrow particle size distribution, and good particle dispersion. This is attributed to the dispersing and regulating effects of ultrasound, which gives the material a larger specific surface area and more active sites, thereby exhibiting excellent performance in applications such as catalysis and photocatalysis.

[0014] (2) The present 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 / 2-2 / 3, greatly improving production efficiency. The prepared ZnCo2O4 particles exhibit uniform nanoscale size, narrow particle size distribution, and an average particle size between 20-50nm, 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 the electrochemical and catalytic properties.

[0015] (3) The catalyst of the present invention catalyzes the CO2 hydrogenation and methanation reaction at a low temperature, thus avoiding carbon deposition, sintering, and agglomeration of the catalyst. Furthermore, the catalyst has a CO2 conversion rate comparable to that of conventional nickel-based catalysts and excellent methane selectivity. Therefore, the invention and implementation of the catalyst can capture CO2 emitted by conventional chemical companies and couple it with green hydrogen to achieve resource utilization of CO2, thus achieving high environmental and economic benefits.

[0016] (4) The catalyst of the present invention catalyzes the CO2 methanation reaction at a low temperature, thereby avoiding carbon deposition, sintering and agglomeration of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

[0019] Figure 2 This is a scanning electron microscope photograph of the catalyst sample obtained in Example 1. DETAILED DESCRIPTION

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting 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 terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0022] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0023] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

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

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

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

[0027] The ZnCo2O4-Y2O3-CeO2 is reduced under a hydrogen atmosphere to obtain the catalyst.

[0028] In a preferred embodiment of the present invention, the preparation method of CeO2 is: adding a precipitant solution to a cerium nitrate solution to carry out a precipitation reaction, collecting the precipitate, and then washing, drying, and calcining the precipitate in sequence to obtain the CeO2.

[0029] In the present invention, the specific steps of adding a precipitant solution to a cerium nitrate solution for a precipitation reaction are as follows: under ultrasonic conditions, an ammonium carbonate solution is added dropwise to the cerium nitrate solution; after the addition is completed, ultrasonic treatment is continued for 15-30 minutes to ensure that the precipitation reaction is complete; the frequency of the ultrasound is 20-50kHz, the power is 100-300W; and the rate of the addition is 1-3mL / 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; and the calcination is performed at a heating rate of 0.2-2°C / min, a temperature of 400-600°C, and a time of 2-4 hours. The present invention does not impose any particular limitation on the amount of the ammonium carbonate solution used; an amount 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 preparation method of ZnCo2O4 comprises the following steps:

[0032] The zinc salt, the cobalt salt and the precipitant are subjected to precipitation reaction in water to obtain a precursor suspension;

[0033] The precursor suspension is subjected to microwave hydrothermal reaction, and a precipitate is collected after the reaction, and the precipitate is 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; the precipitant is NaOH; the molar ratio of Zn in the zinc salt to Co in the cobalt salt is 1:2; the microwave hydrothermal reaction parameters are: microwave power 300-600W, temperature 120-180°C, time 30-90 minutes; the calcination heating rate is 0.2-2°C, temperature 500-750°C, and time 2-4 hours. The present invention does not impose any particular limitation on the amount of sodium hydroxide used; an amount familiar to those skilled in the art that allows sufficient precipitation reaction of the zinc salt and the cobalt salt can be selected.

[0035] In the present invention, the zinc salt, the cobalt salt and the precipitant are subjected to a precipitation reaction in water to obtain a precursor suspension. The specific steps are:

[0036] dissolving zinc salt and cobalt salt in water to obtain a mixed salt solution;

[0037] The mixed salt solution is added dropwise to the aqueous solution of sodium hydroxide under stirring, and stirring is continued for 15-30 minutes after the addition is completed to ensure that the solution is fully mixed and uniform, thereby 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; the mass ratio of ZnCo2O4, Y2O3 and CeO2 in the ZnCo2O4-Y2O3-CeO2 is 50-100:1-10:100.

[0039] As a particle size regulator, a mixture of citric acid and ethylenediamine possesses a unique combination of chemical structure and properties. Their interaction enables precise adsorption onto the target particle surface. Through various mechanisms, such as steric hindrance and charge interaction, this effectively prevents excessive particle aggregation and growth, enabling precise control of particle size and ensuring a narrow, targeted particle size distribution. This is crucial for the preparation of high-end materials requiring extremely precise particle size.

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

[0041] Yttrium nitrate is dissolved in water to prepare a yttrium nitrate solution with a concentration of 0.1-0.3 mol / L, which is then mixed with CeO2, ZnCo2O4 and a particle size regulator and ground; the grinding medium in the grinding process is zirconia balls.

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

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

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

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

[0046] The ZnCo2O4 dispersed on CeO2 in the catalyst of the present invention will be partially reduced during the reduction process to obtain the main active component CoZn alloy species, and the CoZn alloy will be uniformly precipitated from ZnCo2O4 and in close contact with CeO2, thereby enhancing the Co-CeO2 interaction in the catalyst; at the same time, the present invention can also adjust the reduction degree of ZnCo2O4 by controlling the reduction temperature, thereby adjusting the Co in the main active component Co species. 2+ With Co 0 ratio, thereby achieving the Co 2+ The precise control of the ratio can change the adsorption strength of the intermediate product CO*, avoid the formation of by-products, and achieve high methane selectivity. In addition, by controlling the reduction conditions, the contact mode between the main active component CoZn species and CeO2 can be regulated (Co-Zn-O-Ce), thereby regulating the surface oxygen vacancies, thereby achieving the control of the adsorption state of the intermediate product and enhancing the activation ability of CO2.

[0047] In the catalyst system of the present invention, CeO2 has a certain degree of reducibility and can produce a synergistic effect with the loaded active component Co species, regulating the electronic structure and dispersion state of the active component, facilitating the adsorption and activation of the active component on the reactants, and improving the performance of the CO2 low-temperature methanation reaction. In terms of the physical properties of the modified Co-based catalyst, doping with an appropriate amount of CeO2 helps increase oxygen vacancies. By anchoring the Co species, the Co-CeO2 interaction in the catalyst is enhanced, avoiding sintering and agglomeration of active sites under reaction conditions, and improving the stability of the catalyst to meet the needs of long-term industrial application. At the same time, the abundant oxygen vacancies in CeO2 itself also facilitate the adsorption and activation of CO2.

[0048] The acidity or alkalinity of a catalyst affects the adsorption and reaction behavior of reactants and active components on its surface. In the catalyst system of the present invention, alkaline Y2O3 acts as a coagent, facilitating the adsorption and activation of CO2, thereby promoting low-temperature methanation reactions. The catalyst also exhibits excellent resistance to carbon deposition during low-temperature CO2 methanation. The synergistic effect of the three oxides significantly enhances the catalyst's catalytic activity, enabling efficient catalytic conversion of CO2 at low temperatures without the addition of precious metals. The catalyst exhibits excellent selectivity, low-temperature catalytic activity, and a long service life.

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

[0050] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0051] Example 1

[0052] Preparation of CeO2: Dissolve cerium nitrate Ce(NO3)2·6H2O in deionized water to prepare a cerium nitrate solution (100 mL) with a concentration of 0.2 mol / L; dissolve ammonium carbonate ((NH4)2CO3) in deionized water to prepare an ammonium carbonate solution (100 mL) with a concentration of 0.5 mol / L; place the prepared cerium nitrate solution in a reaction vessel in an ultrasonic generator, turn on the ultrasound, set the ultrasonic frequency to 20 kHz, and the power to 100 W; under the action of ultrasound, add the ammonium carbonate solution dropwise at a rate of 1 mL / min to ensure that the solution is fully mixed and precipitated. Precipitation reaction; After the addition is completed, continue ultrasonic treatment for 15 minutes to ensure that the precipitation reaction is complete; After the precipitation reaction is completed, stop ultrasonication, filter the reaction mixture through a vacuum filtration device, and collect the precipitate; Wash the precipitate with deionized water until the conductivity of the filtrate is lower than 5μS / cm to remove impurity ions and ensure the purity of the product; Place the washed precipitate in a vacuum drying oven and dry it at 60°C for 24 hours to obtain a dry precursor powder; Transfer the precursor powder to a muffle furnace for calcination at a calcination temperature of 400°C and a calcination time of 4 hours. The heating rate is controlled at 0.2°C / min. During this process, the precursor undergoes thermal decomposition and is converted into high-purity, high-activity CeO2;

[0053] Preparation of ZnCo2O4: Weigh zinc nitrate (NO3)2·6H2O and cobalt nitrate Co(NO3)2·6H2O respectively, accurately mix them according to the Zn:Co molar ratio of 1:2, dissolve them in deionized water to prepare a mixed metal salt solution, and the solution concentration is controlled at 0.1 mol / L (100 mL); weigh sodium hydroxide NaOH as a precipitant, dissolve it in deionized water, and prepare an alkaline solution with a concentration of 1 mol / L (100 mL); add the above mixed metal salt solution dropwise to the alkaline solution, and continue magnetic stirring during the addition process. After the addition is completed, continue stirring for 15 minutes to fully mix the solution to form a precursor suspension; The suspension was transferred to a microwave hydrothermal reactor, and the filling degree of the reactor was controlled at 60%. The microwave power was set to 300 W, the reaction temperature was 120 ° C, and the reaction time was 30 min. 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 alternately with deionized water and anhydrous ethanol three times, and the precipitate was collected by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 60 ° C for 24 h to obtain a ZnCo2O4 precursor powder. The precursor powder was transferred to a muffle furnace for calcination at a temperature of 500 ° C, a calcination time of 4 h, and a heating rate of 0.2 ° C / min.

[0054] Preparation of ZnCo2O4-Y2O3-CeO2:

[0055] The ZnCo2O4 and CeO2 prepared in the above steps were placed in an agate mortar and ground for 30 min to refine the particles and disperse them evenly. The ZnCo2O4 and CeO2 powders were then sieved through a 300-mesh sieve to obtain treated ZnCo2O4 and CeO2 powders. 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 50.5:1:100. The mixture (ratio of 1:1) was placed in a ball mill of a planetary ball mill, and zirconia balls were placed as grinding media. The ball-to-material ratio was 20:1. The ball mill speed was set to 300 rpm and the ball mill was milled for 4 hours to obtain a mixed slurry. The mixed slurry was transferred to a vacuum drying oven and dried at 60 ° C and a vacuum degree of 0.05 MPa for 24 hours to remove moisture and obtain a dried mixed powder. The dried mixed powder was placed in a tube furnace and heated to 300 ° C at a heating rate of 0.2 ° C / min under inert gas protection. It was calcined for 6 hours to promote the formation of Y 3+ Solid phase reaction occurs with ZnCo2O4 and CeO2 to obtain ZnCo2O4-Y2O3-CeO2. Figure 2 It can be seen that the average particle size of ZnCo2O4-Y2O3-CeO2 particles is 30nm and the specific surface area is 110m 2 / g.

[0056] ZnCo2O4-Y2O3-CeO2 was reduced in H2 atmosphere. The reduction conditions were: H2 atmosphere, pressure of 0.1 MPa, temperature of 330℃, space velocity of 400h -1 . The final catalyst is obtained.

[0057] The performance test of the prepared catalyst was carried out in a fixed bed under the following reaction conditions: H2 / CO2 volume flow ratio of 3.0, reaction gas pressure of 0.1 MPa, reaction temperature of 220°C, and space velocity of 10000 h -1 Under the reaction conditions, the CO2 conversion rate was 75.2% and the CH4 selectivity was 98.3%.

[0058] Example 2

[0059] Preparation of CeO2: dissolve cerium nitrate in deionized water to prepare a cerium nitrate solution (100 mL) with a concentration of 0.4 mol / L; dissolve ammonium carbonate as a precipitant in deionized water to prepare an ammonium carbonate solution (100 mL) with a concentration of 1.0 mol / L; place the prepared cerium nitrate solution in a reaction vessel in an ultrasonic generator, turn on the ultrasound, set the ultrasonic frequency to 30 kHz, and the power to 200 W; under the action of ultrasound, add the ammonium carbonate solution dropwise at a rate of 2 mL / min to ensure that the solution is fully mixed and a precipitation reaction occurs; after the addition is completed, , continue ultrasonic treatment for 20 minutes to ensure that the precipitation reaction is complete; after the precipitation reaction is completed, stop ultrasonication, filter the reaction mixture through a vacuum filtration device, and collect the precipitate; wash the precipitate with deionized water until the conductivity of the filtrate is lower than 5μS / cm to remove impurity ions and ensure product purity; place the washed precipitate in a vacuum drying oven and dry it at 70°C for 18 hours to obtain a dry precursor powder; transfer the precursor powder to a muffle furnace for calcination at a calcination temperature of 500°C and a calcination time of 3 hours, with a heating rate controlled at 1°C / min. During this process, the precursor undergoes thermal decomposition and is converted into high-purity, high-activity CeO2;

[0060] Preparation of ZnCo2O4: Weigh zinc nitrate and cobalt nitrate respectively, accurately mix them according to the Zn:Co molar ratio of 1:2, dissolve them in deionized water to prepare a mixed metal salt solution, and control the solution concentration at 0.3 mol / L (100 mL); weigh sodium hydroxide as a precipitant, dissolve it in deionized water, and prepare an alkaline solution with a concentration of 2 mol / L (100 mL); add the above mixed metal salt solution dropwise to the alkaline solution, continue magnetic stirring during the addition process, and continue stirring for 20 minutes after the addition is completed to ensure that the solution is fully mixed to form a precursor suspension; transfer the precursor suspension to a microwave hydrothermal reaction The filling degree of the reactor was controlled at 70%. A microwave-assisted hydrothermal reaction was carried out under the following conditions: a microwave power of 500 W, a reaction temperature of 160° C., and a reaction time of 60 min. After the microwave hydrothermal reaction was completed, the reactor was naturally cooled to room temperature. The product in the reactor was washed alternately with deionized water and anhydrous ethanol four times, and the precipitate was collected by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 70° C. for 18 h to obtain a ZnCo2O4 precursor powder. The precursor powder was transferred to a muffle furnace for calcination at a temperature of 650° C. for 3 h, and a heating rate of 1° C. / min.

[0061] Preparation of ZnCo2O4-Y2O3-CeO2:

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

[0063] ZnCo2O4-Y2O3-CeO2 was reduced in H2 atmosphere. The reduction conditions were: H2 atmosphere, pressure of 1 MPa, temperature of 360℃, space velocity of 1000 h -1 . The final catalyst is obtained.

[0064] The performance of the prepared catalyst was tested in a fixed bed under the following reaction conditions: H2 / CO2 ratio of 4.0, reaction gas pressure of 1 MPa, reaction temperature of 250°C, and space velocity of 15000 h -1 Under the reaction conditions, the CO2 conversion rate was 81.5% and the CH4 selectivity was 98.2%.

[0065] Example 3

[0066] Preparation of CeO2: Dissolve cerium nitrate in deionized water to prepare a 0.6 mol / L cerium nitrate solution (100 mL); dissolve the precipitant ammonium carbonate in deionized water to prepare a 1.5 mol / L ammonium carbonate solution (100 mL); place the prepared cerium nitrate solution in a reaction vessel in an ultrasonic generator, turn on the ultrasound, set the ultrasonic frequency to 50 kHz, and the power to 300 W; under the action of ultrasound, add the ammonium carbonate solution dropwise at a rate of 3 mL / min to ensure that the solution is fully mixed and a precipitation reaction occurs; after the addition is completed, Continue ultrasonic treatment for 30 minutes to ensure that the precipitation reaction is complete; after the precipitation reaction is completed, stop ultrasonication, filter the reaction mixture through a vacuum filtration device, and collect the precipitate; wash the precipitate with deionized water until the conductivity of the filtrate is less than 5μS / cm to remove impurity ions and ensure product purity; place the washed precipitate in a vacuum drying oven and dry it at 80°C for 124 hours to obtain a dry precursor powder; transfer the precursor powder to a muffle furnace for calcination at a temperature of 600°C and a calcination time of 4 hours, with a heating rate controlled at 2°C / min. During this process, the precursor undergoes thermal decomposition and is converted into high-purity, high-activity CeO2;

[0067] Preparation of ZnCo2O4: Weigh zinc nitrate and cobalt nitrate respectively, accurately mix them according to the Zn:Co molar ratio of 1:2, dissolve them in deionized water to prepare a mixed metal salt solution, and control the solution concentration at 0.5 mol / L (100 mL); weigh sodium hydroxide as a precipitant, dissolve it in deionized water, and prepare an alkaline solution with a concentration of 3 mol / L (100 mL); add the above mixed metal salt solution dropwise to the alkaline solution, continue magnetic stirring during the addition process, and continue stirring for 30 minutes after the addition is completed to ensure that the solution is fully mixed to form a precursor suspension; transfer the precursor suspension to a microwave hydrothermal reaction The filling degree of the reactor was controlled at 80%. The microwave power was set to 600 W, the reaction temperature was set to 180° C., and the reaction time was set to 30 min. 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 alternately with deionized water and anhydrous ethanol five times, and the precipitate was collected by centrifugation. The precipitate was placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a ZnCo2O4 precursor powder. The precursor powder was transferred to a muffle furnace for calcination at a temperature of 750° C. for 2 h, and a heating rate of 2° C. / min.

[0068] Preparation of ZnCo2O4-Y2O3-CeO2:

[0069] The ZnCo2O4 and CeO2 prepared in the above steps were placed in an agate mortar and ground for 60 min to refine the particles and disperse them evenly. The ZnCo2O4 and CeO2 powders were then passed through a 120-mesh sieve to obtain treated ZnCo2O4 and CeO2 powders. 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 and ethylenediamine) were weighed. The mixture (9.9 g) was placed in a ball mill of a planetary ball mill, and zirconia balls were placed as grinding media with a ball-to-material ratio of 30:1. The ball mill speed was set to 500 rpm and the mixture was ball milled for 2 h to obtain a mixed slurry. The mixed slurry was transferred to a vacuum drying oven and dried at 70 ° C and a vacuum degree of 0.05 MPa for 12 h to remove moisture and obtain a dried mixed powder. The dried mixed powder was placed in a tube furnace and heated to 500 ° C at a heating rate of 2 ° C / min under inert gas protection and calcined for 3 h to promote Y 3+ Solid phase reaction with ZnCo2O4 and CeO2 produces ZnCo2O4-Y2O3-CeO2. The average particle size of ZnCo2O4-Y2O3-CeO2 is 22nm and the specific surface area is 117m 2 / g.

[0070] ZnCo2O4-Y2O3-CeO2 was reduced in H2 atmosphere. The reduction conditions were: H2 atmosphere, pressure of 2 MPa, temperature of 400℃, space velocity of 2000 h -1 .

[0071] The performance test of the prepared catalyst was carried out in a fixed bed under the following reaction conditions: H2 / CO2 ratio of 4.5, reaction gas pressure of 2 MPa, reaction temperature of 250 °C, and space velocity of 15000 h -1 Under the reaction conditions, the CO2 conversion rate was 89.3% and the CH4 selectivity was 98.8%.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as 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: The following steps are involved: CeO2, ZnCo2O4, yttrium nitrate and a particle size regulator are mixed and ground, and then dried and calcined in sequence to obtain ZnCo2O4-Y2O3-CeO2; The ZnCo2O4-Y2O3-CeO2 is reduced under a hydrogen atmosphere to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that The preparation method of the CeO2 is as follows: adding a precipitant solution to a cerium nitrate solution to carry out a precipitation reaction, collecting the precipitate, and then sequentially washing, drying, and calcining the precipitate to obtain the CeO2.

3. The preparation method according to claim 2, characterized in that The precipitant solvent is 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 heating rate of the calcination is 0.2-2°C / min, the temperature is 400-600°C, and the time is 2-4h.

4. The preparation method according to claim 1, characterized in that The preparation method of ZnCo2O4 comprises the following steps: The zinc salt, the cobalt salt and the precipitant are subjected to precipitation reaction in water to obtain a precursor suspension; The precursor suspension is subjected to microwave hydrothermal reaction, and a precipitate is collected after the reaction, and the precipitate is 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°C, time 30-90min; the calcination heating rate is 0.2-2°C, temperature is 500-750°C, and time is 2-4h.

6. The preparation method according to claim 1, characterized in that 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 the ZnCo2O4-Y2O3-CeO2 is 50-100:1-10:

100.

7. The preparation method according to claim 1, characterized in that The calcination temperature is 0.2-2 ° C, the temperature is 300-500 ° C, and the time is 3-6h; the conditions for reducing the ZnCo2O4-Y2O3-CeO2 in a hydrogen atmosphere are: H2 atmosphere, pressure of 0.1-2MPa, temperature of 330-400 ° C, space velocity of 400-2000h -1 .

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

9. Use of the catalyst according to claim 8 in catalytic CO2 hydrogenation to methane.

10. The use according to claim 9, characterized in that The catalyst is used in catalyzing CO2 hydrogenation to produce methane under the following reaction conditions: H2 / CO2 volume flow ratio of 3.0-5.0, reaction gas pressure of 0.1-2 MPa, reaction temperature of 200-300°C, space velocity of 5000-20000h -1 .

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