A carbon dioxide methanation composite catalyst, its preparation method and application

Abstract

This invention belongs to the field of catalysts and their application technology, and relates to a carbon dioxide methanation composite catalyst, its preparation method, and its application. The preparation method includes: S1, pretreatment of a metal oxide support; S2, mixing the oxide support with a first transition metal salt solution, followed by sequential ultrasonication, impregnation, washing, and drying; adding the dried product to a second transition metal salt solution, followed by sequential ultrasonication, impregnation, washing, drying, and calcination, and finally obtaining an active metal catalyst through a chemical reduction reaction; S3, using a combination of deposition and physical mixing to perform heteroatom hybridization dispersion treatment on the active metal catalyst to obtain the carbon dioxide methanation composite catalyst. The carbon dioxide methanation composite catalyst formed by this invention exhibits excellent selectivity and reactivity in the CO2 methanation reaction.

Description

Technical Field

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

[0002] The greenhouse effect poses a challenge to sustainable development. It is primarily caused by the excessive burning of coal, oil, and natural gas in modern industrial society, releasing large amounts of carbon dioxide into the atmosphere. Therefore, reducing carbon dioxide emissions is crucial to mitigating the greenhouse effect. Currently, carbon dioxide conversion is a key method for emission reduction. Carbon dioxide can serve as a relatively economical raw material for producing valuable fine chemicals, such as CH4. Through carbon dioxide methanation, carbon dioxide can be effectively converted and reused. This conversion not only helps reduce greenhouse gas emissions and mitigate environmental impact but also provides a new source of raw materials for the production of organic compounds.

[0003] The method of carbon dioxide methanation involves the hydrogenation of carbon dioxide to produce methane in the presence of a catalyst. During the hydrogenation conversion, the selectivity and activity of the catalyst affect the conversion rate of carbon dioxide. Existing technologies commonly use metal-based catalysts for methanation, with common metal components including Ni, Fe, Co, Ru, and Pt. Ru-based and Pt-based catalysts have high reactivity in methanation, but their high cost leads to high production costs. Considering both cost and catalytic activity, Ni-based catalysts are the most commonly used for CO2 methanation. With further research into catalysts, researchers have found that bimetallic catalysts generally outperform their corresponding monometallic catalysts. Combining metallic Ni with other active metal promoters to prepare bimetallic catalysts can improve the methanation activity, but it still suffers from low reactivity and poor selectivity. Summary of the Invention

[0004] To address the technical problems of low reactivity and poor selectivity in existing methanation catalysts, this invention provides a carbon dioxide methanation composite catalyst, its preparation method, and its application.

[0005] This invention deposits active metal sites on the surface of a metal oxide support by co-impregnation and introduces nitrogen-containing heterocyclic active groups onto the catalyst surface by ion exchange, forming a carbon dioxide methanation composite catalyst that exhibits excellent selectivity and reactivity in the CO2 methanation reaction.

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

[0007] A method for preparing a carbon dioxide methanation composite catalyst includes the following steps:

[0008] S1, Metal oxide support pretreatment

[0009] The metal oxide support was pretreated by ultrasonic washing, drying and calcination in sequence.

[0010] S2, active metal support

[0011] S2.1. The metal oxide support pretreated in step S1 is added to the first transition metal salt solution and mixed, and then subjected to one ultrasonic treatment, one impregnation, one washing and one drying in sequence; the mass ratio of the metal oxide support to the first transition metal salt solution is 1:10 to 1:15.

[0012] S2.2 After the above-mentioned dried product is mixed with the second transition metal salt solution, it is then subjected to two ultrasonic treatments, two impregnations, two washings, two dryings, and calcination in sequence. The resulting product is then subjected to surface metal reduction by chemical reduction under a reducing gas atmosphere to obtain the active metal catalyst. The mass ratio of the dried product to the second transition metal salt solution is 1:3 to 1:5.

[0013] S3, heteroatom hybridization dispersion treatment

[0014] The active metal catalyst was subjected to heteroatom hybridization dispersion treatment by a combination of deposition and physical mixing. The mass ratio of the heteroatom-containing compound to the active metal catalyst obtained by S2 was 1:1 to 3:1. The precursor was dissolved in an organic solvent, and then heated, stirred, washed, dried and calcined to obtain a carbon dioxide methanation composite catalyst.

[0015] Further specifying, in step S1, the metal oxide support is composed of Al2O3, ZrO2 and MgO, wherein the mass fractions of Al2O3, ZrO2 and MgO are 45%-75%, 15%-40% and 4%-25% respectively.

[0016] Further specifying, in step S1, the ultrasonic washing conditions are 0.5h to 1h; the calcination conditions are: temperature 400℃ to 550℃, time 0.5h to 3h.

[0017] Further specified, in step S2, the first transition metal salt solution and the second transition metal salt solution are both manganese salt solution, nickel salt solution, iron salt solution or cobalt salt solution, and the first transition metal salt solution and the second transition metal salt solution are different, and the mass concentration of the transition metal in the first transition metal salt solution and the second transition metal salt solution is 5% to 20%.

[0018] Further specifying that in step S2, the ultrasonic time is 30 min to 120 min; the reaction conditions for the first impregnation and the second impregnation are: temperature 120℃ to 150℃, reaction time 12 h to 18 h; and the calcination conditions are: temperature 450℃ to 550℃, time 3 h to 6 h.

[0019] Further specifying, in step S2, the chemical reduction conditions are: temperature 350℃~450℃, time 3h~5h; and the reducing gas atmosphere is hydrogen.

[0020] Further specifying, in step S3, the heteroatom-containing compound is one or more of nitrogen-containing compounds, oxygen-containing compounds, and sulfur-containing compounds.

[0021] Further specifying, in step S3, the modification involves mixing the heteroatom-containing compound and the active catalyst precursor, dissolving them in an organic solvent, and heating and stirring at a temperature of 50℃~80℃ for 5h~9h; the calcination is carried out in an inert gas atmosphere at a temperature of 350℃~450℃ for 3h~5h; the organic solvent is any one of methanol, ethanol, and acetone; and the inert gas atmosphere is any one of nitrogen, helium, and argon.

[0022] The carbon dioxide methanation composite catalyst prepared using the aforementioned method.

[0023] The application of the aforementioned carbon dioxide methanation composite catalyst in the hydrogenation conversion of carbon dioxide to methane.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. This invention uses a nanoscale metal oxide support, deposits active transition metal sites on the surface of the oxide support through a co-impregnation method, and introduces heteroatom active groups to modify the active metal catalyst through a combination of deposition and physical mixing methods to improve the reaction activity and selectivity of methanation; the resulting carbon dioxide methanation composite catalyst has excellent CO2 methanation selectivity and activity, and the catalyst has good stability.

[0026] 2. Compared with previous methanation catalysts, this invention achieves effective loading and uniform dispersion of transition metals on the oxide support surface through multiple impregnations, which can effectively improve the catalytic conversion activity and increase the methane conversion rate.

[0027] 3. This invention promotes the uniform distribution of transition metals on the oxide support surface by adding heteroatoms, prevents transition metal aggregation, provides more active sites for subsequent carbon dioxide methanation, improves the selectivity of catalytic conversion to methane, and reduces the generation of byproducts.

[0028] 4. The catalyst prepared by this invention has good stability and can maintain catalytic activity during long-term reaction processes.

[0029] 5. The catalyst of this invention is prepared by multiple impregnation and surface modification. The preparation method is simple, easy to operate, and has prospects for industrial application. Attached Figure Description

[0030] Figure 1 SEM image of the O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst. Detailed Implementation

[0031] The technical solutions protected by this invention will now be described in detail with reference to the embodiments. However, it is obvious that the described embodiments are only some, not all, of the embodiments described in this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the protection scope of this invention.

[0032] This invention aims to improve the conversion rate and selectivity of carbon dioxide hydrogenation to methane, and prepares a carbon dioxide methanation composite catalyst that can improve the conversion rate and selectivity of carbon dioxide methanation and has good stability.

[0033] This invention provides a method for preparing a carbon dioxide methanation composite catalyst, comprising the following steps:

[0034] S1, Metal oxide support pretreatment

[0035] The metal oxide support was subjected to ultrasonic washing, drying and calcination pretreatment in sequence.

[0036] Preferably, the metal oxide support is dispersed sequentially in ethanol and deionized water and ultrasonically washed, followed by drying and calcination pretreatment to enhance the affinity of the support surface.

[0037] In step S1 of this invention, the metal oxide support is composed of Al2O3, ZrO2 and MgO, wherein the mass fractions of Al2O3, ZrO2 and MgO are 45%-75%, 15%-40% and 4%-25% respectively.

[0038] In step S1 of this invention, the ultrasonic washing time is 0.5h to 1h; the calcination conditions are: temperature 400℃ to 550℃, time 0.5h to 3h.

[0039] S2, active metal support

[0040] S2.1 After adding the metal oxide support from step S1 to the first transition metal salt solution and mixing, the mixture is subjected to one ultrasonic treatment, one impregnation, one washing, and one drying in sequence; the mass ratio of the metal oxide support to the first transition metal salt solution is 1:10 to 1:15.

[0041] S2.2 After the above-mentioned dried product is mixed with the second transition metal salt solution, it is subjected to two ultrasonic treatments, two impregnations, two washings, two dryings and calcination in sequence. The resulting product is then subjected to surface metal reduction by chemical reduction under a reducing gas atmosphere to obtain the active metal catalyst. The mass ratio of the dried product to the transition metal salt solution is 1:3 to 1:5.

[0042] In this invention, both the first transition metal salt solution and the second transition metal salt solution are manganese salt solutions, nickel salt solutions, iron salt solutions, or cobalt salt solutions, and the first transition metal salt solution and the second transition metal salt solution are different; the mass concentration of the transition metal in the first transition metal salt solution and the second transition metal salt solution is 5% to 20%.

[0043] Preferably, the manganese salt solution is prepared from a manganese precursor, the nickel salt solution is prepared from a nickel precursor, the iron salt solution is prepared from an iron precursor, and the cobalt salt solution is prepared from a cobalt precursor. Preferably, the nickel precursor is one or a mixture of nickel nitrate, nickel chloride, nickel sulfate, nickel acetate, and nickel acetylacetonate; the manganese precursor is one or a mixture of manganese nitrate, manganese sulfate, and manganese chloride; the iron precursor is one or a mixture of ferric sulfate, ferric chloride, ferrous sulfite, and ferric nitrate; and the cobalt precursor is one or a mixture of cobalt carbonate, cobalt nitrate, cobalt sulfate, and cobalt chloride.

[0044] In step S2 of this invention, the ultrasonic time is 30 min to 120 min; the reaction conditions for the first impregnation and the second impregnation are: temperature 120℃ to 150℃, reaction time 12 h to 18 h; the calcination conditions are: temperature 450℃ to 550℃, time 3 h to 6 h.

[0045] In step S2 of this invention, the chemical reduction conditions are: temperature 350℃~450℃, time 3h~5h; and the reducing gas atmosphere is hydrogen.

[0046] S3, heteroatom hybridization dispersion treatment

[0047] The active metal catalyst was subjected to heteroatom hybridization dispersion treatment by a combination of deposition and physical mixing. The mass ratio of the heteroatom-containing compound to the active metal catalyst obtained by S2 was 1:1 to 3:1. The precursor was dissolved in an organic solvent, and then heated, stirred, washed, dried and calcined to obtain a carbon dioxide methanation composite catalyst.

[0048] In step S3 of this invention, the heteroatom-containing compound is one or more of nitrogen-containing compounds, oxygen-containing compounds, and sulfur-containing compounds.

[0049] Preferably, the nitrogen-containing compound is one or a mixture of several of urea, ammonium chloride, and ammonium nitrate; the oxygen-containing compound is one or a mixture of several of hydrogen peroxide, acetic acid, and diethyl ether; and the sulfur-containing compound is one or a mixture of several of thiols, carbon disulfide, and hydrogen disulfide.

[0050] In step S3 of this invention, modification involves mixing a heteroatom-containing compound and an active catalyst precursor, dissolving them in an organic solvent, and heating and stirring at 50°C to 80°C for 5 to 9 hours; calcination is carried out in an inert gas atmosphere at 350°C to 450°C for 3 to 5 hours; the organic solvent is any one of methanol, ethanol, and acetone; and the inert gas atmosphere is any one of nitrogen, helium, and argon.

[0051] The carbon dioxide methanation composite catalyst prepared by the above method of the present invention has a large number of active sites and exhibits excellent selectivity and conversion activity for carbon dioxide when applied in the hydrogenation conversion of carbon dioxide to methane.

[0052] The following examples illustrate the method for preparing the catalyst and the performance of the catalyst according to the present invention.

[0053] It should be noted that, unless otherwise specified, the chemicals and reagents used in the following examples are all commercially available products commonly used in the field.

[0054] It should be noted that, unless otherwise specified, the various chemical operations used in the following examples are all conventional operations in the art, such as drying, heating, stirring, washing, etc.

[0055] Example 1

[0056] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0057] S1, Metal oxide support pretreatment

[0058] The metal oxide support was sequentially dispersed in ethanol and deionized water and ultrasonically washed, followed by drying and calcination pretreatment to enhance the affinity of the support surface.

[0059] Specifically, the metal oxide support has a grain size of 20 nm and is composed of 75% alumina powder, 15% zirconium oxide powder and 10% magnesium oxide powder by mass. The powder is dispersed in ethanol and deionized water and ultrasonically washed for 0.5 h, dried at 100 °C for 5 h, and then calcined at 500 °C for 1 h to obtain the oxide support.

[0060] S2, active metal support

[0061] In this embodiment, the two transition metal salt solutions are a nickel salt solution and a manganese salt solution. Specifically, a nickel salt solution is prepared using nickel nitrate and water, and a manganese salt solution is prepared using manganese nitrate. The nickel salt solution is the first transition metal salt solution, and the manganese salt solution is the second transition metal salt solution.

[0062] S2.1 Mix the oxide support and nickel salt solution from step S1 at a mass ratio of 1:10, sonicate for 60 min, transfer to a hydrothermal synthesis reactor, and react at 120℃ for 3 h. After the reaction is complete, dry at 100℃ for 3 h. Repeat the above steps twice to obtain the dried product.

[0063] S2.2 The dried product and manganese salt solution are mixed again at a mass ratio of 1:5, ultrasonically crushed twice for 60 min, and transferred to a hydrothermal synthesis reactor. The mixture is reacted at 120℃ for 3 h. After the reaction is complete, a second drying is performed at 100℃ for 3 h. The above steps are repeated twice to complete the impregnation. Then, the mixture is calcined at 550℃ for 3 h and chemically reduced at 400℃ for 3 h in a hydrogen atmosphere to obtain the metal-supported active catalyst, denoted as Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0064] S3, heteroatom hybridization dispersion treatment

[0065] The surface of the supported metal active catalyst (Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was hybridized and dispersed using heteroatom-containing compounds.

[0066] In this embodiment, the mass ratio of the heteroatom-containing compound to the active metal catalyst is 1:1; the heteroatom-containing compound is a nitrogen-containing compound, preferably urea.

[0067] Specifically, urea and the active catalyst were mixed and dissolved in ethanol, and heated and stirred at 60°C for 5 hours. The resulting solution was filtered to obtain a solid, which was then dried at 100°C for 3 hours. The solid was then calcined at 400°C for 3 hours under a nitrogen atmosphere to finally obtain the carbon dioxide methanation composite catalyst, denoted as N-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0068] Example 2

[0069] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0070] S1, Metal oxide support pretreatment

[0071] This step is the same as in Example 1.

[0072] S2, active metal support

[0073] The difference between this step and Example 1 is that the second transition metal salt solution is a cobalt salt solution. Specifically, a nickel salt solution is prepared using nickel nitrate and water, and a cobalt salt solution is prepared using cobalt nitrate. This cobalt salt solution is then used as the second transition metal salt solution for future reference.

[0074] In this step, the impregnation process is the same as in Example 1, and the metal-supported active catalyst is obtained, which is denoted as Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0075] S3, heteroatom modification

[0076] The surface of the metal-supported active catalyst (Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was hybridized and dispersed using heteroatom-containing compounds.

[0077] The modification process in this step is the same as in Example 1, and the carbon dioxide methanation composite catalyst is finally obtained, which is denoted as N-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0078] Example 3

[0079] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0080] S1, Metal oxide support pretreatment

[0081] This step is the same as in Example 1.

[0082] S2, active metal support

[0083] The difference between this step and Example 1 is that the second transition metal salt solution is an iron salt solution. Specifically, a nickel salt solution is prepared using nickel nitrate and water, and an iron salt solution is prepared using ferric chloride. This iron salt solution is then used as the second transition metal salt solution for future reference.

[0084] In this step, the impregnation process is the same as in Example 1, and the metal-loaded active catalyst is obtained, which is denoted as Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0085] S3, heteroatom modification

[0086] The surface of the supported metal active catalyst (Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was modified with heteroatom-containing compounds.

[0087] The modification process in this step is the same as in Example 1, and the carbon dioxide methanation composite catalyst is finally obtained, which is denoted as N-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0088] Example 4

[0089] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0090] S1, Metal oxide support pretreatment

[0091] The metal oxide support is pretreated by ultrasonic washing, drying, and calcination to obtain the oxide support. This step is the same as in Example 1.

[0092] S2, active metal support

[0093] In this embodiment, the active metal support is the same as in Example 1. The resulting active catalyst with supported metal is denoted as Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0094] S3, heteroatom modification

[0095] Unlike Example 1, the heteroatom-containing compound in this example is a sulfur-containing compound, preferably a thiol.

[0096] The surface of the metal-supported active catalyst (Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was modified with a heteroatom-containing compound. The modification process was as described in Example 1. The resulting carbon dioxide methanation composite catalyst was designated as S-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0097] Example 5

[0098] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0099] S1, Metal oxide support pretreatment

[0100] The metal oxide support is pretreated by ultrasonic washing, drying, and calcination to obtain the oxide support. This step is the same as in Example 1.

[0101] S2, active metal support

[0102] The difference between this step and Example 1 is that the first transition metal salt solution is a nickel salt solution, and the second transition metal salt solution is a cobalt salt solution. Specifically, a nickel salt solution is prepared using nickel nitrate and water, and a cobalt salt solution is prepared using cobalt nitrate.

[0103] In this step, the impregnation process is the same as in Example 1, and the metal-supported active catalyst is obtained, which is denoted as Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0104] S3, heteroatom hybridization dispersion treatment

[0105] Unlike Example 1, the heteroatom-containing compound in this example is a sulfur-containing compound, preferably a thiol.

[0106] The surface of the active metal catalyst (Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was modified with a heteroatom-containing compound, and the modification process was as described in Example 1. The resulting carbon dioxide methanation composite catalyst was designated as S-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0107] Example 6

[0108] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0109] S1, Metal oxide support pretreatment

[0110] The metal oxide support is pretreated by washing, drying, and calcination to obtain the oxide support. This step is the same as in Example 1.

[0111] S2, active metal support

[0112] The difference between this step and Example 1 is that the first transition metal salt solution is a nickel salt solution, and the second transition metal salt solution is an iron salt solution. Specifically, a nickel salt solution is prepared using nickel nitrate and water, and an iron salt solution is prepared using ferric chloride.

[0113] In this step, the impregnation process is the same as in Example 1, and the metal-loaded active catalyst is obtained, which is denoted as Ni-Fe / Al2O3 catalyst.

[0114] S3, heteroatom hybridization dispersion treatment

[0115] Unlike Example 1, the heteroatom-containing compound in this example is a sulfur-containing compound, preferably a thiol.

[0116] The surface of the metal-supported active catalyst (Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was modified with a heteroatom-containing compound, and the modification process was as described in Example 1. The resulting carbon dioxide methanation composite catalyst was designated as S-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0117] Example 7

[0118] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0119] S1, Metal oxide support pretreatment

[0120] The metal oxide support is pretreated by washing, drying, and calcination to obtain the oxide support. This step is the same as in Example 1.

[0121] S2, active metal support

[0122] In this embodiment, the active metal support is the same as in Example 1. The resulting active catalyst with supported metal is denoted as Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0123] S3, heteroatom hybridization dispersion treatment

[0124] Unlike Example 1, the heteroatom-containing compound in this example is an oxygen-containing compound, preferably hydrogen peroxide.

[0125] The surface of the metal-supported active catalyst (Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was modified with a heteroatom-containing compound. The modification process was as described in Example 1. The resulting carbon dioxide methanation composite catalyst was designated as O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0126] Example 8

[0127] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0128] S1, Metal oxide support pretreatment

[0129] The metal oxide support is pretreated by washing, drying, and calcination to obtain the oxide support. This step is the same as in Example 1.

[0130] S2, active metal support

[0131] The difference between this step and Example 1 is that the first transition metal salt solution is a nickel salt solution, and the second transition metal salt solution is a cobalt salt solution. Specifically, a nickel salt solution is prepared using nickel nitrate and water, and a cobalt salt solution is prepared using cobalt nitrate.

[0132] In this step, the impregnation process is the same as in Example 1, and the metal-supported active catalyst is obtained, which is denoted as Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0133] S3, heteroatom modification

[0134] Unlike Example 1, the heteroatom-containing compound in this example is an oxygen-containing compound, preferably hydrogen peroxide.

[0135] The surface of the metal-supported active catalyst (Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was modified with a heteroatom-containing compound, as described in Example 1. The resulting carbon dioxide methanation composite catalyst was designated as O-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0136] Example 9

[0137] This embodiment provides a method for preparing a carbon dioxide methanation composite catalyst, including the following steps:

[0138] S1, Metal oxide support pretreatment

[0139] The metal oxide support is pretreated by washing, drying, and calcination to obtain the oxide support. This step is the same as in Example 1.

[0140] S2, active metal support

[0141] The difference between this step and Example 1 is that the first transition metal salt solution is a nickel salt solution, and the second transition metal salt solution is an iron salt solution. Specifically, a nickel salt solution is prepared using nickel nitrate and water, and an iron salt solution is prepared using ferric chloride.

[0142] In this step, the impregnation process is the same as in Example 1, and the metal-loaded active catalyst is obtained, which is denoted as Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0143] S3, heteroatom hybridization dispersion treatment

[0144] Unlike Example 1, the heteroatom-containing compound in this example is an oxygen-containing compound, preferably hydrogen peroxide.

[0145] The surface of the metal-supported active catalyst (Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was modified with a heteroatom-containing compound, as described in Example 1. The resulting carbon dioxide methanation composite catalyst was designated as O-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0146] The superior performance of the catalyst prepared above was further verified through the following experiments.

[0147] Experiment 1, Morphology

[0148] The O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst prepared in Example 7 was analyzed by scanning electron microscopy (SEM) to obtain its morphology. The results are as follows: Figure 1 As shown.

[0149] See Figure 1 As can be seen, the active transition metals are relatively dispersed on the surface of the oxide support, without agglomeration, and have more active sites for methanation catalytic conversion.

[0150] Experiment 2, Catalytic performance

[0151] The Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst obtained in step S2 of Example 1, the Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst obtained in step S2 of Example 2, and the Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst obtained in step S2 of Example 3 were selected.

[0152] The following catalysts were selected from Examples 1 to 9: N-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst, N-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst, N-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst, S-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst, and S-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst. Catalysts include l2O3-0.15ZrO2-0.1MgO, S-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO, O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO, O-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO, and O-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO.

[0153] This experiment used a fixed-bed catalytic reaction to convert carbon dioxide into methane using the aforementioned catalyst samples. The tail gas from the fixed-bed conversion was then passed into a gas chromatograph for online detection, and the conversion rate of carbon dioxide and the selectivity for methane were calculated.

[0154] The specific experimental procedure was as follows: Each catalyst sample was mixed with quartz sand at a mass ratio of 1:2. The resulting mixture was then filled into a quartz reaction tube, and a reaction gas was introduced. The volume ratio of H2:CO2:He in the reaction gas was 20:5:75. The gas flow rate was controlled at 20 ml / min, the reaction pressure was at or near atmospheric pressure, and the reaction temperature was 450℃. The reacted gas was then passed into a gas chromatograph for online detection, and the conversion rate of carbon dioxide and the selectivity for methane were calculated. The specific conversion rates and selectivities are shown in Tables 1, 2, 3, and 4.

[0155] Table 1. Conversion and selectivity of bimetallic catalysts

[0156] catalyst <![CDATA[CO2 conversion rate]]> <![CDATA[CH4 selectivity]]> <![CDATA[Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 85.1 99.1 <![CDATA[Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 81.4 98.5 <![CDATA[Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 81.6 98.9

[0157] Table 2 Conversion and selectivity of N-doped catalysts

[0158] catalyst <![CDATA[CO2 conversion rate]]> <![CDATA[CH4 selectivity]]> <![CDATA[N-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.9 100 <![CDATA[N-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.3 100 <![CDATA[N-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.2 100

[0159] Table 3 Selectivity and conversion rate of S-doped catalysts

[0160] catalyst <![CDATA[CO2 conversion rate]]> <![CDATA[CH4 selectivity]]> <![CDATA[S-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.2 100 <![CDATA[S-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.1 100 <![CDATA[S-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.5 100

[0161] Table 4. Selectivity and conversion rate of O-doped catalysts

[0162] catalyst <![CDATA[CO2 conversion rate]]> <![CDATA[CH4 selectivity]]> <![CDATA[O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 99.2 100 <![CDATA[O-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.1 100 <![CDATA[O-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO]]> 98.0 100

[0163] Based on the CO2 selectivity and conversion rates obtained from the tables above, the O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst exhibits better catalytic conversion performance.

[0164] Experiment 3, Cyclic Stability

[0165] Sample: O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst

[0166] The specific experimental procedure was as follows: the above catalyst sample was mixed with quartz sand, and the mass ratio of quartz sand to catalyst sample was 1:2; the mixture was filled into a quartz reaction tube, and a reaction gas was introduced, with the volume ratio of H2:CO2:He in the reaction gas being 20:5:75; the gas flow rate was controlled at 20 ml / min, the reaction pressure was at or near atmospheric pressure, and the reaction temperature was 450℃; the catalyst activity under long-term operation is shown in Table 5.

[0167] Table 5. Catalyst activity determination during long-term operation.

[0168] Reaction time / h <![CDATA[CO2 conversion rate / %]]> <![CDATA[CH4 selectivity / %]]> 20 99.2 100 50 99.2 100 100 99.1 100 200 99.2 100 300 99.1 100 400 99.0 100

[0169] As can be seen from Table 5, when the catalyst runs for 400 h, the CO2 conversion rate remains above 99% and the selectivity for CH4 reaches 100%, indicating that the catalyst prepared in this invention maintains high catalytic activity and good stability during long-term reaction.

[0170] Experiment 4: Comparison of multiple immersions

[0171] In Examples 1 to 3, two impregnations were used in the preparation process, and the number of impregnations was compared.

[0172] Comparative Example 1: Referring to Example 1, a metal-loaded active catalyst, namely Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst, was obtained by a single impregnation.

[0173] Comparative Example 2: Referring to Example 2, a metal-loaded active catalyst was obtained by a single impregnation, namely Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0174] Comparative Example 3: Referring to Example 3, a metal-loaded active catalyst was obtained by a single impregnation, namely Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0175] Experimental method: The metal-loaded active catalysts obtained by double impregnation in Examples 1 to 3 were compared with the metal-loaded active catalysts obtained by single impregnation in Comparative Examples 1 to 3. Then, referring to the method in Experiment 2, the conversion rate of carbon dioxide and the selectivity for methane were calculated. The results are shown in Table 6.

[0176] Table 6 Comparison of catalytic effects at different impregnation times

[0177]

[0178] As shown in Table 6, compared to single impregnation, double impregnation improves the catalyst's conversion rate for carbon dioxide and its selectivity for methane. This indicates that multiple impregnation promotes the deposition of transition metals on the oxide support surface, increasing active sites; combined with subsequent surface modification, this significantly enhances the catalytic conversion activity and improves the conversion rate and selectivity of methane.

[0179] In the above embodiments of the present invention, the first transition metal salt solution can be replaced with a manganese salt solution, an iron salt solution, or a cobalt salt solution; the nitrogen-containing compound can be replaced with other nitrogen-containing compounds such as ammonium chloride or ammonium nitrate; the oxygen-containing compound can be replaced with other oxygen-containing compounds such as acetic acid or diethyl ether; and the sulfur-containing compound can be replaced with other sulfur-containing compounds such as carbon disulfide or hydrogen disulfide. The mass ratio of the raw materials and the reaction parameters can be changed. The resulting carbon dioxide methanation composite catalyst has the same effect as the catalyst prepared in the above embodiments, exhibiting excellent selectivity and conversion activity for the carbon dioxide methanation reaction.

[0180] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbon dioxide methanation composite catalyst, characterized in that, Includes the following steps: S1, Metal oxide support pretreatment The metal oxide support was pretreated by ultrasonic washing, drying and calcination in sequence; the metal oxide support was composed of Al2O3, ZrO2 and MgO. S2, active metal support S2.

1. The metal oxide support pretreated in step S1 is added to the first transition metal salt solution and mixed, and then subjected to one ultrasonic treatment, one impregnation, one washing and one drying in sequence; the mass ratio of the metal oxide support to the first transition metal salt solution is 1:10 to 1:

15. S2.2 After the above-mentioned dried product is mixed with the second transition metal salt solution, it is then subjected to two ultrasonic treatments, two impregnations, two washings, two dryings, and calcination in sequence. The resulting product is then subjected to surface metal reduction by chemical reduction under a reducing gas atmosphere to obtain the active metal catalyst. The mass ratio of the dried product to the second transition metal salt solution is 1:3 to 1:

5. Both the first and second transition metal salt solutions are manganese salt solutions, nickel salt solutions, iron salt solutions, or cobalt salt solutions, and the first and second transition metal salt solutions are different. S3, heteroatom hybridization dispersion treatment Heteroatoms were introduced into the active metal catalyst by a combination of deposition and physical mixing to achieve heteroatom hybridization dispersion. The mass ratio of the heteroatom-containing compound to the active metal catalyst obtained from S2 was 1:1 to 3:

1. The active metal catalyst and the heteroatom-containing compound were dissolved in an organic solvent, and then heated, stirred, washed, dried, and calcined to obtain a carbon dioxide methanation composite catalyst. Heteroatom-containing compounds are one or more of nitrogen-containing compounds, oxygen-containing compounds, and sulfur-containing compounds; Nitrogen-containing compounds are one or a mixture of urea, ammonium chloride, and ammonium nitrate; oxygen-containing compounds are one or a mixture of hydrogen peroxide, acetic acid, and diethyl ether; sulfur-containing compounds are one or a mixture of thiols, carbon disulfide, and hydrogen disulfide.

2. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that, In step S1, the mass fractions of Al2O3, ZrO2, and MgO are 45%-75%, 15%-40%, and 4%-25%, respectively.

3. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that, In step S1, the ultrasonic washing time is 0.5h to 1h; the calcination conditions are: temperature 400℃ to 550℃, time 0.5h to 3h.

4. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that, In step S2, the mass concentration of the transition metal in the first transition metal salt solution and the second transition metal salt solution is 5% to 20%.

5. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that, In step S2, the ultrasonic time is 30 min to 120 min; the reaction conditions for the first impregnation and the second impregnation are: temperature 120℃ to 150℃, reaction time 12 h to 18 h; the calcination conditions are: temperature 450℃ to 550℃, time 3 h to 6 h.

6. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that, In step S2, the chemical reduction conditions are: temperature 350℃~450℃, time 3h~5h.

7. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that, In step S3, the heteroatom-containing compound and the active metal catalyst are mixed and dissolved in an organic solvent, and heated and stirred at 50℃~80℃ for 5h~9h; calcination is carried out in an inert gas atmosphere at 350℃~450℃ for 3h~5h; the organic solvent is any one of methanol, ethanol and acetone.

8. The carbon dioxide methanation composite catalyst prepared by the method of claim 1.

9. The application of the carbon dioxide methanation composite catalyst as described in claim 8 in the preparation of methane by carbon dioxide hydrogenation conversion.

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