Carbon dioxide methanation composite catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts and applications thereof, and relates to a carbon dioxide methanation composite catalyst and a preparation method and applications thereof, and the preparation method comprises the following steps: S1, metal oxide carrier pretreatment; s2, adding the oxide carrier into a first transition metal salt solution, mixing, and sequentially carrying out primary ultrasonic treatment, primary dipping, primary washing and primary drying; and adding the dried product into a second transition metal salt solution, mixing, sequentially carrying out secondary ultrasonic treatment, secondary impregnation, secondary washing, secondary drying and roasting, and finally carrying out chemical reduction reaction to obtain the active metal catalyst. And S3, carrying out heteroatom hybridization dispersion treatment on the active metal catalyst by adopting a deposition and physical mixing combined method to obtain the carbon dioxide methanation composite catalyst. The carbon dioxide methanation composite catalyst formed by the invention shows excellent selectivity and reaction activity in a CO2 methanation reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts and their applications, and relates to a carbon dioxide methanation composite catalyst and a preparation method and application thereof. Background Art

[0002] The greenhouse effect has brought challenges to the sustainable development of society. The greenhouse effect is mainly caused by the excessive burning of coal, oil and natural gas in modern industrial society. After the combustion of these fuels, a large amount of carbon dioxide gas is released into the atmosphere. Therefore, in order to improve the greenhouse effect, it is necessary to reduce carbon dioxide emissions. At present, emissions are reduced through carbon dioxide conversion; carbon dioxide can be used as a relatively economical raw material for the production of valuable fine chemicals, such as CH4. Through the carbon dioxide methanation reaction, the effective conversion of carbon dioxide and the reuse of carbon resources are achieved. The conversion not only helps to reduce greenhouse gas emissions and reduce the impact on the environment, but also provides a new source of raw materials for the production of organic compounds.

[0003] The method of carbon dioxide methanation is: in the presence of a catalyst, carbon dioxide is hydrogenated to generate methane; during the hydrogenation conversion process, the selectivity and activity of the catalyst will affect the conversion rate of carbon dioxide. The commonly used methanation catalysts in the prior art are metal-based catalysts, and the commonly used metal components mainly include Ni, Fe, Co, Ru, Pt, etc. Ru-based and Pt-based catalysts are catalysts with high methanation reaction activity, but they are expensive, resulting in high costs; from the perspective of cost and catalytic activity, Ni-based catalysts are the most commonly used catalysts for CO2 methanation reactions. With the deepening of catalyst research, researchers have found that the reaction performance of bimetallic catalysts is generally better than that of corresponding monometallic catalysts. Combining metal Ni with other active metal additives to prepare bimetallic catalysts can improve the methanation reaction activity of the catalyst, but there are still defects such as low reaction activity and poor selectivity. Summary of the invention

[0004] Based on the technical problems of low reaction activity and poor selectivity of existing methanation catalysts, the present invention provides a carbon dioxide methanation composite catalyst and a preparation method and application thereof.

[0005] The present invention deposits active metal sites on the surface of a metal oxide carrier by a co-impregnation method, and introduces nitrogen-containing heterocyclic active groups into the catalyst surface by an ion exchange method. The formed carbon dioxide methanation composite catalyst exhibits excellent selectivity and reaction activity in the CO2 methanation reaction.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

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

[0008] S1. Pretreatment of metal oxide carrier

[0009] The metal oxide support is sequentially subjected to ultrasonic washing, drying and calcination pretreatment;

[0010] S2. Active metal loading

[0011] S2.1, adding the metal oxide support pretreated in step S1 to the first transition metal salt solution and mixing, and then sequentially subjecting to one ultrasonic treatment, one impregnation, one washing and one drying; 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 subjected to secondary ultrasound, secondary impregnation, secondary washing, secondary drying and roasting in sequence, and the surface metal of the obtained product is reduced by a chemical reduction method under a reducing gas atmosphere to obtain an 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 and dispersion treatment

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

[0015] It is further defined that in step S1, the metal oxide carrier is composed of Al2O3, ZrO2 and MgO, and the mass fractions of Al2O3, ZrO2 and MgO are 45%-75%, 15%-40% and 4%-25% respectively.

[0016] It is further defined that in step S1, the ultrasonic washing condition is for 0.5 h to 1 h; the calcination condition is for 400° C. to 550° C. and for 0.5 h to 3 h.

[0017] It is further defined that in step S2, the first transition metal salt solution and the second transition metal salt solution are both 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, 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] It is further defined that in step S2, the ultrasonic time is 30 minutes to 120 minutes; the reaction conditions of the first impregnation and the second impregnation are: temperature 120°C to 150°C, reaction time 12h to 18h; the calcination conditions are: temperature 450°C to 550°C, time 3h to 6h.

[0019] It is further defined that in step S2, the chemical reduction conditions are: temperature 350°C to 450°C, time 3h to 5h; and the reducing gas atmosphere is hydrogen.

[0020] It is further defined that in step S3, the heteroatom-containing compound is one or more of a nitrogen-containing compound, an oxygen-containing compound and a sulfur-containing compound.

[0021] It is further defined that in step S3, the modification is to mix the heteroatom-containing compound and the active catalyst precursor and then dissolve them in an organic solvent, and heat and stir them at a temperature of 50°C to 80°C for 5h to 9h; the calcination is carried out in an inert gas atmosphere at a temperature of 350°C to 450°C for 3h to 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] A carbon dioxide methanation composite catalyst prepared by the method for preparing the carbon dioxide methanation composite catalyst.

[0023] The carbon dioxide methanation composite catalyst is used in the preparation of methane by hydrogenation conversion of carbon dioxide.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention adopts a nano-scale metal oxide carrier, deposits active transition metal sites on the surface of the oxide carrier by a co-impregnation method, and introduces heteroatom active groups to modify the active metal catalyst by a method combining deposition and physical mixing, so as to improve the reaction activity and selectivity of methanation; the formed carbon dioxide methanation composite catalyst has excellent CO2 methanation selectivity and activity, and the catalyst stability is good.

[0026] 2. Compared with the previous methanation catalysts, the present invention can effectively improve the activity of catalytic conversion and the conversion rate of methane by adding multiple impregnations to achieve effective loading and uniform dispersion of transition metals on the surface of the oxide carrier.

[0027] 3. The present invention promotes the uniform distribution of transition metals on the surface of the oxide carrier by adding heteroatoms, prevents the agglomeration of transition metals, provides more active sites for the subsequent methanation of carbon dioxide, improves the selectivity of catalytic conversion into methane, and reduces the generation of by-products.

[0028] 4. The catalyst prepared by the present invention has good stability and can maintain catalytic activity during a long reaction process.

[0029] 5. The catalyst of the present invention is prepared by multiple impregnation and surface modification. The preparation method is simple, easy to operate, and has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the SEM electron microscope image of O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst. DETAILED DESCRIPTION

[0031] The technical solution protected by the present invention is now described in detail in conjunction with the embodiments. However, it is obvious that the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention starts from improving the conversion rate and selectivity of carbon dioxide hydrogenation to methane, and prepares a carbon dioxide methanation composite catalyst, which can improve the conversion rate and selectivity of carbon dioxide methanation and has good stability.

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

[0034] S1. Pretreatment of metal oxide carrier

[0035] The metal oxide support is pretreated by ultrasonic washing, drying and calcination in sequence.

[0036] Preferably, the metal oxide support is dispersed in ethanol and deionized water in sequence for ultrasonic washing, and then pre-treated by drying and calcining to enhance the affinity of the support surface.

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

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

[0039] S2. Active metal loading

[0040] S2.1. Add the metal oxide support of step S1 to the first transition metal salt solution and mix, then sequentially perform one ultrasonic treatment, one impregnation treatment, one washing treatment and one drying treatment; 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 secondary ultrasound, secondary impregnation, secondary washing, secondary drying and calcination in sequence. The surface metal of the obtained product is reduced by a chemical reduction method under a reducing gas atmosphere to obtain an active metal catalyst; the mass ratio of the dried product to the transition metal salt solution is 1:3 to 1:5.

[0042] In the present invention, the first transition metal salt solution and the second transition metal salt solution are both 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; in the first transition metal salt solution and the second transition metal salt solution, the mass concentration of the transition metal 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 a mixture of one or more of nickel nitrate, nickel chloride, nickel sulfate, nickel acetate and nickel acetylacetonate, the manganese precursor is a mixture of one or more of manganese nitrate, manganese sulfate and manganese chloride; the iron precursor is a mixture of one or more of iron sulfate, iron chloride, iron sulfite and iron nitrate; the cobalt precursor is a mixture of one or more of cobalt carbonate, cobalt nitrate, cobalt sulfate and cobalt chloride.

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

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

[0046] S3. Heteroatom hybridization and dispersion treatment

[0047] The active metal catalyst is subjected to heteroatom hybridization and dispersion treatment by a method combining deposition and physical mixing, and the mass ratio of the heteroatom-containing compound to the active metal catalyst obtained by S2 is 1:1 to 3:1; the precursor is 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 the present invention, the heteroatom-containing compound is one or more of a nitrogen-containing compound, an oxygen-containing compound and a sulfur-containing compound.

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

[0050] In step S3 of the present invention, the modification is to mix the heteroatom-containing compound and the active catalyst precursor and then dissolve them in an organic solvent, and heat and stir them at a temperature of 50°C to 80°C for 5h to 9h; the calcination is carried out in an inert gas atmosphere at a temperature of 350°C to 450°C for 3h to 5h; the organic solvent is any one of methanol, ethanol and acetone; the inert gas atmosphere is any one of nitrogen, helium and argon.

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

[0052] The method for preparing the catalyst of the present invention and the performance of the catalyst are described below through several groups of specific examples.

[0053] It should be noted that, unless otherwise specified, the chemicals, reagents, etc. used in the following examples are all conventional commercial products in the art.

[0054] It should be noted that, unless otherwise specified, the various chemical operations used in the following examples are 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, comprising the following steps:

[0057] S1. Pretreatment of metal oxide carrier

[0058] The metal oxide carrier is dispersed in ethanol and deionized water in sequence for ultrasonic washing, and then pretreated by drying and calcining to enhance the affinity of the carrier surface.

[0059] Specifically, the metal oxide carrier 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; it is dispersed in ethanol and deionized water in turn for ultrasonic washing for 0.5 h, dried at 100° C. for 5 h, and then calcined at 500° C. for 1 h to obtain the oxide carrier.

[0060] S2. Active metal loading

[0061] In this embodiment, the two transition metal salt solutions are a nickel salt solution and a manganese salt solution. Specifically, nickel nitrate and water are used to prepare the nickel salt solution, and manganese nitrate is used to prepare the manganese salt solution. Then 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 of step S1 in a mass ratio of 1:10, ultrasonically crush for 60 min, transfer to a hydrothermal synthesis reactor, and react at 120°C for 3 h; after the reaction is completed, dry at 100°C for 3 h, repeat the above steps twice to obtain a dry product.

[0063] S2.2, the dried product and the manganese salt solution are mixed in a mass ratio of 1:5, and ultrasonically crushed for 60 minutes, and transferred to a hydrothermal synthesis reactor, and reacted at a temperature of 120°C for 3 hours; after the reaction is completed, the secondary drying is completed at a temperature of 100°C for 3 hours, and the above steps are repeated twice, and the impregnation is completed. Then, the product is calcined at a temperature of 550°C for 3 hours, and chemically reduced at a temperature of 400°C for 3 hours in a hydrogen atmosphere to obtain a metal-loaded active catalyst, which is recorded as Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0064] S3. Heteroatom hybridization and dispersion treatment

[0065] The surface of the metal-loaded active catalyst (Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was treated by hybridization and dispersion 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 are mixed and dissolved in ethanol, and heated and stirred at 60°C for 5 hours; the solid obtained by filtering the solution after the reaction is dried at 100°C for 3 hours; and the solid is calcined at 400°C for 3 hours in a nitrogen atmosphere to finally obtain a carbon dioxide methanation composite catalyst, which is recorded 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, comprising the following steps:

[0070] S1. Pretreatment of metal oxide carrier

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

[0072] S2. Active metal loading

[0073] This step is different from Example 1 in that the second transition metal salt solution is a cobalt salt solution. Specifically, nickel nitrate and water are used to prepare a nickel salt solution, and cobalt nitrate is used to prepare a cobalt salt solution, and then the cobalt salt solution is used as the second transition metal salt solution for standby use.

[0074] In this step, the impregnation process is carried out in accordance with Example 1 to obtain a metal-loaded active catalyst, which is recorded as Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0075] S3. Heteroatom modification

[0076] The surface of the metal-loaded active catalyst (Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was treated by hybridization and dispersion using heteroatom-containing compounds.

[0077] The modification process of this step is referred to Example 1, and finally a carbon dioxide methanation composite catalyst is obtained, which is recorded 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, comprising the following steps:

[0080] S1. Pretreatment of metal oxide carrier

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

[0082] S2. Active metal loading

[0083] This step is different from Example 1 in that the second transition metal salt solution is an iron salt solution. Specifically, nickel nitrate and water are used to prepare a nickel salt solution, and iron chloride is used to prepare an iron salt solution, and then the iron salt solution is used as the second transition metal salt solution for standby use.

[0084] In this step, the impregnation process is carried out in accordance with Example 1 to obtain a metal-loaded active catalyst, which is recorded as Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0085] S3. Heteroatom modification

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

[0087] The modification process of this step is referred to Example 1, and finally a carbon dioxide methanation composite catalyst is obtained, which is recorded 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, comprising the following steps:

[0090] S1. Pretreatment of metal oxide carrier

[0091] The metal oxide carrier is subjected to ultrasonic washing, drying and calcination pretreatment to obtain an oxide carrier. This step is the same as in Example 1.

[0092] S2. Active metal loading

[0093] In this example, the active metal loading is the same as that in Example 1. An active catalyst loaded with metal is obtained, which is recorded as Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0094] S3. Heteroatom modification

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

[0096] The metal-loaded active catalyst (Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was surface modified by using a heteroatom-containing compound. The modification process was referred to Example 1. Finally, a carbon dioxide methanation composite catalyst was obtained, which was recorded 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, comprising the following steps:

[0099] S1. Pretreatment of metal oxide carrier

[0100] The metal oxide carrier is subjected to ultrasonic washing, drying and calcination pretreatment to obtain an oxide carrier. This step is the same as in Example 1.

[0101] S2. Active metal loading

[0102] This step is different from Example 1 in 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, nickel nitrate and water are used to prepare the nickel salt solution, and cobalt nitrate is used to prepare the cobalt salt solution.

[0103] In this step, the impregnation process is carried out in accordance with Example 1 to obtain a metal-loaded active catalyst, which is recorded as Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0104] S3. Heteroatom hybridization and dispersion treatment

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

[0106] The active metal catalyst (Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was surface modified by using a heteroatom-containing compound, and the modification process was referred to Example 1. Finally, a carbon dioxide methanation composite catalyst was obtained, which was recorded 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, comprising the following steps:

[0109] S1. Pretreatment of metal oxide carrier

[0110] The metal oxide support is pre-treated by washing, drying and calcining to obtain an oxide support. This step is the same as in Example 1.

[0111] S2. Active metal loading

[0112] This step is different from Example 1 in 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, nickel nitrate and water are used to prepare the nickel salt solution, and ferric chloride is used to prepare the iron salt solution.

[0113] In this step, the impregnation process is carried out in accordance with Example 1 to obtain a metal-loaded active catalyst, which is designated as Ni-Fe / Al2O3 catalyst.

[0114] S3. Heteroatom hybridization and dispersion treatment

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

[0116] The metal-loaded active catalyst (Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was surface modified by using a heteroatom-containing compound, and the modification process was referred to Example 1. Finally, a carbon dioxide methanation composite catalyst was obtained, which was recorded 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, comprising the following steps:

[0119] S1. Pretreatment of metal oxide carrier

[0120] The metal oxide support is pre-treated by washing, drying and calcining to obtain an oxide support. This step is the same as in Example 1.

[0121] S2. Active metal loading

[0122] In this example, the active metal loading is the same as that in Example 1. An active catalyst loaded with metal is obtained, which is recorded as Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0123] S3. Heteroatom hybridization and dispersion treatment

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

[0125] The metal-loaded active catalyst (Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was surface modified by using a heteroatom-containing compound. The modification process was referred to Example 1. Finally, a carbon dioxide methanation composite catalyst was obtained, which was recorded 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, comprising the following steps:

[0128] S1. Pretreatment of metal oxide carrier

[0129] The metal oxide support is pre-treated by washing, drying and calcining to obtain an oxide support. This step is the same as in Example 1.

[0130] S2. Active metal loading

[0131] This step is different from Example 1 in 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, nickel nitrate and water are used to prepare the nickel salt solution, and cobalt nitrate is used to prepare the cobalt salt solution.

[0132] In this step, the impregnation process is carried out in accordance with Example 1 to obtain a metal-loaded active catalyst, which is recorded as Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0133] S3. Heteroatom modification

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

[0135] The metal-loaded active catalyst (Ni-Co / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was surface modified by using a heteroatom-containing compound, and the modification process was referred to Example 1. Finally, a carbon dioxide methanation composite catalyst was obtained, which was recorded 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, comprising the following steps:

[0138] S1. Pretreatment of metal oxide carrier

[0139] The metal oxide support is pre-treated by washing, drying and calcining to obtain an oxide support. This step is the same as in Example 1.

[0140] S2. Active metal loading

[0141] This step is different from Example 1 in 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, nickel nitrate and water are used to prepare the nickel salt solution, and ferric chloride is used to prepare the iron salt solution.

[0142] In this step, the impregnation process is carried out in accordance with Example 1 to obtain a metal-loaded active catalyst, which is recorded as Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0143] S3. Heteroatom hybridization and dispersion treatment

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

[0145] The metal-loaded active catalyst (Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst) was surface modified by using a heteroatom-containing compound, and the modification process was referred to Example 1. Finally, a carbon dioxide methanation composite catalyst was obtained, which was recorded as O-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0146] The performance superiority of the catalyst prepared above was further verified by the following test.

[0147] Test 1: Morphology

[0148] The O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst prepared in Example 7 was taken and the SEM morphology was obtained by electron microscopy. The results are as follows: Figure 1 shown.

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

[0150] Test 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 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, S-Ni-Co / 0.75A l2O3-0.15ZrO2-0.1MgO catalyst, S-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst, O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst, O-Ni-Co / 0.75Al2O3-0.15ZrO2-0.1Mg O catalyst and O-Ni-Fe / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst.

[0153] In this test, the above catalyst samples were used to hydrogenate carbon dioxide into methane through a fixed-bed catalytic reaction. The tail gas from the fixed-bed conversion was passed into a gas chromatograph for online detection, and the conversion rate of carbon dioxide and the selectivity to methane were calculated.

[0154] The specific test process is: each of the above catalyst samples is mixed with quartz sand, and the mass ratio of quartz sand to catalyst sample is 1:2; the mixture formed after mixing is filled into a quartz reaction tube, and the reaction gas is introduced, and the volume ratio of H2:CO2:He in the reaction gas is 20:5:75; the gas flow rate is controlled to be 20ml / min, the reaction pressure is normal pressure or near normal pressure, and the reaction temperature is 450℃; the gas after the reaction is introduced into a gas chromatograph for online detection, and the conversion rate of carbon dioxide and the selectivity to methane are calculated. The specific conversion rate and selectivity are shown in Table 1, Table 2, Table 3 and Table 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 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 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] Judging from the CO2 selectivity and conversion rate obtained in the above tables, the O-Ni-Mn / 0.75Al2O3-0.15ZrO2-0.1MgO catalyst has better catalytic conversion performance.

[0164] Test 3: Cyclic stability

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

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

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

[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] It can be seen from Table 5 that when the catalyst operation time is 400h, the CO2 conversion rate is still maintained at more than 99%, and the CH4 selectivity reaches 100%, indicating that the catalyst prepared by the present invention maintains a high catalytic activity and good stability during a long reaction process.

[0170] Test 4: Multiple immersion comparison

[0171] In Examples 1 to 3, two impregnations were used in the preparation, 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 one-time impregnation.

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

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

[0175] Test method: Take the metal-loaded active catalysts obtained by double impregnation in Examples 1 to 3 and the metal-loaded active catalysts obtained by single impregnation in Comparative Examples 1 to 3 respectively; then refer to the method of Test 2 to calculate the conversion rate of carbon dioxide and the selectivity to methane. The results are shown in Table 6.

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

[0177]

[0178] As can be seen from Table 6, compared with one impregnation, two impregnations can improve the catalyst's conversion rate to carbon dioxide and selectivity to methane. This shows that multiple impregnations can promote the deposition of transition metals on the surface of the oxide support and increase active sites; combined with subsequent surface modification, the catalytic conversion activity is greatly improved, and the conversion rate and selectivity of methane are improved.

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

[0180] The above are only 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, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to perform equivalent substitutions on some of the technical features therein. However, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a carbon dioxide methanation composite catalyst, characterized in that: The following steps are involved: S1. Pretreatment of metal oxide carrier The metal oxide support is sequentially subjected to ultrasonic washing, drying and calcination pretreatment; S2. Active metal loading S2.1, adding the metal oxide support pretreated in step S1 to the first transition metal salt solution and mixing, and then sequentially subjecting to one ultrasonic treatment, one impregnation, one washing and one drying; 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 subjected to secondary ultrasound, secondary impregnation, secondary washing, secondary drying and roasting in sequence, and the surface metal of the obtained product is reduced by a chemical reduction method under a reducing gas atmosphere to obtain an active metal catalyst; the mass ratio of the dried product to the second transition metal salt solution is 1:3 to 1:5; S3. Heteroatom hybridization and dispersion treatment The active metal catalyst is subjected to heteroatom hybridization and dispersion treatment by a method combining deposition and physical mixing, and the mass ratio of the heteroatom-containing compound to the active metal catalyst obtained by S2 is 1:1 to 3:1; the precursor is dissolved in an organic solvent, and then heated, stirred, washed, dried, and calcined to obtain a carbon dioxide methanation composite catalyst.

2. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that: In the step S1, the metal oxide carrier is composed of Al2O3, ZrO2 and MgO, and 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 the step S1, the ultrasonic washing time is 0.5h to 1h; the calcination conditions are: temperature 400°C to 550°C, 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 first transition metal salt solution and the second transition metal salt solution are both 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; in the first transition metal salt solution and the second transition metal salt solution, the mass concentration of the transition metal 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 of the first impregnation and the second impregnation are: temperature 120° C. to 150° C., reaction time 12 h to 18 h; the calcination conditions are: temperature 450° C. to 550° C., 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° C. to 450° C., and time 3 h to 5 h.

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 is one or more of a nitrogen-containing compound, an oxygen-containing compound and a sulfur-containing compound.

8. The method for preparing the carbon dioxide methanation composite catalyst according to claim 1, characterized in that: In step S3, the modification is to mix the heteroatom-containing compound and the active catalyst precursor and then dissolve them in an organic solvent, and heat and stir them at a temperature of 50°C to 80°C for 5h to 9h; the calcination is carried out in an inert gas atmosphere at a temperature of 350°C to 450°C for 3h to 5h; the organic solvent is any one of methanol, ethanol and acetone.

9. A carbon dioxide methanation composite catalyst prepared by the method for preparing the carbon dioxide methanation composite catalyst according to claim 1.

10. Use of the carbon dioxide methanation composite catalyst as claimed in claim 9 in the production of methane by hydrogenation conversion of carbon dioxide.

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