A catalyst, its preparation and use in the carbon dioxide methanation reaction

Abstract

The present application belongs to the technical field of catalyst development, and relates to preparation of a composite catalyst and application of the composite catalyst in carbon dioxide methanation reaction. The present application adopts a calcination method to prepare a nano-carbon material loaded non-noble metal single-atom catalyst or nano-metal catalyst, the loading amount of the metal is 1-15wt% (calculated by the metal), and the catalyst has good carbon dioxide methanation activity and selectivity. The catalyst provided by the present application can convert carbon dioxide into methane with high selectivity, and oxygen, nitrogen and other heteroatoms on the surface of the carbon carrier can anchor the metal single atom or nano-particle, so that the metal single atom or nano-particle has good thermal stability. The present application develops a preparation method of a carbon material loaded single-atom or nano catalyst, the raw material source is wide, no noble metal is used, the cost of the catalyst is low, and the catalyst is suitable for large-scale preparation.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst development, in particular to the preparation of a catalyst and its application in a carbon dioxide methanation reaction, belonging to relevant technologies for the comprehensive utilization of carbon dioxide. Technical Background

[0002] With the rapid development of the chemical industry, carbon dioxide (CO2) emissions from the combustion of fossil fuels are increasing, and the concentration of carbon dioxide in the atmosphere is also rising, causing an increasingly serious greenhouse effect. How to effectively convert carbon dioxide into usable resources has become an urgent problem for researchers. Therefore, the field of carbon dioxide conversion and utilization has become the focus of many researchers. In response to problems such as global warming caused by the greenhouse effect, governments around the world and the United Nations have taken a large number of measures in the past few decades. One potential solution is to use hydrogen produced by electrolysis of water from renewable energy sources such as wind power and photovoltaics to react with carbon dioxide captured from the atmosphere, and use carbon dioxide hydrogenation to produce fuels or chemicals. This solution can not only solve the environmental problems caused by the increase in carbon dioxide concentration in the atmosphere, but also alleviate the current over-reliance on fossil resources to a certain extent, realize the clean and efficient utilization of carbon resources, and thus achieve carbon neutrality.

[0003] Carbon dioxide methanation is the core technology in the above application fields. Due to the chemical inertness and high thermodynamic stability of carbon dioxide, the design of catalyst is the key to achieve carbon dioxide activation. Carbon dioxide methanation reaction is a typical exothermic reaction (ΔH 298K =-164.86 kJ·mol -1 ), but due to the chemical inertness of carbon dioxide, the activation energy of the carbon dioxide methanation reaction is usually high. Therefore, it is necessary to increase the reaction temperature to promote the activation of carbon dioxide or design a highly active catalyst to reduce the activation energy of the reaction. In the existing technology, the carbon dioxide methanation catalyst usually needs to be pre-reduced in a hydrogen atmosphere at a certain temperature, and then switch to a mixed gas of carbon dioxide and hydrogen for reaction. Usually, at low temperatures (200-350°C), the activity of the carbon dioxide methanation catalyst is not high, and the conversion rate is generally less than 50%; generally above 400°C, the catalyst has higher activity, but it is easy to cause crystal agglomeration at high temperatures, resulting in poor stability of the catalyst; at the same time, in the methanation reaction of carbon dioxide, the selectivity of methane is difficult to reach 100%, and it contains a small amount of carbon monoxide, which limits its large-scale application. Summary of the Invention

[0004] The present invention provides a method for preparing a carbon material-supported single-atom or nanometal catalyst. The catalyst prepared using the present invention exhibits good methane selectivity under the reaction conditions for carbon dioxide methanation (200-400°C, 0.1-3.0 MPa). The catalyst of the present invention prevents incomplete hydrogenation of carbon dioxide to form carbon monoxide as a byproduct. Furthermore, the catalyst is simple to prepare and does not use precious metals, thereby reducing catalyst costs.

[0005] To achieve the above objectives, the present invention adopts the following scheme.

[0006] The present invention provides a method for preparing a catalyst, which comprises the following steps:

[0007] (1) The metal precursor, oxygen-containing chelating agent, solvent and carbon support are uniformly mixed by stirring, grinding and / or ultrasonication, and after standing (standing time is more than 30 minutes, preferably 60 to 120 minutes), the solid and liquid are separated by centrifugation and / or filtration, and the solid insoluble matter is dried to obtain a supported metal-chelating agent precursor A;

[0008] (2) uniformly mixing the ligand, solvent, and the supported metal-chelate precursor A prepared above by stirring, grinding, and / or ultrasonication, allowing the mixture to stand for at least 30 minutes, preferably 60 to 120 minutes, and separating the solid and liquid by centrifugation or filtration, and then drying the solid insoluble matter to obtain a supported catalyst precursor B;

[0009] (3) calcining the supported catalyst precursor B prepared above to obtain a carbon material supported single atom catalyst and / or nano metal catalyst.

[0010] Based on the above technical solution, in step (1), the metal precursor is one or more of nitrates, sulfates, hydrochlorides, formates, acetates, malates, and citrates of one or more of the metals Ti, Fe, Co, Ni, and Cr, preferably one or more of nitrates, acetates, and malates;

[0011] The oxygen-containing chelating agent is one or more of erythritol, L-arabinose, D-glucose, D-fructose, D-xylose, D-mannose, and D-galactose, preferably one or more of erythritol, D-glucose, D-fructose, and D-galactose;

[0012] The solvent is one or more of tetrahydrofuran, petroleum ether, water, methanol, ethanol, N,N-dimethylformamide, and dimethyl sulfoxide, preferably one or more of tetrahydrofuran, water, and ethanol;

[0013] The carbon carrier is one or more of activated carbon, ordered mesoporous carbon, nanocarbon spheres, graphite, carbon black, carbon nanotubes, and carbon nanofibers, preferably one or more of activated carbon, carbon nanotubes, carbon nanofibers, and ordered mesoporous carbon; the particle size of activated carbon, ordered mesoporous carbon, nanocarbon spheres, graphite, and carbon black is 10 to 200 μm (preferably 10 to 100 μm), and the average pore size is 1 to 200 nm (preferably 2 to 100 nm); the average length of carbon nanotubes and carbon nanofibers is 10 to 200 μm (preferably 10 to 100 μm), and the inner diameter is 2 to 100 nm (preferably 2 to 50 nm); the drying temperature is 60 to 180° C. (preferably 70 to 130° C.), and the drying time is 0.1 to 6.0 h (preferably 1.0 to 4.0 h).

[0014] Based on the above technical solution, in step (2), the ligand is one or more of glycine, glutamic acid, melamine, dicyandiamide, o-phenanthroline, o-aminoazobenzene, N-methylpyrrolidone, triphenylphosphine, triphenylphosphine oxide, and benzylphosphonic acid, preferably one or more of glycine, melamine, dicyandiamide, o-phenanthroline, and triphenylphosphine; the solvent is one or more of tetrahydrofuran, petroleum ether, water, methanol, ethanol, N,N-dimethylformamide, and dimethyl sulfoxide, preferably one or more of tetrahydrofuran, water, and ethanol; the drying temperature is 60 to 180° C. (preferably 70 to 130° C.), and the drying time is 0.1 to 6.0 h (preferably 1.0 to 4.0 h).

[0015] Based on the above technical solution, the ratio of each substance in step (1) is metal precursor: oxygen-containing chelating agent: carbon support = 1:1:1 to 10:2:1 (mass ratio), preferably 1:1:1 to 6:2:1 (mass ratio); the mass ratio of the ligand in step (2) to the supported metal-chelating agent precursor prepared above is = 1:1: to 6:1 (mass ratio), preferably 1:1 to 4:1 (mass ratio).

[0016] Based on the above technical solution, in step (3), the calcination atmosphere is one or more of nitrogen, argon, helium, carbon monoxide, carbon dioxide, and nitric oxide, preferably one or more of nitrogen, argon, and carbon dioxide; the calcination gas flow rate per gram of raw material is 20 to 450 mL·min -1 , preferably 40 to 300 mL min -1 ; The calcination temperature is 300-1000°C, preferably 600-900°C; the heating rate from room temperature to the calcination temperature is 1-10°C·min -1 , preferably 1~5℃·min -1 ; Calcination time 0.5 ~ 10.0h, preferably 1.0 ~ 4.0h.

[0017] Another aspect of the present invention provides the use of the above-synthesized carbon material loaded with single-atom or nano-metal catalysts in carbon dioxide methanation reaction.

[0018] Based on the above technical solution, in the application, the reaction temperature is 200-400°C (preferably 250-350°C), the reaction pressure is 0.1-5.0 MPa (preferably 1.0-3.0 MPa), and the gas space velocity (based on the mass of the catalyst) is 1000-8000 mL·gcat. -1 ·h -1 (Preferably 2000 to 6000 mL gcat -1 ·h -1 The feed gas is a mixture of H2 and CO2, wherein the molar ratio of H2 to CO2 is 1.0 to 5.0 (preferably 2.0 to 4.0). The reactor is a fixed bed reactor, and the feed method is continuous. The product is first passed through a cold tank to remove the generated water, and the exhaust gas is analyzed for composition by gas chromatography.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) A method for preparing carbon-supported non-precious metal single-atom or nano-metal catalysts has been developed, which can produce a high-load non-precious metal single-atom or nano-metal catalyst. This method is simple and easy to operate, has a wide range of raw material sources, and is suitable for large-scale preparation and industrial application. Compared with other oxide supports, using carbon materials as supports can recover the metal components in the catalyst, realize the reuse of metal resources, and further reduce the cost of the catalyst.

[0021] (2) Single atoms or nanoparticles on the surface of the catalyst are anchored by nitrogen atoms or oxygen atoms on the surface of the carrier, which can ensure that they do not agglomerate or sinter at higher temperatures. Compared with traditional carbon material-loaded metal catalysts, the catalyst has better stability. At the same time, no precious metals are used, which, on the one hand, reduces the production cost of the catalyst, and on the other hand, avoids the problem of poisoning and deactivation of precious metals caused by carbon monoxide produced as a by-product during the reaction.

[0022] The present invention uses a calcination method to prepare a carbon material-supported non-precious metal single-atom catalyst or nano-metal catalyst, wherein the metal loading is 1 to 15 wt% (calculated as metal), and has good carbon dioxide methanation activity and selectivity. The catalyst provided by the present invention can convert carbon dioxide into methane with high selectivity. Heteroatoms such as oxygen and nitrogen on the surface of the carbon support can anchor metal single atoms or nanoparticles, resulting in good thermal stability. The present invention develops a method for preparing a carbon material-supported single-atom or nano-catalyst, which has a wide range of raw material sources, does not use precious metals, has low catalyst cost, and is suitable for large-scale preparation. Therefore, the present invention has broad application prospects in the large-scale preparation of non-precious metal carbon-based supported single-atom and nano-metal catalysts and in carbon dioxide methanation reaction systems. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the examples, but the scope of the present invention is not limited in any way.

[0024] Example 1

[0025] 1.80 g of titanium acetate, 0.60 g of D-glucose, 0.30 g of carbon nanotubes (average length 50 μm, inner diameter 20 nm) and 10.0 g of methanol were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80 ° C for 1.5 h to obtain a supported metal-chelating agent precursor. Then, 1.0 g of triphenylphosphine, 10.0 g of methanol and 0.25 g of the supported metal-chelating agent precursor prepared above were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80 ° C for 3.0 h to obtain a supported metal catalyst precursor; the prepared supported nanometal catalyst precursor was calcined at 900 ° C in an argon atmosphere for 2.5 h (the heating rate from room temperature to the calcination temperature was 5.0 ° C·min -1 , gas flow rate per gram of raw material is 220 mL·min -1 ) to prepare supported nanometal catalyst 1. High-resolution spherical aberration electron microscopy (HAADF-STEM) demonstrated that the metal was distributed on the support in the form of nanoparticles. The nanoparticles had a particle size of 5 to 50 nm and an average particle size of 13 nm. Inductively coupled plasma optical emission spectroscopy (ICP-OES) determined the metal loading to be 9.4 wt%.

[0026] The prepared catalyst was used to conduct a carbon dioxide hydrogenation reaction evaluation test. The specific evaluation conditions are as follows: reaction temperature 500°C, reaction pressure 1.0 MPa, gas space velocity (based on catalyst mass) 6000 mL·gcat -1 ·h -1The feed gas was a mixture of H₂ and CO₂ with a molar ratio of 4.0. A fixed-bed reactor was used, with continuous feeding. The product was first passed through a cooling tank to remove generated water, and the tail gas was analyzed by gas chromatography. The carbon dioxide conversion and product selectivity are listed in Table 1.

[0027] Example 2

[0028] 1.20 g of cobalt nitrate hexahydrate, 0.80 g of D-erythritol, 0.40 g of carbon nanofibers (average length 40 μm, inner diameter 15 nm) and 10.0 g of ethanol were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 80 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 1.0 h to obtain a supported metal-chelate precursor; then 1.20 g of melamine, 10.0 g of ethanol and 0.30 g of the supported metal-chelate precursor prepared above were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 2.0 h to obtain a supported single atom catalyst precursor; the prepared supported single atom catalyst precursor was calcined at 800° C. in a nitrogen atmosphere for 3.0 h (the heating rate from room temperature to the calcination temperature was 5.0° C. min -1 , gas flow rate per gram of raw material is 150 mL min -1 ) to prepare supported single-atom catalyst 2. High-resolution spherical aberration electron microscopy (HAADF-STEM) confirmed that the metal was distributed on the support in a monodisperse manner, and inductively coupled plasma optical emission spectroscopy (ICP-OES) determined that the metal loading was 6.1 wt%.

[0029] The prepared catalyst was used to conduct a carbon dioxide hydrogenation reaction evaluation test. The specific evaluation conditions are as follows: reaction temperature 400°C, reaction pressure 0.5 MPa, gas space velocity (based on catalyst mass) 5500 mL·gcat -1 ·h -1 The molar ratio of H₂ to CO₂ in the feed gas was 4.0. A fixed-bed reactor was used, with continuous feeding. The product was first passed through a cooling tank to remove generated water, and the tail gas was analyzed by gas chromatography. The carbon dioxide conversion and product selectivity are listed in Table 1.

[0030] Example 3

[0031] 2.80 g of ferric chloride, 1.40 g of D-galactose, 0.70 g of ordered mesoporous carbon (average particle size 80 μm, average pore size 30 nm) and 10.0 g of water were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80 ° C for 1.5 h to obtain a supported metal-chelating agent precursor; then 0.80 g of glycine, 8.0 g of tetrahydrofuran and 0.20 g of the supported metal-chelating agent precursor prepared above were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80 ° C for 2.5 h to obtain a supported nano-metal catalyst precursor; the prepared supported nano-metal catalyst precursor was calcined at 850 ° C in a carbon dioxide atmosphere for 2.5 h (the heating rate from room temperature to the calcination temperature was 4.0 ° C min -1 , gas flow rate per gram of raw material is 250 mL·min -1 ), a supported nanometal catalyst 3 was prepared. High-resolution spherical aberration electron microscopy (HAADF-STEM) demonstrated that the metal was distributed on the support in the form of nanoparticles. The nanoparticles had a particle size of 4 to 40 nm and an average particle size of 11 nm. Inductively coupled plasma optical emission spectroscopy (ICP-OES) determined the metal loading to be 8.4 wt%.

[0032] The prepared catalyst was used to conduct a carbon dioxide hydrogenation reaction evaluation test. The specific evaluation conditions are as follows: reaction temperature 400°C, reaction pressure 2.0 MPa, gas space velocity (based on catalyst mass) 4000 mL·gcat -1 ·h -1 The molar ratio of H₂ to CO₂ in the feed gas was 3.0. A fixed-bed reactor was used, with continuous feeding. The product was first passed through a cooling tank to remove generated water, and the tail gas was analyzed by gas chromatography. The carbon dioxide conversion and product selectivity are listed in Table 1.

[0033] Example 4

[0034] 1.30 g nickel nitrate hexahydrate, 1.30 g D-fructose, 0.65 g activated carbon (average particle size 90 μm, average pore size 20 nm) and 10.0 g water were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 90 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 1.5 h to obtain a supported metal-chelate precursor; then 0.68 g dicyandiamide, 10.0 g methanol and 0.34 g of the supported metal-chelate precursor prepared above were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 90 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 3.0 h to obtain a supported single atom catalyst precursor; the prepared supported single atom catalyst precursor was calcined at 850° C. in a nitrogen atmosphere for 3.0 h (the heating rate from room temperature to the calcination temperature was 5.0° C. min -1 , gas flow rate per gram of raw material is 200 mL·min -1 ) to prepare supported single-atom catalyst 4. High-resolution spherical aberration electron microscopy (HAADF-STEM) confirmed that the metal was distributed on the support in a monodisperse form, and inductively coupled plasma optical emission spectroscopy (ICP-OES) showed that the metal loading was 5.6 wt%.

[0035] The prepared catalyst was used to conduct a carbon dioxide hydrogenation reaction evaluation test. The specific evaluation conditions were as follows: reaction temperature 450°C, reaction pressure 2.0 MPa, gas space velocity (based on catalyst mass) 4000 mL·gcat -1 ·h -1 The molar ratio of H₂ to CO₂ in the feed gas was 4.0. A fixed-bed reactor was used, with continuous feeding. The product was first passed through a cooling tank to remove generated water, and the tail gas was analyzed by gas chromatography. The carbon dioxide conversion and product selectivity are listed in Table 1.

[0036] Example 5

[0037] 2.68 g of chromium nitrate nine hydrate, 1.34 g of D-fructose, 0.67 g of carbon nanofibers (average length 40 μm, inner diameter 15 nm) and 10.0 g of ethanol were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 1.0 h to obtain a supported metal-chelating agent precursor; then 0.78 g of o-phenanthroline, 10.0 g of methanol and 0.30 g of the supported metal-chelating agent precursor prepared above were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 3.0 h to obtain a supported nano-metal catalyst precursor; the prepared supported nano-metal catalyst precursor was calcined at 900° C. in a nitrogen atmosphere for 3.0 h (the heating rate from room temperature to the calcination temperature was 4.0° C. min -1, gas flow rate per gram of raw material is 200 mL·min -1 ), a supported nanometal catalyst 5 was prepared. High-resolution spherical aberration electron microscopy (HAADF-STEM) confirmed that the metal was distributed on the support in the form of nanoparticles. The nanoparticles had a particle size of 4 to 50 nm and an average particle size of 15 nm. Inductively coupled plasma optical emission spectroscopy (ICP-OES) determined the metal loading to be 9.5 wt%.

[0038] The prepared catalyst was used to conduct a carbon dioxide hydrogenation reaction evaluation test. The specific evaluation conditions are as follows: reaction temperature 400°C, reaction pressure 1.0 MPa, gas space velocity (based on catalyst mass) 4500 mL·gcat -1 ·h -1 The molar ratio of H₂ to CO₂ in the feed gas was 3.0. A fixed-bed reactor was used, with continuous feeding. The product was first passed through a cooling tank to remove generated water, and the tail gas was analyzed by gas chromatography. The carbon dioxide conversion and product selectivity are listed in Table 1.

[0039] Example 6

[0040] 1.38 g of ferric nitrate, 0.55 g of D-galactose, 0.84 g of carbon nanofibers (average length 60 μm, inner diameter 15 nm) and 10.0 g of methanol were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 90 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 1.0 h to obtain a supported metal-chelating agent precursor; then 0.73 g of melamine, 10.0 g of methanol and 0.35 g of the supported metal-chelating agent precursor prepared above were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 90 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 2.0 h to obtain a supported single atom catalyst precursor; the prepared supported single atom catalyst precursor was calcined at 800° C. in an argon atmosphere for 2.0 h (the heating rate from room temperature to the calcination temperature was 4.0° C. min -1 , gas flow rate per gram of raw material is 150 mL min -1 ) to prepare supported single-atom catalyst 6. High-resolution spherical aberration electron microscopy (HAADF-STEM) confirmed that the metal was distributed on the support in a monodisperse form, and inductively coupled plasma optical emission spectroscopy (ICP-OES) determined that the metal loading was 6.8 wt%.

[0041] The prepared catalyst was used to conduct a carbon dioxide hydrogenation reaction evaluation test. The specific evaluation conditions are as follows: reaction temperature 500°C, reaction pressure 1.0 MPa, gas space velocity (based on catalyst mass) 6000 mL·gcat -1 ·h -1The molar ratio of H₂ to CO₂ in the feed gas was 2.0. A fixed-bed reactor was used, with continuous feeding. The product was first passed through a cooling tank to remove generated water, and the tail gas was analyzed by gas chromatography. The carbon dioxide conversion and product selectivity are listed in Table 1.

[0042] Example 7

[0043] 1.20 g of cobalt chloride, 1.20 g of D-glucose, 0.60 g of activated carbon (average particle size 90 μm, average pore size 20 nm) and 10.0 g of ethanol were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 60 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 1.5 h to obtain a supported metal-chelating agent precursor; then 0.450 g of dicyandiamide, 10.0 g of ethanol and 0.40 g of the supported metal-chelating agent precursor prepared above were placed in a 50 mL beaker, stirred and mixed thoroughly, ultrasonicated, allowed to stand for 80 min and then centrifuged, and the insoluble matter was dried in an oven at 80° C. for 3.5 h to obtain a supported nano-metal catalyst precursor; the prepared supported nano-metal catalyst precursor was calcined at 800° C. in a nitrogen atmosphere for 3.0 h (the heating rate from room temperature to the calcination temperature was 4.5° C. min -1 , gas flow rate per gram of raw material is 180 mL·min -1 ) to prepare supported nanometal catalyst 7. High-resolution spherical aberration electron microscopy (HAADF-STEM) confirmed that the metal was distributed on the support in the form of nanoparticles. The particle size of the nanoparticles ranged from 4 to 35 nm, with an average particle size of 10 nm. Inductively coupled plasma optical emission spectroscopy (ICP-OES) determined the metal loading to be 8.4 wt%.

[0044] The prepared catalyst was used to conduct a carbon dioxide hydrogenation reaction evaluation test. The specific evaluation conditions were as follows: reaction temperature 450°C, reaction pressure 2.0 MPa, gas space velocity (based on catalyst mass) 4000 mL·gcat -1 ·h -1 The molar ratio of H₂ to CO₂ in the feed gas was 4.0. A fixed-bed reactor was used, with continuous feeding. The product was first passed through a cooling tank to remove generated water, and the tail gas was analyzed by gas chromatography. The carbon dioxide conversion and product selectivity are listed in Table 1.

[0045] Comparative Example 1

[0046] Patent CN108855092B discloses a catalyst for carbon dioxide methanation and its preparation method. The catalyst was prepared by the method disclosed in the patent: first, 0.5g of aluminum oxide was weighed, 0.7g of nickel nitrate hexahydrate was dissolved in water to prepare a solution, the aluminum oxide was placed in the solution and immersed for 2.0h, and then dried, calcined and pressed into tablets to obtain the catalyst of Comparative Example 1. High-resolution spherical aberration electron microscopy (HAADF-STEM) was used to prove that the metal was distributed on the carrier in the form of nanoparticles, the particle size of the nanoparticles was 10 to 60nm, and the average particle size was 25nm. The specific evaluation conditions were a reaction temperature of 400°C, a reaction pressure of 1.0MPa, and a gas space velocity (based on the mass of the catalyst) of 5000mL·gcat -1 ·h -1 The molar ratio of H2 to CO2 in the raw gas is 4.0. The carbon dioxide conversion rate and the selectivity of each product are listed in Table 1.

[0047] Comparative Example 2

[0048] Using activated carbon as a carrier, a supported nickel-based catalyst was prepared: first, 0.5 g of activated carbon was weighed, 0.7 g of nickel nitrate hexahydrate was dissolved in water to prepare a solution, the activated carbon was placed in the solution and immersed for 2.0 h, and then dried and calcined to obtain the catalyst of Comparative Example 2. High-resolution spherical aberration electron microscopy (HAADF-STEM) was used to prove that the metal was distributed on the carrier in the form of nanoparticles, the particle size of the nanoparticles was 8 to 40 nm, and the average particle size was 20 nm. The specific evaluation conditions were a reaction temperature of 400 ° C, a reaction pressure of 1.0 MPa, and a gas space velocity (based on the mass of the catalyst) of 5000 mL gcat. -1 ·h -1 The molar ratio of H2 to CO2 in the raw gas is 4.0. The carbon dioxide conversion rate and the selectivity of each product are listed in Table 1.

[0049] Table 1 Carbon dioxide methanation performance of different catalysts

[0050]

[0051]

[0052] Compared to traditional inorganic carrier-supported catalysts, the catalyst nanoparticles prepared using the method of this invention are evenly dispersed and have a smaller particle size, and some catalysts are single-atom catalysts. Compared to traditional supported catalysts, the catalysts prepared using this method have a higher degree of dispersion, effectively improving metal utilization. In carbon dioxide hydrogenation reactions, they significantly improve carbon dioxide conversion and methane selectivity, while reducing carbon monoxide selectivity.

[0053] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0054] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a composite catalyst, characterized in that: The following steps are involved: (1) The metal precursor, oxygen-containing chelating agent, solvent and carbon support are mixed uniformly by one or more methods including stirring, grinding and / or ultrasound, and after standing, the solid and liquid are separated by centrifugation and / or filtration. The standing time is more than 30 minutes, and the solid insoluble matter is dried to obtain a supported metal-chelating agent precursor A; (2) The ligand, solvent and the supported metal-chelating agent precursor A prepared above are mixed uniformly by one or more methods including stirring, grinding and / or ultrasound, and after standing, the solid and liquid are separated by centrifugation or filtration. The standing time is more than 30 minutes, and the solid insoluble matter is dried to prepare a supported catalyst precursor B; (3) calcining the supported catalyst precursor B prepared above to obtain a carbon material-supported single-atom catalyst and / or nano-metal catalyst; In step (1), the metal precursor is one or more of nitrates, sulfates, hydrochlorides, formates, acetates, malates, and citrates of one or more of the metals Ti, Fe, Ni, and Cr. The oxygen-containing chelating agent is one or more of erythritol, L-arabinose, D-glucose, D-fructose, D-xylose, D-mannose, and D-galactose. In step (2), the ligand is one or more of glycine, glutamic acid, melamine, dicyandiamide, o-phenanthroline, o-aminoazobenzene, N-methylpyrrolidone, triphenylphosphine, triphenylphosphine oxide, and benzylphosphonic acid.

2. The preparation method according to claim 1, characterized in that In step (1), the metal precursor is one or more of nitrates, acetates, and malates of one or more of the metals Ti, Fe, Ni, and Cr; The oxygen-containing chelating agent is one or more of erythritol, D-glucose, D-fructose, and D-galactose; In step (2), the ligand is one or more of glycine, melamine, dicyandiamide, o-phenanthroline, and triphenylphosphine.

3. The preparation method according to claim 1, characterized in that In step (1), the solvent is one or more of tetrahydrofuran, petroleum ether, water, methanol, ethanol, N,N-dimethylformamide, and dimethyl sulfoxide. The carbon support is one or more of activated carbon, ordered mesoporous carbon, carbon nanospheres, graphite, carbon black, carbon nanotubes, and carbon nanofibers. The particle size of the activated carbon, ordered mesoporous carbon, carbon nanospheres, graphite, and carbon black is 10-200 mm, and the average pore size is 1-200 nm. The average length of the carbon nanotubes and carbon nanofibers is 10-200 mm, and the inner diameter is 2-100 nm. The drying temperature is 60-180°C, and the drying time is 0.1-6.0 h.

4. The preparation method according to claim 3, characterized in that In step (1), the solvent is one or more of tetrahydrofuran, water, and ethanol; The carbon carrier is one or more of activated carbon, carbon nanotubes, carbon nanofibers, and ordered mesoporous carbon; the particle size of the activated carbon, ordered mesoporous carbon, carbon nanospheres, graphite, and carbon black is 10-100 mm, and the average pore size is 2-100 nm; the average length of the carbon nanotubes and carbon nanofibers is 10-100 mm, and the inner diameter is 2-50 nm; the drying temperature is 70-130°C, and the drying time is 1.0-4.0 h.

5. The preparation method according to claim 1, characterized in that In step (2), the solvent is one or more of tetrahydrofuran, petroleum ether, water, methanol, ethanol, N,N-dimethylformamide, and dimethyl sulfoxide. The drying temperature is 60~180 °C and the drying time is 0.1~6.0 h.

6. The preparation method according to claim 5, characterized in that In step (2), the solvent is one or more of tetrahydrofuran, water, and ethanol; The drying temperature is 70~130 °C and the drying time is 1.0~4.0 h.

7. The preparation method according to claim 1, 2 or 3, characterized in that: The mass ratio of each substance in step (1) is metal precursor: oxygen-containing chelating agent: carbon support = 1:1:1~10:2:1; the mass ratio of the ligand in step (2) to the supported metal-chelating agent precursor prepared above is 1:1:~6:

1.

8. The preparation method according to claim 7, characterized in that The mass ratio of each substance in step (1) is 1:1:1 to 6:2:1 for metal precursor: oxygen-containing chelating agent: carbon carrier; and the mass ratio of the ligand in step (2) to the supported metal-chelating agent precursor prepared above is 1:1 to 4:

1.

9. The preparation method according to claim 1, characterized in that In step (3), the calcination atmosphere is one or more of nitrogen, argon, helium, carbon monoxide, carbon dioxide, and nitric oxide, and the calcination gas flow rate per gram of raw material is 20~450 mL min -1 ; calcination temperature is 300~1000 °C; heating rate from room temperature to calcination temperature is 1~10 °C min -1 , calcination time 0.5~10.0 h.

10. The preparation method according to claim 9, characterized in that In step (3), the calcination atmosphere is one or more of nitrogen, argon, and carbon dioxide; the calcination gas flow rate per gram of raw material is 40~300 mL min -1 ; calcination temperature is 600~900 °C; heating rate from room temperature to calcination temperature is 1~5 °C min -1 ; Calcination time is 1.0~4.0 h.

11. A carbon material synthesized by the preparation method according to any one of claims 1 to 10 loaded with single-atom and / or nano-metal catalysts.

12. Use of the carbon material according to claim 11 loaded with single atom and / or nano metal catalysts in carbon dioxide methanation reaction.

13. The use according to claim 12, characterized in that In the application, the reaction temperature is 250-600 °C, the reaction pressure is 0.1-5.0 MPa, and the gas space velocity is 1000-8000 mL gcat based on the mass of the catalyst. -1 h -1 , the raw gas is a mixture of H2 and CO2, in which the molar ratio of H2 to CO2 is 1.0~5.

0.

14. The use according to claim 13, characterized in that In the application, the reaction temperature is 300-500 °C, the reaction pressure is 1.0-3.0 MPa, and the gas space velocity is 2000-6000 mL gcat based on the mass of the catalyst. -1 h -1 , the raw gas is a mixture of H2 and CO2, in which the molar ratio of H2 to CO2 is 2.0~4.

0.

15. The use according to claim 12, 13 or 14, characterized in that The reactor adopts a fixed bed and the feeding method adopts continuous feeding. The product first passes through a cold tank to remove the generated water, and the tail gas is analyzed for composition using gas chromatography.

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