Cobalt-based catalyst and preparation method and application thereof

Abstract

The invention provides a cobalt-based catalyst and a preparation method and application thereof. The preparation method of the cobalt-based catalyst comprises the following steps: (1) preparing CoMn composite metal oxalate by adopting an oxalic acid precipitation method; (2) calcining the CoMn composite metal oxalate to obtain a CoMn composite metal oxide; (3) loading the Na element onto the CoMn composite metal oxide by adopting an impregnation method to obtain a cobalt-based catalyst precursor; and (4) carbonizing the cobalt-based catalyst precursor to obtain the cobalt-based catalyst. The cobalt-based catalyst prepared by the invention is applied to a reaction for preparing low-carbon olefin by light-driven synthesis gas conversion, and efficient conversion of CO and high selectivity of low-carbon olefin can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation, in particular to a cobalt-based catalyst and a preparation method and application thereof. BACKGROUND

[0002] Low carbon olefins (including ethylene, propylene and butene) are raw materials for chemicals such as polymers, medicines and solvents, and their demand is large and increasing year by year. Although the production of low carbon olefins in China has formed a certain scale, the self-sufficiency rate is low, and the contradiction between supply and demand still exists. Traditional low carbon olefin production is mainly obtained by petroleum cracking, cracking and other methods. China's fossil resources have the characteristics of "rich in coal, less oil and lack of gas", and a large amount of imported oil is needed to meet the huge demand for low carbon olefins in China. The process of using coal as raw material to prepare low carbon olefins is more suitable for the characteristics of China's fossil resources, can realize high value-added utilization of coal, and get rid of the dependence on imported oil. Fischer-Tropsch reaction is a process in which synthesis gas (CO and H2) is converted into C2+ (C2+ represents the number of C atoms greater than or equal to 2) products under specific conditions using a catalyst. By optimizing the reaction temperature, reaction pressure and regulating the catalyst structure, the product distribution and product selectivity can be regulated. For example, using a specific catalyst can convert synthesis gas into low carbon olefins at 200-300℃ and normal pressure. Through the normal pressure Fischer-Tropsch reaction, the synthesis gas derived from coal gasification production is converted into low carbon olefins, which has very important application prospect and practical significance. The catalyst is the core of Fischer-Tropsch synthesis reaction, and its activity, selectivity and stability directly determine the efficiency and product distribution of the conversion of synthesis gas into hydrocarbon products. SUMMARY

[0003] The purpose of the present application is to provide a cobalt-based catalyst and a preparation method and application thereof, so as to realize the efficient conversion of synthesis gas and the high selectivity of low carbon olefins. The specific technical solutions are as follows:

[0004] The first aspect of the present application provides a preparation method of a cobalt-based catalyst, which comprises the following steps:

[0005] (1) preparing CoMn composite metal oxalate by adopting oxalic acid precipitation method;

[0006] (2) calcining the CoMn composite metal oxalate to obtain CoMn composite metal oxide;

[0007] (3) loading Na element onto the CoMn composite metal oxide by adopting impregnation method to obtain cobalt-based catalyst precursor;

[0008] (4) carbonizing the cobalt-based catalyst precursor to obtain the cobalt-based catalyst.

[0009] In some embodiments of the present application, in the step (1), the step of preparing the CoMn composite metal oxalate salt comprises: dissolving a cobalt salt and a manganese salt in a solvent to obtain a mixed metal salt solution, dissolving oxalic acid dihydrate in the solvent to obtain an oxalic acid solution, adding the mixed metal salt solution into the oxalic acid solution to react for 0.5-2 hours, obtaining a precipitate through solid-liquid separation, washing and drying the precipitate to obtain the CoMn composite metal oxalate salt.

[0010] In some embodiments of the present application, the cobalt salt is at least one selected from the group consisting of cobalt nitrate, cobalt chloride, and cobalt acetylacetonate, the manganese salt is at least one selected from the group consisting of manganese nitrate, manganese chloride, and manganese sulfate, and the solvent is at least one selected from the group consisting of deionized water, ethanol, and dimethyl sulfoxide; the concentration of the mixed metal salt solution is 0.05-2 mol / L, the concentration of the oxalic acid solution is 0.5-1 mol / L, and the molar ratio of metal ions in the mixed metal salt solution to oxalic acid dihydrate in the oxalic acid solution is 1:(1-5).

[0011] In some embodiments of the present application, in the step (3), the step of preparing the cobalt-based catalyst precursor comprises: adding the CoMn composite metal oxide into deionized water, mixing uniformly to obtain a suspension, adding an aqueous sodium salt solution into the suspension, stirring for 1-3 hours, and drying and calcining to obtain the cobalt-based catalyst precursor.

[0012] In some embodiments of the present application, in the suspension, the mass ratio of the CoMn composite metal oxide to deionized water is 1:(2-10); the aqueous sodium salt solution is at least one selected from the group consisting of an aqueous sodium nitrate solution, an aqueous sodium chloride solution, and an aqueous sodium sulfate solution, the concentration of Na element in the aqueous sodium salt solution is 0.01-0.1 g / mL, and the mass-volume ratio of the CoMn composite metal oxide to the aqueous sodium salt solution is 1:(0.1-1).

[0013] In some embodiments of the present application, in the step (2) and / or the step (3), the calcining comprises: heating to 300-500℃ at a heating rate of 1-5℃ / min under an air atmosphere, and maintaining the temperature for 2-4 hours.

[0014] In some embodiments of the present application, in the step (4), the carbonization comprises: heating to 220-320℃ at a heating rate of 1-5℃ / min under a synthesis gas atmosphere, and maintaining the temperature for 4-10 hours; the synthesis gas comprises CO, H2, and an inert gas, and the molar ratio of the CO, H2, and the inert gas is 1:(0.5-2):(0.0625-0.125).

[0015] The second aspect of the present application provides a cobalt-based catalyst prepared by the preparation method provided in the first aspect of the present application.

[0016] In some embodiments of the present application, the cobalt-based catalyst has a structural formula of Co z MnC x O y -Na, wherein 2≤z≤10, 1≤x≤5, and 1≤y≤10.

[0017] The third aspect of the present application provides a use of the cobalt-based catalyst provided in the second aspect of the present application for catalyzing photo-driven synthesis gas conversion to produce low-carbon olefins.

[0018] The present application has the following beneficial effects:

[0019] The present application provides a cobalt-based catalyst, a preparation method thereof, and an application thereof. The preparation method of the cobalt-based catalyst comprises the following steps: (1) preparing a CoMn composite metal oxalate by using an oxalic acid precipitation method; (2) calcining the CoMn composite metal oxalate to obtain a CoMn composite metal oxide; (3) loading a Na element onto the CoMn composite metal oxide by using an impregnation method to obtain a cobalt-based catalyst precursor; and (4) carbonizing the cobalt-based catalyst precursor to obtain the cobalt-based catalyst. The preparation method is simple and easy to operate, has strong operability, and has the advantages of being green and economical. The cobalt-based catalyst prepared by the present application is applied to a reaction of photo-driven synthesis gas conversion to produce low-carbon olefins, the catalyst has high CO hydrogenation activity under light and normal pressure conditions, realizes efficient conversion of CO and high selectivity of low-carbon olefins, has high practical production application value, and has the advantage of being highly stable. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0021] Figure 1 The XRD pattern of the cobalt-based catalyst prepared for Example 1 of the present application;

[0022] Figure 2 The HAADF-STEM photo of the cobalt-based catalyst prepared for Example 1 of the present application;

[0023] Figure 3 The HR-HAADF-STEM photo of the cobalt-based catalyst prepared for Example 1 of the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the present application will be clearly and completely described below with reference to the embodiments of the present application and the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. All other embodiments obtained by those skilled in the art based on the present application are within the scope of the present application.

[0025] The first aspect of the present application provides a preparation method of a cobalt-based catalyst, comprising the following steps:

[0026] (1) preparing CoMn composite metal oxalate by using an oxalic acid precipitation method;

[0027] (2) calcining the CoMn composite metal oxalate to obtain a CoMn composite metal oxide;

[0028] (3) loading Na element onto the CoMn composite metal oxide by using an impregnation method to obtain a cobalt-based catalyst precursor;

[0029] (4) carbonizing the cobalt-based catalyst precursor to obtain a cobalt-based catalyst.

[0030] The inventors find that Co element has good dissociation capacity for CO, and Co-based catalysts are widely used in industrial synthesis gas conversion. When Co species exists in the form of Co2C, it has a relatively suitable carbon chain growth capacity and olefin selectivity, and under normal pressure conditions, the catalytic product is mainly low-carbon olefins. Co2C is mainly obtained by carbonizing treatment of Co oxides, which needs to be carried out with the assistance of Na + By adding metal oxide additives, the dissociation of H2 is strengthened, and the dissociated H can improve the CO dissociation capacity on Co2C, further improving the reaction activity. By using Na + The CoMn composite metal oxide modified by Na is used as a precursor, and a manganese oxide modified Co2C catalyst can be obtained by carbonization treatment. The catalyst obtained in the present application has good light absorption and heat generation capacity, and the manganese oxide and Co2C can play a synergistic role. The carbide of Co has good CO activation capacity and suitable carbon chain growth capacity, and the oxide of Mn has good H2 molecule dissociation capacity. The catalyst obtained in the present application is used in the reaction of light-driven synthesis gas conversion for preparing low-carbon olefins, realizing light-driven synthesis gas conversion and high selectivity for low-carbon olefins, and having good application prospect. In the present application, low-carbon olefins refer to olefins with carbon atom number less than or equal to 4, including ethylene, propylene, butylene, etc.

[0031] In some embodiments of the present application, in step (1), the step of preparing the CoMn composite metal oxalate salt comprises: dissolving a cobalt salt and a manganese salt in a solvent to obtain a mixed metal salt solution, dissolving oxalic acid dihydrate in a solvent to obtain an oxalic acid solution, adding the mixed metal salt solution to the oxalic acid solution and reacting for 0.5-2 h, and then performing solid-liquid separation to obtain a precipitate, which is washed and dried to obtain the CoMn composite metal oxalate salt. For example, the reaction time of the mixed metal salt solution and the oxalic acid solution can be 0.5 h, 1 h, 1.5 h, 2 h, or a range defined by any two of the above values.

[0032] In some embodiments of the present application, the cobalt salt is at least one selected from the group consisting of cobalt nitrate, cobalt chloride, and cobalt acetylacetonate, the manganese salt is at least one selected from the group consisting of manganese nitrate, manganese chloride, and manganese sulfate, and the solvent is at least one selected from the group consisting of deionized water, ethanol, and dimethyl sulfoxide; the concentration of the mixed metal salt solution is 0.05-2 mol / L, the concentration of the oxalic acid solution is 0.5-1 mol / L, and the molar ratio of metal ions in the mixed metal salt solution to oxalic acid dihydrate in the oxalic acid solution is 1:(1-5). For example, the concentration of the mixed metal salt solution can be 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.3 mol / L, 1.6 mol / L, or 2 mol / L, or a range defined by any two of the above values, the concentration of the oxalic acid solution can be 0.5 mol / L, 0.7 mol / L, or 1 mol / L, or a range defined by any two of the above values, and the molar ratio of metal ions in the mixed metal salt solution to oxalic acid dihydrate in the oxalic acid solution can be 1:1, 1:2, 1:3, 1:4, 1:5, or a range defined by any two of the above values.

[0033] In the present application, the mixed metal salt solution can be added dropwise to the oxalic acid solution at a fast reaction rate, and stirring can be performed at a fast speed from the beginning of the dropwise addition to the end of the reaction. The speed of the dropwise addition and the speed of the stirring are not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the speed of the dropwise addition can be 1 mL / min, and the stirring speed can be 500 r / min.

[0034] In the present application, the solid-liquid separation operation includes but is not limited to centrifugation, etc.; the purpose of the washing is to wash away excess oxalic acid, for example, the precipitate can be washed to neutral with ethanol by centrifugation.

[0035] In some embodiments of the present application, in step (3), the step of preparing the cobalt-based catalyst precursor comprises: adding the CoMn composite metal oxide into deionized water, mixing uniformly to obtain a suspension, adding an aqueous sodium salt solution into the suspension, stirring for 1 h to 3 h, and obtaining the cobalt-based catalyst precursor through drying and calcination. For example, the stirring time can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or a range defined by any two of the above values. The stirring speed in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the stirring speed can be 300 r / min.

[0036] In some embodiments of the present application, in the suspension, the mass ratio of the CoMn composite metal oxide to the deionized water is 1:(2-10); the aqueous sodium salt solution is selected from at least one of an aqueous sodium nitrate solution, an aqueous sodium chloride solution, and an aqueous sodium sulfate solution, the concentration of Na element in the aqueous sodium salt solution is 0.01 g / mL to 0.1 g / mL, and the mass-to-volume ratio of the CoMn composite metal oxide to the aqueous sodium salt solution is 1:(0.1-1). For example, the mass ratio of the CoMn composite metal oxide to the deionized water can be 1:2, 1:4, 1:5, 1:7, 1:8, 1:10, or a range defined by any two of the above values; the concentration of Na element in the aqueous sodium salt solution can be 0.01 g / mL, 0.03 g / mL, 0.05 g / mL, 0.08 g / mL, 0.1 g / mL, or a range defined by any two of the above values; and the mass-to-volume ratio of the CoMn composite metal oxide to the aqueous sodium salt solution can be 1:0.1, 1:0.4, 1:0.6, 1:0.8, 1:1, or a range defined by any two of the above values. In the present application, the mass-to-volume ratio refers to the mass of the CoMn composite metal oxide to the volume of the aqueous sodium salt solution.

[0037] The drying method in the above-mentioned steps (1) and (3) is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, drying can be performed in an oven at 80°C.

[0038] In some embodiments of the present application, in step (2), the calcination comprises: increasing the temperature to 300°C to 500°C at a temperature increasing rate of 1°C / min to 5°C / min under an air atmosphere, and maintaining the temperature for 2 h to 4 h. For example, the temperature increasing rate can be 1°C / min, 3°C / min, 5°C / min, or a range defined by any two of the above values; the calcination temperature can be 300°C, 350°C, 400°C, 450°C, 500°C, or a range defined by any two of the above values; and the holding time can be 2 h, 2.5 h, 3 h, 4 h, or a range defined by any two of the above values.

[0039] In some embodiments of the present application, in step (3), the calcination comprises: heating to 300-500℃ at a heating rate of 1-5℃ / min under an air atmosphere, and maintaining for 2-4h. For example, the heating rate can be 1℃ / min, 3℃ / min, 5℃ / min, or a range defined by any two of the above values; the calcination temperature can be 300℃, 350℃, 400℃, 450℃, 500℃, or a range defined by any two of the above values; and the maintaining time can be 2h, 2.5h, 3h, 4h, or a range defined by any two of the above values.

[0040] In the present application, the calcination conditions in step (2) and step (3) can be the same or different, as long as they are within the scope of the present application.

[0041] In some embodiments of the present application, in step (4), the carbonization comprises: heating to 220-320℃ at a heating rate of 1-5℃ / min under a synthesis gas atmosphere, and maintaining for 4-10h; the synthesis gas comprises CO, H2 and an inert gas, and the molar ratio of CO, H2 and the inert gas is 1:(0.5-2):(0.0625-0.125). For example, the heating rate can be 1℃ / min, 2℃ / min, 4℃ / min, 5℃ / min, or a range defined by any two of the above values; the calcination temperature can be 220℃, 250℃, 280℃, 300℃, 320℃, or a range defined by any two of the above values; the maintaining time can be 4h, 5h, 6.5h, 8h, 10h, or a range defined by any two of the above values; and the molar ratio of CO, H2 and the inert gas can be 1:0.5:0.0625, 1:1:0.08, 1:2:0.125, or a range defined by any two of the above values. In the present application, the inert gas can include, but is not limited to, Ar, N2, etc., which does not participate in the carbonization reaction and only serves as an internal standard gas for analysis.

[0042] The second aspect of the present application provides a cobalt-based catalyst prepared by the preparation method of the first aspect of the present application.

[0043] In some embodiments of the present application, the cobalt-based catalyst has the structural formula of Co z MnC x O y -Na, wherein 2≤z≤10, 1≤x≤5, and 1≤y≤10. The catalyst can improve the photo-driven synthesis gas conversion under normal pressure conditions through the synergistic effect of MnO and Co2C, and has good selectivity to low-carbon olefins. In addition, the above-mentioned cobalt-based catalyst needs to be sealed and stored to reduce contact with air.

[0044] The third aspect of the present application provides a use of the cobalt-based catalyst provided by the second aspect of the present application for catalyzing the light-driven synthesis gas conversion to produce low-carbon olefins. The cobalt-based catalyst of the present application can be applied to the flow-type reactor light-driven synthesis gas conversion to produce low-carbon olefins, and can also be applied to the batch-type reactor light-driven synthesis gas conversion to produce low-carbon olefins. The catalyst does not need to be treated after the reaction and can be continuously reused.

[0045] Examples

[0046] Hereinafter, the embodiments of the present application will be described more specifically by citing examples and comparative examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0047] Test methods and equipment:

[0048] X-ray diffraction test (XRD):

[0049] An X-ray diffractometer, model D8 powder diffractometer, produced by Bruker Corporation, Germany, was used for the test, with the following parameters: 35 kV, 40 mA, continuous mode, scanning speed of 10° per minute, scanning range of 20-80°, and copper target.

[0050] Cobalt-based catalyst morphology test:

[0051] High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and high-resolution high-angle annular dark-field scanning transmission electron microscopy (HR-HAADF-STEM) were used to test the morphology of the cobalt-based catalyst, respectively.

[0052] Example 1

[0053] Preparation of cobalt-based catalyst

[0054] Under room temperature, 11.64 g of cobalt nitrate hexahydrate and 2.86 g of 50 wt% aqueous manganese nitrate solution were dissolved in 24 mL of ethanol to obtain a mixed metal salt solution. 9.08 g of oxalic acid dihydrate was dissolved in 144 mL of ethanol to obtain an oxalic acid solution. The concentration of the mixed metal salt solution was 2 mol / L, and the concentration of the oxalic acid solution was 0.5 mol / L. The molar ratio of metal ions in the mixed metal salt solution to oxalic acid dihydrate in the oxalic acid solution was 1:1.5. The mixed metal salt solution was added dropwise into the oxalic acid solution at a stirring speed of 500 r / min, and the dropwise addition rate of the mixed metal salt solution was 1 mL / min. After the dropwise addition was completed, the stirring and aging reaction were continued for 2 h. The precipitate was obtained by centrifugation and washed by centrifugation. The precipitate was washed with ethanol until it was neutral. Then, the precipitate was dried in an oven at 80℃ for 12 h and calcined in a muffle furnace for 3 h. The calcination temperature was 400℃, and the temperature rising rate was 2℃ / min. Thus, a CoMn composite metal oxide was obtained.

[0055] 1 g of the CoMn composite metal oxide was mixed with 2 mL of deionized water, 1 mL of an aqueous sodium nitrate solution (0.019 g / mL) was added, and the mixture was stirred at 300 r / min for 2 h. The mixture was dried in an oven at 80℃ for 12 h. The dried sample was calcined in a muffle furnace for 3 h. The calcination temperature was 400℃, and the temperature rising rate was 2℃ / min. Thus, a cobalt-based catalyst precursor was obtained. 0.05 g of the cobalt-based catalyst precursor was carbonized in a tube furnace in an atmosphere of 32% CO + 64% H2 + 4% Ar (the molar ratio of CO, H2 and Ar was 1:2:0.125) for 10 h. The carbonization temperature was 260℃, and the temperature rising rate was 1℃ / min. Thus, Co5MnC x O y -Na catalyst.

[0056] <Performance test of cobalt-based catalyst>

[0057] 0.05 g of the cobalt-based catalyst prepared above was placed on a catalyst carrier of a flow-type photo-thermal reactor, and was flattened. Then, the reactor was sealed. The flow-type photo-thermal reactor was purged with 0.1 MPa of synthesis gas for 20 min, so that the original air in the reactor was exhausted. The photo-driven synthesis gas conversion reaction for producing low-carbon olefins was carried out under the reaction condition of light irradiation. The light intensity was set to 2.83 W / cm 2 , the reaction gas was a mixed gas of CO, H2 and Ar, the molar ratio of CO, H2 and Ar was 1:1:0.083, the flow rate of the reaction gas was 3000 mL / (g cat ·h), and the pressure was 0.1 MPa. The photo-driven synthesis gas conversion reaction for producing low-carbon olefins was carried out under the above conditions.

[0058] The CO conversion rate and the olefin / alkane ratio were calculated using an online gas chromatograph. The specific calculation formula is as follows:

[0059] wherein F CO,in represents the molar flow of the reaction gas CO into the flow-through photo-thermal reactor, F CO,out represents the molar flow of CO out of the flow-through photo-thermal reactor.

[0060] alkene to alkane ratio

[0061] wherein F is the molar amount of product, i is the number of C atoms of the hydrocarbon (i = 2-4), C ＝ is the alkene, C p is the alkane.

[0062] The conversion of CO was 8.7%, the alkene to alkane ratio was 6.3, and the selectivity to low carbon olefins was high.

[0063] Example 2

[0064] Except that the carbonization time was 5 h and the heating rate was 5°C / min, the cobalt-based catalyst obtained was Co5MnC x O y -Na, the light intensity was set to 2.33 W / cm 2 , the reaction gas was a mixture of CO, H2, and Ar, the molar ratio of CO, H2, and Ar was 1:2:0.083, and the rest was the same as in Example 1.

[0065] The conversion of CO was 4.0%, the alkene to alkane ratio was 10.9, and the selectivity to low carbon olefins was high.

[0066] Comparative Example 1

[0067] Except that the CoMn composite metal oxide was not impregnated with Na element and the mass of cobalt nitrate hexahydrate was 4.66 g, the cobalt-based catalyst obtained was Co2MnC x O y , and the rest was the same as in Example 1.

[0068] The conversion of CO was 3.6%, the alkene to alkane ratio was 3.4, and the selectivity to low carbon olefins was low.

[0069] Figure 1 is the XRD pattern of the cobalt-based catalyst prepared in Example 1 of the present application, it can be seen from Figure 1 that the Co species in the cobalt-based catalyst exists in the form of cobalt oxide and cobalt carbide, Figure 2 is the HAADF-STEM image of the cobalt-based catalyst prepared in Example 1 of the present application, Figure 3 is the HR-HAADF-STEM image of the cobalt-based catalyst prepared in Example 1 of the present application, it can be seen from Figure 2 and Figure 3It can be seen that the particle size of Co species in the cobalt-based catalyst is about 20 nm.

[0070] It can be seen from Example 1, Example 2 and Comparative Example 1 that the cobalt-based catalyst prepared by the preparation method of the present application is used for photo-driven synthesis gas conversion to prepare low-carbon olefins, which realizes efficient conversion of CO and high selectivity to low-carbon olefins.

[0071] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a cobalt-based catalyst, comprising the following steps: (1) preparing a CoMn composite metal oxalate by an oxalic acid precipitation method; (2) calcining the CoMn composite metal oxalate to obtain a CoMn composite metal oxide; (3) loading Na element onto the CoMn composite metal oxide by an impregnation method to obtain a cobalt-based catalyst precursor; (4) carbonizing the cobalt-based catalyst precursor to obtain the cobalt-based catalyst.

2. The production method according to claim 1, wherein, In the step (1), the step of preparing the CoMn composite metal oxalate comprises: dissolving a cobalt salt and a manganese salt in a solvent to obtain a mixed metal salt solution, dissolving oxalic acid dihydrate in the solvent to obtain an oxalic acid solution, adding the mixed metal salt solution into the oxalic acid solution for 0.5-2 hours of reaction, obtaining a precipitate through solid-liquid separation, washing and drying the precipitate to obtain the CoMn composite metal oxalate.

3. The production method according to claim 2, wherein, The cobalt salt is at least one selected from cobalt nitrate, cobalt chloride and cobalt acetylacetonate, the manganese salt is at least one selected from manganese nitrate, manganese chloride and manganese sulfate, and the solvent is at least one selected from deionized water, ethanol and dimethyl sulfoxide; the concentration of the mixed metal salt solution is 0.05-2 mol / L, the concentration of the oxalic acid solution is 0.5-1 mol / L, and the molar ratio of metal ions in the mixed metal salt solution to oxalic acid dihydrate in the oxalic acid solution is 1:(1-5).

4. The production method according to claim 1, wherein In the step (3), the step of preparing the cobalt-based catalyst precursor comprises: adding the CoMn composite metal oxide into deionized water, mixing uniformly to obtain a suspension, adding a sodium salt aqueous solution into the suspension, stirring for 1-3 hours, and drying and calcining to obtain the cobalt-based catalyst precursor.

5. The production method according to claim 4, wherein In the suspension, the mass ratio of the CoMn composite metal oxide to deionized water is 1:(2-10); the sodium salt aqueous solution is at least one selected from a sodium nitrate aqueous solution, a sodium chloride aqueous solution and a sodium sulfate aqueous solution, the concentration of Na element in the sodium salt aqueous solution is 0.01-0.1 g / mL, and the mass-volume ratio of the CoMn composite metal oxide to the sodium salt aqueous solution is 1:(0.1-1).

6. The production method according to claim 1 or 4, wherein In the step (2) and / or the step (3), the calcining comprises: heating to 300-500℃ at a heating rate of 1-5℃ / min under an air atmosphere, and keeping for 2-4 hours.

7. The production method according to claim 1, wherein In the step (4), the carbonizing comprises: heating to 220-320℃ at a heating rate of 1-5℃ / min under a synthesis gas atmosphere, and keeping for 4-10 hours; the synthesis gas comprises CO, H2 and an inert gas, and the molar ratio of the CO, H2 and inert gas is 1:(0.5-2):(0.0625-0.125). 8.A cobalt-based catalyst prepared by the method according to any one of claims 1-7.

9. The cobalt-based catalyst of claim 8, wherein, The cobalt-based catalyst has a structural formula of Co z MnC x O y -Na, wherein 2≤z≤10, 1≤x≤5, and 1≤y≤10. 10.Use of the cobalt-based catalyst according to claim 8 for catalyzing photo-driven synthesis gas conversion to prepare low-carbon olefins.

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