Iron-based catalyst and use thereof

Abstract

The present application relates to a kind of iron-based catalyst for carbon dioxide hydrogenation synthesis C 2+ Alcohols and application. The prepared iron-based catalyst is spherical Fe3O4, modified with alkali metal and transition metal; The addition of reducing agent in the preparation process makes Fe not need to experience Fe2O3 to Fe3O4, the addition of electrostatic stabilizer can promote the uniform and stable growth of Fe3O4 particles, and it is not necessary to use nitrate as metal source and high temperature calcination and other steps, avoid causing environmental pollution and the problem that metal component is easy to sinter in the preparation process. The catalyst provided by the present application can directly convert CO2 into C 2+ Alcohols, the conversion rate of CO2 can reach 41.6%, the selectivity of CO is about 5%, the selectivity of C 2+ Alcohols / total alcohol can reach 98.4%, the space-time yield of C 2+ Alcohols can reach 112.9mg g cat ‑ 1 h ‑1 .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to an iron-based catalyst for synthesizing C 2+ alcohols from carbon dioxide and its application BACKGROUND

[0002] Since the industrial revolution, mankind has massively exploited fossil energy in nature and discharged CO2 and other greenhouse gases into the environment. Excessive discharge of CO2 has caused a series of environmental problems such as greenhouse effect and ocean acidification. Climate reports show that the global average temperature will increase by about 2℃ in 2050 and by 4℃ in 2100, which poses a great threat to the survival and development of mankind. In order to stabilize the concentration of CO2 in the atmosphere, not only the discharge of CO2 should be reduced, but also the technology of CO2 capture, storage and utilization (CCUS) should be developed. Compared with traditional fossil fuels, CO2 is a rich, non-toxic and renewable carbon source. Using it as an industrial raw material to produce alkanes, alkenes, arenes, alcohols, gasoline and other high-value chemicals can not only effectively alleviate the environmental problems caused by excessive discharge of CO2, but also reduce the over-reliance on fossil energy, which is of great significance to the sustainable development of energy and chemical industry.

[0003] Among the numerous chemicals produced from CO2, alcohol compounds have wide applications and large market demand. Methanol is a commonly used C1 intermediate in chemical production and can also be used directly as a clean fuel. Compared with methanol, C 2+ alcohols have higher energy density, lower saturated vapor pressure and lower water affinity, and are more suitable as fuels and fuel additives. C 2+ The alcohols such as ethanol, propanol and butanol obtained by separation can be used as raw materials and intermediates for the production of other chemicals. At present, ethanol and butanol are mainly produced by fermentation of sugars in agricultural products such as potatoes, corn and sugarcane, which consumes agricultural products and generates a large amount of separation cost. Heavier alcohols are mainly produced by hydration of corresponding petroleum-derived olefins on acidic catalysts, which does not conform to the concept of green and efficient production. Therefore, the process of directly producing alcohol compounds from renewable CO2 resources has attracted widespread attention.

[0004] At present, the catalyst for synthesizing C 2+ alcohols from CO2 by direct catalytic hydrogenation can be divided into noble metal and non-noble metal catalysts. However, since the synthesis of alcohols involves multiple steps, in order to achieve higher CO2 conversion and selectivity to C 2+ alcohols, the catalyst must have multiple functions such as activation of CO2, adsorption of intermediate products, adjustment of surface active species, carbon chain growth and low selectivity to by-products. Therefore, Cu-Co, Cu-Fe and other multi-active site catalysts have become the focus of research on catalysts for the production of C 2+ alcohols from CO2.

[0005] In recent years, traditional catalytic materials used in Fischer-Tropsch synthesis, such as Cu, Co, and Fe, have been modified for use in the catalytic hydrogenation of CO2 to C. 2+ Alcohol reaction. Yang et al. synthesized Co3O4 nanorods with low reducing power and high RWGS reactivity. Their supported Cu-based catalyst was tested at 250 °C, 3 MPa, and 36000 mL g / L. cat -1 h -1 Under these conditions, a CO2 conversion rate of 13.9% and a yield of 1.87 mmol g were obtained. cat -1 h -1 The ethanol yield (Angewandte Chemie-International Edition, 2019, 58(33):11242-11247). Huang et al. reported a K, Mn modified FeC catalyst, which, at 300℃, 3MPa, and 6000mL g, yielded ethanol at 300℃, 3MPa, and 6000mL g. cat -1 h -1 Under these conditions, the CO2 conversion rate is greater than 40%, C 2+ The selectivity for alcohols exceeded 10%, and the proportions of propanol and butanol in the alcohol products exceeded 30% (Industrial & Engineering Chemistry Research, 2022, 61(21):7266-7274). Lu et al. prepared Na-promoted Fe3O4 microsphere catalysts at 300℃, 0.5MPa, and 2500mL g. cat -1 h -1 Under certain conditions, the main product is olefin (approximately 68%); however, when the reaction pressure is increased to 3 MPa, the main product becomes alcohol (approximately 42%). Multiple characterization results indicate that high pressure promotes the increase of oxygen vacancies, and the large number of oxygen vacancies leads to insufficient hydrogenation of adsorbed CO2, promoting the production of CHO*, which is a key intermediate in the production of ethanol. (Catalysis Science & Technology, 2021, 11(23): 7694-7703).

[0006] Currently, there are some methods for synthesizing C from CO2 hydrogenation. 2+ Catalysts for alcohols have been patented. Several reported patents are listed below with detailed explanations:

[0007] Chinese patent CN202310575287.X discloses a method for producing CO2 by hydrogenation. 2+Catalyst for alcohol and its preparation method and application. The patent reports that the Fe-based catalyst modified by additives is prepared by coprecipitation method, under the conditions of 300 ℃, 3 MPa, 3000 mL g cat -1 h -1 , the CO2 conversion rate is 40.2%, the C 2+ alcohol / total alcohol is 96.6%, but the CO selectivity is high.

[0008] Chinese patent CN202210207836.3 discloses the title: preparation method and application of copper-iron-zinc-based catalyst for preparing C 2+ alcohol by CO2 hydrogenation. The patent reports that the salt solution and modified metal solution are mixed by physical mixing method, under the conditions of 310 ℃, 4 MPa, 7200 mL g cat -1 h -1 , the CO2 conversion rate is 10.6%, the C 2+ alcohol / total alcohol is 95.3%, and the C 2+ alcohol space-time yield is 58.2 mg g cat -1 h -1 .

[0009] In summary, compared with other catalysts, Fe-based catalyst has excellent RWGS ability and carbon chain growth ability, and is widely used in the preparation of C 2+ chemicals by CO2 hydrogenation. However, Fe-based catalysts used for preparing oxygen-containing compounds have the problem of insufficient non-dissociation activation ability of CO, resulting in high selectivity of hydrocarbons such as alkanes in the product. Therefore, it is necessary to improve the selectivity of alcohol products by modifying the catalyst and optimizing the reaction conditions. SUMMARY

[0010] The purpose of the present application is to overcome the shortcomings of low selectivity of C 2+ alcohol and low CO2 conversion rate in the existing CO2 hydrogenation synthesis of C 2+ alcohol reaction, and to provide a transition metal and alkali metal modified spherical iron-based catalyst by utilizing the structure of spherical Fe3O4 and the interaction between the active components to promote the formation and reduction of the active components. Another purpose of the present application is to provide the application of the above catalyst in the preparation of C 2+ alcohol from CO2 hydrogenation. The catalyst prepared by the present application has the reaction performance of catalyzing CO2 hydrogenation to prepare C 2+ alcohol, and can generate C 2+ alcohol with high selectivity under certain reaction conditions, which has good application prospect.

[0011] The technical scheme of the present application is as follows: an iron-based catalyst is prepared by the following method, and the specific steps are as follows:

[0012] (1) Iron salt, transition metal salt is dissolved in solvent to prepare solution, then reducing agent and electrostatic stabilizer are added to the solution, after stirring, hydrothermal reaction, cooling, centrifugation, washing, drying, transition metal modified spherical Fe3O4 is obtained;

[0013] (2) Alkali metal source is prepared into aqueous solution, then it is immersed on the spherical Fe3O4 obtained in step (1), after ultrasonic, vacuum drying, alkali metal and transition metal modified spherical Fe3O4 catalyst is obtained.

[0014] Preferably, the iron salt in step (1) is one of ferric nitrate, ferric chloride or ferric sulfate; the transition metal salt is one of nitrate, chloride or sulfate of transition metal, wherein the transition metal is one or several of Mn, Zn, Cu; the solvent is one of water, ethylene glycol or glycerol; the reducing agent is one of sodium acetate or oxalic acid; the electrostatic stabilizer is one of trisodium citrate, sodium phosphate, polyvinylpyrrolidone.

[0015] Preferably, the molar ratio of iron salt to transition metal salt is 1:(0.1-1); the mass ratio of reducing agent to iron salt is (0.2-2):1; the mass ratio of electrostatic stabilizer to iron salt is (0.01-0.2):1.

[0016] Preferably, the temperature of hydrothermal reaction in step (1) is 100-200℃, and the time of hydrothermal reaction is 6-24h.

[0017] Preferably, the alkali metal source in step (2) is one of sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, rubidium carbonate or cesium carbonate; the mass of alkali metal source is 1-10% of the mass of spherical Fe3O4.

[0018] Preferably, the vacuum drying temperature in step (2) is 60-100℃, and the drying time is 8-24h.

[0019] The application also provides the use of the above-mentioned iron-based catalyst in the preparation of C 2+ alcohol by carbon dioxide hydrogenation in a fixed bed reactor. The specific steps are as follows: first, the catalyst is loaded in the constant temperature zone of the middle part of the reaction tube of the fixed bed reactor, and quartz sand is loaded above and below the reaction tube; open the gas bypass valve on the fixed bed reactor, and fill the reducing gas into it to reduce and activate the catalyst; then open the standby valve on the fixed bed reactor, and then open the gas bypass valve of H2 and CO2 mixed gas to fill the reaction gas into it; then open the total valve of H2 and CO2 mixed gas to adjust to the required reaction pressure, and set the reaction temperature and reaction space velocity on the fixed bed reactor, and then start the reaction.

[0020] Preferably, the reducing gas is H2; the reduction temperature is 300-500 DEG C; the reduction time is 4-12h; the molar ratio of H2 to CO2 during the catalytic reaction is 1.0-4.0; the reaction pressure is 1-5MPa; the reaction temperature is 250-400 DEG C; and the reaction space velocity is 5000-15000mL / (g cat ·h)。

[0021] The prepared iron-based catalyst is spherical Fe3O4 modified by alkali metals and transition metals; the addition of the reducing agent in the preparation process makes Fe not need to undergo Fe2O3 to Fe3O4, and the addition of the electrostatic stabilizer can promote the uniform and stable growth of Fe3O4 particles, and the use of nitrate as a metal source and high-temperature calcination and other steps are not needed, thereby avoiding environmental pollution and the problem of easy sintering of metal components in the preparation process.

[0022] Beneficial effects:

[0023] (1) The present application prepares a catalyst with a transition metal modified spherical Fe3O4 as an active component and an alkali metal as an auxiliary active component. The catalyst is mainly used for the preparation of C 2+ alcohol from CO2 hydrogenation, significantly improves the conversion rate of CO2 and the space-time yield of target product C 2+ alcohol, and the conversion rate of CO2 can reach 41.6%, and the space-time yield of C 2+ alcohol can reach 112.9mg g cat -1 h -1 .

[0024] (2) The catalyst provided by the present application promotes the stable growth of spherical Fe3O4 particles by adding different reducing agents and electrostatic stabilizers in the preparation process by the solvothermal method, and the particle size is uniformly dispersed.

[0025] (3) The alkali metal and transition metal modified spherical Fe3O4 catalyst prepared by the present application has a transition metal modified Fe3O4 as an active component, Fe3O4 as an active phase of RWGS reaction, promotes the adsorption of CO2, and thus improves the conversion rate of CO2; the transition metal provides active sites for CO non-dissociation activation, promotes the dispersion of Fe and the formation of oxygen vacancies on the surface of the catalyst, is conducive to the adsorption of oxygen by the catalyst to form oxygen-containing intermediates, and thus improves the space-time yield of C 2+ alcohol.

[0026] (4) The catalyst provided by the present application is stable in nature after 100h of continuous reaction, and does not appear obvious deactivation, which is conducive to improving the service life of the catalyst.

[0027] (5) The catalyst provided by the present application has cheap and easily available raw materials, and the preparation method is simple, which is conducive to realizing mass production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM image of the spherical Fe3O4 catalyst prepared in Example 5. DETAILED DESCRIPTION

[0029] The present application is described in detail below with the following specific examples, which should be understood as merely illustrative and explanatory, and not as any limitation to the scope of the present application.

[0030] Example 1

[0031] First, 8.11 g (0.03 mol) of FeCl3·6H2O, 1.023 g (0.006 mol) of CuCl2·2H2O and 0.409 g (0.003 mol) of ZnCl2 were weighed and dissolved in 150 mL of ethylene glycol, and stirred at room temperature for 20 min; 16.22 g of sodium acetate and 1.622 g of trisodium citrate were added to the above prepared metal salt solution, and stirred for 40 min; the above solution was transferred to a 200 mL hydrothermal kettle, and hydrothermally treated at 200°C for 24 h; after the hydrothermal kettle was cooled, the filter cake was washed with ethanol and deionized water for several times, and finally dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst. In addition, 0.0265 g of anhydrous K2CO3 was dissolved in a mixed solvent of 1 mL of deionized water and 1 mL of ethanol, and ultrasonically treated until completely dissolved; the K2CO3 solution was added dropwise into 1.50 g of the precursor powder with constant stirring, and then transferred to a vacuum oven at 100°C for drying for 24 h; after drying, the iron-based catalyst was obtained by grinding.

[0032] Catalytic performance of the catalyst in the synthesis of C 2+ Evaluation of the alcohol reaction performance

[0033] The catalyst was loaded in the constant temperature zone in the middle of the reaction tube, and quartz sand was loaded in the upper and lower parts of the reaction tube; the catalyst was reduced under the following conditions: temperature 300°C, reduction time 4 h; after reduction, the raw material was fed at a molar ratio of H2 / CO2 50:50 and a space velocity of 5000 mL / (g cat ·h), the temperature was lowered to 250°C, the reaction system was slowly pressurized to reach a reaction pressure of 1 MPa, and the reaction was started. The results of the catalyst reaction are shown in Table 1.

[0034] Example 2

[0035] First, 8.11 g (0.03 mol) of FeCl3·6H2O, 3.765 g (0.015 mol) of Mn(NO3)2·4H2O and 2.044 g (0.015 mol) of ZnCl2 were weighed and dissolved in 150 mL of ethylene glycol, and stirred at room temperature for 20 min; 1.622 g of sodium oxalate and 0.0811 g of sodium phosphate were weighed and added to the above prepared metal salt solution, and stirred for 40 min; the above solution was transferred to a 200 mL hydrothermal kettle, and hydrothermally treated at 100 ℃ for 6 h; after the hydrothermal kettle was cooled, the filter cake was washed with ethanol and deionized water for several times, and finally dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst. In addition, 0.069 g of anhydrous Na2CO3 was dissolved in a mixed solvent of 1 mL of deionized water and 1 mL of ethanol, and ultrasonically treated until completely dissolved; the Na2CO3 solution was added dropwise into 1.50 g of the precursor powder using a pipette while stirring, and then transferred to a vacuum oven at 60 ℃ for drying for 8 h; after drying, the iron-based catalyst was obtained by grinding.

[0036] Catalytic performance of the catalyst in the synthesis of C 2+ Evaluation of the reaction performance of the alcohol

[0037] The catalyst was loaded in the constant temperature zone in the middle of the reaction tube, and quartz sand was loaded in the upper and lower parts of the reaction tube; the catalyst was reduced under the following conditions: temperature 500 ℃, reduction time 12 h; after reduction, the raw material was fed at a molar ratio of H2 / CO2 80:20 and a space velocity of 15000 mL / (g cat ·h), the temperature was lowered to 400 ℃, the reaction system was slowly pressurized to reach a reaction pressure of 5 MPa, and the reaction was started. The results of the catalyst reaction are shown in Table 1.

[0038] Example 3

[0039] Firstly, 12.0 g (0.03 mol) Fe2(SO4)3, 0.958 g (0.006 mol) CuSO4, 1.134 g (0.006 mol) Zn(NO3)2 were dissolved in 150 mL ethylene glycol, stirred at room temperature for 20 min; 6.0 g sodium oxalate, 0.6 g polyvinylpyrrolidone were added into the above prepared metal salt solution, and stirred for another 40 min; the above solution was transferred into a 200 mL hydrothermal kettle, and hydrothermally treated at 120 ℃ for 15 h; after the hydrothermal kettle was cooled, the filter cake was washed with ethanol and deionized water for several times, and finally dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst. In addition, 0.086 g KOH was dissolved in a mixed solvent of 1 mL deionized water and 1 mL ethanol, and ultrasonically treated until completely dissolved; the KOH solution was added dropwise into 1.50 g of the precursor powder using a pipette while stirring constantly; after mixing uniformly, the mixture was transferred into a vacuum oven at 70 ℃ and dried for 15 h; after drying, the iron-based catalyst was obtained by grinding.

[0040] Catalyst for synthesizing C 2+ Performance evaluation of alcohol reaction

[0041] The catalyst was loaded in the constant temperature zone in the middle of the reaction tube, and quartz sand was loaded in the upper and lower parts of the reaction tube; the catalyst was reduced under the following conditions: temperature 350 ℃, reduction time 6 h; after reduction, the raw material was fed at a molar ratio of H2 / CO2 60:40 and a space velocity of 8000 mL / (g cat ·h); the temperature was maintained at 350 ℃, the reaction system was slowly pressurized to reach a reaction pressure of 2.0 MPa, and the reaction was started. The results of the catalyst reaction are shown in Table 1.

[0042] Example 4

[0043] Firstly, 12.0 g (0.03 mol) Fe2(SO4)3, 0.958 g (0.006 mol) CuSO4, 1.134 g (0.006 mol) Zn(NO3)2 were dissolved in 150 mL ethylene glycol, stirred at room temperature for 20 min; 6.0 g sodium oxalate, 0.6 g polyvinylpyrrolidone were added into the above prepared metal salt solution, and stirred for another 40 min; the above solution was transferred into a 200 mL hydrothermal kettle, and hydrothermally treated at 120 ℃ for 15 h; after the hydrothermal kettle was cooled, the filter cake was washed with ethanol and deionized water for several times, and finally dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst. In addition, 0.086 g KOH was dissolved in a mixed solvent of 1 mL deionized water and 1 mL ethanol, and ultrasonically treated until completely dissolved; the KOH solution was added dropwise into 1.50 g of the precursor powder using a pipette while stirring constantly; after mixing uniformly, the mixture was transferred into a vacuum oven at 70 ℃ and dried for 15 h; after drying, the iron-based catalyst was obtained by grinding.2+ The alcohol reaction performance evaluation will be loaded in the middle of the reaction tube of the catalyst constant temperature zone, the upper and lower parts of the reaction tube are each loaded with quartz sand; the catalyst is reduced, the reduction conditions are: temperature 450°C, reduction time 10h; after the reduction is completed, the raw material space velocity is 9000mL / (g cat ·h) feeding, cooling to 400°C, the reaction system slowly increases the pressure, reaches the reaction pressure 2.5MPa, starts the reaction. The catalyst reaction results are shown in Table 1.

[0044] Example 5

[0045] First, 8.11g (0.03mol) FeCl3·6H2O, 1.02g (0.006mol) CuCl2·2H2O, 0.818g (0.006mol) ZnCl2 are weighed and dissolved in 150mL ethylene glycol, stirred at room temperature for 20min; 10.80g sodium acetate, 1.32g trisodium citrate are weighed and added to the above prepared metal salt solution, continue to stir for 40min; the above solution is transferred to a 200mL hydrothermal kettle, hydrothermal treatment at 200°C for 10h; after the hydrothermal kettle is cooled, the filter cake is washed with ethanol and deionized water for several times, and finally the filter cake is dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst, as shown in Figure 1 The prepared catalyst is a uniformly dispersed spherical structure. In addition, 0.053g anhydrous K2CO3 is dissolved in 1mL deionized water and 1mL ethanol to form a mixed solvent, ultrasonic treatment until completely dissolved, using a pipette to drop the K2CO3 solution into 1.50g precursor powder drop by drop and continuously stir, after mixing evenly, transfer to a vacuum oven at 80°C for drying for 24h, after drying, grind to obtain an iron-based catalyst.

[0046] The catalyst catalyzes the synthesis of C 2+ Alcohol reaction performance evaluation

[0047] The catalyst is loaded in the middle of the reaction tube of the constant temperature zone, the upper and lower parts of the reaction tube are each loaded with quartz sand; the catalyst is reduced, the reduction conditions are: temperature 350°C, reduction time 9h; after the reduction is completed, the raw material space velocity is 10000mL / (g cat ·h) feeding, cooling to 320°C, the reaction system slowly increases the pressure, reaches the reaction pressure 5.0MPa, starts the reaction. The catalyst reaction results are shown in Table 1.

[0048] Example 6

[0049] Firstly, 8.11 g (0.03 mol) of FeCl3·6H2O, 1.188 g (0.006 mol) of MnCl2·4H2O were weighed and dissolved in 150 mL of glycerol, stirred at room temperature for 20 min; then 10.80 g of sodium acetate, 1.32 g of sodium phosphate were dissolved in the above prepared metal salt solution, and the above solution was transferred to a 200 mL hydrothermal kettle, and hydrothermal treatment was carried out at 200 ℃ for 10 h; after the hydrothermal kettle was cooled, the filter cake was washed with ethanol and deionized water for several times, and finally the filter cake was dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst. In addition, 0.053 g of anhydrous K2CO3 was dissolved in a mixed solvent composed of 1 mL of deionized water and 1 mL of ethanol, and ultrasonic treatment was carried out until complete dissolution. The K2CO3 solution was added dropwise into 1.50 g of precursor powder using a pipette while stirring, and then transferred to a vacuum oven at 80 ℃ for drying for 24 h. After drying, the iron-based catalyst was obtained by grinding. 2+ Performance evaluation of alcohol synthesis reaction

[0050] The catalyst was loaded in the constant temperature zone in the middle of the reaction tube, and quartz sand was loaded in the upper and lower parts of the reaction tube; the catalyst was reduced under the following conditions: temperature 350 ℃, reduction time 9 h; after reduction, the raw material space velocity was 5000 mL / (g cat ·h) under the condition of H2 / CO2 molar ratio 75:25, the temperature was lowered to 320 ℃, the reaction system was slowly pressurized to reach a reaction pressure of 3.0 MPa, and the reaction was started. The results of the catalyst reaction are shown in Table 1.

[0051] Example 7

[0052] Firstly, 8.11 g (0.03 mol) of FeCl3·6H2O, 2.55 g (0.015 mol) of CuCl2·2H2O, 0.818 g (0.006 mol) of ZnCl2, 1.188 g (0.006 mol) of MnCl2·4H2O were weighed and dissolved in 150 mL of glycol, stirred at room temperature for 20 min; then 12.50 g of sodium oxalate, 1.02 g of trisodium citrate were dissolved in the above prepared metal salt solution, and the above solution was transferred to a 200 mL hydrothermal kettle, and hydrothermal treatment was carried out at 200 ℃ for 10 h; after the hydrothermal kettle was cooled, the filter cake was washed with ethanol and deionized water for several times, and finally the filter cake was dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst. In addition, 0.053 g of anhydrous K2CO3 was dissolved in a mixed solvent composed of 1 mL of deionized water and 1 mL of ethanol, and ultrasonic treatment was carried out until complete dissolution. The K2CO3 solution was added dropwise into 1.50 g of precursor powder using a pipette while stirring, and then transferred to a vacuum oven at 60 ℃ for drying for 15 h. After drying, the iron-based catalyst was obtained by grinding.

[0053] Catalyst catalyzes carbon dioxide hydrogenation to synthesize C 2+ Alcohol reaction performance evaluation

[0054] The catalyst was loaded in the constant temperature zone in the middle of the reaction tube, and quartz sand was loaded in the upper and lower parts of the reaction tube. The catalyst was reduced under the following conditions: temperature 360°C, reduction time 9h. After reduction, the raw material was fed at a space velocity of 6000 mL / (g cat h) at a H2 / CO2 molar ratio of 65:35, and the reaction system was slowly pressurized to reach a reaction pressure of 2.5 MPa, and the reaction started. The catalyst reaction results are shown in Table 1.

[0055] Comparative Example 1

[0056] First, 8.11 g of FeCl3·6H2O was dissolved in 150 mL of ethylene glycol and stirred at room temperature for 20 min. Then 10.80 g of sodium acetate and 1.32 g of trisodium citrate were dissolved in the above prepared metal salt solution, and the solution was transferred to a 200 mL hydrothermal kettle, which was hydrothermally treated at 200°C for 10 h. After the hydrothermal kettle was cooled, the filter cake was washed with ethanol and deionized water for several times, and finally dried in a vacuum drying oven overnight to obtain a Fe3O4 catalyst. In addition, 0.053 g of anhydrous K2CO3 was dissolved in a mixed solvent of 1 mL of deionized water and 1 mL of ethanol, and ultrasonic treatment was performed until complete dissolution. The K2CO3 solution was added dropwise into 1.50 g of precursor powder with constant stirring, and after mixing evenly, it was transferred to a vacuum oven at 80°C for drying for 24 h. After drying, the K 0.02 / Fe3O4 catalyst was obtained.

[0057] Catalyst catalyzes carbon dioxide hydrogenation to synthesize C 2+ Alcohol reaction performance evaluation

[0058] The catalyst was loaded in the constant temperature zone in the middle of the reaction tube, and quartz sand was loaded in the upper and lower parts of the reaction tube. The catalyst was reduced under the following conditions: temperature 350°C, reduction time 9h. After reduction, the raw material was fed at a space velocity of 5000 mL / (g cat h) at a H2 / CO2 molar ratio of 75:25, and the reaction system was slowly pressurized to reach a reaction pressure of 3.0 MPa, and the reaction started. The catalyst reaction results are shown in Table 1.

[0059] Comparative Example 2

[0060] First, 8.11 g of FeCl3·6H2O was dissolved in 50 mL of deionized water; 5.60 g of KOH was dissolved in 100 mL of deionized water. The metal salt solution and KOH solution were simultaneously added dropwise to a three-necked flask using a syringe pump, adjusting the rate to maintain the pH at 8.5. After titration, the solution was aged overnight at room temperature, washed with deionized water and ethanol until neutral, dried at 60 °C for 12 h, and calcined at 400 °C for 2 h to obtain iron oxide. Additionally, 0.053 g of anhydrous K2CO3 was dissolved in a mixed solvent of 1 mL of deionized water and 1 mL of ethanol, and sonicated until completely dissolved. The K2CO3 solution was then added dropwise to 1.50 g of precursor powder using a pipette while continuously stirring with a glass rod. After thorough mixing, the mixture was transferred to a vacuum oven at 80 °C and dried for 24 h, then calcined at 400 °C for 2 h, and ground to obtain K... 0.02 / Fe2O3 catalyst.

[0061] Catalyst for the catalytic hydrogenation of carbon dioxide to C 2+ Evaluation of alcohol reactivity

[0062] The catalyst was packed into the isothermal zone in the middle of the reaction tube, with quartz sand packed at the top and bottom. The catalyst was then reduced under the following conditions: temperature 350℃, reduction time 9 h. After reduction, the catalyst was further reduced according to an H2 / CO2 molar ratio of 75:25 and a feed space velocity of 5000 mL / (g). cat h) Feed the material, cool it to 320℃, and slowly increase the pressure of the reaction system to reach a reaction pressure of 3.0 MPa to start the reaction. The catalyst reaction results are shown in Table 1.

[0063] Table 1. Results of catalyst reaction

[0064]

[0065] In Table 1: C - It is an alkane product; C ＝ ROH is an olefin product; ROH is an alcohol product; STY is a C 2+ Space-time yield of alcohol products; the above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made in accordance with the above embodiments are included within the scope of protection of the present invention.

Claims

1. An iron-based catalyst characterized in that The method is as follows: (1) dissolving iron salt and transition metal salt in solvent to prepare a solution, then adding reducing agent and electrostatic stabilizer to the solution, stirring, hydrothermal reaction, cooling, centrifuging, washing, and drying to obtain transition metal modified spherical Fe3O4; wherein the transition metal salt is one of nitrate, chloride or sulfate of transition metal, wherein the transition metal is one or several of Mn, Zn and Cu; the reducing agent is one of sodium acetate or sodium oxalate; the electrostatic stabilizer is one of trisodium citrate, sodium phosphate or polyvinylpyrrolidone; the temperature of hydrothermal reaction is 100-200℃, and the time of hydrothermal reaction is 6-24h; (2) preparing an aqueous solution of alkali metal source, then immersing the solution on the spherical Fe3O4 obtained in step (1), and obtaining alkali metal and transition metal modified spherical Fe3O4 catalyst after ultrasonic treatment and vacuum drying.

2. The iron-based catalyst according to claim 1, characterized in that: The iron salt in step (1) is one of ferric nitrate, ferric chloride or ferric sulfate; and the solvent is one of water, ethylene glycol or glycerol.

3. The iron-based catalyst of claim 1, wherein: The molar ratio of iron salt to transition metal salt is 1:(0.1-1); the mass ratio of reducing agent to iron salt is (0.2-2):1; and the mass ratio of electrostatic stabilizer to iron salt is (0.01-0.2):

1.

4. The iron-based catalyst of claim 1, wherein: The alkali metal source in step (2) is one of sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, rubidium carbonate or cesium carbonate; and the mass of the alkali metal source is 1-10% of the mass of the spherical Fe3O4.

5. The iron-based catalyst of claim 1, wherein: The vacuum drying temperature in step (2) is 60-100℃, and the drying time is 8-24h.

6. A method for producing carbon dioxide hydrogenation C using an iron-based catalyst as described in claim 1 in a fixed-bed reactor. 2+ Applications of alcohols.

7. Use according to claim 6, characterized in that: First, the catalyst is filled in the constant temperature zone in the middle of the reaction tube of the fixed bed reactor, and quartz sand is filled in the upper and lower parts of the reaction tube; the gas bypass valve on the fixed bed reactor is opened, and reducing gas is filled into the fixed bed reactor to reduce and activate the catalyst; then the standby valve on the fixed bed reactor is opened, and the gas bypass valve of H2 and CO2 mixed gas is opened to fill reaction gas into the fixed bed reactor; then the total valve of H2 and CO2 mixed gas is opened to adjust to the required reaction pressure; and the reaction temperature and space velocity are set on the fixed bed reactor to start the reaction.

8. Use according to claim 7, characterized in that: The reducing gas is H2; the reduction temperature is 300-500℃; the reduction time is 4-12h; and the molar ratio of H2 to CO2 in the catalytic reaction process is 1.0-4.0; The reaction pressure is 1-5MPa; the reaction temperature is 250-400℃; and the reaction space velocity is 5000-15000 mL / (g cat • h).

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