Na-containing spinel type iron-cobalt bimetallic catalyst as well as preparation method and application thereof

Abstract

The invention provides a Na-containing spinel type iron-cobalt bimetallic catalyst and a preparation method and application thereof, and relates to the technical field of catalysts.The method comprises the steps that iron source soluble salt and cobalt source soluble salt are dissolved in deionized water, and ammonia water is added to prepare an alkaline mixed solution; the alkaline mixed solution is placed in a hydrothermal reaction kettle for a hydrothermal reaction, and an iron-cobalt bimetallic oxide reaction product is obtained; the iron-cobalt bimetallic oxide reaction product is subjected to suction filtration and washing with a NaOH-containing aqueous solution, the mass fraction of Na in the catalyst is controlled to be 0.1-3 wt.% by regulating and controlling the concentration and the volume of the NaOH aqueous solution for washing, and the Na-containing spinel type iron-cobalt bimetallic catalyst is obtained after drying. By regulating and controlling the mass fraction of Na in the catalyst, the directional regulation and control of product distribution in the CO2 hydrogenation reaction can be realized, and the product requirements of various different application scenes can be met.

Description

Technical Field

[0001] This disclosure relates to the technical field of catalysts, and more particularly to a Na-containing spinel-type iron-cobalt bimetallic catalyst, its preparation method, and its application. Background Technology

[0002] With the advancement of global carbon neutrality goals, the resource-based conversion of CO2 has become a research hotspot in the energy and chemical engineering field. Among these efforts, the catalytic hydrogenation of CO2 into high-value hydrocarbon compounds is a crucial pathway for realizing the resource utilization of CO2. Biomass gasification syngas, as a renewable carbon-based feedstock, is mainly composed of CO, CO2, and H2. Hydrogenating CO2 and H2 from this syngas to produce hydrocarbons enables the synergistic utilization of biomass resources and CO2, which is of great significance for reducing dependence on fossil fuels and alleviating environmental pollution.

[0003] However, the inherent compositional characteristics of biomass gasification syngas present numerous technical challenges to subsequent CO2 hydrogenation to hydrocarbons reactions. Traditional catalytic systems are ill-suited to the requirements of this reaction system. Specifically, the problems are as follows: First, the CO2 content in biomass gasification syngas is as high as 21-30 vol.%, far exceeding the requirement of less than 5% CO2 content in the feed gas for traditional Fischer-Tropsch synthesis processes. This high CO2 content leads to a decrease in the partial pressures of CO and H2 in the reaction system, severely inhibiting the hydrogenation activity of the catalyst and significantly reducing the selectivity of hydrocarbon products. Second, existing single-metal catalysts used for CO2 hydrogenation have significant performance defects. Although iron-based catalysts possess certain reverse water-gas shift activity and carbon chain growth capabilities, they are limited by the Anderson-Schulz-Flory (ASF) distribution, making it difficult to precisely control the carbon chain distribution of the products. The first problem is that cobalt-based catalysts cannot be used to selectively produce a specific range of hydrocarbons. Furthermore, cobalt-based catalysts exhibit excessive methanation in high-CO2 mixed gas systems, making it almost impossible to produce high-carbon long-chain hydrocarbons. Neither approach can balance catalytic activity and product selectivity. Thirdly, while researchers have attempted to modify bimetallic spinel catalysts with alkali metals to improve the product distribution of CO2 hydrogenation, existing alkali metal-modified spinel-type iron-cobalt bimetallic catalysts either have inflexible alkali metal content control or complex preparation processes, making it difficult to achieve precise adjustment of alkali metal content through simple preparation methods. Consequently, they cannot achieve the desired product distribution of C2-C4 short-chain hydrocarbons and C4-C4 long-chain hydrocarbons. 5+ The selective and directional regulation of long-chain hydrocarbons is challenging, but existing modified catalyst preparation processes often involve cumbersome steps, demanding conditions, and high raw material costs, hindering industrial-scale application.

[0004] To address the aforementioned problems, a method was developed that features a simple and mild preparation process, and allows for easy control of the alkali metal content, thereby achieving the optimal balance between C2-C4 and C4 alkali metals in the CO2 hydrogenation reaction. 5+Catalysts with flexible and adjustable selectivity for hydrocarbons have become key to promoting the industrial application of CO2 hydrogenation to hydrocarbon production technology in high CO2 content systems. Summary of the Invention

[0005] This disclosure provides a Na-containing spinel-type iron-cobalt bimetallic catalyst, its preparation method, and its application, in order to at least solve the above-mentioned technical problems existing in the prior art.

[0006] According to a first aspect of this disclosure, a method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst is provided, the method comprising: An alkaline mixed solution is prepared by dissolving soluble salts of iron and cobalt sources in deionized water and adding ammonia. The alkaline mixed solution was placed in a hydrothermal reactor for hydrothermal reaction to obtain the iron-cobalt bimetallic oxide reaction product; The reaction product of the iron-cobalt bimetallic oxide was washed by filtration with an aqueous solution containing NaOH. By adjusting the concentration and volume of the NaOH aqueous solution used for washing, the mass fraction of Na in the catalyst was controlled at 0.1~3 wt.%. After drying, a spinel-type iron-cobalt bimetallic catalyst containing Na was obtained.

[0007] In one embodiment, the molar ratio of the iron-source soluble salt to the cobalt-source soluble salt, calculated as Fe:Co, is 2:(0.8~1.2).

[0008] In one embodiment, the iron source soluble salt is at least one of iron nitrate, chloride, and sulfate; the cobalt source soluble salt is at least one of cobalt nitrate, chloride, and sulfate; and the pH of the alkaline mixed solution adjusted with ammonia is 8-10, providing a suitable alkaline environment for the co-precipitation of iron-cobalt hydroxide and the subsequent formation of spinel crystals.

[0009] In one embodiment, the iron source soluble salt is ferric nitrate nonahydrate, and the cobalt source soluble salt is cobalt nitrate hexahydrate; the mass ratio of ferric nitrate nonahydrate to deionized water is 1:(15~25), and the amount of ammonia added is 0.08~0.12 mol, so as to achieve uniform dispersion and controllable dissociation of iron and cobalt ions in the solution.

[0010] In one embodiment, the temperature of the hydrothermal reaction is 120~200℃, and the time of the hydrothermal reaction is 8~24h.

[0011] In one embodiment, the vacuum filtration washing is a reduced pressure vacuum filtration washing, wherein the vacuum filtration pressure is controlled at 0.05~0.08MPa and the washing rate is 50~100mL / min during the washing process.

[0012] In one embodiment, the concentration of the NaOH-containing aqueous solution is 0.05~0.1mol / L, and the washing volume is 0.5~1.5L.

[0013] According to a second aspect of this disclosure, a Na-containing spinel-type iron-cobalt bimetallic catalyst is provided, characterized in that it is prepared by the preparation method described above; the catalyst has a pure-phase spinel crystal structure, and Na is combined with iron-cobalt bimetallic oxide in the form of interstitial doping, surface adsorption or surface composite oxide, the mass fraction of Na is 0.1~3 wt.%, and the molar ratio of Fe to Co is 2:(0.8~1.2).

[0014] According to a third aspect of this disclosure, an application of a Na-containing spinel-type iron-cobalt bimetallic catalyst in a CO2 hydrogenation reaction is provided. The catalyst is characterized in that it is packed into a fixed-bed reactor, and a mixed feed gas containing CO2 and H2 is introduced to carry out the CO2 hydrogenation reaction. The distribution of hydrocarbon products in the CO2 hydrogenation reaction is directionally controlled by adjusting the mass fraction of Na in the catalyst. The CO2 content in the mixed feed gas is 5-30 vol.%.

[0015] In one embodiment, the process conditions for the CO2 hydrogenation reaction are: reaction temperature 280~350℃, reaction pressure 1~4MPa, molar ratio of H2 to CO2 3:1, and volume hourly space velocity of the mixed feed gas 4000~8000mL / g / h; by adjusting the mass fraction of Na, the selectivity of C2-C4 hydrocarbons is adjustable between 40%~50%, and the selectivity of C5+ hydrocarbons is adjustable between 30%~40%.

[0016] This disclosure provides a Na-containing spinel-type iron-cobalt bimetallic catalyst, its preparation method, and its application. The preparation method utilizes soluble iron and cobalt source salts as raw materials and precisely controls the iron-cobalt molar ratio. Ammonia water is used to adjust the alkalinity, achieving uniform co-precipitation of iron and cobalt ions. A hydrothermal reaction is then used to directionally synthesize an iron-cobalt bimetallic oxide precursor. Finally, the mass fraction of Na in the catalyst is precisely controlled by filtration and washing with NaOH aqueous solution. The overall process is simple, mild, and has wide raw material compatibility. It can ensure the formation of a pure spinel crystal form and avoid the formation of impurity oxides through the weak alkalinity of ammonia water, and the Na content can be precisely controlled within the range of 0.1~3 wt.% through the washing process. By flexibly adjusting within a certain range, the presence and distribution of Na in the catalyst can be effectively controlled, ultimately yielding a Na-containing spinel-type iron-cobalt bimetallic catalyst. This catalyst possesses both a regular spinel crystal phase structure and optimized surface electronic properties. The synergistic effect of the iron-cobalt bimetallic catalyst and the regulatory effect of the Na promoter are fully utilized. At the same time, the preparation method introduces no excess impurity ions throughout the process, avoiding interference with the catalyst's active sites. The preparation efficiency is high and the product reproducibility is good, laying a high-quality catalytic foundation for the targeted regulation of hydrocarbon product distribution in subsequent CO2 hydrogenation reactions. It has significant prospects for industrial-scale application.

[0017] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0018] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings. Several embodiments of this disclosure are illustrated in the drawings by way of example and not limitation, in which: In the accompanying drawings, the same or corresponding reference numerals indicate the same or corresponding parts.

[0019] Figure 1 A schematic flowchart of a method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst according to an embodiment of the present disclosure is shown. Figure 2 The XRD patterns of catalysts prepared according to embodiments and comparative examples of this disclosure are shown; Figure 3 A schematic diagram illustrating the catalytic performance of catalysts prepared according to embodiments and comparative examples of this disclosure is shown. Detailed Implementation

[0020] To make the objectives, features, and advantages of this disclosure more apparent and understandable, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0021] CO2 hydrogenation to produce high-value hydrocarbons is an important pathway for realizing the resource utilization of carbon resources, especially the catalytic conversion of high-CO2-content feedstock gases such as biomass gasification syngas, which is currently a research focus. However, existing iron-cobalt-based catalysts suitable for such feedstock gases suffer from cumbersome preparation processes and insufficient precision in controlling the content of alkali metal promoters, making it difficult to achieve targeted control of C2-C4 and C5+ hydrocarbon products in the CO2 hydrogenation reaction through simple means, thus restricting the industrial application of this technology. Therefore, this invention provides a method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst, as well as the catalyst obtained by this method and its application in the CO2 hydrogenation reaction. The technical solution of this invention is described in detail below.

[0022] like Figure 1 The present disclosure provides a schematic flowchart of a method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst, including the following steps: S1. Dissolve soluble iron source salts and soluble cobalt source salts in deionized water, and add ammonia water to prepare an alkaline mixed solution.

[0023] This step is the nucleation preparation stage of the catalyst precursor. The core objective is to achieve uniform dispersion and controllable hydrolysis of iron and cobalt ions, laying the foundation for the subsequent formation of pure-phase spinel crystals. A catalyst capable of dissociating Fe... 3+ Co 2+ Using soluble iron and cobalt salts as raw materials, the soluble iron and cobalt salts are added to deionized water at room temperature and stirred until completely dissolved to form a homogeneous and transparent solution. Then, ammonia water is added dropwise to adjust the solution to alkalinity. Ammonia water, as a weak base, can achieve Fe... 3+ Co 2+ The homogeneous hydrolysis generates iron-cobalt hydroxide coprecipitate, ultimately yielding a suspension of alkaline mixed solution with a stable pH of 8-10. This alkalinity range is the optimal environment for subsequent spinel crystal growth.

[0024] In one example, the iron-source soluble salt is at least one of iron nitrate, chloride, and sulfate; the cobalt-source soluble salt is at least one of cobalt nitrate, chloride, and sulfate. The molar ratio of the iron-source soluble salt to the cobalt-source soluble salt raw materials, calculated as Fe and Co, is 2:(0.8~1.2). This molar ratio is the optimal coordination ratio for spinel-type iron-cobalt bimetallic oxide Fe2CoO4, ensuring that iron and cobalt ions are coordinated according to the tetrahedral and octahedral sites of the spinel crystal form during the subsequent hydrothermal reaction, thus reducing the formation of impurity oxides.

[0025] In one example, the soluble salt for iron is ferric nitrate nonahydrate, and the soluble salt for cobalt is cobalt nitrate hexahydrate. The mass ratio of ferric nitrate nonahydrate to deionized water is 1:(15~25), and the amount of ammonia added is 0.08~0.12 mol to achieve uniform dispersion and controllable dissociation of iron and cobalt ions in the solution. In this example, the mass ratio of ferric nitrate nonahydrate to deionized water is controlled at 1:(15~25). At this ratio, the salts can fully dissolve to form a homogeneous iron-cobalt mixed salt solution. This avoids insufficient salt dissolution and uneven ion dispersion due to insufficient deionized water, and also prevents the raw material concentration from being too low due to excessive deionized water, which would affect the formation efficiency and crystal nucleus uniformity of subsequent iron-cobalt hydroxide coprecipitation. The amount of ammonia added is precisely controlled at 0.08~0.12 mol. This amount can stabilize the pH of the iron-cobalt mixed solution in the optimal alkalinity range of 8~10, ensuring that the Fe in the solution is within the optimal range. 3+ Co 2+ The hydrolysis reaction is fully carried out to generate a uniform coprecipitate of iron-cobalt hydroxide, which enables the controllable dissociation and coordination of iron-cobalt ions. It also avoids the problem of excessive alkalinity of the solution due to excessive ammonia, which would cause the iron-cobalt hydroxide to precipitate too quickly and the precursor particles to be uneven in size. This lays a uniform precursor foundation for the directional growth of pure phase spinel crystals in the subsequent hydrothermal reaction.

[0026] S2. The alkaline mixed solution is placed in a hydrothermal reactor for hydrothermal reaction to obtain the iron-cobalt bimetallic oxide reaction product.

[0027] This step is the core step for the directional growth of spinel crystals, achieving the crystal transformation of the iron-cobalt hydroxide precursor through a high-temperature, high-pressure hydrothermal environment. The alkaline mixed solution prepared in step S1 is loaded into the polytetrafluoroethylene liner of a hydrothermal reactor, filling 60%–80% of the liner's volume. After sealing, the hydrothermal reaction is carried out. The self-generated pressure within the reactor promotes the ordered coordination of iron-cobalt ions, ensuring the complete transformation of the precursor into an iron-cobalt bimetallic oxide with regular tetrahedral and octahedral sites. The hydrothermal reaction temperature is 120–200℃, and the reaction time is 8–24 hours. This temperature range is suitable for the crystal transformation of spinel-type iron-cobalt bimetallic oxides. Too low a temperature results in insufficient crystal transformation, easily forming amorphous iron-cobalt oxides; too high a temperature leads to excessive crystal growth, reducing the catalyst's specific surface area and active sites. The reaction time can be flexibly adjusted according to the reaction temperature; the higher the temperature, the shorter the reaction time can be, ensuring the complete transformation of iron-cobalt hydroxide into spinel-type bimetallic oxides. Preferably, the hydrothermal reaction temperature is 170~190℃ and the reaction time is 6~10h.

[0028] After the hydrothermal reaction is completed, the reactor is naturally cooled to room temperature to avoid sudden cooling that could cause crystal cracking or an increase in lattice defects. The reaction product taken out after cooling is an iron-cobalt bimetallic oxide with a spinel-based crystal structure and a surface rich in hydroxyl groups and oxygen vacancies, which can be directly used in subsequent Na content control steps.

[0029] S3. The reaction product of the iron-cobalt bimetallic oxide is washed by filtration with an aqueous solution containing NaOH. By adjusting the concentration and volume of the NaOH aqueous solution used for washing, the mass fraction of Na in the catalyst is controlled at 0.1~3 wt.%. After drying, a spinel-type iron-cobalt bimetallic catalyst containing Na is obtained.

[0030] This step involves precise control and stabilization of the Na content in the catalyst. Controllable Na doping and adsorption are achieved through adjusting washing parameters, simultaneously stabilizing the catalyst crystal structure. The reaction product of the iron-cobalt bimetallic oxide is washed by vacuum filtration using a 0.05–0.1 mol / L NaOH aqueous solution, with a total washing volume of 0.5–1.5 L. By controlling the concentration and volume of the washing solution, the mass fraction of Na in the catalyst is maintained at 0.1–3 wt.%. The concentration of the washing solution is 0.05–0.1 mol / L, which ensures sufficient Na content during the washing process. + Slow release and controlled adsorption avoid Na2+ degradation caused by high concentrations of NaOH. + Excessive doping and local enrichment. The mass fraction of Na is precisely controlled within the range of 0.1–3 wt.%, which is the optimal Na control range for the CO2 hydrogenation reaction, enabling precise adjustment of the electronic properties of the catalyst surface and the concentration of oxygen vacancies.

[0031] During the filtration and washing process, the NaOH aqueous solution contains Na + It combines with iron-cobalt bimetallic oxides in three ways: firstly, it adsorbs onto oxygen anion sites or hydroxyl groups on the catalyst surface through electrostatic interaction, forming surface-adsorbed Na + Secondly, it embeds itself in the interstitial lattice of spinel crystals, forming interstitial doped Na. + This bonding method is the main bonding form, which can effectively control the lattice electron density and oxygen vacancy concentration of the catalyst; thirdly, it forms Na-Fe-O or Na-Co-O composite oxides with trace amounts of amorphous iron and cobalt ions on the catalyst surface, forming a surface composite phase Na. + The synergistic effect of the three combination forms can achieve precise control over the acidity / alkalinity and redox properties of the catalyst surface.

[0032] After filtration and washing, the product is dried at 60-90℃ for 8-14 hours to remove free and bound water, thereby stabilizing the crystal structure of the catalyst and finally obtaining a nanoparticle-type iron-cobalt bimetallic catalyst containing Na spinel. This catalyst does not require additional calcination, reduction or other post-treatment and can be directly used for CO2 hydrogenation reaction.

[0033] In the above scheme, soluble salts of iron and cobalt sources are used as raw materials, and the iron-cobalt molar ratio is precisely controlled. Ammonia water is used to adjust the alkalinity to achieve uniform co-precipitation of iron and cobalt ions. Then, a hydrothermal reaction is used to directionally synthesize the iron-cobalt bimetallic oxide precursor. Finally, the mass fraction of Na in the catalyst is precisely controlled by filtration and washing with NaOH aqueous solution. The overall process is simple to operate, has mild conditions, and is widely adaptable to raw materials. It can ensure the pure phase formation of spinel crystals and avoid the formation of impurity oxides through the weak alkalinity of ammonia water, and the Na content can be controlled between 0.1% and 3 wt.% through precise control of the washing process. By flexibly adjusting within a certain range, the presence and distribution of Na in the catalyst can be effectively controlled, ultimately yielding a Na-containing spinel-type iron-cobalt bimetallic catalyst. This catalyst possesses both a regular spinel crystal phase structure and optimized surface electronic properties. The synergistic effect of the iron-cobalt bimetallic catalyst and the regulatory effect of the Na promoter are fully utilized. At the same time, the preparation method introduces no excess impurity ions throughout the process, avoiding interference with the catalyst's active sites. The preparation efficiency is high and the product reproducibility is good, laying a high-quality catalytic foundation for the targeted regulation of hydrocarbon product distribution in subsequent CO2 hydrogenation reactions. It has significant prospects for industrial-scale application.

[0034] This disclosure also provides a Na-containing spinel-type iron-cobalt bimetallic catalyst. The catalyst has a pure-phase spinel crystal structure. Na is combined with iron-cobalt bimetallic oxide in the form of interstitial doping, surface adsorption, or surface composite oxide. The mass fraction of Na is 0.1~3 wt.%, and the molar ratio of Fe to Co is 2:(0.8~1.2).

[0035] This disclosure also provides an application of a Na-containing spinel-type iron-cobalt bimetallic catalyst in CO2 hydrogenation reaction, comprising: loading the catalyst into a fixed-bed reactor, introducing a mixed feed gas containing CO2 and H2 to carry out CO2 hydrogenation reaction, and achieving directional control of the distribution of hydrocarbon products in CO2 hydrogenation reaction by adjusting the mass fraction of Na in the catalyst; wherein the CO2 content in the mixed feed gas is 5~30 vol.%.

[0036] This catalyst is highly adaptable to feed gas systems with high CO2 content. By adjusting the mass fraction of Na in the catalyst, the distribution of hydrocarbon products can be directionally regulated, significantly improving the product control flexibility and feed gas compatibility of CO2 hydrogenation to hydrocarbons. The specific application is as follows: the CO2 hydrogenation reaction system includes a fixed-bed reactor, a gas chromatograph, a mass flow controller, a tail gas treatment device, and a computer. The connection method is as follows: a Na-containing spinel-type iron-cobalt bimetallic catalyst is packed into the fixed-bed reactor; the mass flow controller is connected to the reactor inlet to control the CO2 and H2 inlet ratio and flow rate; the reactor outlet is connected to the gas chromatograph for analyzing reaction products; the tail gas treatment device is connected to the gas chromatograph outlet to treat unreacted gases; and the computer is connected to the gas chromatograph to record and analyze product distribution data. Preferably, the conditions for the CO2 hydrogenation reaction are: temperature 280–350 °C, pressure 1–4 MPa, H2 / CO2 molar ratio 3:1, and volumetric hourly space velocity (VHSV) 4000–8000 mL / g / h. As a further preferred embodiment, the conditions for the CO2 hydrogenation reaction are: temperature 300 °C, pressure 3 MPa, H2 / CO2 molar ratio 3:1, and volume hourly space velocity (VHSV) 6000 mL / g / h. Preferably, the hydrocarbon products include C2-C4 hydrocarbons and C5+ hydrocarbons. By adjusting the Na mass fraction, the selectivity for C2-C4 hydrocarbons is adjustable between 40% and 50%, and the selectivity for C5+ hydrocarbons is adjustable between 30% and 40%. In this application, the CO2 content of the mixed feed gas is 5~30 vol.%, which can be directly adapted to feed gas systems with different CO2 contents, such as traditional Fischer-Tropsch syngas and biomass gasification syngas. No pretreatment such as decarbonization or ratio adjustment of the feed gas is required, significantly simplifying the process and reducing industrial application costs. During the reaction, the distribution of hydrocarbon products in the O2 hydrogenation reaction can be directionally controlled by adjusting the mass fraction of Na in the catalyst (0.1~3 wt.%). Fine adjustments to the Na mass fraction can precisely change the surface electron density, oxygen vacancy concentration, and surface acidity / basicity of the catalyst, thereby controlling the activation efficiency of CO2 molecules and the carbon chain growth path, achieving selective control of hydrocarbon products with different carbon chains.

[0037] In the aforementioned CO2 hydrogenation reaction system, this catalyst fully leverages the synergistic catalytic effect of the Fe-Co bimetallic compound and the regulatory effect of the Na promoter. The spinel crystal structure constructed by the iron-cobalt bimetallic compound provides abundant and efficient active sites for CO2 hydrogenation, ensuring a high CO2 conversion rate. Meanwhile, different amounts of Na guide the product distribution of the catalytic reaction through interstitial doping and surface adsorption, enabling the catalyst to adapt to a wide range of CO2 contents from 5 to 30 vol.% of feed gas while flexibly controlling hydrocarbon products. This provides an efficient and convenient catalytic solution for the industrial application of CO2 hydrogenation to hydrocarbon production technology.

[0038] The following section will provide a detailed explanation of this solution, including specific technical solutions, process parameters, implementation methods, and accompanying drawings.

[0039] Example 1 A method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst includes the following steps: (1) Measure 40 mL of deionized water and place it in a reaction vessel. Under stirring conditions at room temperature, add 2.02 g of ferric nitrate nonahydrate and 0.73 g of cobalt nitrate hexahydrate in sequence. Continue stirring until the solid is completely dissolved to obtain a mixed iron-cobalt salt solution (Fe:Co molar ratio is 2:1). Then slowly add 0.1 mol of ammonia water to the solution, stir evenly and adjust the solution to be alkaline to obtain an alkaline mixed suspension.

[0040] (2) Transfer the above alkaline mixed suspension to the polytetrafluoroethylene liner of a 100 mL hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, and place it in a constant temperature oven for hydrothermal reaction at 180 °C for 8 h.

[0041] (3) After the hydrothermal reaction is completed, the hydrothermal synthesis vessel is taken out and naturally cooled to room temperature. The iron-cobalt bimetallic oxide product in the vessel is collected. The product is placed in a Buchner funnel and washed by vacuum filtration with 0.1 mol / L NaOH aqueous solution. The Na mass fraction in the product is precisely controlled to be 1 wt.% according to theory. The actual Na mass fraction in the product is 0.99 wt.%. After washing, the filter cake product is transferred to a drying oven and dried at 60 ℃ for 12 h to obtain spinel-type iron-cobalt bimetallic catalyst, which is denoted as 0.99Na-Fe2Co1.

[0042] Example 2 A method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst includes the following steps: (1) Measure 40 mL of deionized water and place it in a reaction vessel. Under stirring conditions at room temperature, add 2.02 g of ferric nitrate nonahydrate and 0.73 g of cobalt nitrate hexahydrate in sequence. Continue stirring until the solid is completely dissolved to obtain a mixed iron-cobalt salt solution (Fe:Co molar ratio is 2:1). Then slowly add 0.1 mol of ammonia water to the solution, stir evenly and adjust the solution to be alkaline to obtain an alkaline mixed suspension.

[0043] (2) Transfer the above alkaline mixed suspension to the polytetrafluoroethylene liner of a 100 mL hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, and place it in a constant temperature oven for hydrothermal reaction at 180 °C for 8 h.

[0044] (3) After the hydrothermal reaction is completed, the hydrothermal synthesis vessel is taken out and naturally cooled to room temperature. The iron-cobalt bimetallic oxide product in the vessel is collected. The product is placed in a Buchner funnel and washed by vacuum filtration with 0.02 mol / L NaOH aqueous solution. The Na mass fraction in the product is precisely controlled to be 0.2 wt.% according to theory. The actual Na mass fraction in the product is 0.17 wt.%. After washing, the filter cake product is transferred to a drying oven and dried at 60 ℃ for 12 h to obtain spinel-type iron-cobalt bimetallic catalyst, which is denoted as 0.17Na-Fe2Co1.

[0045] Example 3 A method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst includes the following steps: (1) Measure 40 mL of deionized water and place it in a reaction vessel. Under stirring conditions at room temperature, add 2.02 g of ferric nitrate nonahydrate and 0.73 g of cobalt nitrate hexahydrate in sequence. Continue stirring until the solid is completely dissolved to obtain a mixed iron-cobalt salt solution (Fe:Co molar ratio is 2:1). Then slowly add 0.1 mol of ammonia water to the solution, stir evenly and adjust the solution to be alkaline to obtain an alkaline mixed suspension.

[0046] (2) Transfer the above alkaline mixed suspension to the polytetrafluoroethylene liner of a 100 mL hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, and place it in a constant temperature oven for hydrothermal reaction at 180 °C for 8 h.

[0047] (3) After the hydrothermal reaction is completed, the hydrothermal synthesis vessel is taken out and naturally cooled to room temperature. The iron-cobalt bimetallic oxide product in the vessel is collected. The product is placed in a Buchner funnel and washed by vacuum filtration with 0.05 mol / L NaOH aqueous solution. The Na mass fraction in the product is precisely controlled to be 0.5 wt.% according to theory. The actual Na mass fraction in the product is 0.46 wt.%. After washing, the filter cake product is transferred to a drying oven and dried at 60 ℃ for 12 h to obtain spinel-type iron-cobalt bimetallic catalyst, which is denoted as 0.46Na-Fe2Co1.

[0048] Example 4 A method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst includes the following steps: (1) Measure 40 mL of deionized water and place it in a reaction vessel. Under stirring conditions at room temperature, add 2.02 g of ferric nitrate nonahydrate and 0.73 g of cobalt nitrate hexahydrate in sequence. Continue stirring until the solid is completely dissolved to obtain a mixed iron-cobalt salt solution (Fe:Co molar ratio is 2:1). Then slowly add 0.1 mol of ammonia water to the solution, stir evenly and adjust the solution to be alkaline to obtain an alkaline mixed suspension.

[0049] (2) Transfer the above alkaline mixed suspension to the polytetrafluoroethylene liner of a 100 mL hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, and place it in a constant temperature oven for hydrothermal reaction at 180 °C for 8 h.

[0050] (3) After the hydrothermal reaction is completed, the hydrothermal synthesis vessel is taken out and naturally cooled to room temperature. The iron-cobalt bimetallic oxide product in the vessel is collected. The product is placed in a Buchner funnel and washed by vacuum filtration with 0.3 mol / L NaOH aqueous solution. The Na mass fraction in the product is precisely controlled to be 3.0 wt.% according to theory. The actual Na mass fraction in the product is 2.69 wt.%. After washing, the filter cake product is transferred to a drying oven and dried at 60 ℃ for 12 h to obtain spinel-type iron-cobalt bimetallic catalyst, which is denoted as 2.69Na-Fe2Co1.

[0051] Comparative Example 1 A method for preparing a spinel-type iron-cobalt bimetallic catalyst includes the following steps: (1) Measure 40 mL of deionized water and place it in a reaction vessel. Under stirring conditions at room temperature, add 2.02 g of ferric nitrate nonahydrate and 0.73 g of cobalt nitrate hexahydrate in sequence. Continue stirring until the solid is completely dissolved to obtain a mixed iron-cobalt salt solution (Fe:Co molar ratio is 2:1). Then slowly add 0.1 mol of ammonia water to the solution, stir evenly and adjust the solution to be alkaline to obtain an alkaline mixed suspension.

[0052] (2) Transfer the above alkaline mixed suspension to the polytetrafluoroethylene liner of a 100 mL hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, and place it in a constant temperature oven for hydrothermal reaction at 180 °C for 8 h.

[0053] (3) After the hydrothermal reaction is completed, the hydrothermal synthesis vessel is taken out and naturally cooled to room temperature. The iron-cobalt bimetallic oxide product in the vessel is collected. The product is placed in a Buchner funnel and washed with deionized water under reduced pressure. After washing, the filter cake product is transferred to a drying oven and dried at 60 °C for 12 h to obtain a spinel-type iron-cobalt bimetallic catalyst, denoted as Fe2Co1.

[0054] Catalyst characterization and performance The catalysts prepared in Examples 1-4 and Comparative Example 1 were characterized as follows: 1. XRD like Figure 2 As shown, the diffraction peaks of the catalysts prepared in Examples 1-4 and Comparative Example 1 all correspond perfectly to the characteristic peak positions of the CoFe2O4 standard, and no other impurity phase diffraction peaks appear, indicating that the catalysts prepared by the method disclosed herein are all pure-phase spinel type. The introduction of Na does not destroy the integrity of the spinel crystal form, but only combines through interstitial doping, surface adsorption, etc., without changing the core crystal phase of the catalyst.

[0055] 2. Catalytic performance The catalysts prepared in Examples 1-4 and Comparative Example 1 were respectively packed into fixed-bed reactors and subjected to a test at 300 °C, 2 MPa, H2 / CO2 molar ratio of 3:1, and volume hourly space velocity of 2000 h⁻¹. -1 CO2 hydrogenation performance was tested under the following conditions, and the test results are as follows: Figure 3 As shown.

[0056] Figure 3 The bar charts showing the product distribution, CO2 conversion rate, and CO selectivity of the CO2 hydrogenation reaction reveal that the CO2 conversion rate initially increases and then decreases as the Na mass fraction increases from 0 to 2.69%. CO selectivity gradually increases with increasing Na content because Na enhances the activity of the reverse water-gas shift reaction (RWGS), promoting the conversion of CO2 to CO. However, excessive Na inhibits further hydrogenation of CO to form hydrocarbons. The carbon chain distribution of hydrocarbon products changes significantly with increasing Na content. In Na-free Fe2Co1, C2... = -C4 = (Olefins) accounted for the largest proportion, approximately 50%; as the Na content increased, C2... 0 -C4 0 The proportion of (alkanes) increased, while C 5+The proportion of long-chain hydrocarbons increased slightly; when the Na content reached 2.69%, the proportion of CH4 (methane) increased significantly (approximately 20%), while the proportion of long-chain hydrocarbons decreased. This indicates that by controlling the mass fraction of Na in the catalyst (0.1~3 wt.%), the product distribution of olefins → alkanes → long-chain hydrocarbons in the CO2 hydrogenation reaction can be directionally controlled, making it suitable for liquefied petroleum gas (C2~C4) and jet fuel (C4). 5+ The product requirements of different application scenarios, such as CO2 hydrogenation to produce high-value hydrocarbons, fully demonstrate the practical value of the catalyst of this invention in CO2 hydrogenation to produce high-value hydrocarbons.

[0057] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this disclosure can be achieved, and this is not limited herein.

[0058] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0059] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing a Na-containing spinel-type iron-cobalt bimetallic catalyst, characterized in that, The method includes: An alkaline mixed solution is prepared by dissolving soluble salts of iron and cobalt sources in deionized water and adding ammonia. The alkaline mixed solution was placed in a hydrothermal reactor for hydrothermal reaction to obtain the iron-cobalt bimetallic oxide reaction product; The reaction product of the iron-cobalt bimetallic oxide was washed by filtration with an aqueous solution containing NaOH. By adjusting the concentration and volume of the NaOH aqueous solution used for washing, the mass fraction of Na in the catalyst was controlled at 0.1~3 wt.%. After drying, a spinel-type iron-cobalt bimetallic catalyst containing Na was obtained.

2. The method for preparing the Na-containing spinel-type iron-cobalt bimetallic catalyst according to claim 1, characterized in that, The molar ratio of the iron-source soluble salt to the cobalt-source soluble salt, calculated as Fe:Co, is 2:(0.8~1.2).

3. The method for preparing the Na-containing spinel-type iron-cobalt bimetallic catalyst according to claim 1, characterized in that, The iron source soluble salt is at least one of iron nitrate, chloride, and sulfate; the cobalt source soluble salt is at least one of cobalt nitrate, chloride, and sulfate; the pH of the alkaline mixed solution adjusted by ammonia is 8-10, providing a suitable alkaline environment for the co-precipitation of iron-cobalt hydroxide and the subsequent formation of spinel crystals.

4. The method for preparing the Na-containing spinel-type iron-cobalt bimetallic catalyst according to claim 3, characterized in that, The iron source soluble salt is ferric nitrate nonahydrate, and the cobalt source soluble salt is cobalt nitrate hexahydrate; the mass ratio of ferric nitrate nonahydrate to deionized water is 1:(15~25), and the amount of ammonia added is 0.08~0.12mol, so as to achieve uniform dispersion and controllable dissociation of iron and cobalt ions in the solution.

5. The method for preparing the Na-containing spinel-type iron-cobalt bimetallic catalyst according to claim 1, characterized in that, The hydrothermal reaction temperature is 120~200℃, and the hydrothermal reaction time is 8~24h.

6. The method for preparing the Na-containing spinel-type iron-cobalt bimetallic catalyst according to claim 1, characterized in that, The filtration washing is a reduced pressure filtration washing, in which the filtration pressure is controlled at 0.05~0.08MPa and the washing rate is 50~100mL / min.

7. The method for preparing the Na-containing spinel-type iron-cobalt bimetallic catalyst according to claim 6, characterized in that, The concentration of the NaOH-containing aqueous solution is 0.05~0.1mol / L, and the washing volume is 0.5~1.5L.

8. A Na-containing spinel-type iron-cobalt bimetallic catalyst, characterized in that, The catalyst is prepared by any one of claims 1 to 7; the catalyst is a pure phase spinel crystal structure, Na is combined with iron-cobalt bimetallic oxide in the form of interstitial doping, surface adsorption or surface composite oxide, the mass fraction of Na is 0.1 to 3 wt.%, and the molar ratio of Fe to Co is 2:(0.8 to 1.2).

9. The application of a Na-containing spinel-type iron-cobalt bimetallic catalyst as described in claim 8 in the CO2 hydrogenation reaction, characterized in that, The catalyst is packed into a fixed-bed reactor, and a mixed feed gas containing CO2 and H2 is introduced to carry out a CO2 hydrogenation reaction. By adjusting the mass fraction of Na in the catalyst, the distribution of hydrocarbon products in the CO2 hydrogenation reaction can be directionally controlled. The CO2 content in the mixed feed gas is 5~30 vol.%.

10. The application according to claim 9, characterized in that, The process conditions for the CO2 hydrogenation reaction are as follows: reaction temperature 280~350℃, reaction pressure 1~4MPa, molar ratio of H2 to CO2 3:1, and volume hourly space velocity of the mixed feed gas 4000~8000mL / g / h; by adjusting the mass fraction of Na, the selectivity of C2-C4 hydrocarbons is adjustable between 40%~50%, and the selectivity of C5+ hydrocarbons is adjustable between 30%~40%.

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