Iron-doped mesoporous alumina@carbon core-shell structure catalyst and preparation method and application thereof

Abstract

Iron-doped mesoporous alumina@carbon core-shell structure catalyst, preparation method and application thereof, the core-shell structure with iron-doped mesoporous alumina as the inner core and carbon layer encapsulation outside, through in-situ sol-gel method, the atomic level or nanometer level uniform dispersion of iron species in the alumina framework is realized, F127 is used as the template agent to construct the mesoporous channel structure, sodium citrate is used as the dispersant, concentrated hydrochloric acid plays a dual catalytic function, not only speeds up the hydrolysis of aluminum isopropyl alcohol to form a uniform aluminum-based sol network, but also promotes the complexation reaction of PVP and potassium ferrocyanide, by using the multiple effects of PVP reducing agent, carbon precursor and core-shell structure directing agent, the in-situ reduction of iron and the assembly of carbon precursor are completed simultaneously in the sol formation process; after subsequent calcination, the Fe / OMA@C catalyst with stable structure and excellent catalytic performance is obtained, the catalyst is applied to the CO2 desorption of alcohol amine solution, and high catalytic activity and excellent cycle stability can be shown, and the CO2 capture and regeneration energy consumption is effectively reduced.

Description

Technical Field

[0001] This invention relates to a catalyst, specifically an iron-doped mesoporous alumina@carbon core-shell structure catalyst and its preparation method, as well as the application of the catalyst in reducing the energy consumption of CO2 desorption from alkanolamine solutions, belonging to the fields of catalyst synthesis technology and carbon dioxide capture technology. Background Technology

[0002] With the increasing severity of global warming, carbon dioxide (CO2) capture, utilization, and storage (CCUS) technology has become a key approach. Chemical absorption, particularly the amine solution absorption method, is currently the most widely used CO2 capture technology in industry. This technology utilizes an amine solution (such as monoethanolamine MEA) to react chemically with CO2 at low temperatures to form carbamates, which then decompose in reverse at high temperatures, releasing CO2 and regenerating the absorbent. However, the regeneration process of this technology is extremely energy-intensive, typically accounting for 60-70% of the total energy consumption of the capture process, becoming a major bottleneck limiting its large-scale adoption.

[0003] To reduce regeneration energy consumption, researchers have attempted to introduce solid acid catalysts into alkanolamine solutions. By providing additional acidic sites, these catalysts accelerate the desorption rate of CO2, thereby lowering the regeneration temperature or shortening the regeneration time. Alumina (Al2O3) is widely used as a catalyst support due to its high specific surface area, abundant surface acidic sites, and good thermal stability. However, traditional alumina catalysts suffer from the following problems: First, the catalytic activity of alumina alone is limited, making it difficult to meet the requirements for efficient desorption; second, the metal active components (such as Fe and Ni) supported by impregnation are easily dissolved and lost in the alkaline environment of the alkanolamine solution, leading to rapid catalyst deactivation; furthermore, conventional synthesis methods struggle to achieve high dispersion of active components and precise control of pore structure.

[0004] In recent years, carbon materials have been introduced into desorption catalyst systems due to their excellent electron transport properties and chemical stability. Carbon-coated structures can effectively suppress the loss of metal components, while modulating the electronic properties and surface acidity of the support through interfacial interactions. However, the preparation of existing carbon-coated catalysts usually employs a multi-step method, namely, first synthesizing a metal / oxide support, and then coating it with an external carbon source. This process is cumbersome and the uniformity of the carbon layer is difficult to control. Summary of the Invention

[0005] The purpose of this invention is to provide an iron-doped mesoporous alumina@carbon core-shell structure catalyst, its preparation method, and its application. The preparation method is simple, and the prepared catalyst has a stable structure and excellent catalytic performance. When this catalyst is applied to CO2 desorption from alkanolamine solution, it can exhibit high catalytic activity and excellent cycle stability, effectively reducing the energy consumption for CO2 capture and regeneration.

[0006] To achieve the above objectives, the present invention provides a method for preparing an iron-doped mesoporous alumina@carbon core-shell structured catalyst, comprising the following steps: S1: Add template agent F127 and sodium citrate to anhydrous ethanol, seal to prevent solvent evaporation, stir to dissolve, then add concentrated hydrochloric acid (37wt%) dropwise, and stir thoroughly to form a mixed transparent solution; S2: Add polyvinylpyrrolidone (PVP) and potassium ferrocyanide (as an iron source) to the mixed transparent solution obtained in step S1, stir to dissolve, heat to 70~90℃, stir for 0.5~2h, and the solution turns blue; S3: Add aluminum isopropoxide to the solution obtained in step S2 and stir at 30~50℃ for 12~36h to form a sol precursor; S4: Dry the sol precursor obtained in step S3 to obtain a solid precursor; S5: The solid precursor obtained in step S4 is calcined at 400~800℃ for 2~6h under an inert atmosphere, cooled, washed to remove soluble residual salts, and dried to obtain the iron-doped mesoporous alumina@carbon core-shell structure catalyst.

[0007] Preferably, in step S1, the mass concentration of the template agent F127 in anhydrous ethanol is 0.15~0.175 g / mL; the mass concentration of sodium citrate in anhydrous ethanol is 0.015~0.025 g / mL; and the mass concentration of concentrated hydrochloric acid in anhydrous ethanol is 0.075~0.09 g / mL.

[0008] Preferably, in step S2, the mass concentration of polyvinylpyrrolidone (PVP) in anhydrous ethanol is 0.04~0.07 g / mL, and the mass concentration of potassium ferrocyanide in anhydrous ethanol is 0.012~0.022 g / mL.

[0009] Preferably, in step S3, the mass concentration of aluminum isopropoxide in anhydrous ethanol is 0.15~0.175 g / mL.

[0010] Preferably, in step S4, the drying temperature is 60~100℃ and the drying time is 12~36h; in step S5, the calcination heating rate is 2~10℃ / min and the inert atmosphere is nitrogen or argon.

[0011] The present invention also provides an iron-doped mesoporous alumina@carbon core-shell structure catalyst, which is prepared by the above preparation method; the catalyst has a core-shell structure, the core being iron-doped mesoporous alumina, and the outer shell being an in-situ encapsulated amorphous carbon layer; wherein the iron element is uniformly distributed in the alumina framework in the form of atomic or nanoscale, and the carbon layer is wrapped around the surface of the alumina.

[0012] Preferably, the catalyst has a specific surface area of ​​200-400 m².2 / g, with an average pore size of 3~8nm and an iron content of 0.5~5.0 wt%.

[0013] This invention also provides an application of an iron-doped mesoporous alumina@carbon core-shell structure catalyst in the desorption of CO2 from an alkanolamine solution.

[0014] Preferably, the amine solution is a monoethanolamine (MEA), N-methyldiethanolamine (MDEA), or a mixture thereof, and the CO2 desorption temperature is 90°C.

[0015] Preferably, the amount of catalyst used is 0.03 to 1.0 wt% of the mass of the alkanolamine solution.

[0016] Compared with existing technologies, this invention constructs a core-shell structure with iron-doped mesoporous alumina as the core and a carbon layer as the outer encapsulation. The carbon layer, as the outer encapsulation layer, not only effectively prevents the dissolution of iron species in alkaline alkanolamine solutions but also regulates the distribution of acidic sites in alumina through the interaction of different component interfaces, thereby improving catalytic activity. This invention utilizes an in-situ sol-gel method to achieve atomic or nanoscale uniform dispersion of iron species within the alumina framework, avoiding particle agglomeration problems caused by traditional impregnation methods and increasing the abundance of active sites at the surface. This invention uses F127 as a template agent to construct the mesoporous channel structure, which increases the specific surface area, resulting in more uniform dispersion of active components and reducing agglomeration. Sodium citrate, as a dispersant, can... This invention inhibits the excessively rapid nucleation of iron-based particles, thereby obtaining active sites with small particle size and uniform distribution. Concentrated hydrochloric acid plays a dual catalytic role, not only accelerating the hydrolysis of aluminum isopropoxide to form a uniform aluminum-based sol network, but also promoting the complexation reaction between polyvinylpyrrolidone (PVP) and potassium ferrocyanide. Crucially, this invention utilizes the multiple roles of PVP as a reducing agent, carbon precursor, and core-shell structure directing agent, using potassium ferrocyanide as the iron source, to simultaneously complete the in-situ reduction of iron and the assembly of carbon precursor during sol formation. After subsequent calcination, a well-dispersed Fe / OMA@C catalyst is obtained, which can significantly improve the electron transfer characteristics and structural stability of the material, while eliminating the cumbersome process of traditional multi-step synthesis of core-shell structures.

[0017] When the Fe / OMA@C catalyst of this invention is used for CO2 desorption from alkanolamine solutions, the interfacial synergy between the doped alumina core and the carbon shell enhances proton-coupled electron transport, accelerates the breaking of CN bonds in urethane esters, and promotes mass transport of reactive species such as urethane esters in the alkanolamine solution through mesoporous channels. This significantly reduces the desorption activation energy, increases the desorption rate, and reduces regeneration energy consumption by 30-40%, with minimal activity decay after multiple cycles. Furthermore, due to the physical shielding effect of the carbon layer and the strong interaction between iron and the alumina support, the Fe / OMA@C catalyst exhibits extremely low iron dissolution after cycling in alkanolamine solutions, demonstrating excellent cycle stability and effectively reducing CO2 capture and regeneration energy consumption. Attached Figure Description

[0018] Figure 1 This is a transmission electron microscope (TEM) image of the Fe / OMA@C catalyst of this invention. Figure 2 This is an elemental surface scan distribution diagram of the Fe / OMA@C catalyst of the present invention; Figure 3 The N2 adsorption-desorption isotherm and pore size distribution diagram of the Fe / OMA@C catalyst of this invention are shown below. Figure 4 A comparison chart of CO2 desorption amounts in MEA alcoholamine solutions; Figure 5 A comparison chart of CO2 desorption rates in MEA alcoholamine solutions; Figure 6 The graph shows the cyclic stability test results of the Fe / OMA@C catalyst in MEA alkanolamine solution. Figure 7 The catalytic desorption performance of Fe / OMA@C in MDEA and MDEA+MEA mixed aqueous solutions is shown. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments and comparative examples, but the scope of protection of the present invention is not limited to the following embodiments. All raw materials used in the embodiments are commercially available analytical grade reagents. Example 1

[0020] A method for preparing an iron-doped mesoporous alumina@carbon core-shell structured catalyst includes the following steps: S1: Add 3.2g template agent F127 and 0.4g sodium citrate to a beaker containing 20ml anhydrous ethanol. Stir with a rotor for 5min and then add 1.6g concentrated hydrochloric acid with a mass fraction of 37wt.%. Seal the beaker with sealing film to prevent solvent evaporation. Stir thoroughly for 3h to form a mixed transparent solution. S2: After stirring, add 1.00g of polyvinylpyrrolidone (PVP) and 0.31g of potassium ferrocyanide to the mixed transparent solution obtained in step S1. After stirring to dissolve, heat to 80℃ and stir for 1 hour until the solution turns blue. S3: Add 3.26g of ground aluminum isopropoxide to the solution obtained in step S2, and continue stirring in a magnetic stirrer at 40℃ for 24h to form a sol precursor; S4: Transfer the beaker containing the sol precursor to an oven and dry it at a constant temperature of 80℃ for 24 hours to obtain the solid precursor. S5: The solid precursor obtained in step S4 is placed in a tube furnace, nitrogen N2 is introduced, and the temperature is raised to 500℃ at a heating rate of 5℃ / min. Then it is calcined at a constant temperature for 4 hours. After calcination, it is washed three times by centrifugation with deionized water to remove residual salts on the surface. Then it is dried in an oven at 80℃ to obtain the catalyst, named Fe / OMA@C-1.

[0021] Characterization results: Transmission electron microscopy (TEM) images and elemental surface scan distribution maps are shown below. Figure 1 and 2 As shown, the obtained catalyst has a microspherical structure, with an amorphous carbon layer covering the surface of the Fe-doped alumina nanospheres, and iron is highly dispersed on the catalyst nanospheres; the iron content is 2.1 wt.%. N2 adsorption-desorption tests were performed, as shown... Figure 3 As shown, the catalyst has a specific surface area of ​​125 m². 2 / g, with an average pore size of 3.9nm; Example 2

[0022] A method for preparing an iron-doped mesoporous alumina@carbon core-shell structured catalyst includes the following steps: S1: Add 3g template agent F127 and 0.3g sodium citrate to a beaker containing 20ml anhydrous ethanol, add a rotor and stir magnetically for 5min, then add 1.5g concentrated hydrochloric acid with a mass fraction of 37wt.%, seal the beaker with sealing film to prevent solvent evaporation, and stir thoroughly for 3h to form a mixed transparent solution. S2: After stirring, add 0.8g of polyvinylpyrrolidone (PVP) and 0.24g of potassium ferrocyanide (as an iron source) to the mixed transparent solution obtained in step S1. After stirring to dissolve, heat to 80℃ and stir for 1 hour until the solution turns blue. S3: Add 3g of ground aluminum isopropoxide to the solution obtained in step S2, and continue stirring in a magnetic stirrer at 40℃ for 24h to form a sol precursor. S4: Transfer the beaker containing the sol precursor to an oven and dry it at a constant temperature of 80℃ for 24 hours to obtain the solid precursor. S5: The solid precursor obtained in step S4 is placed in a tube furnace, nitrogen N2 is introduced, and the temperature is raised to 400℃ at a heating rate of 5℃ / min. Then it is calcined at a constant temperature for 4 hours. After calcination, it is washed three times by centrifugation with deionized water to remove residual salts on the surface. Then it is dried in an oven at 80℃ to obtain the catalyst, named Fe / OMA@C-2.

[0023] Characterization results: Specific surface area is 179 m². 2 / g, with an average pore size of 4.5nm and an iron content of 1.6wt.%, the Fe-doped alumina nanospheres are covered with an amorphous carbon layer. Example 3

[0024] A method for preparing an iron-doped mesoporous alumina@carbon core-shell structured catalyst includes the following steps: S1: Add 3.5g template agent F127 and 0.5g sodium citrate to a beaker containing 20ml anhydrous ethanol. Stir with a rotor for 5min and then add 1.8g concentrated hydrochloric acid with a mass fraction of 37wt.%. Seal the beaker with sealing film to prevent solvent evaporation. Stir thoroughly for 3h to form a mixed transparent solution. S2: After stirring, add 1.4g of polyvinylpyrrolidone (PVP) and 0.44g of potassium ferrocyanide (as an iron source) to the mixed transparent solution obtained in step S1. After stirring to dissolve, heat to 80℃ and stir for 1 hour until the solution turns blue. S3: Add 3.5g of ground aluminum isopropoxide to the solution obtained in step S2, and continue stirring in a magnetic stirrer at 40℃ for 24h to form a sol precursor; S4: Transfer the beaker containing the sol precursor to an oven and dry it at a constant temperature of 80℃ for 24 hours to obtain the solid precursor. S5: The solid precursor obtained in step S4 is placed in a tube furnace, Ar gas is introduced, and the temperature is raised to 500°C at a heating rate of 5°C / min. Then it is calcined at a constant temperature for 4 hours. After calcination, it is washed three times by centrifugation with deionized water to remove residual salts on the surface. Then it is dried in an oven at 80°C to obtain the catalyst, named Fe / OMA@C-3.

[0025] Characterization results: Specific surface area is 176 m² 2 / g, with an average pore size of 4.2nm and an iron content of 2.0wt.%, the Fe-doped alumina nanospheres are covered with an amorphous carbon layer.

[0026] Comparative Example 1 Comparative Example 1 provides a mesoporous alumina catalyst without iron doping and carbon layer coating, used to illustrate the structural and performance advantages of the catalyst of the present invention. The preparation method is as follows: (1) Add 3.2g template agent F127 and 0.4g sodium citrate to a beaker containing 20ml anhydrous ethanol, stir for 5min, then add 1.6g hydrochloric acid (37wt.%), seal and continue stirring for 3h; (2) Add 3.26g of aluminum isopropoxide, seal and stir at 40°C for 24h to form a sol precursor; (3) After drying at 80℃ for 24h, it was calcined at 500℃ for 4h in an air atmosphere in a tube furnace to obtain a mesoporous alumina catalyst, which was named OMA.

[0027] Characterization results: Specific surface area is 285 m². 2 / g, with an average pore size of 4.5nm, no iron doping, and no carbon layer.

[0028] Comparative Example 2 Comparative Example 2 provides a catalyst made of iron-doped mesoporous alumina without a carbon layer coating, used to illustrate the effect of the carbon layer on catalytic performance. The preparation method is as follows: (1) Synthesize the iron-containing sol precursor according to steps (1) to (3) of Example 1; (2) After drying, it is placed in a tube furnace and calcined at 500°C for 4 hours in an air atmosphere to completely oxidize and remove the carbon components, thus obtaining an iron-doped mesoporous alumina catalyst, named Fe / OMA.

[0029] Application performance test 1 Test method: Take 100 mL of 30 wt.% monoethanolamine (MEA) rich solution (CO2 loading of 0.6~0.68 mol CO2 / mol MEA), add 0.05 g of the catalyst prepared in the above examples and comparative examples, place them in a three-necked flask with reflux condenser, place it on a heating mantle, and heat at 90°C for desorption testing. Use a stopwatch and a wet flow meter to record the desorption time and CO2 desorption amount. Simultaneously test the CO2 desorption rate trend of the Fe / OMA@C catalyst of the examples after 10 cycles. The blank experiment is conducted without adding catalyst; the ethanolamine solution is heated to 90°C and desorption is performed directly. The comparison curves of CO2 desorption amount and desorption rate between the blank experiment, comparative example, and example catalysts are shown below. Figure 4 and Figure 5 As shown, the desorption rate change curve for 10 cycles in Example 1 is as follows: Figure 6 As shown.

[0030] Table 1. Comparison of desorption capacity and desorption rate performance of catalysts prepared in blank experiment, implementation class, and comparative example in MEA solution. The test results in Table 1 show that the catalysts Fe / OMA@C-1, Fe / OMA@C-2, and Fe / OMA@C-3 ​​prepared in Examples 1-3 of this invention showed a 27% increase in desorption capacity compared to the blank experiment without catalyst, which is higher than that of the undoped iron mesoporous alumina (16%), indicating that iron doping can effectively improve catalytic activity. Compared with the Fe / OMA catalyst without carbon layer coating (Comparative Example 2), the catalyst of this invention with carbon layer coating maintains high desorption efficiency while exhibiting very low metal dissolution after 10 cycles, high chemical properties and structural stability, and virtually no decay in catalytic desorption rate. This indicates that the carbon layer has excellent encapsulation and protection effect on iron species, significantly improving the catalyst's resistance to leaching and cycle stability. Furthermore, there is an interfacial synergistic effect between the carbon layer and the iron-doped mesoporous alumina, which significantly improves the proton coupling electron effect, reduces the activation energy of urethane decomposition, and significantly increases the desorption capacity and desorption rate in the alkanolamine solution.

[0031] Application Performance Test 2: 100 mL of different alkanolamine solutions were taken, namely 15 wt.% MDEA alkanolamine and a mixed aqueous solution of MDEA (5 wt.%) + MEA (25 wt.%). 0.05 g of the catalyst prepared in Example 1 was added, and the solution was placed in a three-necked flask with a reflux condenser. The flask was then placed on a heating mantle and heated at 90 °C for desorption testing. The desorption time and CO2 desorption amount were recorded using a stopwatch and a wet flow meter. The catalytic desorption performance curves were compared with the blank experiment without the catalyst. Figure 7 As shown in the figure. The test results indicate that the catalyst prepared in this invention exhibits significant catalytic desorption performance in MDE, increasing the desorption capacity, accelerating the desorption rate in a mixed aqueous solution of MEA+MEDA, and improving the desorption efficiency.

[0032] The method for preparing the iron-doped mesoporous alumina@carbon core-shell structure catalyst provided by this invention is simple, uses readily available raw materials, and is easy to scale up for production. This catalyst can be widely used in chemical absorption CO2 capture processes, effectively reducing regeneration energy consumption, and has good industrial application prospects and economic benefits.

[0033] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing an iron-doped mesoporous alumina@carbon core-shell structure catalyst, characterized in that, Includes the following steps: S1: Add template agent F127 and sodium citrate to anhydrous ethanol, seal, stir to dissolve, then add concentrated hydrochloric acid (37wt%) dropwise, and stir thoroughly to form a mixed transparent solution; S2: Add polyvinylpyrrolidone and potassium ferrocyanide to the mixed transparent solution obtained in step S1, stir to dissolve, heat to 70~90℃, stir for 0.5~2h, and the solution turns blue. S3: Add aluminum isopropoxide to the solution obtained in step S2 and stir at 30~50℃ for 12~36h to form a sol precursor; S4: Dry the sol precursor obtained in step S3 to obtain a solid precursor; S5: The solid precursor obtained in step S4 is calcined at 400~800℃ for 2~6h under an inert atmosphere, cooled, washed, and dried to obtain the iron-doped mesoporous alumina@carbon core-shell structure catalyst.

2. The method for preparing an iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 1, characterized in that, In step S1, the mass concentration of the template agent F127 in anhydrous ethanol is 0.15~0.175 g / mL; the mass concentration of sodium citrate in anhydrous ethanol is 0.015~0.025 g / mL; and the mass concentration of concentrated hydrochloric acid in anhydrous ethanol is 0.075~0.09 g / mL.

3. The method for preparing an iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 2, characterized in that, In step S2, the mass concentration of polyvinylpyrrolidone in anhydrous ethanol is 0.04~0.07 g / mL, and the mass concentration of potassium ferrocyanide in anhydrous ethanol is 0.012~0.022 g / mL.

4. The method for preparing an iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 2, characterized in that, In step S3, the mass concentration of aluminum isopropoxide in anhydrous ethanol is 0.15~0.175 g / mL.

5. The method for preparing an iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 4, characterized in that, In step S4, the drying temperature is 60~100℃ and the drying time is 12~36h; in step S5, the calcination heating rate is 2~10℃ / min and the inert atmosphere is nitrogen or argon.

6. An iron-doped mesoporous alumina@carbon core-shell structure catalyst, characterized in that, The catalyst is prepared by any one of the preparation methods described in claims 1-5; the catalyst has a core-shell structure, with the core being iron-doped mesoporous alumina and the outer shell being an in-situ encapsulated amorphous carbon layer; wherein the iron element is uniformly distributed in the alumina framework in the form of atomic or nanoscale, and the carbon layer is wrapped around the surface of the alumina.

7. The iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 6, characterized in that, The catalyst has a specific surface area of ​​200~400m². 2 / g, with an average pore size of 3~8nm and an iron content of 0.5~5.0wt%.

8. The application of the iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 7 in CO2 desorption from alkanolamine solution.

9. The application of the iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 8 in CO2 desorption from alkanolamine solution, characterized in that, The amine solution is a monoethanolamine (MEA), N-methyldiethanolamine (MDEA), or a mixture thereof, and the CO2 desorption temperature is 90°C.

10. The application of the iron-doped mesoporous alumina@carbon core-shell structure catalyst according to claim 8 in the CO2 desorption of alkanolamine solution, characterized in that, The amount of catalyst used is 0.03~1.0 wt% of the mass of the alkanolamine solution.

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