A three-stage synergistic catalyst for CO2 hydrogenation to aromatics and its preparation method

Abstract

The application provides a tertiary synergistic catalyst for CO2 hydrogenation to arenes and a preparation method thereof, and belongs to the technical field of catalytic chemistry and energy chemical industry. x ZnZr 1‑x O2, 0.05<=x<=0.15, the active center layer is Fe monatomic, and the shell layer is ZSM-5 molecular sieve. In the catalyst, the high-density oxygen vacancy of the first-stage core layer effectively activates CO2 molecules; the second-stage Fe monatomic site promotes C-C coupling reaction; and the third-stage ZSM-5 shell layer realizes high-efficiency cyclization selectivity of arenes through the molecular sieve characteristics. The synergistic effect of the three stages significantly improves the selectivity of arene generation, and the value can reach 55-65%, wherein the proportion of C6-C8 arenes is more than 80%. Meanwhile, the CO2 conversion rate can be stably maintained in the range of 30-40%.

Description

Technical Field

[0001] This invention relates to the fields of catalytic chemistry and energy chemical engineering, and in particular to a three-stage synergistic catalyst for the hydrogenation of CO2 to aromatics and its preparation method. Background Technology

[0002] Aromatic hydrocarbons are a class of organic compounds with aromatic structures, mainly including benzene, toluene, and xylene. They play a crucial role in modern industry, widely used in plastics, rubber, dyes, pharmaceuticals, and fine chemicals. Traditional aromatic hydrocarbon production relies primarily on petrochemical processes, such as naphtha cracking or reforming. This process is highly dependent on fossil resources and releases large amounts of greenhouse gases like carbon dioxide, resulting in a severe environmental burden. Utilizing CO2 as a carbon source to directly synthesize aromatic hydrocarbons through hydrogenation represents a promising green chemical pathway. This approach can effectively reduce carbon emissions and achieve high-value-added transformation of waste materials, offering significant environmental and economic benefits.

[0003] The reaction pathway for the hydrogenation of CO2 to produce aromatics is complex, typically involving several key steps: First, CO2 needs to be activated to generate a reactive C1 intermediate; then, a carbon chain is formed through a C-C coupling reaction; subsequently, the carbon chain undergoes further cyclization and dehydrogenation reactions, ultimately producing the aromatic product. However, this reaction process faces numerous technical challenges in practice. First, the stable structure of the CO2 molecule itself and its high activation energy result in a low conversion rate in the reaction, limiting the overall efficiency improvement. Second, the inefficient C-C coupling reaction easily generates byproducts such as methane and lower-carbon alkanes, significantly reducing the selectivity and yield of aromatics. Finally, the catalyst is prone to carbon deposition or sintering of active sites during the reaction, leading to structural deterioration and decreased catalytic activity, thus affecting the stability and sustainability of the reaction.

[0004] Currently, most catalysts used for CO2 hydrogenation to aromatics are bifunctional composite systems, such as catalysts combining metal oxides and molecular sieves. Although these catalysts can achieve CO2 activation and aromatics generation to some extent, the synergy between their functions is poor. Specifically, the metal oxide part usually has strong CO2 activation ability, while the molecular sieve part is mainly responsible for cyclization and dehydrogenation reactions, but there is a significant lack of functional matching between the two. In addition, the metal active centers have low dispersion in the catalyst and are prone to agglomeration, thereby reducing catalytic efficiency and selectivity. For example, although ZnZrO2-based catalysts have good CO2 activation ability, they are weak in promoting CC coupling and are difficult to achieve high aromatics yields; while Fe-based catalysts have certain advantages in CC coupling, the metal particles are prone to agglomeration, leading to increased by-products and decreased aromatics selectivity. On the other hand, although the commonly used ZSM-5 molecular sieve performs well in catalyzing cyclization reactions, the spatial distance between it and the CO2 activation center is difficult to control precisely, resulting in significant resistance to mass transfer and affecting the overall efficiency of the reaction.

[0005] Therefore, in order to effectively overcome the key problems existing in the current CO2 hydrogenation to aromatics technology, it is urgent to develop a new catalyst system. Summary of the Invention

[0006] This invention aims to address the problems of insufficient CO2 activation capacity, low CC coupling efficiency, poor aromatic selectivity, and unsatisfactory catalyst stability in current CO2 hydrogenation to aromatics catalysts. It provides a three-stage synergistic catalyst for CO2 hydrogenation to aromatics and its preparation method. The catalyst provided by this invention achieves highly efficient synergistic catalysis of the three-step reaction of "CO2 activation—CC coupling—cyclization dehydrogenation" through precise design of the core layer, single-atom active sites, and molecular sieve shell, thereby significantly improving aromatic yield and enhancing catalyst stability.

[0007] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is a three-stage synergistic core-shell catalyst, comprising a core layer, an active center layer, and a shell layer; wherein the core layer is Ga. x ZnZr 1-x O2, 0.05≤x≤0.15, active center layer is Fe single atom, shell layer is ZSM-5 molecular sieve.

[0008] The second technical solution of the present invention is a method for preparing the above-mentioned three-stage synergistic core-shell catalyst, comprising the following steps: Gallium, zirconium, and zinc sources were subjected to a solvothermal reaction in a solvent. After the reaction, solid-liquid separation was performed, followed by calcination of the resulting solid product to obtain Ga. x ZnZr 1-xO2; Photochemical deposition was used in the Ga x ZnZr 1-x Fe single atoms were loaded onto the O2 surface to obtain Fe single-atom modified Ga. x ZnZr 1-x O2; Hydrothermal method for single-atom modified Ga x ZnZr 1-x ZSM-5 molecular sieve shells were synthesized on the O2 surface to obtain the three-stage synergistic core-shell catalyst.

[0009] The third technical solution of the present invention is the application of the above-mentioned three-stage synergistic core-shell catalyst in the catalytic hydrogenation of CO2 to aromatics.

[0010] The present invention discloses the following technical effects: The catalyst system constructed in this invention exhibits excellent stability, controllability, and reaction efficiency. Fe single atoms are stably anchored to the support surface in a Fe-O4 coordination structure, with interatomic distances exceeding 0.5 nm, effectively suppressing their aggregation behavior. Furthermore, the ZSM-5 ultrathin shell structure significantly reduces the carbon deposition rate, ensuring that the catalyst's catalytic activity decreases by less than 5% after 100 hours of continuous operation (in contrast, traditional catalysts typically experience activity degradation exceeding 20% ​​within 50 hours).

[0011] In terms of controllability, this system can precisely adjust the synergistic mechanism between various catalytic active sites by systematically controlling the doping ratio of Ga, the loading of Fe single atoms, and the thickness of the ZSM-5 shell, thereby achieving directional control of reaction performance and meeting the needs of diverse reaction conditions.

[0012] This catalyst achieves a three-stage synergistic catalytic reaction mechanism: in the first stage, high-density oxygen vacancies in the core layer effectively activate CO2 molecules; in the second stage, Fe single-atom sites promote C-C coupling reactions; and in the third stage, the ZSM-5 shell, through its molecular sieve properties, achieves highly efficient cyclization selectivity for aromatics. The synergistic effect of these three stages significantly improves the selectivity for aromatic formation, reaching 55–65%, with C6–C8 aromatics accounting for over 80%. Simultaneously, the CO2 conversion rate can be stably maintained within the range of 30–40%, significantly outperforming current mainstream bifunctional catalysts (whose aromatic selectivity is typically below 45%).

[0013] In summary, this invention has successfully overcome key scientific and engineering problems such as low conversion efficiency, poor product selectivity, and insufficient catalyst stability in the process of CO2 hydrogenation to aromatics by constructing a three-stage synergistic catalytic system, providing an innovative technical path for the efficient resource utilization of CO2. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 Ga obtained in Embodiment 1 of the present invention 0.1 ZnZr 0.9 O2 core layer XRD; Figure 2 Ga obtained in Embodiment 1 of the present invention 0.1 ZnZr 0.9 SEM and EDS images of the O2 core layer; Figure 3 The image shows the FT-EXAFS absorption spectrum of Fe single atom (Fe-O4) in Example 1 of this invention. Figure 4 The Ga with a core-shell structure in Embodiment 1 of the present invention 0.1 ZnZr 0.9 Transmission electron microscopy (TEM) image of O2@Fe@ZSM-5 catalyst. Detailed Implementation

[0016] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0017] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0018] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0019] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0020] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0021] The three-stage synergistic core-shell catalyst system provided by this invention should possess the following characteristics: First, it should be able to efficiently activate CO2 molecules and improve their conversion rate; second, it should have good CC coupling ability, thereby reducing the formation of by-products and improving the selectivity of aromatics; finally, it should be able to achieve precise control of the cyclization reaction to ensure the stable formation of aromatic structures. Simultaneously, the structural stability of the catalyst also needs to be significantly improved to extend its service life and enhance the feasibility of industrial applications.

[0022] The first aspect of this invention provides a three-stage synergistic core-shell catalyst, comprising a core layer, an active center layer, and a shell layer; wherein the core layer is Ga. x ZnZr 1-x O2, 0.05≤x≤0.15, active center layer is Fe single atom, shell layer is ZSM-5 molecular sieve.

[0023] More preferably, x = 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14 or 0.15.

[0024] In a preferred embodiment of the present invention, the Fe single atom is anchored to the surface of the core layer in a Fe-O4 coordination structure, and the Fe single atom accounts for 0.3%-1.0% of the total mass of the Fe single atom and the core layer; the thickness of the shell layer is 5-20 nm.

[0025] More preferably, the Fe single atom accounts for 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0% of the total mass of the Fe single atom and the core layer.

[0026] In this invention: Core layer: Ga-modified ZnZrO2, with the general chemical formula Ga x ZnZr 1-xO2 (x=0.05-0.15). Ga doping significantly increased the oxygen vacancy concentration in ZnZrO2 materials (35%-45% higher than unmodified samples), thereby enhancing the adsorption and activation capacity of CO2 (CO2 chemisorption increased by 20%-30%), providing abundant C1-type active intermediates (such as CO*, HCOO*) for subsequent reactions.

[0027] Active center: Employs atomically dispersed Fe single atoms, with a loading controlled within the range of 0.3-1.0 wt%. The Fe single atoms exist stably in a Fe-O4 coordination structure, with a spacing greater than 0.5 nm, effectively preventing metal particle aggregation. This structure can efficiently catalyze the C-C coupling reaction of C1 intermediates to generate olefins or long-chain hydrocarbon intermediates (C... 2+ Hydrocarbon selectivity is increased by 40%-50%, while methane formation is significantly inhibited (methane selectivity is less than 10%).

[0028] Shell: A ZSM-5 molecular sieve with a thickness of 5-20 nm is used as the outer layer structure. This shell has a moderate Brønsted acid site density (1.0-1.5 × 10⁻⁶). 14 cm -2 This structure can selectively catalyze the cyclization and dehydrogenation of olefins or long-chain hydrocarbon intermediates to generate aromatic products. Simultaneously, the shell effectively inhibits excessive hydrogenation, reducing the formation of alkane byproducts (by 20%-30%). Furthermore, the ultrathin shell structure significantly reduces mass transfer resistance between reactants and products, helping to prevent carbon deposition of intermediates within the molecular sieve channels.

[0029] This catalyst has a high specific surface area (250-400 m²). 2 ( / g) and good pore volume (0.3-0.6 cm³) 3 ( / g), which ensures sufficient exposure of active sites while also possessing excellent mass transfer performance.

[0030] A second aspect of the present invention provides a method for preparing the above-mentioned three-stage synergistic core-shell catalyst, comprising the following steps: Gallium, zirconium, and zinc sources were subjected to a solvothermal reaction in a solvent. After the reaction, solid-liquid separation was performed, followed by calcination of the resulting solid product to obtain Ga. x ZnZr 1-x O2; Photochemical deposition was used in the Ga x ZnZr 1-x Fe single atoms were loaded onto the O2 surface to obtain Fe single-atom modified Ga. x ZnZr 1-x O2 (denoted as Fe / Ga) x ZnZr 1-x O2); Hydrothermal method for single-atom modified Ga x ZnZr 1-x ZSM-5 molecular sieve shells were synthesized on the O2 surface to obtain the three-stage synergistic core-shell catalyst (denoted as Ga). x ZnZr 1-x O2@Fe@ZSM-5).

[0031] In a preferred embodiment of the present invention, the gallium source is gallium nitrate or gallium acetate, the zirconium source is zirconium nitrate or zirconium acetate, and the zinc source is zinc nitrate or zinc acetate; the solvent is a mixed solvent of ethanol and water, with a volume ratio of ethanol to water of 1:1.

[0032] In a preferred embodiment of the present invention, the temperature of the solvothermal reaction is 120-180℃, the time is 20-30h, and the heating rate is 1-3℃ / min.

[0033] More preferably, the temperature of the solvothermal reaction is 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C.

[0034] More preferably, the solvothermal reaction time is 20h, 22h, 24h, 26h, 28h or 30h.

[0035] In a preferred embodiment of the present invention, the calcination temperature is 500~750℃, the time is 3~5h, and the heating rate is 2~3℃ / min.

[0036] More preferably, the calcination temperature is 500°C, 550°C, 600°C, 650°C, 700°C, or 750°C.

[0037] More preferably, the roasting time is 3h, 3.5h, 4h, 4.5h or 5h.

[0038] In a preferred embodiment of the present invention, photochemical deposition is used on the Ga x ZnZr 1-x A method for loading Fe single atoms onto an O2 surface includes the following steps: loading Ga... x ZnZr 1-x O2 was uniformly dispersed in the Fe salt solution, and then irradiated with light under a protective atmosphere.

[0039] In a preferred embodiment of the present invention, the Fe salt in the Fe salt solution is either ferric nitrate or ferric acetate.

[0040] In a preferred embodiment of the present invention, the wavelength of the light is 300-400nm, the power is 300W, and the irradiation time is 1-3h.

[0041] In a preferred embodiment of the present invention, a hydrothermal method is used to modify Fe single-atom Ga x ZnZr 1-x A method for synthesizing ZSM-5 molecular sieve shells on an O2 surface includes the following steps: mixing a silicon source, an aluminum source, and a template agent with water until homogeneous, and then adding the Fe single-atom modified Ga... x ZnZr 1-x The reaction was carried out by hydrothermal reaction with O2. After the reaction was completed, the resulting solid product was washed, dried and calcined in sequence.

[0042] In a preferred embodiment of the present invention, the silicon source is tetraethyl orthosilicate (TEOS), the aluminum source is aluminum isopropoxide, the template agent is an aqueous solution of tetrapropylammonium hydroxide (TPAOH), and the concentration of the aqueous solution of tetrapropylammonium hydroxide is 25 wt%; the molar ratio of silicon in the silicon source, aluminum in the aluminum source and tetrapropylammonium hydroxide is 100:(2-4):(12-15).

[0043] In a preferred embodiment of the present invention, the Ga modified with the Fe single atom is added. x ZnZr 1-x When O2 is present, add it at a solid-liquid ratio of 1:50-60 (g / mL).

[0044] The hydrothermal reaction is carried out at a temperature of 160-180℃ for a duration of 24-48 hours. The calcination temperature is 550-600℃, and the time is 5-6 hours. The template agent is removed by calcination.

[0045] A third aspect of the present invention provides the application of the above-mentioned three-stage synergistic core-shell catalyst in the catalytic hydrogenation of CO2 to aromatics.

[0046] In a preferred embodiment of the present invention, the method for catalytic CO2 hydrogenation to produce aromatics is as follows: The catalytic reaction is carried out in a mixture of H2 and CO2 using the aforementioned three-stage synergistic core-shell catalyst.

[0047] More preferably, the molar ratio of H2 to CO2 is 2.5-3.5:1; More preferably, the reaction conditions for the catalytic reaction are: a reaction temperature of 320-360℃, a reaction pressure of 2.5-3.5 MPa, and a space velocity of 2500-4000 h⁻¹. -1 .

[0048] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0049] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0050] Example 1 Ga x ZnZr 1-x Preparation of O2@Fe@ZSM-5 catalyst (x=0.1, Fe loading 0.5wt%, ZSM-5 thickness 10 nm): (1) Preparation of Ga 0.1 ZnZr 0.9 O2 Core Layer: 0.58 g Ga(NO3)3·9H2O, 2.97 g Zn(NO3)2·6H2O, and 4.29 g Zr(NO3)4·5H2O were dissolved in 50 mL of ethylene glycol-water (1:1 volume ratio) mixed solvent and stirred thoroughly for 30 minutes. The resulting solution was then transferred to a 100 mL hydrothermal reactor and reacted at 150 °C for 24 hours (heating rate 2 °C / min). After the reaction was complete, the system was cooled, and the product was centrifuged, washed, and dried at 60 °C. Subsequently, it was calcined at 500 °C for 4 hours (heating rate 2 °C / min) to finally obtain Ga. 0.1 ZnZr 0.9 O2 material (XRD pattern as shown) Figure 1 As shown, the SEM and EDS images are as follows: Figure 2 (As shown).

[0051] Electron paramagnetic resonance (EPR) testing showed that the oxygen vacancy concentration of this material was 2.8 × 10⁻⁶. 18 spins / g, compared to pure ZnZrO2 (1.9×10⁻⁶). 18 The spins / g ratio increased by 47%.

[0052] (2) Loading Fe single atoms to prepare Fe / Ga 0.1 ZnZr 0.9 O2 composite material: 2 g Ga 0.1 ZnZr 0.9 O2 material was dispersed in 100 mL of deionized water, and 0.028 g of Fe(NO3)3·9H2O (Fe loading 0.5 wt%) was added. Stirring continued for 30 minutes. Subsequently, under nitrogen protection, the sample was irradiated with 365 nm ultraviolet light for 2 hours to promote uniform dispersion of Fe species on the material surface. After treatment, the sample was centrifuged and dried to obtain Fe / Ga. 0.1 ZnZr 0.9 O2 composite material.

[0053] X-ray absorption fine structure (XAFS) analysis shows that ( Figure 3Fe exists in the form of Fe-O4 coordination, and the average interatomic spacing of Fe atoms is 0.6 nm, confirming that it is a single-atom dispersed state.

[0054] (3) Fe / Ga 0.1 ZnZr 0.9 ZSM-5 shell growth on O2 surface: A precursor solution was prepared by mixing 10 g tetraethoxysilane (TEOS), 0.23 g aluminum isopropoxide, 5 g tetrapropylammonium hydroxide (TPAOH) aqueous solution (25 wt%), and 100 g deionized water, and stirred for 2 hours to ensure homogeneity. 2 g Fe / Ga 0.1 ZnZr 0.9 O2 material was added to the above precursor solution, fully dispersed, and then transferred to a reactor for crystallization at 170°C for 36 hours. After crystallization, the product was calcined at 550°C in air for 6 hours to remove the template agent, finally obtaining Ga with a core-shell structure. 0.1 ZnZr 0.9 O2@Fe@ZSM-5 catalyst.

[0055] Transmission electron microscopy (TEM) Figure 4 Observations show that the shell thickness of ZSM-5 is approximately 10 nm. BET surface area measurements indicate a specific surface area of ​​320 m². 2 / g, pore volume 0.45 cm³ 3 / g. NH3-TPD analysis results show that the density of Brønsted acid sites on the catalyst surface is 1.2 × 10⁻⁶ g. 14 cm -2 .

[0056] Example 2 Ga x ZnZr 1-x Preparation of O2@Fe@ZSM-5 catalyst (x=0.05, Fe loading 0.3wt%, ZSM-5 thickness 5nm): (1) Preparation of Ga 0.05 ZnZr 0.95 O2 core layer: Same as step (1) in Example 1, except that 0.29 g of Ga(NO3)3·9H2O (x=0.05) is used, and the reaction is carried out at 120℃ for 30 hours to obtain Ga 0.05 ZnZr 0.95 O2.

[0057] The oxygen vacancy concentration of this material is 2.6 × 10⁻⁶. 18 The spins / g is 37% higher than that of pure ZnZrO2.

[0058] (2) Fe single-atom loading to prepare Fe / Ga 0.05ZnZr 0.95 O2 composite material: Same as step (2) in Example 1, except that the amount of Fe(NO3)3·9H2O is 0.017 g (corresponding to a loading of 0.3 wt%), and Fe / Ga is obtained by irradiation with 300 nm ultraviolet light for 1 hour. 0.05 ZnZr 0.95 O2 composite material, in which Fe exists in the form of Fe-O4 coordination and the interatomic spacing is 0.7 nm.

[0059] (3) Fe / Ga 0.05 ZnZr 0.95 O2 surface growth of ZSM-5 shell: Same as step (3) in Example 1, except that the reaction is carried out at 160℃ for 24 hours to obtain Ga with core-shell structure. 0.05 ZnZr 0.95 O2@Fe@ZSM-5 catalyst. The ZSM-5 shell thickness is 5 nm, and the specific surface area of ​​this catalyst is 250 m². 2 / g, pore volume 0.3 cm³ 3 / g, Brønsted acid site density is 1.0×10⁻⁶ 14 cm -2 .

[0060] Example 3 Ga x ZnZr 1-x Preparation of O2@Fe@ZSM-5 composite catalyst (x=0.15, Fe loading 1.0 wt%, ZSM-5 shell thickness 20 nm): (1) Preparation of Ga 0.15 ZnZr 0.85 O2 core layer: Same as step (1) in Example 1, except that the mass of Ga(NO3)3·9H2O is 0.87g (corresponding to x=0.15), and the reaction is carried out at 180℃ for 20 hours to obtain Ga 0.15 ZnZr 0.85 O2. The oxygen vacancy concentration of this material reaches 2.9 × 10⁻⁶. 18 The oxygen vacancy content was increased by 53% compared to pure ZnZrO2 material, with spins / g.

[0061] (2) Fe single-atom loading to prepare Fe / Ga 0.15 ZnZr 0.85 O2 composite material: Same as step (2) in Example 1, except that the amount of Fe(NO3)3·9H2O is 0.056 g (corresponding to a loading of 1.0 wt%), and the reaction is carried out under 400 nm wavelength ultraviolet light irradiation for 3 hours to obtain Fe / Ga 0.15ZnZr 0.85 O2 composite material. Characterization results show that Fe is anchored to the support surface in a Fe-O4 coordination structure, with a spacing of 0.55 nm between adjacent Fe single atoms.

[0062] (3) Fe / Ga 0.15 ZnZr 0.85 O2 surface growth of ZSM-5 shell: Same as step (3) in Example 1, except that the reaction is carried out at a crystallization temperature of 180℃ for 48 hours to obtain Ga with a core-shell structure. 0.15 ZnZr 0.85 O2@Fe@ZSM-5 catalyst. The ZSM-5 shell thickness is approximately 20 nm. The resulting composite catalyst has a specific surface area of ​​400 m². 2 / g, pore volume 0.6 cm³ 3 / g, and has a high Brønsted acid site density of 1.5×10⁻⁶. 14 cm -2 .

[0063] Comparative Example 1 Undoped Ga catalyst (ZnZrO2@Fe@ZSM-5) The preparation method is the same as that of the catalyst in Example 1, except that the introduction of Ga element is omitted (i.e., x=0), and the ZnZrO2@Fe@ZSM-5 catalyst is synthesized with an oxygen vacancy concentration of 1.9×10⁻⁶. 18 spins / g.

[0064] Comparative Example 2 Fe catalyst supported in nanoparticle form (Ga x ZnZr 1-x O2@Fe NPs@ZSM-5) (1) Same as step (1) in Example 1, Ga is obtained. 0.1 ZnZr 0.9 O2 materials.

[0065] (2) Fe loading by impregnation method: 2g Ga 0.1 ZnZr 0.9 O2 material was dispersed in 100 mL of deionized water, and 2.80 g of Fe(NO3)3·9H2O (Fe loading 5.0 wt%) was added. The mixture was stirred continuously for 30 minutes, centrifuged, and dried. The sample was then calcined at 500 °C for 4 hours. [The remaining text appears to be incomplete and requires further context.] 0.1 ZnZr 0.9 Fe nanoparticles with a particle size of 5–10 nm are formed on the O2 surface, resulting in Fe / Ga 0.1 ZnZr 0.9 O2 composite material.

[0066] (3) Same as step (3) in Example 1.

[0067] Comparative Example 3 (1) Same as step (1) in Example 1 (2) Same as step (2) in Example 1.

[0068] (3) Same as step (3) in Example 1, except that the crystallization time is extended from 36 hours to 72 hours to obtain a catalyst with a ZSM-5 shell thickness of 30 nm.

[0069] Catalytic performance evaluation The catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were applied to the CO2 hydrogenation to aromatics reaction. The reaction conditions were set as follows: temperature 340°C, pressure 3 MPa, molar ratio of hydrogen to carbon dioxide 3, and gas space velocity 3000 h⁻¹. -1 Product analysis: Online analysis was performed using gas chromatography (Panno GC1949), with a TCD detector for CO and CH4 detection and an FID detector for C. 2+ For the determination of hydrocarbons, aromatic products are effectively separated using an HP-5 capillary column.

[0070] The experimental results are shown in Table 1 below: Table 1

[0071] The catalysts constructed in Examples 1 to 3 significantly enhanced the oxygen vacancy concentration due to the introduction of Ga, promoted the efficient coupling between Fe single atoms and the support, and formed a synergistic effect with the ultrathin ZSM-5 shell, exhibiting excellent CO2 conversion performance (conversion rate 30–40%), high aromatic selectivity (55–65%), and good reaction stability (performance degradation of less than 5% within 100 hours).

[0072] In Comparative Example 1 (without Ga), the insufficient number of oxygen vacancies resulted in weak CO2 activation, leading to a significant decrease in both conversion rate and selectivity. In Comparative Example 2 (using Fe nanoparticles), the low C–C coupling efficiency and the generation of more byproducts resulted in a significant decrease in aromatic selectivity. In Comparative Example 3 (with an excessively thick ZSM-5 shell), the increased mass transfer resistance led to a decrease in aromatic selectivity, while the carbon deposition phenomenon intensified, weakening catalytic stability.

[0073] In summary, the three-stage synergistic core-shell structure catalyst designed in this invention significantly improves the reaction efficiency of CO2 hydrogenation to aromatics through Ga-modified ZnZrO2 core layer, precise anchoring of atomic-level Fe single atoms, and optimized configuration of the ultrathin ZSM-5 shell. This catalyst exhibits outstanding advantages in high CO2 conversion, high aromatics selectivity, and good stability, demonstrating significant application potential in the fields of carbon resource recycling and green chemical engineering.

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A three-stage synergistic core-shell catalyst, characterized in that, It consists of a core layer, an active center layer, and a shell layer; the core layer is Ga. x ZnZr 1-x O2, 0.05≤x≤0.15, active center layer is Fe single atom, shell layer is ZSM-5 molecular sieve.

2. The three-stage synergistic core-shell catalyst according to claim 1, characterized in that, The Fe single atoms are anchored to the surface of the core layer in a Fe-O4 coordination structure, and the Fe single atoms account for 0.3%-1.0% of the total mass of the Fe single atoms and the core layer; the thickness of the shell layer is 5-20 nm.

3. A method for preparing the three-stage synergistic core-shell catalyst according to claim 1, characterized in that, Includes the following steps: Gallium, zirconium, and zinc sources were subjected to a solvothermal reaction in a solvent. After the reaction, solid-liquid separation was performed, followed by calcination of the resulting solid product to obtain Ga. x ZnZr 1-x O2; Photochemical deposition was used in the Ga x ZnZr 1-x Fe single atoms were loaded onto the O2 surface to obtain Fe single-atom modified Ga. x ZnZr 1-x O2; Hydrothermal method for single-atom modified Ga x ZnZr 1-x ZSM-5 molecular sieve shells were synthesized on the O2 surface to obtain the three-stage synergistic core-shell catalyst.

4. The preparation method according to claim 3, characterized in that, The gallium source is gallium nitrate or gallium acetate, the zirconium source is zirconium nitrate or zirconium acetate, and the zinc source is zinc nitrate or zinc acetate; the solvent is a mixture of ethanol and water, with a volume ratio of ethanol to water of 1:

1.

5. The preparation method according to claim 3, characterized in that, The solvothermal reaction is carried out at a temperature of 120-180℃ for 20-30 hours, with a heating rate of 1-3℃ / min.

6. The preparation method according to claim 3, characterized in that, The calcination temperature is 500~750℃, the time is 3~6h, and the heating rate is 2~3℃ / min.

7. The preparation method according to claim 3, characterized in that, Photochemical deposition was used in the Ga x ZnZr 1-x A method for loading Fe single atoms onto an O2 surface includes the following steps: loading Ga... x ZnZr 1-x O2 was uniformly dispersed in the Fe salt solution, and then irradiated with light under a protective atmosphere.

8. The preparation method according to claim 7, characterized in that, When the light is irradiated, the wavelength of the light is 300-400nm, the power is 300W, and the irradiation time is 1-3h.

9. The preparation method according to claim 3, characterized in that, Hydrothermal method for single-atom modified Ga x ZnZr 1-x A method for synthesizing a ZSM-5 molecular sieve shell on an O2 surface includes the following steps: mixing a silicon source, an aluminum source, and a template agent with water until homogeneous, and then adding the Fe single-atom modified Ga. x ZnZr 1-x The reaction was carried out by hydrothermal reaction with O2. After the reaction was completed, the resulting solid product was washed, dried and calcined in sequence.

10. The application of the three-stage synergistic core-shell catalyst as described in claim 1 in the catalytic hydrogenation of CO2 to aromatics.

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