Multifunctional catalyst for ammonia synthesis and preparation method thereof

Abstract

The invention belongs to the technical field of catalytic synthesis of ammonia, and particularly relates to a multifunctional catalyst for ammonia synthesis and a preparation method thereof. The invention relates to a multifunctional catalyst for ammonia synthesis, the multifunctional catalyst has a three-dimensional composite structure, and comprises: a carrier which is cordierite ceramic; the interior of the cordierite ceramic is provided with a mesoporous structure formed by carrying out acid pickling treatment on the cordierite ceramic; an active coating, wherein the active coating is gamma-aluminum oxide loaded on the carrier; and a bifunctional active component, wherein the bifunctional active component comprises platinum metal and barium oxide which are loaded on the active coating layer.

Description

Technical Field

[0001] This invention belongs to the field of catalytic ammonia synthesis technology, and particularly relates to a multifunctional catalyst for ammonia synthesis and its preparation method. Background Technology

[0002] Ammonia, one of the world's most produced chemical products, is a cornerstone of modern chemical industry. It is not only an indispensable core raw material for the production of nitrogen fertilizers (such as urea and ammonium nitrate), directly impacting global food security, but also plays a vital role in numerous fields including defense, medicine, and materials science. In recent years, with the increasing global demand for clean energy, ammonia, with its high energy density, ease of liquefaction, storage and transportation, and carbon-free combustion, has been regarded as a highly promising zero-carbon fuel and hydrogen carrier, highlighting its strategic importance. However, currently, over 90% of global ammonia production still relies on the century-old Haber-Bosch process. This process uses iron-based catalysts to directly synthesize nitrogen and hydrogen under harsh conditions of high temperature (approximately 400-500°C) and high pressure (15-30 MPa). This production method not only consumes approximately 1-2% of global energy but also accounts for nearly 1.8% of global anthropogenic greenhouse gas emissions, posing a serious challenge. Therefore, developing new, efficient, and green ammonia synthesis routes under mild conditions (such as atmospheric pressure and low temperature) has become a common goal pursued by the global scientific and industrial communities.

[0003] To replace or supplement the Haber-Bosch process, researchers have explored various new technological pathways for ammonia synthesis under mild conditions. Among these, developing novel, highly efficient catalysts is a core research direction. For example, while ruthenium (Ru)-based noble metal catalysts exhibit high activity under relatively mild conditions, the scarcity of noble metals, their high cost, and their high sensitivity to impurities significantly limit their large-scale industrial application. Meanwhile, emerging synthesis technologies such as electrocatalysis and photocatalysis have also attracted considerable attention, promising to directly synthesize ammonia using electricity or light energy generated from renewable energy sources (such as solar and wind power). However, these technologies are currently in the early stages of laboratory research, generally facing technical bottlenecks such as low Faraday efficiency, slow ammonia production rates, and poor catalyst stability, and are still a long way from practical application. Furthermore, other methods such as plasma activation and chemical chain synthesis are also difficult to promote due to insufficient energy efficiency or complex processes. Overall, existing ammonia synthesis technologies under mild conditions still face significant gaps in catalytic efficiency, economic cost, and industrial feasibility.

[0004] In the search for novel technological pathways, technologies in the field of automotive exhaust purification offer potential inspiration for ammonia synthesis. In the exhaust treatment systems of lean-burn engines, catalysts known as "lean NOx capture (LNT)" or "NOx storage reduction (NSR)" are widely used. These catalysts typically use ceramic supports such as cordierite, loaded with high specific surface area coatings such as γ-alumina, and employ noble metals such as platinum (Pt) as redox active centers, with alkaline earth metal oxides such as barium oxide (BaO) as NOx storage components. Their working principle is to capture NOx under oxygen-rich (lean-burn) conditions and reduce it to harmless nitrogen under brief periods of rich combustion. Those skilled in the art have recognized that, in the process of rich combustion reduction, in addition to the target product nitrogen, a small amount of ammonia is inevitably generated as a byproduct. However, in the context of exhaust purification technology, the amount of ammonia generated is usually low, and its value lies in its use as a reducing agent in downstream selective catalytic reduction (SCR) units, consumed on-site to further purify NOx. The entire system's design and optimization revolve around "maximizing NOx elimination" rather than "maximizing ammonia production." Therefore, how to overcome the limitations of existing technological approaches, discover and utilize a novel catalytic system, and achieve large-scale, efficient ammonia synthesis under mild conditions while ensuring readily available raw materials and controllable costs is a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a multifunctional catalyst for ammonia synthesis and its preparation method.

[0006] Firstly, a multifunctional catalyst for ammonia synthesis employs the following technical solution: A multifunctional catalyst for ammonia synthesis, the multifunctional catalyst having a three-dimensional composite structure, comprising: The carrier is cordierite ceramic; the interior of the cordierite ceramic has a mesoporous structure formed by acid washing of the cordierite ceramic. An active coating, wherein the active coating is γ-alumina supported on the carrier; and A bifunctional active component comprising platinum metal and barium oxide loaded on the active coating.

[0007] Furthermore, the cordierite ceramic is a honeycomb ceramic with a diameter of 10mm~20mm and a height of 40mm~60mm.

[0008] Furthermore, the mass ratio of platinum metal, barium oxide, and γ-aluminum oxide is 0.5~1.5:15~25:90~110.

[0009] Furthermore, the particle size of the γ-alumina is 125 μm to 180 μm.

[0010] Secondly, a method for preparing a multifunctional catalyst for ammonia synthesis adopts the following technical solution: A method for preparing a multifunctional catalyst for ammonia synthesis includes the following steps: Step (1): Immerse the cordierite ceramic carrier in a hydrochloric acid solution with a mass fraction of 30%~35% and stir at a speed of 200r / min~400r / min for 20min~40min to form a mesoporous structure on the carrier. Step (2): The carrier treated in step (1) is immersed in a coating solution containing γ-alumina, and then dried and calcined to form an active γ-alumina coating. In step (3), the platinum metal precursor and barium oxide precursor are sequentially loaded onto the support treated in step (2) using the initial wet impregnation method, and drying and calcination are performed after each loading to obtain the multifunctional catalyst.

[0011] Furthermore, before step (1), a pretreatment step is included: the cordierite ceramic carrier is heated to 350℃~450℃ at a heating rate of 8℃ / min~12℃ / min and calcined at a constant temperature for 4h~6h.

[0012] Further, in step (2), the coating solution is prepared by mixing γ-alumina with hydrochloric acid solution, wherein the mass fraction of the hydrochloric acid solution is 30%~35%, and the mass-volume ratio of the γ-alumina to the hydrochloric acid solution is 0.15 g / mL~0.25 g / mL.

[0013] Further, in step (2), the drying temperature is 70℃~90℃ and the drying time is 6h~10h; in step (2), the calcination temperature is 450℃~550℃, the heating rate is 8℃ / min~12℃ / min, and the constant temperature calcination is 4h~6h.

[0014] Furthermore, in step (3), the drying temperature is 70℃~90℃ and the drying time is 6h~10h; in step (3), the calcination temperature is 450℃~550℃ and the constant temperature calcination is 4h~6h.

[0015] Further, in step (3), the platinum metal precursor is an aqueous solution of chloroplatinic acid hydrate, and the barium oxide precursor is an aqueous solution of barium acetate.

[0016] The beneficial effects of this invention are: This invention provides a multifunctional catalyst for ammonia synthesis. By acid-washing a cordierite ceramic support, a rich mesoporous structure is precisely constructed within it. This mesoporous structure not only significantly increases the specific surface area of ​​the support, providing numerous anchoring sites for the subsequent loading of active components, ensuring high loading capacity and high dispersion, but also greatly improves the mass transfer efficiency during the reaction process, ensuring that reactant molecules can quickly reach the active centers and product molecules can desorb promptly. Furthermore, the introduction of a γ-alumina active coating further expands the effective surface area of ​​the catalyst and provides a highly dispersed and stable loading environment for the two bifunctional active components, platinum metal and barium oxide. In the catalytic reaction, barium oxide can efficiently capture and enrich nitrogen-containing reactants on the catalyst surface, while the highly dispersed platinum metal active centers, utilizing their unique electronic structure, can efficiently promote the breaking of key chemical bonds (such as NO bonds) and the formation of product chemical bonds (such as NH bonds) at a lower energy barrier. This multi-level synergistic effect formed by the support structure, coating and active components significantly enhances the overall active site density and accessibility of the catalyst, ultimately enabling it to achieve efficient ammonia synthesis under mild conditions of atmospheric pressure and below 400°C, demonstrating excellent catalytic performance and good industrial application potential. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the mechanism of a multifunctional catalyst for ammonia synthesis provided in Example 3 of the present invention participating in the thermocatalytic synthesis of ammonia.

[0018] Figure 2 This is a SEM image of a multifunctional catalyst for ammonia synthesis provided in Example 3 of the present invention.

[0019] Figure 3 This is a SEM image of a multifunctional catalyst for ammonia synthesis provided in Comparative Example 1 according to the present invention. Detailed Implementation

[0020] The following detailed description, in conjunction with embodiments, provides a further specific account of the multifunctional catalyst for ammonia synthesis and its preparation method according to the present invention. For the sake of simplicity, this document cannot exhaustively list all alternative technical features and embodiments included in the present invention. Therefore, those skilled in the art should understand that any technical feature and embodiment within this embodiment does not limit the scope of protection of the present invention, which includes all alternative technical features and embodiments adopted by those skilled in the art without inventive effort. Specifically, any embodiment obtained by replacing any technical feature in the present invention or by combining any two or more technical features provided by the present invention should be within the scope of protection of the present invention.

[0021] This embodiment provides a multifunctional catalyst for ammonia synthesis, which has a three-dimensional composite structure. Its core is a cordierite ceramic support, which undergoes an acid-washing process to transform its original dense internal structure into a mesoporous framework structure. This mesoporous structure provides an excellent physical basis for the adhesion of subsequent coatings. A layer of γ-alumina is uniformly loaded as an active coating on the acid-washed support surface. This active coating not only protects the support but also significantly expands the macroscopic surface area of ​​the catalyst. Platinum (Pt) metal and barium oxide (BaO) are highly dispersedly loaded on this γ-alumina active coating as bifunctional active components. Platinum metal exists in the form of nanoparticles, serving as the main redox active center; barium oxide acts as a NOx adsorption functional component, responsible for capturing and enriching nitrogen-containing reactants.

[0022] The catalyst structure provided in the above embodiments exhibits significant technical advantages through multi-level synergistic effects. First, the mesoporous structure formed within the cordierite support through acid washing greatly increases the specific surface area and pore volume, providing abundant anchoring sites for the active components and significantly improving mass transfer efficiency during the reaction process, ensuring that reactant molecules can rapidly and unimpededly reach the catalytic active sites. Second, the γ-alumina active coating, with its nanoscale porous structure, further amplifies the effective surface area of ​​the catalyst, providing an ideal platform for the efficient dispersion of platinum and barium components. The highly dispersed platinum metal nanoparticles, acting as redox centers, can effectively reduce the activation energy of the reaction based on their d-band electronic structure, promoting the breaking of NO bonds and the formation of NH bonds; simultaneously, the surface alkaline sites of barium oxide can specifically capture NOx molecules. This synergistic effect in structure and function enables the catalyst to achieve efficient ammonia synthesis under mild conditions (e.g., atmospheric pressure, ≤400℃), exhibiting excellent catalytic activity.

[0023] The multifunctional catalyst provided in this embodiment participates in the core reaction of thermocatalytic ammonia synthesis. Figure 1 The reaction equation is as follows: (R1) (R2) (R3) (R4) (R5) (R6) (R1-R4) represents the nitrogen oxide storage reaction process, and (R5-R6) represents the reduction synthesis of ammonia reaction process.

[0024] In a preferred embodiment of this example, the cordierite ceramic carrier employs a honeycomb ceramic structure with specific dimensions. Specifically, the diameter of the honeycomb ceramic carrier is controlled within the range of 10mm to 20mm, and its height is controlled within the range of 40mm to 60mm. This size specification facilitates laboratory-scale performance evaluation and lays the foundation for future modular scale-up and application in distributed ammonia synthesis units.

[0025] Limiting the carrier size within this range ensures that, in a typical reactor, the gas flow can pass through the catalyst bed at a suitable space velocity. This guarantees sufficient contact time between gas molecules and the active sites of the catalyst to complete the reaction, while avoiding problems such as excessive pressure drop or incomplete reaction caused by an excessively long or short bed. This size optimization helps to maintain low system energy consumption while achieving high conversion rates, balancing catalytic efficiency and engineering feasibility.

[0026] In a specific formulation embodiment, the mass ratio of each active component in the catalyst is optimized. Specifically, the mass ratio of platinum metal, barium oxide, and γ-alumina as its supporting substrate is controlled within the range of 0.5~1.5:15~25:90~110. For example, in a typical preparation process, approximately 1 part by mass of platinum metal and approximately 20 parts by mass of barium oxide are supported relative to 100 parts by mass of γ-alumina.

[0027] As an expensive precious metal, platinum's dosage within this range ensures sufficient catalytic active sites while controlling costs. The barium oxide content ensures enough sites to capture reactants without excessive amounts covering or clogging pores, thus affecting mass transfer and platinum activity. This optimized ratio achieves an optimal match between platinum's catalytic reduction capacity and barium's adsorption capacity, thereby maximizing overall catalyst performance while optimizing economic benefits.

[0028] In one embodiment of this example, the γ-alumina powder used to prepare the active coating has a particle size that is strictly screened and controlled within the range of 125 μm to 180 μm. The γ-alumina raw material with this particle size range is used when preparing the coating solution.

[0029] The particle size of γ-alumina is one of the key factors in forming a uniform and robust coating. Using a particle size in the range of 125 μm to 180 μm allows for the formation of a stable suspension with suitable rheological properties when mixed with hydrochloric acid solution to prepare the coating solution. This ensures that during the coating process, the coating can uniformly cover the acid-washed cordierite support surface and effectively penetrate into the mesoporous structure. Finally, after drying and calcination, a strong, uniform, and structurally stable active coating is formed, avoiding the risk of coating peeling under the thermal shock and gas flow erosion of the catalytic reaction, thus guaranteeing the long-term mechanical stability and service life of the catalyst.

[0030] This embodiment provides a method for preparing a multifunctional catalyst, including the following steps: Step (1), acid washing treatment: The cordierite ceramic carrier is completely immersed in an industrial-grade hydrochloric acid solution with a mass fraction of 30%-35%. At room temperature, the solution is stirred using a magnetic stirrer at a speed of 200r / min~400r / min for 20min~40min. This process forms mesopores inside the ceramic through the controlled corrosion effect of hydrochloric acid. After treatment, the carrier is removed and rinsed repeatedly with a large amount of deionized water until the pH of the washing effluent is neutral (pH≈7) to ensure no residual hydrochloric acid. Finally, the washed carrier is placed in a forced-air drying oven and dried at 80℃ for 8h.

[0031] Step (2), loading the active coating: Immerse the pickled and dried carrier in a pre-prepared coating solution containing γ-alumina and let it stand for about 30 minutes. After taking it out, first dry it at 80℃ for 8 hours to preliminarily fix the coating, and then transfer it into a muffle furnace, raise the temperature to 500℃ and calcine it at a constant temperature for 5 hours to make the γ-alumina firmly bond with the carrier.

[0032] Step (3), loading the bifunctional active component: The initial wet impregnation method is used. The support with the γ-alumina coating is immersed in a platinum metal precursor (such as an aqueous solution of chloroplatinic acid). After the solution is completely absorbed, it is removed and dried at 80°C for 8 hours and calcined at 500°C for 5 hours to complete the platinum loading. After cooling, the support is then immersed in a barium oxide precursor (such as a barium acetate solution). Similarly, after the solution is completely absorbed, it is dried at 80°C for 8 hours and calcined at 500°C for 5 hours. After this step, a multifunctional catalyst is finally obtained.

[0033] This preparation method successfully constructed a three-dimensional composite structure with synergistic effects by controlling the steps. The acid washing in step (1) is the key to forming a mesoporous structure and increasing the specific surface area, laying the foundation for subsequent loading. The coating process in step (2) ensures the uniformity and stability of the high surface area active coating. The stepwise initial wet impregnation and calcination in step (3) ensure that the two active components, platinum and barium, can be loaded on the surface of the active coating in a highly dispersed state, avoiding mutual coverage or agglomeration, and maximizing the exposure and utilization rate of active sites.

[0034] Before step (1) above, a pretreatment step for the carrier is also included. Specifically, the original cordierite ceramic carrier is placed in a muffle furnace and heated from room temperature to a target temperature range of 350℃ to 450℃ at a heating rate of 8℃ / min to 12℃ / min. After reaching the target temperature, it is calcined at that temperature for 4 to 6 hours. After calcination, the carrier is allowed to cool naturally to room temperature.

[0035] This pretreatment step effectively removes impurities such as organic matter, dust, and grease from the surface and pores of the cordierite ceramic carrier. High-temperature calcination yields a clean carrier surface, ensuring the uniformity and effectiveness of subsequent acid washing steps, as well as the adhesion and performance stability of the final catalyst coating.

[0036] In some embodiments, step (2) of the preparation method of the coating solution includes the following steps: taking 1g of γ-alumina powder with a particle size of 125μm~180μm, adding it to 5mL of hydrochloric acid solution with a mass fraction of 30%-35%, so that the solid-liquid mass-volume ratio is in the range of 0.15 g / mL~0.25 g / mL. Then, using a magnetic stirrer, stirring continuously at a speed of about 300r / min for 30min until a uniform, non-agglomerated suspension is formed, which is the coating solution.

[0037] In some embodiments, in step (2), after the carrier is coated with the coating liquid, it is first dried in a forced-air drying oven at a temperature of 70°C to 90°C for 6 to 10 hours. Subsequently, the dried carrier is transferred to a muffle furnace and heated to 450°C to 550°C at a heating rate of 8°C / min to 12°C / min, and calcined at this temperature for 4 to 6 hours.

[0038] In some embodiments, in step (3), after the platinum metal precursor solution and the barium oxide precursor solution are impregnated by the initial wet impregnation method respectively, the same heat treatment process is strictly followed after each impregnation operation: first, drying at a temperature of 70℃~90℃ for 6h~10h, and then transferring to a muffle furnace for constant calcination at a temperature range of 450℃~550℃ for 4h~6h.

[0039] The low-temperature drying step removes moisture from the impregnation solution. The high-temperature calcination step completely decomposes the precursor salts (such as chloroplatinic acid and barium acetate) and transforms them into platinum metal and barium oxide in nanoscale particle form. The controlled calcination temperature effectively inhibits the migration and agglomeration (i.e., sintering) of active metal / metal oxide particles at high temperatures, thus ensuring that the final catalyst has extremely high active site dispersion, which is a prerequisite for achieving high catalytic activity.

[0040] In some embodiments, in step (3), when loading platinum metal, an aqueous solution of chloroplatinic acid hydrate (H2PtCl6·6H2O) dissolved in deionized water is used. When loading barium oxide, an aqueous solution of barium acetate (Ba(CH3COO)2) dissolved in deionized water is used.

[0041] Both chloroplatinic acid hydrate and barium acetate exhibit excellent water solubility, making it easy to prepare impregnation solutions with uniform and stable concentrations. More importantly, they can cleanly and completely decompose into the target active species (metallic platinum and barium oxide) during calcination. Their decomposition products (such as HCl, CO2, and H2O) are all volatile substances and will not introduce harmful impurity ions such as sulfur, sodium, and potassium into the catalyst. These impurity ions may cover active sites or alter the catalyst's acidity or basicity, leading to catalyst poisoning or performance degradation. Therefore, using these two precursors ensures the preparation of high-purity, highly active catalysts.

[0042] Example Example 1 This embodiment 1 provides a multifunctional catalyst, comprising a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The support is cordierite honeycomb ceramic with a diameter of 10 mm and a height of 40 mm, and has a mesoporous structure formed by acid washing. The active coating is γ-alumina with a particle size of 125 μm. The bifunctional active component includes platinum metal and barium oxide, with a mass ratio of platinum metal, barium oxide, and γ-alumina of approximately 0.5:15:110.

[0043] This embodiment 1 also provides a method for preparing a multifunctional catalyst, comprising the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 10 mm and a height of 40 mm in a muffle furnace, heat it from room temperature to 350 °C at a heating rate of 8 °C / min, and calcine it at this temperature for 6 hours. After calcination, allow it to cool naturally to room temperature in the furnace for later use.

[0044] Step (2), acid washing treatment: The pretreated cordierite ceramic support was immersed in a 30% hydrochloric acid solution and continuously stirred at 200 r / min for 20 min on a magnetic stirrer. After treatment, the support was removed and rinsed repeatedly with a large amount of deionized water until the pH of the washing effluent was approximately 7. Subsequently, the support was placed in a 70℃ forced-air drying oven and dried for 10 h.

[0045] Step (3), preparation of coating solution: accurately weigh 1.5g of γ-alumina powder with a particle size of 125μm, add it to 10mL of hydrochloric acid solution with a mass fraction of 30%, and stir continuously at a speed of 300r / min for 30min until a uniform and stable suspension is formed, which is the coating solution.

[0046] Step (4), loading the active coating: The pickled and dried carrier is completely immersed in the above coating solution, and removed after standing for 30 minutes. The carrier with the coating is dried at 70°C for 10 hours, and then transferred to a muffle furnace, where the temperature is programmed to rise to 450°C at a rate of 8°C / min, and calcined at this temperature for 6 hours to form a strong γ-alumina active coating.

[0047] Step (5), loading the bifunctional active component: Using the initial wet impregnation method, the support carrying the active coating is first immersed in an aqueous solution of chloroplatinic acid hydrate (H2PtCl6·6H2O) prepared according to the target loading amount (mass ratio 0.5). After the solution is completely absorbed by the support, it is taken out and dried at 70℃ for 10h, and then calcined at 450℃ for 6h. After cooling, the initial wet impregnation method is used again, immersing the support in an aqueous solution of barium acetate (Ba(CH3COO)2) prepared according to the target loading amount (mass ratio 15). After the solution is completely absorbed, it is taken out and dried at 70℃ for 10h, and then calcined at 450℃ for 6h, finally obtaining the multifunctional catalyst of Example 1.

[0048] Example 2 This embodiment 2 provides a multifunctional catalyst, which includes a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The support is cordierite honeycomb ceramic with a diameter of 20 mm and a height of 60 mm, and has a mesoporous structure formed by acid washing. The active coating is γ-alumina with a particle size of 180 μm. The bifunctional active component includes platinum metal and barium oxide, with a mass ratio of platinum metal, barium oxide, and γ-alumina of approximately 1.5:25:90.

[0049] This embodiment 2 also provides a method for preparing a multifunctional catalyst, including the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 20 mm and a height of 60 mm in a muffle furnace, heat it from room temperature to 450 °C at a heating rate of 12 °C / min, and calcine it at this temperature for 4 hours. After calcination, allow it to cool naturally to room temperature in the furnace for later use.

[0050] Step (2), acid washing treatment: The pretreated cordierite ceramic support was immersed in a 35% hydrochloric acid solution and continuously stirred at 400 r / min for 40 min on a magnetic stirrer. After treatment, the support was removed and rinsed repeatedly with a large amount of deionized water until the pH of the washing effluent was approximately 7. Subsequently, the support was placed in a 90℃ forced-air drying oven for 6 h.

[0051] Step (3), preparation of coating solution: accurately weigh 2.5g of γ-alumina powder with a particle size of 180μm, add it to 10mL of hydrochloric acid solution with a mass fraction of 35%, and stir continuously at a speed of 300r / min for 30min until a uniform and stable suspension is formed, which is the coating solution.

[0052] Step (4), loading the active coating: The pickled and dried carrier is completely immersed in the above coating solution, and removed after standing for 30 minutes. The carrier with the coating is dried at 90°C for 6 hours, and then transferred to a muffle furnace, where the temperature is programmed to rise to 550°C at a rate of 12°C / min, and calcined at this temperature for 4 hours to form a strong γ-alumina active coating.

[0053] Step (5), loading the bifunctional active component: Using the initial wet impregnation method, the carrier carrying the active coating is first immersed in an aqueous solution of chloroplatinic acid hydrate prepared according to the target loading amount (mass ratio 1.5). After the solution is completely absorbed by the carrier, it is taken out and dried at 90°C for 6 hours, and then calcined at 550°C for 4 hours. After cooling, the initial wet impregnation method is used again, immersing the carrier in an aqueous solution of barium acetate prepared according to the target loading amount (mass ratio 25). After the solution is completely absorbed, it is taken out and dried at 90°C for 6 hours, and then calcined at 550°C for 4 hours, finally obtaining the multifunctional catalyst of Example 2.

[0054] Example 3 This embodiment 3 provides a multifunctional catalyst, comprising a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The support is cordierite honeycomb ceramic with a diameter of 15 mm and a height of 50 mm, and has a mesoporous structure formed by acid washing. The active coating is γ-alumina with a particle size of 150 μm. The bifunctional active component includes platinum metal and barium oxide, with a mass ratio of platinum metal, barium oxide, and γ-alumina of approximately 1.0:20:100.

[0055] This embodiment 3 also provides a method for preparing a multifunctional catalyst, including the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 15 mm and a height of 50 mm in a muffle furnace, heat it from room temperature to 400 °C at a heating rate of 10 °C / min, and calcine it at this temperature for 5 hours. After calcination, allow it to cool naturally to room temperature in the furnace for later use.

[0056] Step (2), acid washing treatment: The pretreated cordierite ceramic carrier was immersed in a 33.6% hydrochloric acid solution and continuously stirred at 300 r / min for 30 min on a magnetic stirrer. After treatment, the carrier was removed and rinsed repeatedly with a large amount of deionized water until the pH of the washing effluent was approximately 7. Subsequently, the carrier was placed in an 80℃ forced-air drying oven for 8 h.

[0057] Step (3), preparation of coating solution: accurately weigh 2.0g of γ-alumina powder with a particle size of 150μm, add it to 10mL of hydrochloric acid solution with a mass fraction of 33.6%, and stir continuously at a speed of 300r / min for 30min until a uniform and stable suspension is formed, which is the coating solution.

[0058] Step (4), loading the active coating: The pickled and dried carrier is completely immersed in the above coating solution, and removed after standing for 30 minutes. The carrier with the coating is dried at 80°C for 8 hours, and then transferred to a muffle furnace, where the temperature is programmed to rise to 500°C at a rate of 10°C / min, and calcined at this temperature for 5 hours to form a strong γ-alumina active coating.

[0059] Step (5), loading the bifunctional active component: Using the initial wet impregnation method, the support carrying the active coating was first immersed in an aqueous solution of chloroplatinic acid hydrate prepared according to the target loading amount (mass ratio 1.0). After the solution was completely absorbed by the support, it was taken out and dried at 80°C for 8 hours, and then calcined at 500°C for 5 hours. After cooling, the initial wet impregnation method was used again, immersing the support in an aqueous solution of barium acetate prepared according to the target loading amount (mass ratio 20). After the solution was completely absorbed, it was taken out and dried at 80°C for 8 hours, and then calcined at 500°C for 5 hours. Finally, the multifunctional catalyst of Example 3 was obtained, and its SEM morphology is shown in [image missing]. Figure 2 .

[0060] Example 4 Example 4 provides a multifunctional catalyst comprising a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The support is cordierite honeycomb ceramic with a diameter of 12 mm and a height of 55 mm, and its interior has a mesoporous structure formed by acid washing. The active coating is γ-alumina with a particle size of 130 μm. The bifunctional active component includes platinum metal and barium oxide, with a mass ratio of platinum metal, barium oxide, and γ-alumina of approximately 0.8:22:105.

[0061] This embodiment 4 also provides a method for preparing a multifunctional catalyst, including the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 12 mm and a height of 55 mm in a muffle furnace, heat it from room temperature to 380°C at a heating rate of 9°C / min, and calcine it at this temperature for 5.5 h. After calcination, allow it to cool naturally to room temperature in the furnace for later use.

[0062] Step (2), acid washing treatment: The pretreated cordierite ceramic carrier was immersed in a 31% hydrochloric acid solution and continuously stirred at 250 r / min for 35 min on a magnetic stirrer. After treatment, the carrier was removed and rinsed repeatedly with a large amount of deionized water until the pH of the washing effluent was approximately 7. Subsequently, the carrier was placed in an 85℃ forced-air drying oven for 7 h.

[0063] Step (3), preparation of coating solution: accurately weigh 1.8g of γ-alumina powder with a particle size of 130μm, add it to 10mL of hydrochloric acid solution with a mass fraction of 31%, and stir continuously at a speed of 300r / min for 30min until a uniform and stable suspension is formed, which is the coating solution.

[0064] Step (4), loading the active coating: The pickled and dried carrier is completely immersed in the above coating solution, and removed after standing for 30 minutes. The carrier with the coating is dried at 85°C for 7 hours, and then transferred to a muffle furnace, where the temperature is programmed to rise to 480°C at a rate of 9°C / min, and calcined at this temperature for 5.5 hours to form a strong γ-alumina active coating.

[0065] Step (5), loading the bifunctional active component: Using the initial wet impregnation method, the carrier carrying the active coating is first immersed in an aqueous solution of chloroplatinic acid hydrate prepared according to the target loading amount (mass ratio 0.8). After the solution is completely absorbed by the carrier, it is taken out and dried at 85°C for 7 hours, and then calcined at 480°C for 5.5 hours. After cooling, the initial wet impregnation method is used again, immersing the carrier in an aqueous solution of barium acetate prepared according to the target loading amount (mass ratio 22). After the solution is completely absorbed, it is taken out and dried at 85°C for 7 hours, and then calcined at 480°C for 5.5 hours, finally obtaining the multifunctional catalyst of Example 4.

[0066] Example 5 This embodiment 5 provides a multifunctional catalyst, comprising a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The support is cordierite honeycomb ceramic with a diameter of 18 mm and a height of 45 mm, and has a mesoporous structure formed by acid washing. The active coating is γ-alumina with a particle size of 170 μm. The bifunctional active component includes platinum metal and barium oxide, with a mass ratio of platinum metal, barium oxide, and γ-alumina of approximately 1.2:18:95.

[0067] This embodiment 5 also provides a method for preparing a multifunctional catalyst, comprising the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 18 mm and a height of 45 mm in a muffle furnace, heat it from room temperature to 420 °C at a heating rate of 11 °C / min, and calcine it at this temperature for 4.5 h. After calcination, allow it to cool naturally to room temperature in the furnace for later use.

[0068] Step (2), acid washing treatment: The pretreated cordierite ceramic support was immersed in a 34% hydrochloric acid solution and continuously stirred at 350 r / min for 25 min on a magnetic stirrer. After treatment, the support was removed and rinsed repeatedly with a large amount of deionized water until the pH of the washing effluent was approximately 7. Subsequently, the support was placed in a 75℃ forced-air drying oven and dried for 9 h.

[0069] Step (3), preparation of coating solution: accurately weigh 2.2g of γ-alumina powder with a particle size of 170μm, add it to 10mL of hydrochloric acid solution with a mass fraction of 34%, and stir continuously at a speed of 300r / min for 30min until a uniform and stable suspension is formed, which is the coating solution.

[0070] Step (4), loading the active coating: The pickled and dried carrier is completely immersed in the above coating solution, and removed after standing for 30 minutes. The carrier with the coating is dried at 75°C for 9 hours, and then transferred to a muffle furnace, where the temperature is programmed to rise to 520°C at a rate of 11°C / min, and calcined at this temperature for 4.5 hours to form a strong γ-alumina active coating.

[0071] Step (5), loading the bifunctional active component: Using the initial wet impregnation method, the carrier carrying the active coating is first immersed in an aqueous solution of chloroplatinic acid hydrate prepared according to the target loading amount (mass ratio 1.2). After the solution is completely absorbed by the carrier, it is taken out and dried at 75°C for 9 hours, and then calcined at 520°C for 4.5 hours. After cooling, the initial wet impregnation method is used again, immersing the carrier in an aqueous solution of barium acetate prepared according to the target loading amount (mass ratio 18). After the solution is completely absorbed, it is taken out and dried at 75°C for 9 hours, and then calcined at 520°C for 4.5 hours, finally obtaining the multifunctional catalyst of Example 5.

[0072] Example 6 Example 6 provides a multifunctional catalyst, comprising a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The characteristics of the catalyst in this example are basically the same as those in Example 3.

[0073] This embodiment 6 also provides a method for preparing a multifunctional catalyst, comprising the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 15 mm and a height of 50 mm in a muffle furnace, heat it from room temperature to 400 °C at a heating rate of 10 °C / min, and calcine it at this temperature for 5 h.

[0074] Step (2), acid washing: The pretreated cordierite ceramic carrier is immersed in a 33.6% hydrochloric acid solution and stirred at 300 r / min for 30 min. After washing until neutral, it is dried at 90℃ for 6 h.

[0075] Step (3), preparation of the application solution: prepared according to the same method as in Example 3.

[0076] Step (4), loading active coating: after the acid-washed carrier is immersed in the coating solution for 30 min, it is taken out and dried at 90℃ for 6 h, then heated to 550℃ at a rate of 10℃ / min, and calcined at this temperature for 5 h.

[0077] Step (5), loading the bifunctional active components: Platinum and barium were loaded in steps using the initial wet impregnation method. After each loading, the substrate was dried at 90°C for 6 hours and then calcined at 550°C for 5 hours to finally obtain the multifunctional catalyst of Example 6.

[0078] Example 7 Example 7 provides a multifunctional catalyst, comprising a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The characteristics of the catalyst in this example are basically the same as those in Example 3.

[0079] This embodiment 7 also provides a method for preparing a multifunctional catalyst, comprising the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 15 mm and a height of 50 mm in a muffle furnace, heat it from room temperature to 400 °C at a heating rate of 10 °C / min, and calcine it at this temperature for 5 h.

[0080] Step (2), acid washing: The pretreated cordierite ceramic carrier is immersed in a 33.6% hydrochloric acid solution and stirred at 300 r / min for 30 min. After washing until neutral, it is dried at 70℃ for 10 h.

[0081] Step (3), preparation of the application solution: prepared according to the same method as in Example 3.

[0082] Step (4), loading active coating: after the acid-washed carrier is immersed in the coating solution for 30 min, then taken out and dried at 70℃ for 10 h, then heated to 450℃ at a rate of 10℃ / min, and calcined at this temperature for 5 h.

[0083] Step (5), loading the bifunctional active components: Platinum and barium were loaded stepwise using the initial wet impregnation method. After each loading, the catalyst was dried at 70°C for 10 h, and then calcined at 450°C for 5 h to finally obtain the multifunctional catalyst of Example 7.

[0084] Example 8 This embodiment 8 provides a multifunctional catalyst, which includes a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The characteristics of the catalyst in this embodiment are basically the same as those in embodiment 3.

[0085] This embodiment 8 also provides a method for preparing a multifunctional catalyst, comprising the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 15 mm and a height of 50 mm in a muffle furnace, heat it from room temperature to 450 °C at a heating rate of 8 °C / min, and calcine it at this temperature for 4 h.

[0086] Step (2), acid washing treatment: The pretreated cordierite ceramic carrier is immersed in a 33.6% hydrochloric acid solution and stirred at 300 r / min for 30 min. After washing until neutral, it is dried at 80℃ for 8 h.

[0087] Step (3), preparation of the application solution: prepared according to the same method as in Example 3.

[0088] Step (4), loading active coating: after the acid-washed carrier is immersed in the coating solution for 30 minutes, then taken out and dried at 80°C for 8 hours. Then the temperature is increased to 500°C at a rate of 10°C / min and calcined at this temperature for 5 hours.

[0089] Step (5), loading bifunctional active components: Platinum and barium were loaded stepwise using the initial wet impregnation method. After each loading, the substrate was dried at 80°C for 8 hours and then calcined at 500°C for 5 hours to finally obtain the multifunctional catalyst of Example 8.

[0090] Comparative Example Comparative Example 1: Catalyst that has not undergone acid washing treatment Comparative Example 1 provides a catalyst comprising a support, an active coating supported on the support, and a bifunctional active component supported on the active coating. The support is cordierite honeycomb ceramic with a diameter of 15 mm and a height of 50 mm; its interior has not undergone acid washing and does not possess a mesoporous structure. The active coating is γ-alumina with a particle size of 150 μm. The bifunctional active component comprises platinum metal and barium oxide, with a mass ratio of platinum metal, barium oxide, and γ-alumina of approximately 1.0:20:100.

[0091] Comparative Example 1 also provides a method for preparing a catalyst, comprising the following steps: Step (1), Pretreatment: Place the cordierite honeycomb ceramic carrier with a diameter of 15 mm and a height of 50 mm in a muffle furnace, heat it from room temperature to 400 °C at a heating rate of 10 °C / min, and calcine it at this temperature for 5 hours. After calcination, allow it to cool naturally to room temperature in the furnace for later use.

[0092] Step (2), preparation of coating solution: accurately weigh 2.0g of γ-alumina powder with a particle size of 150μm, add it to 10mL of hydrochloric acid solution with a mass fraction of 33.6%, and stir continuously at a speed of 300r / min for 30min until a uniform and stable suspension is formed, which is the coating solution.

[0093] Step (3), loading the active coating: The pretreated but un-acid-washed carrier is completely immersed in the above coating solution, and removed after standing for 30 minutes. The carrier with the coating is dried at 80°C for 8 hours, and then transferred to a muffle furnace, where the temperature is programmed to rise to 500°C at a rate of 10°C / min, and calcined at this temperature for 5 hours.

[0094] Step (4), loading the bifunctional active component: Using the initial wet impregnation method, the support carrying the active coating was first immersed in an aqueous solution of chloroplatinic acid hydrate prepared according to the target loading amount. After the solution was completely absorbed by the support, it was removed, dried at 80℃ for 8 hours, and then calcined at 500℃ for 5 hours. After cooling, the initial wet impregnation method was used again, immersing the support in an aqueous solution of barium acetate prepared according to the target loading amount. After the solution was completely absorbed, it was removed, dried at 80℃ for 8 hours, and then calcined at 500℃ for 5 hours. Finally, the catalyst of Comparative Example 1 was obtained, and its SEM morphology is shown in [image missing]. Figure 3 .

[0095] Comparative Example 2: Catalyst treated with physical methods (ultrasonic cleaning) instead of acid washing Comparative Example 2 provides a catalyst supported on cordierite honeycomb ceramic with a diameter of 15 mm and a height of 50 mm. This ceramic has undergone ultrasonic water washing and does not possess a mesoporous structure. The remaining components and proportions are the same as in Example 3.

[0096] Comparative Example 2 also provides a method for preparing a catalyst, comprising the following steps: Step (1), Preprocessing: Same as step (1) in Example 3.

[0097] Step (2), physical cleaning treatment: Immerse the pretreated cordierite ceramic carrier in deionized water and perform ultrasonic cleaning for 30 minutes to remove surface dust. After treatment, place the carrier in an 80℃ forced-air drying oven to dry for 8 hours.

[0098] Steps (3) to (5) are exactly the same as steps (3) to (5) of Example 3, and the catalyst of Comparative Example 2 is finally obtained.

[0099] Comparative Example 3: Catalyst lacking barium oxide component Comparative Example 3 provides a catalyst with a structure similar to that of Example 3, but its bifunctional active component contains only platinum metal and does not contain barium oxide.

[0100] Comparative Example 3 also provides a method for preparing a catalyst, comprising the following steps: Steps (1) to (4) are exactly the same as steps (1) to (4) in Example 3.

[0101] Step (5), loading the single-functional active component: using the initial wet impregnation method, only the carrier carrying the active coating is immersed in the aqueous solution of chloroplatinic acid hydrate prepared according to the target loading amount. After the solution is completely absorbed, it is taken out, dried at 80°C for 8 hours, and then calcined at 500°C for 5 hours. The step of loading barium acetate is omitted, and the catalyst of Comparative Example 3 is finally obtained.

[0102] Comparative Example 4: Catalyst lacking platinum metal component Comparative Example 4 provides a catalyst with a structure similar to that of Example 3, but its bifunctional active component contains only barium oxide and does not contain platinum metal.

[0103] Comparative Example 4 also provides a method for preparing a catalyst, comprising the following steps: Steps (1) to (4) are exactly the same as steps (1) to (4) in Example 3.

[0104] Step (5), loading the single-functional active component: using the initial wet impregnation method, only the carrier carrying the active coating is immersed in the barium acetate aqueous solution prepared according to the target loading amount. After the solution is completely absorbed, it is taken out, dried at 80°C for 8 hours, and then calcined at 500°C for 5 hours. The step of loading chloroplatinic acid hydrate is omitted, and the catalyst of Comparative Example 4 is finally obtained.

[0105] Comparative Example 5: Catalyst lacking γ-alumina active coating Comparative Example 5 provides a catalyst in which bifunctional active components (platinum metal and barium oxide) are directly supported on an acid-washed cordierite support, without containing a γ-alumina active coating.

[0106] Comparative Example 5 also provides a method for preparing a catalyst, comprising the following steps: Step (1), Preprocessing: Same as step (1) in Example 3.

[0107] Step (2), pickling treatment: Same as step (2) in Example 3.

[0108] Step (3), loading the bifunctional active component: The acid-washed support was directly immersed in an aqueous solution of chloroplatinic acid hydrate using the initial wet impregnation method. After drying and calcination, it was then immersed in an aqueous solution of barium acetate for a second drying and calcination. The drying and calcination conditions were the same as in step (5) of Example 3, and the catalyst of Comparative Example 5 was finally obtained.

[0109] Comparative Example 6: Catalyst treated with alkali instead of acid washing Comparative Example 6 provides a catalyst supported on cordierite honeycomb ceramic with a diameter of 15 mm and a height of 50 mm. This catalyst has been treated with an alkaline solution, resulting in a different internal pore structure and surface chemical properties compared to that formed by acid washing. The remaining components and proportions are the same as in Example 3.

[0110] Comparative Example 6 also provides a method for preparing a catalyst, comprising the following steps: Step (1), Preprocessing: Same as step (1) in Example 3.

[0111] Step (2), Alkali treatment: The pretreated cordierite ceramic support is immersed in a sodium hydroxide (NaOH) solution with a molar concentration equivalent to that of hydrochloric acid, and continuously stirred at 300 r / min for 30 min. After treatment, the support is washed until neutral and then dried at 80℃ for 8 h.

[0112] Steps (3) to (5) are exactly the same as steps (3) to (5) of Example 3, and the catalyst of Comparative Example 6 is finally obtained.

[0113] Performance testing To verify the performance of the multifunctional catalyst described in this invention, the catalyst samples prepared in Examples 1-8 and Comparative Examples 1-6 were subjected to the following performance tests.

[0114] I. Test Indicators and Methods 1. Characterization of the physical structure of the catalyst Test steps: The specific surface area of ​​the catalyst was determined using a low-temperature nitrogen physical adsorption method. The specific testing procedure was as follows: Approximately 0.2 g of the prepared catalyst sample was precisely taken, placed in a sample tube, and pretreated on a physical adsorption instrument. The pretreatment step included degassing the sample under vacuum at 300°C for 4 hours to thoroughly remove adsorbed moisture and impurities from its surface and pores. After pretreatment, the sample tube was transferred to the analysis station, and nitrogen adsorption-desorption isotherms were measured at 77 K (liquid nitrogen temperature). After the test, based on the obtained isotherm data, the specific surface area of ​​the catalyst was calculated using the Brunauer-Emmett-Teller (BET) multipoint method within the relative pressure P / P0 range of 0.05 to 0.35.

[0115] 2. Coating stability test Test steps: The stability of the coating was evaluated using an ultrasonic detachment test. The specific test procedure was as follows: First, the prepared intact catalyst sample was accurately weighed on an analytical balance, and its initial mass was recorded as W1. Then, the sample was placed in a 500 mL beaker containing 250 mL of deionized water, ensuring complete immersion. This beaker was then placed in an ultrasonic cleaning tank with a power of 100 W and a frequency of 40 kHz for 30 minutes of ultrasonic treatment to simulate a strong mechanical vibration environment. After treatment, the sample was carefully removed, and its surface was gently rinsed with a small amount of deionized water to remove loose detached material. It was then placed in a 110°C forced-air drying oven for 4 hours until constant weight was achieved. After the sample cooled to room temperature in a desiccator, it was accurately weighed again, and its final mass was recorded as W2. Finally, the coating detachment rate was calculated using the formula: Coating ultrasonic detachment rate (%) = (W1 - W2) / (Total coating mass) × 100%.

[0116] 3. Catalytic activity test Test steps: The ammonia synthesis activity of the catalyst was evaluated in an atmospheric pressure fixed-bed reactor. The specific testing procedure was as follows: A complete catalyst sample (e.g., the 15mm × 50mm sample prepared in Example 3) was packed into the isothermal zone of a quartz tube reactor and fixed at both ends with quartz wool. Before the activity test, the catalyst was first activated in situ, i.e., the temperature was programmed to rise to 400°C at a rate of 10°C / min under a nitrogen atmosphere and held for 1 hour, followed by cooling to a reaction temperature of 350°C. After the temperature stabilized, the gas was switched to a simulated reaction gas, precisely controlled by a mass flow controller, with a composition of 1% NO, 3% H2, 5% H2O (introduced via a steam generator), and N2 as a balance gas. The total gas flow rate was adjusted according to the catalyst volume to ensure a constant GHSV of 30,000 h⁻¹. -1 The catalyst was stabilized under these conditions (350℃, atmospheric pressure) for 1 hour to ensure the reaction reached a steady state. During the reaction and after reaching steady state, an online Fourier transform infrared spectrometer was used to continuously analyze the gas composition at the reactor outlet, and the volume fraction of ammonia (NH3) in the outlet gas at steady state was recorded. Finally, based on the outlet ammonia concentration at steady state, the ammonia synthesis rate (mmol·g⁻¹) was calculated using the formula: -1 ·h -1 The ammonia synthesis rate of the catalyst is calculated as follows: (Total gas flow rate (L / h) × Outlet NH3 concentration (%)) / (22.4 (L / mol) × Total catalyst mass (g)) × 1000 (mmol / mol).

[0117] Performance data The above performance tests were performed on the samples of Examples 1-8 and Comparative Examples 1-6, and the data obtained are summarized in Table 1 below.

[0118] Table 1. Comparison of performance data between Examples 1-8 and Comparative Examples 1-6

[0119] As shown in Table 1, comparing the data of Example 3 with those of Comparative Examples 1, 2, and 6, it can be seen that the specific surface area of ​​Example 3 (125.1 m²) is significantly higher. 2 / g) is much higher than that of Comparative Example 1 (14.5 m 2 / g), Comparative Example 2 (19.8 m 2 / g) and Comparative Example 6 (32.6 m 2 The acid pickling process effectively constructs a mesoporous structure, a feat unmatched by other treatment methods. Furthermore, the coating peeling rate in Example 3 (1.5%) was significantly lower than that in Comparative Examples 1, 2, and 6, indicating that the mesoporous structure formed by acid pickling greatly enhances coating adhesion. Ultimately, this is reflected in the activity, with Example 3 showing a significantly higher ammonia synthesis rate (25.5 mmol·g). -1 ·h -1 The improvement was more than 12 times that of Comparative Example 1, more than 7 times that of Comparative Example 2, and nearly 5 times that of Comparative Example 6. This fully demonstrates that "acid washing to form a mesoporous structure" is the key to achieving high performance, and the huge improvement in structure and performance it brings is unpredictable by conventional physical or chemical treatment methods.

[0120] Compared with Comparative Example 5, Example 3 showed a specific surface area and ammonia synthesis rate approximately three times higher, and its coating stability was also significantly better. This demonstrates that the γ-alumina active coating, as a high specific surface area intermediate layer, is crucial for the efficient dispersion of active components and the overall stability of the catalyst.

[0121] Compared with Comparative Example 3, although the two have similar physical structures, the ammonia synthesis rate of the latter decreased sharply to 4.0 mmol·g. -1 ·h -1 This demonstrates that barium oxide, as a NOx adsorption component, plays an indispensable role in enriching reactants near the active site and improving reaction efficiency.

[0122] Compared with Comparative Example 3, the ammonia synthesis rate of the latter was almost zero (0.1 mmol·g⁻¹). -1 ·h -1 This proves that platinum metal is the core of the catalytic reaction, and the reaction cannot proceed without it.

[0123] Data from Examples 1-8 show that catalysts prepared within the defined process parameter ranges all exhibit high specific surface areas (>115 m²).2 Low coating peeling rate (<2.6%) and high ammonia synthesis activity (>22 mmol·g). -1 ·h -1 ).

[0124] For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, but obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this invention.

Claims

1. A multifunctional catalyst for ammonia synthesis, characterized in that, The multifunctional catalyst has a three-dimensional composite structure, comprising: The carrier is cordierite ceramic; the interior of the cordierite ceramic has a mesoporous structure formed by acid washing of the cordierite ceramic. An active coating, wherein the active coating is γ-alumina supported on the carrier; and A bifunctional active component comprising platinum metal and barium oxide loaded on the active coating.

2. The multifunctional catalyst according to claim 1, characterized in that, The cordierite ceramic is a honeycomb ceramic with a diameter of 10mm~20mm and a height of 40mm~60mm.

3. The multifunctional catalyst according to claim 1, characterized in that, The mass ratio of platinum metal, barium oxide, and γ-aluminum oxide is 0.5~1.5:15~25:90~110.

4. The multifunctional catalyst according to claim 1, characterized in that, The particle size of the γ-alumina is 125 μm to 180 μm.

5. A method for preparing a multifunctional catalyst for ammonia synthesis, characterized in that, Includes the following steps: Step (1): Immerse the cordierite ceramic carrier in a hydrochloric acid solution with a mass fraction of 30%~35% and stir at a speed of 200r / min~400r / min for 20min~40min to form a mesoporous structure on the carrier. Step (2): The carrier treated in step (1) is immersed in a coating solution containing γ-alumina, and then dried and calcined to form an active γ-alumina coating. In step (3), the platinum metal precursor and barium oxide precursor are sequentially loaded onto the support treated in step (2) using the initial wet impregnation method, and drying and calcination are performed after each loading to obtain the multifunctional catalyst.

6. The preparation method according to claim 5, characterized in that, Before step (1), a pretreatment step is also included: the cordierite ceramic carrier is heated to 350℃~450℃ at a heating rate of 8℃ / min~12℃ / min and calcined at a constant temperature for 4h~6h.

7. The preparation method according to claim 5, characterized in that, In step (2), the coating solution is prepared by mixing γ-alumina with hydrochloric acid solution, wherein the mass fraction of the hydrochloric acid solution is 30%~35%, and the mass-volume ratio of γ-alumina to the hydrochloric acid solution is 0.15 g / mL~0.25 g / mL.

8. The preparation method according to claim 5, characterized in that, In step (2), the drying temperature is 70℃~90℃ and the drying time is 6h~10h; in step (2), the calcination temperature is 450℃~550℃, the heating rate is 8℃ / min~12℃ / min, and the constant temperature calcination is 4h~6h.

9. The preparation method according to claim 5, characterized in that, In step (3), the drying temperature is 70℃~90℃ and the drying time is 6h~10h; in step (3), the calcination temperature is 450℃~550℃ and the constant temperature calcination is 4h~6h.

10. The preparation method according to claim 5, characterized in that, In step (3), the platinum metal precursor is an aqueous solution of chloroplatinic acid hydrate, and the barium oxide precursor is an aqueous solution of barium acetate.

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