Ruthenium-based ammonia synthesis catalysts based on high-entropy oxide supports and preparation and use thereof

Abstract

The application discloses a ruthenium-based ammonia synthesis catalyst, a preparation method thereof and application of the catalyst in catalytic synthesis of ammonia. The ruthenium-based ammonia synthesis catalyst comprises a high-entropy oxide carrier and a ruthenium active component supported on the carrier; the high-entropy oxide is a single solid solution phase formed by oxides of at least three of Mg, Ca, Sr and Ba and at least two of La, Ce, Pr, Nd and Sm. The preparation method comprises the following steps: mixing soluble salts corresponding to each metal constituting the high-entropy oxide with an organic foaming agent in water, evaporating and concentrating to form a gel, heat-treating the gel at 110-150 DEG C to make the gel foam, and obtaining a porous and fluffy solid precursor; grinding the solid precursor and performing joule heating treatment in a non-oxidizing atmosphere, instantaneously heating the solid precursor to 600-1200 DEG C within 10 seconds, keeping the temperature for 1-10 seconds, and then cooling to obtain the high-entropy oxide carrier; and supporting the ruthenium active component on the high-entropy oxide carrier to obtain the ruthenium-based ammonia synthesis catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a ruthenium-based ammonia synthesis catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is an important raw material for the production of fertilizers, dyes, and explosives. It is also an ideal hydrogen energy carrier, being a zero-carbon molecule with a high hydrogen storage content (17.6 wt%) and high bulk density (121 kg H2 / m³). 3 It can be stored and transported by liquefying H2 at 8 ℃ and 2.5 MPa.

[0003] The current industrial ammonia synthesis process, using the Haber-Bosch process, operates under high temperature and pressure conditions of 400-500℃ and 10-30 MPa, consuming 1%-2% of the global energy supply and emitting approximately 670 million tons of carbon dioxide annually. The ammonia synthesis industry is energy-intensive. The key to solving the high energy consumption of the traditional ammonia synthesis industry lies in improving catalytic reaction efficiency and reducing reaction temperature and pressure. This necessitates the development of low-temperature, low-pressure, and highly active ammonia synthesis catalysts.

[0004] Currently, iron catalysts are the main catalysts used in ammonia synthesis. For example, patent specification CN106799232A discloses a room-temperature solid-phase reaction-modified iron-based ammonia synthesis catalyst, its preparation method, and its application. The process involves uniformly mixing the iron-based ammonia synthesis catalyst, an iron precursor, and a solid reagent, followed by grinding, ball milling, or stirring. This allows the iron precursor and solid reagent to react on an iron-based ammonia synthesis catalyst support. After the reaction, the product is filtered, washed, dried, and then heat-treated under air, nitrogen, argon, or vacuum conditions to obtain the final iron-based ammonia synthesis catalyst modified with nano-iron. The nano-iron loading is 0.1-20 wt%.

[0005] Compared to iron catalysts, ruthenium catalysts exhibit higher ammonia synthesis activity under low-temperature and low-pressure conditions, significantly reducing energy consumption in the ammonia synthesis industry and earning them the reputation of second-generation ammonia synthesis catalysts. Magnesium oxide, aluminum oxide, lanthanum oxide, and cerium oxide, among other metal oxides, are commonly used as supports for ruthenium-based ammonia synthesis catalysts due to their strong surface basicity and high electron transport capabilities. Furthermore, under high-temperature and high-pressure conditions, metal oxides maintain a stable structure, preventing the formation of methane under ruthenium catalysis, as seen with carbon supports, which would otherwise lead to carbon support loss and ultimately catalyst deactivation. Currently, Cs-Ru / MgO catalysts are already in commercial use for ammonia synthesis.

[0006] However, while metal oxide materials do not suffer from methanation issues, they suffer from low specific surface area, which is detrimental to the dispersion of ruthenium. Furthermore, ruthenium catalysts supported on alkaline earth metal oxides suffer from severe hydrogen over-adsorption (hydrogen poisoning), limiting their application. In recent years, with the deepening research on rare earth oxides, their unique variable valence properties have led to extremely high activity in ammonia synthesis when Ru is supported on them. Patent document CN102258998B records a CeO2-supported Ru-based catalyst exhibiting extremely high activity. However, the weak basicity of rare earth metal oxides and their composites hinders ammonia desorption. Therefore, high-entropy oxides formed from alkaline earth metals and rare earth metals can combine the advantages of both, further improving the ammonia synthesis activity of ruthenium catalysts supported on metal oxides. Simultaneously, due to the significant difference in ionic radii between alkaline earth metals and rare earth metals, highly distorted high-entropy oxide supports can be obtained. To use high-entropy oxides as supports for ammonia synthesis catalysts, a simple method for preparing high-specific-surface-area high-entropy oxides must be developed. Patent document CN118026294A describes a method for preparing high specific surface area high-entropy oxides using a microemulsion method by introducing a surfactant, which adds a mixing process between the aqueous and oil phases, but the operation is relatively cumbersome. Patent document CN116037149B prepares high-entropy oxides with a relatively high specific surface area by introducing a template agent. Both of these methods involve the introduction and removal of new substances during the preparation process, which is relatively cumbersome, and the product morphology is prone to collapse during subsequent calcination. In the prior art, template agent methods (such as CN116037149A) and microemulsion methods (such as CN118026294A) have been developed to obtain high specific surface area high-entropy oxides. However, these methods generally suffer from problems such as complex process flow (involving the introduction and removal of templates / surfactants), high energy consumption, and long cycle time. More importantly, the transition metal-based high-entropy oxides prepared by these methods, in the highly reducing and high hydrogen partial pressure environment of ammonia synthesis, have electronic structures that are insufficient to provide effective electronic aids for the noble metal ruthenium, failing to fundamentally solve the hydrogen poisoning problem of ruthenium-based catalysts. Although Joule heating technology has been used in materials synthesis (e.g., CN119592990A), its research focus is on the precise control model of the cooling process. How to utilize the instantaneous ultra-high temperature rise characteristics of Joule heating, combined with alkaline earth-rare earth precursors of specific compositions, to simultaneously achieve porous structure locking, high-entropy solid solution formation, and high-activity defect construction in a one-step process, thereby creating a hydrogen poisoning-resistant support suitable for ammonia synthesis, remains a gap in research.

[0007] Therefore, it is imperative to develop a simple and easy method for preparing high specific surface area, high entropy oxides. A ruthenium-based ammonia synthesis catalyst support that can effectively disperse metallic ruthenium and possesses high stability is crucial for developing low-temperature, low-pressure, and highly active ammonia synthesis catalysts. Summary of the Invention

[0008] To address the aforementioned technical problems and shortcomings in this field, the present invention provides a ruthenium-based ammonia synthesis catalyst, its preparation method, and its applications.

[0009] In existing technologies, methods for increasing the specific surface area of ​​high-entropy oxides (such as template agent methods and microemulsion methods) are often complex, and the resulting transition metal-based materials are difficult to meet the specific requirements of the ammonia synthesis reaction for the electronic properties of the support. Furthermore, traditional high-temperature calcination processes easily lead to the collapse of porous structures and grain growth. This invention aims to overcome these limitations.

[0010] The specific technical solution is as follows:

[0011] In a first aspect, the present invention provides a ruthenium-based ammonia synthesis catalyst, comprising a high-entropy oxide support and a ruthenium (Ru) active component supported on the support;

[0012] The high-entropy oxide is a single solid solution phase formed by oxides of at least three of Mg, Ca, Sr, and Ba, and at least two of La, Ce, Pr, Nd, and Sm. This unique combination of elements is specifically designed for the electronic promoter effect in ammonia synthesis catalysis, aiming to optimize the electronic state of the Ru active center and alleviate hydrogen poisoning.

[0013] In the X-ray diffraction (XRD) pattern of the high-entropy oxides, the characteristic peaks of each metal oxide merge to form one or more broadened main diffraction peaks, and there are no sharp, independent diffraction peaks of any single metal oxide.

[0014] Furthermore, the high-entropy oxide has a highly porous structure formed and locked by instantaneous ultrafast heat treatment.

[0015] Furthermore, the specific surface area of ​​the high-entropy oxide is not less than 18 m². 2 / g, preferably 18-50 m 2 / g.

[0016] Furthermore, the high-entropy oxide contains metal elements in equal molar ratios.

[0017] In some preferred embodiments, the loading of the ruthenium active component is 1wt%-15wt% based on the total mass of the ruthenium-based ammonia synthesis catalyst, for example, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, etc., preferably 4wt%-10wt%.

[0018] In some preferred embodiments, the method for preparing the high-entropy oxide support includes the following steps:

[0019] S1, the soluble salts corresponding to each metal that make up the high entropy oxide are mixed with an organic foaming agent in water and then evaporated and concentrated to form a gel. The gel is then heat-treated at 110-150℃ (e.g., 130℃) to foam the gel and obtain a porous and fluffy solid precursor.

[0020] S2, the solid precursor is ground and then subjected to Joule heating treatment. The Joule heating treatment is carried out in a non-oxidizing atmosphere. The solid precursor is instantaneously heated to 600-1200℃ (e.g., 800℃, 1000℃, etc.) within 10 seconds (e.g., within 1 second) and held at that temperature for 1-10 seconds (e.g., 5 seconds), and then cooled to obtain a high-entropy oxide support.

[0021] In some preferred embodiments, in step S1, the soluble salt includes a nitrate.

[0022] In step S1, the organic foaming agent is an organic acid that has a chelating effect on the metal ions constituting the high-entropy oxide and can decompose to produce gas when heated, including one or more of citric acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), and oxalic acid.

[0023] In some preferred embodiments, in step S1, the molar ratio of the organic foaming agent to the total molar ratio of the metal ions constituting the high-entropy oxide is (1.2-3.0):1, for example, 2:1, etc.

[0024] In some preferred embodiments, in step S2, the average heating rate of the Joule heating treatment is not less than 500°C / s, preferably not less than 1000°C / s.

[0025] In step S2, the non-oxidizing atmosphere can be an inert atmosphere, a vacuum atmosphere, etc. The inert atmosphere refers to a gaseous atmosphere that does not participate in the reaction, such as a nitrogen atmosphere.

[0026] In a second aspect, the present invention provides a method for preparing the ruthenium-based ammonia synthesis catalyst described in the first aspect, comprising the steps of:

[0027] S1, the soluble salts corresponding to each metal that make up the high entropy oxide are mixed with an organic foaming agent in water and then evaporated and concentrated to form a gel. The gel is then heat-treated at 110-150℃ (e.g., 130℃) to foam the gel and obtain a porous and fluffy solid precursor.

[0028] S2, the solid precursor is ground and then subjected to Joule heating treatment. The Joule heating treatment is carried out in a non-oxidizing atmosphere. The solid precursor is instantaneously heated to 600-1200℃ (e.g. 800℃, 1000℃, etc.) within 10 seconds (e.g. 1 second) and held at that temperature for 1-10 seconds (e.g. 5 seconds). Then it is cooled to obtain a high-entropy oxide support.

[0029] S3, ruthenium active components are loaded onto the high-entropy oxide support to obtain the ruthenium-based ammonia synthesis catalyst.

[0030] In some preferred embodiments, in step S1, the soluble salt includes a nitrate.

[0031] In step S1, the organic foaming agent is an organic acid that has a chelating effect on the metal ions constituting the high-entropy oxide and can decompose to produce gas when heated, including one or more of citric acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), and oxalic acid.

[0032] In some preferred embodiments, in step S1, the molar ratio of the organic foaming agent to the total molar ratio of the metal ions constituting the high-entropy oxide is (1.2-3.0):1.

[0033] In some preferred embodiments, in step S2, the average heating rate of the Joule heating treatment is not less than 500°C / s, preferably not less than 1000°C / s.

[0034] In step S2, the non-oxidizing atmosphere can be an inert atmosphere, a vacuum atmosphere, etc. The inert atmosphere refers to a gaseous atmosphere that does not participate in the reaction, such as a nitrogen atmosphere.

[0035] In step S3, existing conventional loading methods can be used to load the ruthenium active component, such as the excess impregnation method. The ruthenium source used for loading the ruthenium active component can be dodecyltriruthenium, ruthenium chloride, ruthenium nitrite, etc., which are loaded onto a high-entropy oxide support with high specific surface area and high defect concentration, and then post-treated by drying to obtain the final ruthenium-based ammonia synthesis catalyst.

[0036] In the preparation method of the high-entropy oxide support and ruthenium-based ammonia synthesis catalyst of this invention, a synergistic process of foaming agent-assisted construction of a porous precursor framework and Joule heating-induced instantaneous ultrafast crystallization is employed. Step S1, gel foaming, forms a porous metal-organic framework precursor with a loose network structure. This process utilizes the gas generated during the decomposition of the foaming agent to create pores in situ. Step S2, ultrafast thermal shock, achieves two key effects: first, it causes the foaming agent to decompose instantaneously, removing it before the pore structure collapses; second, it enables rapid interdiffusion and crystallization of various metal oxides at the atomic scale, forming a single solid solution phase with abundant defects, thereby freezing and preserving the high specific surface area and porous structure.

[0037] Traditional methods (such as muffle furnace calcination) involve slow heating, leading to gradual pore coalescence, framework collapse, and significant grain growth in the precursor under prolonged thermal action, resulting in a decrease in specific surface area. This invention employs Joule heating for ultra-rapid heating, its core innovation lying in its absolute advantage in time scale: the decomposition of the foaming agent and the crystallization of the carrier are completed within seconds or even sub-seconds, far faster than the kinetic process of pore structure destruction, thus maximizing the preservation of the porous framework of the precursor and achieving a high specific surface area. Simultaneously, the instantaneous high temperature promotes uniform elemental mixing, forming a single solid solution with high configurational entropy and lattice distortion, generating numerous surface defect sites that can be used to stabilize and activate Ru atoms.

[0038] In the ammonia synthesis reaction, the support not only needs high physical dispersibility (high specific surface area) but also chemical electron donor functionality to optimize the reaction pathway. Alkaline earth metal oxides (such as MgO and CaO) are strongly alkaline; rare earth metal oxides (such as CeO2 and La2O3) are excellent electron donors with variable oxidation states and excellent oxygen storage and release capabilities. This invention is the first to combine these two to construct a high-entropy oxide support: ① Utilizing the combination of alkaline earth and rare earth elements with large differences in ionic radii, lattice distortion is amplified, forming a higher concentration of active defects; ② The introduction of rare earth elements can regulate the redox properties of the support, while alkaline earth elements provide a stable alkaline environment. The synergistic effect of these two elements can effectively control the electron cloud density of the supported Ru atoms, weakening their excessive adsorption of reactive hydrogen in the reaction intermediate, thereby significantly alleviating the fatal hydrogen poisoning phenomenon in ammonia synthesis. This is something that transition metal-based high-entropy oxide supports cannot achieve.

[0039] Thirdly, the present invention provides the application of the ruthenium-based ammonia synthesis catalyst described in the first aspect for the catalytic synthesis of ammonia. This ruthenium-based ammonia synthesis catalyst is particularly suitable for energy-saving ammonia synthesis processes at low temperatures and low pressures.

[0040] Fourthly, the present invention provides a method for catalytic synthesis of ammonia, comprising: using the ruthenium-based ammonia synthesis catalyst described in the first aspect, catalyzing the reaction of nitrogen and hydrogen to synthesize ammonia under conditions of 300-500°C (e.g., 400°C) and 1-10 MPa (e.g., 5 MPa).

[0041] The ruthenium-based ammonia synthesis catalyst of this invention is used at 400°C, 5 MPa, and a space velocity of 10,000 h⁻¹. -1 Under the test conditions of H2:N2 volume ratio of 3:1, the ammonia synthesis reaction rate is not less than 20 mmol·g. cat -1 ·h -1 Furthermore, after a 100-hour stability test, the activity decay was no more than 10%.

[0042] Compared with the prior art, the beneficial effects of this invention are as follows:

[0043] 1. Innovation in carrier materials: A new type of alkaline earth-rare earth-based high-entropy oxide carrier was successfully created. This material possesses both high specific surface area (≥18 m²) and high specific surface area. 2 With its high defect concentration and unique strong electron-donating ability, it is a dedicated design to address the challenges of easy sintering and hydrogen poisoning of ammonia synthesis catalyst supports.

[0044] 2. Innovative Preparation Process: An integrated process for foaming agent pore creation and Joule heating for instantaneous shaping was developed. This process is simple, rapid, and energy-efficient. By using ultra-fast heating as a physical means, it cleverly avoids the damage of high temperatures to the porous structure and solves the contradiction between high-entropy oxides' specific surface area and thermal stability.

[0045] 3. Excellent catalytic performance: The obtained ruthenium-based ammonia synthesis catalyst exhibits high activity, high selectivity, and excellent stability in the ammonia synthesis reaction. The high specific surface area ensures high Ru dispersion; the high defect concentration of the support provides abundant anchoring sites for Ru; and the electronic synergistic effect of alkaline earth and rare earth elements effectively enhances intrinsic activity and inhibits deactivation. This invention provides a novel material system and a feasible preparation scheme for developing next-generation low-temperature, low-pressure, high-efficiency ammonia synthesis catalysts. Attached Figure Description

[0046] Figure 1 The images show the XRD patterns of the carriers in Example 1 and Comparative Examples 1-3.

[0047] Figure 2 The ammonia synthesis catalysts of Example 1 and Comparative Examples 1-3 were subjected to a temperature of 400°C for 10,000 h. -1 space velocity, H2:N2 molar ratio 3:1, reaction rate (r) m Result image.

[0048] Figure 3 This is a transmission electron microscopy elemental mapping of the carrier in Example 1.

[0049] Figure 4 The diagram shows the hydrogen temperature programmed desorption (H2-TPD) of the ammonia synthesis catalyst in Example 1 and Comparative Example 1. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0051] Example 1:

[0052] In this embodiment, a catalyst was prepared using a high-entropy oxide composed of five elements: Mg, Ca, La, Ce, and Ba as a support and loaded with 4 wt.% Ru.

[0053] 1. Preparation of high-entropy oxide supports:

[0054] Equivalent amounts of 0.02 mol each of magnesium nitrate, calcium nitrate, lanthanum nitrate, cerium nitrate, and barium nitrate were dissolved in 100 mL of deionized water and stirred at 500 rpm for 0.5 h. Citric acid was added at a molar ratio of 1:2 (total molar of metal ions to citric acid monohydrate), and stirring was continued for another 0.5 h until completely dissolved. The mixture was heated in an 80°C water bath to evaporate the solution until a viscous gel was formed. The gel was transferred to an oven and heat-treated at 130°C for 12 hours to allow it to fully foam, yielding a fluffy, porous solid precursor.

[0055] The aforementioned precursor was ground into a fine powder. 0.5 g of the powder was weighed, evenly spread on carbon cloth, and wrapped. The wrapped sample was placed in the reaction chamber of a Joule heating apparatus, and a vacuum was applied to below 10 Pa. A pulsed current was then applied to instantaneously heat the sample to 800 °C (estimated average heating rate >1000 °C / s), and this temperature was maintained for 5 seconds before the power was cut off, allowing it to cool naturally to room temperature under vacuum, yielding a high-entropy oxide support powder. This process achieved instantaneous decomposition of the foaming agent and ultra-rapid crystallization of the oxide.

[0056] 2. Ru active component loading:

[0057] 0.34 g of triruthenium dodecylcarbonyl was weighed and dissolved in 80 mL of tetrahydrofuran (THF). 4 g of the support powder obtained after Joule heating was added. The mixture was stirred at 400 rpm for 12 hours, followed by rotary evaporation at 60 °C to remove the THF solvent. The resulting solid was dried overnight in a vacuum oven at 60 °C to obtain the final catalyst, denoted as C1. Its Ru loading was determined to be 4.0 wt.% by ICP-OES.

[0058] Example 2:

[0059] The only difference from Example 1 is that the Joule heating treatment was instantaneously heated to 600°C, and all other aspects were the same, resulting in catalyst C2.

[0060] Example 3:

[0061] The only difference from Example 1 is that the Joule heating treatment was instantaneously heated to 1000°C, and all other aspects were the same, resulting in catalyst C3.

[0062] Example 4:

[0063] The only difference from Example 1 is that the Joule heating treatment was instantaneously heated to 1200°C, and all other aspects were the same, resulting in catalyst C4.

[0064] Example 5:

[0065] The only difference from Example 1 is that barium nitrate is replaced with an equimolar amount of strontium nitrate; all other aspects are the same, resulting in catalyst C5.

[0066] Example 6:

[0067] The only difference from Example 1 is the change in the amount of dodecyltriruthenium carbonyl, so that the Ru loading in the final catalyst C6 is 2.0 wt.%, while the rest are the same.

[0068] Example 7:

[0069] The only difference from Example 1 is the change in the amount of dodecyltriruthenium carbonyl, so that the Ru loading in the final catalyst C7 is 6.0 wt.%, and the rest are the same.

[0070] Example 8:

[0071] The only difference from Example 1 is the change in the amount of dodecyltriruthenium carbonyl, so that the Ru loading in the final catalyst C8 is 8.0 wt.%, while the rest are the same.

[0072] Comparative Example 1:

[0073] 1. Preparation of high-entropy oxide supports:

[0074] A solid precursor was prepared according to Example 1.

[0075] The ground precursor powder was placed in an alumina crucible and then placed in a muffle furnace. Under air atmosphere, the temperature was increased from room temperature to 800°C at a rate of 5°C / min, and held at 800°C for 4 hours, followed by furnace cooling. This support is designated D1-Support.

[0076] 2. Ru active component loading:

[0077] Referring to Example 1, the only difference is that the support is replaced with D1-Support, and all other aspects are the same, resulting in catalyst D1 with a Ru loading of 4.0 wt.%.

[0078] Comparative Example 2:

[0079] 1. Preparation of high-entropy oxide supports:

[0080] Equivalent amounts of 0.02 mol each of ferric nitrate, cobalt nitrate, nickel nitrate, chromium nitrate, and manganese nitrate were dissolved in 100 mL of deionized water and stirred at 500 rpm for 0.5 h. Citric acid was added at a molar ratio of total metal ions to citric acid monohydrate of 1:2, and stirring was continued for another 0.5 h until completely dissolved. The mixture was heated in an 80°C water bath to evaporate until a viscous gel was formed. The gel was transferred to an oven and heat-treated at 130°C for 12 hours to allow it to fully foam, yielding a fluffy, porous solid precursor.

[0081] The aforementioned precursor was ground into a fine powder. 0.5 g of the powder was weighed, evenly spread on carbon cloth, and wrapped. The wrapped sample was placed in the reaction chamber of a Joule heating apparatus, and a vacuum was applied to below 10 Pa. A pulsed current was then applied to instantaneously heat the sample to 800 °C (estimated average heating rate >1000 °C / s), and this temperature was maintained for 5 seconds before the power was cut off, allowing it to cool naturally to room temperature under vacuum, yielding the high-entropy oxide support powder D2-Support. This process achieved instantaneous decomposition of the foaming agent and ultra-fast crystallization of the oxide.

[0082] 2. Ru active component loading:

[0083] Referring to Example 1, the only difference is that the support is replaced with D2-Support, and all other aspects are the same, resulting in catalyst D2 with a Ru loading of 4.0 wt.%.

[0084] Comparative Example 3:

[0085] Following the template agent coprecipitation method described in CN116037149A, a support with the same composition (Mg, Ca, La, Ce, Ba) as in Example 1 was prepared. Five nitrates were dissolved in water in equal molar amounts, and hexadecyltrimethylammonium bromide was added as a template agent. The mixture was coprecipitated with ammonia, filtered, washed, and dried, then calcined in a muffle furnace at 800°C for 4 hours. The resulting support was loaded with 4 wt.% Ru, as described in Example 1, and the resulting catalyst was designated D3.

[0086] The supports of Example 1 and Comparative Examples 1-3 were characterized by XRD, such as... Figure 1 As shown, the catalyst in Example 1 exhibited only a set of broad, fused diffraction peaks, which could not be identified as standard diffraction peaks of any single component (such as MgO, CeO2, etc.). This indicates the successful formation of a solid solution phase with a single fluorite structure, confirming the successful preparation of the high-entropy oxide. In Comparative Example 1, in addition to the solid solution main phase, obvious BaCO3 impurity phase peaks were observed, with some Ba species precipitated and dispersed on the surface. The support in Comparative Example 2 showed characteristic peaks of a spinel structure. XRD analysis of the support in Comparative Example 3 showed it to be a multiphase mixture.

[0087] The specific surface area of ​​the supports obtained in Examples 1-8 and Comparative Examples 1-3 was determined by nitrogen physical adsorption, and the results are shown in Table 1.

[0088] Table 1

[0089]

[0090] To test the catalytic activity of the catalyst prepared in this invention, approximately 0.2 g of catalyst (40-60 mesh) was packed into the isothermal section of a fixed-bed reactor. In situ reduction was performed at 450°C for 2 hours in an H2 atmosphere. After reduction, a mixture of H2:N2 molar ratio of 3:1 was introduced, and the catalyst was subjected to reduction at 400°C, 5.0 MPa, and a space velocity of 10000 h⁻¹. -1 Activity was evaluated under standard conditions. Results are shown in [link to results]. Figure 2 Table 2 shows the ammonia synthesis catalysts of Examples 1-8 and Comparative Examples 1-3 at 400°C for 10,000 h. -1 space velocity, H2:N2 molar ratio 3:1, reaction rate (r) m )result.

[0091] Table 2

[0092]

[0093] To determine the stability of the present invention in the ammonia synthesis reaction and its resistance to hydrogen poisoning, approximately 0.2 g of the ammonia synthesis catalyst (40-60 mesh) prepared in Example 1 and Comparative Examples 1-3 were loaded into the isothermal section of a fixed-bed reactor. In situ reduction was performed at 450°C for 2 hours in an H2 atmosphere. After reduction, a H2:N2 molar ratio of 3:1 mixture was used, and the reaction was carried out at 400°C, 5.0 MPa, and a space velocity of 10000 h⁻¹. -1 The activity was evaluated under standard conditions, including a reaction time of 100 h at 400 °C and a space velocity of 10000 h⁻¹. -1 The catalyst activity was evaluated at a pressure of 5 MPa, and the deactivation rate was calculated by comparing it with the initial activity. The results are shown in Table 3.

[0094] Table 3

[0095]

[0096] Comparing Examples 1-4, the effect of Joule heating temperature on catalytic activity in the preparation conditions of high-entropy oxides was adjusted by changing the final Joule heating temperature to 600℃, 1000℃, and 1200℃, respectively. The resulting catalyst supports had specific surface areas of 32.1 m². 2 / g (600℃), 24.5 m 2 / g (1000℃), 18.8 m 2 / g (1200℃), corresponding to initial reaction rates of the catalyst under standard conditions of 28.5, 33.8, and 30.1 mmol·g, respectively. -1 ·h -1 This indicates that 800-1000℃ is the range with optimal performance.

[0097] Comparing Examples 1 and 5, the effect of the elemental composition of the high-entropy oxide on the catalytic activity was investigated. Ba was replaced with Sr in the preparation conditions, while other preparation conditions remained unchanged. The resulting catalyst support had a specific surface area of ​​25.7 m². 2 / g, corresponding to an initial reaction rate of 31.6 mmol·g for the catalyst under standard conditions. -1 ·h -1 .

[0098] Comparing Examples 1 and 6-8, the Ru loading was varied. Following the method of Example 1, catalysts with Ru loadings of 2 wt.%, 6 wt.%, and 8 wt.% were prepared by adjusting the amount of dodecacarbonyltriruthenium. Their initial reaction rates under standard conditions were 18.9, 38.5, and 36.2 mmol·g, respectively. -1 ·h -1 This indicates that 4-8 wt.% is the optimal load range.

[0099] The carrier of Example 1 was characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). TEM showed that the carrier of Example 1 was composed of fine particles of 20-50 nm aggregated together, with well-developed pores inside the particles. Figure 3 The EDS surface scan results clearly show that the five elements Mg, Ca, La, Ce and Ba are uniformly distributed in the selected micro-regions without elemental agglomeration, which directly confirms the formation of high-entropy solid solutions.

[0100] Comparing Example 1 and Comparative Example 1, with identical compositions, the surface area of ​​the carrier prepared by the conventional muffle furnace calcination process is only 3.9 m². 2 / g, while the specific surface area of ​​the carrier obtained by the Joule heating instantaneous crystallization process (C1) of the present invention is 28.3 m². 2 Compared to traditional muffle furnace calcination (D1), the specific surface area of ​​the support increased by more than 7 times, the catalytic activity increased by nearly 4 times, and the stability was significantly improved. This directly demonstrates the crucial role of ultrafast heat treatment in preserving the porous structure of the support and achieving high activity and high stability.

[0101] Comparing Example 1 and Comparative Example 2, under the same preparation process, the specific "alkaline earth-rare earth" combination (C1) of this invention, compared with the common transition metal combination (D2), exhibits nearly twice the catalytic activity and superior stability, even without the highest specific surface area. This demonstrates that the combination of alkaline earth and rare earth metals possesses a unique and essential electronic auxiliary function for the ammonia synthesis reaction, unmatched by other elemental systems.

[0102] Combination Figure 1 Compared with Comparative Example 1 and Comparative Example 3, it is difficult to obtain the single high-entropy solid solution phase (D3 phase impurity) required by the present invention using the conventional template agent method. Even with similar specific surface areas, its activity and stability are far inferior to C1. This indicates that the specific component system of the present invention needs to be combined with the specific process of Joule heating instantaneous crystallization in order to synergistically produce the optimal high-entropy structure and high catalytic performance.

[0103] Compared with Comparative Examples 1-3, except for Example 1, the deactivation percentage of Comparative Examples 1-3 was above 10% after 100 h of evaluation, while that of Example 1 was only 4.8%. This shows that the catalyst has strong resistance to hydrogen poisoning in the ammonia synthesis reaction and can remain stable for a long time under the conditions of ammonia synthesis reaction.

[0104] The catalysts of Example 1 and Comparative Example 1 were characterized by H2-TPD, such as... Figure 4 As shown, comparing the H2-TPD spectra of catalysts C1 and D1 reveals that the hydrogen desorption peak area of ​​C1 is significantly larger than that of D1 in the low-temperature region (<200℃), while the desorption peak area representing strongly adsorbed hydrogen in the high-temperature region (>400℃) is significantly smaller than that of D1. This indicates that the catalyst (C1) of this invention has stronger hydrogen adsorption but weaker adsorption intensity, and hydrogen species are more likely to desorb and participate in the reaction, thus mechanistically confirming its ability to alleviate hydrogen poisoning.

[0105] In summary, this invention first constructs a porous metal-organic precursor using a foaming agent, then employs Joule heating technology to instantaneously heat the precursor to 600-1200℃ within seconds using ultra-high-speed heating (≥500 ℃ / s), achieving rapid crystallization of the support and the construction of a porous structure. This method is simple and efficient, solving the problems of low specific surface area and easy sintering at high temperatures associated with traditional high-entropy oxides. The resulting catalyst possesses both a high specific surface area and a strong electronic aid effect due to the specific element combination, exhibiting high activity, high stability, and excellent resistance to hydrogen poisoning in ammonia synthesis, making it suitable for low-temperature, low-pressure, energy-saving ammonia synthesis processes.

[0106] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A ruthenium-based ammonia synthesis catalyst, characterized in that, Includes a high-entropy oxide support and a ruthenium active component supported on the support; The high-entropy oxide is a single solid solution phase formed by oxides of at least three of Mg, Ca, Sr, and Ba and at least two of La, Ce, Pr, Nd, and Sm; the metal elements in the high-entropy oxide are in equimolar ratios.

2. The ruthenium-based ammonia synthesis catalyst according to claim 1, characterized in that, The specific surface area of ​​the high-entropy oxide is not less than 18 m². 2 / g.

3. The ruthenium-based ammonia synthesis catalyst according to claim 1, characterized in that, Based on the total mass of the ruthenium-based ammonia synthesis catalyst, the loading of the ruthenium active component is 1wt%-15wt%.

4. The method for preparing the ruthenium-based ammonia synthesis catalyst according to any one of claims 1-3, characterized in that, Including the following steps: S1, the soluble salts corresponding to each metal that make up the high entropy oxide are mixed with an organic foaming agent in water and then evaporated and concentrated to form a gel. The gel is then heat-treated at 110-150℃ to foam, resulting in a porous and fluffy solid precursor. S2, the solid precursor is ground and then subjected to Joule heating treatment. The Joule heating treatment is carried out in a non-oxidizing atmosphere. The solid precursor is instantaneously heated to 600-1200°C within 10 seconds and held at that temperature for 1-10 seconds, and then cooled to obtain a high-entropy oxide carrier. S3, ruthenium active components are loaded onto the high-entropy oxide support to obtain the ruthenium-based ammonia synthesis catalyst.

5. The preparation method according to claim 4, characterized in that, In step S1: The soluble salts include nitrates; The organic foaming agent is an organic acid that has a chelating effect on the metal ions that make up the high-entropy oxide and can decompose to produce gas when heated, including one or more of citric acid, tartaric acid, ethylenediaminetetraacetic acid, and oxalic acid. The ratio of the molar amount of the organic foaming agent to the total molar amount of the metal ions constituting the high-entropy oxide is (1.2-3.0):

1.

6. The preparation method according to claim 4, characterized in that, In step S2, the average heating rate of the Joule heating treatment is not less than 500℃ / s.

7. The application of the ruthenium-based ammonia synthesis catalyst according to any one of claims 1-3 for the catalytic synthesis of ammonia.

8. A method for catalytic synthesis of ammonia, characterized in that, include: Using the ruthenium-based ammonia synthesis catalyst according to any one of claims 1-3, nitrogen and hydrogen are catalyzed to synthesize ammonia under conditions of 300-500°C and 1-10 MPa.

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