A high / medium entropy alloy oxide catalyst and its preparation method and application in ammonia synthesis

Abstract

This invention discloses a high-entropy / medium-entropy alloy oxide catalyst, its preparation method, and its application in ammonia synthesis. The high-entropy / medium-entropy alloy oxide catalyst comprises ruthenium (Ru) and / or cobalt (Co) as active components, a composite rare earth oxide of lanthanum oxide, cerium oxide, and samarium oxide as additives, and graphite carbon (GC) as a carrier. The active components and additives are all supported on the carrier. The catalyst achieves a higher ammonia synthesis rate than conventional Ru-based catalysts, and its lower Ru active metal content reduces catalyst preparation costs, thus offering potential industrial applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of ammonia synthesis catalysts and their preparation, and particularly relates to a high / medium entropy alloy oxide catalyst, a preparation method thereof, and application in ammonia synthesis. Background Art

[0002] Ammonia, as an important commodity chemical, is widely used in people's lives. With the development of the times, the use of ammonia is becoming more and more extensive, and people's demand for ammonia is increasing. The traditional Haber-Bosch process uses Fe-based catalysts to synthesize ammonia under high temperature and high pressure conditions, which is accompanied by large energy consumption and carbon dioxide emissions. With the rise of "green ammonia" technology, the process route of "renewable energy → electrolysis of water to produce H2 → synthesis of ammonia → application of ammonia" has attracted widespread attention from researchers (Zhou Y, Wang J, Jiang L, et al. Unraveling the size-dependent effect of Ru-based catalysts on Ammonia synthesis at mild conditions [J]. Journal of Catalyst, 2021, 404: 501-511). However, the outlet pressure of pressurized water electrolysis hydrogen production in my country is currently 1.6-3.2 MPa, and the temperature is below 400°C, which does not match the high temperature and high pressure reaction conditions of the current ammonia synthesis process. In order to couple the water electrolysis hydrogen production process with the ammonia synthesis process and realize environmentally friendly and low-energy ammonia synthesis, it is urgent to develop a catalyst for low-temperature, low-pressure and high-efficiency ammonia synthesis.

[0003] In recent years, Ru-based catalysts have been widely studied due to their excellent performance in ammonia synthesis at low temperature and low pressure. Ru-based catalysts are also considered to be the second generation of industrial ammonia synthesis catalysts. Wang et al. first reported a novel Ru-M (M = La or Y) alloy catalyst for ammonia synthesis. Alloying Ru with rare earth metals can lead to a unique interaction between Ru and rare earth metals to achieve maximum electron donation capacity. By adjusting the electronic structure of the active Ru site, the electron transfer from Ru to the antibonding π orbital of N2 is promoted, thereby accelerating the activation of N2 by weakening the N≡N bond energy (Zhang T, Zhu J, Wang J, et al. Ru alloying with La or Y for ammonia synthesis via integrated dissociative and associative mechanism with superior operational stability [J]. Chemical Engineering Science, 2022, 252: 117-255). High entropy alloy oxides (HEO) or medium entropy alloy oxides (MEO) are a new type of composite metal oxides composed of five or more metals (high entropy) or four metal oxides (medium entropy). Compared with single alloys, the multi-element high / medium entropy alloy oxides give them advantages in corrosion resistance, high temperature performance, high strength, etc. (Lu W, Luo X, Yang Y, et al. Co-free non-equilibrium medium-entropy alloy with outstanding tensile properties [J]. Journal of Alloys and Compounds, 2020, 833, 155074). In recent years, high / medium entropy alloy catalysts have gradually attracted attention in the field of catalysis, but there has been no corresponding research in the field of thermal catalytic ammonia synthesis. Therefore, it is very meaningful to introduce high / medium entropy alloy oxides into the field of ammonia synthesis. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high / medium entropy alloy oxide catalyst, which uses metallic ruthenium (Ru) and / or cobalt (Co) as active components, a composite rare earth oxide of lanthanum oxide, cerium oxide and samarium oxide as an auxiliary agent, and graphite carbon (GC) as a carrier; the active components and auxiliary agents are all loaded on the carrier.

[0005] According to one embodiment of the present invention, the catalyst is a high entropy alloy oxide catalyst, denoted as RuCo x-HEO catalyst, the high entropy alloy oxide catalyst has metal ruthenium and cobalt as active components, lanthanum oxide, cerium oxide and samarium oxide composite rare earth oxide as additives, and graphite carbon as a carrier; the active components and additives are all loaded on the carrier;

[0006] The molar ratio of metallic cobalt to metallic ruthenium is 1-3:1, that is, x is 1-3.

[0007] According to an embodiment of the present invention, in the active component, the ruthenium and cobalt are in a mixed alloy state.

[0008] According to an embodiment of the present invention, in the active component, ruthenium is a simple substance, and / or cobalt is a simple substance.

[0009] According to one embodiment of the present invention, the catalyst is a medium-entropy alloy oxide catalyst, denoted as Ru-MEO catalyst, wherein the medium-entropy alloy oxide catalyst comprises metallic ruthenium as an active component, a composite rare earth oxide of lanthanum oxide, cerium oxide and samarium oxide as an auxiliary agent, and graphite carbon as a carrier; the active component and the auxiliary agent are both loaded on the carrier.

[0010] According to an embodiment of the present invention, in the high entropy alloy oxide catalyst, the molar ratio of the metallic ruthenium, the metallic cobalt, the lanthanum element in lanthanum oxide, the cerium element in cerium oxide and the samarium element in samarium oxide is 1:(1-3):(0.5-1.5):(0.5-1.5):(0.5-1.5); exemplary ratios are 0.3 mmol, 0.3 mmol, 0.3 mmol, 0.3 mmol, and 0.3 mmol.

[0011] According to an embodiment of the present invention, in the medium-entropy alloy oxide catalyst, the molar ratio of the metallic ruthenium, the lanthanum element in lanthanum oxide, the cerium element in cerium oxide and the samarium element in samarium oxide is 1:(0.5-1.5):(0.5-1.5):(0.5-1.5), exemplified by 0.3 mmol, 0.3 mmol, 0.3 mmol, 0.3 mmol.

[0012] According to an embodiment of the present invention, in the high / medium entropy alloy oxide catalyst, the loading amount of metallic ruthenium on the carrier is 1-5wt%, for example, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%.

[0013] According to an embodiment of the present invention, in the high entropy alloy oxide catalyst, the loading amount of metallic cobalt on the carrier is 0.5-8%, for example, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%.

[0014] According to an embodiment of the present invention, in the high / medium entropy alloy oxide catalyst, the metal element Ru and / or the metal element Co, lanthanum oxide, cerium oxide and samarium oxide are uniformly distributed on the carrier.

[0015] The present invention also provides a method for preparing a high / medium entropy alloy oxide catalyst, the method comprising

[0016] (1) mixing a support, o-phenanthroline, a ruthenium precursor, and / or a cobalt precursor, a lanthanum precursor, a cerium precursor, and a samarium precursor in a solvent, and then drying;

[0017] (2) The dried product of step (1) is heated and calcined under an inert gas atmosphere to prepare the catalyst.

[0018] According to an embodiment of the present invention, in step (1), the solvent is selected from water and / or ethanol. When the solvent is a mixed solution of water and ethanol, the volume ratio of water and ethanol can be any.

[0019] According to an embodiment of the present invention, in step (1), the mass ratio of the ruthenium content in the ruthenium precursor to the carrier is (0.01-0.2):1, preferably (0.01-0.05):1, and exemplified by 0.01:1, 0.03:1, and 0.05:1.

[0020] According to an embodiment of the present invention, in step (1), the molar ratio of cobalt in the cobalt precursor to ruthenium in the ruthenium precursor is (0-3):1, exemplified by 1:1, 2:1, and 3:1.

[0021] For example, when the catalyst is a medium entropy alloy oxide catalyst, the molar ratio of cobalt in the cobalt precursor to ruthenium in the ruthenium precursor is 0: 1. When the catalyst is a high entropy alloy oxide catalyst, the molar ratio of cobalt in the cobalt precursor to ruthenium in the ruthenium precursor is (1-3):1.

[0022] According to an embodiment of the present invention, in step (1), the molar ratio of the metal elements in the ruthenium precursor, the lanthanum precursor, the cerium precursor and the samarium precursor is 1:(0.5-1.5):(0.5-1.5):(0.5-1.5).

[0023] According to an embodiment of the present invention, in step (1), the molar ratio of o-phenanthroline to the ruthenium precursor is (3-7.5):1, exemplified by 3:1, 4:1, 5:1, 6:1, 7:1 or 7.5:1.

[0024] According to an embodiment of the present invention, in step (1), the carbon carrier is one or both of activated carbon and graphite carbon, preferably graphite carbon.

[0025] According to an embodiment of the present invention, in step (1), the ruthenium precursor is one or more of ruthenium trichloride, ammonium hexachlororuthenate, metallic ruthenium, and ruthenium nitrosyl nitrate; preferably, ruthenium nitrate.

[0026] According to an embodiment of the present invention, in step (1), the cobalt precursor is one or more of cobalt chloride, cobalt carbonate, cobalt acetylacetonate, and cobalt nitrate; preferably cobalt nitrate.

[0027] According to an embodiment of the present invention, in step (1), the lanthanum precursor is lanthanum nitrate.

[0028] According to an embodiment of the present invention, in step (1), the cerium precursor is cerium nitrate.

[0029] According to an embodiment of the present invention, in step (1), the samarium precursor is samarium nitrate.

[0030] According to an embodiment of the present invention, in step (2), the inert gas is one or more of nitrogen, argon or helium, preferably argon. The purpose of introducing the inert gas is to prevent ruthenium and rare earth metals from being oxidized in the air.

[0031] According to an embodiment of the present invention, ultrasonic mixing can be used in step (1). The present invention has no particular restrictions on the temperature and time of ultrasonic mixing, as long as the raw materials are completely dissolved or partially dissolved. For example, the ultrasonic mixing time is 1 hour. For example, the ruthenium precursor and / or the cobalt precursor, lanthanum precursor, cerium precursor and samarium precursor in step (1) can be added to the carrier under room temperature ultrasonic conditions.

[0032] According to an embodiment of the present invention, in step (1), the drying temperature is 60-100°C, exemplified by 60°C, 70°C, 80°C, 90°C, or 100°C; and the drying time is 2-12 hours, exemplified by 2 hours, 4 hours, 6 hours, 10 hours, or 12 hours.

[0033] According to an embodiment of the present invention, in step (2), the heating and calcining temperature is 600-900°C, exemplarily 600°C, 700°C, 800°C or 900°C; the heating and calcining time is 1-3 hours, exemplarily 1 hour, 2 hours or 3 hours. The heating rate during the heating and calcining is 600-900°C / min.

[0034] According to an embodiment of the present invention, in step (2), the heating and roasting adopts a fast moving fixed bed or a Joule furnace, and during the heating and roasting process, the temperature is raised to 600-900° C. within 1 minute.

[0035] According to an embodiment of the present invention, the method for preparing the catalyst comprises the following steps:

[0036] (1) adding graphite carbon to a mixed solution of ethanol and water in a volume ratio of 1, first adding o-phenanthroline to the solution under ultrasonic conditions, then sequentially adding a ruthenium precursor and / or a cobalt precursor, a lanthanum precursor, a cerium precursor, and a samarium precursor to the mixed solution, and drying the sample after ultrasonication;

[0037] (2) Then, under inert gas, the dried product of step (1) is pushed into a fast moving fixed bed or a Joule furnace for heating and calcining to prepare the catalyst.

[0038] The present invention also provides the catalyst prepared by the above preparation method.

[0039] The present invention also provides use of the above catalyst in catalytic synthesis of ammonia, preferably as a catalyst for synthesizing ammonia, more preferably as a catalyst for synthesizing ammonia under low temperature and low pressure conditions.

[0040] According to an embodiment of the present invention, the temperature of the synthetic ammonia is 300-400°C, exemplarily 300°C, 350°C, and 400°C; the pressure of the synthetic ammonia is 0.5-3 MPa, exemplarily 1 MPa.

[0041] The present invention also provides a method for synthesizing ammonia, which contains at least the above catalyst.

[0042] Beneficial effects of the present invention:

[0043] 1. The present invention utilizes a rapid heating pyrolysis method to synthesize high- and medium-entropy alloy oxide catalysts. These catalysts exhibit excellent activity and stability in ammonia synthesis reactions. The catalyst preparation process is relatively simple, the catalyst exhibits excellent thermal stability, and is readily commercially viable.

[0044] 2. The ammonia synthesis rate of the catalyst of the present invention is superior to that of the traditional Ru-based catalyst. The Ru active metal content in the catalyst is low, which reduces the preparation cost of the catalyst and thus has potential industrial application prospects.

[0045] 3. The present invention introduces high / medium entropy alloy oxide catalysts into the field of ammonia synthesis for the first time, and the catalysts have high activity, providing new research ideas and directions for the subsequent development of more efficient and stable high / medium entropy material catalysts in the field of ammonia synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 XRD spectra of the catalysts prepared in Examples 1, 5, 6 and Comparative Examples 1 to 3.

[0047] Figure 2 Graph showing the ammonia synthesis reaction rates of the catalysts prepared in Examples 1, 5, 6 and Comparative Examples 1 to 3 at 400°C and 1 MPa.

[0048] Figure 3 The XRD spectra of the fresh catalyst and the catalyst after the ammonia synthesis reaction prepared in Example 5 are shown.

[0049] Figure 4 Activation energy diagrams of the catalysts prepared in Examples 1, 5, 6 and Comparative Examples 1 to 3.

[0050] Figure 5 The stability diagram of the catalysts prepared in Example 1 and Example 5 at 400°C and 1 MPa. DETAILED DESCRIPTION

[0051] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0052] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0053] Example 1

[0054] Graphite carbon (1 g, 83.3 mmol) was added to a 50 ml mixture of ethanol and ultrapure water in a 1:1 ratio. O-phenanthroline (0.405 g, 2.25 mmol) was then added to the graphite carbon mixture. Ruthenium nitrate solution (2.50 ml, ruthenium concentration 0.012 g / ml), lanthanum nitrate (0.113 g, 0.3 mmol), cerium nitrate (0.130 g, 0.3 mmol), and samarium nitrate (0.133 g, 0.3 mmol) were then added sequentially to the graphite carbon mixture. After sonication for 1 hour, the solution was dried in a 60°C oven. The dried sample was then calcined in an argon atmosphere at 800°C in a fast-moving fixed bed (heating rate of approximately 800°C / min) for 3 hours. The resulting catalyst was designated 3Ru-MEO, with a Ru loading of 3% on the support.

[0055] Example 2

[0056] Graphite carbon (1 g, 83.3 mmol) was added to a 50 ml mixture of ethanol and ultrapure water in a 1:1 ratio. O-phenanthroline (0.405 g, 2.25 mmol) was then added to the graphite carbon mixture. Ruthenium nitrate solution (0.83 ml, ruthenium concentration of 0.012 g / ml), lanthanum nitrate (0.113 g, 0.3 mmol), cerium nitrate (0.130 g, 0.3 mmol), and samarium nitrate (0.133 g, 0.3 mmol) were then added sequentially to the graphite carbon mixture. After sonication for 1 hour, the solution was dried in a 60°C oven. The dried sample was then calcined in an argon atmosphere at 800°C in a fast-moving fixed bed (heating rate of approximately 800°C / min) for 3 hours. The resulting catalyst was designated 1Ru-MEO, with a Ru loading of 1% on the support.

[0057] Example 3

[0058] Graphite carbon (1 g, 83.3 mmol) was added to a 1:1 mixture of ethanol and ultrapure water (50 ml). O-phenanthroline (0.405 g, 2.25 mmol) was then added to the graphite carbon mixture. Ruthenium nitrate solution (4.2 ml, ruthenium concentration of 0.012 g / ml), lanthanum nitrate (0.113 g, 0.3 mmol), cerium nitrate (0.130 g, 0.3 mmol), and samarium nitrate (0.133 g, 0.3 mmol) were then added to the graphite carbon mixture in sequence. After ultrasonication for 1 hour, the solution was placed in a 60°C oven to dry. The dried sample was then calcined in an 800°C Joule furnace (heating rate of approximately 800°C / min) for 3 hours in an argon atmosphere. The resulting catalyst was designated 5Ru-MEO, where the Ru loading on the support was 5%.

[0059] Example 4

[0060] Graphite carbon (1 g, 83.3 mmol) was added to a 1:1 mixed solution (50 ml) of ethanol and ultrapure water, followed by the addition of o-phenanthroline (0.405 g, 2.25 mmol) to the above graphite carbon mixed solution, and then ruthenium nitrate solution (2.5 ml, ruthenium concentration of 0.012 g / ml), lanthanum nitrate (0.113 g, 0.3 mmol), cerium nitrate (0.130 g, 0.3 mmol), and samarium nitrate (0.133 g, 0.3 mmol) were added to the above graphite carbon mixed solution in sequence. After ultrasonication for 1 h, the solution was placed in an oven at 60 ° C for drying. Then, in an argon atmosphere, the dried samples were pushed into a rapid moving fixed bed and calcined at 600°C, 700°C, and 900°C for 3 hours (the heating rate was 600°C / min, 700°C / min, or 900°C / min, respectively). The final catalysts were recorded as 3Ru-MEO-600, 3Ru-MEO-700, and 3Ru-MEO-900, where the Ru loading on the carrier was 3%.

[0061] Example 5

[0062] Graphitic carbon (1 g, 83.3 mmol) was added to a 50 ml mixture of ethanol and ultrapure water in a 1:1 ratio. O-phenanthroline (0.405 g, 2.25 mmol) was then added to the graphitic carbon mixture. Ruthenium nitrate solution (2.5 ml, ruthenium concentration 0.012 g / ml), cobalt nitrate (0.2619 g, 0.6 mmol), lanthanum nitrate (0.113 g, 0.3 mmol), cerium nitrate (0.130 g, 0.3 mmol), and samarium nitrate (0.133 g, 0.3 mmol) were then added sequentially to the graphitic carbon mixture. After sonication for 1 hour, the solution was oven-dried at 60°C. The dried sample was then calcined in an argon atmosphere on a fast-moving fixed bed at 800°C for 3 hours (heating rate approximately 800°C / min). The resulting catalyst, designated RuCo2-HEO, contained 3.4% Co on the support. That is, the molar ratio of Co simple substance to Ru simple substance is 2:1.

[0063] Example 6

[0064] Graphite carbon (1 g, 83.3 mmol) was added to a 1:1 mixed solution (50 ml) of ethanol and ultrapure water, followed by the addition of o-phenanthroline (0.405 g, 2.25 mmol) to the above graphite carbon mixed solution, and then ruthenium nitrate solution (2.5 ml, ruthenium concentration of 0.012 g / ml), cobalt nitrate (0.0873 g or 0.2619 g, 0.3 or 0.9 mmol), lanthanum nitrate (0.113 g, 0.3 mmol), cerium nitrate (0.130 g, 0.3 mmol), and samarium nitrate (0.133 g, 0.3 mmol) were added to the above graphite carbon mixed solution in sequence. After ultrasonication for 1 h, the solution was placed in a 60 ° C oven for drying. The dried samples were then calcined in an 800°C Joule furnace under an argon atmosphere for 3 hours (at a heating rate of approximately 800°C / min). The resulting catalysts, designated RuCo1-HEO and RuCo3-HEO, contained 1.7% and 5.1% Co on the support, respectively. This means the molar ratios of Co to Ru were 1:1 and 3:1, respectively.

[0065] Comparative Example 1

[0066] Graphite carbon (1g, 83.3mmol) was added to a 1:1 mixed solution of ethanol and ultrapure water (50ml), followed by the addition of o-phenanthroline (0.162g, 0.9mmol) to the graphite carbon mixed solution. Ruthenium nitrate solution (2.5ml, ruthenium concentration of 0.012g / ml) and lanthanum nitrate (0.113g, 0.3mmol) were then added to the graphite carbon mixed solution in sequence. After ultrasonic treatment for 1h, the solution was placed in a 60°C oven to dry. The dried sample was then pushed into an 800°C fast moving fixed bed in an argon atmosphere and calcined for 3h (heating rate of approximately 800°C / min). The resulting catalyst was designated RuLa / GC.

[0067] Comparative Example 2

[0068] Graphite carbon (1g, 83.3mmol) was added to a 1:1 mixed solution of ethanol and ultrapure water (50ml), followed by the addition of o-phenanthroline (0.162g, 0.9mmol) to the graphite carbon mixed solution. Ruthenium nitrate solution (2.5ml, ruthenium concentration of 0.012g / ml) and cerium nitrate (0.130g, 0.3mmol) were then added to the graphite carbon mixed solution in sequence. After ultrasonic treatment for 1h, the solution was placed in a 60°C oven to dry. The dried sample was then pushed into an 800°C fast moving fixed bed in an argon atmosphere and calcined for 3h (heating rate of approximately 800°C / min). The resulting catalyst was designated RuCe / GC.

[0069] Comparative Example 3

[0070] Graphite carbon (1g, 83.3mmol) was added to a 1:1 mixed solution of ethanol and ultrapure water (50ml), followed by the addition of o-phenanthroline (0.162g, 0.9mmol) to the graphite carbon mixed solution. Ruthenium nitrate solution (2.5ml, ruthenium concentration of 0.012g / ml) and samarium nitrate (0.133g, 0.3mmol) were then added to the graphite carbon mixed solution in sequence. After ultrasonic treatment for 1h, the solution was placed in a 60°C oven to dry. The dried sample was then pushed into an 800°C fast moving fixed bed for calcination for 3h (heating rate of approximately 800°C / min) in an argon atmosphere. The resulting catalyst was designated RuSm / GC.

[0071] Comparative Example 4

[0072] Graphite carbon (1 g, 83.3 mmol) was added to a 1:1 mixture of ethanol and ultrapure water (50 ml). O-phenanthroline (0.405 g, 2.25 mmol) was then added to the graphite carbon mixture. Ruthenium nitrate solution (2.5 ml, ruthenium concentration of 0.012 g / ml), cobalt nitrate (0.0873 g, 0.3 mmol), lanthanum nitrate (0.113 g, 0.3 mmol), cerium nitrate (0.130 g, 0.3 mmol), and samarium nitrate (0.133 g, 0.3 mmol) were then added to the graphite carbon mixture in sequence. After sonication for 1 h, the solution was placed in a 60°C oven to dry. The dried sample was then placed in a tube furnace under an argon atmosphere and gradually heated to 800°C (heating rate 1-20°C / min) for calcination for 3 h. The resulting catalyst was designated RuCoLaCeSm, with a Co loading of 1.7%. That is, the molar ratio of the Co simple substance to the Ru simple substance is 1:1.

[0073] Application Examples

[0074] 0.20 g of each catalyst prepared in Examples 1-6 and Comparative Examples 1-4 was used, with a mass space velocity of 60,000 mL g - 1 h -1 Ammonia synthesis rates were measured in a continuous-flow micro-fixed-bed reactor. Changes in NH3 concentration in the exhaust gas were determined by ion chromatography (Thermo Scientific, DIONEX, ICS-600). The reaction gas composition was a 75% H2 + 25% N2 (volume ratio) mixture. Ammonia synthesis reaction rates were measured over different catalysts at 400°C and 1 MPa. The test results are shown in Table 1 below.

[0075] Table 1. Ammonia synthesis performance of different catalysts at 400°C and 1 MPa

[0076]

[0077]

[0078] As shown in Table 1, a comparison of Nos. 1, 2, 3, and 5 shows that the ammonia synthesis activity of Ru-based medium-entropy alloy oxides significantly increases after incorporation with rare earth oxides, demonstrating the excellent ammonia synthesis performance of these catalysts. Nos. 4-6 show the activities of catalysts with different Ru contents. As the Ru content increases, the activity of the catalysts also increases, indicating that Ru is the primary active center. Nos. 5, 7-9 show the activities of catalysts calcined at different temperatures. As the temperature increases from 600°C to 800°C, the activity gradually increases, but decreases at 900°C. Nos. 10-12 show the ammonia synthesis activity of Ru-based high-entropy alloy oxides with different Co content ratios. The activity shows a volcano-like trend with increasing Co content, reaching its peak at 0.6 mmol Co. Nos. 10 and 13 are catalysts obtained by rapid pyrolysis and conventional calcination, respectively. The rapid pyrolysis method exhibits superior ammonia synthesis performance.

[0079] Catalyst performance evaluation

[0080] Figure 1 XRD spectra of the catalysts prepared in Example 1 (3Ru-MEO), Example 5 (RuCo2-HEO), Example 6 (RuCo1-HEO and RuCo3-HEO) and Comparative Examples 1 to 3 (RuLa / GC, RuCe / GC, RuSm / GC). Figure 1 It can be found that there are no obvious metal species peaks in the spectrum, indicating that elemental Ru, lanthanum oxide, cerium oxide and samarium oxide are evenly distributed on the carrier, or elemental Ru, elemental Co, lanthanum oxide, cerium oxide and samarium oxide are evenly distributed on the carrier.

[0081] Figure 2 The ammonia synthesis reaction rate diagram of the catalysts prepared in Examples 1, 5, 6 and Comparative Examples 1 to 3 at 400°C and 1 MPa is shown in FIG. Figure 2 It can be seen that the ammonia synthesis activity of 3Ru-MEO catalyst is 24.7 mmol g -1 h -1 , which are 1.5, 2.2, and 2.7 times those of RuLa / GC, RuCe / GC, and RuSm / GC catalysts, respectively. The ammonia synthesis activity of RuCo2-HEO catalyst is 30.2 mmol g -1 h -1 , which are 1.4 and 1.2 times of those of RuCo1-HEO and RuCo3-HEO catalysts, respectively, indicating that the catalysts 3Ru-MEO, RuCo2-HEO, RuCo1-HEO and RuCo3-HEO of the present invention have excellent ammonia synthesis activity.

[0082] Figure 3 The XRD spectra of the fresh catalyst (RuCo2-HEO) and the catalyst after reaction (RuCo2-HEO-used) prepared in Example 5 are shown in FIG. The catalyst after reaction refers to the catalyst used in the ammonia synthesis reaction. Figure 3 It can be seen that the catalyst did not undergo phase change during the ammonia synthesis reaction, indicating that the high / medium entropy alloy oxide catalyst structure is relatively stable during the reaction.

[0083] Figure 4 The activation energy diagrams of the catalysts prepared in Example 1 (3Ru-MEO), Example 5 (RuCo2-HEO), Example 6 (RuCo1-HEO and RuCo3-HEO), and Comparative Examples 1 to 3 (RuLa / GC, RuCe / GC, RuSm / GC) are shown. The activation energy of the 3Ru-MEO catalyst prepared in Example 1 is 65.3 kJ mol -1 , which is significantly lower than the comparative example RuLa / GC (78.9 kJ mol -1 )、RuCe / GC(89.5kJ mol -1 )、RuSm / GC(90.2kJ mol -1 ) catalyst, the activation energy of RuCo2-HEO catalyst is 65.2 kJ mol -1 , which is significantly lower than RuCo1-HEO (75.9 kJ mol -1 ) and RuCo3-HEO (72.7 kJ mol -1 )catalyst.

[0084] Figure 5 Figure 2 shows the stability of the catalysts prepared in Examples 1 and 5 at 400°C and 1 MPa. The figure shows that the activities of the 3Ru-MEO and RuCo2-HEO catalysts prepared in Examples 1 and 5 did not significantly decrease during the 100-h stability test, indicating that the medium- and high-entropy alloy oxide catalysts prepared in the present invention have good stability.

[0085] The above examples illustrate the embodiments of the present invention. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A high / medium entropy alloy oxide catalyst, characterized in that: The invention uses metallic ruthenium as an active component or metallic ruthenium and cobalt as active components, lanthanum oxide, cerium oxide and samarium oxide composite rare earth oxide as an auxiliary agent, and graphite carbon as a carrier; the active component and auxiliary agent are both loaded on the carrier; In the high entropy alloy oxide catalyst, the molar ratio of the metallic ruthenium, the metallic cobalt, the lanthanum element in lanthanum oxide, the cerium element in cerium oxide, and the samarium element in samarium oxide is 1:(1-3):(0.5-1.5):(0.5-1.5):(0.5-1.5); In the medium-entropy alloy oxide catalyst, the molar ratio of the metallic ruthenium, the lanthanum element in lanthanum oxide, the cerium element in cerium oxide, and the samarium element in samarium oxide is 1:(0.5-1.5):(0.5-1.5):(0.5-1.5); In the high / medium entropy alloy oxide catalyst, the loading amount of metal ruthenium on the carrier is 1 to 5 wt%; In the high entropy alloy oxide catalyst, the loading amount of metal cobalt on the carrier is 0.5 to 8 wt%; The preparation method of the catalyst comprises: (1) mixing a support, o-phenanthroline, a ruthenium precursor, and / or a cobalt precursor, a lanthanum precursor, a cerium precursor, and a samarium precursor in a solvent and drying; (2) heating and calcining the dried product of step (1) under an inert gas atmosphere to prepare the catalyst; In step (2), the temperature of the heating and calcining is 600-900°C; the time of the heating and calcining is 1-3h; and the heating rate during the heating and calcining is 600-900°C / min.

2. The catalyst according to claim 1, characterized in that The catalyst is a high-entropy alloy oxide catalyst, which contains metal ruthenium and cobalt as active components, lanthanum oxide, cerium oxide and samarium oxide composite rare earth oxide as auxiliary agents, and graphite carbon as a carrier; the active components and auxiliary agents are all loaded on the carrier; Wherein, the molar ratio of metallic cobalt to metallic ruthenium is (1-3):

1.

3. The catalyst according to claim 1, characterized in that In the active component, the ruthenium and cobalt are in a mixed alloy state.

4. The catalyst according to claim 1, characterized in that In the active components, ruthenium is a simple substance, and / or cobalt is a simple substance.

5. The catalyst according to claim 1, characterized in that The catalyst is a medium-entropy alloy oxide catalyst, which uses metallic ruthenium as an active component, a composite rare earth oxide of lanthanum oxide, cerium oxide and samarium oxide as an auxiliary agent, and graphite carbon as a carrier; the active component and the auxiliary agent are both loaded on the carrier.

6. The catalyst according to claim 1, characterized in that In the high / medium entropy alloy oxide catalyst, the metal element Ru and / or the metal element Co, lanthanum oxide, cerium oxide and samarium oxide are uniformly distributed on the carrier.

7. The catalyst according to claim 1, characterized in that In step (1), the solvent is selected from water and / or ethanol.

8. The catalyst according to claim 1, characterized in that In step (1), the mass ratio of the ruthenium content in the ruthenium precursor to the carrier is 0.01-0.2:

1.

9. The catalyst according to claim 1, characterized in that In step (1), the molar ratio of cobalt in the cobalt precursor to ruthenium in the ruthenium precursor is 0-3:

1.

10. The catalyst according to claim 1, characterized in that When the catalyst is a medium-entropy alloy oxide catalyst, the molar ratio of cobalt in the cobalt precursor and ruthenium in the ruthenium precursor is 0:1; when the catalyst is a high-entropy alloy oxide catalyst, the molar ratio of cobalt in the cobalt precursor and ruthenium in the ruthenium precursor is (1-3):

1.

11. The catalyst according to claim 1, characterized in that In step (1), the molar ratio of each metal element in the ruthenium precursor, the lanthanum precursor, the cerium precursor and the samarium precursor is 1:(0.5-1.5):(0.5-1.5):(0.5-1.5).

12. The catalyst according to claim 1, characterized in that In step (1), the molar ratio of o-phenanthroline to the ruthenium precursor is (3-7.5):

1.

13. The catalyst according to claim 1, characterized in that In step (1), the carrier is one or both of activated carbon and graphite carbon.

14. The catalyst according to claim 1, characterized in that In step (1), the ruthenium precursor is one or more of ruthenium trichloride, ammonium hexachlororuthenate, metallic ruthenium, and ruthenium nitrosyl nitrate.

15. The catalyst according to claim 1, characterized in that In step (1), the cobalt precursor is one or more of cobalt chloride, cobalt carbonate, cobalt acetylacetonate, and cobalt nitrate.

16. The catalyst according to claim 1, characterized in that In step (1), the lanthanum precursor is lanthanum nitrate.

17. The catalyst according to claim 1, characterized in that In step (1), the cerium precursor is cerium nitrate; In step (1), the samarium precursor is samarium nitrate.

18. The catalyst according to claim 1, characterized in that In step (2), the inert gas is one or more of nitrogen, argon or helium.

19. The catalyst according to claim 1, characterized in that In step (1), the drying temperature is 60-100° C., and the drying time is 2-12 hours.

20. Use of the catalyst according to any one of claims 1 to 19 in catalytic synthesis of ammonia.

21. The use according to claim 20, characterized in that As a catalyst for ammonia synthesis.

22. The use according to claim 20, characterized in that As a catalyst for synthesizing ammonia under low temperature and low pressure conditions.

23. The use according to claim 20, characterized in that The temperature of the synthetic ammonia is 300-400° C., and the pressure of the synthetic ammonia is 0.5-3 MPa.

24. A method for synthesizing ammonia, characterized in that: It contains at least the catalyst according to any one of claims 1 to 19.

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