A bimetallic Ni-Co / MOF catalyst for synthesizing ammonia and a preparation method and application thereof

Abstract

The application discloses a bimetallic Ni-Co / MOF catalyst for synthesizing ammonia as well as a preparation method and application thereof, and belongs to the technical field of synthesizing ammonia. The method comprises the following steps: synthesizing a bimetallic Ni-Co / MOF precursor through a hydrothermal method, then activating the bimetallic Ni-Co / MOF precursor under an inert atmosphere to obtain a Ni-Co / MOF catalyst, and optimizing the electronic structure of the catalyst by adjusting the molar ratio of Ni to Co; mixing the obtained catalyst with quartz sand, filling the quartz sand in a discharge area of a dielectric barrier discharge plasma reactor, and inputting nitrogen and water vapor as raw material gas, so as to catalytically synthesize ammonia under a discharge condition. The application significantly enhances the activity of the catalyst through a bimetallic synergistic effect, and solves the problems of insufficient activity of a single-metal catalyst and low efficiency of a single-plasma system. When the molar ratio of Ni to Co is 3:1, the ammonia synthesis rate is 3.67 mmol.g cat ‑1 ·h ‑1 , the energy efficiency is 0.131 g.kW ‑1 ·h ‑1 , and the ammonia is directly synthesized from nitrogen and water vapor under the conditions of normal temperature and pressure and without external heating, so that a new way is provided for green and low-energy-consumption synthesis of ammonia.

Description

Technical Field

[0001] This invention belongs to the field of ammonia synthesis technology, specifically relating to a bimetallic Ni-Co / MOF catalyst for ammonia synthesis, its preparation method, and its application. Background Technology

[0002] Ammonia is one of the most basic chemical raw materials, widely used in fertilizer and chemical production, and its synthesis technology is crucial to global food security and energy transition. Currently, industrial-scale ammonia synthesis mainly relies on the Haber-Bosch process, which operates under high temperature (400–500 °C) and high pressure (150–300 atm) conditions using iron-based catalysts, consuming 1.0%–2.0% of global energy supply and contributing 1.6% of global carbon emissions. Against the backdrop of dual-carbon goals and the green chemistry transition, developing efficient, low-energy-consumption alternative technologies for ammonia synthesis has become an international research focus.

[0003] Currently, various emerging ammonia synthesis technologies mainly include electrocatalysis, photocatalysis, biological nitrogen fixation, and plasma. Among them, low-temperature plasma (NTP) ammonia synthesis technology achieves efficient activation and reaction of N2 and water vapor (H2O) at room temperature and pressure, breaking through the dependence of traditional thermocatalysis on extreme conditions. High-energy electrons, excited-state particles, and free radicals such as N and NH in plasma can efficiently dissociate inert N≡N bonds. Plasma systems can flexibly adapt to the intermittent power supply of renewable energy sources (such as wind power and photovoltaics), providing a technical path for the large-scale production of green ammonia. Meanwhile, metal-organic framework (MOF) materials, due to their high specific surface area, porous structure, and abundant active sites, are being explored for use in plasma-assisted ammonia synthesis. Chinese patent application CN116253332B discloses a method for using Ni-Co bimetallic MOFs in plasma-assisted ammonia synthesis, which uses nitrogen and hydrogen as raw materials and requires heating to 200℃, achieving an ammonia synthesis rate of 88.21 μmol / g·min (approximately 5.29 mmol / g·h). Chinese patent application CN116832816B discloses a graphitized activated carbon-supported iron-cobalt bimetallic catalyst for thermocatalytic ammonia synthesis, but the reaction conditions still require a pressure of 1 MPa and a temperature of 400℃. It is evident that while replacing hydrogen with water vapor can reduce raw material costs and risks, current technology has not yet achieved highly efficient plasma-catalytic ammonia synthesis using nitrogen and water vapor as raw materials at ambient temperature and pressure.

[0004] In plasma catalytic systems for ammonia synthesis, single-metal catalysts often suffer from decreased activity and insufficient stability due to their limited number of active sites and susceptibility to aggregation. Meanwhile, traditional supports also frequently face challenges such as structural instability, limited porosity regulation, and weak synergistic effects with metal components, hindering the effective utilization of nitrogen and water and further improving the ammonia synthesis rate. Therefore, developing a highly active and stable catalyst system using readily available and inexpensive nitrogen and water as raw materials at ambient temperature and pressure is crucial for achieving green and low-energy ammonia synthesis. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a bimetallic Ni-Co / MOF catalyst for ammonia synthesis, its preparation method and application, so as to solve the technical problem of how to improve the ammonia synthesis rate and energy efficiency at room temperature and pressure using nitrogen and water vapor as raw materials, through the synergistic effect of bimetallic MOF catalyst and plasma.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a bimetallic Ni-Co / MOF catalyst for ammonia synthesis, comprising: dissolving nickel salt, cobalt salt, terephthalic acid and triethylenediamine in an organic solvent, mixing and stirring evenly, subjecting the mixture to hydrothermal reaction, washing, drying, and activation under an inert atmosphere to obtain the Ni-Co / MOF catalyst.

[0007] Preferably, 3-5 mmol of terephthalic acid and 3-5 mmol of triethylenediamine are added to every 40-60 mL of organic solvent; the molar ratio of nickel salt to cobalt salt is (0-4):(0-4).

[0008] Preferably, in the nickel salt and cobalt salt, the molar ratio of Ni to Co is (1~4):1.

[0009] Preferably, the nickel salt is Ni(NO3)2·6H2O; the cobalt salt is Co(NO3)2·6H2O; and the organic solvent is N,N-dimethylformamide. The solvent used for washing is one or two of N,N-dimethylformamide, methanol, and ethanol; washing is performed by centrifugation at 6000-8000 r / min for 3-5 min; drying is carried out overnight at 80-100 ℃.

[0010] Preferably, the mixing and stirring time is 2-3 h; the hydrothermal reaction temperature is 160-180 ℃, and the hydrothermal reaction time is 10-20 h.

[0011] Preferably, activation involves heating to 100-300°C at a rate of 1-5°C / min and maintaining that temperature for 2-4 hours; the inert atmosphere is nitrogen or argon.

[0012] The present invention also discloses a bimetallic Ni-Co / MOF catalyst for ammonia synthesis, which is prepared by the above-described method for preparing a bimetallic Ni-Co / MOF catalyst for ammonia synthesis.

[0013] The present invention also discloses the application of the above-mentioned bimetallic Ni-Co / MOF catalyst for ammonia synthesis in plasma-assisted ammonia synthesis.

[0014] Preferably, the bimetallic Ni-Co / MOF catalyst used for ammonia synthesis is mixed with quartz sand, placed in the discharge region of a low-temperature plasma reactor, and the raw material gas is introduced to start the plasma discharge for ammonia synthesis.

[0015] Preferably, the feed gas is nitrogen and water vapor; the low-temperature plasma reactor is a coaxial cylindrical dielectric barrier discharge reactor with a discharge region length of 50-100 mm and a discharge gap of 1-3 mm; the volume concentration of water vapor in the feed gas is 1-10 vol.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a bimetallic Ni-Co / MOF catalyst for ammonia synthesis. The method employs a one-step hydrothermal approach combined with an inert atmosphere activation strategy, resulting in a simple and easy-to-operate process that eliminates the need for complex post-processing steps such as high-pressure hydrogen reduction or high-temperature carbonization. By controlling the molar ratio of nickel salt to cobalt salt, the electronic structure and local coordination environment of Ni and Co in the MOF material can be effectively adjusted, thereby optimizing the bimetallic synergistic catalytic effect. As shown in Table 1, when the Ni:Co molar ratio is 3:1 (Example 1), the ammonia synthesis rate reaches 3.67 mmol·g. cat -1 ·h -1 However, when using a single-metal Co / MOF (Example 2) or a single-metal Ni / MOF (Example 3), the ammonia synthesis rates were only 1.92 and 2.68 mmol·g, respectively. cat -1 ·h -1 This demonstrates that the bimetallic ratio control strategy of this invention is key to improving catalytic performance. The activation temperature of this invention is only 100-300℃, far lower than the 450-550℃ high-temperature reduction or high-temperature carbonization required by existing preparation methods, significantly reducing energy consumption and preparation costs. Furthermore, the catalyst prepared by this method exhibits stable performance during 48 hours of long-term operation, proving that the preparation method of this invention can effectively inhibit metal particle agglomeration and endow the catalyst with excellent structural stability.

[0017] This invention discloses a bimetallic Ni-Co / MOF catalyst for ammonia synthesis, which combines the structural advantages of high specific surface area and high porosity of MOF materials with the electronic and structural synergistic effects between Ni and Co bimetals. The surface of this material is composed of uniform nanorods, which enhances gas mass transfer performance and allows more free radicals to contact the active sites. The introduction of the bimetal effectively inhibits the aggregation of metal particles during the reaction process, exposing more stable active sites on the catalyst. Furthermore, the presence of multiple nickel-cobalt active sites allows for synergistic effects in nitrogen and water activation, reaction, and product desorption. Compared to single-metal Ni / MOF or Co / MOF, the bimetallic MOF material of this invention exhibits superior catalytic activity and long-term stability in a plasma field, with almost no performance degradation within 48 hours.

[0018] This invention discloses the application of a bimetallic Ni-Co / MOF catalyst for ammonia synthesis in plasma-assisted ammonia synthesis. The bimetallic Ni-Co / MOF catalyst is coupled with low-temperature plasma technology and applied to ammonia synthesis using nitrogen and water vapor as raw materials. By directly using inexpensive, safe, and readily available water vapor instead of high-cost, high-risk hydrogen as the hydrogen source, the cost of raw materials and the safety risks of storage and transportation are fundamentally reduced. The reaction is carried out at room temperature without external heating and under normal pressure, significantly reducing energy consumption. At a Ni to Co molar ratio of 3:1, the ammonia synthesis rate reaches 3.67 mmol·g. cat -1 ·h -1 The energy efficiency reaches 0.131 g·kW. -1 ·h -1 The catalyst exhibits significantly superior performance compared to single-metal catalysts and single-plasma systems; it remains stable during 48 hours of continuous operation, demonstrating promising prospects for industrial application. This invention provides a practical new approach for green, low-energy, and distributed ammonia synthesis processes. Attached Figure Description

[0019] Figure 1 The X-ray diffraction pattern of the Ni3-Co1 / MOF catalyst prepared in Example 1 of this invention; Figure 2 This is a scanning electron microscope image of the Ni3-Co1 / MOF catalyst prepared in Example 1 of the present invention; Figure 3 This is a performance comparison chart of embodiments 1-7 of the present invention; Figure 4 This is a stability diagram of the Ni3-Co1 / MOF catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0022] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0023] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0024] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0025] In this invention, unless otherwise specified, the numerical range "a~b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation for these numerical combinations.

[0026] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0027] The term “and / or” as used in this invention refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0028] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0029] This invention employs a catalytic system combining a bimetallic active component with a metal-organic framework (MOF). By adjusting the molar ratio of the bimetal (e.g., Ni / Co) and leveraging the highly ordered porous structure and tunable coordination environment of the MOF, not only can the aggregation of metal particles be effectively suppressed, but the catalytic activity and stability can also be significantly improved by enhancing the electronic and structural synergistic effects between the two metals. This solvothermal-in-situ doping synergistic strategy provides a new feasible route for achieving efficient and stable plasma-catalyzed ammonia synthesis. It solves the problem of low efficiency in nitrogen and water ammonia synthesis using single-plasma systems, as well as the insufficient activity of traditional single-metal MOF catalysts. Through the bimetallic strategy and structural optimization, the feedstock utilization rate and synthesis rate are improved, thereby achieving more efficient ammonia production.

[0030] This invention provides a method for synthesizing ammonia using a low-temperature plasma-coupled Ni-Co / MOF catalyst, comprising the following steps: 1) Preparation of Ni-Co / MOF catalysts Nickel salt Ni(NO3)2·6H2O, cobalt salt Co(NO3)2·6H2O, terephthalic acid, and triethylenediamine were weighed and dissolved in N,N-dimethylformamide (DMF). The mixture was magnetically stirred until the solids were completely dissolved. The mixed solution was transferred to the lining of a reaction vessel, which was then placed inside and tightened. Finally, the vessel was placed in an oven for hydrothermal reaction. After the hydrothermal reaction, the mixture was washed with an organic solvent until the supernatant was clear and free of impurities. The precipitate was dried overnight to obtain the sample. The dried sample was evenly spread in a quartz boat, which was then placed in the isothermal zone of a tube furnace for activation under an inert gas atmosphere to obtain the Ni-Co / MOF catalyst.

[0031] The molar ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O is (0-4):(0-4). In nickel and cobalt salts, the molar ratio of Ni to Co is (1~4):1.

[0032] The fixed addition amounts of terephthalic acid and triethylenediamine are 3-5 mmol.

[0033] The amount of organic solvent DMF added is 40-60 mL.

[0034] The mixed solution was stirred on a magnetic stirrer for 2-3 hours.

[0035] The mixed solution placed in the reactor is hydrothermally heated at 160-180 ℃ for 10-20 hours.

[0036] The organic solvent used for washing is one or two of DMF, methanol, and ethanol.

[0037] Washing is performed by centrifuging at 6000-8000 r / min for 3-5 min.

[0038] The sample was dried overnight at a temperature of 80-100 ℃.

[0039] During the activation process, the inert gas is either nitrogen or argon. The temperature is increased to 100-300 ℃ at a rate of 1-5 ℃ / min and maintained for 2-4 h for activation.

[0040] 2) Preparation of ammonia by plasma-catalyzed synthesis The Ni-Co / MOF catalyst prepared in step 1) and quartz sand are mixed and uniformly filled into the discharge region of the low-temperature plasma reactor. The raw material gas is introduced into the reactor inlet and the discharge conditions are adjusted to start the discharge. The raw material gas undergoes a catalytic reaction on the surface of Ni-Co / MOF and quartz sand to generate NH3. A dilute sulfuric acid solution is connected to the reactor outlet to collect NH3 for subsequent detection.

[0041] The cryogenic plasma reactor is a coaxial cylindrical DBD reactor. The discharge region length of the cryogenic plasma reactor is 50-100 mm, and the discharge gap ranges from 1 mm. 3 mm, the volume concentration of water vapor in the feed gas is 1-10 vol.

[0042] The Ni-Co / MOF catalyst prepared by this invention has a simple process and is easy to operate. By changing the metal molar ratio, the electronic structure and local environment of Ni and Co in Ni-Co / MOF materials can be significantly adjusted, thereby optimizing the distribution of active sites and the bimetallic synergistic catalytic effect in the catalytic reaction, and increasing the ammonia synthesis rate.

[0043] In this invention, low-temperature plasma coupling of the Ni3-Co1 / MOF catalyst enables an ammonia synthesis rate of 3.67 mmol·g. cat -1 ·h -1 This significantly surpasses the performance of single-metal and other proportioned catalysts. Furthermore, the synergistic ammonia synthesis energy efficiency described in this invention can reach 0.131 g·kW. -1 ·h -1 The Ni3-Co1 / MOF catalyst exhibits excellent ammonia synthesis performance and has promising development prospects.

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0045] Example 1 A method for synthesizing ammonia using a low-temperature plasma-coupled Ni-Co / MOF catalyst includes the following steps: Weigh 2.48 mmol and 0.83 mmol of Ni(NO3)2·6H2O and Co(NO3)2·6H2O, respectively, and dissolve 4 mmol of terephthalic acid and triethylenediamine in 50 mL of N,N-dimethylformamide (DMF) and stir continuously for 3 h. Transfer the mixture to the liner of the reactor, place it in the reactor shell and tighten it, and finally place it in an oven at 170 °C for 16 h. Wash with DMF and ethanol until the solution is clear and free of impurities, and centrifuge at 6000 r / min for 5 min. Finally, dry at 80 °C overnight to obtain the sample.

[0046] The dried sample was evenly spread in a ceramic boat, which was then placed in the isothermal zone of a tube furnace. Under a nitrogen atmosphere, the sample was heated to 200 °C at a heating rate of 3 °C / min and held for 4 hours to obtain the Ni3-Co1 / MOF catalyst.

[0047] The prepared Ni3-Co1 / MOF catalyst and quartz sand were mixed and uniformly filled into the discharge region of the low-temperature plasma reactor. Nitrogen and water vapor were introduced into the reactor inlet, and the discharge conditions were adjusted to start the discharge. The length of the discharge region was 75 mm and the discharge gap was 2 mm, so that the raw material gas could undergo a catalytic reaction on the surface of Ni3-Co1 / MOF and quartz sand to generate NH3.

[0048] Figure 1 The X-ray diffraction pattern of the Ni3-Co1 / MOF catalyst prepared in Example 1 of this invention is shown below. Figure 1 As shown, the X-ray diffraction pattern of the Ni3-Co1 / MOF nanocomposite material prepared in Example 1 matches CCDC number 985792, confirming that Ni-Co / MOF has been successfully synthesized.

[0049] Figure 2 The image shown is a scanning electron microscope (SEM) image of the Ni3-Co1 / MOF catalyst prepared in Example 1 of this invention; Figure 2 As shown, the Ni3-Co1 / MOF catalyst is a smooth and uniform nanorod.

[0050] Figure 4 The stability diagram is shown for the Ni3-Co1 / MOF catalyst prepared in Example 1 of this invention. Figure 4 The Ni3-Co1 / MOF catalyst demonstrated good stability over 48 hours, long-term durability, and excellent catalytic performance, indicating its broad application prospects.

[0051] Example 2 The difference between this embodiment and Example 1 is that 3.31 mmol of Co(NO3)2·6H2O was weighed as a metal salt to prepare Co / MOF materials for catalytic reaction.

[0052] Example 3 The difference between this embodiment and Example 1 is that 3.31 mmol of Ni(NO3)2·6H2O was weighed as a metal salt to prepare Ni / MOF materials for catalytic reaction.

[0053] Example 4 The difference between this embodiment and Example 1 is that 1.65 mmol and 1.65 mmol of Ni(NO3)2·6H2O and Co(NO3)2·6H2O were weighed as metal salts to prepare Ni1-Co1 / MOF materials for catalytic reaction.

[0054] Example 5 The difference between this embodiment and Example 1 is that 2.2 mmol and 1.1 mmol of Ni(NO3)2·6H2O and Co(NO3)2·6H2O were weighed as metal salts to prepare Ni2-Co1 / MOF materials for catalytic reaction.

[0055] Example 6 The difference between this embodiment and Example 1 is that 2.64 mmol and 0.66 mmol of Ni(NO3)2·6H2O and Co(NO3)2·6H2O were weighed as metal salts to prepare Ni4-Co1 / MOF material for catalytic reaction.

[0056] Example 7 This embodiment only performs the ammonia synthesis reaction under single plasma conditions.

[0057] To further verify the technical effect of the present invention, the ammonia synthesis rate and energy efficiency of the plasma catalytic system in Examples 1-7 were shown in Table 1 when the discharge power was 50 W, the total flow rate was 1 L / min, and the water vapor concentration was set to 4.73 vol%.

[0058] Example 8 A method for synthesizing ammonia using a low-temperature plasma-coupled Ni-Co / MOF catalyst includes the following steps: Weigh 2.48 mmol and 0.83 mmol of Ni(NO3)2·6H2O and Co(NO3)2·6H2O, respectively, and dissolve 3 mmol of terephthalic acid and 3 mmol of triethylenediamine in 40 mL of N,N-dimethylformamide (DMF) and stir continuously for 2 h. Transfer the mixture to the liner of the reaction vessel, place it in the reaction vessel shell and tighten it, and finally place it in an oven at 160 °C for 20 h. Wash the solution with DMF and methanol until it is clear and free of impurities, and centrifuge at 8000 r / min for 3 min. Finally, dry at 100 °C overnight to obtain the sample.

[0059] The dried sample was evenly spread in a ceramic boat, which was then placed in the isothermal zone of a tube furnace. Under an argon atmosphere, the sample was heated to 100 °C at a heating rate of 1 °C / min and held for 2 hours to obtain the Ni3-Co1 / MOF catalyst.

[0060] The prepared Ni3-Co1 / MOF catalyst and quartz sand were uniformly mixed and filled into the discharge region of the low-temperature plasma reactor (the discharge region length was 50 mm and the discharge gap was 1 mm). Nitrogen gas and water vapor (water vapor volume concentration was 1 vol%) were introduced into the reactor inlet, and the discharge conditions were adjusted to start the discharge. The discharge power was 50 W and the total flow rate was 1 L / min, so that the raw material gas could undergo a catalytic reaction on the surface of Ni3-Co1 / MOF and quartz sand to generate NH3.

[0061] Example 9 A method for synthesizing ammonia using a low-temperature plasma-coupled Ni-Co / MOF catalyst includes the following steps: Weigh 2.48 mmol and 0.83 mmol of Ni(NO3)2·6H2O and Co(NO3)2·6H2O, respectively, and dissolve 5 mmol of terephthalic acid and 5 mmol of triethylenediamine in 60 mL of N,N-dimethylformamide (DMF) and stir continuously for 2.5 h. Transfer the mixture to the liner of the reaction vessel, place it in the reaction vessel shell and tighten it, and finally place it in an oven at 180 °C for 10 h. Wash with ethanol until the solution is clear and free of impurities, and centrifuge at 7000 r / min for 4 min. Finally, dry at 90 °C overnight to obtain the sample.

[0062] The dried sample was evenly spread in a ceramic boat, which was then placed in the isothermal zone of a tube furnace. Under a nitrogen atmosphere, the sample was heated to 300 °C at a heating rate of 5 °C / min and held for 3 hours to obtain the Ni3-Co1 / MOF catalyst.

[0063] The prepared Ni3-Co1 / MOF catalyst and quartz sand were uniformly mixed and filled into the discharge region of the low-temperature plasma reactor (the discharge region length was 100 mm and the discharge gap was 3 mm). Nitrogen gas and water vapor (water vapor volume concentration was 10 vol%) were introduced into the reactor inlet, and the discharge conditions were adjusted to start the discharge. The discharge power was 50 W and the total flow rate was 1 L / min, so that the raw material gas could undergo a catalytic reaction on the surface of Ni3-Co1 / MOF and quartz sand to generate NH3.

[0064] Example 10 A method for synthesizing ammonia using a low-temperature plasma-coupled Ni-Co / MOF catalyst includes the following steps: Weigh 0.83 mmol and 2.48 mmol of Ni(NO3)2·6H2O and Co(NO3)2·6H2O (i.e., Ni:Co = 1:3), and dissolve 4 mmol of terephthalic acid and 4 mmol of triethylenediamine in 50 mL of N,N-dimethylformamide (DMF) and stir continuously for 3 h. Transfer the mixture to the liner of the reactor, place it in the reactor shell and tighten it, and finally place it in an oven at 170 °C for 16 h. Wash with DMF until the solution is clear and free of impurities, and centrifuge at 6000 r / min for 5 min. Finally, dry at 80 °C overnight to obtain the sample.

[0065] The dried sample was evenly spread in a ceramic boat, which was then placed in the isothermal zone of a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200 °C at a rate of 3 °C / min and held for 4 hours to obtain the Ni1-Co3 / MOF catalyst.

[0066] The prepared Ni1-Co3 / MOF catalyst and quartz sand were uniformly mixed and filled into the discharge region of the low-temperature plasma reactor (discharge region length was 75 mm, discharge gap was 2 mm). Nitrogen gas and water vapor (water vapor volume concentration was 5 vol%) were introduced into the reactor inlet, and the discharge conditions were adjusted to start the discharge. The discharge power was 50 W and the total flow rate was 1 L / min, so that the raw gas could undergo a catalytic reaction on the surface of Ni1-Co3 / MOF and quartz sand to generate NH3.

[0067] Table 1. Ammonia synthesis rates and energy efficiencies for different Ni-Co / MOF catalysts.

[0068] Table 1 shows the ammonia synthesis rate and energy efficiency corresponding to different Ni-Co / MOF catalysts; Figure 3 The following is a performance comparison chart of embodiments 1-7 of the present invention; from Table 1 and Figure 3 It is evident that the Ni3-Co1 / MOF catalyst outperforms catalysts with other ratios. This invention successfully achieved synergistic enhancement between the bimetallic MOF catalyst and plasma by adjusting the Ni / Co bimetallic ratio. An appropriate Ni / Co ratio (3:1) can maximize the electronic and structural synergistic effects between the bimetals, thereby significantly improving the ammonia synthesis rate and energy efficiency.

[0069] In summary, this invention discloses a bimetallic Ni-Co / MOF catalyst for ammonia synthesis, its preparation method, and its application, belonging to the field of ammonia synthesis technology. The method includes: (1) synthesizing a bimetallic Ni-Co / MOF precursor by hydrothermal method, followed by activation under an inert atmosphere to obtain a Ni-Co / MOF catalyst, wherein the electronic structure of the catalyst is optimized by adjusting the molar ratio of Ni to Co; (2) mixing the obtained catalyst with quartz sand and filling it into the discharge zone of a dielectric barrier discharge (DBD) plasma reactor, introducing nitrogen and water vapor as raw materials, and catalytically synthesizing ammonia under discharge conditions. This invention significantly enhances the activity of the catalyst through the bimetallic synergistic effect, solving the problems of insufficient activity of single metal catalysts and low efficiency of single plasma systems. When the preferred Ni:Co molar ratio is 3:1, the ammonia synthesis rate can reach 3.67 mmol·g. cat -1 ·h -1 Energy efficiency reaches 0.131 g·kW -1 ·h -1 This provides a new approach for green, low-energy ammonia synthesis.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a bimetallic Ni-Co / MOF catalyst for ammonia synthesis, characterized in that, include: Nickel salt, cobalt salt, terephthalic acid and triethylenediamine were dissolved in an organic solvent, mixed and stirred evenly, and then activated under an inert atmosphere after hydrothermal reaction, washing and drying to obtain the Ni-Co / MOF catalyst.

2. The method for preparing the bimetallic Ni-Co / MOF catalyst for ammonia synthesis according to claim 1, characterized in that, Add 3-5 mmol of terephthalic acid and 3-5 mmol of triethylenediamine to every 40-60 mL of organic solvent; the molar ratio of the nickel salt to the cobalt salt is (0-4):(0-4).

3. The method for preparing the bimetallic Ni-Co / MOF catalyst for ammonia synthesis according to claim 1, characterized in that, In the nickel salt and cobalt salt, the molar ratio of Ni to Co is (1~4):

1.

4. The method for preparing the bimetallic Ni-Co / MOF catalyst for ammonia synthesis according to claim 1, characterized in that, The nickel salt is Ni(NO3)2·6H2O; the cobalt salt is Co(NO3)2·6H2O; the organic solvent is N,N-dimethylformamide; The solvent used for washing is one or two of N,N-dimethylformamide, methanol, and ethanol; the washing is performed by centrifugation at 6000-8000 r / min for 3-5 min; the drying conditions are overnight drying at 80-100 ℃.

5. The method for preparing the bimetallic Ni-Co / MOF catalyst for ammonia synthesis according to claim 1, characterized in that, The mixing and stirring time is 2-3 h; the hydrothermal reaction temperature is 160-180 ℃, and the hydrothermal reaction time is 10-20 h.

6. The method for preparing the bimetallic Ni-Co / MOF catalyst for ammonia synthesis according to claim 1, characterized in that, The activation involves heating to 100-300℃ at a rate of 1-5℃ / min and maintaining that temperature for 2-4 hours; the inert atmosphere is nitrogen or argon.

7. A bimetallic Ni-Co / MOF catalyst for ammonia synthesis, characterized in that, It was prepared using the method described in any one of claims 1-6 for the preparation of a bimetallic Ni-Co / MOF catalyst for ammonia synthesis.

8. The application of the bimetallic Ni-Co / MOF catalyst for ammonia synthesis as described in claim 7 in plasma-assisted ammonia synthesis.

9. The application of the bimetallic Ni-Co / MOF catalyst for ammonia synthesis according to claim 8 in plasma-assisted ammonia synthesis, characterized in that, The bimetallic Ni-Co / MOF catalyst for ammonia synthesis is mixed with quartz sand and placed in the discharge region of a low-temperature plasma reactor. Raw material gas is introduced, and plasma discharge is initiated to carry out the ammonia synthesis reaction.

10. The application of the bimetallic Ni-Co / MOF catalyst for ammonia synthesis according to claim 8 in plasma-assisted ammonia synthesis, characterized in that, The raw material gas is nitrogen and water vapor; the low-temperature plasma reactor is a coaxial cylindrical dielectric barrier discharge reactor with a discharge region length of 50-100 mm and a discharge gap of 1-3 mm; the volume concentration of water vapor in the raw material gas is 1-10 vol.

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