Graphite carbon modified ruthenium-based catalyst, preparation method thereof and application of graphite carbon modified ruthenium-based catalyst in ammonia synthesis

Abstract

The invention provides a preparation method of a graphite carbon (GC) modified ruthenium-based catalyst and application of the catalyst in ammonia synthesis. The GC-K-Ru / MgO catalyst is obtained by firstly loading graphite carbon on an MgO carrier and then impregnating and loading Ru and K. Wherein the metal Ru is an active center, and the K and the GC are auxiliaries. Graphite carbon not only can promote high dispersion of Ru and reduce the particle size of Ru, but also can promote K to transfer electrons to Ru, accelerate N2 activation and improve the low-temperature and low-pressure ammonia synthesis performance. The ammonia synthesis activity of the catalyst reaches 18.1 mmol g <-1 > h <-1 > at 400 DEG C and 1 MPa, and is about 22 times of that of a Ru / MgO catalyst. The invention provides a new thought for improving the synthesis ammonia performance of the Ru-based catalyst by adopting cheap graphite carbon, and the catalyst is relatively simple and convenient in preparation method, easy to form and beneficial to industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of synthetic ammonia and its catalyst, and specifically relates to a graphite carbon modified ruthenium-based catalyst, a preparation method thereof and application in synthetic ammonia. Background Art

[0002] Ammonia is the basic raw material for modern fertilizer production and an important guarantee for global agricultural production and food security. Ammonia is not only the core component of nitrogen fertilizer, but also widely used in industrial fields, such as refrigerants, explosives, plastics and the synthesis of many chemical products. In recent years, it has been considered as a carbon-free fuel and hydrogen storage carrier with good prospects. The global demand for ammonia is very huge, with an annual output of about 170 million tons of synthetic ammonia, of which more than 96% is produced through the Haber-Bosch Process. This reaction process combines nitrogen (N2) in the air with hydrogen (H2) generated by the cracking of methane (CH4) from fossil fuels (such as natural gas) through an iron-based catalyst under high temperature (400–500 °C) and high pressure (≥150 bar) conditions to further synthesize ammonia. The whole process includes three stages: hydrogen production, ammonia synthesis, and ammonia separation. The energy consumption of this process is extremely huge, accounting for about 2% of global energy use. Moreover, the carbon dioxide emissions produced by this process account for 1.2% of the world’s total greenhouse gas emissions, which not only exacerbates climate change but also aggravates the global environmental crisis.

[0003] How to reduce carbon emissions during ammonia synthesis has become one of the current research focuses. It is very necessary to develop a distributed, economical and renewable energy ammonia synthesis technology that can operate under mild conditions. Use renewable energy (wind, solar, etc.) to generate electricity, and use it to electrolyze water to produce hydrogen. The resulting hydrogen is used as a raw material for synthesizing ammonia. This process is called the electrolysis-driven Haber-Bosch (eHB) process. Unlike traditional processes, the eHB process uses electrolysis of water to produce hydrogen, avoiding the large-scale use of fossil energy, and is expected to achieve low-carbon or even zero-carbon emissions. By developing this process, it is possible to simultaneously achieve clean and efficient utilization of renewable energy, "green ammonia" synthesis, and safe storage and transportation of hydrogen.

[0004] However, the eHB process still faces some technical challenges. For example, the hydrogen output pressure of the current water electrolysis hydrogen production system is relatively low (generally 1.6~3.2 MPa), and the temperature of the H2 obtained by electrolysis after deep dehydration and deoxygenation is about 300~350 ℃. The existing industrial Fe-based catalysts based on fossil resources are difficult to meet the requirements at this temperature. Their catalytic performance is poor at low temperatures, and the high-temperature nitrogen dissociation will lead to high energy consumption, which is inconsistent with the low-carbon goal of the eHB process. Therefore, in order to achieve the complementary integration of synthetic ammonia technology and renewable energy power electrolysis hydrogen production system, it is urgent to develop a relatively mild synthetic ammonia technology (reaction conditions: ≤ 400 ℃ and 1 MPa). The key is to design ammonia synthesis catalysts that maintain high catalytic performance under low temperature and low pressure conditions.

[0005] Compared with traditional Fe-based catalysts, Ru-based catalysts show better ammonia synthesis activity under low temperature and low pressure conditions, making them ideal candidate catalysts for the eHB process. The high d orbital electron density of Ru-based catalysts can well promote the dissociation of N2 molecules and improve the catalytic efficiency of the ammonia synthesis reaction. Although Ru-based catalysts have been studied for many years, how to develop low-cost and efficient Ru catalysts remains one of the challenges in current research. Summary of the invention

[0006] The present invention aims to provide a graphite carbon (GC) modified Ru-based catalyst with low metal loading and high catalytic performance under mild conditions, and provides a corresponding preparation method and application in synthetic ammonia.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: A graphite carbon modified ruthenium-based catalyst GC-K-Ru / MgO, wherein the ruthenium-based catalyst uses metal ruthenium as an active component, uses MgO as a carrier, and uses potassium and graphite carbon as additives, wherein the loading amount of potassium is 1.0-9.0 wt.%, the loading amount of graphite carbon is 2.5-20 wt.%, and the loading amount of metal ruthenium is 0.2-3.0%.

[0008] The preparation method of the above-mentioned graphite carbon modified ruthenium-based catalyst GC-K-Ru / MgO comprises the following steps: (1) Mixing a sodium hydroxide solution and a magnesium chloride solution and heating them for 24 hours to obtain a white product, which is then calcined at high temperature in a muffle furnace to obtain a MgO carrier; the concentration of the magnesium chloride solution is 3.9 mg / mL, and the concentration of the sodium hydroxide is 15.8 mg / mL; (2) adding MgO carrier and graphite carbon to a solvent, mixing and heating to dry, and then calcining in an inert atmosphere to obtain a black powder; (3) The ruthenium precursor and the potassium precursor are successively impregnated onto the black powder, and the catalyst is obtained by high-temperature reduction using a reducing gas.

[0009] Furthermore, the heating temperature in step (1) is 180°C, the high temperature calcination temperature is 400-500°C, and the calcination time is 1-3 h.

[0010] Furthermore, in step (2), the mass ratio of the graphite carbon to the MgO carrier is 0.01-0.25.

[0011] Furthermore, the solvent is selected from one or more of deionized water, ethylene glycol, ethanol and glycerol.

[0012] Furthermore, the calcination temperature in step (2) is 500°C, the inert atmosphere is one of argon, helium or nitrogen; the reducing gas is H2 or H2 / Ar with a volume ratio of 1:9, the reduction temperature is 400-500°C, and the reduction time is 2-6h.

[0013] Furthermore, the ruthenium precursor in step (3) is one or more of ruthenium nitrosyl nitrate, ammonium hexachlororuthenate, ruthenium trichloride, triruthenium dodecacarbonyl, metallic ruthenium, and ruthenium acetylacetonate, preferably ruthenium nitrosyl nitrate.

[0014] Furthermore, the potassium precursor in step (3) is one or more of potassium nitrate, potassium chloride, potassium hydroxide, potassium carbonate, potassium perchlorate, and potassium fluoride, preferably potassium nitrate.

[0015] The above-mentioned graphite carbon modified ruthenium-based catalyst GC-K-Ru / MgO is used in the synthesis of ammonia. The catalyst is used for low-temperature and low-pressure synthesis of ammonia. The reaction temperature of the synthesis of ammonia is 300~400 °C; the reaction pressure is 0.1~1MPa.

[0016] In the present invention, the loading amount refers to the weight of metal Ru and K relative to the catalyst. Taking 5 wt.% K as an example, the weight of metal K is 5 parts relative to 100 parts by weight of the catalyst.

[0017] Compared with the prior art, the beneficial effects of the solution of the present invention are: (1) The present invention provides a new idea for graphite carbon modified Ru-based ammonia synthesis catalyst, which utilizes the good conductivity of graphite carbon to improve the electron donating effect of K additive. Graphite carbon can also promote hydrogen species transfer, alleviate hydrogen poisoning of Ru particles, and improve ammonia synthesis performance.

[0018] (2) The graphite carbon modified Ru catalyst prepared by the present invention has a superior ammonia synthesis reaction rate and good thermal stability compared with the traditional Ru-based catalyst. The catalyst preparation method provided by the present invention is relatively simple, the catalyst yield is high, and there is potential for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The high-resolution transmission electron microscope images and particle size images of Example 1 and Comparative Example 1 are shown.

[0020] Figure 2 These are the XRD results of the catalysts obtained in Example 1, Example 2 (5GC-K-Ru / MgO, 10GC-K-Ru / MgO, 20GC-K-Ru / MgO) and Comparative Example 1.

[0021] Figure 3 The Raman results of the catalysts obtained in Example 1, Example 2 (5GC-K-Ru / MgO, 10GC-K-Ru / MgO, 20GC-K-Ru / MgO) and Comparative Example 1 are shown.

[0022] Figure 4 The ammonia synthesis performance of the catalysts obtained in Example 1, Example 2 and Comparative Example 1 at 400°C and 1 MPa.

[0023] Figure 5 It is the activation energy of the catalysts obtained in Example 1, Example 2 (10GC-K-Ru / MgO, 20GC-K-Ru / MgO) and Comparative Example 1. DETAILED DESCRIPTION

[0024] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary illustrations 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 included in the scope that the present invention is intended to protect.

[0025] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0026] Example 1 Preparation of 15GC-K-Ru / MgO Catalyst (1) 3.0 g MgCl2·6H2O and 1.2 g NaOH were dissolved in 76 mL of a mixed solution of deionized water and ethanol (1:1 v / v) to obtain a NaOH solution and a MgCl2 solution. The NaOH solution was slowly dripped into the MgCl2 solution and stirred for 2 h. The resulting suspension was transferred to a stainless steel autoclave and reacted at 180 °C for 24 h. The white liquid was washed several times with deionized water until the filtrate was neutral and then dried at 60 °C for 24 h. Finally, the white solid powder was calcined at 450 °C in a muffle furnace for 2 h to obtain a MgO support.

[0027] (2) The MgO carrier (0.25 g) and GC (0.0375 g) prepared in step (1) were added to a mixed solution of 15 ml of ionized water and 15 ml of ethanol, and stirred on a magnetic stirrer at 60 °C for 12 h until dry to obtain a black powder, which was then calcined at 500 °C in an argon atmosphere for 2 h.

[0028] (3) Take 0.47 ml of ruthenium nitrate aqueous solution (16.2 mg / ml) and potassium nitrate (0.034 g) dissolved in 3 ml of deionized water, impregnate it on the black powder in step (2), and then reduce it at 400℃ for 2 h in H2 / Ar (1:9) atmosphere. The final catalyst is recorded as 15GC-K-Ru / MgO. The mass of the metal Ru active component is 1.8wt.% of the catalyst mass determined by ICP, the mass of the K promoter is 5.0wt.% of the catalyst mass, and the mass of GC is 15wt.% of the catalyst mass.

[0029] Example 2 Preparation of K-Ru / MgO catalysts with different GC loadings The other preparation steps were the same as those in Example 1, except that the mass of graphite carbon in step (2) was changed to 0.00625 g, 0.0125 g, 0.025 g, and 0.05 g, respectively, to obtain catalysts 2.5GC-K-Ru / MgO, 5GC-K-Ru / MgO, 10GC-K-Ru / MgO, and 20GC-K-Ru / MgO, respectively. The loading amounts are shown in Table 1.

[0030] Example 3 Preparation of 15GC-Ru / MgO Catalysts with Different K Contents (1) 3.0 g MgCl2·6H2O and 1.2 g NaOH were dissolved in 76 mL of a mixed solution of deionized water and ethanol (1:1 v / v) to obtain a NaOH solution and a MgCl2 solution. The NaOH solution was slowly dripped into the MgCl2 solution and stirred for 2 h. The resulting suspension was transferred to a stainless steel autoclave and reacted at 180 °C for 24 h. The white liquid was washed several times with deionized water until the filtrate was neutral and then dried at 60 °C for 24 h. Finally, the white solid powder was calcined at 450 °C in a muffle furnace for 2 h to obtain a MgO support.

[0031] (2) Take 0.25 g MgO and 0.0375 g GC in a beaker, add 15 ml ionized water and 15 ml ethanol to form a mixed solution, add a magnet and stir on a magnetic stirrer at 60 °C until dry, and obtain a black powder, which is calcined at 500 °C in an argon atmosphere for 2 h. Perform the same operation twice more to prepare three portions of black powder with the same composition.

[0032] (3) Potassium nitrate (0.007 g, 0.022 g, 0.051 g) solution dissolved in 3 ml of deionized water and 0.47 ml of ruthenium nitrate aqueous solution (16.2 mg / ml) were respectively taken and impregnated on the black powder in step (2). After reduction at 400 °C for 2 h in a H2 / Ar (1:9) atmosphere, Ru catalysts with different K contents were obtained, named 15GC-1K-Ru / MgO, 15GC-3K-Ru / MgO, and 15GC-7K-Ru / MgO. The mass of the metal Ru active component was 1.8 wt.% of the catalyst mass by ICP determination, and the mass of the K promoter was 1.0 wt.%, 3.0 wt.%, and 7.0 wt.% of the catalyst mass, respectively.

[0033] Example 4 Preparation of 15GC-K-Ru / MgO Catalysts with Different Ru Contents (1) 3.0 g MgCl2·6H2O and 1.2 g NaOH were dissolved in 76 mL of a mixed solution of deionized water and ethanol (1:1 v / v) to obtain a NaOH solution and a MgCl2 solution. The NaOH solution was slowly dripped into the MgCl2 solution and stirred for 2 h. The resulting suspension was transferred to a stainless steel autoclave and reacted at 180 °C for 24 h. The white liquid was washed several times with deionized water until the filtrate was neutral and then dried at 60 °C for 24 h. Finally, the white solid powder was calcined at 450 °C in a muffle furnace for 2 h to obtain a MgO support.

[0034] (2) MgO carrier (0.25 g) and GC (0.0375 g) were placed in a beaker, 15 ml of ionized water and 15 ml of ethanol were added to form a mixed solution, a magnetic bar was added and the mixture was stirred on a magnetic stirrer at 60 °C until dry to obtain a black powder, which was then calcined at 500 °C in an argon atmosphere for 2 h. The same operation was repeated three times to prepare four portions of black powder with the same composition.

[0035] (3) 0.20 ml, 0.33 ml, 0.59 ml, and 0.66 ml of ruthenium nitrate aqueous solution (16.2 mg / ml) and potassium nitrate (0.033 g) solution dissolved in 3 ml of deionized water were respectively taken and impregnated on the black powder in step (2). After reduction at 400 °C for 2 h in a hydrogen atmosphere, catalysts with different Ru contents were obtained, which were named 15GC-5K-0.2Ru / MgO, 15GC-5K-1Ru / MgO, 15GC-5K-2.6Ru / MgO, and 15GC-5K-3.0Ru / MgO. The mass of the metal Ru active component was determined by ICP to be 0.2 wt.%, 1.0 wt.%, 2.6 wt.%, and 3.0 wt.% of the catalyst mass, respectively, and the mass of the K promoter was 5.0 wt.% of the catalyst mass.

[0036] Comparative Example 1 Preparation of K-Ru / MgO Catalyst (1) 3.0 g MgCl2·6H2O and 1.2 g NaOH were dissolved in 76 mL of a mixed solution of deionized water and ethanol (1:1 v / v) to obtain a NaOH solution and a MgCl2 solution. The NaOH solution was slowly dripped into the MgCl2 solution and stirred for 2 h. The resulting suspension was transferred to a stainless steel autoclave and reacted at 180 °C for 24 h. The white liquid was washed several times with deionized water until the filtrate was neutral and then dried at 60 °C for 24 h. Finally, the white solid powder was calcined at 450 °C in a muffle furnace for 2 h to obtain a MgO support.

[0037] (2) Take 0.35 g of the magnesium oxide obtained in step (1) and calcine it in a tube furnace at 500 °C in an argon atmosphere for two hours. Take potassium nitrate (0.055 g) dissolved in 3 ml of deionized water and 0.665 ml of ruthenium nitrate aqueous solution (19.2 mg / ml), impregnate it on MgO, and reduce it in a hydrogen atmosphere at 400 °C for 2 h to obtain a K-Ru / MgO catalyst. The mass of the metal Ru active component determined by ICP is 1.8 wt.% of the catalyst mass, and the mass of the K promoter is 5.0 wt.% of the catalyst mass.

[0038] Comparative Example 2 Preparation of Ru / MgO catalyst The other preparation steps are the same as those in Comparative Example 1, but in step (2), only ruthenium nitrate aqueous solution is impregnated to obtain a Ru / MgO catalyst. The mass of the metal Ru active component is 1.8 wt.% of the catalyst mass as determined by ICP.

[0039] Comparative Example 3 Preparation of K-Ru / MgO Catalyst Promoted by Carbon Black (1) 3.0 g MgCl2·6H2O and 1.2 g NaOH were dissolved in 76 mL of a mixed solution of deionized water and ethanol (1:1 v / v) to obtain a NaOH solution and a MgCl2 solution. The NaOH solution was slowly dripped into the MgCl2 solution and stirred for 2 h. The resulting suspension was transferred to a stainless steel autoclave and reacted at 180 °C for 24 h. The white liquid was washed several times with deionized water until the filtrate was neutral and then dried at 60 °C for 24 h. Finally, the white solid powder was calcined at 450 °C in a muffle furnace for 2 h to obtain a MgO support.

[0040] (2) Take 0.0175 g carbon black and 0.35 g MgO, 0.035 g carbon black and 0.35 g MgO in a beaker, add 10 ml of deionized water and 10 ml of ethanol respectively to form a mixed solution, add a magnet and stir on a magnetic stirrer at 60 °C until dry to obtain a black powder, which is then calcined at 500 °C in an argon atmosphere for 2 h.

[0041] (3) Potassium nitrate (0.048 g) and 0.586 ml of ruthenium nitrate aqueous solution (19.2 mg / ml) dissolved in 3 ml of deionized water were taken and impregnated onto the black powder in step (2). After reduction at 400 °C for 2 h in a 10H2 / Ar atmosphere, Ru catalysts with different carbon black contents were obtained, which were named 5C-K-Ru / MgO and 10C-K-Ru / MgO. The mass of the metal Ru active component in 5C-K-Ru / MgO was 1.8 wt.% of the mass of the catalyst by ICP measurement, and the mass of the K promoter was 5.0 wt.% of the mass of the catalyst. The mass of the metal Ru active component in 10C-K-Ru / MgO was 1.8 wt.% of the mass of the catalyst, and the mass of the K promoter was 5.0 wt.% of the mass of the catalyst.

[0042] Figure 1 The high-resolution transmission electron micrographs of the catalysts prepared in Example 1 and Comparative Example 1 and the corresponding particle size statistics of the ruthenium particles, wherein a represents the catalyst prepared in Example 1 and b represents the catalyst prepared in Comparative Example 1. It can be seen from the figure that the ruthenium particle sizes of the 15GC-K-Ru / MgO and K-Ru / MgO catalysts are 1.7 nm and 2.7 nm, respectively. This indicates that the addition of graphite carbon can reduce the particle size of Ru.

[0043] Figure 2 The XRD test results of Example 1, Example 2 and Comparative Example 1 are shown. It can be seen from the figure that the diffraction peaks are attributed to MgO and GC, indicating that GC is successfully doped into the MgO carrier; at the same time, the figure does not show the metal characteristic peaks of Ru and K, indicating that Ru and K species are highly dispersed in the catalyst.

[0044] Figure 3 The Raman results of the catalysts obtained in Example 1, Example 2 and Comparative Example 1 are shown in Figure 1. The catalyst with GC added has a Raman peak at 1344 cm -1 and 1578 cm -1 Two peaks appeared near the catalyst, which belonged to disordered (D-type) carbon and graphite (G-type) carbon species, respectively. The catalyst without GC added obtained in Comparative Example 1 did not show a peak shape, indicating that the catalyst with GC added had a good degree of graphitization. The intensity ratio of the G peak and the D peak of the catalyst with GC added was calculated (reflecting the degree of graphitization of the carbon material), and the results were found to be similar, indicating that the prepared catalysts had similar structural properties.

[0045] Application Example 1 Performance Evaluation of Ammonia Synthesis Catalyst Take 0.20 g of the catalyst of the comparative example and the embodiment, set the mass space velocity to 60,000 ml·g⁻¹·h⁻¹, and measure the ammonia synthesis rate in a continuous flow micro fixed bed reactor. The concentration change of NH3 in the outlet tail gas is analyzed by ion chromatograph (Thermo Scientific, DIONEX, ICS-600). The composition of the reaction gas is: 75 vol% H2 and 25 vol% N2. The experiment was carried out at 400 ℃ and 1 MPa to measure the ammonia synthesis rate of the catalyst.

[0046] Figure 4 The ammonia synthesis performance of the catalysts obtained from Example 1, Example 2 and Comparative Example 1 at 400 °C and 1 MPa. The results show that as the graphite carbon content increases from 0 wt.% to 20 wt.%, the ammonia synthesis rate of the catalyst first increases and then decreases, presenting a volcano-shaped curve. When the graphite carbon addition amount is 15 wt.%, the ammonia synthesis rate is the highest, which is 18.1 mmolg cat -1 h -1 This indicates that the doping of graphite carbon has a good promoting effect on the K-Ru / MgO catalyst.

[0047] Figure 5 The activation energy curves of the catalysts obtained in Example 1, Example 2 (10GC-K-Ru / MgO, 20GC-K-Ru / MgO) and Comparative Example 1 were measured at 1 MPa and different temperatures. It shows that the activation energy of the 15GC-K-Ru / MgO catalyst is 103.2 kJmol -1 , and the activation energy of the catalyst with GC added is lower than that of the catalyst obtained in Comparative Example 1. This shows that the addition of GC is beneficial to ammonia synthesis.

[0048] Table 1 shows the ammonia synthesis performance test results of the catalysts prepared in Examples 1-4 and Comparative Examples 1-3.

[0049] Table 1. Ammonia synthesis performance of different catalysts at 400 °C When the reaction pressure of No. 1-2 increased from normal pressure to 1.0 MPa, the ammonia synthesis rate of 15GC-K-Ru / MgO increased from 14.8 to 18.1 mmol g -1 h -1 , indicating that the catalyst also performs well in ammonia synthesis rate under normal pressure. From No. 1, 3, 4, 5, and 6, it can be seen that with the increase of graphite carbon content, the ammonia synthesis rate first increases and then decreases, reaching the highest value when the carbon content is 15 wt.%. Then the K content is changed. From No. 1, 7, 8, and 9, it can be seen that when the K loading increases from 1.0 wt% to 7.0 wt%, the ammonia synthesis rate of the catalyst first increases and then decreases, reaching a peak when the K loading is 5.0 wt%. From No. 1, 10, 11, 12, and 13, the graphite carbon and K content are kept unchanged, and the ammonia synthesis rate of the catalyst is increased when the Ru content is increased. No. 14 and 15 show that when graphite carbon is replaced with carbon black, the catalyst does not improve compared with the K-Ru / MgO catalyst, indicating that adding graphite carbon can improve the performance of ammonia synthesis, which may be related to the good conductivity of graphite carbon and the promotion of K to transfer electrons. Comparison between serial numbers 16 and 17 and other serial numbers shows that serial numbers 1-9 of the present application have significantly higher reaction activity, proving that the GC and K additives of the present invention interact with each other and exhibit higher synthetic ammonia activity under mild conditions.

[0050] The above is a description of the exemplary embodiments of the present invention. However, the protection scope 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 should be included in the protection scope of the present invention.

Claims

1. A graphite carbon modified ruthenium-based catalyst GC-K-Ru / MgO, characterized in that: The ruthenium-based catalyst uses metallic ruthenium as an active component, MgO as a carrier, potassium and graphite carbon as additives, the loading amount of potassium is 1.0-9.0 wt.%, the loading amount of graphite carbon is 2.5-20 wt.%, and the loading amount of metallic ruthenium is 0.2-3.0%.

2. The method for preparing the graphite carbon modified ruthenium-based catalyst GC-K-Ru / MgO according to claim 1, characterized in that: The steps include: (1) Mixing a sodium hydroxide solution and a magnesium chloride solution and heating them for 24 hours to obtain a white product, which is then calcined at high temperature in a muffle furnace to obtain a MgO carrier; the concentration of the magnesium chloride solution is 3.9 mg / mL, and the concentration of the sodium hydroxide is 15.8 mg / mL; (2) adding MgO carrier and graphite carbon to a solvent, mixing and heating to dry, and then calcining in an inert atmosphere to obtain a black powder; (3) The ruthenium precursor and the potassium precursor are successively impregnated onto the black powder, and the catalyst is obtained by high-temperature reduction using a reducing gas.

3. The preparation method according to claim 2, characterized in that: The heating temperature in step (1) is 180°C, the high temperature calcination temperature is 400-500°C, and the calcination time is 1-3 h.

4. The preparation method according to claim 2, characterized in that: In step (2), the mass ratio of the graphite carbon to the MgO carrier is 0.01-0.

25.

5. The preparation method according to claim 2, characterized in that: The solvent is selected from one or more of deionized water, ethylene glycol, ethanol and glycerol.

6. The preparation method according to claim 2, characterized in that: The calcination temperature in step (2) is 500°C, the inert atmosphere is one of argon, helium or nitrogen; the reducing gas is H2 or H2 / Ar with a volume ratio of 1:9, the reduction temperature is 400-500°C, and the reduction time is 2-6 h.

7. The preparation method according to claim 2, characterized in that: The ruthenium precursor in step (3) is one or more of ruthenium nitrosyl nitrate, ammonium hexachlororuthenate, ruthenium trichloride, triruthenium dodecacarbonyl, metallic ruthenium, and ruthenium acetylacetonate.

8. The preparation method according to claim 2, characterized in that: The potassium precursor in step (3) is one or more of potassium nitrate, potassium chloride, potassium hydroxide, potassium carbonate, potassium perchlorate, and potassium fluoride.

9. The use of the graphite carbon modified ruthenium-based catalyst GC-K-Ru / MgO in synthetic ammonia according to claim 1, characterized in that: The reaction temperature for synthesizing ammonia is 300~400 °C; the reaction pressure is 0.1~1 MPa.

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