Ruthenium-based amine synthesis catalysts, methods of making and using the same

Abstract

The application discloses a ruthenium-based ammonia synthesis catalyst and a preparation method and application thereof. The method comprises the following steps: step 1, acid treatment and alkali treatment are carried out on cyanamide waste residues; step 2, ball milling treatment is carried out on the waste residues treated in the step 1, and the material after the ball milling is calcined under an inert atmosphere; and step 3, the product after the calcination in the step 2 is mixed with a ruthenium source and an additive and is ball milled to obtain the ruthenium-based ammonia synthesis catalyst; and the mass content of calcium oxide in the ruthenium-based ammonia synthesis catalyst is 60%-80%. The application can solve the problems of easy methanation of a carbon carrier of an ammonia synthesis catalyst and low specific surface area of an alkaline earth metal oxide carrier.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a method for preparing a ruthenium-based ammonia synthesis catalyst using cyanamide waste residue as raw material, the product and application thereof. BACKGROUND

[0002] Ammonia (NH3) is an important raw material for the production of fertilizers, dyes and explosives, and is also an ideal hydrogen energy carrier. It is a zero-carbon molecule with high hydrogen storage content (17.8wt%), high volumetric density (121kg H2 / m 3 , 1MPa), and can be liquefied at 8℃, 2.5MPa to store and transport.

[0003] The Haber-Bosch process currently used in the industrial synthesis of ammonia is carried out at high temperature and high pressure of 400-500℃, 10-30MPa, which consumes 1%-2% of the total global energy supply, and emits about 670 million tons of carbon dioxide per year. The energy consumption of the ammonia synthesis industry is high, and a large amount of greenhouse gases is emitted during the reaction process. In the face of the increasingly severe energy crisis and environmental problems, the traditional ammonia synthesis process is facing great challenges. The key to solving the high energy consumption of the traditional ammonia synthesis industry is to improve the catalytic reaction efficiency and reduce the reaction temperature and pressure, which requires the development of ammonia synthesis catalysts with low temperature, low pressure and high activity.

[0004] The current industrial ammonia synthesis catalyst is mainly iron catalyst. The patent specification with publication number CN106799232A discloses a room temperature solid phase reaction prepared nano-iron modified iron-based ammonia synthesis catalyst and its preparation method and application. The iron-based ammonia synthesis catalyst, the precursor of iron and the solid reagent are uniformly mixed, ground, ball milled or stirred, so that the precursor of iron and the solid reagent react on the carrier of the iron-based ammonia synthesis catalyst. After the reaction, the product is filtered, washed, dried, and heat treated in air, nitrogen, argon or vacuum conditions to obtain the final nano-iron modified iron-based ammonia synthesis catalyst. The nano-iron loading is 0.1-20wt%.

[0005] Compared with iron catalyst, ruthenium catalyst has higher ammonia synthesis activity at low temperature and low pressure, which can greatly reduce the energy consumption of ammonia synthesis industry, and is known as the second generation of ammonia synthesis catalyst. The patent specification with publication number CN114733551A discloses the design, preparation and application of a high-performance Ru-based ammonia synthesis catalyst. By synthesizing a BN carrier, then synthesizing a Ru / BN catalyst, and then loading rare earth elements on the Ru / BN catalyst by an equal volume impregnation method, a RuM / BN catalyst is finally obtained.

[0006] Carbon materials represented by activated carbon, carbon nanotubes and carbon fibers are often used as the carrier of ruthenium-based ammonia synthesis catalysts due to their high specific surface area and strong electron transmission capacity. However, under the conditions of high temperature and high pressure, the carbon carrier is easy to generate methane with hydrogen under the catalysis of metal ruthenium, resulting in the loss of the carbon carrier and the decrease of the activity of the catalyst and finally the deactivation of the catalyst. If graphite and other crystalline carbon materials are directly used as the carrier of the ruthenium-based ammonia synthesis catalyst, the graphite and other crystalline carbon materials need to be subjected to strong oxidation treatment, and the preparation process is complex, the yield is low and the cost is high. In addition, it is difficult to load alkaline earth metal oxides and other additives on the graphite and other crystalline carbon materials, and there is a problem of separation of the graphite and the alkaline earth metal oxides.

[0007] Although the alkaline earth metal oxide material does not have the problem of methanation, it has a low specific surface area, is not conducive to the dispersion of metal ruthenium, and the ruthenium catalyst loaded with the alkaline earth metal oxide has a serious problem of excessive hydrogen adsorption (hydrogen poisoning), which limits its application.

[0008] Therefore, it is very important to develop a ruthenium-based ammonia synthesis catalyst carrier which can effectively disperse metal ruthenium and has high stability for developing an ammonia synthesis catalyst with low temperature, low pressure and high activity. SUMMARY

[0009] In view of the above technical problems and the deficiencies in the prior art, the present application provides a method for preparing a ruthenium-based ammonia synthesis catalyst by using cyanamide waste residue as raw material, the product and the application thereof, wherein the cyanamide waste residue is a by-product of the production process of cyanamide prepared by using calcium cyanamide as raw material. The present application can solve the problems of easy methanation of the carbon carrier of the ammonia synthesis catalyst and low specific surface area of the alkaline earth metal oxide carrier.

[0010] In a first aspect, the present application provides a method for preparing a ruthenium-based ammonia synthesis catalyst by using cyanamide waste residue as raw material, comprising:

[0011] Step 1: acid treatment and alkali treatment of the cyanamide waste residue;

[0012] Step 2: ball milling treatment of the waste residue treated in step 1, and roasting of the milled material in an inert atmosphere;

[0013] Step 3: mixing and ball milling of the product roasted in step 2 with a ruthenium source and an additive to obtain a ruthenium-based ammonia synthesis catalyst; the mass content of calcium oxide in the ruthenium-based ammonia synthesis catalyst is 60%-80%.

[0014] In step 1, the cyanamide waste residue contains calcium carbonate, nitrogen-doped graphite carbon and calcium fluoride. Further, the content of calcium carbonate in the cyanamide waste residue can be 70wt%-90wt%, the content of nitrogen-doped graphite carbon can be 5wt%-10wt%, and the content of calcium fluoride can be 0.5wt%-2wt%. Due to the characteristics of the cyanamide waste residue, the calcium carbonate in the cyanamide waste residue is coated by nitrogen-doped graphite carbon, and the particle size can be 100-1000μm.

[0015] The present application prepares a calcium oxide / graphite composite material through acid etching treatment and alkali etching treatment, and high-energy ball milling and calcination. The calcium oxide / graphite composite material has the following characteristics: a specific surface area of 40-100m 2 / g, wherein the calcium oxide is coated by graphite carbon rich in oxygen defects and doped with nitrogen. The present application further prepares a ruthenium-based ammonia synthesis catalyst using the calcium oxide / graphite composite material as a carrier. Compared with a catalyst using a traditional calcium oxide carrier, the ruthenium-based ammonia synthesis catalyst has the advantages of high specific surface area (up to 40-100m 2 / g or more), high ruthenium dispersion, and high activity.

[0016] In step 1, the cyanamide waste residue can be sequentially subjected to acid treatment and alkali treatment.

[0017] The acid treatment in the present application can regulate the content of calcium carbonate in the material by reacting the acid with the calcium carbonate in the nitrogen-doped graphite carbon coating structure. The acid treatment can also increase the content of oxygen-containing functional groups in the cyanamide waste residue. The acid treatment can also utilize the reconstruction of calcium species on the surface of calcium carbonate in the confined space of the nitrogen-doped graphite carbon coating structure to regulate the interaction between the nitrogen-doped graphite carbon and the calcium carbonate. Finally, after ball milling and heat treatment, the dispersion of calcium oxide, subsequent additives and ruthenium in the calcium oxide / graphite composite material can be improved.

[0018] As a preferred embodiment, the content of calcium oxide in the ruthenium-based ammonia synthesis catalyst is 60%-80%, and the ruthenium-based ammonia synthesis catalyst with this content has excellent catalytic activity. The acid treatment in step 1 can be performed according to this target.

[0019] In step 1, the acid used in the acid treatment can include at least one of nitric acid, hydrochloric acid and sulfuric acid, and is preferably nitric acid, which can further improve the activity of the catalyst.

[0020] In step 1, the concentration of the acid used in the acid treatment can be 0.5-3mol / L, such as 0.5mol / L or 1.5mol / L.

[0021] In step 1, the ratio of the mass of the cyanamide waste residue to the volume of the acid solution used in the acid treatment can be 1-10g:10mL.

[0022] In step 1, the acid treatment can be performed for 0.5-2 hours, such as 0.5 hours, 1 hour, 1.5 hours, etc., and preferably 0.5 hours in some embodiments, and over-treatment with acid can reduce the catalyst activity.

[0023] In step 1, the acid treatment can be performed at a temperature of 30-100℃, such as 60℃, 80℃, etc.

[0024] The base treatment in the present application is to remove base-soluble impurities, such as silicon dioxide, etc., by reaction of a base with a base-soluble compound, so as to improve the catalyst activity.

[0025] In step 1, the base used in the base treatment can include at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, and cesium hydroxide, and preferably sodium hydroxide, which can further improve the catalyst activity.

[0026] In step 1, the concentration of the base used in the base treatment can be 0.01-5 mol / L, such as 0.1 mol / L, 0.5 mol / L, etc.

[0027] In step 1, the ratio of the mass of the cyanamide waste residue to the volume of the base solution used in the base treatment can be 1-10 g:10 mL.

[0028] In step 1, the base treatment can be performed for 0.5-2 hours, such as 0.5 hours, 1 hour, etc.

[0029] In step 1, the base treatment can be performed at a temperature of 30-100℃, such as 50℃, 60℃, etc.

[0030] In step 2, the ball milling treatment can be performed for 0.5-6 hours.

[0031] In step 2, the ball milling treatment can be performed at a speed of 200-400 rpm.

[0032] In step 2, the ball milling treatment can be performed at a ball-to-material ratio of 20-40:1.

[0033] In step 2, the ball milling treatment can be performed in an atmosphere of at least one of a noble gas (such as argon, etc.), nitrogen, and hydrogen.

[0034] In step 2, the inert atmosphere can be at least one of a noble gas (such as argon, etc.) atmosphere and a nitrogen atmosphere.

[0035] In step 2, the calcination can be performed at a temperature of 500-800℃, such as 600℃, 700℃, etc., and preferably 500-600℃, which can further improve the catalyst activity.

[0036] In step 2, the calcination can be performed for 1-3 hours.

[0037] The product after step 2 roasting is a calcium oxide / graphite composite material, and the specific surface area can reach 40-100 m 2 / g, wherein the calcium oxide is coated by nitrogen-doped graphite carbon rich in oxygen defects.

[0038] In step 3, the mass ratio of ruthenium in the ruthenium source to the product after step 2 roasting can be 1-5:100.

[0039] In step 3, the mass ratio of the auxiliary agent to the ruthenium source can be 1-3:1.

[0040] In step 3, the ruthenium source can include at least one of ruthenium nitrosyl nitrate, ruthenium chloride, triruthenium dodecacarbonyl, and ruthenium acetylacetonate.

[0041] In step 3, the auxiliary agent can include at least one of potassium nitrate, barium nitrate, lithium nitrate, cesium nitrate, cerium nitrate, lanthanum nitrate, and yttrium nitrate.

[0042] In step 3, the ball milling time can be 0.5-6h, for example, 1h, etc.

[0043] In step 3, the ball milling speed can be 50-100rpm.

[0044] In step 3, the ball milling ball-to-material ratio can be 5-15:1.

[0045] In step 3, the ball milling atmosphere can be at least one of a rare gas (for example, argon, etc.) atmosphere, a nitrogen atmosphere, and a hydrogen atmosphere.

[0046] The method is simple and easy to operate, and not only can prepare a high-efficiency catalyst for synthesizing ammonia at a low production cost, but also effectively solves the problems of low specific surface area and poor dispersion of metal ruthenium of alkaline earth metal oxide materials, and improves the added value of cyanamide waste residue.

[0047] In a second aspect, the application provides a ruthenium-based ammonia synthesis catalyst prepared by the method of the first aspect.

[0048] In a third aspect, the application provides application of the ruthenium-based ammonia synthesis catalyst of the first aspect in catalyzing synthesis of ammonia.

[0049] Compared with the prior art, the application has the following beneficial effects:

[0050] 1. The application uses nitrogen-doped graphite carbon in cyanamide waste residue to coat calcium carbonate structure, and through acid / alkali etching, ball milling and heat treatment, a nitrogen-doped graphite carbon-coated calcium oxide composite material (specific surface area up to 40-100 m 2 / g) is prepared, which solves the problems of poor activity, low specific surface area and low dispersion of metal ruthenium of calcium oxide as an ammonia synthesis catalyst carrier alone.

[0051] 2、The prepared nitrogen-doped graphite carbon-coated calcium oxide and structure, the graphite and calcium oxide are uniformly coated and mixed at nanoscale, solve the problem of inert surface of graphite material, and the large difference in density between the alkaline earth metal oxide and graphite, and the easy separation of graphite and alkaline earth metal oxide.

[0052] 3、The prepared ruthenium-based ammonia synthesis catalyst has higher activity than the catalyst prepared by directly mixing graphitized carbon and calcium carbonate and the catalyst prepared by using pure calcium carbonate as a carrier. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 is the X-ray diffraction (XRD) pattern of cyanamide waste residue (FZ) and FZ-1-BM6 in Example 1.

[0054] Figure 2 is the outlet ammonia concentration and reaction rate (r -1 ) of the ammonia synthesis catalysts of Example 1 and Comparative Examples 1-3 at 400℃, 10000h m . DETAILED DESCRIPTION

[0055] The application will be further described below in conjunction with the drawings and specific examples. It should be understood that these examples are only used to illustrate the application and not to limit the scope of the application.

[0056] The cyanamide waste residue used in the specific embodiment has a calcium carbonate content of 70wt%-90wt%, a nitrogen-doped graphite carbon content of 5wt%-10wt%, and a calcium fluoride content of 0.5wt%-2wt%. The calcium carbonate in the cyanamide waste residue (still present as calcium carbonate after acid-base treatment, which can be proved by XRD) is coated with nitrogen-doped graphite carbon, and the particle size is 100-1000μm.

[0057] Example 1

[0058] A ruthenium-based ammonia synthesis catalyst was prepared using cyanamide waste residue (XRD results as shown in Figure 1 ) as raw material, including the following steps:

[0059] 1) Acid treatment and base treatment of cyanamide waste residue: first, 80g of cyanamide waste residue was dissolved in 800mL of 1.5mol·L -1 acid solution for acid treatment, and refluxed in a water bath at 80℃ for 0.5 hours. Then, base treatment was performed, i.e., 10g of the acid-treated product was dissolved in 100mL of 0.5mol·L -1 sodium hydroxide solution for base treatment, and refluxed in a water bath at 60℃ for 1 hour. The obtained final product was labeled as FZ-1.

[0060] 2) High-energy milling treatment of FZ-1

[0061] Take 4 g of FZ-1 sample in step 1), add stainless steel ball milling beads with a ball-to-material ratio of 20:1, fill with Ar, and mill at a ball mill speed of 400 rpm for 6 h. Then calcine at 600°C for 2 h under Ar atmosphere. The final product obtained is the support, labeled FZ-1-BM6, and the XRD results are shown in Figure 1 .

[0062] 3) Preparation of ruthenium-based ammonia synthesis catalyst

[0063] Take 3 g of FZ-1-BM6 sample in step 2), then add 0.12 g of triruthenium dodecacarbonyl, 0.15 g of potassium nitrate, and 0.12 g of barium nitrate, and mix ball mill for 1 h at a ball mill speed of 100 rpm, a ball-to-material ratio of 10:1, and an Ar ball mill atmosphere. The ruthenium-based ammonia synthesis catalyst is obtained, with a calcium oxide content of 60 wt% in the catalyst.

[0064] Example 2

[0065] The difference from Example 1 is only that in step 1), the cyanamide waste residue is directly treated with alkali instead of acid treatment, and the rest is the same. The calcium oxide content in the obtained catalyst is 90 wt%.

[0066] Example 3

[0067] The difference from Example 1 is only that in step 1), the concentration of the nitric acid solution is changed to 0.5 mol·L -1 , and the rest is the same. The calcium oxide content in the obtained catalyst is 80 wt%.

[0068] Example 4

[0069] The difference from Example 1 is only that in step 1), the acid treatment temperature is changed to 60°C, and the rest is the same. The calcium oxide content in the obtained catalyst is 75 wt%.

[0070] Example 5

[0071] The difference from Example 1 is only that in step 1), the nitric acid is changed to hydrochloric acid with the same molar concentration, and the rest is the same.

[0072] Example 6

[0073] The difference from Example 1 is only that in step 1), the acid treatment time is changed to 1 hour, and the rest is the same. The calcium oxide content in the obtained catalyst is 10 wt%.

[0074] Example 7

[0075] The difference from Example 1 is only that in step 1), the concentration of the sodium hydroxide solution is changed to 0.1 mol·L -1The rest are the same.

[0076] Example 8

[0077] The difference from Example 1 is only that the alkali treatment temperature in step 1) is changed to 50℃, and the rest are the same.

[0078] Example 9

[0079] The difference from Example 1 is only that the alkali treatment time in step 1) is changed to 0.5h, and the rest are the same.

[0080] Example 10

[0081] The difference from Example 1 is only that the sodium hydroxide solution in step 1) is changed to an equimolar concentration of potassium hydroxide, and the rest are the same.

[0082] Example 11

[0083] The difference from Example 1 is only that the calcination temperature after ball milling in step 2) is changed to 700℃, and the rest are the same.

[0084] Example 12

[0085] The difference from Example 1 is only that the triruthenium dodecacarbonyl in step 3) is changed to an equimolar amount of ruthenium nitrosyl nitrate, and the rest are the same.

[0086] Example 13

[0087] The difference from Example 1 is only that the barium nitrate in step 3) is changed to an equal amount of cerium nitrate, and the rest are the same.

[0088] Comparative Example 1

[0089] A ruthenium-based ammonia synthesis catalyst was prepared using cyanamide waste residue as raw material, including:

[0090] A sample of 3g of cyanamide waste residue without any treatment was weighed, then calcined at 600℃ for 2h under Ar atmosphere as a carrier, then 0.12g of triruthenium dodecacarbonyl, 0.15g of potassium nitrate, and 0.12g of barium nitrate were added and ball milled for 1h, with a ball-to-material ratio of 10:1, a ball milling atmosphere of Ar, and a ball milling speed of 100rpm, to obtain a ruthenium-based ammonia synthesis catalyst.

[0091] Comparative Example 2

[0092] A ruthenium-based ammonia synthesis catalyst was prepared using a mixture of graphite carbon and calcium carbonate as raw material, including:

[0093] Take 1.8 g of calcium carbonate, 1.2 g of graphite, put into a ball mill at 500 rpm ball milling for 6 h, then calcined at 600℃ for 2 h under Ar atmosphere to obtain the carrier, then add 0.12 g of triruthenium dodecacarbonyl, 0.15 g of potassium nitrate, 0.12 g of barium nitrate, mix ball milling for 1 h, the ball milling speed is 100 rpm, the ball to material ratio is 10:1, the ball milling atmosphere is Ar, to obtain the ruthenium-based ammonia synthesis catalyst.

[0094] Comparative Example 3

[0095] The ruthenium-based ammonia synthesis catalyst is prepared by taking calcium carbonate as raw material, including:

[0096] Take 3 g of calcium carbonate, then calcine at 600℃ for 2 h under Ar atmosphere as the carrier, then add 0.12 g of triruthenium dodecacarbonyl, 0.15 g of potassium nitrate, 0.12 g of barium nitrate, mix ball milling for 1 h, the ball milling speed is 100 rpm, the ball to material ratio is 10:1, the ball milling atmosphere is Ar, to obtain the ruthenium-based ammonia synthesis catalyst.

[0097] The specific surface area, pore volume and pore size of the carrier obtained in Examples 1-13 and Comparative Examples 1-3 are shown in Table 1.

[0098] Table 1

[0099] Specific surface area (m 2 / g) Pore volume (cm 3 / g) Example 1 54 0.5 Example 2 54 0.4 Example 3 51 0.3 Example 4 52 0.3 Example 5 50 0.5 Example 6 50 0.3 Example 7 49 0.3 Example 8 46 0.3 Example 9 45 0.2 Example 10 40 0.2 Example 11 45 0.4 Example 12 54 0.5 Example 13 54 0.5 Comparative Example 1 22 0.5 Comparative Example 2 55 0.2 Comparative Example 3 8 0.3

[0100] In order to test the catalytic activity of the catalyst prepared by the present application, 2 mL of the ammonia synthesis catalyst obtained in Examples 1-13 and Comparative Examples 1-3 was respectively placed in the isothermal zone of a fixed bed reaction tube, and a mixed gas with a H2:N2 molar ratio of 3:1 was introduced. After reduction, the catalyst activity was evaluated at a temperature of 375℃, 400℃, a space velocity of 10000 h-1, and a pressure of 5 MPa. The results are shown in Table 2. In Table 2, "-" indicates that no ammonia was detected. -1

[0101] Table 2

[0102]

[0103] Figure 2 The results of the outlet ammonia concentration and reaction rate (r m ) of the ammonia synthesis catalysts of Examples 1 and Comparative Examples 1-3 at 400℃, 10000 h -1 -1 space velocity, and a H2:N2 molar ratio of 3:1 are shown.

[0104] ​Comparative Example 1 (calcium oxide content of 60wt%), Example 2 (calcium oxide content of 90wt%), Example 3 (calcium oxide content of 80wt%), Example 4 (calcium oxide content of 75wt%), Example 6 (calcium oxide content of 10wt%) can be concluded that the catalyst activity in cyanamide waste residue and calcium oxide content presents a "volcano type" curve relationship. When the calcium oxide content is too high, it may cover the active sites of the catalyst, resulting in a decrease in catalyst activity. When the calcium oxide content is too low, it may cause the interaction between the active components of the catalyst and the calcium oxide to weaken, thereby reducing the catalyst activity.

[0105] Comparative Example 1 and Example 5 can be concluded that after changing nitric acid to hydrochloric acid in the acid treatment step, the catalyst activity at 400℃ decreases from 3.49% to 1.73%. The possible reason is that the chloride ion in hydrochloric acid can reduce the electron cloud density of the active component, thereby reducing the catalyst activity.

[0106] Examples 7, 8, 9 and 10 respectively investigate the effects of the concentration of alkali, the alkali treatment temperature, the alkali treatment time, and the alkali type on the catalyst activity. The concentration of alkali decreases from 0.5mol·L -1 to 0.1mol·L -1 , the alkali treatment temperature decreases from 60℃ to 50℃, the alkali treatment time decreases from 1h to 0.5h, and the alkali type changes from sodium hydroxide to potassium hydroxide, all of which can cause the content of impurity SiO2 to be too high, thereby reducing the catalyst activity.

[0107] Example 11 investigates the effect of the calcination temperature after ball milling of the cyanamide waste residue on the catalyst activity. When the calcination temperature increases from 600℃ to 700℃, the particle size of calcium oxide increases, resulting in a decrease in catalyst activity.

[0108] Example 12 investigates the effect of the ruthenium source on the catalyst activity. When the ruthenium source changes from triruthenium dodecacarbonyl to ruthenium nitrosyl nitrate, it has no effect on the catalyst activity.

[0109] Example 13 investigates the effect of the additive on the catalyst activity. When the additive changes from barium nitrate to cerium nitrate, it has no effect on the catalyst activity.

[0110] In addition, it should be understood that, after reading the above description of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached hereto.

Claims

1. A method for preparing a ruthenium-based ammonia synthesis catalyst from cyanamide waste residue, characterized by, The application relates to a ruthenium-based ammonia synthesis catalyst and application thereof. Step 1: acid treatment and alkali treatment of cyanamide waste residue; Step 2: ball milling treatment of the waste residue after step 1 treatment, and roasting of the milled material in an inert atmosphere; Step 3: mixing and ball milling of the product after step 2 roasting, a ruthenium source and an additive to obtain the ruthenium-based ammonia synthesis catalyst; the mass content of calcium oxide in the ruthenium-based ammonia synthesis catalyst is 60%-80%.

2. The method of claim 1, wherein, In step 1: The cyanamide waste residue contains calcium carbonate, nitrogen-doped graphite carbon and calcium fluoride; The content of calcium carbonate in the cyanamide waste residue is 70wt%-90wt%, the content of nitrogen-doped graphite carbon is 5wt%-10wt%, and the content of calcium fluoride is 0.5wt%-2wt%; The calcium carbonate in the cyanamide waste residue is coated by the nitrogen-doped graphite carbon, and the particle size is 100-1000 mu m.

3. The method of claim 1, wherein, In step 1: The acid used in the acid treatment includes at least one of nitric acid, hydrochloric acid and sulfuric acid; The concentration of the acid used in the acid treatment is 0.5-3 mol / L; The acid treatment time is 0.5-2 hours; The mass of the cyanamide waste residue to the volume of the acid solution used in the acid treatment is 1-10 g:10 mL; The acid treatment temperature is 30-100 DEG C.

4. The method of claim 1, wherein, In step 1: The alkali used in the alkali treatment includes at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide and cesium hydroxide; The concentration of the alkali used in the alkali treatment is 0.01-5 mol / L; The alkali treatment time is 0.5-2 hours; The mass of the cyanamide waste residue to the volume of the alkali solution used in the alkali treatment is 1-10 g:10 mL; The alkali treatment temperature is 30-100 DEG C.

5. The method of claim 1, wherein, In step 2: The ball milling treatment time is 0.5-6 hours; The ball milling treatment speed is 200-400 rpm; The ball milling treatment ball-material ratio is 20-40:1; The ball milling treatment atmosphere is at least one of a rare gas atmosphere, a nitrogen atmosphere and a hydrogen atmosphere.

6. The method of claim 1, wherein, In step 2: The inert atmosphere is at least one of a rare gas atmosphere and a nitrogen atmosphere; The roasting temperature is 500-800 DEG C; The roasting time is 1-3 hours.

7. The method of claim 1, wherein, In step 3: The mass ratio of ruthenium in the ruthenium source to the product after step 2 roasting is 1-5:100; The mass ratio of the additive to the ruthenium source is 1-3:1; The ruthenium source includes at least one of nitrosyl ruthenium nitrate, ruthenium chloride, triruthenium dodecacarbonyl and ruthenium acetylacetonate; The additive includes at least one of potassium nitrate, barium nitrate, lithium nitrate, cesium nitrate, cerium nitrate, lanthanum nitrate and yttrium nitrate.

8. The method of claim 1, wherein, In step 3: The ball milling time is 0.5-6 hours; The ball milling speed is 50-100 rpm; The ball milling ball-material ratio is 5-15:1; The ball milling atmosphere is at least one of a rare gas atmosphere, a nitrogen atmosphere and a hydrogen atmosphere.

9. The ruthenium-based ammonia synthesis catalyst prepared according to the method of any one of claims 1 to 8, characterized in that, The mass content of calcium oxide in the ruthenium-based ammonia synthesis catalyst is 60%-80%.

10. The ruthenium-based ammonia synthesis catalyst according to claim 9 is applied in catalytic synthesis of ammonia.

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