CN110813359A - Ruthenium-based ammonia synthesis catalyst with nitrogen-doped porous carbon material as carrier and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of fertilizer catalysts, and in particular relates to a ruthenium-based ammonia synthesis catalyst using nitrogen-doped porous carbon material as a carrier and a preparation method thereof. In the preparation process of the catalyst, zinc nitrate hexahydrate is first dissolved in the alkaline aqueous solution, 2-methylimidazole is dissolved in N,N-dimethylformamide, and then the alkaline aqueous solution is added, and the solution is mixed uniformly and then hydrothermally heated. Reaction and carbonization to obtain nitrogen-doped porous carbon material. The chlorine-free ruthenium compound and polyvinylpyrrolidone are jointly dissolved in an ethylene glycol solution, heated, washed with an ethanol-acetone mixed solution, and then added with an ethanol solution; the above-mentioned porous carbon material is added, stirred, left to stand, separated and dried, and then reduced to obtain the described The ruthenium-based ammonia synthesis catalyst supported by nitrogen-doped porous carbon material not only has a higher specific surface area, but also a higher nitrogen doping amount, so it has a higher ammonia synthesis activity and has a good application. prospect.

Description

A kind of ruthenium-based ammonia synthesis catalyst supported by nitrogen-doped porous carbon material and its preparation backup method

technical field

The invention belongs to the technical field of fertilizer catalysts, and in particular relates to a ruthenium-based ammonia synthesis catalyst using nitrogen-doped porous carbon material as a carrier and a preparation method thereof.

Background technique

The synthetic ammonia industry is a pillar industry of the national economy. The Haber-Bosch method currently used for industrial ammonia synthesis must produce ammonia under harsh conditions of high temperature (400–500 °C) and high pressure (15–30 MPa), making the synthetic ammonia industry a high energy consumption and capital intensive industry. The key to energy saving and consumption reduction in the ammonia synthesis industry is the application of high-performance catalysts. Therefore, the research and design of high-efficiency ammonia synthesis catalysts has always been a research hotspot in the field of catalysis. At present, activated carbon-supported ruthenium catalysts are the most promising ammonia synthesis catalysts for ammonia synthesis under mild conditions. The successful application of ruthenium has greatly reduced the energy consumption of the ammonia synthesis industry, but in order to achieve large-scale industrial application, further in-depth research on carbon-supported ruthenium catalysts with higher performance is required.

With the rapid development of carbon materials in recent years, many new carbon materials have become support materials for metal catalysts. The modification and modification of carbon materials is expected to greatly improve the performance of the prepared metal catalysts. Among them, nitrogen doping in carbon materials can not only remove carbon materials. Oxygen-containing groups on the surface can also affect the electronic properties of the supported metals and the adsorption properties of reactive gases, which is one of the important means for the modification and modification of carbon materials. Patent CN106513030A reported the introduction of melamine nitrogen-containing precursor on the graphitized activated carbon, and the nitrogen-doped activated carbon was obtained after mechanical stirring and mixing, constant temperature water bath heating, and calcination, but the nitrogen content obtained by this method was between 0.72-7.61wt%. between. Patent CN104785255A reported the introduction of nitrogen-containing precursors on commercial activated carbons, after calcination, cooling, and Soxhlet extraction to obtain nitrogen-doped activated carbons with high specific surface area, but the nitrogen content obtained by this method is between 1-10wt%. When it is used as a carrier to prepare a ruthenium catalyst, its ammonia synthesis performance needs to be further improved. Patent CN107694594A reported a kind of using carbon material to mix with metal ion ammonia, carry out microwave reaction in carbon bath under inert atmosphere, obtain the nitrogen-doped carbon material of immobilized metal, but the nitrogen content obtained by this method is 1- 4wt%, and the specific surface area of the prepared material is only 380~450m ² /g. Obviously, the nitrogen-doped carbon materials prepared in the prior art are difficult to maintain high specific surface area and high nitrogen content at the same time, and are not suitable as ideal support materials for ruthenium-based ammonia synthesis catalysts.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a nitrogen-doped porous carbon composite material. By introducing nitrogen functional groups in the preparation process of the composite material, the prepared nitrogen-doped porous carbon composite material carrier has a high specific surface area and a nitrogen doping amount. Therefore, it becomes an ideal support material for ruthenium-based ammonia synthesis catalyst. The prepared ruthenium catalyst has high ammonia synthesis activity, and it can overcome the low activity of the existing commercial carbon material-supported ruthenium catalyst and the nitrogen-doped carbon composite material. The supported ruthenium catalyst has the disadvantages of low specific surface area and low nitrogen content.

To achieve the above object, the present invention adopts the following technical solutions:

In the ruthenium-based ammonia synthesis catalyst supported by the nitrogen-doped porous carbon material, the nitrogen mass fraction of the nitrogen-doped porous carbon composite material is 12%-18%, and the BET specific surface area thereof is 700-900 m ² /g.

The method for preparing a ruthenium-based ammonia synthesis catalyst using a nitrogen-doped porous carbon material as a carrier uses a nitrogen-doped porous carbon composite material as a carrier and ruthenium as an active component, wherein the mass of the nitrogen-doped porous carbon composite material is used as the carrier. Calculated, the addition amount of ruthenium is 1-10wt%.

Specifically include the following steps:

1) Dissolve zinc nitrate hexahydrate in an alkaline aqueous solution;

2) Dissolve dimethylimidazole in N,N-dimethylformamide solution, then add alkaline aqueous solution;

3) After mixing and stirring the solutions obtained in the above steps 1) and 2) evenly, after a certain period of hydrothermal reaction, the obtained suspension is centrifuged, washed and dried to obtain a solid product;

4) carbonizing the solid product obtained in the above step 3) at high temperature to obtain a nitrogen-doped porous carbon composite material;

5) dissolving ruthenium nitrosyl nitrate and polyvinylpyrrolidone together in ethylene glycol solution, then heating the obtained mixed solution to form a thick liquid, and then washing in an ethanol-acetone mixed solution to obtain a solid ruthenium precursor;

6) Disperse the above-mentioned ruthenium precursor in anhydrous ethanol solution, then add it into the nitrogen-doped porous carbon composite material obtained in step (4), stir evenly, let stand for a certain period of time, separate and remove the liquid, dry and reduce to obtain the obtained ruthenium precursor. A ruthenium-based catalyst with nitrogen-doped porous carbon as a carrier is described.

The molar ratio of zinc nitrate in step 1) to the solute in the alkaline aqueous solution in step 1) (1:7)~(1:68);

The alkaline solution described in step 1) and step 2) is sodium hydroxide or potassium hydroxide aqueous solution, and the concentration is 1~8 mol/L; the mass ratio of zinc nitrate hexahydrate and 2-methylimidazole is (1:0.6 )~(1:1); the molar ratio of dimethylimidazole to the solute in the alkaline solution in step 2) is (1:0.2)~(1:1.4). Based on the mass of 2-methylimidazole, 3~6 mL of N,N-dimethylformamide solution is required per gram of 2-methylimidazole.

The temperature of the hydrothermal reaction in step 3) is 100-150°C, and the reaction time is 2-20 hours.

Step 3) in the washing step, an aqueous methanol solution is used as the washing solution, wherein the volume fraction of methanol is not less than 80%; the drying is carried out in a vacuum or an inert gas, and the drying temperature is 50-80 °C.

The high-temperature carbonization treatment temperature in step 4) is 400-900 °C; the treatment time is 1-5 hours; the carbonization process is carried out in a hydrogen-containing mixed gas, wherein the hydrogen content is 3-100% (volume fraction), mixed The other gas components of the gas are a mixture of nitrogen or one or more of the zero-group inert gases.

Step 5) The molar ratio of the ruthenium nitrosyl nitrate and polyvinylpyrrolidone is (1:1)~(1:2), the heating temperature is 160~240 °C, and the heating time is 3~9 hours.

The volume ratio of ethanol and acetone in the ethanol-acetone mixed solution for washing described in step 5) is (1:1) ~ (1:3).

Step 6) The standing time is 1-20 hours; the drying is performed in vacuum or inert gas, the drying temperature is 50-120°C, and the reduction is performed in a hydrogen-containing mixed gas at 300-600°C, The volume fraction of hydrogen in the mixed gas is 3% to 100%, and the reduction time is 0.3 to 36 hours.

Significant advantages of the present invention:

Compared with the prior art, compared with the existing nitrogen-doped carbon and commercial activated carbon-supported ruthenium-based ammonia synthesis catalysts, the catalyst prepared by the present invention not only has higher specific surface area and strength, but also has higher Ammonia synthesis activity, so it has a good application prospect.

Compared with the carbon material carrier, the preparation method of a ruthenium-based ammonia synthesis catalyst with a nitrogen-doped porous carbon material as a carrier disclosed in the present invention has a great advantage. The characteristics of other preparation methods are that nitrogen functional groups are introduced during the preparation of carbon materials, and the prepared nitrogen-doped porous carbon composite material carrier has a higher specific surface area.

Detailed ways

In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1:

1) Dissolve 1.93 g of zinc nitrate hexahydrate in 48 ml of sodium hydroxide solution (6 mol/L);

2) Dissolve 2.104 g of 2-methylimidazole in 9.6 ml of N,N-dimethylformamide (purity 99.5%), then add 6.4 ml of sodium hydroxide (6 mol/L) solution;

3) After mixing and stirring the solutions obtained in the above steps (1) and (2), the solution was heated at a constant temperature of 120 °C in a hydrothermal kettle for 4 hours to obtain a milky white solution, washed with methanol solution, and centrifuged to obtain a solid product , and then dried at a constant temperature in a vacuum drying oven at 80 °C for 12 hours to obtain a solid product;

4) Put the solid product obtained in the above step (3) into a tube furnace, and in a 10% (volume fraction) H ₂ -Ar atmosphere at a heating rate of 2 °C/min to 800 °C for 4 hours for high temperature carbonization, That is, the nitrogen-doped porous carbon material is obtained;

5) 12.52 ml of ruthenium nitrosyl nitrate solution and 1.91 g of polyvinylpyrrolidone were co-dissolved in 120 ml of ethylene glycol solution under ultrasonication and stirring, and then the resulting mixed solution was heated at 200 °C for 3 h in an air atmosphere until A thick liquid is formed, and the above-mentioned collection is washed 5 times with an ethanol-acetone mixed solution (volume ratio 1:3) to obtain a solid ruthenium precursor;

6) Disperse the above ruthenium precursor in 40 ml of anhydrous ethanol solution, then add 1.5 g of the nitrogen-doped porous carbon material obtained in step (4), mix and stir for 12 h, and then let stand for 2 hours to separate and remove the liquid , vacuum drying, the drying temperature is 60 °C, and the drying time is 10 hours, and then reduced at 500 °C in a 10% (volume fraction) H ₂ -Ar atmosphere for 2 h to obtain the nitrogen-doped porous carbon as the carrier ruthenium-based For the catalyst, the amount of ruthenium added is 1.5 wt% based on the mass of the nitrogen-doped porous carbon composite.

Example 2:

1) Dissolve 1.26 g of zinc nitrate hexahydrate in 30 ml of sodium hydroxide solution (6 mol/L);

2) Dissolve 2.104 g of 2-methylimidazole in 15 ml of N,N-dimethylformamide (purity 99.5%), then add 6 ml of sodium hydroxide (6 mol/L) solution;

3) After mixing and stirring the solutions obtained in the above steps (1) and (2), the solution was heated at a constant temperature of 130 °C for 4 hours in a hydrothermal kettle to obtain a milky white solution, which was washed with methanol solution and centrifuged to obtain a solid product , and then dried at a constant temperature in a vacuum drying oven at 70 °C for 12 hours to obtain a solid product;

4) Put the solid product obtained in the above step (3) into a tube furnace, and in a 10% (volume fraction) H ₂ -Ar atmosphere at a heating rate of 2°C/min to 700°C for 5 hours for high temperature carbonization, That is, the nitrogen-doped porous carbon material is obtained;

5) 12.52 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) and 2.1 g of polyvinylpyrrolidone were dissolved together in 130 ml of ethylene glycol solution under ultrasonication and stirring, and then the resulting mixed solution was heated at 210 °C Heating in an air atmosphere for 3.5 h until a thick liquid is formed, the above collection is collected and washed 5 times with an ethanol-acetone mixed solution (volume ratio 1:3) to obtain a solid ruthenium precursor;

6) Disperse the above-mentioned ruthenium precursor in 50 ml of anhydrous ethanol solution, then add 1.5 g of the nitrogen-doped porous carbon material obtained in step (4), mix and stir for 8 h, and then let stand for 3 hours to separate and remove the liquid , vacuum dried at 80 °C for 10 h, and then reduced at 450 °C in a 10% (volume fraction) H ₂ -Ar atmosphere for 3 h to obtain the nitrogen-doped porous carbon-supported ruthenium-based For the catalyst, the amount of ruthenium added was 1.3 wt% based on the mass of the nitrogen-doped porous carbon composite support.

Example 3:

1) Dissolve 1.93 g of zinc nitrate hexahydrate in 48 ml of sodium hydroxide solution (6 mol/L);

2) Dissolve 2.104 g of 2-methylimidazole in 9.6 ml of N,N-dimethylformamide (purity 99.5%), then add 6.4 ml of sodium hydroxide (6 mol/L) solution;

3) After mixing and stirring the solutions obtained in the above steps (1) and (2), the solution was heated at a constant temperature of 140 °C in a hydrothermal kettle for 4 hours to obtain a milky white solution, which was washed with methanol solution and centrifuged to obtain a solid product , and then dried at a constant temperature in a vacuum drying oven at 80 °C for 10 hours to obtain a solid product;

4) Put the solid product obtained in the above step (3) into a tube furnace, and in a pure _H2 atmosphere at a heating rate of 2 °C/min to 900 °C for 3 hours for high temperature carbonization, that is, nitrogen-doped porous carbon is obtained. Material;

5) 12.52 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) and 1.91 g of polyvinylpyrrolidone were dissolved together in 150 ml of ethylene glycol solution under ultrasonication and stirring, and then the resulting mixed solution was heated at 200 °C Heating in an air atmosphere for 3 h until a thick liquid is formed, the above collection is collected and washed with an ethanol-acetone mixed solution (volume ratio 1:3) for 5 times to obtain a solid ruthenium precursor;

6) Disperse the above ruthenium precursor in 40 ml of anhydrous ethanol solution, then add 1.5 g of the nitrogen-doped porous carbon material obtained in step (4), mix and stir for 10 h, and then let stand for 2 hours to separate and remove the liquid , vacuum dried at 60 °C for 10 h, and then reduced at 500 °C in a 30% (volume fraction) H ₂ -Ar atmosphere for 2 h to obtain the nitrogen-doped porous carbon as the carrier ruthenium-based For the catalyst, the amount of ruthenium added is 1.5 wt% based on the mass of the nitrogen-doped porous carbon composite support.

Example 4:

1) Dissolve 1.93 g of zinc nitrate hexahydrate in 48 ml of potassium hydroxide solution (4 mol/L);

2) Dissolve 2.104 g of 2-methylimidazole in 9.6 ml of N,N-dimethylformamide (purity 99.5%), then add 6.4 ml of potassium hydroxide (4 mol/L) solution;

3) After mixing and stirring the solutions obtained in the above steps (1) and (2), the solution was heated and reacted at a constant temperature of 150°C in a hydrothermal kettle for 4 hours to obtain a milky white solution, which was washed 7 times with methanol solution and centrifuged to obtain The solid product was then dried at a constant temperature in a vacuum drying oven at 60°C for 12 hours to obtain a solid product;

4) Put the solid product obtained in the above step (3) into a tube furnace, and in a pure _H2 atmosphere at a heating rate of 5 °C/min to 700 °C for 5 hours for high temperature carbonization, that is, to obtain nitrogen-doped porous carbon Material;

5) 12.52 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) and 2.1 g of polyvinylpyrrolidone were dissolved together in 140 ml of ethylene glycol solution under ultrasonication and stirring, and then the resulting mixed solution was heated at 200 °C Heating in an air atmosphere for 4 h until a thick liquid was formed, the above collection was collected and washed 6 times with an ethanol-acetone mixed solution (volume ratio 1:2) to obtain a solid ruthenium precursor;

6) Disperse the above ruthenium precursor in 50 ml of anhydrous ethanol solution, then add 1.5 g of the nitrogen-doped porous carbon material obtained in step (4), mix and stir for 10 h and then let stand for 2 hours to separate and remove the liquid , vacuum-drying at 80 °C for 10 hours, and then at 500 °C in a 70% (volume fraction) H ₂ -Ar atmosphere for 3 hours to obtain the nitrogen-doped porous carbon as a carrier. For the ruthenium-based catalyst, the amount of ruthenium added is 1.4 wt% based on the mass of the nitrogen-doped porous carbon composite support.

Example 5:

1) Dissolve 3.86 g of zinc nitrate hexahydrate in 48 ml of potassium hydroxide solution (3 mol/L);

2) Dissolve 3.86 g of 2-methylimidazole in 19.2 ml of N,N-dimethylformamide (purity 99.5%), then add 19.2 ml of potassium hydroxide solution (3 mol/L);

3) After the solutions obtained in the above steps (1) and (2) are mixed and stirred uniformly, the solution is heated and reacted at a constant temperature of 120 °C for 5 hours in a hydrothermal kettle to obtain a milky white solution, which is washed with methanol solution and centrifuged to obtain a solid product , and then dried at a constant temperature in a vacuum drying oven at 80 °C for 12 hours to obtain a solid product;

4) Put the solid product obtained in the above step (3) into a tube furnace, and in a 10% (volume fraction) H ₂ -Ar atmosphere at a heating rate of 5 °C/min to 750 °C for 5 hours for high temperature carbonization, That is, the nitrogen-doped porous carbon material is obtained;

5) Dissolve 25 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) and 3.82 g of polyvinylpyrrolidone together in 200 ml of ethylene glycol solution under ultrasonication and stirring, and then the resulting mixed solution was heated at 200 °C. Heating under air atmosphere for 4h until a thick liquid is formed, the above-mentioned collection and washing with ethanol-acetone mixed solution (volume ratio 1:1) for 6 times to obtain solid ruthenium precursor;

6) Disperse the above-mentioned ruthenium precursor in 50 ml of anhydrous ethanol solution, then add 1.5 g of nitrogen-doped porous carbon material obtained in step (4), mix and stir for 12 h, and then let stand for 2 hours to separate and remove the liquid , vacuum dried at 90 °C for 10 hours, and then reduced at 450 °C in an atmosphere of 50% (volume fraction) H ₂ -34% (volume fraction) N ₂ -16% (volume fraction) Ar atmosphere After 15 h, the ruthenium-based catalyst with the nitrogen-doped porous carbon as a carrier was obtained, and the amount of ruthenium added was 3.1 wt % based on the mass of the nitrogen-doped porous carbon composite carrier.

Example 6:

1) Dissolve 1.93 g of zinc nitrate hexahydrate in 48 ml of sodium hydroxide solution (3 mol/L);

2) Dissolve 2.104 g of 2-methylimidazole in 9.6 ml of N,N-dimethylformamide (purity 99.5%), then add 9.6 ml of sodium hydroxide solution (3 mol/L);

3) After mixing and stirring the solutions obtained in the above steps (1) and (2), the solution was heated at a constant temperature of 120 °C in a hydrothermal kettle for 4 hours to obtain a milky white solution, washed with methanol solution, and centrifuged to obtain a solid product , and then dried at a constant temperature in a vacuum drying oven at 80 °C for 12 hours to obtain a solid product;

4) Put the solid product obtained in the above step (3) into a tube furnace, and in a 10% (volume fraction) H ₂ -Ar atmosphere at a heating rate of 5 °C/min to 800 °C for 3 hours to carry out high-temperature carbonization, That is, the nitrogen-doped porous carbon material is obtained;

5) 12.52 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) and 1.91 g of polyvinylpyrrolidone were jointly dissolved in 120 ml of ethylene glycol solution under ultrasonication and stirring, and then the resulting mixed solution was heated at 200 °C Heating in an air atmosphere for 3 h until a thick liquid is formed, the above collection is collected and washed with an ethanol-acetone mixed solution (volume ratio 1:3) for 5 times to obtain a solid ruthenium precursor;

6) Disperse the above-mentioned ruthenium precursor in 50 ml of anhydrous ethanol solution, then add 1.5 g of nitrogen-doped porous carbon material obtained in step (4), mix and stir for 12 h, and then let stand for 2 hours to separate and remove the liquid , vacuum-dried at 90 °C for 10 h, and then reduced at 300 °C in a 10% (volume fraction) H ₂ -Ar atmosphere for 30 h to obtain the nitrogen-doped porous carbon-supported ruthenium-based For the catalyst, the amount of ruthenium added was 1.6 wt% based on the mass of the nitrogen-doped porous carbon composite support.

Example 7:

1) Dissolve 3.86 g of zinc nitrate hexahydrate in 48 ml of sodium hydroxide solution (4 mol/L);

2) Dissolve 4.208 g of 2-methylimidazole in 19.2 ml of N,N-dimethylformamide (purity 99.5%), then add 12.8 ml of sodium hydroxide solution (4 mol/L);

3) After the solutions obtained in the above steps (1) and (2) are mixed and stirred uniformly, the solution is heated and reacted at a constant temperature of 120 °C for 5 hours in a hydrothermal kettle to obtain a milky white solution, which is washed with methanol solution and centrifuged to obtain a solid product , and then dried at a constant temperature of 80 °C in a vacuum drying oven for 12 hours at a heating rate of 5 °C/min to obtain a solid product;

4) Put the solid product obtained in the above step (3) into a tube furnace, and in a pure H ₂ atmosphere at a heating rate of 2 °C/min to 800 °C for 3 hours for high-temperature carbonization, to obtain nitrogen-doped porous carbon Material;

5) Dissolve 25.04 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) and 3.82 g of polyvinylpyrrolidone together in 160 ml of ethylene glycol solution under ultrasonication and stirring, and then the resulting mixed solution was heated at 210 °C Heating in an air atmosphere for 5 h until a thick liquid is formed, the above collection is collected and washed 6 times with an ethanol-acetone mixed solution (volume ratio 1:3) to obtain a solid ruthenium precursor;

6) Disperse the above ruthenium precursor in 60 ml of anhydrous ethanol solution, then add it to the 1.5 g nitrogen-doped porous carbon material obtained in step (4), mix and stir for 12 h and then let stand for 2 hours to separate and remove the liquid , vacuum-dried at 90 °C for 10 h, and then reduced at 500 °C for 3 h in a pure hydrogen atmosphere to obtain the nitrogen-doped porous carbon-supported ruthenium-based catalyst. According to the mass calculation of the carbon composite support, the addition amount of ruthenium is 3wt%.

Comparative Example 1:

1) Pretreatment of commercial activated carbon: Weigh 4.0 g of commercial activated carbon C ₁ , dry and wash it without nitrogen doping, and use it for later use.

2) Dissolving 6.67 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) at 70 °C for 6 h after drying in 6 ml of 50% methanol solution by volume to obtain a ruthenium precursor alcohol solution;

3) Immerse the ruthenium precursor alcohol solution obtained in step 2) into the commercial activated carbon carrier treated in step 1) at 30 °C for 1.5 hours;

4) The prepared sample was dried at 100 °C for 1 h, and then reduced with pure hydrogen at 500 °C for 3 h to obtain a ruthenium-based ammonia synthesis catalyst Ru/C ₁ supported by ordinary activated carbon, which was composited with nitrogen-doped porous carbon. Calculated by the mass of the carrier, the addition amount of ruthenium is 5wt%.

Comparative Example 2:

1) Pretreatment of commercial activated carbon: Weigh 4.0 g of commercial activated carbon C ₄ , dry and wash it without nitrogen doping, and use it for later use.

2) Dissolve 4 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) in 6 ml of 50% methanol solution after drying at 70 °C for 5 h to obtain a ruthenium precursor alcohol solution;

3) Immerse the ruthenium precursor alcohol solution obtained in step 2) into the 2 g commercial activated carbon carrier treated in step 1) at 30 °C for 1.5 hours;

4) The prepared samples were dried at 100 °C for 1 h, and then reduced with pure H ₂ at 500 °C for 3 h to obtain a ruthenium-based ammonia synthesis catalyst Ru/C ₁ supported by ordinary activated carbon, which was composited with nitrogen-doped porous carbon. Calculated by the mass of the carrier, the addition amount of ruthenium is 3wt%.

Comparative Example 3:

1) Pretreatment of commercial activated carbon: Weigh 4.0 g of commercial activated carbon C ₄ , dry and wash it without nitrogen doping, and use it for later use.

2) Dissolve 6.67 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) at 70 °C for 6 h after drying in 6 ml of 50% methanol solution by volume to obtain a ruthenium precursor alcohol solution;

3) Immerse the ruthenium precursor alcohol solution obtained in step 2) into the commercial activated carbon support treated in step 1) at 30 °C for 1.5 hours;

4) The prepared samples were dried at 100 °C for 1 h, and then reduced with pure H ₂ at 500 °C for 3 h to obtain a ruthenium-based ammonia synthesis catalyst Ru/C ₁ supported by ordinary activated carbon, which was composited with nitrogen-doped porous carbon. Calculated by the mass of the carrier, the addition amount of ruthenium is 5wt%.

Comparative Example 4:

1) Preparation of nitrogen-doped carbon-carbon carrier: Weigh 10.0 g of melamine into a covered ceramic crucible, conduct high-temperature polymerization in a tube furnace under _N2 atmosphere, and increase the polymerization temperature to 500 °C at a rate of 5 °C/min. Maintained at ℃ for 3 h to obtain a common nitrogen-doped carbon carrier.

2) 6.67 ml of ruthenium nitrosyl nitrate solution was dried at 70 °C for 6 h and dissolved into 6 ml of 50% methanol solution by volume to obtain a ruthenium precursor alcohol solution;

3) Immerse the ruthenium precursor alcohol solution obtained in step 2) into 2 g of the ordinary nitrogen-doped carbon carrier treated in step 1) at 30 °C for 1 hour;

4) The prepared samples were dried at 100 °C for 1 h, and then reduced with pure H ₂ at 500 °C for 3 h to obtain a ruthenium-based ammonia synthesis catalyst Ru/C ₃ N ₄ supported by ordinary activated carbon, which was doped with nitrogen. According to the mass calculation of the porous carbon composite support, the addition amount of ruthenium is 5wt%.

Comparative Example 5:

1) Preparation of nitrogen-doped carbon-carbon carrier: Weigh 10.0 g of melamine into a covered ceramic crucible, conduct high-temperature polymerization in a tube furnace under _N2 atmosphere, and increase the polymerization temperature to 500 °C at a rate of 5 °C/min. Maintained at ℃ for 3 h to obtain a common nitrogen-doped carbon carrier.

2) Dissolve 2 ml of ruthenium nitrosyl nitrate solution (ruthenium 1.5% w/v) in 6 ml of 50% methanol solution after drying at 70 °C for 4 h to obtain a ruthenium precursor alcohol solution;

3) Immerse the ruthenium precursor alcohol solution obtained in step 2) into 2 g of the ordinary nitrogen-doped carbon carrier treated in step 1) at 30 °C for 1 hour;

4) The prepared samples were dried at 100 °C for 1 h, and then reduced with pure H ₂ at 500 °C for 3 h to obtain a ruthenium-based ammonia synthesis catalyst Ru/C ₃ N ₄ supported by ordinary activated carbon, which was doped with nitrogen. According to the mass calculation of the porous carbon composite support, the addition amount of ruthenium is 1.5wt%.

Catalytic activity was evaluated on the ruthenium catalysts obtained in Examples 1-5 and the ruthenium-based ammonia synthesis catalysts obtained in Comparative Examples 1-3 in a high-pressure activity testing device. The reactor was a fixed bed with an inner diameter of 12 mm. During the test, 0.2 g of catalyst was mixed with larger particle size quartz sand and packed in the isothermal zone of the reactor. The reaction gas is a mixture of nitrogen and hydrogen obtained from ammonia high-temperature catalytic cracking, and the ratio of hydrogen to nitrogen is 3:1; the reaction conditions are: pressure 1 MPa, reaction temperature 400 ℃, reaction space velocity 3.6×10 ⁴ h ^-1 , the results are shown in the table 1.

Table 1 Specific surface area of catalyst and reaction rate of ammonia synthesis

As can be seen from Table 1, under the same conditions, the catalyst prepared by the present invention not only has higher specific surface area, but also has higher ammonia synthesis activity.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (10)

1. A ruthenium-based ammonia synthesis catalyst taking a nitrogen-doped porous carbon material as a carrier is characterized in that: the catalyst takes a nitrogen-doped porous carbon material as a carrier, takes ruthenium as an active component, the mass fraction of nitrogen in the nitrogen-doped porous carbon material is 12-18%, and the addition amount of ruthenium is 1-10wt% calculated by the mass of the nitrogen-doped porous carbon material.

2. A method for preparing a ruthenium-based ammonia synthesis catalyst supported on a nitrogen-doped porous carbon material according to claim 1, characterized in that: the method specifically comprises the following steps:

1) dissolving zinc nitrate hexahydrate in an alkaline aqueous solution;

2) dissolving dimethyl imidazole in N, N-dimethylformamide solution, and then adding alkaline aqueous solution;

3) after the solutions obtained in the steps (1) and (2) are mixed and stirred uniformly, after hydrothermal reaction is carried out for a certain time, the obtained suspension is centrifuged, washed and dried to obtain a solid product;

4) carbonizing the solid product obtained in the step (3) at high temperature to obtain a nitrogen-doped porous carbon composite material;

5) dissolving ruthenium nitrosyl nitrate and polyvinylpyrrolidone into an ethylene glycol solution, heating the obtained mixed solution to form a thick liquid, and washing the thick liquid in an ethanol-acetone mixed solution to obtain a solid ruthenium precursor;

6) and (3) dispersing the ruthenium precursor in an absolute ethyl alcohol solution, adding the solution into the nitrogen-doped porous carbon composite material obtained in the step (4), uniformly stirring, standing for a certain time, separating to remove liquid, drying and reducing to obtain the ruthenium-based catalyst taking the nitrogen-doped porous carbon as a carrier.

3. The ruthenium-based ammonia synthesis catalyst taking nitrogen-doped porous carbon material as a carrier according to claim 2, wherein the molar ratio of zinc nitrate in the step 1) to solute in the alkaline aqueous solution in the step 1) is 1:7 to 1: 68.

4. The ruthenium-based ammonia synthesis catalyst taking nitrogen-doped porous carbon material as a carrier according to claim 2, wherein the alkaline solution in the step 1) and the step 2 is an aqueous solution of sodium hydroxide or potassium hydroxide, and the concentration is 1-8 mol/L; the mass ratio of zinc nitrate hexahydrate to 2-methylimidazole in the steps 1) and 2) is 1: 0.6-1: 1; the molar ratio of the dimethyl imidazole to the solute in the alkaline solution in the step 2) is 1: 0.2-1: 1.4, and each gram of 2-methyl imidazole needs 3-6 mL of N, N-dimethyl formamide solution based on the mass of the 2-methyl imidazole.

5. The ruthenium-based ammonia synthesis catalyst based on nitrogen-doped porous carbon material as carrier according to claim 2, wherein the hydrothermal reaction temperature in step 3) is 100-150 ℃ and the reaction time is 2-20 hours.

6. The ruthenium-based ammonia synthesis catalyst based on nitrogen-doped porous carbon material as carrier according to claim 2, wherein the washing step of step 3) uses methanol aqueous solution as washing liquid, wherein the volume fraction content of methanol is not less than 80%; the drying is carried out in vacuum or inert gas, and the drying temperature is 50-80 ℃.

7. The ruthenium-based ammonia synthesis catalyst based on nitrogen-doped porous carbon material as carrier according to claim 2, wherein the high temperature carbonization temperature in step 4) is 400-900 ℃; the treatment time is 1-5 hours; the carbonization process is carried out in a hydrogen-containing mixed gas, wherein the content of hydrogen is 3-100 vol%, and other gas components of the mixed gas are gases formed by mixing one or more of nitrogen or a zero-group inert gas.

8. The ruthenium-based ammonia synthesis catalyst taking the nitrogen-doped porous carbon material as the carrier according to claim 2, wherein the molar ratio of the ruthenium nitrosyl nitrate to the polyvinylpyrrolidone in the step 5) is 1: 1-1: 2, the heating temperature is 160-240 ℃, and the heating time is 3-9 hours.

9. The ruthenium-based ammonia synthesis catalyst based on nitrogen-doped porous carbon material as carrier according to claim 2, wherein the volume ratio of ethanol to acetone in the ethanol-acetone mixed solution used in the washing in the step 5) is 1: 1-1: 3.

10. The ruthenium-based ammonia synthesis catalyst based on nitrogen-doped porous carbon material as carrier according to claim 2, wherein the standing time in step 6) is 1-20 hours; the drying is carried out in vacuum or inert gas, the drying temperature is 50-120 ℃, the reduction is carried out in hydrogen-containing mixed gas at the temperature of 300-600 ℃, the volume fraction of hydrogen in the mixed gas is 3-100%, and the reduction time is 0.3-36 hours.