Silicon-modified activated carbon-loaded ruthenium-based ammonia synthesis catalyst and preparation method thereof

Abstract

The invention discloses a silicon-modified activated carbon supported ruthenium-based ammonia synthesis catalyst and a preparation method thereof, the content percentage of Si in the catalyst is 0.1-2%, the preparation method of the catalyst comprises the following steps: firstly, adsorbing a silanol ammonia water solution in activated carbon to obtain a silicon-modified activated carbon sample, then introducing ruthenium salt into the silicon-modified activated carbon to obtain a ruthenium-modified activated carbon sample; carrying out high-temperature treatment in a hydrogen-containing atmosphere, and finally introducing barium into the catalyst through an impregnation method to obtain the silicon-modified activated carbon loaded ruthenium-based ammonia synthesis catalyst. Barium is used as an auxiliary agent to provide electrons for ruthenium and promote adsorption and dissociation of nitrogen on ruthenium. Compared with the traditional activated carbon supported ruthenium catalyst, the catalyst provided by the invention has higher ammonia synthesis activity and better application potential.

Description

Technical Field

[0001] The present invention relates to the field of catalyst preparation, and particularly relates to a silicon-modified activated carbon supported ruthenium catalyst and a preparation method thereof. Background Art

[0002] Ammonia (NH3) is an indispensable raw material in industrial production, has always occupied an important position in the basic chemical industry, and is also an important source of chemical fertilizers in agricultural production. However, traditional ammonia production must be carried out under high temperature and high pressure conditions, which is very energy-consuming. Therefore, how to improve the production efficiency of ammonia and find more efficient catalysts has become the research direction of scientists. Carbon-supported metal catalysts have attracted people's attention. At present, many metal catalyst supports for ammonia synthesis are being studied, including materials such as activated carbon, carbon composites, carbon nanotubes, magnesium oxide, and alumina. Among them, activated carbon has been widely used in ammonia synthesis due to its large specific surface area and hierarchical pore structure. After studying the relationship between the calculated turnover frequency of ammonia synthesis and the nitrogen adsorption energy, it was found that using ruthenium as the active metal can improve the catalytic activity. Industrially, alkali metal promoters such as potassium and barium are introduced to change the electronic properties of the active metal ruthenium, accelerate the adsorption and dissociation of nitrogen, and thus greatly improve the reaction rate. However, how to further reduce the reaction conditions required and improve the reaction rate has become an urgent problem to be solved.

[0003] The ammonia synthesis reaction includes steps such as the adsorption, activation, dissociation of nitrogen and hydrogen, the formation and desorption of ammonia, etc. These reaction steps on the catalyst surface will have a great impact on its ammonia synthesis performance. Oxides containing silicon elements usually exhibit certain acidity and are not ideal component materials for ammonia synthesis catalysts. However, recent reports show that the silicon-containing groups generated by introducing silicon elements into cerium oxide supported ruthenium catalysts by the impregnation method can inhibit the strong hydrogen adsorption and hydrogen spillover of hydrogen on the catalyst, thereby promoting the progress of the ammonia synthesis reaction (a silicon-modified cerium oxide supported ruthenium-based ammonia synthesis catalyst and its preparation method, CN202410317784.4), showing the application potential of silicon in ruthenium-based ammonia synthesis catalysts. This is because cerium oxide itself has strong hydrogen storage and redox capabilities, and hydrogen atoms are easily adsorbed, transferred, spilled over and reacted on the catalyst surface; in addition, cerium oxide and silicon oxide are prone to interact with each other. Therefore, silicon in the catalyst can exist in the form of silicon-containing groups, which can inhibit the strong hydrogen adsorption and hydrogen spillover of hydrogen on the catalyst, and is beneficial to promoting the progress of the ammonia synthesis reaction. However, the transfer ability of hydrogen-containing substances on the surface of the activated carbon carrier is weak (Hydrogen Spillover. Facts and Fiction. Chem. Rev., 2012, 112: 2714-2738.). This results in that it is difficult to remove part of the hydrogen after it spills over from ruthenium metal to the carbon carrier, and it is easy to cause hydrogen poisoning, which will be unfavorable for the subsequent adsorption and dissociation of hydrogen and the hydrogenation of nitrogen-containing substances to produce ammonia, and ultimately affect the ammonia synthesis activity of the ruthenium catalyst supported on activated carbon. Summary of the Invention

[0004] In order to solve the deficiencies of ruthenium-based catalysts supported on activated carbon, the present invention proposes a preparation method of a silicon-modified ruthenium-based ammonia synthesis catalyst supported on activated carbon. Compared with traditional ruthenium-based catalysts supported on activated carbon, the catalyst of the present invention introduces a small amount of silicon elements to promote the transfer of hydrogen substances on the catalyst surface, and can significantly improve the ammonia synthesis activity of the ruthenium catalyst supported on activated carbon, and has good application prospects.

[0005] To achieve the object of the invention, the present invention adopts the following technical solutions: A preparation method of a silicon-modified ruthenium-based ammonia synthesis catalyst supported on activated carbon specifically includes the following steps: (1) Placing activated carbon in an ammonia silanol aqueous solution to adsorb silicon to obtain a silicon-modified activated carbon sample, and the ammonia silanol aqueous solution is composed of a silicon-containing compound, ammonia water, alcohol and water; (2) Impregnating the silicon-modified activated carbon sample obtained in step (1) with a ruthenium precursor in an equal volume; (3) Placing the sample obtained in step (2) in a hydrogen atmosphere and performing high-temperature treatment to obtain a silicon-modified ruthenium supported on activated carbon sample; (4) Impregnating the sample obtained in step (3) with a barium precursor, and drying to obtain the silicon-modified ruthenium-based ammonia synthesis catalyst supported on activated carbon.

[0006] Further, the silicon-containing compound described in step (1) is one of tetraethyl orthosilicate or tetrabutyl orthosilicate. Calculated by silicon content, the mass ratio of silicon to activated carbon is 0.01:1 - 0.1:1.

[0007] Further, the alcohol described in step (1) is one of methanol, ethanol or propanol, and the volume ratio of alcohol to water in the silicon alcohol ammonia aqueous solution is 1:1 - 1:4.

[0008] Further, the molar ratio of the silicon-containing compound to the ammonium ion in ammonia water in the silicon alcohol ammonia aqueous solution described in step (1) is 0.01:1 - 0.1:1.

[0009] Further, the ruthenium precursor described in step (2) is one of nitrosyl ruthenium nitrate, ruthenium trichloride or ruthenium acetylacetonate, and the mass ratio of ruthenium metal to activated carbon is 0.003:1 - 0.1:1.

[0010] Further, the temperature of the high-temperature treatment described in step (3) is 200 - 650 °C, and the time is 0.5 - 6 hours.

[0011] Further, the mass ratio of barium metal to activated carbon in the barium precursor in step (4) is 0.01:1 - 0.09:1.

[0012] The above catalyst uses activated carbon as the carrier, ruthenium as the active component, barium as the promoter, and silicon is used to modify the catalyst; wherein the mass ratio of ruthenium to activated carbon is 0.003:1 - 0.1:1, the mass ratio of barium to activated carbon is 0.01:1 - 0.09:1, and the percentage content of silicon in the catalyst is 0.1% - 2%.

[0013] The remarkable advantages of the present invention: Compared with the traditional activated carbon-supported ruthenium catalyst and its preparation method, the silicon-modified activated carbon-supported ruthenium-based ammonia synthesis catalyst provided by the present invention introduces silicon by adsorbing a silicon alcohol ammonia aqueous solution, which can make the silicon content remaining in the catalyst appropriate. The presence of a small amount of silicon can promote the transfer and exchange of hydrogen species on the catalyst surface, inhibit the overflow of hydrogen species from ruthenium to the carbon carrier, and at the same time will not bring an obvious inhibitory effect on the performance of the catalyst. Therefore, it is beneficial to the progress of the ammonia synthesis reaction. Therefore, the prepared silicon-modified activated carbon-supported ruthenium catalyst has good ammonia synthesis performance and has good application prospects. Description of the Drawings

[0014] Figure 1 It is the H2-TPD diagram of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2.

[0015] Figure 2 It is the H2 adsorption diagram of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2 under 1 MPa.

[0016] Figure 3 HAADF and EDS diagrams for Comparative Example 1, where yellow is Ru and cyan is Ba.

[0017] Figure 4 HAADF and EDS diagrams for Example 1. Where yellow is Ru, cyan is Ba, and purple is Si. Detailed implementation manners

[0018] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] Example 1 Prepare 100 mL of an ethanol aqueous solution according to a volume ratio of 1:3, add tetraethyl orthosilicate and ammonia water to obtain a silanol ammonia aqueous solution. Place 2 g of activated carbon in the silanol ammonia aqueous solution, stir at room temperature for 8 hours, then stand for aging for 1 hour, then filter by suction, and dry at 60 °C for 12 hours to obtain a silicon-modified activated carbon sample. The mass ratio of silicon in tetraethyl orthosilicate to activated carbon in the above silanol ammonia aqueous solution is 0.03:1, and the molar ratio of tetraethyl orthosilicate to ammonium in ammonia water is 0.016:1. Impregnate the silicon-modified activated carbon sample with an aqueous solution of nitrosyl ruthenium nitrate with a mass fraction of 8.35% in an equal volume until the mass ratio of ruthenium metal to activated carbon is 0.05:1. After the sample is dried, it is reduced in a pure hydrogen atmosphere at 500 °C for 2 hours. Finally, impregnate the sample obtained in the previous step with an aqueous solution of barium nitrate at 0.03 g / mL in an equal volume, where the mass ratio of barium metal to activated carbon is 0.06:1. After drying, the silicon-modified activated carbon supported ruthenium-based ammonia synthesis catalyst is obtained. ICP characterization shows that the mass fraction of silicon in the catalyst is 0.25%.

[0020] Example 2 Prepare 100 mL of ethanol aqueous solution according to a volume ratio of 1:3, add tetraethyl orthosilicate and ammonia water to obtain a silanol ammonia aqueous solution. Place 2 g of activated carbon into the silanol ammonia aqueous solution, stir at room temperature for 8 hours, then stand for aging for 1 hour, and then carry out suction filtration. Dry at 60 °C for 12 hours to obtain a silicon-modified activated carbon sample. In the above silanol ammonia aqueous solution, the mass ratio of silicon in tetraethyl orthosilicate to activated carbon is 0.09:1, and the molar ratio of tetraethyl orthosilicate to ammonium in ammonia water is 0.1:1. Impregnate the silicon-modified activated carbon sample with an aqueous solution of ruthenium nitrosyl nitrate with a mass fraction of 8.35% in an equal volume until the mass ratio of ruthenium metal to activated carbon is 0.05:1. After the sample is dried, reduce it in a pure hydrogen atmosphere at 500 °C for 3 hours. Finally, impregnate the sample obtained in the previous step with an aqueous solution of barium nitrate at 0.03 g / mL in an equal volume, where the mass ratio of barium metal to activated carbon is 0.06:1. After drying, obtain the silicon-modified activated carbon supported ruthenium-based ammonia synthesis catalyst. ICP characterization shows that the mass fraction of silicon in the catalyst is 0.74%.

[0021] Example 3 Prepare 100 mL of ethanol aqueous solution according to a volume ratio of 1:2, add tetraethyl orthosilicate and ammonia water to obtain a silanol ammonia aqueous solution. Place 2 g of activated carbon into the silanol ammonia aqueous solution, stir at room temperature for 8 hours, then stand for aging for 1 hour, and then carry out suction filtration. Dry at 60 °C for 12 hours to obtain a silicon-modified activated carbon sample. In the above silanol ammonia aqueous solution, the mass ratio of silicon in tetraethyl orthosilicate to activated carbon is 0.07:1, and the molar ratio of tetraethyl orthosilicate to ammonium in ammonia water is 0.08:1. Impregnate the silicon-modified activated carbon sample with an aqueous solution of ruthenium nitrosyl nitrate with a mass fraction of 8.35% in an equal volume until the mass ratio of ruthenium metal to activated carbon is 0.04:1. After the sample is dried, reduce it in a pure hydrogen atmosphere at 500 °C for 5 hours. Finally, impregnate the sample obtained in the previous step with an aqueous solution of barium nitrate at 0.03 g / mL in an equal volume, where the mass ratio of barium metal to activated carbon is 0.08:1. After drying, obtain the silicon-modified activated carbon supported ruthenium-based ammonia synthesis catalyst. ICP characterization shows that the mass fraction of silicon in the catalyst is 0.54%.

[0022] Example 4 Prepare 100 mL of ethanol aqueous solution according to a volume ratio of 1:4, add tetraethyl orthosilicate and ammonia water to obtain a silanol ammonia aqueous solution. Place 2 g of activated carbon in the silanol ammonia aqueous solution, stir at room temperature for 8 hours, then stand for aging for 1 hour, and then filter by suction. After drying at 60 °C for 12 hours, a silicon-modified activated carbon sample is obtained. The mass ratio of silicon in tetraethyl orthosilicate to activated carbon in the above silanol ammonia aqueous solution is 0.1:1, and the molar ratio of tetraethyl orthosilicate to ammonium in ammonia water is 0.066:1. Impregnate the silicon-modified activated carbon sample with a nitrosyl ruthenium nitrate aqueous solution with a mass fraction of 8.35% in an equal volume until the mass ratio of ruthenium metal to activated carbon is 0.07:1. After the sample is dried, it is reduced in a pure hydrogen atmosphere at 500 °C for 2 hours. Finally, impregnate the sample obtained in the previous step with an aqueous barium nitrate solution of 0.03 g / mL in an equal volume, where the mass ratio of barium metal to activated carbon is 0.03:1. After drying, the silicon-modified activated carbon supported ruthenium-based ammonia synthesis catalyst is obtained. ICP characterization shows that the mass fraction of silicon in the catalyst is 1.03%.

[0023] Comparative Example 1 (sample without silicon) Take 2 g of activated carbon and impregnate it with a nitrosyl ruthenium nitrate aqueous solution with a mass fraction of 8.35% in an equal volume until the mass ratio of ruthenium metal to activated carbon is 0.05:1. After the sample is dried, it is reduced in a pure hydrogen atmosphere at 500 °C for 2 hours. Impregnate the sample obtained in the previous step with an aqueous barium nitrate solution of 0.03 g / mL in an equal volume, where the mass ratio of barium metal to activated carbon is 0.06:1. After drying, an activated carbon supported ruthenium-based ammonia synthesis catalyst is obtained.

[0024] Comparative Example 2 (compared with Example 1, changing the introduction order of silicon) Prepare 100 mL of ethanol aqueous solution according to a volume ratio of 1:3, add tetraethyl orthosilicate and ammonia water to obtain a silanol ammonia aqueous solution. Take 2 g of activated carbon and impregnate it with a nitrosyl ruthenium nitrate aqueous solution with a mass fraction of 8.35% in an equal volume until the mass ratio of ruthenium metal to activated carbon is 0.05:1. After the sample is dried, it is reduced in a pure hydrogen atmosphere at 500 °C for 2 hours. Impregnate the sample obtained in the previous step with an aqueous barium nitrate solution of 0.03 g / mL in an equal volume, where the mass ratio of barium metal to activated carbon is 0.06:1. Place the obtained sample in the silanol ammonia aqueous solution, stir at room temperature for 8 hours, then stand for aging for 1 hour, and then filter by suction. After drying at 60 °C for 12 hours. The mass ratio of silicon in tetraethyl orthosilicate to activated carbon in the silanol ammonia aqueous solution is 0.03:1, and the molar ratio of tetraethyl orthosilicate to ammonium in ammonia water is 0.016:1. After drying, the silicon-modified activated carbon supported ruthenium-based ammonia synthesis catalyst is obtained. ICP characterization shows that the mass fraction of silicon in the catalyst is 0.28%.

[0025] Comparative Example 3 (introducing silicon-modified activated carbon by impregnation method first) Prepare 100 mL of ethanol aqueous solution according to a volume ratio of 1:3, add tetraethyl orthosilicate and ammonia water to obtain a silanol ammonia aqueous solution. Take 2 g of activated carbon and impregnate it with the silanol ammonia aqueous solution at room temperature to obtain a silicon-modified activated carbon sample. The mass ratio of silicon in tetraethyl orthosilicate to activated carbon in the silanol ammonia aqueous solution is 0.03:1, and the molar ratio of tetraethyl orthosilicate to ammonium in ammonia water is 0.016:1. Subsequently, impregnate the sample with an aqueous solution of nitrosyl ruthenium nitrate with a mass fraction of 8.35% by equal volume until the mass ratio of ruthenium metal to activated carbon is 0.05:1. After drying, the sample is reduced in a pure hydrogen atmosphere at 500 °C for 2 hours. Impregnate the sample obtained in the previous step with an aqueous solution of barium nitrate at 0.03 g / mL by equal volume, where the mass ratio of barium metal to activated carbon is 0.06:1. After drying, a ruthenium-based ammonia synthesis catalyst supported on silicon-modified activated carbon introduced by the impregnation method is obtained. ICP characterization shows that the mass fraction of silicon in the catalyst is 2.26%.

[0026] Comparative Example 4 (introducing silicon substance without adding barium by impregnation method) Prepare 100 mL of ethanol aqueous solution according to a volume ratio of 1:3, add tetraethyl orthosilicate and ammonia water to obtain a silanol ammonia aqueous solution. Take 2 g of activated carbon and impregnate it with the silanol ammonia aqueous solution at room temperature to obtain a silicon-modified activated carbon sample. The mass ratio of silicon in tetraethyl orthosilicate to activated carbon in the silanol ammonia aqueous solution is 0.03:1, and the molar ratio of tetraethyl orthosilicate to ammonium in ammonia water is 0.016:1. Subsequently, impregnate the sample with an aqueous solution of nitrosyl ruthenium nitrate with a mass fraction of 8.35% by equal volume until the mass ratio of ruthenium metal to activated carbon is 0.05:1. After drying, the sample is reduced in a pure hydrogen atmosphere at 500 °C for 2 hours to obtain a ruthenium-based ammonia synthesis catalyst supported on silicon-modified activated carbon without adding barium. ICP characterization shows that the mass fraction of silicon in the catalyst is 0.3%.

[0027] Figure 1 It is the H2-TPD diagram of the catalysts in Example 1, Comparative Example 1 and Comparative Example 2. In Example 1, silicon is introduced first and then ruthenium substance. In Comparative Example 1, no silicon substance is introduced. In Comparative Example 2, silicon is introduced finally. It can be seen from the figure that the introduction of silicon can significantly improve the hydrogen adsorption capacity of the catalyst, and the high-temperature hydrogen desorption peak in the catalyst moves towards the low-temperature direction, indicating that the hydrogen adsorbed on the catalyst surface is more easily desorbed. Figure 2 It is the H2 adsorption diagram of the catalysts in Example 1, Comparative Example 1 and Comparative Example 2 under 1 MPa. It can be seen from the figure that after introducing silicon by an appropriate method, the adsorption of hydrogen on the catalyst surface can be improved. The hydrogen-rich environment on the catalyst surface is beneficial to the hydrogenation reaction of nitrogen and conducive to the ammonia synthesis reaction. Therefore, the catalyst has a high ammonia synthesis activity. Figures 3 to 4 It is the HAADF and EDS diagrams of Comparative Example 1 and Example 1. It can be seen from the figure that the presence of silicon can change the distribution of Ba element, thus promoting the transfer of hydrogen between silicon and ruthenium.

[0028] The activity evaluation of the catalyst was carried out in a high-pressure activity test device, and the inner diameter of the reactor was a fixed bed of 12 mm. During the test, 0.3 g of the catalyst was mixed with quartz sand of the same particle size at a volume ratio of 1:20 and loaded in the isothermal zone of the reactor. The reaction gas was a nitrogen-hydrogen mixture obtained by the high-temperature catalytic cracking of ammonia, and the hydrogen-nitrogen ratio was 3:1; the reaction conditions were: pressure 1 MPa, reaction temperature 400 °C, reaction space velocity 36000 cm 3 g cat -1 h -1 . The performance results of the catalyst are shown in Table 1.

[0029] Table 1 Performance results of the catalysts in Examples 1-4 and Comparative Examples 1-4 The above are only the 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 covered by the present invention.

Claims

1. A method for preparing a ruthenium-based ammonia synthesis catalyst supported on silicon-modified activated carbon, characterized in that: The specific steps include: (1) placing activated carbon in a silanol ammonia aqueous solution to adsorb silicon to obtain a silicon-modified activated carbon sample, wherein the silanol ammonia aqueous solution is composed of a silicon-containing compound, ammonia water, alcohol and water; (2) impregnating an equal volume of a ruthenium precursor into the silicon-modified activated carbon sample obtained in step (1); (3) placing the sample obtained in step (2) in a hydrogen atmosphere and subjecting it to high temperature treatment to obtain a silicon-modified activated carbon loaded with ruthenium sample; (4) The sample obtained in step (3) is impregnated with a barium precursor, and after drying, the silicon-modified activated carbon-supported ruthenium-based ammonia synthesis catalyst is obtained.

2. The preparation method according to claim 1, characterized in that: The silicon-containing compound in step (1) is one of tetraethyl silicate or tetrabutyl silicate, and the mass ratio of silicon to activated carbon is 0.01:1-0.1:1 based on silicon content.

3. The preparation method according to claim 1, characterized in that: The alcohol in step (1) is one of methanol, ethanol or propanol, and the volume ratio of alcohol to water in the silanol ammonia aqueous solution is 1:1-1:

4.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the silicon-containing compound in the silanol ammonia solution to the ammonium radical in the ammonia water in step (1) is 0.01:1-0.1:

1.

5. The preparation method according to claim 1, characterized in that: The ruthenium precursor in step (2) is one of nitrosyl nitrate ruthenium, ruthenium trichloride or ruthenium acetylacetonate, and the mass ratio of ruthenium metal to activated carbon is 0.003:1-0.1:

1.

6. The method for preparing a catalyst according to claim 1, characterized in that: The temperature of the high temperature treatment in step (3) is 200-650 °C and the time is 0.5-6 hours.

7. The preparation method according to claim 1, characterized in that: In step (4), the mass ratio of barium metal to activated carbon in the barium precursor is 0.01:1-0.09:

1.

8. A ruthenium-based ammonia synthesis catalyst supported on silicon-modified activated carbon obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The catalyst uses activated carbon as a carrier, ruthenium as an active component, barium as an auxiliary agent, and is modified with silicon; the mass ratio of ruthenium to activated carbon is 0.003:1-0.1:1, the mass ratio of barium to activated carbon is 0.01:1-0.09:1, and the percentage of silicon in the catalyst is 0.1%-2%.

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