Ru-based low-temperature high-efficiency ammonia decomposition catalyst, preparation method and application thereof

Abstract

The application discloses a Ru-based low-temperature high-efficiency ammonia decomposition catalyst and a preparation method and application thereof, and belongs to the technical field of catalysts. The catalyst comprises a Co3O4 carrier with a sheet layer structure and loaded active components and auxiliary metals, realizes ultra-high dispersion of the active metal, and greatly improves the ammonia decomposition activity of the catalyst through the synergistic effect between ruthenium and cobalt. One or more of lanthanum, cesium, cerium and magnesium are used as the auxiliary metal, the electron transfer between the carrier and the active metal is promoted, the surface basicity of the catalyst is improved, the interaction between the active components and the ammonia decomposition products is weakened, and the prepared catalyst has the advantages of low noble metal loading, high low-temperature ammonia decomposition activity and high long-term stability.

Description

Technical Field

[0001] This invention relates to the field of ammonolysis hydrogen production catalyst technology, specifically to a Ru-based low-temperature high-efficiency ammonolysis catalyst, its preparation method, and its application. Background Technology

[0002] To address the air pollution and global warming caused by the excessive use of fossil fuels, and to change the global energy landscape by shifting energy consumption from fossil fuels to new renewable and green energy sources, the development and utilization of hydrogen energy is a crucial step. Hydrogen energy has advantages such as wide availability, high calorific value (enthalpy of combustion up to 143 MJ / kg), and environmental friendliness. Hydrogen does not produce CO2 during its use. x and NO x The hydrogen energy process produces pollutants, with the reaction product being H2O, making it an ideal clean energy source, and its development has received considerable attention. Currently, there are abundant and rapidly developing methods for hydrogen energy development, such as hydrogen production from fossil fuel reforming, industrial by-product hydrogen, and biomass hydrogen production. However, due to the low bulk density and flammability of hydrogen, the shortage of hydrogen storage and transportation technologies severely restricts the commercial application and promotion of hydrogen energy.

[0003] Ammonia, as a hydrogen storage material, has advantages such as high hydrogen storage density and mature production technology. It can be liquefied under pressure at room temperature (critical temperature 132.4℃, critical pressure 11.2MPa) and can also be easily solidified into snowflake-like solids. It is extremely soluble in water (1:700), and ammonia has relatively low toxicity, an ignition point above 650℃, and is not easily combustible, making it convenient for hydrogen transportation and storage. Therefore, ammonia decomposition for hydrogen production is considered one of the ideal methods for producing hydrogen in various industrial fields in the future.

[0004] Ru-based catalysts are the most active and effective noble metal catalysts in ammonia decomposition, exhibiting excellent low-temperature activity, but their scarcity makes them expensive. Cobalt, with its suitable nitrogen adsorption energy, is considered one of the most promising metal catalysts for ammonia decomposition; however, pure cobalt oxides exhibit poor activity in ammonia decomposition, mainly due to their low specific surface area resulting in fewer active reaction sites. Colloidal polymers can link layered structures, growing and extending around the layers to obtain large-scale, loosely layered structures. During pyrolysis, these structures retain their framework, facilitating the diffusion of NH3 molecules into the pores. Simultaneously, they effectively increase the specific surface area of ​​Co3O4, and the synergistic effect of Ru and Co enhances the ammonia decomposition activity of the catalyst.

[0005] In the prior art, Chinese patent CN112774676A, entitled "A Method for Preparing a Ruthenium Catalyst Supported by Rare Earth Oxides," discloses a method with a short preparation cycle and simple process. However, its high Ru loading results in high catalyst cost, which is not conducive to industrial production. Patent CN116586059A discloses a method for preparing a Ru-supported catalyst for ammonia decomposition using trivalent rare earth oxides. This catalyst uses Ru clusters as active sites and is uniformly dispersed on a support, but its low-temperature ammonia decomposition activity is low. Given the above, researching and developing high-performance ammonia decomposition catalysts for hydrogen production is of great significance for solving the challenges of hydrogen energy storage and transportation, as current ammonia decomposition hydrogen production catalysts struggle to achieve high catalytic activity at low temperatures. Summary of the Invention

[0006] Based on previous research and existing problems, this invention proposes a Ru-based low-temperature high-efficiency ammonolysis catalyst, its preparation method and application, after further research and analysis. This catalyst has the advantages of ultra-high dispersion of noble metals, high activity of low-temperature ammonia decomposition, and high long-term stability.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a Ru-based low-temperature high-efficiency ammonia decomposition catalyst, wherein the Ru-based catalyst comprises a layered Co3O4 support and supported active components and auxiliary metals, wherein the active components are Ru and metallic Co, and the auxiliary metals are one or a combination of lanthanum, cerium, magnesium, and cesium.

[0008] Preferably, the Ru content accounts for 0.5-3% of the catalyst mass, and the content of the auxiliary component accounts for 5-20% of the catalyst mass.

[0009] The present invention also proposes a method for preparing the aforementioned catalyst, the steps of which are as follows:

[0010] S1. Preparation of Ru-LDH: In a reaction vessel, the ruthenium precursor and cobalt metal salt are dissolved in deionized water at a molar ratio of 1:(49-45), and then a mixed solution of alkaline sodium hydroxide and sodium carbonate is added. The reaction is maintained at 80-150℃ for 6-48 hours. After cooling, the product is removed, filtered, washed until neutral, and dried.

[0011] S2. Preparation of cobalt colloid: Dissolve the cobalt precursor salt in deionized water, dissolve the chelating agent in the solvent, stir for 0.5 h, add the chelating agent solution dropwise to the cobalt solution under continuous stirring, and adjust the solution to neutral. After stirring for 4 h, cobalt colloid is obtained.

[0012] After the Ru-LDH obtained in S3 and S1 is evenly dispersed, it is added to the colloid in S2 to obtain Ru-doped colloid.

[0013] S4. Preparation of auxiliary metal colloid: Dissolve the auxiliary metal precursor salt in deionized water, dissolve the chelating agent in the solvent, stir for 0.5 h, add the chelating agent solution dropwise to the continuously stirred auxiliary metal solution, adjust the solution to neutral, and stir for 4 h to obtain the auxiliary metal colloid.

[0014] S5. The colloids obtained from S3 and S4 are mixed and transferred to a reaction vessel to react, thus obtaining the catalyst precursor.

[0015] S6. Dry the catalyst precursor and grind it into powder;

[0016] S7. The Ru-based catalyst can be obtained by calcining the catalyst precursor powder.

[0017] Preferably, in S1, the ruthenium precursor is one of ruthenium acetylacetonate, ruthenium chloride, ruthenium acetate, triruthenium dodecylcarbonyl, and tris(2,2′-bipyridine)ruthenium chloride.

[0018] Preferably, in S1, the cobalt metal salt is at least one of cobalt acetate, cobalt oxalate, and cobalt nitrate.

[0019] Preferably, in S4, the auxiliary metal precursor salt is one or more of lanthanum nitrate, cerium nitrate, cesium acetate, and magnesium nitrate.

[0020] Preferably, in S2 and S4, the chelating agent is one or more of polyvinylpyrrolidone, citric acid, tartaric acid, gluconic acid, and ethylenediaminetetraacetic acid.

[0021] Preferably, in step S5, the colloid obtained in step S3 is mixed with the colloid obtained in step S4 at a ratio of 1:1 to 0.2, and the mixed colloid is placed in a reaction vessel and reacted at a temperature of 80-150°C and a pressure of 0.1-5 MPa.

[0022] Preferably, the atmosphere used during calcination in S7 is either nitrogen or air, the calcination temperature is 350-600℃, and the calcination time is 3-6 hours.

[0023] Furthermore, this invention proposes an application of the catalyst described above. This Ru-based catalyst is used in an ammonia decomposition hydrogen production process. Before the catalytic reaction, the catalyst is reduced at 350-500°C for 1-2 hours in a reducing atmosphere, and then the ammonia decomposition hydrogen production reaction is carried out at 400-700°C in an NH3 atmosphere, with an NH3 flow rate of 1-20 L / (g). cat ·h).

[0024] Compared with existing technologies, this invention provides a method for preparing and applying a Ru-based low-temperature high-efficiency ammonia decomposition catalyst, which has the following beneficial effects:

[0025] (1) This invention uses Co3O4 as a support and Ru active metal as the "core". The synergistic effect of Co and Ru promotes electron transfer, thereby giving it more basic sites and promoting the ultra-high dispersion of Ru. Compared with traditional catalysts, the catalyst prepared in this invention has a 1.5-3.8 times higher low-temperature ammonolysis efficiency. Its ammonia decomposition efficiency reaches a maximum of 81.03% at 450℃ and 94.31% at 500℃, which is much higher than the ammonia decomposition activity of catalysts prepared by other methods with the same loading.

[0026] (2) This invention also improves the specific surface area by forming a novel high-size lamellar structure from layered double hydroxides and colloids. Mg, Ce, La, and Cs are used as catalyst promoters, thereby reducing the amount of ruthenium used, and ensuring a high conversion rate of ammonia decomposition reaction at a relatively low temperature (400℃). The reduced loading of the precious metal ruthenium lowers the catalyst preparation cost.

[0027] (3) The present invention also discloses the preparation method of the above-mentioned supported catalyst and the effect of the introduction of the promoter on the ammonia decomposition hydrogen production reaction. The appropriate N adsorption energy of Co in the catalyst support is conducive to the adsorption and desorption of the intermediate of the ammonia decomposition reaction. At the same time, the synergistic effect of Co and Ru introduces new active sites, optimizes the electronic structure of Ru, and greatly improves the activity of the catalyst in the ammonia decomposition reaction. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] To provide a clearer and more detailed description of the preparation method of a Ru-based low-temperature high-efficiency ammonia decomposition catalyst provided in the embodiments of the present invention, specific embodiments will be described below.

[0030] Example 1:

[0031] This embodiment proposes a modified Ru-based catalyst for hydrogen production from ammonia decomposition, comprising a layered Co3O4 support and supported active components and auxiliary metals, wherein the active components are Ru and metallic Co, and the ruthenium-based ammonia decomposition hydrogen production catalyst is modified by one or more of barium, lanthanum, cesium, and cerium as auxiliary agents.

[0032] The ruthenium content in the catalyst is 0.5%-3% of the catalyst mass, and the content of auxiliary metals is 5%-20% of the catalyst mass.

[0033] The specific steps for preparing the catalyst described above are as follows:

[0034] Preparation of 5% La-0.5wt% Ru / Co3O4 ammonolysis hydrogen production catalyst:

[0035] (1) Dissolve 4.9 mol of Co(NO3)2·6H2O and 0.1 mol of Ru(acac)3 in 10 L of deionized water and 5 L of methanol, respectively, and then mix them thoroughly. Next, dissolve 10 mol of NaOH and 4 mol of Na2CO3 in 10 L of ultrapure water. In a reaction vessel, rapidly mix the two solutions. React at 110 °C for 12 h, cool down, filter, wash until neutral, and dry at 120 °C to obtain Ru-LDH.

[0036] (2) Dissolve 7.275 kg of Co(NO3)2·6H2O in deionized water and 11.52 kg of citric acid in deionized water. Add the citric acid solution dropwise to the metal salt solution and adjust it to neutral with NH3·H2O. Stir for 4 hours to obtain cobalt colloid.

[0037] (3) Take 400g of Ru-LDH and add it to 1.6kg of cobalt colloid. After stirring, a uniformly dispersed Ru-doped cobalt colloid is obtained.

[0038] (4) Dissolve 162g of La(NO3)2·6H2O in deionized water and 288g of citric acid in deionized water. Mix them thoroughly and adjust to neutral with NH3·H2O. Stir for 4 hours to obtain the auxiliary agent La colloid.

[0039] (5) Take 2.0 kg of Ru-doped cobalt colloid and Mg colloid as an auxiliary agent and place them in a reactor. React at 110℃ and 0.2 MPa for 6 h to obtain the catalyst precursor.

[0040] (6) The catalyst precursor was dried for 12 h, ground and then calcined at 550 °C in air for 4 h to obtain a 5% La-0.5wt% Ru / Co3O4 catalyst.

[0041] (7) After calcination, the catalyst is shaped at 20cm. 2 Apply 10tf of pressure to the surface area to shape it, and then crush it into 20-40 mesh particles.

[0042] Example 2:

[0043] In this embodiment, a 5% Cs-0.5wt% Ru / Co3O4 ammonolysis hydrogen production catalyst was prepared according to Example 1.

[0044] (1) Dissolve 96g of cesium acetate in deionized water and 288g of citric acid in deionized water. Mix them thoroughly and adjust the pH to neutral with NH3·H2O. Stir for 4 hours to obtain the auxiliary agent Cs colloid.

[0045] (2) Take 2.0 kg of Ru-doped cobalt colloid and Cs colloid as an auxiliary agent and place them in a reactor. React at 110℃ and 0.2 MPa for 6 h to obtain the catalyst precursor.

[0046] (3) The catalyst precursor was dried for 12 hours, ground, and then calcined at 550°C in air for 4 hours to obtain a 5%Cs-0.5wt%Ru / Co3O4 catalyst.

[0047] (4) After calcination, the catalyst is shaped at a depth of 20 cm. 2 Apply 10tf of pressure to the surface area to shape it, and then crush it into 20-40 mesh particles.

[0048] Example 3:

[0049] This embodiment follows the preparation of a 5% Mg-0.5wt% Ru / Co3O4 ammonolysis hydrogen production catalyst according to Example 1.

[0050] (1) Dissolve 96g of magnesium nitrate in deionized water and 288g of citric acid in deionized water. Mix them thoroughly and adjust the pH to neutral with NH3·H2O. Stir for 4 hours to obtain the Mg colloid.

[0051] (2) Take 2.0 kg of Ru-doped cobalt colloid and Mg colloid as an auxiliary agent and place them in a reaction vessel. React at 110℃ and 0.2 MPa for 6 h to obtain the catalyst precursor.

[0052] (3) The catalyst precursor was dried for 12 hours, ground, and then calcined at 550°C in air for 4 hours to obtain a 5% Mg-0.5wt% Ru / Co3O4 catalyst.

[0053] (4) After calcination, the catalyst is shaped at a depth of 20 cm. 2 Apply 10tf of pressure to the surface area to shape it, and then crush it into 20-40 mesh particles.

[0054] Example 4:

[0055] This embodiment follows the preparation of a 5% Ce-0.5wt% Ru / Co3O4 ammonolysis hydrogen production catalyst according to Example 1.

[0056] (1) Dissolve 217g of cerium nitrate in deionized water and 288g of citric acid in deionized water. Mix them evenly and adjust the pH to neutral with NH3·H2O. Stir for 4 hours to obtain the auxiliary agent Ce colloid.

[0057] (2) Take 2.0 kg of Ru-doped cobalt colloid and Ce colloid as an auxiliary agent and place them in a reactor. React at 110℃ and 0.2 MPa for 6 h to obtain the catalyst precursor.

[0058] (3) The catalyst precursor was dried for 12 hours, ground, and then calcined at 550°C in air for 4 hours to obtain a 5%Ce-0.5wt%Ru / Co3O4 catalyst.

[0059] (4) After calcination, the catalyst is shaped at a depth of 20 cm. 2 Apply 10tf of pressure to the surface area to shape it, and then crush it into 20-40 mesh particles.

[0060] Comparative Example 1:

[0061] Preparation of 0.5wt% Ru / Co3O4-1 ammonolysis hydrogen production catalyst:

[0062] (1) Dissolve 4.95 mol of Co(NO3)2·6H2O and 0.05 mol of Ru(acac)3 in 10 L of deionized water and 5 L of methanol respectively, and mix them thoroughly. Then dissolve 10 mol of NaOH and 4 mol of Na2CO3 in 10 L of ultrapure water. In a reaction vessel, rapidly mix the two solutions and react at 110 °C for 24 h. After cooling, remove the solution, filter and wash until neutral, and dry at 120 °C to obtain Ru-LDH.

[0063] (2) Dissolve 7.275 kg of Co(NO3)2·6H2O in deionized water and 11.520 kg of citric acid in deionized water. Mix them thoroughly and adjust the pH to neutral with NH3·H2O. Stir for 4 hours to obtain cobalt colloid.

[0064] (3) Take 200g of Ru-LDH and add it to 1.8kg of cobalt colloid. After stirring, a uniformly dispersed Ru-doped cobalt colloid is obtained.

[0065] (4) Take 2.0 kg of Ru-doped cobalt colloid and place it in a reactor. React at 110 °C and 0.2 MPa for 6 h to obtain the catalyst precursor.

[0066] (5) The catalyst precursor was dried for 12 hours, ground, and then calcined at 550°C in air for 4 hours to obtain a 0.5 wt% Ru / Co3O4 catalyst.

[0067] (6) After calcination, the catalyst is shaped at a depth of 20 cm. 2 Apply 10tf of pressure to the surface area to shape it, and then crush it into 20-40 mesh particles.

[0068] Comparative Example 2:

[0069] Preparation of 0.5wt% Ru / Co3O4-2 (impregnation-precipitation method) ammonolysis hydrogen production catalyst:

[0070] (1) Cobalt nitrate was directly calcined at 550℃ in air for 4 hours to obtain Co3O4. A Ru impregnation solution was prepared by dissolving 20g of ruthenium acetylacetonate in 15L of methanol solution. This solution was then impregnated onto 2.0kg of black Co3O4 powder. After impregnation for 24 hours, a catalyst precursor was obtained. This precursor was then dried in an oven at 80℃ for 12 hours to obtain the desired catalyst precursor. The precursor was calcined at 550℃ in air for 4 hours to obtain a 0.5wt% Ru / Co3O4 catalyst.

[0071] (2) After calcination, the catalyst is shaped at a depth of 20 cm. 2 Apply 10tf of pressure to the surface area to shape it, and then crush it into 20-40 mesh particles.

[0072] The catalysts in the embodiments and comparative examples of this invention were tested under the same conditions, wherein the feed gas was 99.999% high-purity ammonia and the space velocity was 5 L / (g). cat The test results are shown in Table 1 below:

[0073]

[0074]

[0075] Comparative Example 1 is a catalyst without added promoters, Comparative Example 2 is a Ru / Co3O4 catalyst prepared by precipitation deposition, and Examples 1-4 are catalysts using different metals as promoters. As shown in Table 1, compared with Comparative Example 1, the ammonia decomposition efficiency of Examples 1-4 is increased by 1.5-4 times at the same temperature. The highest ammonia decomposition efficiency reaches 81.03% at 450℃ and 94.31% at 500℃. Compared with Comparative Example 2, the low-temperature activity of the catalysts in Examples 1-4 is significantly improved.

[0076] This invention utilizes a novel high-size lamellar structure formed by layered double hydroxides and colloids to increase the specific surface area of ​​the catalyst. Mg, Ce, La, and Cs act as catalyst promoters, enhancing the surface basicity of the catalyst and promoting ultra-high dispersion of Ru. Simultaneously, the synergistic effect of Co and Ru introduces new active sites, promotes electron transfer, and optimizes the electronic structure of Ru. This allows the catalyst to maintain a high conversion rate in the ammonia decomposition reaction even at a relatively low Ru loading (0.5 wt%) and a relatively low temperature (400 °C). The reduced loading of the precious metal ruthenium lowers the catalyst preparation cost.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A Ru-based low-temperature high-efficiency ammonia decomposition catalyst, characterized in that, Ru-based catalysts include a layered Co3O4 support and supported active components and auxiliary metals, wherein the active components are Ru and metallic Co, and the auxiliary metals are one or a combination of lanthanum, cerium, magnesium, and cesium. The content of Ru accounts for 0.5-3% of the catalyst mass, and the content of the auxiliary components accounts for 5-20% of the catalyst mass; The steps for preparing the catalyst are as follows: S1. Preparation of Ru-LDH: In a reaction vessel, the ruthenium precursor and cobalt metal salt are dissolved in deionized water at a molar ratio of 1:(45-49), and then a mixed solution of alkaline sodium hydroxide and sodium carbonate is added. The reaction is maintained at 80-150°C for 6-48 hours. After cooling, the product is removed, filtered, washed until neutral, and dried. S2. Preparation of cobalt colloid: Dissolve the cobalt precursor salt in deionized water, dissolve the chelating agent in the solvent, stir for 0.5 h, add the chelating agent solution dropwise to the cobalt solution under continuous stirring, and adjust the solution to neutral. After stirring for 4 h, cobalt colloid is obtained. S3. After uniformly dispersing the Ru-LDH obtained in S1, add it to the colloid in S2 to obtain the Ru-doped colloid. S4. Preparation of auxiliary metal colloid: Dissolve the auxiliary metal precursor salt in deionized water, dissolve the chelating agent in the solvent, stir for 0.5 h, add the chelating agent solution dropwise to the continuously stirred auxiliary metal solution, adjust the solution to neutral, and stir for 4 h to obtain the auxiliary metal colloid. S5. The colloids obtained from S3 and S4 are mixed and transferred to a reaction vessel to react, thus obtaining the catalyst precursor. S6. Dry the catalyst precursor and grind it into powder; S7. The Ru-based catalyst can be obtained by calcining the catalyst precursor powder.

2. The Ru-based low-temperature high-efficiency ammonia decomposition catalyst according to claim 1, characterized in that, In S1, the ruthenium precursor is one of ruthenium acetylacetonate, ruthenium chloride, ruthenium acetate, triruthenium dodecylcarbonyl, or tris(2,2′-bipyridine)ruthenium chloride.

3. The Ru-based low-temperature high-efficiency ammonia decomposition catalyst according to claim 2, characterized in that, In S1, the cobalt metal salt is at least one of cobalt acetate, cobalt oxalate, and cobalt nitrate.

4. The Ru-based low-temperature high-efficiency ammonia decomposition catalyst according to claim 1, characterized in that, In S4, the auxiliary metal precursor salt is one or more of lanthanum nitrate, cerium nitrate, cesium acetate, and magnesium nitrate.

5. A Ru-based low-temperature high-efficiency ammonia decomposition catalyst according to any one of claims 2-4, characterized in that, In S2 and S4, the chelating agent is one or more of polyvinylpyrrolidone, citric acid, tartaric acid, gluconic acid, and ethylenediaminetetraacetic acid.

6. The Ru-based low-temperature high-efficiency ammonia decomposition catalyst according to claim 5, characterized in that, In S5, the colloid obtained in S3 is mixed with the colloid obtained in S4 at a ratio of 1:0.2 to 1. The mixed colloid is placed in a reaction vessel and reacted at a temperature of 80-150°C and a pressure of 0.1-5 MPa.

7. The Ru-based low-temperature high-efficiency ammonia decomposition catalyst according to claim 1, characterized in that, The atmosphere used during the roasting of S7 is either nitrogen or air, the roasting temperature is 350-600°C, and the roasting time is 3-6 hours.

8. The application of the Ru-based low-temperature high-efficiency ammonia decomposition catalyst as described in claim 1, characterized in that, Ru-based catalysts are used in ammonia decomposition for hydrogen production. Before the catalytic reaction, the catalyst is reduced at 350-500°C for 1-2 hours in a reducing atmosphere, followed by ammonia decomposition for hydrogen production at 400-700°C in an NH3 atmosphere with an NH3 flow rate of 1-20 L / (g). cat ·h).

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