Catalyst for hydrogen production by ammonia cracking and method for preparing the same, and method for hydrogen production by ammonia cracking

Abstract

This invention relates to a catalyst for hydrogen production from ammonia cracking, its preparation method, and a method for hydrogen production from ammonia cracking. The catalyst for hydrogen production from ammonia cracking includes a solid support, a first auxiliary metal dispersed and loaded on the surface of the solid support, and active metal nanoparticles anchored on the auxiliary metal. The active metal nanoparticles and the solid support are in interfacial contact through the first auxiliary metal. The active metal nanoparticles are active metals modified with a second auxiliary metal. Both the first and second auxiliary metals are alkali metals. The beneficial effects are that the prepared catalyst for hydrogen production from ammonia cracking has a low active metal loading, high catalytic activity, and strong stability, significantly reducing the amount of precious metals used, improving atom economy, and significantly reducing the industrial production cost of the catalyst for hydrogen production from ammonia cracking.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a catalyst for hydrogen production by ammonia cracking, a method for preparing the catalyst, and a method for hydrogen production by ammonia cracking. Background Technology

[0002] Hydrogen is recognized worldwide as a core element of future energy; however, its production, storage, and transportation require a medium. Ammonia is a key chemical in industrial production, and its zero-carbon, high hydrogen content, and high energy density make it a suitable hydrogen storage carrier, attracting widespread research. Ammonia cracking hydrogen production catalysts mainly consist of three parts: an active metal, a support, and additives. The active metal is the core of the catalyst, directly participating in the adsorption and dissociation reactions of ammonia molecules; the support provides physical support for the active metal and has a crucial impact on the overall performance of the catalyst; and the additives are used to further modify and optimize the catalyst's performance.

[0003] Currently, the active metals in ammonia decomposition catalysts mainly include ruthenium, nickel, cobalt, and iron. Among them, nickel, cobalt, and iron-based catalysts mostly require temperatures above 600℃ to achieve considerable catalytic performance. Ruthenium-based catalysts exhibit excellent performance at lower temperatures; however, ruthenium is expensive.

[0004] The following problems exist with ammonia cracking catalysts for hydrogen production: They require high temperatures to achieve significant catalytic performance, necessitate stringent reaction conditions, and result in high energy consumption. During preparation, the active metal-supported reaction conditions are demanding, requiring high loading levels, leading to low utilization of the supported active metal, poor stability, and high overall preparation costs. Furthermore, active metal support often requires oxygen and high temperatures. For example, Chinese patent CN119972059A describes a single-atom ruthenium-based catalyst using magnesium oxide as a support, employing an oxide support to capture volatile ruthenium species under high-temperature oxygen-containing atmospheres, thus anchoring ruthenium atoms. This method requires high temperatures and an oxygen-containing atmosphere, posing potential safety hazards.

[0005] In addition, most of the existing ammonia decomposition catalyst preparation technologies are small-scale studies in powder form. Whether the catalytic performance changes after the powder catalyst is formed, and the reproducibility of large-scale preparation of powder catalysts, need to be investigated. Summary of the Invention

[0006] (a) Technical problems to be solved In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a catalyst for hydrogen production by ammonia cracking and its preparation method, as well as an ammonia cracking hydrogen production method. It solves the technical problems of strict reaction conditions for active metal loading, high loading, low utilization rate of the loaded active metal, poor stability, and high overall preparation cost in the preparation of existing ammonia cracking hydrogen production catalysts; as well as the technical problems of the disconnect between laboratory research and actual industrial application of existing ammonia cracking hydrogen production catalysts.

[0007] (II) Technical Solution To achieve the above objectives, the main technical solutions adopted by the present invention include: In a first aspect, embodiments of the present invention provide a catalyst for hydrogen production by ammonia cracking, comprising a solid support, a first auxiliary metal dispersed and loaded on the surface of the solid support, and active metal nanoparticles anchored on the auxiliary metal. The active metal nanoparticles and the solid support are in interfacial contact through the first auxiliary metal. The active metal nanoparticles are active metals modified by the second additive; Both the first and second auxiliary metals are alkali metals.

[0008] In a preferred embodiment of the present invention, the solid support of the catalyst for ammonia cracking to produce hydrogen is selected from at least one of alumina, titanium oxide, cerium oxide, lanthanum oxide, silicon oxide, and zirconium oxide. The solid support is at least one of the following shapes: spherical, cylindrical, multi-leaf strip, tubular, cross-shaped ring, stepped ring, honeycomb, porous columnar, foamy, and fibrous.

[0009] The shape of the solid carrier is commercially available and formed by extrusion; the specific shape can be customized as needed.

[0010] In a preferred embodiment of the present invention, the active metal in the catalyst for ammonia cracking to produce hydrogen is selected from at least one of ruthenium, cobalt, iron, and nickel. Both the first additive metal and the second additive metal are selected from at least one of potassium, sodium, barium, and cesium.

[0011] In a preferred embodiment of the present invention, when the active metal in the catalyst for ammonia cracking to produce hydrogen is ruthenium, the mass fraction of ruthenium is 0.1-0.9 wt%, and the mass fraction of the auxiliary metal is 5-30%. When the active metal is nickel, the mass fraction of nickel is 1-10 wt%. When the active metal is cobalt, the mass fraction of cobalt is 0.6-6 wt%; When the active metal is iron, the mass fraction of iron is 2.5-20 wt%. The mass fraction of the first additive metal is 1-30 wt%; The average particle size of the active metal ranges from 1 to 5 nm, wherein when the active metal is ruthenium, the average particle size ranges from 1 to 2 nm.

[0012] Secondly, embodiments of the present invention provide a method for preparing a catalyst for hydrogen production from ammonia cracking, comprising the following steps: S1. Prepare a first solution by preparing the first auxiliary metal compound, impregnate a solid support with the first solution, and dry and calcine the impregnated solid support to obtain an auxiliary metal modified support. S2. Dissolve the active metal compound and the second auxiliary metal compound in a polyol solvent to prepare a mixed reaction solution. Under inert gas protection, heat and reflux at 140-220°C to obtain a suspension of active metal nanoparticles modified with the second auxiliary metal by utilizing the liquid-phase reduction effect of the polyol. The preferred reflux reaction temperature is 160-200°C. S3. The auxiliary metal-modified support prepared in S1 is impregnated in the suspension of active metal nanoparticles. The impregnated auxiliary metal-modified support is then dried and calcined to obtain the catalyst for ammonia cracking to produce hydrogen.

[0013] In S1, the first auxiliary metal is used to modify the solid support to change the acidity, alkalinity and electrical properties of the support, and then to modify the active metal nanoparticles loaded in S2 to enhance catalytic activity and stability.

[0014] In S2, the active metal modified by the second auxiliary metal is a metal nanoparticle with abundant B5 active sites. The second auxiliary metal transfers electrons to the active metal, changing the electron cloud density on the surface of the active metal. This optimization of the electronic structure can promote the adsorption of ammonia gas on the active sites, reduce the activation energy of NH bond dissociation, accelerate dissociation, promote nitrogen association and desorption, and prevent the active sites from being poisoned through hydrogen overflow, thereby optimizing the catalytic performance of the active metal. In addition, the strategy of in-situ liquid-phase reduction of polyols combined with modification by specific alkali metal auxiliary agents results in mild reaction conditions. This process effectively avoids the agglomeration problem caused by thermal migration of metals at high-temperature interfaces, and the metal particles in the prepared suspension are extremely small.

[0015] S3 is dedicated to highly dispersing and loading nanoscale active metal nanoparticles onto the surface of a carrier modified with additive metals.

[0016] In a preferred embodiment of the present invention, the preparation method wherein the first auxiliary metal compound and the second auxiliary metal compound are both selected from at least one of potassium hydroxide, sodium hydroxide, barium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, sodium chloride, and potassium chloride; preferably, they are selected from at least one of potassium hydroxide, sodium hydroxide, and cesium hydroxide. In the first solution: the solvent is water, and the concentration of the first auxiliary metal is 2-6 mol / L; When the first solution impregnates the solid support, the impregnation time is 18-42 hours at room temperature, preferably 24-36 hours.

[0017] The concentration of the first auxiliary metal is 2-6 mol / L, which can meet the requirements for surface modification of different solid supports (pore volume 0.3-0.8 mL / g, particle size 2-5 mm).

[0018] In a preferred embodiment of the present invention, in the preparation method S2, the active metal compound is selected from at least one of ruthenium chloride, ruthenium nitrate, ruthenium acetylacetonate, cobalt nitrate, cobalt chloride, ferric chloride, ferrous chloride, ferrous nitrate, ferrous nitrate, ferrous acetylacetonate, nickel nitrate, nickel chloride, and nickel acetylacetonate; preferably, it is selected from at least one of ruthenium chloride, ruthenium nitrate, nickel nitrate, and nickel chloride. The solvent for the mixed reaction solution is selected from ethylene glycol, propylene glycol, butanediol, glycerol, diethylene glycol, triethylene glycol, or tetraethylene glycol; preferably, it is selected from ethylene glycol, propylene glycol, and butanediol. In the mixed reaction solution: the concentration of the second auxiliary metal is 0.3-5 mol / L, and the molar ratio of the active metal to the second auxiliary metal is 1:3-50; When heating and stirring the reaction, the reaction time is 2-6 hours, preferably 4-6 hours.

[0019] In a preferred embodiment of the present invention, the drying conditions in S2 and S3 of the preparation method are: temperature of 60-120°C, preferably 80-100°C, and drying time of 18-36h, preferably 24-36h. The calcination conditions in S2 and S3 are as follows: heating rate of 2-10℃ / min, preferably 5-10℃ / min, calcination temperature of 400-700℃, preferably 500-600℃, and calcination time of 1-4h, preferably 2-4h.

[0020] Thirdly, embodiments of the present invention provide a method for producing hydrogen from ammonia through cracking, using the catalyst for hydrogen production from ammonia through cracking, or the catalyst for hydrogen production from ammonia through cracking prepared by the preparation method, specifically including the following steps: Step 1, Catalyst Activation: The reactor is filled with a catalyst for ammonia cracking to produce hydrogen. It is heated to the first temperature in an inert gas atmosphere and held at that temperature. Then the gas atmosphere is switched to a mixture of hydrogen and inert gas, and the temperature is raised to the reaction temperature and held at that temperature. Step 2: Maintain the reaction temperature and switch the gas atmosphere to ammonia or a mixture of ammonia and an inert gas. Under the catalytic action of the ammonia cracking hydrogen production catalyst, ammonia decomposes into hydrogen.

[0021] In this process, a mixture of hydrogen and inert gas (volume ratio of 1-9:1-9) is used to reduce and activate the catalyst. Industrially, pure hydrogen or ammonia can be used for activation.

[0022] In step 1, when the temperature is raised to the first temperature, the ratio of catalyst mass to inert gas flow rate per minute (g / ml) is 1:100-400; preferably, it is 1:150-250. The catalyst mass to the flow rate ratio (g / ml) of the hydrogen and inert gas mixture is 1:100-400; preferably, 1:150-250. In step 2, when a mixture of ammonia and inert gas is introduced, the volume ratio of the two is 1-9:1.

[0023] As a preferred embodiment of the present invention, the ammonia cracking method for hydrogen production... In step 1, the mass-to-volume ratio of the catalyst used for ammonia cracking to hydrogen production to the reactor volume is 1:3-30, preferably 1:5-15; The heating rate is 5-20℃ / min; The first temperature is 200-220℃, and the first temperature is maintained for 0.5-3 hours, preferably 0.5-1.5 hours; The reaction temperature is 450-800℃, preferably 500-650℃; The initial temperature and the reaction temperature are both maintained for 0.5-3 hours, preferably 1.5-2.5 hours.

[0024] As a preferred embodiment of the present invention, the ammonia cracking method for hydrogen production... In step 2, the mass ratio of the catalyst used for hydrogen production by ammonia cracking to the flow rate of ammonia gas per minute is 1:50-500 g / ml.

[0025] (III) Beneficial Effects The beneficial effects of this invention are as follows: The catalyst and its preparation method for hydrogen production by ammonia cracking, as well as the ammonia cracking hydrogen production method of this invention, introduce auxiliary metals on the surface of the solid support. The auxiliary metals are distributed on the surface of the support, which can modify the solid support and effectively adjust the acidity, alkalinity and electrical properties of the support surface. This is beneficial for modifying and controlling the size of active metal nanoparticles and the density of B5 active sites. In addition, the auxiliary metals on the support surface can also act as anchors to fix the active metal nanoparticles on the auxiliary metals. The auxiliary metals on the support surface as a whole enhance the catalytic activity and stability.

[0026] Then, the active metal nanoparticles are modified with an auxiliary metal, and the auxiliary transfers electrons to the active metal, changing the electron cloud density on the surface of the active metal. This optimization of the electronic structure can promote the adsorption of ammonia gas on the active sites, reduce the activation energy of NH bond dissociation, accelerate dissociation, promote nitrogen association and desorption, and prevent the active sites from being poisoned through hydrogen overflow, thereby optimizing the catalytic performance of the active metal.

[0027] This strong metal-support interaction (SMSI) effectively restricts the migration of active metal nanoparticles at high temperatures, prevents active metal aggregation and deactivation, enhances the stability of active metal in the catalytic material, inhibits the aggregation of active metal during the reaction, significantly improves the thermal stability and anti-sintering ability of the catalyst, and enables the catalyst to maintain stable activity even after long-term operation, thus extending the catalyst's service life.

[0028] Solid supports enable catalysts to possess low bed pressure drop, high mechanical strength, and vibration resistance, making them suitable for various large-scale ammonia cracking hydrogen production scenarios, extending catalyst lifespan, and promoting industrial applications. Compared to powdered catalysts, catalysts prepared on solid supports can avoid clogging during the catalytic process.

[0029] Compared to conventional high-temperature gas-phase hydrogen reduction processes, the preparation method of this invention employs in-situ liquid-phase reduction of polyols, combined with a strategy of modification using specific alkali metal additives, resulting in mild reaction conditions. This process effectively avoids the agglomeration problem caused by thermal migration of metals at high-temperature interfaces, producing a suspension with extremely small metal particle sizes. The active metal ultimately loaded on the support exhibits an extremely dispersed ultrafine nanoscale state, with an average particle size of 1-3 nm, preventing secondary agglomeration into large particles and thus significantly improving atom utilization and catalytic activity.

[0030] Compared to existing technologies, this preparation method offers advantages such as simplicity, speed, versatility, and ease of scale-up production, making it applicable to the preparation of various supported metal catalysts. Furthermore, the prepared catalyst for ammonia cracking to hydrogen production exhibits low active metal loading, high catalytic activity, and strong stability, significantly reducing the amount of precious metals used, improving atom economy, and substantially lowering the industrial production cost of ammonia cracking to hydrogen catalysts. Attached Figure Description

[0031] Figure 1 The images show the XRD test results of catalysts prepared in some embodiments and comparative examples of this invention. Figure 2 The specific surface area and pore size analysis results of the catalysts prepared in some embodiments and comparative examples of the present invention are as follows: where a is the N2 adsorption-desorption isotherm of each catalyst; b is the pore size distribution analysis diagram of each catalyst. Figure 3 The image shows the electron microscopy characterization of the catalyst prepared in Example 3 of this invention. Figure 4 The image shows the electron microscopy characterization of the catalyst prepared in Comparative Example 2 of this invention. Figure 5The particle size distribution of ruthenium nanoparticles in the catalysts prepared in Example 3 and Comparative Example 2 of this invention is shown in the diagram: where a corresponds to Example 3; b corresponds to Comparative Example 2.

[0032] Figure 6 The conversion data of the catalyst prepared in Example 3 of this invention after running at 10000 mL / g / h for 260 h is shown in the figure. Figure 7 This is a schematic diagram of the catalyst prepared in Example 2 of the present invention. Detailed Implementation

[0033] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0035] Example 1 This embodiment provides a method for preparing a catalyst for hydrogen production from ammonia cracking, the specific steps of which are as follows: (1) Prepare 15 mL of KOH (first auxiliary metal compound) aqueous solution with a concentration of 219.05 g / L (first solution), and then add 10 g of cerium oxide balls (carrier, pore volume 0.766 mL / g, particle size 3.6 mm) to the first solution. Seal the container and let it soak at room temperature for 24 h. Then take it out and filter it. Place the filtered solid in an oven at 80℃ and dry it for 24 h. Then take it out and calcine it at 550℃ for 2 h to obtain the auxiliary metal modified carrier. (2) Prepare 15 mL of RuCl3·3H2O (active metal compound) ethylene glycol solution with a concentration of 17.11 g / L, and then add 8 eq NaOH (second auxiliary metal compound) to obtain a mixed reaction solution; place the mixed reaction solution at 180℃ and stir for 3 h, reflux and collect the recovered liquid into the mixed reaction solution, and after the reaction is completed, the liquid is naturally cooled to room temperature to obtain an active metal nanoparticle suspension (ruthenium nanocolloid solution). (3) Add 10g of the auxiliary metal modified carrier prepared in step (1) to the active metal nanoparticle suspension, seal the container, and immerse it at room temperature for 24 h; then take it out and filter it, and place the filtered solid in an oven at 80℃ to dry for 24 h; then take it out and calcine it at 550℃ for 2 h under nitrogen protection to obtain a catalyst for ammonia cracking to produce hydrogen, named L1.

[0036] The L1 catalyst was characterized by ICP-MS, which showed that the mass fraction of Ru was 0.15%, the mass fraction of K was 9.95%, and the mass fraction of Na was 1.30%.

[0037] Example 2 This embodiment provides a method for preparing a catalyst for hydrogen production from ammonia cracking. The difference between this embodiment and Embodiment 1 is that: In step (1), the carrier is replaced with alumina spheres (pore volume 0.766 mL / g, particle size 3.6 mm). The remaining steps are the same, and a catalyst for hydrogen production from ammonia cracking is obtained, named L2.

[0038] The L2 catalyst was characterized by ICP-MS, which showed that the mass fraction of Ru was 0.14%, the mass fraction of K was 9.90%, and the mass fraction of Na was 1.17%.

[0039] Example 3 This embodiment provides a method for preparing a catalyst for hydrogen production from ammonia cracking. The difference between this embodiment and Embodiment 2 is that: In step (2), the second auxiliary metal compound is replaced with 8 eq KOH; The remaining steps are the same, and a catalyst for hydrogen production by ammonia cracking is obtained, named L3.

[0040] Characterization by ICP-MS revealed that the mass fraction of Ru in the L3 catalyst was 0.4%, and the mass fraction of K was 11.10%. The K was derived from the first and second promoter metal compounds.

[0041] Example 4 This embodiment provides a method for preparing a catalyst for hydrogen production from ammonia cracking. The difference between this embodiment and Embodiment 2 is that: In step (2), the active metal compound is replaced with NiCl2·6H2O (concentration of 600 g / L); The remaining steps are the same, and a catalyst for hydrogen production from ammonia cracking is obtained, named L4.

[0042] The L4 catalyst was characterized by ICP-MS, which showed that the mass fraction of Ni was 8.1%, the mass fraction of K was 7.9%, and the mass fraction of Na was 1.5%.

[0043] Example 5 This embodiment provides a method for preparing a catalyst for hydrogen production from ammonia cracking. The difference between this embodiment and Embodiment 2 is that: In step (2), the solvent in the mixed reaction solution is replaced with propylene glycol in equal volume; The remaining steps are the same, and a catalyst for hydrogen production from ammonia cracking is obtained, named L5.

[0044] The L5 catalyst was characterized by ICP-MS, which showed that the mass fraction of Ru was 0.13%, the mass fraction of K was 9.84%, and the mass fraction of Na was 1.05%.

[0045] Comparative Example 1 This comparative example provides a method for preparing a catalyst for hydrogen production from ammonia cracking. The difference between this comparative example and Example 2 is that: Step (1) is omitted; The remaining steps are the same, and a catalyst for hydrogen production by ammonia cracking is obtained, named I1.

[0046] The I1 catalyst was characterized by ICP-MS, which showed that the mass fraction of Ru was 0.82% and the mass fraction of Na was 2.5%.

[0047] Comparative Example 2 This comparative example provides a method for preparing a catalyst for hydrogen production from ammonia cracking. The difference between this comparative example and Example 2 is that: In step (2), the NaOH in the ethylene glycol solution is adjusted to 3 eq; The remaining steps are the same, and a catalyst for hydrogen production from ammonia cracking is obtained, named I2.

[0048] The I2 catalyst was characterized by ICP-MS, which showed that the mass fraction of Ru was 0.11%, the mass fraction of K was 9.8%, and the mass fraction of Na was 0.6%.

[0049] Comparative Example 3 This comparative example provides a method for preparing a catalyst for hydrogen production from ammonia cracking. The difference between this comparative example and Example 2 is that: In step (3), the nitrogen protection is removed during the calcination step; The remaining steps are the same, and a catalyst for hydrogen production by ammonia cracking is obtained, named I3.

[0050] The I3 catalyst was characterized by ICP-MS, which showed that the mass fraction of Ru was 0.14%, the mass fraction of K was 9.73%, and the mass fraction of Na was 1.15%.

[0051] Application Example 1 This application example provides a method for hydrogen production by ammonia cracking. The method simultaneously tests the catalytic activity of catalysts for hydrogen production by ammonia cracking prepared in Examples 1 to 5 and Comparative Examples 1 to 3. The specific steps are as follows: (1) Weigh 0.1g of catalyst and fill it into a fixed-bed reactor. Heat the reactor to 200℃ at 5℃ / min in an argon atmosphere and keep it for 1h. Then switch the reactor to a mixed gas with a volume ratio of hydrogen:argon = 10:90 and heat it to the reaction temperature at 5℃ / min and keep it for 1h. (2) Switch the ammonia reaction gas in the reactor (use a mixture of ammonia and argon with a volume ratio of 1:1), and use TCD chromatography to test the hydrogen concentration and reaction conversion rate of the reaction outlet gas.

[0052] For the reaction conditions and corresponding ammonia conversion rates for different catalysts, please refer to Table 1.

[0053] Table 1. Reaction conditions and corresponding ammonia conversion rates for different catalysts

[0054] As shown in the table above, all catalysts prepared in the examples exhibited high NH3 conversion rates and remained highly stable over extended periods, with only a slight decrease in NH3 conversion rate. Compared to the L3 catalyst and the ruthenium-based catalyst supported on an alumina support in Chinese patent (publication number CN120189941A), the active metal loading of the L3 catalyst was only 1 / 20. At a space velocity of 30,000 mL / g / h, the NH3 conversion rate of the L3 catalyst was slightly lower than that of the ruthenium-based catalyst supported on an alumina support in Chinese patent (publication number CN120189941A). At space velocities of 20,000 mL / g / h, 10,000 mL / g / h, and 5,000 mL / g / h, the NH3 conversion rates within 10 hours of reaction were all higher than those disclosed in Chinese patent (publication number CN120189941A). The ammonia conversion rate of the L3 catalyst decreased slightly but remained stable after a long continuous reaction of 200h. Compared with catalysts L3 and L4, the ruthenium-based catalyst (L3) has higher activity than the nickel-based catalyst with the same active loading.

[0055] Comparing catalysts L2 and L3, it can be seen that when both the first and second auxiliary metals are K, the catalyst has higher catalytic efficiency and ammonia conversion rate.

[0056] Comparing catalysts L2 with I1 and I2, it is evident that pre-impregnating the support surface with a promoter metal, and adding an appropriate amount of promoter metal during the preparation of the active metal nanoparticle suspension, can significantly improve the catalytic activity and stability of the catalyst. Comparing catalysts L2 and I3, it is clear that using nitrogen protection during the final calcination stage of the catalyst preparation process effectively preserves the valence state of the active metal, thus ensuring its catalytic activity and stability.

[0057] In addition, long-cycle reaction stability tests were conducted on the L3 catalyst; see [link to relevant documentation]. Figure 6The conversion data for L3 catalyst at 10000 mL / g / h for 260 h show that the optimal novel catalyst has excellent catalytic activity and stability at high temperatures, which is beneficial for industrial application.

[0058] See Figure 7 The catalyst prepared in Example 2 has a yield in the kilogram range and has the potential for industrial mass production.

[0059] Test Example 1 This test example involves XRD analysis of the catalysts prepared for ammonia cracking to hydrogen production in Examples 2, 3, and 4, and Comparative Examples 1 and 2. The test results are shown in [reference needed]. Figure 1 .

[0060] from Figure 1 It was observed that characteristic diffraction peaks of γ-Al₂O₃ were observed at 2θ = 37.5°, 35.8°, and 67.3° in the XRD patterns of all catalysts. Characteristic diffraction peaks corresponding to NiO and Ni were found in the L4 catalyst. Notably, characteristic diffraction peaks of Ru species were not observed in the L2, L3, I1, and I2 patterns, indicating that Ru species remained highly dispersed on the support surface and did not form large-sized crystal particles detectable by XRD.

[0061] Test Example 2 This test example analyzes the specific surface area and pore size of the catalysts prepared for ammonia cracking to hydrogen production in Examples 2 and 3 and Comparative Examples 1, 2, and 3. The test results are shown in [reference needed]. Figure 2 a and b in the middle, and Table 2.

[0062] Table 2 Summary of BET analysis results for different catalysts

[0063] See Figure 2 From the N2 adsorption-desorption isotherms of each catalyst, it can be seen that Al2O3, L2, L3, I1, I2, and I3 catalysts all exhibit typical Type IV isotherms in the P / P0 = 0.05-0.95 range, indicating that they are mainly composed of mesoporous structures, and that the mesoporous structures mainly originate from γ-rays. Al2O3 support. See also... Figure 2 Figure b shows that the pore size distribution analysis diagram indicates that this type of catalyst is mainly mesoporous, with an average pore size of about 10.5 nm. After metal loading, the mesoporous pore volume of L2, L3, I1, and I3 catalysts decreased, indicating that the active metal was mainly loaded inside the pores of the support. The mesoporous pore volume of I2 catalyst increased slightly, possibly because some of the active metal was loaded on the surface of the support, forming a new mesoporous structure.

[0064] Referring to Table 2, BET analysis shows that the specific surface area of ​​the I2 catalyst is significantly higher than that of other catalysts, further confirming the above viewpoint. Furthermore, catalyst L3 showed almost no significant changes in specific surface area and pore structure before the ammonia decomposition reaction and after a long-term stability test at 500℃ for 260 hours, demonstrating its excellent stability under long-term high-temperature operation.

[0065] Test Example 3 This test example focuses on the electron microscopy characterization of the catalysts prepared in Example 2 and Comparative Example 3 for ammonia cracking to hydrogen production. The test results are shown in [reference needed]. Figure 3 and Figure 4 .

[0066] See Figure 3 and Figure 4 Electron microscopy results show that the catalysts L3 and I2 have lattice spacings of 0.204 nm and 0.206 nm, respectively, corresponding to the Ru (101) crystal plane. This Ru structure is rich in highly active B5 sites.

[0067] Furthermore, a lattice spacing of 0.213 nm, corresponding to the Ru(002) crystal plane structure, was found in the HRTEM image of L3. This ruthenium crystal form may contribute to the ammonia decomposition activity. Many ruthenium nanoclusters or particles with a diameter less than 2 nm were found in the HAADF images of both L3 and I2. The metallic bright spots in L3 were more dispersed and fewer in number compared to I2. EDS elemental scanning revealed that in catalyst L3, Ru was uniformly distributed in a highly dispersed dot-like form throughout the entire field of view, with no aggregation observed. In catalyst I2, the ruthenium elemental scanning points were more numerous and concentrated than in L3. The distribution range of Ru points in both catalysts completely overlapped with the distribution areas of Al, O, and K, proving that Ru was not only attached to the support surface but was uniformly dispersed throughout the entire support area, including the channels or interior. Moreover, C (from the polyol solvent) and K elements in both catalysts were also uniformly distributed throughout the entire support area, which is beneficial for inhibiting active metal aggregation, regulating the charge distribution of the support, effectively promoting electron transfer, and enhancing catalytic activity.

[0068] See Figure 5From the ruthenium nanoparticle size distribution diagrams of samples a (L3) and b (I2), it can be seen that the ruthenium particles in the L3 catalyst are mainly distributed between 1-2 nm, with an average particle size of 1.94 nm. The ruthenium particles in the I2 catalyst are mainly distributed between 1.5-3 nm, with an average particle size of 2.54 nm, consistent with the results of XRD, BET analysis, and HRTEM characterization. This indicates that reducing the amount of the second auxiliary metal compound leads to the aggregation of ruthenium nanoparticles during the preparation of the active metal nanoparticle suspension. The larger ruthenium nanoparticle size in I2 results in differences in the catalytic activity for ammonia decomposition, while L3, with particles smaller than 2 nm, exhibits higher catalytic performance.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0070] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0071] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0072] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0073] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, for example, sequentially. For instance, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For instance, the method may also include step (c), indicating that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0074] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0075] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

Claims

1. A catalyst for hydrogen production from ammonia cracking, characterized in that, It includes a solid support, a first auxiliary metal dispersed on the surface of the solid support, and active metal nanoparticles anchored on the auxiliary metal; The active metal nanoparticles and the solid support are in interfacial contact through the first auxiliary metal. The active metal nanoparticles are active metals modified by the second additive; Both the first and second auxiliary metals are alkali metals.

2. The catalyst for hydrogen production from ammonia cracking as described in claim 1, characterized in that, The solid support is selected from at least one of alumina, titanium oxide, cerium oxide, lanthanum oxide, silicon oxide, and zirconium oxide; The solid support is at least one of the following shapes: spherical, cylindrical, multi-leaf strip, tubular, cross-shaped ring, stepped ring, honeycomb, porous columnar, foamy, and fibrous.

3. The catalyst for hydrogen production from ammonia cracking as described in claim 1, characterized in that, The active metal is selected from at least one of ruthenium, cobalt, iron, and nickel; Both the first additive metal and the second additive metal are selected from at least one of potassium, sodium, barium, and cesium.

4. The catalyst for hydrogen production from ammonia cracking as described in claim 3, characterized in that, When the active metal is ruthenium, the mass fraction of ruthenium is 0.1-0.9 wt%, and the mass fraction of the auxiliary metal is 5-30%. When the active metal is nickel, the mass fraction of nickel is 1-10 wt%. When the active metal is cobalt, the mass fraction of cobalt is 0.6-6 wt%; When the active metal is iron, the mass fraction of iron is 2.5-20 wt%. The mass fraction of the first additive metal is 1-30 wt%; The average particle size of the active metal ranges from 1 to 5 nm.

5. A method for preparing a catalyst for ammonia cracking to hydrogen production as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Prepare a first solution by preparing the first auxiliary metal compound, impregnate a solid support with the first solution, and dry and calcine the impregnated solid support to obtain an auxiliary metal modified support. S2. Dissolve the active metal compound and the second auxiliary metal compound in a polyol solvent to prepare a mixed reaction solution. Under inert gas protection, heat and reflux at 140-220°C to prepare a suspension of active metal nanoparticles modified by the second auxiliary metal by utilizing the liquid-phase reduction effect of the polyol. S3. The auxiliary metal-modified support prepared in S1 is impregnated in the suspension of active metal nanoparticles. The impregnated auxiliary metal-modified support is then dried and calcined to obtain the catalyst for ammonia cracking to produce hydrogen.

6. The preparation method according to claim 5, characterized in that, Both the first auxiliary metal compound and the second auxiliary metal compound are selected from at least one of potassium hydroxide, sodium hydroxide, barium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, sodium chloride, and potassium chloride. In the first solution: the solvent is water, and the concentration of the first auxiliary metal is 2-6 mol / L; When impregnating the solid support with the first solution, the impregnation time is 18-42 hours at room temperature.

7. The preparation method according to claim 5, characterized in that, In S2, the active metal compound is selected from at least one of ruthenium chloride, ruthenium nitrate, ruthenium acetylacetonate, cobalt nitrate, cobalt chloride, ferric chloride, ferrous chloride, ferrous nitrate, ferrous nitrate, ferric acetylacetonate, nickel nitrate, nickel chloride, and nickel acetylacetonate. The solvent for the mixed reaction solution is selected from ethylene glycol, propylene glycol, butanediol, glycerol, diethylene glycol, triethylene glycol, or tetraethylene glycol; In the mixed reaction solution: the concentration of the second auxiliary metal is 0.3-5 mol / L, and the molar ratio of the active metal to the second auxiliary metal is 1:3-50; When heating and stirring, the reaction time is 2-6 hours.

8. The preparation method according to claim 5, characterized in that, The drying conditions in S2 and S3 are: temperature 60-120℃, drying time 18-36h; The calcination conditions for S2 and S3 are as follows: heating rate of 2-10℃ / min, calcination temperature of 400-700℃, and calcination time of 1-4h.

9. A method for producing hydrogen by ammonia cracking, characterized in that, The catalyst for hydrogen production from ammonia cracking according to any one of claims 1 to 4, or the catalyst for hydrogen production from ammonia cracking prepared by any one of claims 5 to 8, specifically includes the following steps: Step 1, Catalyst Activation: The reactor is filled with a catalyst for ammonia cracking to produce hydrogen. It is heated to the first temperature in an inert gas atmosphere and held at that temperature. Then the gas atmosphere is switched to a mixture of hydrogen and inert gas, and the temperature is raised to the reaction temperature and held at that temperature. Step 2: Maintain the reaction temperature and switch the gas atmosphere to ammonia or a mixture of ammonia and an inert gas. Under the catalytic action of the ammonia cracking hydrogen production catalyst, ammonia decomposes into hydrogen.

10. The ammonia cracking method for hydrogen production as described in claim 9, characterized in that, In step 1, the mass-to-volume ratio of the catalyst used for ammonia cracking to hydrogen production to the reactor volume is 1:3-30; The heating rate is 5-20℃ / min; The first temperature is 200-220℃, and the first temperature is maintained for 0.5-3 hours. The reaction temperature is 450-800℃; Both the initial temperature and the reaction temperature should be maintained at these temperatures for 0.5-3 hours.

11. The ammonia cracking method for hydrogen production as described in claim 9, characterized in that, In step 2, the mass ratio of the catalyst used for hydrogen production by ammonia cracking to the flow rate of ammonia gas per minute is 1:50-500 g / ml.

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